Quantum theory: observation and reality [Archive]

The Man

20th July 2008, 12:12 PM

If my surmise is correct and you are asking about “Quantum thoery: observation and reality” (since I have no idea what anything after that statement is suppose to mean), then you might want to check out the Transactional Interpretation of Quantum Mechanics.

http://www.npl.washington.edu/ti/

3.7 Collapse and Nonlocality in the Transactional Interpretation
In the TI the collapse of the state vector is interpreted as the completion of the transaction started by the OW and the CW exchanged between emitter and absorber. The emergence of the transaction from the SV does not occur at some particular location in space or at some particular instant of time, but rather forms along the entire four-vector which connects the emission locus with the absorption locus (or loci in the case of multiple correlated particles). The transaction employs both retarded and advanced waves which propagate, respectively, along positive and negative lightlike (or timelike) four-vectors. Since the sum of these four-vectors can span spacelike and negative timelike or lightlike intervals, the "influence" of the transaction in enforcing the correlations of the quantum event is explicitly both nonlocal and atemporal.
Fig. 5 shows an example of such combinations of four-vector for a two photon transaction corresponding to an event in the Freedman-Clauser experiment. Note that although all of the waves in the transaction lie along lightlike world lines, the "influence" which enforces the correlations between the two polarization measurements spans a spacelike interval and is therefore nonlocal. This nonlocality is an explicit feature of the TI arising from the use of advanced waves.
Schrödinger (1935), in analyzing the EPR paradox, concluded that at least part of the problem lay in the way time is used in quantum mechanics (in the context of the CI). The CI treats time in an essentially classical non-relativistic way, and as we have seen in Section 2.5, this leads to inconsistencies with relativity or causality in any non-subjective CI description of collapse in, for example, the Freedman-Clauser experiment. The root of the inconsistencies lies in the implicit assumption of the CI that the SV collapse occurs at a particular instant at which a particular measurement is made and "knowledge" is gained, that before this instant the SV is in its full uncollapsed state, and that there can be a well-defined "before" and "after" in the collapse description. In the TI the collapse, i.e., the development of the transaction, is atemporal and thus avoids the contradictions and inconsistencies implicit in any time-localized SV collapse.
Further, the TI description does not need to invoke arbitrary collapse triggers such as consciousness, etc., because it is the absorber rather than the observer which precipitates the collapse of the SV, and this can occur atemporally and nonlocally across any sort of interval between elements of the measuring apparatus. This will be discussed further in the context of gedanken experiments in Section 4.

Yuri Nalyssus

20th July 2008, 04:21 PM

If my surmise is correct and you are asking about “Quantum thoery: observation and reality” (since I have no idea what anything after that statement is suppose to mean), then you might want to check out the Transactional Interpretation of Quantum Mechanics.

3.7 Collapse and Nonlocality in the Transactional Interpretation
In the TI the collapse of the state vector is interpreted as the completion of the transaction started by the OW and the CW exchanged between emitter and absorber. The emergence of the transaction from the SV does not occur at some particular location in space or at some particular instant of time, but rather forms along the entire four-vector which connects the emission locus with the absorption locus (or loci in the case of multiple correlated particles). The transaction employs both retarded and advanced waves which propagate, respectively, along positive and negative lightlike (or timelike) four-vectors. Since the sum of these four-vectors can span spacelike and negative timelike or lightlike intervals, the "influence" of the transaction in enforcing the correlations of the quantum event is explicitly both nonlocal and atemporal.
Fig. 5 shows an example of such combinations of four-vector for a two photon transaction corresponding to an event in the Freedman-Clauser experiment. Note that although all of the waves in the transaction lie along lightlike world lines, the "influence" which enforces the correlations between the two polarization measurements spans a spacelike interval and is therefore nonlocal. This nonlocality is an explicit feature of the TI arising from the use of advanced waves.
Schrödinger (1935), in analyzing the EPR paradox, concluded that at least part of the problem lay in the way time is used in quantum mechanics (in the context of the CI). The CI treats time in an essentially classical non-relativistic way, and as we have seen in Section 2.5, this leads to inconsistencies with relativity or causality in any non-subjective CI description of collapse in, for example, the Freedman-Clauser experiment. The root of the inconsistencies lies in the implicit assumption of the CI that the SV collapse occurs at a particular instant at which a particular measurement is made and "knowledge" is gained, that before this instant the SV is in its full uncollapsed state, and that there can be a well-defined "before" and "after" in the collapse description. In the TI the collapse, i.e., the development of the transaction, is atemporal and thus avoids the contradictions and inconsistencies implicit in any time-localized SV collapse.
Further, the TI description does not need to invoke arbitrary collapse triggers such as consciousness, etc., because it is the absorber rather than the observer which precipitates the collapse of the SV, and this can occur atemporally and nonlocally across any sort of interval between elements of the measuring apparatus. This will be discussed further in the context of gedanken experiments in Section 4.

Oh well yes, I mean who doesn't know that... in fact I was just about to say the same myself.

Yuri

beeksc1

23rd July 2008, 01:53 PM

Please write in a way that makes sense. Thanks. :)

Almost all the time, it do make sense; :D I just do not care to edit my posts.

Have across sources reporting that:
Observation influences reality
Each quanta can exist in more than one place at the same time

In between the "have" and "across", I missed the word "come"

I have come across sources reporting that:
Observation influences reality.

Was there supposed to be a particular question in the OP? :boggled:

Concerning the research of quantum mechanics/thoery, what does the evidence indicate, especially about matter, observation, and reality

Sorry :) I forgot the question mark.

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This thread concerns quantum theory and how the evidence relates to matter, observation, matter. Asking to further clarify the topic can help move forward the information that is passed along on this forum. But a post that is directly/indirectly intended to derail the topic or stiffen it, is not called for. There are two questions in the original post.

1. What is the current evidence for QM?
2. What are the differences (if any) between matter and reality?

Sorry, if the questions were not posted to your liking. This thread just discusses QM is a respectful and peaceful manner.

Quantum theory is very fascinating; yet, the technical aspects can be very challenging to wrap your mind around. And, some people on this forum can prolly boil it down, so others can more fully understand the technical parts.

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Just getting to the point that matter and reality seem to be two different animals. Unobserved matter is the physical energy (quanta), which is postulated to exist in more than one place at a time. And reality is constructed when observation takes places. Observation provides a focal point for the quantum energy, which is known as matter.

A science article that relates to the topic of this thread:

Quantum Theory Demonstrated: Observation Affects Reality (ScienceDaily)

ScienceDaily (Feb. 27, 1998) — REHOVOT, Israel, February 26, 1998--One of the most bizarre premises of quantum theory, which has long fascinated philosophers and physicists alike, states that by the very act of watching, the observer affects the observed reality.

In a study reported in the February 26 issue of Nature (Vol. 391, pp. 871-874), researchers at the Weizmann Institute of Science have now conducted a highly controlled experiment demonstrating how a beam of electrons is affected by the act of being observed. The experiment revealed that the greater the amount of "watching," the greater the observer's influence on what actually takes place.
http://www.sciencedaily.com/releases/1998/02/980227055013.htm

The referenced journal article:

Dephasing in electron interference by a 'which-path' detector (Buks et al., 1998)

Wave-particle duality, as manifest in the two-slit experiment, provides perhaps the most vivid illustration of Bohr's complementarity principle: wave-like behaviour (interference) occurs only when the different possible paths a particle can take are indistinguishable, even in principle1.

http://cat.inist.fr/?aModele=afficheN&cpsidt=2186578

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As this was published in 1998, it would seem that there would be more research to challenge or further confirm this evidence.

Any other evidence that relates to matter, observation, and reality?

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Observation is based upon interaction of waveforms?

Right on; so what does that (^) mean, in more of layman terms?

Waveform (Wiki)

Waveform means the shape and form of a signal such as a wave moving in a solid, liquid or gaseous medium.

In many cases the medium in which the wave is being propagated does not permit a direct visual image of the form. In these cases, the term 'waveform' refers to the shape of a graph of the varying quantity against time or distance.

This is a general definition; what is does a waveform refer to in QM?

Is waveform just another name for the quanta?

Like, observation focuses the waveforms of physical reality to construct an experience, which is known as reality?

+++

Niels Bohr (quoted in Heisenberg, Werner (1971). Physics and Beyond, 206, New York: Harper and Row.)

For those who are not shocked when they first come across quantum theory cannot possibly have understood it.

Physics and Beyond (World Perspectives)
http://www.amazon.com/Physics-Beyond-Perspectives-Werner-Heisenberg/dp/0049250205

Ziggurat

23rd July 2008, 03:47 PM

1. What is the current evidence for QM?

Far too much to list comprehensively. Many people like the double slit experiment (http://en.wikipedia.org/wiki/Double_slit_experiment) as a prototype example. Personally I'm partial to the Stern-Gerlach experiment (http://en.wikipedia.org/wiki/Stern-Gerlach_experiment). Historically, the absorption and emission lines of gasses was very important, along with the photoelectric effect.

2. What are the differences (if any) between matter and reality?

Look up the words in a dictionary, and the provided definitions will be very different. Under standard usage, this question is therefore nonsensical. I presume you intend to use one or both words in a nonstandard manner, but without indicating how you intend to use the words, I really can only refer you to a dictionary.

Just getting to the point that matter and reality seem to be two different animals. Unobserved matter is the physical energy (quanta), which is postulated to exist in more than one place at a time. And reality is constructed when observation takes places. Observation provides a focal point for the quantum energy, which is known as matter.

No. Particles (in the quantum mechanics sense) are matter. They have energy, but they are not themselves energy. They can exchange energy, they can gain or loose energy, but at no point do they become energy unless they undergo matter-antimatter pair anihilation.

Quantum Theory Demonstrated: Observation Affects Reality (ScienceDaily)

This is less profound than commonly thought. Essentially it's just saying that at the microscopic level, the only way to measure something is to bump it with something else, and the moment you bump what you're observing, you've changed it. Nothing mysterious about it, and the basic idea exists in classical physics as well. The only change that quantum mechanics introduces is essentially the idea of a minimum size to how hard you "bump" what you're looking at (classically, you can bump with arbitrary lightness).

This is a general definition; what is does a waveform refer to in QM?

The usual term is wave function, not waveform. And the wave function provides the complete (and only) description of a particle in quantum mechanics. There are various interpretations of what exactly the wave function means. As a practical matter, the Copenhagen interpretation (http://en.wikipedia.org/wiki/Copenhagen_interpretation) is sufficient, though many find it unsatisfying on an intellectual level.

Is waveform just another name for the quanta?

"quanta" is frequently used to describe discrete changes in the energy of a quantum mechanical system. It's important to understand that though changes in a given system may be discrete, this does NOT mean that there's a fundamental unit of energy.

pgwenthold

23rd July 2008, 04:55 PM

The usual term is wave function, not waveform. And the wave function provides the complete (and only) description of a particle in quantum mechanics. There are various interpretations of what exactly the wave function means.

Yes, there are various interpretations of what the wave function _means_, but there is no ambiguity about what the wave function IS, or technically "what it refers to." The wave function is a mathematical function for the system from which the physical properties can be obtained by using the appropriate operator. That's what the "wave function" refers to. It is called a "wave" function because the functional form resembles that used to describe waves (discrete behavior comes from applying boundary conditions, for the most part). The Schroedinger equation, which the wave function satisfies, is a wave equation (and is actually just an energy operator)

The physical interpretation of the wave function is a different question, and is more a matter of philosophy than anything else. It's kind of like the whole "wave/particle" duality thing. We have a hard time describing certain systems as waves or particles; however, there is no ambiguity in the math - they are what they are, with the given properties as described by the wave function. Neither wave nor particle is an adequate description of them. The wave function is.

beeksc1

23rd July 2008, 06:28 PM

Stern–Gerlach experiment (Wiki)

In quantum mechanics, the Stern–Gerlach experiment, named after Otto Stern and Walther Gerlach, is a celebrated 1922 experiment on the deflection of particles, often used to illustrate basic principles of quantum mechanics. It can be used to demonstrate that electrons and atoms have intrinsically quantum properties, and how measurement in quantum mechanics affects the system being measured.

Stern and Gerlach: How a Bad Cigar Helped Reorient Atomic Physics (PhysicsToday)

The demonstration of space quantization, carried out in Frankfurt, Germany, in 1922 by Otto Stern and Walther Gerlach, ranks among the dozen or so canonical experiments that ushered in the heroic age of quantum physics. Perhaps no other experiment is so often cited for elegant conceptual simplicity. From it emerged both new intellectual vistas and a host of useful applications of quantum science. Yet even among atomic physicists, very few today are aware of the historical particulars that enhance the drama of the story and the abiding lessons it offers. Among the particulars are a warm bed, a bad cigar, a timely postcard, a railroad strike, and an uncanny conspiracy of Nature that rewarded Stern and Gerlach. Their success in splitting a beam of silver atoms by means of a magnetic field startled, elated, and confounded pioneering quantum theorists, including several who beforehand had regarded an attempt to observe space quantization as naive and foolish.

Meaning of matter

1 (physics) The basic structural component of the universe. Matter usually has mass and volume.

http://en.wiktionary.org/wiki/matter

Meaning of reality

1. The entirety of all that is real.
2. The state of being actual or real
3. Each individual's own subjective perception of that which is real

http://en.wiktionary.org/wiki/reality

Yes, this poster is familiar with the standard definition; just looking for how a person might define those terms in his own words and relate them to physics and QM.

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"quanta" is frequently used to describe discrete changes in the energy of a quantum mechanical system. It's important to understand that though changes in a given system may be discrete, this does NOT mean that there's a fundamental unit of energy.

So, quanta is a frequency that embodies a certain wavelength, which has certain potentials toward energy-formation and particular tendencies toward the relevant physical system?

The wave function is a mathematical function for the system from which the physical properties can be obtained by using the appropriate operator. That's what the "wave function" refers to. It is called a "wave" function because the functional form resembles that used to describe waves (discrete behavior comes from applying boundary conditions, for the most part). The Schroedinger equation, which the wave function satisfies, is a wave equation (and is actually just an energy operator)

So, a wave function is a digital form of representation, which maps out the inner-workings of a certain piece of matter or a particular phenomena?

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Quanta is a singly entity of quantifiable properties, which has certain amounts of energy-potential and particular tendencies toward physical manifestations (which are perceived as reality)?

A wave function is a mathematical code that describes a certain physical phenomena, which is being measured, plotted, graphed, analyzed; etc?

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Yes, listing all the evidence that concerns quantum mechanism is not possible; yet, certain experiments (some which have been posted) are key. The body of evidence seems to indicate that matter is independent of observation reality; yet, reality is dependent upon observation. Reality is a experience that takes shapes through conscious observation of the energy-potentials of physical matter and those tendencies toward its physical manifestations. [Conjecture] Reality can be (to some extent) subjectively formed through the observation of physical matter.

Can it be postulated that our thoughts, behaviors, perspective; etc help to create our unfolding future?

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So, do empiricists quantify the nature of reality; or do empiricists measure constructions of reality? Or is top-notch science assessing a physical threshold that manifests itself somewhere within and throughout the nature of reality and those pertaining to physical constructions of reality, such as those of time and space?

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Neils Bohr

The very nature of the quantum theory thus forces us to regard the space-time co-ordination and the claim of causality, the union of which characterizes the classical theories, as complementary but exclusive features of the description, symbolizing the idealization of observation and definition respectively.
http://209.85.215.104/search?q=cache:IJNN6Z-dvj4J:www.nd.edu/~dhoward1/Copenhagen%2520Myth%2520A.pdf+forces+us+to+regard+ the+space-time+coordination+and+the+claim+of+causality,+the+ union+of+which+characterizes+the+classical+theorie s,+as+complementary+but+exclusive+features+of+the+ description,+symbolizing+the+idealization+of+obser vation+and+description,+respectively&hl=en&ct=clnk&cd=4&gl=us&client=firefox-a

pgwenthold

23rd July 2008, 07:20 PM

So, a wave function is a digital form of representation, which maps out the inner-workings of a certain piece of matter or a particular phenomena?

No, it is not. It is exactly what I said it is in my post above.

A wave function ultimately is descriptive, not proscriptive. It "maps out" nothing, much less the "inner workings" of anything.

And it certainly is not "digital," by any reasonable concept of the word.

Reality Check

23rd July 2008, 08:00 PM

...snip...Meaning of matter

http://en.wiktionary.org/wiki/matter

Meaning of reality

http://en.wiktionary.org/wiki/reality

Yes, this poster is familiar with the standard definition; just looking for how a person might define those terms in his own words and relate them to physics and QM.

As you can see there is no relationship between matter and reality - they are two separate things.
However physics and QM often describe matter.
Physics and QM can be considered as mathematical models that have predictions that match our perception of reality.

So, quanta is a frequency that embodies a certain wavelength, which has certain potentials toward energy-formation and particular tendencies toward the relevant physical system?

Not quite: A quantum (http://en.wikipedia.org/wiki/Quantum)
In physics, a quantum (plural: quanta) is an indivisible entity of a quantity that has the same units as the Planck constant and is related to both energy and momentum of elementary particles of matter (called fermions) and of photons and other bosons. The word comes from the Latin "quantus," for "how much." Behind this, one finds the fundamental notion that a physical property may be "quantized", referred to as "quantization". This means that the magnitude can take on only certain discrete numerical values, rather than any value, at least within a range. There is a related term of quantum number.

So, a wave function is a digital form of representation, which maps out the inner-workings of a certain piece of matter or a particular phenomena?

No (see the previous post).

Quanta is a singly entity of quantifiable properties, which has certain amounts of energy-potential and particular tendencies toward physical manifestations (which are perceived as reality)?
see above - there are no "tendencies" in the quantum.

A wave function is a mathematical code that describes a certain physical phenomena, which is being measured, plotted, graphed, analyzed; etc?

You are getting closer: It is a mathematical function that contains all of the possible states of a system. It appears in the Schrödinger equation (http://en.wikipedia.org/wiki/Schr%C3%B6dinger_equation) and other QM equations. These describe how the wave function changes over time.

Yes, listing all the evidence that concerns quantum mechanism is not possible; yet, certain experiments (some which have been posted) are key. The body of evidence seems to indicate that matter is independent of observation reality; yet, reality is dependent upon observation. Reality is a experience that takes shapes through conscious observation of the energy-potentials of physical matter and those tendencies toward its physical manifestations. [Conjecture] Reality can be (to some extent) subjectively formed through the observation of physical matter.

Our observation of macroscopic matter seems to indicate that matter is independent of observation reality.
Our observation of matter on the small scale reveals that it is in fact dependant on the observation reality.

Can it be postulated that our thoughts, behaviors, perspective; etc help to create our unfolding future?

Not in this topic. Take it to Religion and Philosophy.

So, do empiricists quantify the nature of reality; or do empiricists measure constructions of reality? Or is top-notch science assessing a physical threshold that manifests itself somewhere within and throughout the nature of reality and those pertaining to physical constructions of reality, such as those of time and space?

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Neils Bohr

http://209.85.215.104/search?q=cache:IJNN6Z-dvj4J:www.nd.edu/~dhoward1/Copenhagen%2520Myth%2520A.pdf+forces+us+to+regard+ the+space-time+coordination+and+the+claim+of+causality,+the+ union+of+which+characterizes+the+classical+theorie s,+as+complementary+but+exclusive+features+of+the+ description,+symbolizing+the+idealization+of+obser vation+and+description,+respectively&hl=en&ct=clnk&cd=4&gl=us&client=firefox-a
Sound like more stuff for the Religion and Philosophy topic or at least translating into more lucid English.
"do empiricists quantify the nature of reality" -> "do scientists study the nature of reality": Yes
"do empiricists measure constructions of reality" -> "do scientists make measurements": Yes
The last sentence doe not scan.

beeksc1

23rd July 2008, 09:39 PM

A wave function ultimately is descriptive, not proscriptive. It "maps out" nothing, much less the "inner workings" of anything.

Allright.

Wave function (Wiki)

A wave function or wavefunction is a mathematical tool used in quantum mechanics to describe any physical system. It is a function from a space that maps the possible states of the system into the complex numbers. The laws of quantum mechanics (i.e. the Schrödinger equation) describe how the wave function evolves over time.

As you can see there is no relationship between matter and reality - they are two separate things.
However physics and QM often describe matter.

No relationship? I can see that one way; but, it seems that an Earthly reality would cease to exist, if the matter was not there to aid that reality.

Yea, the related explorations that concern philosophical questions may be better suited for another section.

Relativity, Quantum Mechanics, and Classical Physics: Evidence for a Close Link Between the Three Theories (Tane, 2004)

Relativity and Quantum Mechanics are closely linked with one another in Classical Physics, their link being detectable through a revision of some basic equations.

http://66.102.1.104/scholar?num=100&hl=en&lr=&newwindow=1&safe=off&q=cache:ivNgGEdJCpcJ:d1002391.mydomainwebhost.com/JOT/Articles/6-6/Tane.pdf+%22Relativity,+Quantum+Mechanics,+and+Cla ssical+Physics%22

So, Newtonian physics and quantum theory are compatible.

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Quantum theory is

the branch of physics which studies matter and energy at the level of atoms and other elementary particles, and substitutes probabilistic mechanisms for classical Newtonian ones.

http://en.wiktionary.org/wiki/quantum_mechanics

Journal articles have shown that:
Observation affects reality; that is

when under observation, electrons are being "forced" to behave like particles and not like waves.

http://www.sciencedaily.com/releases/1998/02/980227055013.htm

In Classical Physics and in Quantum Mechanics, quantum particles can exist in more than one place at a time; that is

an object can be in two different points of space at the same time is not a dream. It is a fundamental data implicitly written in the basic equations of Physics and Mathematics, whose credibility has been warranted for long time by their ability to describe (and often forecast) experimental observations.

http://66.102.1.104/scholar?num=100&hl=en&lr=&newwindow=1&safe=off&q=cache:ivNgGEdJCpcJ:d1002391.mydomainwebhost.com/JOT/Articles/6-6/Tane.pdf+%22Relativity,+Quantum+Mechanics,+and+Cla ssical+Physics%22

It has been noted that there is no relationship among matter and reality.

Unobserved matter "behaves" like waves; yet, observation shapes matter into a form that is characteristic of particles.

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Concerning the unobserved object, which "can be in two different points of space at the same time," does observation provide a focal point for that object? Or...
Does observation localize the unobserved matter? Another way...
Does observation help to determine how the unobserved matter manifests itself, in the state known as reality?

As matter, observation, and reality have to share (some kind of) relationship, what is the link among matter and reality?

Reality Check

23rd July 2008, 10:37 PM

Allright.

Wave function (Wiki)

No relationship? I can see that one way; but, it seems that an Earthly reality would cease to exist, if the matter was not there to aid that reality.

Yea, the related explorations that concern philosophical questions may be better suited for another section.

Relativity, Quantum Mechanics, and Classical Physics: Evidence for a Close Link Between the Three Theories (Tane, 2004)

http://66.102.1.104/scholar?num=100&hl=en&lr=&newwindow=1&safe=off&q=cache:ivNgGEdJCpcJ:d1002391.mydomainwebhost.com/JOT/Articles/6-6/Tane.pdf+%22Relativity,+Quantum+Mechanics,+and+Cla ssical+Physics%22

So, Newtonian physics and quantum theory are compatible.

+++

Quantum theory is

http://en.wiktionary.org/wiki/quantum_mechanics

Journal articles have shown that:
Observation affects reality; that is

http://www.sciencedaily.com/releases/1998/02/980227055013.htm

In Classical Physics and in Quantum Mechanics, quantum particles can exist in more than one place at a time; that is

http://66.102.1.104/scholar?num=100&hl=en&lr=&newwindow=1&safe=off&q=cache:ivNgGEdJCpcJ:d1002391.mydomainwebhost.com/JOT/Articles/6-6/Tane.pdf+%22Relativity,+Quantum+Mechanics,+and+Cla ssical+Physics%22

It has been noted that there is no relationship among matter and reality.

Unobserved matter "behaves" like waves; yet, observation shapes matter into a form that is characteristic of particles.

+++

Concerning the unobserved object, which "can be in two different points of space at the same time," does observation provide a focal point for that object? Or...
Does observation localize the unobserved matter? Another way...
Does observation help to determine how the unobserved matter manifests itself, in the state known as reality?

As matter, observation, and reality have to share (some kind of) relationship, what is the link among matter and reality?
There is no link between matter and reality. They are 2 different things. You could have a universe that did not have any matter in it and that would be as real as a universe with matter in it. It just so happens that we exist in a universe with matter.

There are no quantum particles in "Classical Physics".

"Unobserved matter "behaves" like waves" is wrong. They have a wave function (which actually has little to do with waves). When the matter is observed it can act like a wave or a particle.
Unobserved matter is as real as observed matter (it is just that its state has not been measure yet).

"Concerning the unobserved object, which "can be in two different points of space at the same time," does observation provide a focal point for that object? ": No

Observation does affect reality on a quantum level, e.g the Quantum Zeno effect. It does not affect reality on a macroscopic level.

Newtonian physics and quantum theory are NOT compatible. There a links and similarities but there also incompatible phenomena, e.g there is no such thing a quantum entanglement in classical physics.

MattusMaximus

23rd July 2008, 11:12 PM

I teach physics, and one thing that is so tricky about discussing QM with non-physics folk is the issue of language.

Take this current thread - people are not using common terminology and it simply leads to a lot of confusion. And trust me, QM is confusing enough as it is! It seems to me that in order to have any meaningful progress on this discussion, we all need to have a common definition of "reality" from which to work.

Personally, in discussions of quantum physics such as this one, I like to define "reality" as "what can be measured in the lab". This makes sense to me, because ultimately, the process of methodological naturalism (i.e., the scientific method) boils down to making measurements. We can all also agree, I hope, that measuring something is giving us some kind of useful information.

I suggest that we try sticking to something more solid like that, otherwise we'll very quickly drift off into the land of philosophy. This is, after all, supposed to be a science thread...

So, back to the original question earlier in the thread... am I to assume that what is being asked is "Does the act of observation affect the measurement of a system?"?

If that is the question, then my answer is yes.

MattusMaximus

23rd July 2008, 11:25 PM

No relationship? I can see that one way; but, it seems that an Earthly reality would cease to exist, if the matter was not there to aid that reality.

Again, see my previous post. Before we get too far into this, we need to have a common agreement on how to define "reality".

Relativity, Quantum Mechanics, and Classical Physics: Evidence for a Close Link Between the Three Theories (Tane, 2004)

http://66.102.1.104/scholar?num=100&hl=en&lr=&newwindow=1&safe=off&q=cache:ivNgGEdJCpcJ:d1002391.mydomainwebhost.com/JOT/Articles/6-6/Tane.pdf+%22Relativity,+Quantum+Mechanics,+and+Cla ssical+Physics%22

So, Newtonian physics and quantum theory are compatible.

No, not really. Once you get to systems of particles (atoms, say) beyond roughly 100,000 or so, the quantum effects essentially get averaged out and the system will exhibit classical behavior. Quantum effects are only dominant on very small size scales.

ETA: Note that one exception to this general rule is a curious state of matter called a Bose-Einstein condensate (http://en.wikipedia.org/wiki/Bose_Einstein_condensate), which exhibits some quantum properties on a macroscopic scale.

http://66.102.1.104/scholar?num=100&hl=en&lr=&newwindow=1&safe=off&q=cache:ivNgGEdJCpcJ:d1002391.mydomainwebhost.com/JOT/Articles/6-6/Tane.pdf+%22Relativity,+Quantum+Mechanics,+and+Cla ssical+Physics%22

It has been noted that there is no relationship among matter and reality.

Again, what do you mean by "reality" here? We cannot make any progress on the discussion until we work this out.

Unobserved matter "behaves" like waves; yet, observation shapes matter into a form that is characteristic of particles.

Two key points here:

1. It seems to me that you have an understandable confusion on the point of what is called wave-particle duality (WPD) (http://en.wikipedia.org/wiki/Wave_particle_duality). WPD is the view that all matter (protons, neutrons, electrons, muons, quarks, etc) exhibits both the properties of a wave and of a particle. This doesn't necessarily mean that matter is a wave or is a particle - matter just behaves like both. I have a nice analogy to give you if you are still confused on this point.

2. When you talk about "observation shaping the waves into a particle", you seem to be referring to something called the Copenhagen interpretation of QM (http://en.wikipedia.org/wiki/Copenhagan_interpretation), which involves a process called wavefunction collapse. (http://en.wikipedia.org/wiki/Wavefunction_collapse) Is this what you're talking about?

Concerning the unobserved object, which "can be in two different points of space at the same time," does observation provide a focal point for that object? Or...
Does observation localize the unobserved matter? Another way...
Does observation help to determine how the unobserved matter manifests itself, in the state known as reality?

As matter, observation, and reality have to share (some kind of) relationship, what is the link among matter and reality?

I'm not sure what to make of this question. Let's deal with my earlier points first, so as not to get ahead of ourselves and lead to an even more confusing discussion.

Jimbo07

24th July 2008, 09:18 AM

I teach physics, and one thing that is so tricky about discussing QM with non-physics folk is the issue of language.

Which may be why, when I was taking QM, we were taught math. Language was used in the bar, afterward...

Ziggurat

24th July 2008, 10:55 AM

Yes, this poster is familiar with the standard definition; just looking for how a person might define those terms in his own words and relate them to physics and QM.

Matter is, roughly speaking, any massive particle. Reality includes space and time. Space and time are not matter. So that's an obvious part of the difference.

So, a wave function is a digital form of representation,

No. There is nothing digital about a wave function. One may represent it or approximate it with a digital representation of it, but that's not the same thing. The distinction has nothing to do with quantum mechanics either, it exists for classical properties too.

Quanta is a singly entity of quantifiable properties,

No. It almost always refers to energy. Position is quantifiable, but particles don't have quanta of position.

The body of evidence seems to indicate that matter is independent of observation reality; yet, reality is dependent upon observation.

A better way of phrasing this is that the time evolution of the universe (how things change over time) is affected by observation.

Can it be postulated that our thoughts, behaviors, perspective; etc help to create our unfolding future?

It can be. The problem is, this is an unscientific postulate. By that, I don't mean it's necessarily wrong, I mean it's unfalsifiable (just like it's unfalsifiable that your entire life is really just a dream). And it's also unnecessary to explain anything.

Perpetual Student

24th July 2008, 11:03 AM

So, back to the original question earlier in the thread... am I to assume that what is being asked is "Does the act of observation affect the measurement of a system?"?

If that is the question, then my answer is yes.

I do not believe that is true in Bohmian mechanics, which is as consistent with experimental results as the Copenhagen interpretation. Do you disagree?

Ziggurat

24th July 2008, 11:13 AM

I do not believe that is true in Bohmian mechanics, which is as consistent with experimental results as the Copenhagen interpretation. Do you disagree?

This is incorrect. How the measurement affects the system is different, but that it affects the system remains (as it must in order to agree with experiment). In the Bohm interpretation, the measurement of a particle doesn't directly change the properties of a particle, but it will affect the evolution of the accompanying wave, which will change the future time evolution of that wave and hence the future position of the particle.

INRM

24th July 2008, 11:37 AM

Oh well yes, I mean who doesn't know that... in fact I was just about to say the same myself.

Yuri

So, with Transactional Interpretation the "waves" that go forward and back in time are made of light? Or something that's light-like? Or some other wave?

I'm not sure of this part -- but I remember that even photons can send waves forward and back -- and if that's so, how does a photon produce another photon or another wave forward and back in time?

INRM

Perpetual Student

24th July 2008, 12:13 PM

This is incorrect. How the measurement affects the system is different, but that it affects the system remains (as it must in order to agree with experiment). In the Bohm interpretation, the measurement of a particle doesn't directly change the properties of a particle, but it will affect the evolution of the accompanying wave, which will change the future time evolution of that wave and hence the future position of the particle.

Please bear with me; I am a mathematician, not a physicist. My understanding of Bohmian mechanics is that the behavior of the wave and the particle are totally deterministic, based on initial conditions, and are not affected by observation. Specifically, the wave behaves strictly with "standard linear differential quantum-mechanical equations of motion," and is also not affected by observation (whatever that means). Is that not so?

The Man

24th July 2008, 01:45 PM

So, with Transactional Interpretation the "waves" that go forward and back in time are made of light? Or something that's light-like? Or some other wave?

I'm not sure of this part -- but I remember that even photons can send waves forward and back -- and if that's so, how does a photon produce another photon or another wave forward and back in time?

INRM

The Transactional Interpretation is based on Feynman Wheeler absorber theory which is based on the fact that Maxwell’s equations have both forward (retarded) and reverse (advanced) time solutions. So it is based fundamentally on electromagnetic waves, of which visible light is just a narrow band. Strong and weak interactions although not electromagnetic are also based on a model similar to that of electromagnetism (QED), the weak nuclear force being combined with electro-magnetism in electro-weak theory and the strong nuclear force defined by QCD which is somewhat analogues to QED. These theories give us the description of those three forces as the exchange of virtual particles to which a generalized absorber theory (not specifically electromagnetic) can be applied. For particles (or a wave packet) the Wave function is general consider a time developing probability distribution of finding (or detecting) the particle in a particular state at a given position or momentum.

http://en.wikipedia.org/wiki/Wave_packet

Ziggurat

24th July 2008, 02:05 PM

Please bear with me; I am a mathematician, not a physicist. My understanding of Bohmian mechanics is that the behavior of the wave and the particle are totally deterministic, based on initial conditions, and are not affected by observation. Specifically, the wave behaves strictly with "standard linear differential quantum-mechanical equations of motion," and is also not affected by observation (whatever that means). Is that not so?

Sort of. Between observations, the wave function obeys deterministic quantum mechanics. The particle's true state, however, is hidden between measurements. It is constrained by the wave function, but beyond that, we cannot tell whether it's deterministic or random, and if it is deterministic, we do not know what determines it. But regardless, the wave function still collapses upon measurement. The collapse process itself is now deterministic (it always collapses around the particle's state), but it still collapses, and future time evolution is now constrained by that collapse. So measurements still affect the system.

There is no possible theory of quantum mechanics which does not have measurement affecting the system being measured, because that aspect is experimentally observed. Exactly why and how many vary between interpretations, but any interpretation which tries to exclude this entirely will not be consistent with experiments. Randomness must be included somehow as well: either it's inherent to measurement processes ("collapse" is real and random, ala Copenhagen), in the rules for the time evolution of some hidden variable, or in the indeterminacy of some aspect of our experimental setup (random quantum state of our macroscopic measurement apparatus, random initial but deterministically evolving hidden variables, etc).

INRM

24th July 2008, 02:30 PM

The Transactional Interpretation is based on Feynman Wheeler absorber theory which is based on the fact that Maxwell’s equations have both forward (retarded) and reverse (advanced) time solutions. So it is based fundamentally on electromagnetic waves, of which visible light is just a narrow band. Strong and weak interactions although not electromagnetic are also based on a model similar to that of electromagnetism (QED), the weak nuclear force being combined with electro-magnetism in electro-weak theory and the strong nuclear force defined by QCD which is somewhat analogues to QED. These theories give us the description of those three forces as the exchange of virtual particles to which a generalized absorber theory (not specifically electromagnetic) can be applied. For particles (or a wave packet) the Wave function is general consider a time developing probability distribution of finding (or detecting) the particle in a particular state at a given position or momentum.

http://en.wikipedia.org/wiki/Wave_packet

So EM, Weak-Nuclear forces are somehow working together to exchange virtual particles which are going forward and back in time? Isn't virtual particles like that background radiation, casimir effect, and hawking-radiation thing? I didn't know those particles went backwards and forward in time?

INRM

Vorpal

24th July 2008, 02:35 PM

Observation is an interaction, and there is no such thing as a purely one-way interaction. In the Bohm interpretation, the system and its environment has some wavefunction Ψ that evolves according to the Schrödinger equation. If the system is decoupled from the environment, there will be a conditional wavefunction that also obeys the Schrödinger equation, effectively independently. A measurement, i.e., interaction with the environment, interrupts the Schrödinger evolution of the conditional wavefunction, but it isn't a "collapse" in the Copenhagen sense because it doesn't actually go away.

Reality Check

24th July 2008, 02:44 PM

So EM, Weak-Nuclear forces are somehow working together to exchange virtual particles which are going forward and back in time? Isn't virtual particles like that background radiation, casimir effect, and hawking-radiation thing? I didn't know those particles went backwards and forward in time?

INRM
It is not virual particles. It is wave functions.

lomiller

24th July 2008, 03:03 PM

No, not really. Once you get to systems of particles (atoms, say) beyond roughly 100,000 or so, the quantum effects essentially get averaged out and the system will exhibit classical behavior. Quantum effects are only dominant on very small size scales.

Which kind of highlights why “Moores Law” is nearing its end. Current microprocessors have transistors that are as small as 70 atoms across; the next generation of processors due out next year (if Moores law continued) will be as small as 45 atoms across.

INRM

24th July 2008, 04:29 PM

It is not virual particles. It is wave functions.

Then what did your statement about virtual-particles have to do with the statement?

Look, I'm not trying to be difficult here. I just don't get it.

INRM

sol invictus

24th July 2008, 04:52 PM

Randomness must be included somehow as well: either it's inherent to measurement processes ("collapse" is real and random, ala Copenhagen), in the rules for the time evolution of some hidden variable, or in the indeterminacy of some aspect of our experimental setup (random quantum state of our macroscopic measurement apparatus, random initial but deterministically evolving hidden variables, etc).

As I'm sure you know, local hidden variable theories are ruled out by Bell type experiments. Non-local ones are highly problematic.

But there is another option - in the many worlds interpretation the evolution of the wavefunction is always deterministic, but the results look random to the observer(s).

Reality Check

24th July 2008, 06:19 PM

Then what did your statement about virtual-particles have to do with the statement?

Look, I'm not trying to be difficult here. I just don't get it.

INRM
The Man's statement about virtual particles was part the description of forces in QCD and QED. The actual mathematics is about the wavefunction.

The Transactional Interpretation is based on Feynman Wheeler absorber theory which is based on the fact that Maxwell’s equations have both forward (retarded) and reverse (advanced) time solutions. So it is based fundamentally on electromagnetic waves, of which visible light is just a narrow band. Strong and weak interactions although not electromagnetic are also based on a model similar to that of electromagnetism (QED), the weak nuclear force being combined with electro-magnetism in electro-weak theory and the strong nuclear force defined by QCD which is somewhat analogues to QED. These theories give us the description of those three forces as the exchange of virtual particles to which a generalized absorber theory (not specifically electromagnetic) can be applied. For particles (or a wave packet) the Wave function is general consider a time developing probability distribution of finding (or detecting) the particle in a particular state at a given position or momentum.

Also see Transactional Interpretation (http://en.wikipedia.org/wiki/Transactional_interpretation) which is more fully explained by John Cramer here (http://www.npl.washington.edu/npl/int_rep/tiqm/TI_toc.html) and on many other web sites.

Perpetual Student

24th July 2008, 07:07 PM

It is claimed that Bohmian Mechanics is just as consistent with experimental results as is the Copenhagen interpretation. I am not aware of any controversy or dispute of this claim. It appears to leave one with a choice of which counter-intuitive theory to accept:

Copenhagen: The atomic world in not deterministic, leading to a number of metaphysical paradoxes.

Bohm: The atomic world is deterministic but non local, leading to other metaphysical paradoxes.

There have been some responses here by posters who are clearly not up to speed on Bohmian mechanics. Are there any comments from any one with a good understanding of Bohmiam mechanics?

INRM

24th July 2008, 09:13 PM

The Man's statement about virtual particles was part the description of forces in QCD and QED. The actual mathematics is about the wavefunction.

Also see Transactional Interpretation (http://en.wikipedia.org/wiki/Transactional_interpretation) which is more fully explained by John Cramer here (http://www.npl.washington.edu/npl/int_rep/tiqm/TI_toc.html) and on many other web sites.

Dude! I don't f*ckin' get it! I could have read what Cramer wrote -- I need an simple bottom line explanation...

Perpetual Student,

What's Bohmian Mechanics?

Reality Check

24th July 2008, 09:26 PM

Dude! I don't f*ckin' get it! I could have read what Cramer wrote -- I need an simple bottom line explanation...

Simple bottom line explanation:
When there is a measurement of the property of a system, a "hand-shake" or transaction happens between all possible states of the system to determine what the state of the system is.

Reality Check

24th July 2008, 09:56 PM

DrRocket

24th July 2008, 10:52 PM

The body of evidence for Quantum mechanics

...
Observation influences reality
Each quanta can exist in more than one place at the same time

I think your question basically boils down to: Quantum mechanics appears not to make much sense, so what is the data that supports this weird theory anyway ?

Whether you dig into the transactional interpretation of quantum mechanics or look for some other interpretation, you are going to remain a bit confused. If you are not confused then you should really start to worry.

One of the best every physicists when it comes to quantum theory was Richard Feynman. Here is a wonderful quote from him.

"There was a time when the newspapers said that only twelve men understood the theory of relativity. I do not believe that there ever was such a time. There might have been a time when only one man did, because he was the only guy who caught on, before he wrote his paper. But after people read the paper, a lot of people understood the theory of relativity in some way or other, certainly more than twelve. On the other hand, I can safely say that nobody understands quantum mechanics." – Richard P. Feynman in The Character of Physical Law

The evidence supporting quantum mechanics is basically a huge body of experiment in which quantum theory, particularly quantum electrodynamics, has provided consistent agreement with what is observed, to about 16 decimal places. It is a terribly confusing theory, but it works. If it didn't work your radio wouldn't work either, and we would not be having this discussion because your computer would be non-functional as well.

If you would like to see just how weird it can get, you might take a look at the book More than One Mystery by Mark Silverman. http://www.amazon.com/More-Than-One-Mystery-Explorations/dp/0387943765

sol invictus

25th July 2008, 02:50 AM

Copenhagen: The atomic world in not deterministic, leading to a number of metaphysical paradoxes.

Such as?

Bohm: The atomic world is deterministic but non local, leading to other metaphysical paradoxes.

The biggest problem with Bohm, in my view, is that it is non-local in a way that probably makes it incompatible with Lorentz invariance. That's what I was referring to when I said above that non-local hidden variable theories (such as Bohm's) are very problematic. Until someone demonstrates otherwise I don't see the point in spending much time thinking about it.

There have been some responses here by posters who are clearly not up to speed on Bohmian mechanics. Are there any comments from any one with a good understanding of Bohmiam mechanics?

I'm reasonably familiar with it. What would you like to know?

Perpetual Student

25th July 2008, 06:52 PM

sol invictus:

Thanks for your response concerning Bohmian mechanics.
Such as? (Referring to metaphysical paradoxes of the Copenhagen interpretation).
How about:
1. “Superposition” of physical location and other physical quantities,
2. Wave-particle duality,
3. Collapse of the wave function caused by the act of human “observation.”
Have you become so accustomed to the paradoxes of the Copenhagen interpretation, that you have become habituated to the point of unawareness?

Thanks for pointing out the incompatibility of Bohm with Lorentz invariance. I’m going to look into that question.
I appreciate your offer to discuss Bohmian mechanics further. I’ll follow up after I spend a little time with the Lorenz transformation. I would be happy to exchange non-locality for the strangeness of the prevailing Copenhagen dogma -- but only if it is justifiable.

I was initially drawn to the jref forums by an ad I saw in Scientific American for Terence Witt’s book. I have concluded he is an air-headed narcissist. For one thing, his treatment of “infinity” is abominable! Too bad -- the advertisement had so much promise.

As I have mentioned before, I am a retired mathematician dabbling in quantum physics, relativity and how they relate to cosmological questions. All help is needed and appreciated.

INRM

25th July 2008, 09:00 PM

Or a more complex bottom line explanation:
Quantum mechanics involves equations such as Schrödinger equation that are symmetric with respect to time-inversion (this is also true of Maxwell's electromagnetic equations). This means that it is just as valid to have a wavefunction that describes a system evolving into the past as it is to have a wavefunctions describing a system evolving into the future (the usual situation).
The Transactional Interpretaion states that both happen, e.g. in a system consisting of an emitter that transfers energy to an absorber the following happens:

The emitter sends out an “offer wave” forward in time (retarded wave).
The absorber responds with a “confirmation wave” backward in time (advanced wave).
The process repeats until energy and momentum is transferred and the transaction is completed (wave function collapse).

Okay what's Maxwell's electromagnetic equations? And has Quantum-Mechanics actually proven that waves or systems that can evolve into the past or into the future?

Additionally, why do most if not all of the universe go forward in time and you have this stuff going backwards?

Also, this transactional interpretation, when combined with the afshar experiment (which had photons and their waves being measured at the same time) kind of invalidate the Heisenberg Uncertainty theory, and also invalidate all forms of randomness?

My opinion is that it actually does, although I've never been able to get a straight forward answer as to why it would or wouldn't.

INRM

sol invictus

25th July 2008, 11:16 PM

Such as? (Referring to metaphysical paradoxes of the Copenhagen interpretation).
How about:
1. “Superposition” of physical location and other physical quantities,
2. Wave-particle duality,
3. Collapse of the wave function caused by the act of human “observation.”
Have you become so accustomed to the paradoxes of the Copenhagen interpretation, that you have become habituated to the point of unawareness?

#3 is not correct (or at best is incomplete) - collapse of the wave function occurs when there is any interaction with a macroscopic device, not just from human observation.

I don't regard these as paradoxes, no. A paradox is a logical inconsistency, indicating that the theory is wrong and must be corrected. There is no such inconsistency there.

I would be happy to exchange non-locality for the strangeness of the prevailing Copenhagen dogma -- but only if it is justifiable.

Words like "dogma" aren't going to help the conversation along much. As for justifiability, as you are no doubt aware the experimental evidence for QM is overwhelming. The computer you're reading this post on would not exist without it. The same goes for Lorentz invariance. So as I said, until someone demonstrates a version of Bohmian QM compatible with relativity, it's not very interesting.

I was initially drawn to the jref forums by an ad I saw in Scientific American for Terence Witt’s book. I have concluded he is an air-headed narcissist. For one thing, his treatment of “infinity” is abominable! Too bad -- the advertisement had so much promise.

Welcome to the forum. Witt is a classic physics crackpot - you'll find hundreds like him if you look around the internet.

As I have mentioned before, I am a retired mathematician dabbling in quantum physics, relativity and how they relate to cosmological questions. All help is needed and appreciated.

Sounds like fun! What kind of math did you do?

Reality Check

26th July 2008, 12:17 AM

Perpetual Student

26th July 2008, 09:52 AM

#3 is not correct (or at best is incomplete) - collapse of the wave function occurs when there is any interaction with a macroscopic device, not just from human observation.

I don't regard these as paradoxes, no. A paradox is a logical inconsistency, indicating that the theory is wrong and must be corrected. There is no such inconsistency there.

Words like "dogma" aren't going to help the conversation along much. As for justifiability, as you are no doubt aware the experimental evidence for QM is overwhelming. The computer you're reading this post on would not exist without it. The same goes for Lorentz invariance. So as I said, until someone demonstrates a version of Bohmian QM compatible with relativity, it's not very interesting.

Welcome to the forum. Witt is a classic physics crackpot - you'll find hundreds like him if you look around the internet.

Sounds like fun! What kind of math did you do?

In what way is the concept of "superposition" not contrary to common experience, paradoxical and counterintuitive? You seem to give a lot of slack to the Copenhagen interpretation.

The word “dogma” can be “loaded.” That is not the meaning I had in mind.

I am well aware of the success of QM and the role of the Lorentz transformation in SR. Nevertheless, I am seeing claims that Bohm’s interpretation of QM does not change that. As to Lorentz invariance, some sources claim that the Schroedinger equation itself is not compatible with Lorentz invariance, irrespective of the choice between Bohm and Copenhagen? Am I missing something?

My mathematics career was a bit mundane -- teaching at the university level and actuarial work. In any case, it does not provide the needed tools for these subjects. I hope that the few neurons that I possess (that can still fire from time to time) will help me through this. I have just begun this quest – I would like to know a little more about the universe before returning to oblivion.

Are you familiar with the Stanford Encyclopedia of Philosophy article about Bohmian mechanics? If not, it may be worth reading.

INRM

26th July 2008, 12:58 PM

Maxwell's equations (http://en.wikipedia.org/wiki/Maxwell%27s_equations)
Yes - Quantum-Mechanics equations read the same with time negative.
No one knows.
No.

1.) What experiments may I ask, have *proven* equations can evolve forward or back in time? Because I don't know how reliable an equation is if it hasn't been proven (I could be wrong though) through experiments.

2.) No one knows which part? Whether it would disprove the Heisenberg Uncertainty Equation? Or all randomness?

INRM

MattusMaximus

26th July 2008, 02:45 PM

In what way is the concept of "superposition" not contrary to common experience, paradoxical and counterintuitive? You seem to give a lot of slack to the Copenhagen interpretation.

You should note that the concept of superposition did not originate with QM - originally the notion of superposition was used to describe the behavior of various kinds of wave phenomena. These include constructive and destructive interference, standing waves, beats, two-source interference patterns, shock-wave formation, etc. The concept of superposition was applied to water waves, sound waves, and light waves long before QM came on the scene, so it was a classically originated and understood concept.

One formulation of QM is through the definition of something called a wave function (http://en.wikipedia.org/wiki/Wave_function), because it was observed that both photons (energy) and electrons (matter) exhibit wave-like behavior when studied in, for example, Young's double slit experiment. (http://en.wikipedia.org/wiki/Double-slit_experiment)

You should also note that this isn't the only formulation of QM. In the early years of the theory, another formulation was through the use of matrices called matrix mechanics (http://en.wikipedia.org/wiki/Werner_Heisenberg#Matrix_Mechanics_and_the_Nobel_P rize). It was shown long ago that both the wave function and matrix mechanics formulations of QM are mathematically equivalent.

Based upon these facts, I think it is much more appropriate to speak of the wave function as a kind of mathematical tool that helps us conceptually to bridge the classical / quantum divide. This is my preferred view of the issue.

I am well aware of the success of QM and the role of the Lorentz transformation in SR. Nevertheless, I am seeing claims that Bohm’s interpretation of QM does not change that. As to Lorentz invariance, some sources claim that the Schroedinger equation itself is not compatible with Lorentz invariance, irrespective of the choice between Bohm and Copenhagen? Am I missing something?

Yes, you are missing something. It was shown decades ago by P.A.M. Dirac and others that QM (including the Schrodinger equation formulation) is consistent and compatible with Lorentz invariance and Special Relativity in a theory called Quantum Electro-Dynamics (QED). (http://en.wikipedia.org/wiki/Quantum_electrodynamics)

And, before you ask, yes we know that QED works. We have oodles of technology (such as your computer) based off the physics of QED.

My mathematics career was a bit mundane -- teaching at the university level and actuarial work. In any case, it does not provide the needed tools for these subjects. I hope that the few neurons that I possess (that can still fire from time to time) will help me through this. I have just begun this quest – I would like to know a little more about the universe before returning to oblivion.

What are the forms of mathematics of which you are knowledgeable? In order to get a decent understanding of QM, SR, and QED you need to have the proper math under your belt. I'd say that you need to understand partial differential equations, multivariable calculus, matrix algebra, and some tensor calculus to get there.

sol invictus

26th July 2008, 03:09 PM

In what way is the concept of "superposition" not contrary to common experience, paradoxical and counterintuitive? You seem to give a lot of slack to the Copenhagen interpretation.[/quote[

Superposition works in any formulation of QM including Bohm's. In fact it works for any linear differential equation (including, as MM says, most wave eqs), as you must know if you know some math.

[quote]As to Lorentz invariance, some sources claim that the Schroedinger equation itself is not compatible with Lorentz invariance, irrespective of the choice between Bohm and Copenhagen?

The SE is not Lorentz invariant as you can see at a glance. But as MM says, in the standard interpretations it is the non-relativistic limit of various relativistic theories (QED in the case of electrons). I don't know how to make a relativistic formulation of Bohm, so the same cannot be said there.

Are you familiar with the Stanford Encyclopedia of Philosophy article about Bohmian mechanics? If not, it may be worth reading.

I had a look. It reads like something written by a philosopher rather than a physicist, which makes me suspicious. It also seems to have a strong pro-Bohmian bias...

The Man

26th July 2008, 05:00 PM

Okay what's Maxwell's electromagnetic equations? And has Quantum-Mechanics actually proven that waves or systems that can evolve into the past or into the future?

Additionally, why do most if not all of the universe go forward in time and you have this stuff going backwards?

Also, this transactional interpretation, when combined with the afshar experiment (which had photons and their waves being measured at the same time) kind of invalidate the Heisenberg Uncertainty theory, and also invalidate all forms of randomness?

My opinion is that it actually does, although I've never been able to get a straight forward answer as to why it would or wouldn't.

INRM

If the equations work, which have been demonstrated and they include advanced (or reverse time solutions) then there should be no reason why those solutions should not be included, unless some reason can be found as to why those other solutions would be suppressed.

This is initially what inspired Wheeler and Feynman to develop absorber theory that the equations have both solutions but our universe appears dominated by retarded (or forward time) interactions. The half amplitude retarded wave (from the emitter) combines with the half amplitude advanced wave (from the absorber) which is 180 degrees out of phase. That phase shift in the advanced wave puts it in phase with the retarded wave going forward in time (a reverse time 180 degree out of phase wave is like an in phase forward time wave). This results in a full amplitude retarded wave going from the emitter to the absorber (or the forward time interaction). The advanced wave from the emitter is suppressed by the advanced and out of phase wave of the absorber going backwards in time from the emitter. Likewise the retarded wave of the absorber is suppressed by the out of phase retarded wave of the emitter going forward in time from the absorber, so the waves constructively interfere between the emitter and absorber but destructively interfere before and after the transaction.

No, the transactional interpretation does not invalidate Heisenberg Uncertainty, what is does do is move the reason for the collapse of the state vector, from the specific act of observation, to the absorber (and the confirmation wave) which may not necessarily be part of any particular conscious observation. More specifically it moves the time and location of the sate vector collapse from any particular time and position of any possible observation to that collapse happening along the entire four vector of the transaction. The resulting “collapsed” wave function still adheres to the uncertainty principle. Randomness is likewise still intact but would become somewhat more definitive as the probability of some future absorber.

Thanks, Reality Check, for your accurate and descriptive posts on this subject.

INRM

26th July 2008, 08:39 PM

If the equations work, which have been demonstrated and they include advanced (or reverse time solutions) then there should be no reason why those solutions should not be included, unless some reason can be found as to why those other solutions would be suppressed.

Okay, so the equations work as described, and as such the reverse-time sections *should* be true as well as a result?

However if they have actually done experiments where they sent waves or photons forward and backwards in time, what experiments were these?

INRM

Reality Check

27th July 2008, 01:48 AM

1.) What experiments may I ask, have *proven* equations can evolve forward or back in time? Because I don't know how reliable an equation is if it hasn't been proven (I could be wrong though) through experiments.

2.) No one knows which part? Whether it would disprove the Heisenberg Uncertainty Equation? Or all randomness?

INRM
1) No experiments are needed. The same equations that describe things going foward in time are just as vaid when time is reversed.
2) "Additionally, why do most if not all of the universe go forward in time and you have this stuff going backwards? "

sol invictus

27th July 2008, 03:21 AM

In fairness to INRM there is a very deep question one can ask, namely why there is an "arrow of time" at all. In other words, why do things happen differently going forward in time rather than backwards, given that the fundamental equations of physics are time-reversal invariant*?

We know part of the answer, which is that we live during a phase of the universe's evolution where it is still strongly affected by a very special "initial" condition (just after the big bang, say) which leads to a solution to the equations which is asymmetric in time. But we don't know why those were the initial conditions.

*To be precise they are CPT invariant, but that's just as good for these purposes.

Skwinty

27th July 2008, 04:32 AM

Question here.
Don't the laws of thermodynamics dictate the flow of time?
Order to disorder? Increasing entropy and all that.

sol invictus

27th July 2008, 06:14 AM

Question here.
Don't the laws of thermodynamics dictate the flow of time?
Order to disorder? Increasing entropy and all that.

Yes, but that's only the first layer of the answer. Thermodynamics is a coarse description of microphysics - that is, it describes the average behavior of large numbers of particles. Its laws must follow from the microphysics, because they are fully determined by it - and yet the microphysical equations are time-reversal invariant.

So one can ask why there is a second law of thermodynamics - what defines the direction in which entropy increases. The answer, at least the second layer of it, is as I indicated above.

The Man

27th July 2008, 08:23 AM

Okay, so the equations work as described, and as such the reverse-time sections *should* be true as well as a result?

Actually, as I indicated in my previous post those advanced solutions must be just as valid as the retarded solutions (since they are part of the same equations). The best you can do is to show how the advanced solutions might be suppressed, as they are considered to be in the TI (Transactional Interpretation) before the transaction and the retarded solutions suppressed after the transaction.

However if they have actually done experiments where they sent waves or photons forward and backwards in time, what experiments were these?
INRM

Well based on Maxwell’s equations that would be any experiment that involves electro-magnetic radiation.

Now if you want an experiment that might confirm TI, you might find it in the Afshar Experiment, as John G. Cramer considers a possibility.

http://www.analogsf.com/0412/altview.shtml

Does this mean that the theory of quantum mechanics has also been falsified? No indeed! The quantum formalism has no problem in predicting the Afshar result. A simple quantum mechanical calculation using the standard formalism shows that the wires should intercept only a very small fraction of the light. The problem encountered by the Copenhagen and Many-Worlds Interpretations is that the Afshar Experiment has identified a situation in which these popular interpretations of quantum mechanics are inconsistent with the quantum formalism itself.

What about the Transactional Interpretation, which describes each quantum process as a handshake between a normal "offer" wave (y) and a back-in-time advanced "confirmation" wave (y*)? The offer waves from the laser pass through both pinholes and cancel at the positions of the zeroes in the interference pattern. Therefore, no transactions can form at these locations, and the wires can intercept only a very small amount of light. Thus, the Transactional interpretation is completely consistent with the results of the Afshar Experiment and with the quantum formalism.

Some more articles by John G. Cramer

http://www.npl.washington.edu/av/

An excellent slide show

http://faculty.washington.edu/jcramer/PowerPoint/AAAS_20060621%20.ppt

For me, the jury is still out, I find that the lack of “which way” knowledge for the photon paths not intercepted, tends to invalidate the experiment as a refutation of Copenhagen complementation but I am still researching the various explanations of the results.

INRM

27th July 2008, 03:35 PM

The Man,

Actually, as I indicated in my previous post those advanced solutions must be just as valid as the retarded solutions (since they are part of the same equations). The best you can do is to show how the advanced solutions might be suppressed, as they are considered to be in the TI (Transactional Interpretation) before the transaction and the retarded solutions suppressed after the transaction.

Well based on Maxwell’s equations that would be any experiment that involves electro-magnetic radiation.

Did maxwell's equations ever test for this, or did he do any test that verified this? Or do the equations simply logically follow that reverse time solutions were possible?

Now if you want an experiment that might confirm TI, you might find it in the Afshar Experiment, as John G. Cramer considers a possibility.

http://www.analogsf.com/0412/altview.shtml

Did the Afshar experiment actually confirm the existance of the advanced waves, and retarded waves, or just standard light-waves? I'm curious because the reading of the quote seems to suggest that it is "consistant" with the TI theory, but I'm not sure if it also means "conclusive" (am I wrong?)...

For me, the jury is still out, I find that the lack of “which way” knowledge for the photon paths not intercepted, tends to invalidate the experiment as a refutation of Copenhagen complementation but I am still researching the various explanations of the results.

The Copenhagen complementation includes the Heisenberg Uncertainty principle correct? Does it include all forms of randomness, or just the Heisenberg Uncertainty principle?

When you speak of "which way" paths, do you mean forward and backwards waves?

leon_heller

27th July 2008, 04:08 PM

Okay what's Maxwell's electromagnetic equations?

INRM

http://www.google.co.uk/search?hl=en&q=maxwell+equations&btnG=Google+Search&meta=

Leon

Perpetual Student

27th July 2008, 04:49 PM

“Superposition” of waves is a meaningful and quite an intuitive phenomenon; the mathematics and the physical reality are easily understood. Superposition of the location of a particle or other attribute like spin may be mathematically transparent but is quite counterintuitive physically.

Bohmian mechanics does away with superposition of quantum states.

Sheldon Goldstein, the author of the Stanford Encyclopedia article, is a physicist at Rutgers, not a philosopher. Unfortunately, I can’t find much else about him on the net.
There are various interesting links at the end of the Stanford Encyclopedia article, including correspondence between Goldstein and Murray Gell-Mann and Steven Weinberg. He is a self proclaimed champion (my choice of words) of Bohm’s theories. Both Gell-Mann and Weinberg seemed to have taken his correspondence seriously enough to warrant responses.

Thank you MM and s i for your input. My mathematics is marginally adequate for my quest; I do need to shake off some rust -- especially in the area of tensor calculus. Now that I am retired, this is my job!

Perpetual Student

27th July 2008, 04:52 PM

“Superposition” of waves is a meaningful and quite an intuitive phenomenon; the mathematics and the physical reality are easily understood. Superposition of the location of a particle or other attribute like spin may be mathematically transparent but is quite counterintuitive physically.

Bohmian mechanics does away with superposition of quantum states.

Sheldon Goldstein, the author of the Stanford Encyclopedia article, is a physicist at Rutgers, not a philosopher. Unfortunately, I can’t find much else about him on the net.
There are various interesting links with the Stanford Encyclopedia article, including correspondence between Goldstein and Murray Gell-Mann and Steven Weinberg. He is a self proclaimed champion (my choice of words) of Bohm’s theories. Both Gell-Mann and Weinberg seemed to have taken his correspondence seriously enough to warrant responses.

Thank you MM and s i for your input. My mathematics is marginally adequate for my quest; I do need to shake off some rust -- especially in the area of tensor calculus. Now that I am retired, this is my job!

The Man

27th July 2008, 05:43 PM

The Man,

Did maxwell's equations ever test for this, or did he do any test that verified this? Or do the equations simply logically follow that reverse time solutions were possible?

How many times do I have to say it, the equations have been verified and they allow reverse time solutions.

I do not know how one might confirm or disprove the existence of the advanced waves (or I would be doing it).

Did the Afshar experiment actually confirm the existance of the advanced waves, and retarded waves, or just standard light-waves? I'm curious because the reading of the quote seems to suggest that it is "consistant" with the TI theory, but I'm not sure if it also means "conclusive" (am I wrong?)...

A “standard light wave” would normally be considered a retarded wave.

As I said the jury is still out for me, so I certainly do not consider it conclusive at this time, but then who am I anyway. I suggest you read up on the conclusions about the experiment and try to determine for yourself.

The Copenhagen complementation includes the Heisenberg Uncertainty principle correct? Does it include all forms of randomness, or just the Heisenberg Uncertainty principle?

Actually Copenhagen complementation is just a generalized extension of the Uncertainty principle complementation to wave particle duality, Heisenberg’s Uncertainty principle was developed as Fourier transforms of the energy and momentum aspects of a wave packet.

When you speak of "which way" paths, do you mean forward and backwards waves?

No, in that application the “which way” was referring to what slit or hole of the double slit experiment the photon could be identified to have passed through.

INRM

27th July 2008, 08:03 PM

How many times do I have to say it, the equations have been verified and they allow reverse time solutions.

I do not know how one might confirm or disprove the existence of the advanced waves (or I would be doing it).

So obviously the equations allow reverse time solutions but reverse time solutions have not been proven...

A “standard light wave” would normally be considered a retarded wave.

How so? The "retarded" term would mean the wave would have to appear to be moving slower than light would normally move I would assume because if it's going forward in time, the wave would seem to be moving really slow right?

Actually Copenhagen complementation is just a generalized extension of the Uncertainty principle complementation to wave particle duality, Heisenberg’s Uncertainty principle was developed as Fourier transforms of the energy and momentum aspects of a wave packet.

Thank you for the detail

INRM

MattusMaximus

27th July 2008, 10:18 PM

Vorpal

28th July 2008, 12:07 AM

How so? The "retarded" term would mean the wave would have to appear to be moving slower than light would normally move I would assume because if it's going forward in time, the wave would seem to be moving really slow right?
Let's back up a bit to something simpler. Take a charge moving in any physically reasonable manner whatsoever. If you watch the charge, the information where the charge has moved from one moment to the next will not be immediately available to you because of the limitation of lightspeed. But also because of this limitation, the field some distance r away from the charge should be deducible from what the charge distribution and current was a time of r/c in the past. So we call t' = t - r/c retarded time and have all kinds of nice solutions that look like waves propagating from the source. The stranger part is that we can also define advanced time t" = t + r/c and have all kinds of solutions there as well, that look like either waves propagating outward backward in time or converging to the source in normal time.

You're right--the advanced wave solutions are typically thrown out as unphysical. But it isn't a trivial thing. Maxwell's equations are both linear and symmetric in time, so in fact the general solution is a superposition of the retarded and advanced solutions. If elementary charges do not interact with their own field and absorption is a kind of reflection (advanced<->retarded), then an emitted advanced wave interferes destructively with its reflected retarded counterpart, which passed back through it and interferes constructively with the emitted retarded wave. End result: we see a net retarded wave, but we get it without artificially throwing out half the solutions to Maxwell's equations. It's not a total victory, because we replaced one ad hoc process (throwing out solutions) with others (e.g., no-self-interactions). However, there are other advantages to this approach--and unfortunately also other problems.

But most of those issues are not directly relevant here--the transactional interpretation is only qualitatively similar. The emitted retarded "offer wave" is responded with an advanced "confirmation wave", with the full physical interaction described by their sum. Once again, with destructive interference at most places--remember that this isn't really a theory, but rather a re-interpretation of an existing theory.

sol invictus

28th July 2008, 01:02 AM

Bohmian mechanics does away with superposition of quantum states.

That's false, of course - if it were true Bohmian mechanics would be ruled out immediately by experiment. The Schrodinger equation is unchanged, and (like any other linear diff. eq.) it allows solutions to be superposed. The only thing that changes with Bohm is that one adds an extraneous ingredient, namely a set of positions for the particles which are fully determined by the wavefunction. This changes the interpretation of the meaning of the superposition of two (say) position eigenstates, but it does not alter the math.

Sheldon Goldstein, the author of the Stanford Encyclopedia article, is a physicist at Rutgers, not a philosopher. Unfortunately, I can’t find much else about him on the net.

He appears to be in the math department there, actually.

The Man

28th July 2008, 08:05 AM

So obviously the equations allow reverse time solutions but reverse time solutions have not been proven...

As they have not been disproven either, an important aspect you should not leave out.

How so? ...

Because they appear to be moving forward in time, as most things do.

The "retarded" term would mean the wave would have to appear to be moving slower than light would normally move I would assume because if it's going forward in time, the wave would seem to be moving really slow right? ...

Other then what Vorpal has written, in some cases (as in a retarded bomb) the term “retarded” refers to a reduction in velocity, in this case it specifically refers to the delay (in time) between when the photon is emitted and when it is absorbed.

http://en.wikipedia.org/wiki/Retarded_time

Thank you for the detail

INRM

No problem

Ziggurat

28th July 2008, 11:39 AM

Bohmian mechanics does away with superposition of quantum states.

I highly doubt that. Among other things, whether or not a particular quantum state is a "superposition" depends upon the basis set you want to use (a "pure" state in one basis set is necessarily a superposition in another basis set), and I don't see why Bohmian mechanics would prevent you from switching basis sets.

Perpetual Student

28th July 2008, 12:04 PM

He appears to be in the math department there, actually.

Yes, but he is identified as a physicist in his correspondence with Weinberg. The math and physics departments at Rutgers may be organized in a non-typical way, or he is a physicist in the math dept.(?)

INRM

28th July 2008, 12:20 PM

As they have not been disproven either, an important aspect you should not leave out.

It's kind of funny that if this was on the religion forum and we were discussing something of that sort and I said "the existance of XYZ had not been disproven either" I'd get jumped on with "You can't prove a negative!"

I thought skeptics were supposed to restrain judgement on an issue until proven true...

I'm simply saying that if it hasn't been proven true, then why should we automatically assume it's true. Speculate sure, but if one has not proven that it's true, one should not automatically assume it to be so. That's not skeptical, that's faithful.

Because they appear to be moving forward in time, as most things do.

Everything pretty much moves forward in time. How exactly do you distinguish if a beam of light is moving forward in time faster than the rest of time?

Other then what Vorpal has written, in some cases (as in a retarded bomb) the term “retarded” refers to a reduction in velocity, in this case it specifically refers to the delay (in time) between when the photon is emitted and when it is absorbed.

http://en.wikipedia.org/wiki/Retarded_time

But if they detected the photon's emission... how do they know it was retarded? Were they able to ascertain that?

INRM

Perpetual Student

28th July 2008, 06:57 PM

MM and s i:

At the risk of belaboring a point, below is a quote from an article (written by David Albert (Columbia University) in the May 1994 edition of Scientific American:
"Notwithstanding all the evidence to the contrary presented above, Bohm's theory presumes that particles are the sorts of things that are invariably located in one or another particular place. In addition, Bohm's theory is a great deal clearer than is the Copenhagen interpretation about what the world is made of. In Bohm's account, wave functions are not merely mathematical objects but physical ones, physical things. Bohm treats them somewhat like classical force fields, such as gravitational and magnetic fields. What wave functions do in Bohm's theory (just as classical force fields do) is to in effect push the particles around, to guide them, as it were, along their proper courses.
The laws that govern the evolutions of those wave functions in time are stipulated to be precisely the standard linear differential quantum-mechanical equations of motion--but this time with no exceptions whatever. There are other laws in Bohm's theory as well that dictate how those wave functions push their respective particles around. All those laws are fully deterministic. Therefore, the positions of all the particles in the world at any time, and the world's complete quantum-mechanical wave function at that time, can be calculated with certainty from the positions of all the particles in the world and the world's complete quantum-mechanical wave function at any earlier time."

It seems that the above description precludes "superposition” of the location of particles, which is an essential part of the Copenhagen interpretation and is an important counter aspect of Bohmian mechanics.

Vorpal

28th July 2008, 07:34 PM

I'm simply saying that if it hasn't been proven true, then why should we automatically assume it's true.
What are you talking about? Advanced waves are widely held to be non-physical because of their acausal behavior. No one automatically assumes that they exist. The explicit admission of advanced electromagnetic waves by Dirac, Wheeler, and Feynman was done to solve specific problems of classical electromagnetism, among which are electron self-energy (which is infinite without advanced wave solutions but finite with them) and others. How well such models solve the problems they intend to solve is a matter of debate, but if they did so adequately, we would be justified in believing that advanced waves exist exactly because the model says they do. If the model does not not perform adequately, we would not be justified in believing they exist.

Speculate sure, but if one has not proven that it's true, one should not automatically assume it to be so. That's not skeptical, that's faithful.
See above. Please don't pretend that they came just because.

Everything pretty much moves forward in time. How exactly do you distinguish if a beam of light is moving forward in time faster than the rest of time?
I'm not sure if I can parse this. A beam of light in vacuum is always moving at the same speed.

But if they detected the photon's emission... how do they know it was retarded? Were they able to ascertain that?
The principle of causality.

---

If you see an electromagnetic plane wave coming in from infinity, there's nothing to distinguish it from an outgoing plane wave going backwards in time. That's just the mathematical formalism. But that isn't what the issue is all about.
Problem: Action-at-a-distance.
Solution: At each moment, treat a distribution as if it instantaneously comes into and then out of existence. Then the a charge would send out spherical waves that inform other charges of its existence, and things like the Coulomb interaction are actually due to that wavefront.
Problem: The full solution is half-retarded and half-advanced.
Now, here we don't get a clean solution. If we simply discard the advanced component, we get some problems, such as divergent self-energy for electrons. Nor is it plausible to simply re-interpret the outgoing advanced solution as an incoming retarded wave: this would mean that there is a perfectly spherical wave incident the charge at any given moment--where did it come from and how was it generated?

The W-F model is that the advanced wave really is there, but destructively interferes with the response from the other charges, so we observe only the retarded waves. This isn't something ad hoc: admission of advanced waves was intended to solve the difficulties that EM has with point-charges. Many physicists, including Feynman himself, concluded later that the model doesn't do a very good job of this, but the point remains that advanced waves were never any sort of article of faith. Besides, the advanced waves of transactional QM were intended to solve somewhat different problems.

INRM

29th July 2008, 12:25 AM

What are you talking about? Advanced waves are widely held to be non-physical because of their acausal behavior.

Huh? How can something be non physical? It follows some law of physics right? If so it's physical.

No one automatically assumes that they exist. The explicit admission of advanced electromagnetic waves by Dirac, Wheeler, and Feynman was done to solve specific problems of classical electromagnetism, among which are electron self-energy (which is infinite without advanced wave solutions but finite with them) and others.

What exactly is electron self-energy? If the electron self-energy is infinite without advanced-wave solutions, doesn't that sort of prove there are advanced waves? Or is there some other way that might yield plausible (finite) results for electron self-energy?

The principle of causality.

So, there were definetly retarded-waves in the afshar experiment... in the form of a delayed energy release? Have they been able to conclude that the retarded-wave is likely to be the result of a transactional interpretation, or it's just an energy release of some sort.

If you see an electromagnetic plane wave coming in from infinity, there's nothing to distinguish it from an outgoing plane wave going backwards in time. That's just the mathematical formalism. But that isn't what the issue is all about.
Problem: Action-at-a-distance.
Solution: At each moment, treat a distribution as if it instantaneously comes into and then out of existence. Then the a charge would send out spherical waves that inform other charges of its existence, and things like the Coulomb interaction are actually due to that wavefront.
Problem: The full solution is half-retarded and half-advanced.
Now, here we don't get a clean solution. If we simply discard the advanced component, we get some problems, such as divergent self-energy for electrons. Nor is it plausible to simply re-interpret the outgoing advanced solution as an incoming retarded wave: this would mean that there is a perfectly spherical wave incident the charge at any given moment--where did it come from and how was it generated?

You just gave me a bunch of gibberish that I don't completely understand. I don't know what a Coulomb or a Coulomb interaction, or self-energy, or outgoing plane-wave. I'm not a physicist.

The W-F model is that the advanced wave really is there, but destructively interferes with the response from the other charges, so we observe only the retarded waves. This isn't something ad hoc: admission of advanced waves was intended to solve the difficulties that EM has with point-charges. Many physicists, including Feynman himself, concluded later that the model doesn't do a very good job of this, but the point remains that advanced waves were never any sort of article of faith.

What's the W-F model?

Besides, the advanced waves of transactional QM were intended to solve somewhat different problems.

What problems? Collapsing wave functions right?

INRM

Vorpal

29th July 2008, 01:38 AM

Huh? How can something be non physical? It follows some law of physics right? If so it's physical.
If you watch a movie backwards, all the mechanical interactions are physically possible, but it doesn't mean that it's physically reasonable overall.

What exactly is electron self-energy?
Think about assembling a charge distribution. As you bring in more and more bits of charge, you have to do work against the electromagnetic forces due to the charges already there. This work is stored in the field. Now, imagine doing the same thing for an individual electron, assembling its "bits" of charge. There's another way of thinking about it as well that doesn't involve trying to decompose the electron: electromagnetic fields carry momentum, so the field of an electron contributes to its mass. The problem is that if an electron is a point-particle, this mass contribution is infinite. And it doesn't really help to think of the electron as having positive size that's just very small--experimentally, the electron, if it has any positive size, is still much smaller than the "classical electron radius" predicted by attributing electron mass entirely to due to the field.

(Actually, the real problem is electron self-force: as the electron moves, its field lags behind it slighly, and the predicted force of this retarded field on the electron is infinite. Allowing it to have an advanced field as well cancels this infinity, incidently eliminating the self-energy term from this force.)

If the electron self-energy is infinite without advanced-wave solutions, doesn't that sort of prove there are advanced waves?
Well, that depends on whether the model is plausible in other ways.

Or is there some other way that might yield plausible (finite) results for electron self-energy?
There are many different ways, although I'd hesitate to call any of them plausible. It's an open problem.

You just gave me a bunch of gibberish that I don't completely understand. I don't know what a Coulomb or a Coulomb interaction, ...
You know that law about the force between charges being proportional to the product of the charges and inversely proportional to the square of the distance between them? That's Coulomb's law. The problem is in how the other charges know where the charge is in the first place.

... or self-energy, or outgoing plane-wave. I'm not a physicist.
Alright, just imagine a light beam going to the right. Question: how do you know it's not a light beam going to the left that happens to be traveling backwards in time? Mathematically, they're indistinguishable. You can always re-interpret a wave behaving one way forwards in time as a wave behaving in the opposite manner backwards in time. Imagine an electron emitting a spherical wave going outward. No problem. Now, imagine it running backwards: a spherical wave converging perfectly onto the electron. That's how a spherical advanced wave emitted by the electron would look like to us. But if you look at it at face value, you'd conclude that somehow the other charges in the universe conspired to generate a perfectly spherical wave centered right on that particular electron (and are doing so all the time!). And that's one reason why advanced waves are considered unphysical: we just don't see those kinds of things.

What's the W-F model?
The Wheeler-Feynman absorber model involving advanced waves. (Note again that here, things conspire to make the net effect that of a retarded wave, with destructive interference over the "unphysical" parts.)

What problems? Collapsing wave functions right?
Yes. As for the particulars of the Afshar experiment, I think that I'm neither familiar enough with that issue nor competent enough to judge at this time. Sorry.

sol invictus

29th July 2008, 06:38 AM

At the risk of belaboring a point

You know some math, right? If so you know what a linear differential equation is, and that its solutions can be superposed to generate a new solution... right?

That's all it means to say that one can "superpose" quantum states. It's a specific, technical term. My best guess at your confusion is that you're using the term in a different and more vague way.

It is true that in Bohm one always knows precisely where the particles are. It is not true that one cannot make superpositions of wavefunctions.

I worked out a few small examples to see what happens. For a free particle in a momentum eigenstate (a plane wave with momentum k), Bohm tells us (quite reasonably) that x(t) = k t + x0, where x0 is a constant. As advertised, our ignorance of the particle's position (in the form of the integration constant) plays the role of quantum uncertainty. For a superposition of momentum eigenstates-a standing wave, for example-Bohm says x(t) = x0 (again, reasonable since <p>=0).

If we take a position eigenstate at t=0 (a delta function, or even a Gaussian of any width, it doesn't seem to matter) centered at x1 I get something a little pathological: x(t) = x1 + c t^{1/2}, c a constant. I'm not sure how to interpret the branch cut at t=0, although perhaps it has to do with the infinite volume. Maybe I made a mistake there... in any case, as you can see nothing stops us from taking superpositions.

The Man

29th July 2008, 07:25 AM

It's kind of funny that if this was on the religion forum and we were discussing something of that sort and I said "the existance of XYZ had not been disproven either" I'd get jumped on with "You can't prove a negative!"

Again just to add to what Vorpal has said, “You can’t prove a negative” is not always correct, for example I can easily prove that there is no one in my bathroom (or the proposition that someone is in my bathroom is false) simply by looking and finding no one there. It is just sometimes more difficult (or not possible) to prove a negative when the proposition becomes more complex. For example I doubt that I could prove that there are not “hidden” dimensions in my bathroom, as the premise itself makes those dimensions “hidden” and undetectable.

I thought skeptics were supposed to restrain judgement on an issue until proven true...

Skeptics are just skeptical and this must also include issues considered proven, so skeptics are always questioning the validity of data, even data they might have already judged as valid.

I'm simply saying that if it hasn't been proven true, then why should we automatically assume it's true. Speculate sure, but if one has not proven that it's true, one should not automatically assume it to be so. That's not skeptical, that's faithful.

I do not think anyone on this thread has claimed that it must be true and it is certainly not my point in this discussion to try and convince someone that it must be true (since I do not subscribe to that position myself) My point in bringing it up in this discussion is so that it can be addressed as a plausible interpretation for the topic of this thread “Quantum theory: observation and reality”.

INRM

29th July 2008, 09:23 AM

Vorpal,
If you watch a movie backwards, all the mechanical interactions are physically possible, but it doesn't mean that it's physically reasonable overall.

I thought if it's covered in the laws of physics it doesn't matter if it's reasonable or not, just possible.

Think about assembling a charge distribution. As you bring in more and more bits of charge, you have to do work against the electromagnetic forces due to the charges already there. This work is stored in the field. Now, imagine doing the same thing for an individual electron, assembling its "bits" of charge. There's another way of thinking about it as well that doesn't involve trying to decompose the electron: electromagnetic fields carry momentum, so the field of an electron contributes to its mass. The problem is that if an electron is a point-particle, this mass contribution is infinite. And it doesn't really help to think of the electron as having positive size that's just very small--experimentally, the electron, if it has any positive size, is still much smaller than the "classical electron radius" predicted by attributing electron mass entirely to due to the field.

I don't exactly know what a charge distribution is...

(Actually, the real problem is electron self-force: as the electron moves, its field lags behind it slighly, and the predicted force of this retarded field on the electron is infinite. Allowing it to have an advanced field as well cancels this infinity, incidently eliminating the self-energy term from this force.)

Why would it be infinite? Wouldn't the charge just dissipate as the electron moves away?

Well, that depends on whether the model is plausible in other ways.

Interesting point.

There are many different ways, although I'd hesitate to call any of them plausible. It's an open problem.

Interesting.

You know that law about the force between charges being proportional to the product of the charges and inversely proportional to the square of the distance between them? That's Coulomb's law. The problem is in how the other charges know where the charge is in the first place.

Forces of repulsion and attraction depend on how close they are to each other. Okay, that I understand -- I just didn't know it was called Coulomb's Law.

Alright, just imagine a light beam going to the right. Question: how do you know it's not a light beam going to the left that happens to be traveling backwards in time? Mathematically, they're indistinguishable. You can always re-interpret a wave behaving one way forwards in time as a wave behaving in the opposite manner backwards in time.

Then how do you prove or disprove it?

Imagine an electron emitting a spherical wave going outward. No problem. Now, imagine it running backwards: a spherical wave converging perfectly onto the electron. That's how a spherical advanced wave emitted by the electron would look like to us. But if you look at it at face value, you'd conclude that somehow the other charges in the universe conspired to generate a perfectly spherical wave centered right on that particular electron (and are doing so all the time!). And that's one reason why advanced waves are considered unphysical: we just don't see those kinds of things.

Weird, why isn't such a wave detected? Why wouldn't you just see one go out, and another race in and neutralize it?

The Wheeler-Feynman absorber model involving advanced waves. (Note again that here, things conspire to make the net effect that of a retarded wave, with destructive interference over the "unphysical" parts.)

To make sense of it.

Yes. As for the particulars of the Afshar experiment, I think that I'm neither familiar enough with that issue nor competent enough to judge at this time. Sorry.

Same here...

The Man,

Again just to add to what Vorpal has said, “You can’t prove a negative” is not always correct, for example I can easily prove that there is no one in my bathroom (or the proposition that someone is in my bathroom is false) simply by looking and finding no one there. It is just sometimes more difficult (or not possible) to prove a negative when the proposition becomes more complex. For example I doubt that I could prove that there are not “hidden” dimensions in my bathroom, as the premise itself makes those dimensions “hidden” and undetectable.

Well, I know that you can sometimes prove a negative, but that argument often popped up. I was just illustrating that if I pulled such an argument on that forum, I'd get swamped with that response.

I do not think anyone on this thread has claimed that it must be true and it is certainly not my point in this discussion to try and convince someone that it must be true (since I do not subscribe to that position myself) My point in bringing it up in this discussion is so that it can be addressed as a plausible interpretation for the topic of this thread “Quantum theory: observation and reality”.

It certainly seemed like you believed whole-heartedly it was true.

In either case, I'm wondering how they were able to determine the "retarded" wave was emitted as a result of the Transactional Interpretation. Was it the result of timing, or the pattern of emission, or both, or something like that?

INRM

Perpetual Student

29th July 2008, 11:30 AM

That's all it means to say that one can "superpose" quantum states. It's a specific, technical term. My best guess at your confusion is that you're using the term in a different and more vague way.

It is true that in Bohm one always knows precisely where the particles are. It is not true that one cannot make superpositions of wavefunctions.

Sol invictus:

I have come to realize that I may have been misusing the word “superposition” due to my ignorance of physics – sorry.

The conventional sense of superposition of waves or forces is quite clear.

Where I have been using (perhaps inappropriately) the word superposition of location (or spin) of a particle, I have meant that part of the Copenhagen interpretation that determines that the position of the particle is “smeared out” in accordance with a probability distribution dictated by the square of the Schrödinger wave function. That thesis, as I understand it, is not that the particle has a probability of position based on that function, but that it actually exists in a smeared out manner in all the possible locations dictated by the probability distribution. Furthermore, this smeared out status is then affected by “observation” leading to the collapse of the wave function and a definite position of the particle. It is this counter intuitive part of the Copenhagen interpretation, (that leads to pop culture stuff like “What the bleep…”) that I have a problem with and appears to make Bohmian mechanics a better interpretation (for me).

Bohm’s interpretation is that the wave function is a kind of force field that pushes the totally deterministic particle around. Furthermore, there is no difference demonstrated by experimental results between the two interpretations. I have learned that consistency with Lorentz invariance has not been established (yet) for Bohmian mechanics, which is connected with the non-locality inherent in Bohm’s theory. There are a number of physicists who believe that a “fully invariant theory” can be constructed for Bohmian mechanics; however I am not in a position to evaluate this hope and it does remain a critical weakness of Bohm’s theories.

Vorpal

29th July 2008, 01:56 PM

I thought if it's covered in the laws of physics it doesn't matter if it's reasonable or not, just possible.
The backwards movie is allowed by the laws of mechanics, but not thermodynamics. It doesn't mean it's impossible in the absolute sense. Say you have a glass of water and some food coloring or something. You put it in and watch it spread, giving a fairly uniform color. It is technically possible (in the sense of having a positive probability) that the molecules are arranged in such a way that the natural laws separate the dye into a little droplet again, but it doesn't mean that we should take such a possibility seriously. If we were suddenly started to observe such things routinely, we would conclude that there is some specialized mechanism that makes them do that, because such an arrangement would simply be much too perfect to happen by chance.

It's a similar thing here in EM. A charge could emit a retarded wave that jiggles every other charge some time later. But Maxwell's equation also allow it to emit an advanced wave that jiggles every other charge.... some time earlier. To avoid problems of causality, we could re-interpret this to have the every other charge suddenly emitting a wave that converges perfectly to our first charge, but again this kind of thing is much too improbable to happen by chance without a some specialized mechanism.

I don't exactly know what a charge distribution is...
Exactly what it sounds like: an arrangement of charges. Say you want to have two charges side-by-side. The work done in bringing the second charge to the first against the electromagnetic forces is the energy associated with that arrangement, i.e., energy of the resulting electromagnetic field itself.

Why would it be infinite? Wouldn't the charge just dissipate as the electron moves away?
Think about it this way: there is an energy associated with having a little ball of charge, which we can formally calculate as the work done by bringing pieces of that ball together. It turns out that the result is inversely proportional to the radius of the ball. However, the electron is a point-particle, so this diverges to infinity. If you push a charge, it emits radiation, which carries energy and momentum. You can't get any momentum without force (which is really just the rate of change of momentum), which means that the charge pushes the field. But to conserve momentum, there should be a force back on the charge. Once again, this diverges for point-particles, but interestingly, it doesn't if advanced effects are allowed (it cancels the diverging term with an identical diverging term).

Point-particles in classical EM are still considered an open problem. There are similar difficulties in quantum electrodynamics, although also methods to side-step them. (Renormalization might be described as introducing several unphysical things and playing them against each other to cancel out their mutual "unphysicalness".)

Forces of repulsion and attraction depend on how close they are to each other. Okay, that I understand -- I just didn't know it was called Coulomb's Law.
Yeah. But Coulomb's law itself apparently gives a "spooky action-at-a-distance." But we can remove this in the manner previously described, to have all interactions be explicitly local.

Then how do you prove or disprove it?
The primary test would be to see whether you can send information back in time. The secondary test would be whether such effects are required to make sense of your physics.

Weird, why isn't such a wave detected? Why wouldn't you just see one go out, and another race in and neutralize it?
Because it's possible for two waves to interfere completely destructively with one another.

sol invictus

29th July 2008, 03:20 PM

<snip for brevity>

Fair enough - sounds like we're now more or less on the same page. My most basic problem with Bohm, beyond the issue of Lorentz invariance - and I think most physicists would probably agree with me here - is that it adds a layer of complication where none is needed. That is, the predictions are identical to Copenhagen and many worlds (at least as far as I know), so why does one need to bother to solve this extraneous equation for the position of the particles? As physicists we are trained to look for the simplest possible theory that matches observation, and Bohm is unquestionably more complicated than Copenhagen.

Beyond that, the issue of Lorentz invariance goes beyond just finding a relativistic version of the theory. Feynman taught us that quantum mechanics can be thought of as a path integral (a sum over every possible chain of events, weighted by the exponential of the classical action of that sequence). That formalism naturally generalizes to relativity, and it underlies all of modern quantum field theory - a theory which has produced the most accurate predictions in human history. Given the overwhelming evidence it is very difficult to believe that formalism is wrong, and yet Bohm seems sharply in conflict with it.

The Man

29th July 2008, 04:55 PM

The Man,

Well, I know that you can sometimes prove a negative, but that argument often popped up. I was just illustrating that if I pulled such an argument on that forum, I'd get swamped with that response.

I know, some people are limited in their repertoire and are not willing to deal with the ebb and flow of a discussion; usually they have one or more trump cards (like “can’t prove a negative”) that they play when most other things fail. It is probably the most common I’ve seen, the other being the “you can never really prove anything" argument, perhaps not but we certainly get close enough for my tastes. I think you will find the current posters on this thread (from what I have seen of them) will specifically address your questions or problems as best they can and not just play some standard trump or “get out of jail free” card

It certainly seemed like you believed whole-heartedly it was true.

No, I just consider it plausible like the two better known main QM interpretations, CI and MW. Personally I’ve always considered myself a Copenhagen Interpretation kind of guy, but I generally do not like tying myself down to one particular interpretation when they all have benefits and defects. I can certainly understand how one might get the impression that you did, as I am usually bringing up TI in QM discussions. Which is primarily because I find it interesting, compelling, usually not currently part of the discussion and I am interested in hearing others peoples’ take on it, but that does not mean I’m ready to hang my hat on it.

In either case, I'm wondering how they were able to determine the "retarded" wave was emitted as a result of the Transactional Interpretation. Was it the result of timing, or the pattern of emission, or both, or something like that?
INRM

As an interpretation it really can not result in the emission of anything but just attempts to explain the apparent predominance of retarded solutions as the constructive interference of the retarded and advanced waves of the transaction.

ChthonicTonic

29th July 2008, 05:18 PM

Ziggurat,

I adore the Stern-Gerlach experiment! It's one of those instances where you get totally non-intuitive results from the mathematics. So, of course, you head off to the lab to test this. Amazingly, results match the math wonderfully. Unfortunately, a lot of physics hobbyists get a little peeved when I tell them that they have to study differential equations to really appreciate the beauty of QM.

Perpetual Student

29th July 2008, 05:25 PM

Feynman taught us that quantum mechanics can be thought of as a path integral (a sum over every possible chain of events, weighted by the exponential of the classical action of that sequence). That formalism naturally generalizes to relativity, and it underlies all of modern quantum field theory - a theory which has produced the most accurate predictions in human history.

Thanks for this. I had not been aware of this concept of Feynman. You've given me something new to learn. Now, I'm off to do a search of Feynman and QM...

INRM

30th July 2008, 01:15 PM

As an interpretation it really can not result in the emission of anything but just attempts to explain the apparent predominance of retarded solutions as the constructive interference of the retarded and advanced waves of the transaction.

So the interpretation is based on the fact that there are a lot of retarded waves (delayed emissions) and lots of constructive-interference patterns (What's a constructive and destructive interference pattern while we're at it) suggesting that it could be the TI in action?

INRM
BTW: I know CI is Copenhagen Interpretation, but what's MW?

MattusMaximus

30th July 2008, 03:29 PM

So the interpretation is based on the fact that there are a lot of retarded waves (delayed emissions) and lots of constructive-interference patterns (What's a constructive and destructive interference pattern while we're at it) suggesting that it could be the TI in action?

Here is a link on some general info about wave interference (http://en.wikipedia.org/wiki/Constructive_interference). Also, here is a link to a Java applet (http://www.falstad.com/ripple/ex-2source.html) which allows you to simulate such wave interference - please note that these are things commonly seen in the lab all the time. As a matter of fact, I just did a lecture to my college class on Monday where I demonstrated for them such wave interference with water, sound, and light waves.

INRM
BTW: I know CI is Copenhagen Interpretation, but what's MW?

MW stands for Many-Worlds, which is another very interesting interpretation of quantum mechanics. Read up on it at this link. (http://en.wikipedia.org/wiki/Many_worlds)

INRM

31st July 2008, 11:59 AM

MW stands for Many-Worlds, which is another very interesting interpretation of quantum mechanics. Read up on it at this link. (http://en.wikipedia.org/wiki/Many_worlds)

Thank you for the link...

INRM

INRM

2nd August 2008, 05:38 PM

Well, if anyone has any more information regarding new-findings and such in this area, please respond

Perpetual Student

3rd August 2008, 11:12 AM

Well, if anyone has any more information regarding new-findings and such in this area, please respond

The Stanford University Encyclopedia has a pretty good article:

plato.stanford.edu/entries/qm-manyworlds

Darkhole

7th August 2008, 04:08 PM

Found this:

Rochester Physicist's Quantum-"Uncollapse" Hypothesis Verified
http://www.rochester.edu/news/show.php?id=3220

Fredrik

7th August 2008, 04:51 PM

Thanks for this. I had not been aware of this concept of Feynman. You've given me something new to learn. Now, I'm off to do a search of Feynman and QM...

Check out this book (http://www.amazon.com/QED-Strange-Princeton-Science-Library/dp/0691125759/ref=pd_bbs_sr_6?ie=UTF8&s=books&qid=1218149401&sr=8-6) or these lectures (http://www.vega.org.uk/video/subseries/8).

Reality Check

7th August 2008, 05:11 PM

Found this:
http://www.rochester.edu/news/show.php?id=3220
If you are interested in the technical details of the experiment then there is a preprint: Uncollapsing of a quantum state in a superconducting phase qubit (http://arxiv.org/abs/0806.3547v1)

Perpetual Student

9th August 2008, 11:54 AM

I have a question for the physicists:

Some months ago I read Brian Greens “frozen river” description of special relativity. It appears that this would imply a totally deterministic universe, which would then contradict the probabilistic nature of the Copenhagen interpretation. Any comments?

INRM

9th August 2008, 12:32 PM

Regarding Dr. Andrew Jordan's experiment. Doesn't this kind of completely refute the Heisenberg Uncertainty Equation?

How good a measurement can they take? A completely accurate one? Or a pretty good one?

What does this experiment state of randomness (nonexistant, sort of existant, existant)?

I'm thinking it might actually disprove. If you can tell from the character of the partial collapse what the particle's character (collapsed) will look like, you can tell that a lesser partial collapse's character will look like the partial-collapses character, which will look like the particle. You could also infer that the particle will look like the particle will look like a partially-collapsed wave of a certain character.

Think of a ball, and a fuzzy blurred image of a ball, and a blur. Eventually you can infer that that particular blur pattern will equate (if partially collapsed) to the fuzzy blurred image pattern of a ball, and when fully collapsed, one can infer from the fuzzy blurred image pattern of a ball will equate to the image of the ball. Eventually I suppose you could eventually tell what every single uncollapsed wave will look like partially collapsed and collapsed right? Of course, I don't honestly know how much processing power it would take to remember all that.

INRM

sol invictus

9th August 2008, 12:53 PM

Some months ago I read Brian Greens “frozen river” description of special relativity.

What is that?

It appears that this would imply a totally deterministic universe, which would then contradict the probabilistic nature of the Copenhagen interpretation. Any comments?

Hard to say without knowing what it is... but there is no conflict between special relativity and QM. It's only once gravity is added that things get tricky.

Perpetual Student

9th August 2008, 06:54 PM

What is that?
Hard to say without knowing what it is... but there is no conflict between special relativity and QM. It's only once gravity is added that things get tricky.

The Fabric of the Cosmos: Space, Time, and the Texture of Reality (2004) is the second book on theoretical physics, cosmology and string theory written by Brian Greene, professor and co-director of Columbia's Institute for Strings, Cosmology, and Astroparticle Physics

Chapter five, The Frozen River, deals with the question, "Does time flow?" One of the key points in this chapter deals with special relativity. Observers moving relative to each other have different conceptions of what exists at a given moment, and hence they have different conceptions of reality. The conclusion is that time does not flow, as all things simultaneously exist at the same time.

sol invictus

9th August 2008, 11:12 PM

Chapter five, The Frozen River, deals with the question, "Does time flow?" One of the key points in this chapter deals with special relativity. Observers moving relative to each other have different conceptions of what exists at a given moment, and hence they have different conceptions of reality. The conclusion is that time does not flow, as all things simultaneously exist at the same time.

Hmm - are you completely sure that's what he says? It is true that observers disagree on the timing of some events (this is referred to as the "relativity of simultaneity"). However it does not follow from that - and it is not true - that all things happen simultaneously. Spacetime events can either be separated in time, so that all observers will agree on their temporal ordering, or they can be separated in space, so that observers will disagree on their ordering. The first case is called timelike, the second spacelike.

The distinction is precisely the speed of light - if light can propagate from one event to the other they are timelike separated. If not, they are spacelike. Then so long as nothing can propagate faster than light, causality is preserved (because all observers agree on the time-ordering of events which can influence each other).

Perpetual Student

10th August 2008, 12:35 AM

Hmm - are you completely sure that's what he says? It is true that observers disagree on the timing of some events (this is referred to as the "relativity of simultaneity"). However it does not follow from that - and it is not true - that all things happen simultaneously. Spacetime events can either be separated in time, so that all observers will agree on their temporal ordering, or they can be separated in space, so that observers will disagree on their ordering. The first case is called timelike, the second spacelike.

The distinction is precisely the speed of light - if light can propagate from one event to the other they are timelike separated. If not, they are spacelike. Then so long as nothing can propagate faster than light, causality is preserved (because all observers agree on the time-ordering of events which can influence each other).

Sorry, I will not be at home for a couple of weeks and do not have access to the book. My previous statement is a description of his book taken from an article about the book, which coincides very well with my recollection.
I will pursue this further when I return home at the end of the month. If you would be willing to indulge me in a discussion about it at that time, I would appreciate it. At the time I read the book, the seeming conflict with the Copenhagen interpretation did not occur to me.
Now, please do not misunderstand me. I am not naïve enough to believe I have thought of something new. I have no doubt that this seeming contradiction is only due to my flawed understanding of QM and SR, or if there really is an apparent contradiction, it has been well studied and analyzed and reconciled.
In the meantime, the following is the best I can do:
As I recall, Greene described events that are simultaneous because of the relative motions and distance of the events. He used the well known transformation formula the included both the relative velocity and distance of the events. He did mention that the speed of light would prohibit communication and any causality between the events if they were very for apart, but that would not negate the fact that they would be simultaneous (If one waited long enough, eventually the light from a long distance would arrive and one could potentially determine when that event was simultaneous).
Consequently, an extraterrestrial being in a very for away galaxy moving toward the earth at a given velocity would be existing simultaneously with the earth of the future – decades, hundreds of thousands of years into the future – depending on the velocity. That same being could then exist in our past by moving away from the earth. From that description, it would appear that past, present and future all exist and are part of the “frozen river” that he describes. Would that not make the universe totally deterministic, ruling out any randomness predicted by QM?
That is the best I can do without the book in my hands. If you think I have misunderstood something or my recollection in wrong, please set me straight.

Sorry, I'm not at home for a couple of weeks and do not have access to the book. My previous statent is a description of his book taken from the Wikipedia articel about the book, which coincedes with my recolection.

Perpetual Student

10th August 2008, 12:54 AM

Here is the Wikipedia article about the book:

http://en.wikipedia.org/wiki/The_Fabric_of_the_Cosmos

Note the description of Chapter 5.

Reality Check

10th August 2008, 06:16 AM

Sorry, I will not be at home for a couple of weeks and do not have access to the book. My previous statement is a description of his book taken from an article about the book, which coincides very well with my recollection.
I will pursue this further when I return home at the end of the month. If you would be willing to indulge me in a discussion about it at that time, I would appreciate it. At the time I read the book, the seeming conflict with the Copenhagen interpretation did not occur to me.
Now, please do not misunderstand me. I am not naïve enough to believe I have thought of something new. I have no doubt that this seeming contradiction is only due to my flawed understanding of QM and SR, or if there really is an apparent contradiction, it has been well studied and analyzed and reconciled.
In the meantime, the following is the best I can do:
As I recall, Greene described events that are simultaneous because of the relative motions and distance of the events. He used the well known transformation formula the included both the relative velocity and distance of the events. He did mention that the speed of light would prohibit communication and any causality between the events if they were very for apart, but that would not negate the fact that they would be simultaneous (If one waited long enough, eventually the light from a long distance would arrive and one could potentially determine when that event was simultaneous).
Consequently, an extraterrestrial being in a very for away galaxy moving toward the earth at a given velocity would be existing simultaneously with the earth of the future – decades, hundreds of thousands of years into the future – depending on the velocity. That same being could then exist in our past by moving away from the earth. From that description, it would appear that past, present and future all exist and are part of the “frozen river” that he describes. Would that not make the universe totally deterministic, ruling out any randomness predicted by QM?
That is the best I can do without the book in my hands. If you think I have misunderstood something or my recollection in wrong, please set me straight.

Sorry, I'm not at home for a couple of weeks and do not have access to the book. My previous statent is a description of his book taken from the Wikipedia articel about the book, which coincedes with my recolection.
"Would that not make the universe totally deterministic, ruling out any randomness predicted by QM?"
The short answer is no.
QM is not really random and so there not really any "randomness predicted by QM". Systems evolve according to the deterministic Schrödinger equation. A measurement though does involve the probability of the wavefunction collapsing to a specific state. This is certainly non-deterministic but not (IMHO) random (i.e. the wavefunction cannot collapse to any state).
Brian Green may have a new take on the definition of time but QM will still apply.

sol invictus

10th August 2008, 07:56 AM

Note the description of Chapter 5.

Well, I think Greene is just trying to describe special relativity in laymen's terms. The question of whether time "flows" seems to me too vague to be answered properly.

In special relativity it is true that there is no absolute time, any more than there is absolute space. Moreover the two are intrinsically entangled in a highly non-intuitive way. However there is a strict ordering of cause and effect.

Events which are timelike separated can be causally connected; spacelike separated events cannot. The definition of spacelike versus timelike is whether or not light can propagate from one spacetime point to the other. All observers agree on the time ordering of timelike separated events, but they do not agree on the time ordering of spacelike events.

Mathematically this is related to the behavior of hyperbolic differential equations, which have a cone of influence. That is, if you make a perturbation at a point at time t=0, the influence of that perturbation on the solution will be confined to a cone (a spatial region which starts at the point and grows with time, called the lightcone for relativistic equations). Any event in the cone can be influenced by the perturbation; those without cannot.

That is in contrast to non-relativistic equations such as the Schrodinger equation, where perturbations can instantaneously makes themselves felt throughout space. However modern physics is based on a set of theories called relativistic quantum field theories, which are relativistic versions of quantum mechanics (containing the Schrodinger equation as a limit). These theories are both quantum mechanical and perfectly consistent with relativistic causality.

The Man

10th August 2008, 09:08 AM

If you are interested in the technical details of the experiment then there is a preprint: Uncollapsing of a quantum state in a superconducting phase qubit (http://arxiv.org/abs/0806.3547v1)

I haven’t had the time to read trough the paper yet, but I did find this article about another experiment with phase qubit that may need to be taken into account.

http://www.physorg.com/news137164506.html

"The resonator is the electrical equivalent of a pendulum," Hofheinz said. "In quantum mechanics the energy, or amplitude of motion of this pendulum, only comes in finite steps, in quanta. We first carefully prepared the resonator in these quantum states, and showed we could do this controllably and then measure the states. Then we 'kicked' the pendulum directly, a method where the amplitude can take on any value, and appears to not be limited to these quanta. But when we look at the resonator with our qubit, we see that the amplitude does come in steps,
but that the resonator is actually in several such states at the same time, so that on average it looks like it is not limited to the quantum states."

Another article on the “Uncollapsing” experiment.

http://www.physorg.com/news137245970.html

Perpetual Student

10th August 2008, 11:37 AM

However modern physics is based on a set of theories called relativistic quantum field theories, which are relativistic versions of quantum mechanics (containing the Schrodinger equation as a limit). These theories are both quantum mechanical and perfectly consistent with relativistic causality.

Thanks again for your thoughtful responses.
You had earlier described relativistic quantum field theories in another context. Apparently, there is no debate about the compatibility of QM and SR – from the perspective of the underlying mathematics.
However, my question concerns the real world interpretation of the mathematics. If it is true that all time is forever determined, as Greene contends, how can there be any probabilistic interpretation of QM? It is this probabilistic interpretation that has lead physicists to believe that the universe in not deterministic. That creates an apparent contradiction.
I know my statement here is somewhat repetitive; I need to have my library (and specifically Greene’s book) to pursue this question further.
In the meantime, let me ask, how can Greene’s description (for laymen) be so inexact? The special relativity transformations of time appear to be very straightforward and readily understood. Whether the events in question are spacelike or timelike does not appear to be at issue. Greene’s thesis does not involve causality.

Perpetual Student

10th August 2008, 11:55 AM

QM is not really random and so there not really any "randomness predicted by QM". Systems evolve according to the deterministic Schrödinger equation. A measurement though does involve the probability of the wavefunction collapsing to a specific state. This is certainly non-deterministic but not (IMHO) random (i.e. the wavefunction cannot collapse to any state).
Brian Green may have a new take on the definition of time but QM will still apply.

Why then is the probabilistic nature of QM the basis for physicists claiming that the universe is not deterministic?

sol invictus

10th August 2008, 12:54 PM

If it is true that all time is forever determined, as Greene contends, how can there be any probabilistic interpretation of QM? It is this probabilistic interpretation that has lead physicists to believe that the universe in not deterministic. That creates an apparent contradiction.

The mathematics of QM is not in conflict with SR. To be precise, the wavefunctions describing quantum fields evolve in a way that's fully consistent with relativity (and hence causality). No causal influence can propagate outside the lightcone; if you'd like I can explain the technical definition of that, and how one checks it to be sure.

However there is another question, logically independent of this issue of relativistic causality, which is how one interprets that wavefunction once one has solve for it. Before addressing that one should clearly separate these two issues (1, whether the wavefunctions evolve in a way consistent with relativistic causality, and 2, whether the interpretation of those wavefunctions allows the universe to be deterministic).

Issue 2 can be addressed in the context of non-relativistic QM, where we can forget about relativistic issues entirely. Is that what you are asking about?

INRM

10th August 2008, 01:15 PM

From what I'm reading about this "partial wave function collapse", and from The Man's link ( http://www.physorg.com/news137164506.html )

Leads me to believe the universe does not just lack true randomness (as Reality Check said, basically stating that there is some uncertainty, but it's not random) but is ultimately completely deterministic.

INRM

Reality Check

10th August 2008, 01:50 PM

Why then is the probabilistic nature of QM the basis for physicists claiming that the universe is not deterministic?
It all depends on your definition of random. If the universe was truely random then we would not be able to define physical laws. If the universe was truely deterministic then QM would not work. So the universe is something inbetween. In my experience physicists who work at the microscopic level say that is is not deterministic (that does not mean that it is random) while physicists who work at the macroscopic level call it deterministic.

Perpetual Student

10th August 2008, 03:39 PM

It all depends on your definition of random. If the universe was truely random then we would not be able to define physical laws. If the universe was truely deterministic then QM would not work. So the universe is something inbetween. In my experience physicists who work at the microscopic level say that is is not deterministic (that does not mean that it is random) while physicists who work at the macroscopic level call it deterministic.
As I understand it, the supposed non-deterministic nature of the quantum world cancels out (smoothes out?) to a deterministic macro world. Is that a reasonable description?

However there is another question, logically independent of this issue of relativistic causality, which is how one interprets that wavefunction once one has solve for it. Before addressing that one should clearly separate these two issues (1, whether the wavefunctions evolve in a way consistent with relativistic causality, and 2, whether the interpretation of those wavefunctions allows the universe to be deterministic).

Issue 2 can be addressed in the context of non-relativistic QM, where we can forget about relativistic issues entirely. Is that what you are asking about?

Perhaps, but I am not sure.
Question: Do you disagree with Brian Greene's description of all time being totally determined due to SR?
In any case, I'll have to return to these questions in a couple of weeks when I am able.
Thank you both for your responses.

Reality Check

10th August 2008, 04:02 PM

As I understand it, the supposed non-deterministic nature of the quantum world cancels out (smoothes out?) to a deterministic macro world. Is that a reasonable description?

That is correct - quantum mechanics reduces to classical mechanics in the macro world.
But even there we have to be careful about our expectations of a "deterministic macro world", e.g. weather is macroscopic but we cannot predict it locally beyond a week or so (see chaos theory (http://en.wikipedia.org/wiki/Chaos_theory)). Also see the Stability of the Solar System (http://en.wikipedia.org/wiki/Stability_of_the_Solar_System) for chaos on a bigger and longer scale.

sol invictus

10th August 2008, 04:42 PM

Question: Do you disagree with Brian Greene's description of all time being totally determined due to SR?

I have not been able to figure out what the statement is, so I can't say for sure. It is true that in relativistic theories - as in all other theories of physics (modulo the QM subtlety of my item 2 above) - the future is determined by the present in the sense that initial conditions suffice to uniquely determine the future evolution of the system. However that is not at all in conflict with causality - on the contrary, it is a central part of it.

Perpetual Student

11th August 2008, 10:33 AM

I have not been able to figure out what the statement is, so I can't say for sure.
(regarding Brian Greene's description of all time being totally determined due to SR?)

Greene spends a good deal of time in his book developing and describing his "frozen river" concept. I am perplexed by your comment. If you would indulge me, I would like to revisit this in a couple of weeks. Thanks.

VonNeumann

11th August 2008, 10:59 PM

The backwards movie is allowed by the laws of mechanics, but not thermodynamics. It doesn't mean it's impossible in the absolute sense. Say you have a glass of water and some food coloring or something. You put it in and watch it spread, giving a fairly uniform color. It is technically possible (in the sense of having a positive probability) that the molecules are arranged in such a way that the natural laws separate the dye into a little droplet again, but it doesn't mean that we should take such a possibility seriously. If we were suddenly started to observe such things routinely, we would conclude that there is some specialized mechanism that makes them do that, because such an arrangement would simply be much too perfect to happen by chance.

It's a similar thing here in EM. A charge could emit a retarded wave that jiggles every other charge some time later. But Maxwell's equation also allow it to emit an advanced wave that jiggles every other charge.... some time earlier. To avoid problems of causality, we could re-interpret this to have the every other charge suddenly emitting a wave that converges perfectly to our first charge, but again this kind of thing is much too improbable to happen by chance without a some specialized mechanism.

Exactly what it sounds like: an arrangement of charges. Say you want to have two charges side-by-side. The work done in bringing the second charge to the first against the electromagnetic forces is the energy associated with that arrangement, i.e., energy of the resulting electromagnetic field itself.

Think about it this way: there is an energy associated with having a little ball of charge, which we can formally calculate as the work done by bringing pieces of that ball together. It turns out that the result is inversely proportional to the radius of the ball. However, the electron is a point-particle, so this diverges to infinity. If you push a charge, it emits radiation, which carries energy and momentum. You can't get any momentum without force (which is really just the rate of change of momentum), which means that the charge pushes the field. But to conserve momentum, there should be a force back on the charge. Once again, this diverges for point-particles, but interestingly, it doesn't if advanced effects are allowed (it cancels the diverging term with an identical diverging term).

Point-particles in classical EM are still considered an open problem. There are similar difficulties in quantum electrodynamics, although also methods to side-step them. (Renormalization might be described as introducing several unphysical things and playing them against each other to cancel out their mutual "unphysicalness".)

Yeah. But Coulomb's law itself apparently gives a "spooky action-at-a-distance." But we can remove this in the manner previously described, to have all interactions be explicitly local.

The primary test would be to see whether you can send information back in time. The secondary test would be whether such effects are required to make sense of your physics.

Because it's possible for two waves to interfere completely destructively with one another.

Sorry for dredging this up from so far back in the thread, but I don't understand your comment:

"But Coulomb's law itself apparently gives a "spooky action-at-a-distance." But we can remove this in the manner previously described, to have all interactions be explicitly local."

How is classical Coulomb's law representative of spookyactionatadistance? I thought the classical propogation of the electric field obeys S.R. and all is local.

sol invictus

12th August 2008, 09:15 AM

How is classical Coulomb's law representative of spookyactionatadistance? I thought the classical propogation of the electric field obeys S.R. and all is local.

I'm not sure if this is what Vorpal meant, but it's true that Coulomb's law by itself is not enough for locality/causality.

For example, consider a single charge at rest. It has the standard 1/r^2 field. Now move the charge a foot to the right. There is a simple solution to Coulomb's law consistent with the new configuration, which is simply 1/r^2 centered at the new point. But that is NOT the correct solution, since it would involve the field changing instantaneously infinitely far away. Of course CL has many other solutions too, but to see which is the correct one in this case you need the rest of Maxwell's equations. CL alone does not suffice to determine a solution, even when supplemented with boundary conditions.

INRM

13th August 2008, 10:52 AM

I got a quick question... if time can flow forward and back, does that mean there's more than one dimension of time?

INRM

Reality Check

13th August 2008, 01:46 PM

I got a quick question... if time can flow forward and back, does that mean there's more than one dimension of time?

INRM
No

beeksc1

18th August 2008, 03:13 PM

^ Time is unidimensional?

I can buy that. But, before that question; is time linear or cyclic?

If time is linear, yes time would seem to entail only one dimension.
If time is cyclic; time would seemingly be multidimensional or transdimenional.

One unsolved problem in physics is whether time travel is theoretically or practically possible.
Another unsolved, physical mystery is whether nature has more than four spacetime dimensions.

To say that time only adheres to one fundamental dimension of physical reality seems to be a proposition.
Another proposition might say time is measurement that quantifies a certain construction of reality. That is, reality is not being measured; a construction of reality is being measured.

Time can be objectively measured (gauged, assessed) by agreed upon standards, such as Planck time or a millisecond. But just like the experience of hue (color, the spectral composition of visible light), a person's interpretation of how much time has passed (the experience of duration) is subjective.

As time can refer to uncountable expressions and countable phenomena, time (in the philosophical sense) seems to entail more than one dimension. In the context of empiricism, time traditionally is seen as involving one dimension; nonetheless, the nature (essence) of time may involve more than one dimension.

(I am well aware that many people who posts on threads like this one have a more technical understanding of physics and QM than does the typical human. A peaceful discussion is sought-after. Thank you for sharing your knowledge, perspective...)

Is time linear or cyclic?

As this discussion in the science subforum, are there recent journal articles definitely reporting that the fundamentals of time pertain to one dimension? Or other evidence indicating this?

Just wandering if there is text that explains the unidimensionality of time or if you can elaborate upon that?

Peace.

~beeks

INRM

18th August 2008, 03:33 PM

beeksc1,

Time is undimensional? I thought time was the 4th-dimension...

INRM

sol invictus

18th August 2008, 03:39 PM

I can buy that. But, before that question; is time linear or cyclic?

If time is linear, yes time would seem to entail only one dimension.
If time is cyclic; time would seemingly be multidimensional or transdimenional.

If so, you're not using the term "dimension" the way physicists or mathematicians do. Making a direction cyclic doesn't change the fact that it's still only one direction. If this confuses you, remember that you can find the dimension of anything by asking how many coordinates you need to specify a point in it. For example, latitude and longitude specify a point on the surface of the earth, so it's two dimensional (despite being curved).

One unsolved problem in physics is whether time travel is theoretically or practically possible.

Well, not really. If time travel (into the past) is possible, essentially everything we know about physics is wrong. So I wouldn't call that an "unsolved problem", exactly.

Is time linear or cyclic?

If it's cyclic, the period is certainly much longer than the current age of the universe. That possibility cannot be ruled out, although for it to be possible would require some new physics beyond what has ever been observed.

As this discussion in the science subforum, are there recent journal articles definitely reporting that the fundamentals of time pertain to one dimension? Or other evidence indicating this?

Not sure if you're still using "dimension" in the sense you did above, so I can't answer that.