The Present Moment in Spacetime?

[p764rds]

An operational definition is a physical experiment that you could perform, a step-by-step recipe for physically determining the result. For example, Einstein's synchronization procedure is an operational definition of simultaneity using light.

So what step-by-step physical procedure could you perform using entanglement to define simultaneity?

I would entangle two particles - maybe held in a crystal lattice - so they would have to be electrons in this case. Then take one on a high speed trip on an aeroplane, so that it lorentz time shifted a second - or as large as we could practically manage. Then on return from this trip measure the correlation of the two particles. It should come out to be >10,000 times the speed of light again even though one particle was a second older than the other. (Entanglement correlation experiments have already been done and proved it to be >10,000 times the speed of light, I can dig out the refs if you want).

 

[workmad3]

I would entangle two particles - maybe held in a crystal lattice - so they would have to be electrons in this case. Then take one on a high speed trip on an aeroplane, so that it lorentz time shifted a second - or as large as we could practically manage. Then on return from this trip measure the correlation of the two particles. It should come out to be >10,000 times the speed of light again even though one particle was a second older than the other. (Entanglement correlation experiments have already been done and proved it to be >10,000 times the speed of light, I can dig out the refs if you want).

That doesn't define any form of simultaneity though. My view is that entanglement is actually a way of adhering to the SR view of simultaneous spaces in a correct fashion. If you have two observers carefully selected, their simultaneous spaces will differ as to which measurement of an entangled pair occurred first. Therefore the two measurements must always match and 'instantaneously' fix the measurement of the other because you never have a way of knowing if you measured first or second (it changes depending on where you observed the measurement from)

 

[p764rds]

That doesn't define any form of simultaneity though. My view is that entanglement is actually a way of adhering to the SR view of simultaneous spaces in a correct fashion. If you have two observers carefully selected, their simultaneous spaces will differ as to which measurement of an entangled pair occurred first. Therefore the two measurements must always match and 'instantaneously' fix the measurement of the other because you never have a way of knowing if you measured first or second (it changes depending on where you observed the measurement from)

Entanglement correlations has nothing to do with SR or GR.
The two particles (one older than the other) could be physically placed right next to each other - no clock problems then.

 

[workmad3]

Entanglement correlations has nothing to do with SR or GR.
The two particles (one older than the other) could be physically placed right next to each other - no clock problems then.

That doesn't remove the problem from consideration in general principles, just shows that you can construct a problem where the effect is negligible.

The point of simultaneity is to define exactly when 2 things can be regarded as 'the same time'. There is no way to pinpoint an exact point on the world-line of one particle in an entangled pair that corresponds to the moment when a measurement was performed on the other particle of the pair. Furthermore, when simultaneous spaces are taken into consideration you can't even say for certain which of the measurements was performed first (the 'first' measurement depends on the observer's position). That is hardly conducive to defining a notion of absolute simultaneousness using entangled pairs of particles.

 

[p764rds]

That doesn't remove the problem from consideration in general principles, just shows that you can construct a problem where the effect is negligible.

The point of simultaneity is to define exactly when 2 things can be regarded as 'the same time'. There is no way to pinpoint an exact point on the world-line of one particle in an entangled pair that corresponds to the moment when a measurement was performed on the other particle of the pair. Furthermore, when simultaneous spaces are taken into consideration you can't even say for certain which of the measurements was performed first (the 'first' measurement depends on the observer's position). That is hardly conducive to defining a notion of absolute simultaneousness using entangled pairs of particles.

The world line is horizontal and its not a Minkowski space or riemann space.

 

[Dale]

I would entangle two particles - maybe held in a crystal lattice - so they would have to be electrons in this case. Then take one on a high speed trip on an aeroplane, so that it lorentz time shifted a second - or as large as we could practically manage. Then on return from this trip measure the correlation of the two particles. It should come out to be >10,000 times the speed of light again even though one particle was a second older than the other. (Entanglement correlation experiments have already been done and proved it to be >10,000 times the speed of light, I can dig out the refs if you want).

How does that define simultaneity?

For example, the Einstein simultaneity convention is as follows: two clocks are placed at rest wrt each other, the first sends a pulse of light when it reads t0, it is received at the other when it reads t1 and is immediately reflected back, the reflection is received back at the first clock when it reads t2. The two clocks are synchronized iff t1=(t0+t2)/2.

So that is how you can operationally define wether or not two clocks are synchronized using light. Could you try again using entanglement?

The world line is horizontal and its not a Minkowski space or riemann space.

The worldlines of the entangled particles are certainly not horizontal. This situation is not any different than the Einstein convention where the worldlines of the clocks are vertical in the clocks' frame, but the simultaneity thus defined is horizontal.

 

[p764rds]

How does that define simultaneity?

For example, the Einstein simultaneity convention is as follows: two clocks are placed at rest wrt each other, the first sends a pulse of light when it reads t0, it is received at the other when it reads t1 and is immediately reflected back, the reflection is received back at the first clock when it reads t2. The two clocks are synchronized iff t1=(t0+t2)/2.

So that is how you can operationally define wether or not two clocks are synchronized using light. Could you try again using entanglement?

OK, here is an experiment along the einstein's train method for you to examine:

Arrange for entangled particles, at A and remotely at B.
Set up a light transmitter half way between the two locations A and B. Switch the central light transmitter on so light goes to A and B.
When the light arrives at A then decohere the particles (at A) state by observation. Check for when correlation is lost at B. We check for the time difference between light arrival and correlation loss.
Loss of correlation will be found to occur simultaneously with the light's arrival at B and observation at A when light arrives there.

The worldlines of the entangled particles are certainly not horizontal. This situation is not any different than the Einstein convention where the worldlines of the clocks are vertical in the clocks' frame, but the simultaneity thus defined is horizontal.

The world line for *correlation of states* of entangled particles certainly is horizontal. The correlated states behave as if still together, alternativley that 'infinite speed' correlates the states no matter where or when as long as they remain entangled. This latter view is not a good description of what is happening IMO. (Better is the perceived zero separation).

 

[DrGreg]

Check for when correlation is lost at B.

And how, precisely, would you do that? Keep measuring its state until it suddenly changes? That will never happen; once you've measured the state it won't change.

 

[Dale]

In addition to Dr Gregs objection there is the following problem.

We check for the time difference between light arrival and correlation loss.
Loss of correlation will be found to occur simultaneously with the light's arrival at B and observation at A when light arrives there.

Since different frames disagree about whether or not the light pulses arrive simultaneously at A and B then, acording to this, they will also disagree about whether or not the loss of correlation is simultaneous.

By the way, thank you for seriously attempting this. As I mentioned earlier I have seen this proposed several times. You are, in my experience, the first person who actually tried to do the operational definition. Please don't feel bad about the objections raised by me and Dr Greg; I believe they are essentially impossible to avoid, but for some reason they are not apparent to many people.

 

[p764rds]

In addition to Dr Gregs objection there is the following problem. Since different frames disagree about whether or not the light pulses arrive simultaneously at A and B then, acording to this, they will also disagree about whether or not the loss of correlation is simultaneous.

By the way, thank you for seriously attempting this. As I mentioned earlier I have seen this proposed several times. You are, in my experience, the first person who actually tried to do the operational definition. Please don't feel bad about the objections raised by me and Dr Greg; I believe they are essentially impossible to avoid, but for some reason they are not apparent to many people.

Einsteins train for the correlated states of entangled particles : The simultaneous events are lightning strikes at A and B on the train at the front (A) and back (B) of the train. Now change the event of a lightning strikes for a loss of correlation between entangled particles at A and their particle-partners at B. Arrange for experimenters to wave flags when particle A's correlation is observed (so decohering entanglement).

An experimenter in the middle of the train views the strike as simultaneous because light travels the same distance down and up the train to him in the middle, so he sees both experimenters waving flags at the same time - simultaneously.

But the experimenter on the platform, who was initially in the same position as the experimenter in the middle on the train sees the B wave a flag before A waves a flag. Why?
Because in the time between the actual flag waving and viewing that event, the train had traveled and so A was nearer the platform experimenter and B was farther away. So the light needs longer to travel from B to platform experimenter and less time from A to plaform experimenter. So the the platform experimenter says the flag waving was not simultaneous.


If the velocity of light were infinite (its not of course), then the train would travel no distance in the time it takes light to go from A and B to the middle of the train. Same for the observer on the platform. In this case the experimenters on the train and the platform would see the correlation events as simultaneous.

If we view quantum states as being able to 'know' other correlated quantum states (at infinite speed), then the time difference at which they 'know' a partner has been disentangled is instantaneous wherever they are (its theoretically infinite, although experimentally >10,000*c is so far proved). And the correlation loss 'events' are in their perspective (quantum states) all simultaneous regardless of position or time.

 

[Dale]

Einsteins train for the correlated states of entangled particles : The simultaneous events are lightning strikes at A and B on the train at the front (A) and back (B) of the train. Now change the event of a lightning strikes for a loss of correlation between entangled particles at A and their particle-partners at B. Arrange for experimenters to wave flags when particle A's correlation is observed (so decohering entanglement).

The experimenter at A waves his flag when he observes the particles. How does the experimenter at B know when to wave his flag?

So the the platform experimenter says the flag waving was not simultaneous.

And therefore the procedure does not define a universal simultaneity but only simultaneity in one reference frame.

And the correlation loss 'events' are in their perspective (quantum states) all simultaneous regardless of position or time.

The question isn't whether or not they are simultaneous regardless of position or time, but rather whether or not they are simultaneous regardless of reference frame.

 

[p764rds]

The experimenter at A waves his flag when he observes the particles. How does the experimenter at B know when to wave his flag?

I am still preparing a comprehensive answer to this...

"So the the platform experimenter says the flag waving was not simultaneous."

And therefore the procedure does not define a universal simultaneity but only simultaneity in one reference frame.

The experimenter on the platform would not see the correlation loss as simultaneous compared to the experimenter on the train, because he is seeing light and not quantum state correlations.The two (flag waving and correlation loss) do not then coincide for the
experimenter on the platform as they do on the train. i.e. its no longer flag waving that indicates correlation loss as it is for experimenter on the train.
-Think of the platform experimenter with a 3rd entangled particle. They all decohere at the same moment as the particle that caused the decoherence.

The question isn't whether or not they are simultaneous regardless of position or time, but rather whether or not they are simultaneous regardless of reference frame.

Quantum correlations is not about the laws of physics in any frame being the same (as in SR), nor is the velocity of correlation finite as assumed in SR for light - so the reference frame plays no role. (An 'infinite speed' is non-relative - then relative speed of reference frame makes no difference).

 

[Dale]

I really appreciate this conversation. This is the most rational discussion I have had on this topic. In particular I congratulate you for the following realization:

The two (flag waving and correlation loss) do not then coincide for the experimenter on the platform as they do on the train. i.e. its no longer flag waving that indicates correlation loss as it is for experimenter on the train.

I believe that the idea you have arrived at in this sentence is logically correct. What you have described here is a violation of the 1st postulate, and only such a system could logically establish the universal simultaneity that you propose.

However, the QM laws which define the decorrelation etc. are all Lorentz invariant and therefore obey the 1st postulate. Also, if the flag waving does not indicate the correlation loss then what does? (this probably goes back to the above question that you are "still preparing a comprehensive answer" for, so I can certainly wait for both answers in one if you prefer)

 

[p764rds]

P764RDS: "Einsteins train for the correlated states of entangled particles : The simultaneous events are lightning strikes at A and B on the train at the front (A) and back (B) of the train. Now change the event of a lightning strikes for a loss of correlation between entangled particles at A and their particle-partners at B. Arrange for experimenters to wave flags when particle A's correlation is observed (so decohering entanglement)."


The experimenter at A waves his flag when he observes the particles. How does the experimenter at B know when to wave his flag?

B would not be able to wave his flag in real time because he would not know if the particles had been unentangled without first referring to A's results and doing a Bell test or similar. Causality would prevent him from finding out if the particles had been unentangled - because if it were possible then faster than light information could be transmitted.

 

[Dale]

B would not be able to wave his flag in real time because he would not know if the particles had been unentangled without first referring to A's results and doing a Bell test or similar. Causality would prevent him from finding out if the particles had been unentangled - because if it were possible then faster than light information could be transmitted.

You are exactly correct. This is precisely the feature that makes it so that the laws of QM can both be fully relativistic and yet predict this kind of FTL action.

 

[ConradDJ]

To me, the lessons here are --

Relativity says, when it comes to spacelike-separated events, there is no objective fact about which happens first... it depends on the reference-frame.

Since quantum correlations can occur betweeen spacelike-separated events, those correlations should not be described in a way that assumes an objective time-order between the events, i.e. A's measurement of a particle "causes" the entangled particle at B to be in an opposite state.

It's hard to envision the world described by Relativity and QM, because we're used to thinking about the world in Euclidean spacetime, where there's a single universal "now" for all observers, dividing past from future. Hence the temptation to think that quantum correlation justifies our usual way of thinking about the present moment.

In Relativity, each observer has a "now" that unambiguously divides his past from his future, and the "nows" of different observers are related in a way that always respects that division for each observer. For example, I can never see something that happens and tell you about it, while it's still in your future.

So we live in a world where past, present and future are meaningful everywhere in the web of communication between us, from each observer's point of view, and the cause-and-effect ordering of events is also meaningful within that web. But there are also correlations among events that don't communicate information, and don't have a causal connection.

Hard to envision such a world, but I think it's important to try. Otherwise we're trying to create more fundamental theories without a clear picture corresponding to the basic facts already established.

 

[atyy]

So we live in a world where past, present and future are meaningful everywhere in the web of communication between us, from each observer's point of view, and the cause-and-effect ordering of events is also meaningful within that web. But there are also correlations among events that don't communicate information, and don't have a causal connection.

If I remember right, there's an interesting discussion of this in Aharonov and Rohrlich's "Quantum Paradoxes: Quantum Theory for the Perplexed" - which is unfortunately not on Google books, and whose argument I also did not master sufficiently to reproduce off the top of my head.

 

[ConradDJ]

If I remember right, there's an interesting discussion of this in Aharonov and Rohrlich's "Quantum Paradoxes: Quantum Theory for the Perplexed"

Thanks. Looking around for those names I found a paper on whether QM might be the only theoretical structure that can consistently combine non-local correlations with the local "causal" structure of Relativity. No definite conclusion, but in case anyone's interested:

http://arxiv.org/PS_cache/quant-ph/pdf/9709/9709026v2.pdf"

 

[p764rds]

Thanks. Looking around for those names I found a paper on whether QM might be the only theoretical structure that can consistently combine non-local correlations with the local "causal" structure of Relativity. No definite conclusion, but in case anyone's interested:

http://arxiv.org/PS_cache/quant-ph/pdf/9709/9709026v2.pdf"

Thanks for your reference, I was looking for that paper but could not remember its details.

Here's a paper that is being argued in the quantum physics section of this forum:
“Reconciling Spacetime and the Quantum: Relational Blockworld and the Quantum Liar Paradox,”
W.M. Stuckey, Michael Silberstein & Michael Cifone, Foundations of Physics 38, No. 4, 348 – 383 (2008),
quant-ph/0510090.



Also here is an ipod series on quantum physics, BlockUniverse etc:
http://www.ipod.org.uk/reality/reality_mysterious_flow.asp