Are entangled photons ‘touching’ in time?

[martu]

At the creation of a pair of entangled particles we can say that the time of creation for each photon is equal, that is for a pair of entangled photons p1 and p2

te1 = te2 = 0

where ten is the creation time of photon n.

Here we’re going to use a slightly modified spacetime diagram, in this spacetime diagram the x axis and y axis represent the spatial dimensions and the time axis, ct, is the z axis perpendicular to the (x, y) plane. The z dimension is suppressed to help us picture what is going on.

Picture the two entangled photons as created at the point (0, 0, 0) and they go in opposite directions along the x axis. So for our entangled photons p1 and p2 we can say at the time of emission

(x1, y1) = (x2, y2) = (0, 0)

And also

(dx1/dy1) = (dx2/dy2)

Here is the extra step – our time axis is not a plane but a line. What does that mean? Well it means for each event en we define it’s spatial and temporal co-ordinates not as (x, y, t) but (x, y) and (t) that is we plot the path of an object through time as a line in the (x, y) plane and a different line ‘up’ the time axis. If your spacetime diagram is on a page our path through time can be represented as a line coming out of the page. All objects move ‘up’ the time axis at the same rate, c.

A consequence of this is that for our entangled pair of photons they travel ‘up’ the time line together, at least until one of them experiences an event. Or to put it another way at any time tn the two photons will be on the t axis at the same point. Any objects that are created at the same time and at the same spatial dimension are ‘touching’ in time and can, and indeed will, influence the other when a conserved property of one changes, the follows directly from the conservation principle.

Another way to look at it is that the photons share a clock from the event of their creation until one of them experiences another event. Indeed for every event you can consider that a unique point is created on the t axis which ‘moves’ up the t axis. This point is our clock and any objects that share a clock will influence each other, objects will no longer share a clock when they experience another event.

Does this make sense to anyone? We have a violation of locality but only for a very special subset of events where time and space are exactly equal. This is very rare in the universe hence we do not see locality violated often. We also cannot violate causality – the only direction you can go in time is ‘up’ the time axis so even though we have faster than light influence we can’t go back in time at all.

[Soapy Sam]

The problem with discussions of this nature is that they impinge so little on "normal reality" that common sense scarcely applies- so it's honestly near impossible for the average person to say what is "sensible in this context" and what is not.

Your argument sounds superficially credible to me, but we need someone who can say if it makes sense mathematically.
(Not that such is definitive, but it does seem likely to be a shade more definitive than a merely verbal argument.)

[Reality Check]

It seems to make sense to me. The photons are "touching in time" and separated by space, i.e. they are traveling separately through spacetime.

However quantum entanglement (http://en.wikipedia.org/wiki/Quantum_entanglement) is not really a "conservation principle".

[martu]

It seems to make sense to me. The photons are "touching in time" and separated by space, i.e. they are traveling separately through spacetime.

However quantum entanglement (http://en.wikipedia.org/wiki/Quantum_entanglement) is not really a "conservation principle".

Can you elaborate on the last sentence please?

[martu]

The problem with discussions of this nature is that they impinge so little on "normal reality" that common sense scarcely applies- so it's honestly near impossible for the average person to say what is "sensible in this context" and what is not.

Your argument sounds superficially credible to me, but we need someone who can say if it makes sense mathematically.
(Not that such is definitive, but it does seem likely to be a shade more definitive than a merely verbal argument.)

Agreed.

[Reality Check]

Can you elaborate on the last sentence please?
Quantum entanglement (http://en.wikipedia.org/wiki/Quantum_entanglement) is that measurement of an entangled property of one photon determines the property of the other photon (as in your OP).

A conservation principle is that a system has a conserved quantity at all times.

[martu]

Quantum entanglement (http://en.wikipedia.org/wiki/Quantum_entanglement) is that measurement of an entangled property of one photon determines the property of the other photon (as in your OP).

A conservation principle is that a system has a conserved quantity at all times.

Yep and what I was trying to say is that the two entangled photons should be considered as one system until they experience another event because they are 'touching’ in time. This explains how measuring one affects the other no matter how far apart spatially they are.

[gnome]

I don't know if this makes any sense, but is it plausible to think of them as the same photon for the applicable time?

[martu]

I don't know if this makes any sense, but is it plausible to think of them as the same photon for the applicable time?

I'm pretty sure the maths is OK but whether this answers the questions raised by QM and locality is one for the experts.

To answer your question I don't think so as they are in different locations in space. Same location in time however.

[Reality Check]

Yep and what I was trying to say is that the two entangled photons should be considered as one system until they experience another event because they are 'touching’ in time. This explains how measuring one affects the other no matter how far apart spatially they are.
The 'touching’ in time concept unfortunately does not explain this. It also applies to any 2 non-entangled photons and measuring one of these does not affect the other. Think about 2 photons emitted from 2 different atoms at the same time (te1 = te2 = 0).
It is the entanglement that is the reason for the correlation between the 2 photon measurements.

[gnome]

I'm pretty sure the maths is OK but whether this answers the questions raised by QM and locality is one for the experts.

To answer your question I don't think so as they are in different locations in space. Same location in time however.

I'm thinking of the same photon, simultaneously located in two different places (effectively).

I have no idea if this image is at all useful.

[martu]

The 'touching’ in time concept unfortunately does not explain this. It also applies to any 2 non-entangled photons and measuring one of these does not affect the other. Think about 2 photons emitted from 2 different atoms at the same time (te1 = te2 = 0).
It is the entanglement that is the reason for the correlation between the 2 photon measurements.

Those two photons are not created at the same point (x, y).

[Reality Check]

Those two photons are not created at the same point (x, y).
Neither do the entangled photons have to be (as in your example).
Quantum entanglement of particles does not require them to be in the same location at some point in time, e.g. Experiment demonstrates quantum entanglement between atoms a metre apart (http://www.iontrap.umd.edu/popular_press/PhysTodayNov07.pdf).

[martu]

Neither do the entangled photons have to be (as in your example).
Quantum entanglement of particles does not require them to be in the same location at some point in time, e.g. Experiment demonstrates quantum entanglement between atoms a metre apart (http://www.iontrap.umd.edu/popular_press/PhysTodayNov07.pdf).

That does require that the two photons emitted are at the same point at the same time namely in the beam splitter.

Let’s see if I have understood that article. We have an event at the same point in time and space where the photons are emitted by the ions creating an entangled state between one ion and one photon. Then when the photons ‘mingle’ at the beam splitter there is a chance that the two photons will be entangled. Conclusion - every time there is an entanglement ‘created’ between two objects they are at the same point and time.

Is this in error?

Are there any experiments where two entangled particles do not ‘touch’ each other spatially at all? Yes I get that these two atoms aren’t touching but they are in an entangled state with photons that do touch.

[martu]

I'm thinking of the same photon, simultaneously located in two different places (effectively).

I have no idea if this image is at all useful.

That would mean that this one photon had two paths through spacetime which I do not think is permissable but I may very well be wrong, I'll see if I can dig anything up about this. One of the physicists here may know the answer to this immediately.

[martu]

I'm thinking of the same photon, simultaneously located in two different places (effectively).

I have no idea if this image is at all useful.

Actually thinking about this a different way if it was the same photon what would it's spin be?

[Reality Check]

That does require that the two photons emitted are at the same point at the same time namely in the beam splitter.

Let’s see if I have understood that article. We have an event at the same point in time and space where the photons are emitted by the ions creating an entangled state between one ion and one photon. Then when the photons ‘mingle’ at the beam splitter there is a chance that the two photons will be entangled. Conclusion - every time there is an entanglement ‘created’ between two objects they are at the same point and time.

Is this in error?
Yes that is in error.
The experiment produces 2 entangled atoms not photons. The atoms are never in contact. They are in 2 different magnetic traps over a metre apart.
The photons in the experiment are used to demonstrate that the atoms are entangled.

[martu]

Yes that is in error.
The experiment produces 2 entangled atoms not photons. The atoms are never in contact. They are in 2 different magnetic traps over a metre apart.
The photons in the experiment are used to demonstrate that the atoms are entangled.

No it produces entangled ions and photons it says so clearly in the text:

…collapses the wavefunction into a state in which the two ions, as well as the photons, are entangled with each other.

I take it there is something I am missing here?

[sol invictus]

There's no reason why two entangled particles ever had to occupy the same spot. There's also no reason why two non-entangled particles couldn't be produced in the same place at the same time (to as much accuracy is entangled particle pairs sometimes are).

So it's hard to see how this idea would work, even if it were necessary to explain something.

[martu]

There's no reason why two entangled particles ever had to occupy the same spot.

Is this opinion based on theory or experiment?

There's also no reason why two non-entangled particles couldn't be produced in the same place at the same time (to as much accuracy is entangled particle pairs sometimes are).

How could we know they weren't entangled? How could you produce a pair of non entangled particles at the same point wont you violate conserved properties for the system?

So it's hard to see how this idea would work, even if it were necessary to explain something.

I think the idea that two or more particles can be at the same unique spot in time no matter how far apart they are could explain entanglement don't you? Completely theoretically mind you, I am well aware it seems to be wrong.

[sol invictus]

Is this opinion based on theory or experiment?

Both. You can, for example, entangle two atoms using EM fields. The atoms were never in the same spot. That works theoretically and experimentally.

How could we know they weren't entangled?

By measuring them.

How could you produce a pair of non entangled particles at the same point wont you violate conserved properties for the system?

It depends what they are and how you produce them. It also depends on what you mean by "same point".


I think the idea that two or more particles can be at the same unique spot in time no matter how far apart they are could explain entanglement don't you? Completely theoretically mind you, I am well aware it seems to be wrong.

No, to be honest I don't see how such an idea could work.

[martu]

Both. You can, for example, entangle two atoms using EM fields. The atoms were never in the same spot. That works theoretically and experimentally.

Can you show me a link to this experiment please?

As ever thanks again to you and RealityCheck for the use of your physics brains.

[gnome]

Actually thinking about this a different way if it was the same photon what would it's spin be?

An interesting point. My cursory study of this shows that entangled particles tend to have opposite spin. That might squash the usefulness of trying to think of them as the same particle co-located.

[Reality Check]

No it produces entangled ions and photons it says so clearly in the text:

I take it there is something I am missing here?
There are two entanglements that I can see.
The first is between each ion and the photon that it emited.
The second is between the ions. This is established when the "experimenters select only those excitation events that result in photons recorded by both detectors within 15 ns after the excitation".

As far as I know, the photons are not entangled with each other.

[martu]

There are two entanglements that I can see.
The first is between each ion and the photon that it emited.
The second is between the ions. This is established when the "experimenters select only those excitation events that result in photons recorded by both detectors within 15 ns after the excitation".

As far as I know, the photons are not entangled with each other.

Ok. When are the ions entangled before or after the photons mingle? What does the author mean by mingle anyway?

[martu]

An interesting point. My cursory study of this shows that entangled particles tend to have opposite spin. That might squash the usefulness of trying to think of them as the same particle co-located.

Exactly they have to be different.

[martu]

Neither do the entangled photons have to be (as in your example).
Quantum entanglement of particles does not require them to be in the same location at some point in time, e.g. Experiment demonstrates quantum entanglement between atoms a metre apart (http://www.iontrap.umd.edu/popular_press/PhysTodayNov07.pdf).

Can you do this experiment without the two photons mingling?

[Skeptic]

(Derail)

Every time QM weirdness -- with its 11 dimensions, all hidden somewhere incredibly close to us yet untouchable, time moving backward, etc. -- is discussed, I am reminded of the old limmerick:

The creatures of other dimensions
Cause earthlings great consternation.
They can sneak up to you
And give you a screw
Before you divined their intention.

[Reality Check]

Can you do this experiment without the two photons mingling?
The 2 photons are never "mingled" as in quantum entangled.
What they mean by "mingle" is pass through the half-mirror within a 15 ns window.

[Reality Check]

Ok. When are the ions entangled before or after the photons mingle? What does the author mean by mingle anyway?
The ions quantum states are entangled by the selection of the photon that each emit. This selection is done after the photons are detected, i.e. after they "mingle".
What the author means by "mingle" is pass through the half-silvered mirror within a 15 ns window.
If they wanted to say entangled then they would have said entangled.

ETA:
The middle column on page 17 states that the photons are entangled by the requirement that both detectors detect photons.

[martu]

The 2 photons are never "mingled" as in quantum entangled.
What they mean by "mingle" is pass through the half-mirror within a 15 ns window.

Why is mingling required?

[martu]

The ions quantum states are entangled by the selection of the photon that each emit. This selection is done after the photons are detected, i.e. after they "mingle".
What the author means by "mingle" is pass through the half-silvered mirror within a 15 ns window.
If they wanted to say entangled then they would have said entangled.

ETA:
The middle column on page 17 states that the photons are entangled by the requirement that both detectors detect photons.

Erm forgive my dumbness but doesn't your ETA contradict your original post?

[martu]

(Derail)

Every time QM weirdness -- with its 11 dimensions, all hidden somewhere incredibly close to us yet untouchable, time moving backward, etc. -- is discussed, I am reminded of the old limmerick:

The creatures of other dimensions
Cause earthlings great consternation.
They can sneak up to you
And give you a screw
Before you divined their intention.

If time is the 4th dimension
there is one thing I aught to mention
though this photon is here
and that photon is there
if entagled they're at one location

[Reality Check]

Erm forgive my dumbness but doesn't your ETA contradict your original post?
Yes if you mean "As far as I know, the photons are not entangled with each other.". Now I know better.

[Reality Check]

Why is mingling required?
To entangle the quantum state of the ions as stated in the middle column of page 17.

The experiment shows that quantum state of ions separaterd by a metre or more can be entangled The demostraion of the entanglement is described on the next page - page 18.
There is also another interesting aspect: The entanglement of the ions is establshed by causing the entanglement of photons at an arbitary distance from the ions.

[martu]

To entangle the quantum state of the ions as stated in the middle column of page 17.

The experiment shows that quantum state of ions separaterd by a metre or more can be entangled The demostraion of the entanglement is described on the next page - page 18.
There is also another interesting aspect: The entanglement of the ions is establshed by causing the entanglement of photons at an arbitary distance from the ions.

Right thanks.

I contend that when the photons mingle we have the two photons and the two ions at the same point in time hence the ions become entangled. Before the photons mingle the ions are not entangled.

[Reality Check]

Right thanks.

I contend that when the photons mingle we have the two photons and the two ions at the same point in time hence the ions become entangled. Before the photons mingle the ions are not entangled.
That is right. Before the photons are mingled the ions are not entangled. If the photons are then detected within the 15 ns window the ions should be entangled. This is then demonstrated to be the case with the detection of the hyperfine state of the ions.

[sol invictus]

Can you show me a link to this experiment please?


Here's an example, with links to the papers: http://blogs.discovermagazine.com/80beats/2009/06/04/the-biggest-spooky-system-ever-seen-4-entangled-ions/

By the way, all the atoms in a Bose-Einstein condensate are entangled with each other, even though the condensate can be relatively large, and it can be achieved simply by cooling the atoms sufficiently.

[Tumbleweed]

Here's an example, with links to the papers: http://blogs.discovermagazine.com/80beats/2009/06/04/the-biggest-spooky-system-ever-seen-4-entangled-ions/

By the way, all the atoms in a Bose-Einstein condensate are entangled with each other, even though the condensate can be relatively large, and it can be achieved simply by cooling the atoms sufficiently.
I read your link and it seems to infer that this entanglement involves a mechanical system. One pair of ions is set vibrating, the other pair responds. So we get back to the Mars thing again: If I set two ions vibrating on Earth, two entangled particles do likewise on Mars. Why is this not an instantaneous switch?

[martu]

Here's an example, with links to the papers: http://blogs.discovermagazine.com/80beats/2009/06/04/the-biggest-spooky-system-ever-seen-4-entangled-ions/.

From your link:

The first step to achieving these synchronized vibrations relied on standard techniques to entangle the spins of the beryllium ions in each pair.

What are these standard techniques? Do they involve bringing the entangled pairs together at one point in space and time?

By the way, all the atoms in a Bose-Einstein condensate are entangled with each other, even though the condensate can be relatively large, and it can be achieved simply by cooling the atoms sufficiently.

From this paper Entanglement concentration in Bose-Einstein condensates (http://web.mit.edu/lhenders/www/papers/bec.pdf)

Since entanglement cannot be created by local operations on separate systems, entangled pairs of systems need to be created at a source and then distributed to distant parties.


Bose-Einstein condensates fit my picture as you have to ‘distribute’ the entanglement which I would say is bringing two particles together at the same point in time then doing this over and over again resulting in all the atoms sharing a point in time.

[martu]

That is right. Before the photons are mingled the ions are not entangled. If the photons are then detected within the 15 ns window the ions should be entangled. This is then demonstrated to be the case with the detection of the hyperfine state of the ions.

So do you have any other objections to my idea?

[martu]

I read your link and it seems to infer that this entanglement involves a mechanical system. One pair of ions is set vibrating, the other pair responds. So we get back to the Mars thing again: If I set two ions vibrating on Earth, two entangled particles do likewise on Mars. Why is this not an instantaneous switch?

Because you couldn't use it as a switch. Unless you can show me how?

[Reality Check]

So do you have any other objections to my idea?
Other than it does not work, no.
Entangled objects are entangled because their quantum states are entangled, not because you state that they were at the same position and time. The theory and experiments shows that the objects need not be at the same position or time.

IMO - there is probably an experiment out there that has 2 entangled photons emitted from the same atom at different times.

Note that the entangled photons in this case not only start from different positions but they also start at different times. Within a 15 ns window does not mean that the photons were emitted at the exact some time. You might say that time begins when they entangle at the half-silvered mirror but then what about their effect on the ions?

You also have the entangled ions which are definitely at different positions and they can emit the (non-entangled) photons at different times within the 15 ns window.

[Reality Check]

What are these standard techniques? Do they involve bringing the entangled pairs together at one point in space and time?

You should be able to look up the standard techniques yourself.
They usually involve lasers of specific frequencies to place ions in specific quantum states.


From this paper Entanglement concentration in Bose-Einstein condensates (http://web.mit.edu/lhenders/www/papers/bec.pdf)
Bose-Einstein condensates fit my picture as you have to ‘distribute’ the entanglement which I would say is bringing two particles together at the same point in time then doing this over and over again resulting in all the atoms sharing a point in time.
It does not fit your picture (note the word teleportation in the abstract).

The paper's abstract is quite clear that the technique is about concentrating the degree of entanglements of atoms that make up a Bose-Einstein condensates.
We propose a scheme for demonstrating entanglement swapping (i.e. teleportation of entanglement) using trapped Bose-Einstein condensates. This is accomplished by detection of the total number of atoms leaking out of two adjacent traps. We describe how this scheme may be used to concentrate entanglement shared between two parties in the form of entangled condensates

At no time during the process are all the atoms in the Bose-Einstein condensates at the same point in space or time.

Note that the entanglement is "teleported", i.e. the atoms are never close to each other.

[sol invictus]

I read your link and it seems to infer that this entanglement involves a mechanical system. One pair of ions is set vibrating, the other pair responds. So we get back to the Mars thing again: If I set two ions vibrating on Earth, two entangled particles do likewise on Mars. Why is this not an instantaneous switch?

In the Copenhagen interpretation, because it's random. In MW, because both things happen (so it's effectively random in each).


What are these standard techniques? Do they involve bringing the entangled pairs together at one point in space and time?


No.


Bose-Einstein condensates fit my picture as you have to ‘distribute’ the entanglement which I would say is bringing two particles together at the same point in time then doing this over and over again resulting in all the atoms sharing a point in time.

No, the atoms never come together. Two atoms can become entangled by (for example) exchanging a photon or other particle between them.

[martu]

Other than it does not work, no.
Entangled objects are entangled because their quantum states are entangled, not because you state that they were at the same position and time. The theory and experiments shows that the objects need not be at the same position or time. .

You need to follow it through. The following describes the independent events that occur, Event 1 is the emission of one of the photons, Event 2 is the emission of the other and Event 3 is the mingling of the photons.

Event 1:

Ion1 and Photon1 are at the same place and time. Result Ion1 and Photon1 become entangled.

Event 2

Ion2 and Photon2 are at the same place and time. Result Ion2 and Photon2 become entangled.

Event 3

Photon1 and Photon2 are at the same place and time. Result Photon1 and Photon2 become entangled. But we have also have to consider that Photon1 and Photon2 are at the same point in time as Ion1 and Ion2 respectively. Consequence? Ion1 and Ion2 are at the same point in time also and become entangled.

This is logically consistent do you agree?

It also predicts that only some runs will produce entanglement as the photons will not consistently meet at the same point at the beam splitter. I admit I can’t follow the reasons in the text as to why they only get so few correlations can you enlighten me?

Also this sentence:

Entangled objects are entangled because their quantum states are entangled, not because you state that they were at the same position and time.

Says things are entangled because they are entangled, a tautology. Why are entangled objects entangled in your opinion?

IMO - there is probably an experiment out there that has 2 entangled photons emitted from the same atom at different times.

This would show me wrong without a doubt but I can’t find an example of this at all.

Note that the entangled photons in this case not only start from different positions but they also start at different times. Within a 15 ns window does not mean that the photons were emitted at the exact some time. You might say that time begins when they entangle at the half-silvered mirror but then what about their effect on the ions?

You also have the entangled ions which are definitely at different positions and they can emit the (non-entangled) photons at different times within the 15 ns window.

See above for a description of the three events.

[martu]

You should be able to look up the standard techniques yourself.
They usually involve lasers of specific frequencies to place ions in specific quantum states.


It does not fit your picture (note the word teleportation in the abstract).

The paper's abstract is quite clear that the technique is about concentrating the degree of entanglements of atoms that make up a Bose-Einstein condensates.


At no time during the process are all the atoms in the Bose-Einstein condensates at the same point in space or time.

Note that the entanglement is "teleported", i.e. the atoms are never close to each other.

I will look into this a bit more, thanks for the information.

Note that my description of the 3 events in my post above does not require that the atoms are close to each as long as they were, at one point at least, at the same point in time as a carrier particle like a photon. This is how the entanglement is 'teleported'.

[martu]

No, the atoms never come together. Two atoms can become entangled by (for example) exchanging a photon or other particle between them.

Yes as I describe in my 3 events above.

[sol invictus]

IMO - there is probably an experiment out there that has 2 entangled photons emitted from the same atom at different times.
This would show me wrong without a doubt but I can’t find an example of this at all.

I don't understand your idea at any level, so I can't comment whether this will show it to be wrong. But it's certainly true that the same atom can and will emit 2 photons at different times, and the two photons will be entangled with each other.

For example an atom in an excited state that decays to its ground state in two stages, by emitting two separate photons.

[sol invictus]

Here (http://arxiv.org/abs/quant-ph/0509165) you go. Slightly more complex than what I had in mind, but it does the job:

"Thus, the excited atom emits a first photon, entangled with the atom in ground states as discussed before [14]. In the second part, the atom is subsequently excited by the pump, and emits a second photon and swaps its entanglement with the first photon (already outside the cavity) to the second photon. The whole process now generates an entangled photon pair."

[martu]

I don't understand your idea at any level, so I can't comment whether this will show it to be wrong. But it's certainly true that the same atom can and will emit 2 photons at different times, and the two photons will be entangled with each other.

For example an atom in an excited state that decays to its ground state in two stages, by emitting two separate photons.

Ok thanks do you have a link that details this process please? My cursory Google search was inconclusive.

ETA: Just caught post 50 ignore this thanks sol

[martu]

Here (http://arxiv.org/abs/quant-ph/0509165) you go. Slightly more complex than what I had in mind, but it does the job:

"Thus, the excited atom emits a first photon, entangled with the atom in ground states as discussed before [14]. In the second part, the atom is subsequently excited by the pump, and emits a second photon and swaps its entanglement with the first photon (already outside the cavity) to the second photon. The whole process now generates an entangled photon pair."

This fits with what I am saying actually. We have two events:

Event 1:
Atom emits photon1 at a unique point in time. Atom and photon1 are now entangled.

Event 2:
Atom emits photon2 at a unique point in time. Atom and photon2 are now entangled. However the Atom is already at the same point in time as photon1 hence photon1 and photon2 are now at the same point in time and consequently entangled.

I doubt this will help as you can’t seem to follow what I’m saying unfortunately. I will probably have to write all this out mathematically.

Thanks all this has been helpful.

[Reality Check]

See above for a description of the three events.
Your 3 events are nothing to do with the experiment.
The real events as described in the experiment are:
Event 1:
Ion1 emits Photon1. They are not at the same place and time. They are not entangled.
In QM the ion and the electron emitting the photon have no set position - rather they have a probability distribution in space.
If you like the "place" of the ion is the average position of its nucleus and the "place" of the photon is the average position of the electron emitting it. These are different.

Event 2
Ion2 emits Photon2. They are not at the same place and time. They are not entangled.

Event 3
Photon1 and Photon2 are not at the same place and time. They are in the region of the half-silvered mirror. They not entangled.

Event 4.
Only those events that the detector shows that Photon1 and Photon2 are in the 15 nanosecond window are selected. Result: Ion1 and Ion2 are entangled. Photon1 and Photon2 are entangled.

It is the detection that causes the entanglement.

[sol invictus]

This fits with what I am saying actually.

Probably the question to ask you is, what are you trying to accomplish? QM and QFT already describe entangled phenomena in a certain way. They give sharp, mathematical predictions that have been born out of tens of thousands of sophisticated experiments. So they're clearly either correct or very good approximations to correct.

But they don't describe entanglement in anything like the language you're suggesting (since your theory contains no math I can't say anything more than that). So, what are you after? Are you trying to find an entirely new theory that will replace QM and QFT? Or are you simply trying to find a way to explain in words how entanglement is possible? If it's the first, forget the words and write a real theory, with math. If it's the second, why can't I connect the words you're saying to what I know about QM and QFT?

[martu]

Your 3 events are nothing to do with the experiment.
The real events as described in the experiment are:
Event 1:
Ion1 emits Photon1. They are not at the same place and time. They are not entangled.
In QM the ion and the electron emitting the photon have no set position - rather they have a probability distribution in space.


Ok I am obviously missing something.

If you can spare me more time can you tell me why the bolded part is true? The text flatly contradicts this:

Page 17 first column third paragraph:

Before the two photons mingle at the beamsplitter's half mirror, the only quantum entanglement is between each ion and the photon it emitted

[martu]

Probably the question to ask you is, what are you trying to accomplish? QM and QFT already describe entangled phenomena in a certain way. They give sharp, mathematical predictions that have been born out of tens of thousands of sophisticated experiments. So they're clearly either correct or very good approximations to correct.

But they don't describe entanglement in anything like the language you're suggesting (since your theory contains no math I can't say anything more than that). So, what are you after? Are you trying to find an entirely new theory that will replace QM and QFT? Or are you simply trying to find a way to explain in words how entanglement is possible? If it's the first, forget the words and write a real theory, with math. If it's the second, why can't I connect the words you're saying to what I know about QM and QFT?

No I am not trying to replace anything at all in fact it was the discussion of Bell’s theorem in the deterministic thread which led me here. I accept QM and QFT as being correct, experiment tells us this (for now, new evidence in the future and so on…). So it’s the bolded sentence, to your question:

why can't I connect the words you're saying to what I know about QM and QFT?

Because we speak different languages when it comes to physics. Ok perhaps not different languages but you are fluent whereas I have some basic conversational physics. But I can follow most of the maths, I spent too much of my time at university on the rugby pitch or in the bar but I did manage to get a maths degree while I was there.

The whole idea is based on postulating whether we can say things can be next to each other or touching in time in the same way they can be touching each other in space. If we can and the maths works then messages between them will be instantaneous much the same way that messages between objects touching in space are instantaneous. Instantaneous messages are required for entanglement and here we are.

Does this sound like complete nonsense from the off?

[Reality Check]

Ok I am obviously missing something.

If you can spare me more time can you tell me why the bolded part is true? The text flatly contradicts this:

Page 17 first column third paragraph:
The bolded part is wrong. It should be "They (the two photons) are not entangled)" and only for the second event.

More points about why the "touching in time" concept has nothing to do with quantum entanglement (other than the theory has nothing about this and the experiment contradicts it).

It also applies if there are 2 unconnected atoms that just happen to emit photons at the same time. In other words it states that quantum entanglement is a common state in emissions such as starlight or lasers. Scientists are obviously wasting their time doing all these complex quantum entanglement experiments :rolleyes:.

Take a state that is a combination of 2 independent states, i.e. the 2 wave functions are added together. Plug them into the time dependent Schrödinger equation. What you get out after some time is still 2 wave functions that are added together. The states are still independent and have not mixed. The states have not mixed. A measurement on one state will have no effect on the other state.

[Reality Check]

The whole idea is based on postulating whether we can say things can be next to each other or touching in time in the same way they can be touching each other in space. If we can and the maths works then messages between them will be instantaneous much the same way that messages between objects touching in space are instantaneous. Instantaneous messages are required for entanglement and here we are.

Does this sound like complete nonsense from the off?
It is right up to the last sentence which is "complete nonsense" :).
There are no messages, i.e. as in information passing between the photons at speeds greater then light.
Entanglement imples instantaneous collapse of the wave function. Instantaneous messages do not make quantutum states entangled. Instantaneous messages do not require that the photons be touching.

What entanglement requires is entanglment of the quantum states. If the quantum states are not intangled then a measurement of one photon will not effect the other photon.

ETA:
You seem to think that "touching in time" means instantaneous messages (the second to last sentence). This is not true.
If the message speed is finite then the space between the photons means a finite time for the messages to travel.
If the message speed is infinite then it does not matter whether the photons are "touching in time" or not. All messages between any photons at any point in spacetime are instantaneous.

[sol invictus]

I've gone back to your OP to try to make sense of it.

At the creation of a pair of entangled particles we can say that the time of creation for each photon is equal, that is for a pair of entangled photons p1 and p2

te1 = te2 = 0

where ten is the creation time of photon n.

Here we’re going to use a slightly modified spacetime diagram, in this spacetime diagram the x axis and y axis represent the spatial dimensions and the time axis, ct, is the z axis perpendicular to the (x, y) plane. The z dimension is suppressed to help us picture what is going on.

Fine.

Picture the two entangled photons as created at the point (0, 0, 0) and they go in opposite directions along the x axis. So for our entangled photons p1 and p2 we can say at the time of emission

(x1, y1) = (x2, y2) = (0, 0)

And also

(dx1/dy1) = (dx2/dy2)

OK.

Here is the extra step – our time axis is not a plane but a line.

Huh? The time axis is always a line, it's an axis. Did you mean the opposite?

What does that mean? Well it means for each event en we define it’s spatial and temporal co-ordinates not as (x, y, t) but (x, y) and (t) that is we plot the path of an object through time as a line in the (x, y) plane and a different line ‘up’ the time axis. If your spacetime diagram is on a page our path through time can be represented as a line coming out of the page. All objects move ‘up’ the time axis at the same rate, c.

That makes no sense. Objects occupy one location at any given time, and that location changes as a function of time. Therefore the trajectory of an object through spacetime is indeed a line, but it's a single line and it's at some angle to the z-axis that's less than or equal to 45 degrees on your diagram.


A consequence of this is that for our entangled pair of photons they travel ‘up’ the time line together, at least until one of them experiences an event.

No idea what you mean. The photons are flying off in opposite directions AND advancing in time; they are detected some distance away in different places some time after they were emitted.

Or to put it another way at any time tn the two photons will be on the t axis at the same point.

But that would mean both photons remain at x=y=0, which they don't.

No I am not trying to replace anything at all in fact it was the discussion of Bell’s theorem in the deterministic thread which led me here. I accept QM and QFT as being correct, experiment tells us this (for now, new evidence in the future and so on…).

Right, OK, that's why I went back to the OP.

Instantaneous messages are required for entanglement and here we are.

No, they're not. In MW there is nothing instantaneous, everything is local, nothing suddenly changes.

[martu]

The bolded part is wrong. It should be "They (the two photons) are not entangled)" and only for the second event.

More points about why the "touching in time" concept has nothing to do with quantum entanglement (other than the theory has nothing about this and the experiment contradicts it).

You agree that the ion and the photon are entangled as the text clearly states?

It also applies if there are 2 unconnected atoms that just happen to emit photons at the same time. In other words it states that quantum entanglement is a common state in emissions such as starlight or lasers. Scientists are obviously wasting their time doing all these complex quantum entanglement experiments :rolleyes:.

Firstly no it doesn’t apply if two atoms are unconnected remember that bit about being at the same place too?

Entanglement is common but the problem is decoherence after the entanglement event hence the complex experiments. Or am I wrong again?

Take a state that is a combination of 2 independent states, i.e. the 2 wave functions are added together. Plug them into the time dependent Schrödinger equation. What you get out after some time is still 2 wave functions that are added together. The states are still independent and have not mixed. The states have not mixed. A measurement on one state will have no effect on the other state.

I know this and haven’t said they will mix. I am struggling to get my message across, bear with me.

[martu]

It is right up to the last sentence which is "complete nonsense" :).
There are no messages, i.e. as in information passing between the photons at speeds greater then light.
Entanglement imples instantaneous collapse of the wave function. Instantaneous messages do not make quantutum states entangled. Instantaneous messages do not require that the photons be touching.

What entanglement requires is entanglment of the quantum states. If the quantum states are not intangled then a measurement of one photon will not effect the other photon.

You keep repeating that entanglement requires entanglement which doesn’t explain anything does it?

ETA:
You seem to think that "touching in time" means instantaneous messages (the second to last sentence). This is not true.
If the message speed is finite then the space between the photons means a finite time for the messages to travel.
If the message speed is infinite then it does not matter whether the photons are "touching in time" or not. All messages between any photons at any point in spacetime are instantaneous.

Consider this – we have two hypothetical identical rigid objects A and B and they are touching (spatially). If I push A then B will also be pushed. OK? What is the time difference between the push of A and the push of B?

[martu]

Huh? The time axis is always a line, it's an axis. Did you mean the opposite?

No I meant that the time for any event is found on the z axis so if we consider (x, y) to be our spatial plane the time co-ordinate is always at some point (0, 0, t). The event’s spatial location will be at (x, y) so to get a complete description of an event we have the spatial coordinates (x, y) and a time coordinate (t). But we do not plot (x, y, t) we plot (x, y) and separately (t), consider the time co-ordinate as the clock for this event.

That makes no sense. Objects occupy one location at any given time, and that location changes as a function of time. Therefore the trajectory of an object through spacetime is indeed a line, but it's a single line and it's at some angle to the z-axis that's less than or equal to 45 degrees on your diagram.

Consider the simple example of two entangled photons created by Spontaneous Parametric Down Conversion. At the time that the single photon ‘splits’ into two photons we have

p1 is at location (x1, y1)
p2 is at location (x2, y2)

where

(x1, y1) = (x2, y2)

For simplicity assume that the photons are travelling in opposite directions along the x axis.

To say the photon are at the same point in time and entangled is to say that

t1 = t2

until one experiences a new event. They share a clock which moves along the time axis.

So after 1 second we have on the x, y plane

p1 is at location (-c, 0)
p2 is at location (c, 0)

but on the time axis we have

p1 is at time c
p2 is at time c

touching in time.

No idea what you mean. The photons are flying off in opposite directions AND advancing in time; they are detected some distance away in different places some time after they were emitted.


ct1 = ct2

I am running out of words to be honest, I think I’ll have a go at writing this out mathematically.

[sol invictus]

No I meant that the time for any event is found on the z axis so if we consider (x, y) to be our spatial plane the time co-ordinate is always at some point (0, 0, t). The event’s spatial location will be at (x, y) so to get a complete description of an event we have the spatial coordinates (x, y) and a time coordinate (t). But we do not plot (x, y, t) we plot (x, y) and separately (t), consider the time co-ordinate as the clock for this event.

I understand those words, but what's the point of following that procedure? We draw these plots so that we can tell where the particles are. Doing things your way we'll have two lines for each particle, neither of which represents its position.

Worse, those lines can intersect or coincide even when the particles are not entangled and never interact. For example two pairs of particles produced at different times at the same point would produce four coinciding lines, even though the two pairs might not be entangled with each other. Similarly two particles that actually coincide and therefore can interact cannot be distinguished from two particles that pass across the same point at different times and therefore cannot interact.

Basically this way of drawing diagrams removes lots of relevant information, which is not the point of making a plot. And we cannot even interpret the one piece of info that two t-axis lines coincide to determine anything, as you can see from that example.

As for the math, it simply isn't the case in standard QM that two entangled particles "coincide", or that the time axis is relevant to them in any special way compared to non-entangled particles. "Entangled" means nothing more and nothing less than that the full state cannot be written as a product of a state for particle 1 times a state for particle 2.

[Reality Check]

You agree that the ion and the photon are entangled as the text clearly states?

Yes. Each ion is entangled with the photon that it emits.


Firstly no it doesn’t apply if two atoms are unconnected remember that bit about being at the same place too?

You need to state your concept more clearly then.
Remember that if you state it mathematically then you will have to the prove that an entangled quantum state emerges from your mathematics.
So far you have not even got close to that.

If your concept is that two objects that are ever in the same place at the same time, e.g. the 2 photons in your OP, will have their quantum states magically entangled somehow then the 2 ion experiment proves your concept to be wrong.

The ions are never in the same place. The ions are never "touching in time". But they are entangled.
Thus the formation of entangled quantum states does not need the objects being entangled to be in the same place at any time nor does it need for them to be "touching in time".

This makes the rest of your post (and this thread) moot.

[Reality Check]

You keep repeating that entanglement requires entanglement which doesn’t explain anything does it?

It explains everything. It is the entanglement that explains the behaviour of the entangled objects.
Your concept explains nothing. All it is is the assumption by you that something that has nothing to to with quantum entanglement will somehow magically create entanglement. Theory and experiment disproves this.


Consider this – we have two hypothetical identical rigid objects A and B and they are touching (spatially). If I push A then B will also be pushed. OK? What is the time difference between the push of A and the push of B?
Why consider that? It has nothing to do with any quantum entanglemnet experiment. At the point that the measurments are made the entangled particles are not "touching (spatially)".

I will wait for you to come back with the mathematical treatment of your concept before comenting further. It will be interesting to see how you get entangled states from your concept.

My guess is that you will start with 2 systems in pure quantum states (http://en.wikipedia.org/wiki/Pure_state), allow them to be at the same position, set t = 0, plug the composite system into Schrödinger's equation and get .... a composite system consisting of pure quantum states!

[martu]

Thanks both of you, this conversation has helped me understand a few things. You're both right about the maths and maybe I am trying to use words (badly obviously) to describe the existing maths as you suggest Reality Check, I honestly hadn’t thought of that. It’s one thing to follow the maths (as I can when I read a physics text) it’s another to fully understand it, as you’re both probably aware you don’t really grasp the maths behind something until you use it.

I'll be back with some maths if I can. Thanks again.

[martu]

Entanglement is common but the problem is decoherence after the entanglement event hence the complex experiments. Or am I wrong again?

Sorry one final thing I meant to add to my previous post, Reality Check is my statement above correct?

[Reality Check]

Sorry one final thing I meant to add to my previous post, Reality Check is my statement above correct?
I do not know.

IMO Entanglement is not common given that it needs the quantum states to be manipulated using things that do not appear often in nature, e.g. lasers, specific configurations of magnetic fields (NMR), etc.

[martu]

I do not know.

IMO Entanglement is not common given that it needs the quantum states to be manipulated using things that do not appear often in nature, e.g. lasers, specific configurations of magnetic fields (NMR), etc.

If we assume that events exists where the parties are not entangled we have to conclude that events exist where one, or more, of the conservation laws is violated.

[Reality Check]

If we assume that events exists where the parties are not entangled we have to conclude that events exist where one, or more, of the conservation laws is violated.
I do not now what you mean.

There are definitely events where "the parties are not entangled", e.g. two arbitary electrons collide (same position, same time and so meets the criteria for your concept). Which one, or more, of the conservation laws is violated in that case?

[martu]

I do not now what you mean.

There are definitely events where "the parties are not entangled", e.g. two arbitary electrons collide (same position, same time and so meets the criteria for your concept). Which one, or more, of the conservation laws is violated in that case?

Really? What experiments show electrons colliding resulting in no entanglement where decoherence hasn't occurred?

Maybe I am way off here but I thought if any two elctrons collided spin would have to be conserved after the collision. Not only spin but any conserved property hence we can say they are entangled.

[Reality Check]

Really? What experiments show electrons colliding resulting in no entanglement where decoherence hasn't occurred?

Maybe I am way off here but I thought if any two elctrons collided spin would have to be conserved after the collision. Not only spin but any conserved property hence we can say they are entangled.
I do not know of any such experiments. But the fact that the electrons are in pure quantum states (not really mentioned in my post) means that they are never entangled to start with and can never be entangled by the collision.

And yes spin is conserved during the collision. So what?
So is energy, mass and charge.

[sol invictus]

Entanglement is common but the problem is decoherence after the entanglement event hence the complex experiments.

That's correct.


There are definitely events where "the parties are not entangled", e.g. two arbitary electrons collide (same position, same time and so meets the criteria for your concept).

Actually Martu is correct: they will be entangled in that case.

But the fact that the electrons are in pure quantum states (not really mentioned in my post) means that they are never entangled to start with and can never be entangled by the collision.

I think you're confusing entanglement with mixing here. "Entangled states" usually refers to pure states, and unentangled states can become entangled via interactions.

[martu]

Actually Martu is correct: they will be entangled in that case.

Stopped clocks and all that.....

Thanks for the clarification.