# Sr + epr

1. Feb 4, 2009

### Austin0

Assuming a system A with v=.8c wrt system B
At x=0 in A we have 4 EPR "transmitters" wih receivers at x=10 , x=(-10) in A and x'=10, x'=(-10) in B
At x=0=x' at time t=0=t' an instantaeous epr polarization event is transmitted simultaneously by the four transmitters.
Can anyone suggest a way to come up with the reception times at the four separate sites????

2. Feb 4, 2009

### Staff: Mentor

What's an "EPR transmitter"?

3. Feb 4, 2009

### Austin0

Obviously this is considering a totally hypothetical and unlikely reality. I probably should have said device or system. Some system that enables tangled photons to be present at both locations. And so presents the possibility of interaction at the "transmitter " location to effect observable change at the "receiver" location. From what I have read of current experimentation with down conversion crystals etc. I dont seriously expect this to be a real eventuality but I am very interested in the hypothetical possibilities as far as how the phenomena could be interpreted in SR. ie. predict the hypothetical times.

4. Feb 4, 2009

### Staff: Mentor

Please explain how an EPR setup with entangled photons allows an experimenter at location A to send a signal to an experimenter at location B. (All the experimenters do is select a detector position and record the results of a polarization measurement.)

5. Feb 4, 2009

### JesseM

You should know that it's been shown to be theoretically impossible to use entanglement to transmit information FTL according to orthodox QM--the predictions of QM would have to be wrong for this to work. Anyway, even if we assume they are wrong, I don't get what an "instantaneous epr polarization event" is or what it would mean to be "transmitted"--normally when people (incorrectly) imagine that EPR could be used for FTL information transmission, they're imagining that one member of an entangled pair is measured in such a way that an experimenter measuring the other, distant member of the pair can instantly learn what measurement the first experimenter made. In this case there'd be no central "transmitter" sending information to each of the two experimenters, it'd just be because of the "spooky" instantaneous connection that is imagined to remain between the two particles even when they have been moved apart (at slower than light speeds). Anyway, since we know EPR doesn't actually work this way, wouldn't it be simpler to drop the whole concept of EPR and just talk about an FTL transmitter without specifying what laws of physics it's based on (whether EPR or tachyons or wormholes or what?) No matter how it works, assigning coordinates to the events of transmitting and receiving information can be done in the same way, just by looking at the readings on local clocks next to the transmitters and receivers.

6. Feb 4, 2009

### Austin0

Isnt the concept that a change in polarization at one location would be able to instantaneously effect a change in polarization of the paired photon at the other location.
My memory is dim but isnt that the conceptual basis that Einstein et al were working on when they originally came up with the hypothesis???

7. Feb 4, 2009

### Staff: Mentor

As JesseM explains in his post above, the correlation between polarization measurements cannot be used to send a signal between the two experimenters.

8. Feb 5, 2009

### Austin0

[1] Is somewhat the idea I was working with. But as you say that was not important to the question. What was important was the absence of any implications of mass , real or imaginary , no additive velocities to consider. SO consider it instantaneous wormholes.
[2] This was the real question and I have no idea how to figure out what the local clocks next to the transmitters and receivers could possibly read. Hence my posting .
Thanks

9. Feb 5, 2009

### Austin0

I have a question for you. My knowledge of electrodynamics is slight, so I dont know,, but do you think it could have been proven in the Maxwell-Lorentz mathematical structure [pre QM] that hypothetical electron tunneling was impossible,, or not????

I am somewhat sceptical of the idea of proofs of impossibility, especially considering the last centuries, logic defying revelations , not that I hold much chance for EPR info transference.
From what I have read, at this point it seems to be mainly statistical inferences made only after comparison of the results from both ends of the experiments, so at best it might confirm some connection between particles but no signs of real time communications.
I still find it hard to definitively rule it out as a possibility.
In any case aside from the hypothetical do you have any ideas of how to assign times
to the events as pure "if they could be sent then .......
Thanks

10. Feb 5, 2009

Staff Emeritus
In short, "I haven't done the work myself, and indeed, don't know enough to be able to do it myself, but believe that you're doing it incorrectly." This is a very difficult position to support.

QM makes specific predictions. One of those predictions is that one cannot send information faster than light in this manner. Now, it's a logical possibility than QM is wrong and that this is possible (although QM is one of the best tested theories, so most people feel this is very unlikely) but it is not a logical possibility that QM lets you do this.

11. Feb 5, 2009

### JesseM

Sure. But again, I didn't say that communication using EPR correlations was definitely impossible, I just said it was impossible "according to orthodox QM" (i.e. if orthodox QM is correct then entanglement can't be used to pass information FTL, a result called Eberhard's theorem)--it's possible that orthodox QM's equations are not completely correct and that it would actually make inaccurate predictions about the behavior of entangled particles in certain situations. That's how "impossibility" proofs in theoretical physics always work, they are necessarily conditional on the correctness of a given set of laws.

12. Feb 6, 2009

### Austin0

Originally Posted by Austin0
My knowledge of electrodynamics is slight ... I am somewhat sceptical of the idea of proofs of impossibility,

You will note that I was not refering to this specific proof so was not saying that anyone was doing anything incorrectly.
Would you say that you have no reservations with regard to the "idea" of proofs of a negative????

Original post Austin0
My knowledge of electrodynamics is slight, so I dont know,, but do you think it could have been proven in the Maxwell-Lorentz mathematical structure [pre QM] that hypothetical electron tunneling was impossible,, or not????
____________________________________________________________________________
I assume that your knowledge of classical electrodynamics is far beyond mine so I would be interested in your answer to this actual question I posed.
Thanks

13. Feb 6, 2009

### Austin0

Thanks for the reference I will be interested to see it.
As I said in my last post I agree with you as far as it is not important for this hypothetical question ,if it is EPR or quantum tunneling or even if it is actually possible.

Originally posted JesseM
[1] . SO consider it instantaneous wormholes.
[2] This was the real question and I have no idea how to figure out what the local clocks next to the transmitters and receivers could possibly read. Hence my posting .
SO if you have a way to calculate specific times I would defintely like to see them
Thanks

14. Feb 6, 2009

### JesseM

In the case of wormholes it would depend on the physical details of how they were created. From what I've read, wormholes have the property that their proper time stays synched even if they are moved around, so if both mouths were created at the same location with no initial time delay (so jumping in one mouth pops you out the other mouth at space and time coordinates that are only negligibly different from the space and time coordinate where you jumped in, assuming travel time through the throat of the wormhole is also negligible), then if initially synchronized clocks are attached to each mouth at that point, this means that in future no matter how you move them around, if you jump into one mouth when its clock reads T you'll exit the other mouth when its clock reads approximately T too. This is one of the reasons traversable wormholes are suggested to allow for the possibility of time travel, since you can move the mouths around such that from an external observer's point of view one wormhole's clock is considerably behind the other's--see this section of the wormhole wiki article:
Anyway, the fact that the wormhole's proper times stay synched means that if you create both mouths at the same location and then move them apart at equal and opposite velocities in some frame, then the connection between them will be instantaneous in that frame--for example, if in that frame mouth A is at x=10 and mouth B is at x=35, then if something enters mouth A at t=14 it will exit mouth B at t=14 too. From there you can use the Lorentz transformation to figure out the coordinates in other frames. Of course the use of inertial frames here is a bit of a cheat since a wormhole involves curved spacetime, but a wormhole can exist in an "asymptotically flat" spacetime where the curvature approaches zero as the distance from the mouths increases, and I suppose we can assume we're dealing with very small wormholes so the curvature becomes very close to flat at distances which are tiny compared to the distance between the two mouths, in which case treating the wormhole as an instantaneous connection in flat SR spacetime would probably be fine as an approximation.

15. Feb 6, 2009

Staff Emeritus
But that's even worse. Now you're disbelieving a proof without any specific objection to that proof.

16. Feb 6, 2009

### Austin0

Why do you only pick out isolated pieces of what I say to respond to?

I have never even seen the proof, although I plan to, having gotten the reference from JesseM

I dont "disbelieve" the proof. As I have said in other posts; whether or not it is actually possible is not important, any more than it is important whether tachyons are actually possible or not.
I simply made a general statement regarding any proof of a negative. I am not in any way trying to promote the idea that EPR is actually possible. Or declare that the proof is wrong.

17. Feb 8, 2009

### Austin0

So far the only responses to my simple hypothetical situation have been questions regarding the premise ,which I am sure you understand is a simple if conditional.
No response at all to the actual question of assigning coordinates.

18. Feb 8, 2009

### JesseM

I did answer in the case of a mini-wormhole (post #14)--again, you'd just figure out the proper time each mouth has experienced since the two were created at a common location, and whatever the proper time of one mouth when something is dropped in, it should pop out the other mouth at almost the same value of proper time for that mouth.

19. Feb 8, 2009

### Austin0

Does this mean that all four locations would observe reception at t=0 = t' ???

20. Feb 8, 2009

### JesseM

No, why would it mean that? Suppose in the unprimed frame the two mouths were moved apart with equal and opposite velocities, so at t=0 both mouths have the same proper time T. Then in this frame it will be true that that if something enters one mouth at t=0 it will exit the other mouth at t=0. However, in the primed frame the velocities of the mouths were not equal and opposite, so their proper times are not equal at t'=0. If you know that in the unprimed frame the first mouth had proper time T at (x=x1, t=0) and the second mouth had proper time T at (x=x2, t=0), then you can just do a Lorentz transform on these coordinates to find the coordinates in the primed frame that both mouths had proper time T (or if you like you can actually calculate the velocities as they were moved apart in this frame and use that to find their proper time using time dilation, you'll get the same answer either way), and it must still be true in the primed frame that if the object or signal was dropped into one mouth when it had proper time T then the object or signal will come out the other mouth when it had proper time T, so the coordinates of the object/signal entering and exiting in the primed frame can just be found by doing a Lorentz transform on the coordinates of these events in the unprimed frame.

If you're trying to suggest that the coordinates of the same pair of events in different inertial frames in flat spacetime could ever not be related by the Lorentz transform, then you are contradicting relativity; there is no way the postulates of SR could be correct and yet this would not be true.

Last edited: Feb 8, 2009