AETHER: The Physicalists' God

[drkitten]

Originally Posted by cyberdyno

You know what, you were right, that was too controversial, so I changed it.

It wasn't controversial at all. It was simply wrong; no controversy involved.

If light had rest mass, then (as LLH pointed out) it would be able to travel at any speed between 0 and just under the speed of light, and we would see it travel at many different speeds, including a walking pace. The fact that we do not see it travel at many different speeds indicates that light has no rest mass and therefore travels at the speed of light.

[six7s]

Originally Posted by drkitten

The fact that we do not see it travel at many different speeds indicates that light has no rest mass and therefore travels at the speed of light.

I'm pretty much in the dark concerning light - and I have a hunch I ain't alone

Furthermore, I have heard it said that "there's no such thing as a stupid question, but they're the easiest to answer", so I'll ask:

Is there perhaps a (relevant) difference between velocity and speed at play here?

[Mobyseven]

Originally Posted by six7s

I'm pretty much in the dark concerning light - and I have a hunch I ain't alone

Furthermore, I have heard it said that "there's no such thing as a stupid question, but they're the easiest to answer", so I'll ask:

Is there perhaps a (relevant) difference between velocity and speed at play here?

Nope. Velocity is a vector, which means it has a direction as well as a magnitude. If one were to talk about the velocity of light, you'd have to specify the direction it was travelling in, but the magnitude would be the same.

More the point is that the value 'c' (as in the famous equation) is the speed of light in a vacuum. Light can slow down travelling through different mediums, which is what causes things like refraction.

[cyberdyno]

As I said, we are still debating the issue. Photons do have an internal structure, and time does slow down at near c speeds, the question is does time comes to a full stop, is there any internal process going on?

process = mass

(a) Goldhaber, AS (1971). "Terrestrial and Extraterrestrial Limits on The Photon Mass". Reviews of Modern Physics 43: 277–96.. doi:10.1103/RevModPhys.43.277.
(b) Fischbach, E; Kloor H, Langel RA, Lui ATY, and Peredo M (1994). "New Geomagnetic Limits on the Photon Mass and on Long-Range Forces Coexisting with Electromagnetism". Physical Review Letters 73: 514–17.. doi:10.1103/PhysRevLett.73.514.
(c) Official particle table for gauge and Higgs bosons S. Eidelman et al. (Particle Data Group) Physics Letters B 592, 1 (2004)
(d) Davis, L; Goldhaber AS and Nieto MM (1975). "Limit on Photon Mass Deduced from Pioneer-10 Observations of Jupiter's Magnetic Field". Physical Review Letters 35: 1402–1405.. doi:10.1103/PhysRevLett.35.1402.
(e) Luo, J; Shao CG, Liu ZZ, and Hu ZK (1999). "Determination of the limit of photon mass and cosmic magnetic vector with rotating torsion balance". Physical Review A 270: 288–292..
(f) Schaeffer, BE (1999). "Severe limits on variations of the speed of light with frequency". Physical Review Letters 82: 4964–4966.. doi:10.1103/PhysRevLett.82.4964.
(g) Luo, J; Tu LC, Hu ZK, and Luan EJ (2003). "New experimental limit on the photon rest mass with a rotating torsion balance". Physical Review Letters 90: Art. No. 081801. doi:10.1103/PhysRevLett.90.081801.
(h) Williams, ER; Faller JE and Hill HA (1971). "New Experimental Test of Coulomb's Law: A Laboratory Upper Limit on the Photon Rest Mass". Physical Review Letters 26: 721–724. doi:10.1103/PhysRevLett.26.721.
(i) Lakes, R (1998). "Experimental Limits on the Photon Mass and Cosmic Magnetic Vector Potential". Physical Review Letters 80: 1826. doi:10.1103/PhysRevLett.80.1826.
(j) 2006 PDG listing for photon W.-M. Yao et al. (Particle Data Group) Journal of Physics G 33, 1 (2006).
(k) Adelberger, E; Dvali, G and Gruzinov, A (2007). "Photon Mass Bound Destroyed by Vortices". Physical Review Letters 98: Art. No. 010402. doi:10.1103/PhysRevLett.98.010402.

Wikipedia

------------------

The energy of a system that emits a photon is decreased by the energy E of the photon as measured in the rest frame of the emitting system, which may result in a reduction in mass in the amount E / c2. Similarly, the mass of a system that absorbs a photon is increased by a corresponding amount.

This concept is applied in a key prediction of QED, the theory of quantum electrodynamics begun by Dirac (described above). QED is able to predict the magnetic dipole moment of leptons to extremely high accuracy; experimental measurements of these magnetic dipole moments have agreed with these predictions perfectly. The predictions, however, require counting the contributions of virtual photons to the mass of the lepton. Another example of such contributions verified experimentally is the QED prediction of the Lamb shift observed in the hyperfine structure of bound lepton pairs, such as muonium and positronium.

Since photons contribute to the stress-energy tensor, they exert a gravitational attraction on other objects, according to the theory of general relativity. Conversely, photons are themselves affected by gravity; their normally straight trajectories may be bent by warped spacetime, as in gravitational lensing, and their frequencies may be lowered by moving to a higher gravitational potential, as in the Pound-Rebka experiment.

Wikipedia

[PingOfPong]

Linky

Quote:

Alternative theories of the photon include a term that behaves like a mass, and this gives rise to the very advanced idea of a "massive photon". If the rest mass of the photon were non-zero, the theory of quantum electrodynamics would be "in trouble" primarily through loss of gauge invariance, which would make it non-renormalisable; also, charge conservation would no longer be absolutely guaranteed, as it is if photons have zero rest mass. But regardless of what any theory might predict, it is still necessary to check this prediction by doing an experiment.

It is almost certainly impossible to do any experiment that would establish the photon rest mass to be exactly zero. The best we can hope to do is place limits on it. A non-zero rest mass would introduce a small damping factor in the inverse square Coulomb law of electrostatic forces. That means the electrostatic force would be weaker over very large distances.

Likewise, the behavior of static magnetic fields would be modified. An upper limit to the photon mass can be inferred through satellite measurements of planetary magnetic fields. The Charge Composition Explorer spacecraft was used to derive an upper limit of 6 × 10-16 eV with high certainty. This was slightly improved in 1998 by Roderic Lakes in a laboratory experiment that looked for anomalous forces on a Cavendish balance. The new limit is 7 × 10-17 eV. Studies of galactic magnetic fields suggest a much better limit of less than 3 × 10-27 eV, but there is some doubt about the validity of this method.

It doesn't look to me like anyone is trying to establish a rest mass for photons. Instead, they are trying to place a limit on what it could be if physics is wrong in the assumption that there is no rest mass. I guess it has important implications in QED theory.

[Dancing David]

Originally Posted by six7s

I'm pretty much in the dark concerning light - and I have a hunch I ain't alone

Furthermore, I have heard it said that "there's no such thing as a stupid question, but they're the easiest to answer", so I'll ask:

Is there perhaps a (relevant) difference between velocity and speed at play here?

It is beyond me, light has no rest mass but only relatavistic mass.

This thread has a section about it.

http://www.randi.org/forumlive/showthread.php?t=115349

It is answered fairly quickly but gets deep very quickley.

[Roboramma]

Originally Posted by drkitten

It wasn't controversial at all. It was simply wrong; no controversy involved.

If light had rest mass, then (as LLH pointed out) it would be able to travel at any speed between 0 and just under the speed of light, and we would see it travel at many different speeds, including a walking pace. The fact that we do not see it travel at many different speeds indicates that light has no rest mass and therefore travels at the speed of light.

Don't neutrinos travel at (or very near to) c? And wasn't there (or isn't there...) a question about whether or not they have rest mass - something being looked into by experimentalists?

I don't know if the question has been answered, or what value was arrived at if it was, but doesn't that suggest that it's possible for a particle to only be able to travel near c, and yet have a rest mass?

[drkitten]

Originally Posted by Roboramma

Don't neutrinos travel at (or very near to) c? And wasn't there (or isn't there...) a question about whether or not they have rest mass - something being looked into by experimentalists?

Yes, yes, and yes. They travel (in our neighborhood) at "very near" c, and that's a new (and exciting) finding coming out of the experimentalists, mostly in Japan at the SuperKamiokande.

Quote:

I don't know if the question has been answered, or what value was arrived at if it was, but doesn't that suggest that it's possible for a particle to only be able to travel near c, and yet have a rest mass?

Not really; the only reason that neutrinos "always" travel at near c is because of our local environment; the sun is our primary source of neutrinos (and they're difficult to make in useful quantities), and at the energies it creates them, they move very fast indeed. We don't know how to make low-speed neutrinos, nor can we find significant other sources of neutrinos to compare solar neutrinos with. Even if we could find them, merely detecting the damn things is difficult and if you think about how bright the sun is and how bright distant stars aren't, you see the problem. (Esp. since there's no such thing as "night" since neutrinos will happily pass through the earth unmolested.)

If you want an analogy, imagine a tribe of scientists living halfway up Niagara Falls asking whether or not water always moves really really fast. The answer is "Yes --- here." But move two miles downstream and the answer would change. Except in this case, we can't move that far downstream; we're kind of stuck in the local environment of the sun.

In the case of light, we can create artificial light more or less at will in any amount we want, and we can also calibrate measurements of the speed of light with the speed of distance sources. We can measure "red shift," for example, and calibrate it with tremendous accuracy to the speed of the source (as GR predicts). What we can't do is find instances where the motion of the source has any impact on the speed of the transmitted light. This finding actually predates GR and is one of the reasons we believe that the speed of light is constant --- it's easy to set up an experiment where the speed of light would vary if it could.

It's much harder to set up such an experiment with neutrinos, which is why they had to use the multi-zillion dollar SuperKamioKande instead of testing it in a freshman physics lab.

[drkitten]

Originally Posted by cyberdyno

As I said, we are still debating the issue.

Yes, you did say that before.

You were wrong when you said it before. You were still wrong when you said it again. While you may be "debating" the issue, physicists aren't.

The papers on "measuring photon mass" that you cite are typically technical papers about measurement techniques and how close to zero the error bars can come.

[Roboramma]

Thanks drkitten - I never even considered the problem of finding neutrinos not produced by the sun.

[cyberdyno]

Originally Posted by drkitten

Yes, you did say that before.

You were wrong when you said it before. You were still wrong when you said it again. While you may be "debating" the issue, physicists aren't.

The papers on "measuring photon mass" that you cite are typically technical papers about measurement techniques and how close to zero the error bars can come.

How close to zero the error bars can come? You mean, they don't know?

[Roboramma]

Originally Posted by cyberdyno

How close to zero the error bars can come? You mean, they don't know?

One thing that I think is worth mentioning is that experiment isn't the only way that we can know things - theory also helps.

For instance, I don't have to wait to see where jupiter will be one year from now to know where I should point my telescope - we've got a pretty good theory that allows me to predict it.

Similarly, Maxwell's equations show that light should propagate at c. The experimental evidence supports this, sure, but really, even if it didn't, we could be relatively confident until we had experimental evidence to suggest otherwise, and if it did it would probably lead to some new science - because it would conflict with otherwise very well supported theoretical physics.

If my sister tells me that she's going to mexico city, and later calls me from a mexican area code, I don't need her to tell me that she is in fact in mexico city - I can be pretty confident that's where she is, even though my "experimental data" (the area code that showed up on my caller display) only confirms this with relatively large 'error bars'. She could be in a completely different part of mexico.

[drkitten]

Originally Posted by cyberdyno

How close to zero the error bars can come? You mean, they don't know?

No, they don't know. The size of the error bars in a typical physics experiment is often determined as much or more by the tolerances of the equipment (which is an engineering issue, not a physics issue) or by the technique of the operating scientist (which is a human factors issue, not a physics issue). Much of the point of research into these "basic elements" such as the speed of light or the inverse-square law is to improve instrumentation and measurement techniques.

Of course, if we actually came up with a measurement that was significantly different from the accepted speed of light (and the measurement held up), that would indeed put the cat among the pigeons, since it would mean (among other things) that most of the physics that has been done since 1905 is fundamentally wrong. But since "significantly" different inherently relies on the error bars in the measurement, you can see why physicists would be interested in measuring c with greater and greater precision even though they already know (for theoretical reasons) what the answer is.

[Jimbo07]

Originally Posted by drkitten

(which is an engineering issue, not a physics issue)

... unless it's an engineering issue constrained by the physics...

[The Man]

Originally Posted by cyberdyno

As I said, we are still debating the issue. Photons do have an internal structure, and time does slow down at near c speeds,

What internal structure would that be and how did you arrive at that conclusion?

Originally Posted by cyberdyno

the question is does time comes to a full stop, is there any internal process going on?

In essence yes it does stop, in the proper parlance a photon is said to experience no passage of proper time. So even if you could demonstrate some internal structure, from the photon’s reference frame there could be no processes.

ETA:
http://en.wikipedia.org/wiki/Proper_time

Quote:

This is referred to as the line element of the spacetime. s may be spacelike, lightlike, or timelike. Spacelike paths cannot be physically traveled (as they require moving faster than light). Lightlike paths can only be followed by light beams, for which there is no passage of proper time. Only timelike paths can be traveled by massive objects, in which case the invariant interval becomes the proper time .

[drkitten]

Originally Posted by The Man

What internal structure would that be and how did you arrive at that conclusion?

The internal structure of a photon?

"A 90-pound "folded-box-structure" backbone of aluminum honeycomb composite panels. Interior panels are glued to this chassis to create a tub within a tub. The monocoque is then surrounded front and back with subframes of chromoly. [...] Scissor doors, deep side-air intakes, fender louvres, and a low fighter-plane-style greenhouse complete the racetrack-ready purrfection."

Carbon-fiber body, low-weight V8 engine, six-speed manual transmission --- and no fuzzy dice unless you put them there yourself.

[The Man]

Originally Posted by drkitten

The internal structure of a photon?

"A 90-pound "folded-box-structure" backbone of aluminum honeycomb composite panels. Interior panels are glued to this chassis to create a tub within a tub. The monocoque is then surrounded front and back with subframes of chromoly. [...] Scissor doors, deep side-air intakes, fender louvres, and a low fighter-plane-style greenhouse complete the racetrack-ready purrfection."

Carbon-fiber body, low-weight V8 engine, six-speed manual transmission --- and no fuzzy dice unless you put them there yourself.

Well I guess that’s why they cost so much

Quote:

At a lofty $210,000

Quote:

And the red-hottest version of this mostly carbon-fiber (1980 pounds dry) two-seater is the MT900 Photon powered by a tweaked Chevrolet Z06 350-cube LS6 small-block V-8 making 435 horsepower. (A box-stock Z06 weighs over 3100 pounds.)

Hey, wait a minute I thought a “Photon” had zero rest mass (without the fuzzy dice)?

[drkitten]

Originally Posted by The Man

Well I guess that’s why they cost so much






Hey, wait a minute I thought a “Photon” had zero rest mass (without the fuzzy dice)?

You think that's the rest mass? You think I'm spending $200,000+ on something to PARK IT IN THE GARAGE?

It only looks yellow in the photo. It's actually painted red, but that's the blue-shift you're seeing.

[cyberdyno]

Originally Posted by drkitten

"A 90-pound "folded-box-structure" backbone of aluminum honeycomb composite panels. Interior panels are glued to this chassis to create a tub within a tub. The monocoque is then surrounded front and back with subframes of chromoly. [...] Scissor doors, deep side-air intakes, fender louvres, and a low fighter-plane-style greenhouse complete the racetrack-ready purrfection."

Carbon-fiber body, low-weight V8 engine, six-speed manual transmission --- and no fuzzy dice unless you put them there yourself.

The fundamental nature of the photon is believed to be understood theoretically; the prevailing Standard Model predicts that the photon is a gauge boson of spin 1, without mass and without charge, that results from a local U(1) gauge symmetry and mediates the electromagnetic interaction. However, physicists continue to check for discrepancies between experiment and the Standard Model predictions, in the hope of finding clues to physics beyond the Standard Model.

------------------------

Photon structure

Main article: Quantum Chromodynamics
According to Quantum Chromodynamics, a real photon can interact both as a point-like particle, or as a collection of quarks and gluons, i.e., like a hadron. The structure of the photon is determined not by the traditional valence quark distributions as in a proton, but by fluctuations of the point-like photon into a collection of partons.

----------------------------

Contributions to the mass of a system
See also: Mass in special relativity and Gravitation
The energy of a system that emits a photon is decreased by the energy E of the photon as measured in the rest frame of the emitting system, which may result in a reduction in mass in the amount E / c2. Similarly, the mass of a system that absorbs a photon is increased by a corresponding amount.

This concept is applied in a key prediction of QED, the theory of quantum electrodynamics begun by Dirac (described above). QED is able to predict the magnetic dipole moment of leptons to extremely high accuracy; experimental measurements of these magnetic dipole moments have agreed with these predictions perfectly. The predictions, however, require counting the contributions of virtual photons to the mass of the lepton. Another example of such contributions verified experimentally is the QED prediction of the Lamb shift observed in the hyperfine structure of bound lepton pairs, such as muonium and positronium.

Since photons contribute to the stress-energy tensor, they exert a gravitational attraction on other objects, according to the theory of general relativity. Conversely, photons are themselves affected by gravity; their normally straight trajectories may be bent by warped spacetime, as in gravitational lensing, and their frequencies may be lowered by moving to a higher gravitational potential, as in the Pound-Rebka experiment.


Wikipedia

------------------------

They are still spending time and money on this question, right? That means the issue is not settled; there is still debate going on.

[cyberdyno]

Jun Luo, Liang-Cheng Tu, Zhong-Kun Hu, and En-Jie Luan
Department of Physics, Huazhong University of Science and Technology, Wuhan 430074, People’s Republic of China

Received 24 August 2002; published 26 February 2003

A rotating torsion balance method is used to detect the product of the photon mass squared and the ambient cosmic vector potential Ae. The signal is modulated by rotating the torsion balance to ensure the effectiveness of detection for all possible orientations of the vector potential. The influences of sidereal disturbances of environment are also removed by virtue of this modulation method. The experimental result shows μγ2Ae<1.1×10-11   T m/m2, with μγ-1 as the characteristic length associated with photon mass. If the ambient cosmic vector potential Ae is 1012   T m due to cluster level fields, we obtain a new upper limit on photon mass of 1.2×10-51   g.



©2003 The American Physical Society

URL: http : // link. aps. org/abstract /PRL/v90/ e081801
DOI: 10.1103/PhysRevLett.90.081801
PACS: 12.20.Fv, 14.70.Bh, 98.80.Cq

See Also
Reply: Jun Luo, Liang-Cheng Tu, Zhong-Kun Hu, and En-Jie Luan, Luo et al. Reply:, Phys. Rev. Lett. 91, 149102 (2003)

Reply: Alfred Scharff Goldhaber and Michael Martin Nieto, Problems with the Rotating-Torsion-Balance Limit on the Photon Mass, Phys. Rev. Lett. 91, 149101 (2003)

Physics News Update: Physics News Update, Number 625, Story #2 (2003).

[The Man]

Originally Posted by cyberdyno

Photon structure

Main article: Quantum Chromodynamics
According to Quantum Chromodynamics, a real photon can interact both as a point-like particle, or as a collection of quarks and gluons, i.e., like a hadron. The structure of the photon is determined not by the traditional valence quark distributions as in a proton, but by fluctuations of the point-like photon into a collection of partons.

Oh please, did you even explore the references you have given?

Sure, in some photon collisions mass can be created.

http://en.wikipedia.org/wiki/Two-photon_physics

Quote:

Two-photon physics, also called gamma-gamma physics, is a branch of particle physics for the interactions between two photons. If the energy in the center of mass system of the two photons is large enough, matter can be created

And structure can just refer to..


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

Quote:

Structure is a fundamental and sometimes intangible notion covering the recognition, observation, nature, and stability of patterns and relationships of entities.

In this case "stucture" is the observation of the interaction of two photons slamming into each other with sufficient energy in the center of mass system to turn the relativistic mass of those photons, in that reference frame, to the rest mass of the particles resulting from that collision. Not that photons are comprised of those particles or have that rest mass.

As some on this forum like to say “Wikipedia” is not science. Science is a method, one part of that method is exploring and understanding the references you wish to site in order to ensure that you are using and applying those references properly. A lot of science is just built on referencing the work of others and improving it (as Einstein did). “Wikipedia” is just a reference resource like any other, and some may say worse then most. Now, good science can come from crappy references (by demonstrating those deficiencies) and crappy Science can come from good references (by not exploring or understanding those references, or the science involved). Your situation seems to be the latter.

[cyberdyno]

If there is structure then there must be process, and if there is process there is mass.

[The Man]

Originally Posted by cyberdyno

If there is structure then there must be process, and if there is process there is mass.

So, conversely (by your reasoning), if there are no processes, then there can be no structure and no mass.

Originally Posted by The Man

In essence yes it does stop, in the proper parlance a photon is said to experience no passage of proper time. So even if you could demonstrate some internal structure, from the photon’s reference frame there could be no processes.

ETA:
http://en.wikipedia.org/wiki/Proper_time

Oh, look no time thus no processes, no structure and no mass (in the photon’s reference frame). Does that make it clear for you now?

[Roboramma]

Originally Posted by The Man

So, conversely (by your reasoning), if there are no processes, then there can be no structure and no mass.

I don't think that follows from what he said. He said:
If A then B.
You say, that must mean:
If B then A

Which, correct me if I'm wrong, doesn't follow.

That aside, thanks for your posts in this thread.

[The Man]

Originally Posted by Roboramma

I don't think that follows from what he said. He said:
If A then B.
You say, that must mean:
If B then A

Which, correct me if I'm wrong, doesn't follow.

Actually, I said it must mean if no B then no A, since if A then B, so it does follow. But that’s all just logical semantics, and may actually have been conversely converse (opposite in sequence as well as negated).

Originally Posted by Roboramma

That aside, thanks for your posts in this thread.

You’re welcome, I’m glad someone other then me is reading them.

“Photon structure” is a very interesting field of study and is based on long established principles. From the terminology it is easy to be confused and think that “structure” refers to the photon being made up of subcomponents and not just the “structure” of how photons can interact (specifically at high energies). The former being untrue and converse to some of those long established principles, the latter being that interesting field of study.

[Dancing David]

Originally Posted by cyberdyno

If there is structure then there must be process, and if there is process there is mass.

If there is dog there must be fur, if there is fur it is a cat.

[Roboramma]

Originally Posted by The Man

Actually, I said it must mean if no B then no A, since if A then B, so it does follow. But that’s all just logical semantics, and may actually have been conversely converse (opposite in sequence as well as negated).

Just read that again. You're quite right.

[cyberdyno]

Originally Posted by Dancing David

If there is dog there must be fur, if there is fur it is a cat.

If there is dog there must be fur, if there is fur it is a mammal.