Does SR actually forbid FTL travel?

[PAllen]

If two events are causally connected, the idea is that the event with smaller entropy is naturally interpreted as "cause" of the event with larger entropy.

So how does that say anything at all about my information paradox? There is no event of its being written anywhere in the 4-manifold, and that is the paradox, not any issue of ordering of events.

I think my answer is appropriate: causeless entities of many types are possible in GR solutions. If one is bothered by this, you must look outside of (or beyond) GR to rule these out.

[Edit: Let me note that my scenario has an event of writing down the play, but no event of authoring the play. The physiology of copying or recalling are considered to be distinguishable from authoring/creating. Thus the crux of the problem is the absence of an authoring event anywhere in the spacetime.]

 

[Demystifier]

So how does that say anything at all about my information paradox?

Here is how. Shakespeare lived at time t1, while you sent him the text of the book at time t2>t1. The second law of thermodynamics implies that entropy S satisfies S(t2)>S(t1). Therefore, my resolution of the paradox is based on the claim that Shakespeare's writing is the "cause", while your sending of the book is the "consequence". In other words, you sent him the book at t2 BECAUSE he wrote it at t1, and not vice versa. So it was Shakespeare who wrote the book first, not you. Not because it seems intuitive to me, but because I know that at his time the entropy was lower.

A natural question is the following. But what if you decided to send him a distorted book? The answer, consistent with the Novikov self-consistency principle, is that you could NOT do that. This, of course, contradicts the assumption that you have free will, but the known laws of physics contradict free will even without FTL travel. If nature is deterministic, there is no free will. If nature is probabilistic, there is no free will again.

In other words, free will is only an illusion. You do what the laws of physics tell you to do, but then your consciousness, unable to see the real cause of your actions, interpret the actions as being "chosen freely".

 

[Goodison_Lad]

In other words, free will is only an illusion. You do what the laws of physics tell you to do, but then your consciousness, unable to see the real cause of your actions, interpret the actions as being "chosen freely".

Just in case anybody's interested: there's an interesting debate on this running in the Philosophy area:

https://www.physicsforums.com/showthread.php?t=568146&highlight=free+will

 

[PAllen]

Here is how. Shakespeare lived at time t1, while you sent him the text of the book at time t2>t1. The second law of thermodynamics implies that entropy S satisfies S(t2)>S(t1). Therefore, my resolution of the paradox is based on the claim that Shakespeare's writing is the "cause", while your sending of the book is the "consequence". In other words, you sent him the book at t2 BECAUSE he wrote it at t1, and not vice versa. So it was Shakespeare who wrote the book first, not you. Not because it seems intuitive to me, but because I know that at his time the entropy was lower.

That was all obvious to me, and irrelevant. You don't seem to get my point. I am comparing two consistent worlds:

1) Shakespeare created the play at t1. Our world.

2) Shakespeare received the play at t0, wrote it in his hand at t1, I sent it at t2 back to t0.

My issue with (2) has nothing to do with free will or the order of events. It doesn't matter whether you say t1 was the first of these events. The act of writing something from memory and creating it are physically distinguishable neurological processes. In (2), the act of creating the play no where exists. No ordering of events can change this. Further, since Shakespeare physically aged between t0 and t1, I do not buy the argument that t1 was the first of these events, but that is irrelevant to my main issue.

So, my claim remains, neither Novikov nor thermodynamic arguments do anything at all to resolve the problem of causeless information paradoxes. My partial resolution is to note that GR also perfectly allows causeless objects (like eternal WH/BH), so there is really nothing more unexpected about causeless information.

[Edit: also, please note, from my first post on this, I propose that only an image or modern copy is sent from t2 to t0. Shakespeare might choose to burn it after writing it out in his hand.]

 

[Demystifier]

2) Shakespeare received the play at t0, wrote it in his hand at t1, I sent it at t2 back to t0.

Ah, so I misunderstood you. Now it is clear that t0 is the earliest moment of time at which the text of the book exists. So, I think your paradox is - who is the true author of the book? I would say, and I think you would agree, that the answer is: Nobody - it just appeared spontaneously at t0. Shakespeare is only the first guy who discovered it, but it existed even before his discovery.

 

[PAllen]

Ah, so I misunderstood you. Now it is clear that t0 is the earliest moment of time at which the text of the book exists. So, I think your paradox is - who is the true author of the book? I would say, and I think you would agree, that the answer is: Nobody - it just appeared spontaneously at t0. Shakespeare is only the first guy who discovered it, but it existed even before his discovery.

Exactly.

 

[Whovian]

Ah, so I misunderstood you. Now it is clear that t0 is the earliest moment of time at which the text of the book exists. So, I think your paradox is - who is the true author of the book? I would say, and I think you would agree, that the answer is: Nobody - it just appeared spontaneously at t0. Shakespeare is only the first guy who discovered it, but it existed even before his discovery.

This raises another question. Say someone's capable of time travel. They have a device which they give to their friend to free themselves in their own past. Their friend then frees the first person and gives the device to the first person ... and the first person accidentally gives the one their friend received from themselves to their friend, instead of the one they had all along which they were planning to give to their friend. How old is that device? Shouldn't it have crumbled to dust by now?

 

[DrSnarl]

This raises another question. Say someone's capable of time travel. They have a device which they give to their friend to free themselves in their own past. Their friend then frees the first person and gives the device to the first person ... and the first person accidentally gives the one their friend received from themselves to their friend, instead of the one they had all along which they were planning to give to their friend. How old is that device? Shouldn't it have crumbled to dust by now?

I think this and other questions of time travel do not have to be paradoxes. It is reasonable to state that any time loop will result in multiple, overlapping spaces that are related only in that they share the same time. There is no reason why such a loop could not be infinite, resulting in an infinite number of overlapping spaces.

Causality is thus preserved. In your scenario, the device will eventually crumble, and there will be no more time loops (at least not at that point in space-time).

In the Shakespeare play scenario, Shakespeare wrote the play. However, in one set of space coordinates, he essentially received the play from the overlapping version of himself (the one located in the overlapping space).

I suppose you could call these spaces "multiple dimensions", but that is kind of misleading, as they do not have to be global. There is also no reason (philosophically speaking, at least) why these overlapping spaces could not re-merge in the future. In other words, there is no issue with the Shakespeare who received the play via time travel meeting up with the Shakespeare who wrote it.

 

[DrSnarl]

One technique for limiting the impact of paradoxes is to propose, e.g. the Novikov Consistency conjecture (see, for example http://en.wikipedia.org/wiki/Novikov_self-consistency_principle ).

Novikov Self-Consistency seems like a bit of a stretch to me. What would happen in the Shakespeare scenario? Would it be like the movie "Final Destination", where "fate" just seems to have your number, foiling you at every turn as you try to send the play back in time? It may be logically consistent, but it seems pretty fanciful.

 

[Whovian]

Yea, I don't like Novikov. I've thought of sort of the general concept of what could become a theory that sort of brings Novikov and the multiple universe theory together, or, at least, gives a reason for Novikov, but if all my previous modifiers haven't notified you, it's highly speculative and actually yields no testable predictions that aren't yielded by Novikov.

 

[DaveC426913]

In the Shakespeare play scenario, Shakespeare wrote the play. However, in one set of space coordinates, he essentially received the play from the overlapping version of himself (the one located in the overlapping space).

Yes, I've heard of this hypothesis. Essentially, traveling into the past is not traveling into your own past, it is traveling into a past that was identical to yours, but that no longer will be. I guess that's tantamount to splitting off a whole universe when you time travel into the past.

 

[PAllen]

In the context of SR with tachyons (and my author-less Hamlet scenario can readily be constructed this way), the problem with universe splitting as a solution (rather than Novikov + you must accept causeless information), is that every event of tachyon creation or absorption must split the universe, because any such event represents time travel for some class of inertial observers. Also, there is no model of universe splitting in either SR or GR, so you must add the phenomenology of this. So, pick your poison if you want FTL in SR or GR. To me, the more parsimonious theory is clearly Novikov + acceptance of causeless entitities. However, my honest opinion is that I don't accept author-less plays, and therefore I believe:

- tachyons will never be observed
- a successor to GR will avoid CTC's, singularities (note: I don't believe GR as a physical theory, even its current form, really allows wormholes or alcubierre drive because of the negative energy requirement; but CTC's and singularities occur without negative energy).
- no form of FTL (=time travel) will ever exist.

 

[DrSnarl]

In the context of SR with tachyons (and my author-less Hamlet scenario can readily be constructed this way), the problem with universe splitting as a solution (rather than Novikov + you must accept causeless information), is that every event of tachyon creation or absorption must split the universe, because any such event represents time travel for some class of inertial observers. Also, there is no model of universe splitting in either SR or GR, so you must add the phenomenology of this. So, pick your poison if you want FTL in SR or GR. To me, the more parsimonious theory is clearly Novikov + acceptance of causeless entitities. However, my honest opinion is that I don't accept author-less plays, and therefore I believe:

- tachyons will never be observed
- a successor to GR will avoid CTC's, singularities (note: I don't believe GR as a physical theory, even its current form, really allows wormholes or alcubierre drive because of the negative energy requirement; but CTC's and singularities occur without negative energy).
- no form of FTL (=time travel) will ever exist.

Everything you said makes sense. I agree completely regarding tachyons (along with the prediction that they will never be observed). However, your third assertion (that any form of FTL = time travel in some inertial frame) brings us full circle.

I still do not understand how SR equates teleportation to time travel. Set aside for the moment that there is no known mechanism for teleportation; I am trying to figure out why SR says that (unless you allow for time travel) such a mechanism CANNOT exist.

Just so we are discussing the same thing, by "teleportation", I mean an instantaneous coordinate shift in space while preserving a sub-c frame of reference. This is an important distinction. I completely understand why tachyons would result in time travel.

It seems to me that SR does not allow for teleportation, not because it violates causality, but because the result would create the unresolvable paradox described in the thought experiment with which I started this thread. Another way of looking at it is that SR does not tell us anything about what would happen if we teleported.

Personally, I think the idea of teleportation is far fetched. However, if a science fiction author were to postulate undiscovered physical laws that allowed for teleportation, would those laws conflict with SR by very definition, regardless of what they were? I am picking on teleportation, but the same argument applies to any FTL coordinate shift while in a sub-c reference frame.

 

[PAllen]

Teleportation trivially leads to time travel in SR as follows (again, also assuming principle of relativity - same laws in all inertial frame):

1) Teleport to a rocket traveling at .9c. Pure coordinate shift in the home frame.

2) Teleport back home from the rocket. Pure coordinate shift in the rocket frame.

You arrive home before you left. Teleportation is pure FTL. How can it be different from tachyons in the phenomena it allows?

However, teleportation is really much more absurd than tachyons. There is no plausible theoretical framework for it that I've seen for it (while there are, up to a point, consistent theoretical frameworks for tachyons and GR time travel options). Note that so called quantum teleportation does not involve transmission of matter, nor does it even allow sending FTL messages.

In any case, my position is that neither SR per se, and certainly not GR, preclude certain fanciful FTL/time travel(or message) scenarios. What they do say is that FTL + relativity principle => time travel, with the concomitant choices (and I don't distinguish between time travel by messages versus matter; the choices for dealing with the results are the same).

I don't see any unresolvable paradoxes with teleportation=FTL=time travel - just choices I find implausible.

 

[DrSnarl]

1) Teleport to a rocket traveling at .9c. Pure coordinate shift in the home frame.

2) Teleport back home from the rocket. Pure coordinate shift in the rocket frame.

You arrive home before you left. Teleportation is pure FTL. How can it be different from tachyons in the phenomena it allows?

I think that thought experiment does not appear to create a paradox because we are only considering one frame of reference. Add a rocket at home that is also traveling at .9c, and now you have a problem. Consider the following additions to your experiment:

1) You have three clocks. One you keep with you (your clock). One you leave at home (home stationary clock). One you put on your home rocket (home rocket clock - not the distant rocket that we will teleport to).
2) Synchronize all these clocks so that they read 0.
3) Accelerate the home rocket to 0.9c (towards the away rocket). All clocks still read 0.

4) Teleport to the away rocket. Let's go ahead and accelerate the away rocket after you get there so that you don't instantly accelerate to 0.9c by splattering on the back of the spaceship. (I know, all of our accelerations are instantaneous, so why should this bother us now?)
- After teleporting (but before accelerating), here is what the clocks will read:
From "home stationary perspective":
----home stationary clock = 0
----home rocket clock = 0
----your clock = 0
From "home rocket perspective":
----home stationary clock=0
----home rocket clock=0
----your clock=FUTURE
From "your perspective":
----home stationary clock=0
----home rocket clock=FUTURE
----your clock=0

5) Now, accelerate in the "away rocket" to 0.9c away from home. Here are the new clocks:
From "home stationary perspective":
----home stationary clock = 0
----home rocket clock = 0
----your clock = PAST
From "home rocket perspective":
----home stationary clock = 0
----home rocket clock = 0
----your clock = 0
From "your perspective":
----home stationary clock = PAST
----home rocket clock = 0
----your clock = 0

6) Finally, teleport back home. Here are the new clocks:
From "home stationary perspective":
----home stationary clock = 0
----home rocket clock = 0
----your clock = PAST
From "home rocket perspective":
----home stationary clock = 0
----home rocket clock = 0
----your clock = 0
From "your perspective":
----home stationary clock = PAST
----home rocket clock = 0
----your clock = 0

If you only look at the "home stationary clock", then it would appear that you traveled back into the past. However, the home clock also thinks that it traveled into your past. Additionally, the home rocket thinks that nobody traveled into anybody's past.

According to SR, once you are back home, everyone should agree on the value of everyone else's clocks (they don't have to be the same values, but they should agree on what those values are).

Which clock values are incorrect?

 

[PAllen]

I think that thought experiment does not appear to create a paradox because we are only considering one frame of reference. Add a rocket at home that is also traveling at .9c, and now you have a problem. Consider the following additions to your experiment:

1) You have three clocks. One you keep with you (your clock). One you leave at home (home stationary clock). One you put on your home rocket (home rocket clock - not the distant rocket that we will teleport to).
2) Synchronize all these clocks so that they read 0.
3) Accelerate the home rocket to 0.9c (towards the away rocket). All clocks still read 0.

4) Teleport to the away rocket. Let's go ahead and accelerate the away rocket after you get there so that you don't instantly accelerate to 0.9c by splattering on the back of the spaceship. (I know, all of our accelerations are instantaneous, so why should this bother us now?)
- After teleporting (but before accelerating), here is what the clocks will read:
From "home stationary perspective":
----home stationary clock = 0
----home rocket clock = 0
----your clock = 0
From "home rocket perspective":
----home stationary clock=0
----home rocket clock=0
----your clock=FUTURE
From "your perspective":
----home stationary clock=0
----home rocket clock=FUTURE
----your clock=0

5) Now, accelerate in the "away rocket" to 0.9c away from home. Here are the new clocks:
From "home stationary perspective":
----home stationary clock = 0
----home rocket clock = 0
----your clock = PAST
From "home rocket perspective":
----home stationary clock = 0
----home rocket clock = 0
----your clock = 0
From "your perspective":
----home stationary clock = PAST
----home rocket clock = 0
----your clock = 0

6) Finally, teleport back home. Here are the new clocks:
From "home stationary perspective":
----home stationary clock = 0
----home rocket clock = 0
----your clock = PAST
From "home rocket perspective":
----home stationary clock = 0
----home rocket clock = 0
----your clock = 0
From "your perspective":
----home stationary clock = PAST
----home rocket clock = 0
----your clock = 0

If you only look at the "home stationary clock", then it would appear that you traveled back into the past. However, the home clock also thinks that it traveled into your past. Additionally, the home rocket thinks that nobody traveled into anybody's past.

According to SR, once you are back home, everyone should agree on the value of everyone else's clocks (they don't have to be the same values, but they should agree on what those values are).

Which clock values are incorrect?

I am not going analyze all your verbiage above. It's all unnecessary distraction. This repeats stuff others have commented on. I don't need to deal in clocks at all. The space time path for the the teleportation round trip connects one event on a timelike world line to an earlier event on a timelike world line. Different frames will have different views on which teleportation went back in time and by how much, but all will agree on the order of events on a timelike worldline, and all will agree that your two teleportations have you arrive at an event your world line before you left. All will agree with the amount you have gone back along your initial timelike world line.

[edit: taking a quick look at your write, the thing that is just plain wrong is that there is never frame dependence on what any actual clock reads, however overly complex you make your scenario. There is disagreement only on the order teleportation end point events and coordinate time differences between these endpoints. By construction, no clock time passes for a teleported clock. I would have to correct most of what you wrote, and I am not willing to bother.]

 

[DrSnarl]

I am not going analyze all your verbiage above. It's all unnecessary distraction. This repeats stuff others have commented on. I don't need to deal in clocks at all. The space time path for the the teleportation round trip connects one event on a timelike world line to an earlier event on a timelike world line. Different frames will have different views on which teleportation went back in time and by how much, but all will agree on the order of events on a timelike worldline, and all will agree that your two teleportations have you arrive at an event your world line before you left. All will agree with the amount you have gone back along your initial timelike world line.

I certainly don't fault you for not wanting to analyze my "verbiage"; in fact, at admire your willingness to continue in this thread at all.

I'll try to be as concise as possible: observers in all frames must agree not only on the order of events, but also exactly on how far back in time you went, if all observers are co-located with you. Your thought experiment shows that they do not. I merely took your thought experiment and listed out clock values to illustrate this.

Perhaps the extra rocket was a distraction. Here is the basic problem: when you teleport home, you travel into your home's past, but your home also travels into your past. That is obviously bogus.

 

[PAllen]

I certainly don't fault you for not wanting to analyze my "verbiage"; in fact, at admire your willingness to continue in this thread at all.

I'll try to be as concise as possible: observers in all frames must agree not only on the order of events, but also exactly on how far back in time you went, if all observers are co-located with you. Your thought experiment shows that they do not. I merely took your thought experiment and listed out clock values to illustrate this.

Perhaps the extra rocket was a distraction. Here is the basic problem: when you teleport home, you travel into your home's past, but your home also travels into your past. That is obviously bogus.

1) All observers need not and do not agree on the order of events with spacelike separation (e.g. the endpoints of a teleportation). Observers need not agree on the amount of coordinate time difference between these spacelike separated events (could be 0, -5, + 10 depending on observer). All of this is fine and normal for SR.

2) All observes do agree on order and amount of proper time between events on a timelike world line. Thus all agree (despite different interpretations of what each teleport represented), that e.g. you left with your clock reading 5:00 pm, and arrived at a point on your world line where your past copy has 4:00 pm. You and your past self are next to each other. You have 5:00, they have 4:00. All frames agree on this.

 

[Austin0]

On the last paragraph, nonsense. No one knowledgeable says entanglement can't transfer information FTL because it would violate SR. Instead they say entanglement can't transfer information because the actual mathematics of entanglement says it can't. Period. Note, especially, that you can't even verify that you have successfully produced entanglement without transferring information from one place to another by some other means. Then, (long) after the fact, you can verify you successfully entangled interactions.

Although everything you have said here is true , isn't it also true that:
if the findings developed after the fact, that entangled interactions have occurred, are accurate, then this seems to infer non-local instantaneous transfer of information.
Not at all useful for human communication of information , for the reason you pointed out, but information just the same . On the particle level a transmission of a change of state of some kind from one location to another.
Am I missing or misinterpreting some aspect of the experiments?.

 

[PAllen]

Ok, I had some time to fool with this. Taking your scenario, clarifying that rocket movement is in +x direction and teleportation is in +x direction. I will use 'your' exactly where you did. Then my disagreement starts at your (4): (4) All clocks read zero. This is frame independent. According to home rocket,'your clock' is now in its PAST, but still reads zero. According to "your perspective", all clocks are still zero and in the PRESENT - "your clock" is still in same frame as home stationary clock, just teleported.

(5) All clocks still read zero for everyone (we are assuming effectively instant accelerations and effectively zero time betweein (4) and (5)). "your clock" is in past compared to "home rocket", and "home clock" is now in future compared to "away clock" (and also according to "your clock"). But they all stil read zero. Note, home rocket thinks teleport was into past from its 'present', away rocket (now that it is going .9c) thinks teleport was to its present from its future.

(6) Teleport back, in away rocket's frame, to away rocket's now simultaneous point on home world line. This will bring you to, say, -1 on this world line. What everyone agrees: your orginal world line ended at its reading of zero. Your 0 time self is now located at -1 on the home world line. Your past self clock reads -1, your coincident present self clock reads 0. All agree on this. Home rocket and away rocket both think the second teleport was a simultaneous teleport (in (5), they both considered the first teleport to be in the past direction). Home stationary observer thinks the second teleport was into the past.

There are no discrepancies about what clocks read, or about sequence and time differences on the home, timelike world line. There are only SR typical differences on the interpretation of events with spacelike relation.

 

[PAllen]

Although everything you have said here is true , isn't it also true that:
if the findings developed after the fact, that entangled interactions have occurred, are accurate, then this seems to infer non-local instantaneous transfer of information.
Not at all useful for human communication of information , for the reason you pointed out, but information just the same . On the particle level a transmission of a change of state of some kind from one location to another.
Am I missing or misinterpreting some aspect of the experiments?.

Correlation is not information. You may have a mental model that correlation requires causation or information transfer, but that is not part of the quantum entanglement model. The parsimonious interpretation is that there exists causeless distant correlation. [Edit: better: there exists a single non-local measurement of an entangled state that is classically interpreted as two correlated distant measurements. And now we can ... but I won't... get into the various quantum interpretations.]

 

[Austin0]

Does SR actually imply that FTL travel would allow for violations of causality? Here is some reasoning to suggest that it does not:

Any thoughts?

Here's a different perspective:
IMHO SR has nothing to say about FTL as it is simply outside it's domain of applicability.
FTL values entered in the Lorentz math produce imaginary results.
Entered into the Addition of V's formula they produce nonsensical, inconsistent results and consequences.
The clocks in SR are synchronized using light speed so any readings or predictions with regard to an FTL particle have no real basis. All interpretations of time ordering of disparate events is based on this particular synchronicity. But this is not taken to be actual simultaneity but only operational ordering of events which of course works fine for c and below.
But is it reasonable to think this will automatically apply to imaginary particles or velocities?

Using your example of teleportation: The concept is of instantaneous translation between two points. Absolute simultaneity of occurrence at separate locations. How can SR predict when that instant will occur at a location in another frame?
That would only be possible if the clocks in the initial frame were absolutely synchronous.
But we know that is not the case by the principles of SR itself.
SO for me, expecting SR to meaningfully make predictions regarding FTL is equivalent to thinking Thermodynamics or low temperature physics will produce meaningful predictions for temperatures below 0^o K
So I guess in effect I am agreeing with you and think you can proceed with your teleportation experiments without necessarily violating causality :-)

 

[Austin0]

Correlation is not information. You may have a mental model that correlation requires causation or information transfer, but that is not part of the quantum entanglement model. The parsimonious interpretation is that there exists causeless distant correlation. [Edit: better: there exists a single non-local measurement of an entangled state that is classically interpreted as two correlated distant measurements. And now we can ... but I won't... get into the various quantum interpretations.]

It appears that I may have misunderstood the experiments. I thought that actions at one location , change in polarization for eg. displayed a statistically significant result at a separate location. This seems like cause and effect. It is correlation that explains or is the mechanism for the effect, I get that , but why would it be considered there was no causality involved.
Of am I in error regarding the actual parameters of the experiments?
Thanks

 

[PAllen]

It appears that I may have misunderstood the experiments. I thought that actions at one location , change in polarization for eg. displayed a statistically significant result at a separate location. This seems like cause and effect. It is correlation that explains or is the mechanism for the effect, I get that , but why would it be considered there was no causality involved.
Of am I in error regarding the actual parameters of the experiments?
Thanks

It doesn't matter what order you do the measurements. Further, what order they are done is frame dependent. How do you propose which way causality goes? All that you know is that if you later compare measurements, there was correlation that cannot be explained classically.

 

[DrSnarl]

(4) All clocks read zero. This is frame independent. According to home rocket,'your clock' is now in its PAST, but still reads zero. According to "your perspective", all clocks are still zero and in the PRESENT - "your clock" is still in same frame as home stationary clock, just teleported.

So am I wrong then in thinking that when you accelerate towards a distant observer, you move into its future (and when you accelerate away, you move into its past)? If that is false, then I apparently do not understand the resolution to the twin paradox.

 

[DrSnarl]

It appears that I may have misunderstood the experiments. I thought that actions at one location , change in polarization for eg. displayed a statistically significant result at a separate location. This seems like cause and effect. It is correlation that explains or is the mechanism for the effect, I get that , but why would it be considered there was no causality involved.
Of am I in error regarding the actual parameters of the experiments?
Thanks

I read about an experiment (perhaps the same one to which you are referring) when the experimenter used an elaborate setup to cause a stream of photons with unknown polarity to create an interference pattern, similar to the double-slit experiment. Using this with a stream of entangled photons, they inserted a polarizing filter into one of the streams, in effect collapsing the uncertainty in the other stream and causing the interference pattern to vanish.

Granted, they were not able to use this to communicate FTL (or it obviously would have made the news). The reason why is that they were dealing with multiple wavelengths, and they had to filter out the photons of the incorrect wavelength, which required information from both ends. However, the idea definitely seems like it merits further investigation.

 

[PAllen]

So am I wrong then in thinking that when you accelerate towards a distant observer, you move into its future (and when you accelerate away, you move into its past)? If that is false, then I apparently do not understand the resolution to the twin paradox.

Apparently you do not. The only role acceleration plays in the twin differential aging is to allow a twin to separate from and than meet the other again. Further, your motion never affects a different observer's simultaneity. What you can say is that using conventional Lorentz simultaneity, accelerating towards a distant object causes it to 'move' towards your past. You're the one changing simultaneity as you accelerate.

 

[Austin0]

It doesn't matter what order you do the measurements. Further, what order they are done is frame dependent. How do you propose which way causality goes? All that you know is that if you later compare measurements, there was correlation that cannot be explained classically.

I have researched the experiments but only found superficial accounts lacking in relevant details of parameters and methods. As I understand it paired photons from a down conversion crystal are identically polarized on emission. That a change of polarization is applied to one photon stream and a comparable change is detected in the other.
Otherwise, if it is a case of simply measuring at separate locations why wouldn't correlation be expected if they started out being identical??

 

[Austin0]

I read about an experiment (perhaps the same one to which you are referring) when the experimenter used an elaborate setup to cause a stream of photons with unknown polarity to create an interference pattern, similar to the double-slit experiment. Using this with a stream of entangled photons, they inserted a polarizing filter into one of the streams, in effect collapsing the uncertainty in the other stream and causing the interference pattern to vanish.

Granted, they were not able to use this to communicate FTL (or it obviously would have made the news). The reason why is that they were dealing with multiple wavelengths, and they had to filter out the photons of the incorrect wavelength, which required information from both ends. However, the idea definitely seems like it merits further investigation.

Hi No I missed that one but find it fascinating. it seems so much more direct and unequivocal than the statistical studies derived from detector results. if you cn remember where you read it I would be grateful. Thanks

 

[Austin0]

Apparently you do not. The only role acceleration plays in the twin differential aging is to allow a twin to separate from and than meet the other again. Further, your motion never affects a different observer's simultaneity. What you can say is that using conventional Lorentz simultaneity, accelerating towards a distant object causes it to 'move' towards your past. You're the one changing simultaneity as you accelerate.

Wouldn't it perhaps be more correct to say it puts that observer in your past moving toward your present? ;-)