Can Exceeding the Speed of Light Really Mean Time Travel?

[Sean Pan]

Your opinion on"exceeding the speed of light means the ability to return to the past"

I personally think this assertion is absurd, so I'm wondering why so many people(including physicists) think this is true.

 

[GeorgeDishman]

I personally think this assertion is absurd, so I'm wondering why so many people(including physicists) think this is true.

The equivalence of the two unavoidably comes out of the geometry of relativity.

Many people, including many physicists, think that returning to the past (or "violating causality") is absurd, hence they treat "exceeding the speed of light" through space as equally absurd.

 

[Sean Pan]

The equivalence of the two unavoidably comes out of the geometry of relativity.

Many people, including many physicists, think that returning to the past (or "violating causality") is absurd, hence they treat "exceeding the speed of light" through space as equally absurd.

Could you please explain why this comes out of the geometry of relativity. I think exceding the speed of light can only "observe" events happened in the past as can be easily found by drawing a space-time diagram, but it seemed that they still can't return to the past.

 

[harrylin]

I personally think this assertion is absurd, so I'm wondering why so many people(including physicists) think this is true.

Put like that it indeed doesn't make much sense. What no doubt is meant, is that it is inconsistent with relativity theory, as it causes a paradox: According to SR, as determined with certain reference systems that are moving relative to you, that same object will travel to the past. Of course, according to SR that cannot happen because nothing can travel faster than light.

 

[Sean Pan]

Put like that it indeed doesn't make much sense. What no doubt is meant, is that it is inconsistent with relativity theory, as it causes a paradox: According to SR, as determined with certain reference systems that are moving relative to you, that same object will travel to its past. Of course, according to SR that cannot happen because nothing can travel faster than light.

Can you show me how can an observer travel to its past when its speed is over the speed of light? As mathematics fails here ,I prefer using space-time diagram to discribe this kind of situation. In this way, in a certain reference system the world line of the object moving with its speed over c is just a space-like curve which still cannot reach the region represent the events of the past .

 

[Fredrik]

If a particle goes from Earth to the moon faster than light in one inertial coordinate system, then there's another inertial coordinate system in which the event where the particle is on the moon has a smaller time coordinate than the event where the particle is on Earth. So if we use this coordinate system to describe the events, we would have to say that the particle went from the moon to Earth, not the other way round. If we also insist on thinking of the event where the particle is on Earth as the cause of the event where the particle is on the moon, then it makes sense to say that the particle went back in time.

Of course, this is only a difference between how the same sequence of events is described in terms of two different coordinate systems. So it's not really time travel. However, if you have two devices that can send particles faster than light, it seems that you can use them to "really" send messages back in time. (See the argument in this post). Since this leads to nonsense results, the most natural conclusion is that there are no particles that move faster than light.

There are a few other possibilities, for example: 1. The time it takes to emit and/or detect an FTL particle grows at least linearly with the distance it travels. (This would prevent the recipient of the first message to send a reply that reaches the sender of the original message before he sent it). 2. The equations of motion of the matter in the universe doesn't have any solutions that describe someone who both chooses to carry out an experiment like the one I described in the post I linked to, and succeeds. (Yes, this one is even weirder than the first one).

 

[harrylin]

Can you show me how can an observer travel to its past when its speed is over the speed of light?

I hoped to have clarified that the argument is the other way round: nobody can travel over the speed of light, for it implies that he would travel to the past according to measurements with certain other inertial reference systems. (note: "its" was a bit too strong and I modified that now; and for a clear understanding it's good to avoid the word "observer").

As mathematics fails here ,I prefer using space-time diagram to discribe this kind of situation. In this way, in a certain reference system the world line of the object moving with its speed over c is just a space-like curve which still cannot reach the region represent the events of the past .

Sorry, I don't have drawing tools ready now. Why would you say that mathematics fails here? It's very simple algebra.

Also, as Fredrik pointed out, it inverses the course of events as interpreted in different systems- and that messes up such things as cause and effect. For example, consider a traveler who does that: I think that if one then interprets it as travel the other way round in a certain reference system, the traveler would magically have appeared at an earlier time and disappeared at a later time. But obviously no one would interpret such observations as either time travel or disappearances, it would simply disprove relativity.

 

[Demystifier]

I personally think this assertion is absurd, so I'm wondering why so many people(including physicists) think this is true.

I agree that it is absurd. Exceeding the speed of light is not more paradoxical than watching the movie backwards. Even if you can watch the world/movie in that way, you don't really travel to the past.

 

[GeorgeDishman]

Could you please explain why this comes out of the geometry of relativity. I think exceding the speed of light can only "observe" events happened in the past as can be easily found by drawing a space-time diagram, but it seemed that they still can't return to the past.

We can always only observe within our past light cones so just as you can't hear a bullet traveling faster than sound until it has passed you, you can't see a tachyon gun being fired until after you have been hit.

Attached are three spacetime diagrams. Worldline A-B is Albert and C-D is Cindy. Albert is evil so at event 'E' he shoots Cindy with a tachyon gun, the particles travel at 10c. Cindy is grazed on the forearm at event 'F'.

The second diagram shows those events from Cindy's frame, note that Albert's shot seems to travel backwards in time from her perspective. She picks up her tachyon gun at event 'G' and shoots back. The particles again travel at 10c hitting Albert at event 'H'. Cindy is the better shot and Albert drops dead, just before picking up his gun and firing at Cindy. His posthumous view of the whole exchange is shown in the third diagram.

The moral is don't play with tachyon guns or you might find you've been a zombie!

p.s. The applet I used for the sketches is here:
http://www.reagenix.com/personal/sci/space_time/test.html

p.p.s. To reach your own past, launch your spaceship from a tachyon cannon, the flightpath is A-E-F-G-H on the same diagrams.

 

[Naty1]

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

 

[Drakkith]

Hrmmm. I don't understand what the graphs represent very well. What are they called and where can I find out more on them?

Do they represent the sequence of events as perceived by each person? IE does graph number 2 represent the frame of Cindy and show what she sees, which is of course limited by light speed?
Is this paradoxical effect simply because the graph is set to have c as the limit?

 

[pervect]

I personally think this assertion is absurd, so I'm wondering why so many people(including physicists) think this is true.

Probably you are imagining some sort of preferred-frame theory, either by accident or design, while they are assuming that relativity is valid and specifically that the Lorentz transform applies.

The "tachyon pistol" duel is an example of some of the problems you get if you assume that things can go faster than light and that the Lorentz transform is correct.

http://sheol.org/throopw/tachyon-pistols.html


The initial problem statement didn't specifically say that relativity was to be applied, so it's mildly ambiguous. However, if you post to a relativity forum it's a reasonable "implied" assumption.

Some people claim that there is a way to make tachyons (FTL waves) compatible with relativity. This seems to involve waves that can't be localized well enough in time to determine exactly when they were emitted. So the tachyon pistol example illustrates the problems classically, a full quantum treatment MIGHT give you a few more minor loopholes.

 

[GeorgeDishman]

Hrmmm. I don't understand what the graphs represent very well. What are they called and where can I find out more on them?

If you mean the ones in my post, they are just standard spacetime diagrams. The applet linked in the post let's you draw worldlines and events then the slider at the top controls the velocity of the observing frame. The java implements the Lorentz Transforms. I just used it to draw a simple demonstration of the equivalence of FTL and a time-like loop, the text explains what is shown. Basically it is just the grandfather paradox with a different storyline. The OP in message #5 said "I prefer using space-time diagram to discribe this kind of situation." so that's what I did.

 

[Drakkith]

If you mean the ones in my post, they are just standard spacetime diagrams. The applet linked in the post let's you draw worldlines and events then the slider at the top controls the velocity of the observing frame. The java implements the Lorentz Transforms. I just used it to draw a simple demonstration of the equivalence of FTL and a time-like loop, the text explains what is shown. Basically it is just the grandfather paradox with a different storyline. The OP in message #5 said "I prefer using space-time diagram to discribe this kind of situation." so that's what I did.

So if the Lorentz transformations used 10c as the speed limit instead of c, there would be no problem correct?

 

[Sean Pan]

Thanks for all of you above. When treating FTL particles, does Lorentz Boost still make sense? Anyone have studied that?

 

[GeorgeDishman]

So if the Lorentz transformations used 10c as the speed limit instead of c, there would be no problem correct?

If you move the slider on the applet to the right, vertical lines rotate clockwise while horizontal lines rotate anticlockwise. They coincide at 45 degrees. The letter 'c' is used to represent that angle which also acts as a speed limit. If you want to represent the angle by 10c then light would move at a speed of 10c and "FTL" would mean traveling faster than 10c, the physics would not be affected. The letter is only a symbol.

 

[GeorgeDishman]

Thanks for all of you above. When treating FTL particles, does Lorentz Boost still make sense? Anyone have studied that?

The transforms are purely geometric, they make as much sense as saying that a picture will rotate if you rotate the paper on which it is drawn even if you exceed 45 degrees. That is why physicists consider that exceeding the speed of light is problematic and that the consequences appear "absurd".

Have we adequately clarified the connection between the two in your original question?

 

[yuiop]

Hrmmm. I don't understand what the graphs represent very well. What are they called and where can I find out more on them?

Do they represent the sequence of events as perceived by each person? IE does graph number 2 represent the frame of Cindy and show what she sees, which is of course limited by light speed?
Is this paradoxical effect simply because the graph is set to have c as the limit?

They are called "spacetime diagrams" and yes, basically graph 2 is how things look in Cindy's rest frame. The diagrams conventionally have space (distance) along the horizontal axis and time along the vertical axis. Try out the applet posted by George http://www.reagenix.com/personal/sci/space_time/test.html. If you draw a line at 45 degrees to the vertical representing the null worldline of a photon and move the slider you will notice that the line remains at 45 degrees for all observers demonstrating the constancy of the speed of light for all observers.

Also note that in graph 2 produced by George, it can be interpreted that Cindy fired two tachyon shots at evil Alex and Alex looks like the innocent victim of an unprovoked (double) attack by Cindy. Once we accept that FTL interactions, then notions of what was the cause and what was the effect no longer make any sense. Cindy's claim that she was acting in self defence and that Alex fired the first shot, looks pretty week because Alex was dead before he made the alleged initial attack. The prosecution claim that Cindy fired the first shot instantly killing poor Alex and then fired another shot into his dead body for good measure. We also have the problem of defining histories in a universe that allows FTL interactions. For example, was Alex alive or dead between events E and H?

.. When treating FTL particles, does Lorentz Boost still make sense? Anyone have studied that?

If we take a series of events along an FTL worldine and then carry out a Lorentz boost, then the transformation makes perfect sense if we only consider the events as a series of independent (non causally linked) spacelike events. If we claim that the events are the worldline of a particle then nothing makes sense as explained elsewhere in the current thread.

 

[Drakkith]

So the graph uses a lorentz transformation correct? The tachyons appear to travel back in time because the lorentz transformation is set up as c as the speed limit? IE if 10c was the speed limit then the tachyons would not travel back in time? I'm just asking about the math aspect, not the real physical aspect.

 

[yuiop]

So the graph uses a lorentz transformation correct? The tachyons appear to travel back in time because the lorentz transformation is set up as c as the speed limit? IE if 10c was the speed limit then the tachyons would not travel back in time? I'm just asking about the math aspect, not the real physical aspect.

I think that is correct. If c is the speed limit and the speed of light was c/10 (in a given reference frame because the speed of light would no longer be invariant) then particles traveling at greater than the speed of light, but less than the maximum speed c, would not go back in time. Tachyons are generally described as particles that exceed the speed of light, but that is only accurate if we assume that the speed of light is exactly the maximum speed c (and that photons have no residual rest mass that is currently unmeasurable). If we define tachyons as particles that exceed the maximum possible speed limit c (the invariant speed), then all tachyons will appear to go backwards in time in certain reference frames.

 

[Drakkith]

Got it.

 

[GeorgeDishman]

The prosecution claim that Cindy fired the first shot instantly killing poor Alex and then fired another shot into his dead body for good measure.

Looking at events E and F, although F seems to happen "first", it is the burn on Cindy's arm produced by the firing of the gun at E by the remains of Alex, so the effect precedes the cause.

Of course that's the point, the gun was fired by the corpse unless we insist that the timelike loop must be self-consistent.

 

[GeorgeDishman]

So the graph uses a lorentz transformation correct?

Correct, the transforms are built into the applet to calculate the coordinates of the lines and events as you move the slider.

The tachyons appear to travel back in time because the lorentz transformation is set up as c as the speed limit? IE if 10c was the speed limit then the tachyons would not travel back in time? I'm just asking about the math aspect, not the real physical aspect.

The transforms are actually set up on the screen with c=1, if you draw a line and then move the slider, it limits at one horizontal unit per vertical unit. The word "tachyon" means going faster than that limiting value, there aren't two different quantities being represented either in the applet or the math or the real world physics.

 

[Drakkith]

The transforms are actually set up on the screen with c=1, if you draw a line and then move the slider, it limits at one horizontal unit per vertical unit. The word "tachyon" means going faster than that limiting value, there aren't two different quantities being represented either in the applet or the math or the real world physics.

Ok, so if the lorentz transformation is correct and the limiting speed is c, then any hypothetical tachyon would go back in time in certain frames? Thus there cannot be faster than light travel?

 

[Fredrik]

Thanks for all of you above. When treating FTL particles, does Lorentz Boost still make sense? Anyone have studied that?

Yes, they do, but keep in mind that every Lorentz transformation is associated with a velocity of magnitude less than c. So there are no Lorentz transformations that boost to a frame in which a FTL particle is at rest.

There are some really counterintuitive things about FTL particles. In particular, if I measure a particle going to the right at 10c, then someone going to the right at 0.5c will measure the particle going faster than 10c, not slower.

Ok, so if the lorentz transformation is correct and the limiting speed is c, then any hypothetical tachyon would go back in time in certain frames?

Yes.

Thus there cannot be faster than light travel?

No. It's not obvious that this implies that tachyons don't exist. You need a more sophisticated argument that involves two tachyon transmitters (like the one I linked to in post #6), and even then the conclusion is just that either FTL particles don't exist, or they have some really counterintuitive properties. (Much more counterintuitive than the weird thing I mentioned in this post).

 

[Austin0]

There are some really counterintuitive things about FTL particles. In particular, if I measure a particle going to the right at 10c, then someone going to the right at 0.5c will measure the particle going faster than 10c, not slower.

Hi Fredrik
Teleportation came up in another similar thread.
Instantaneous translation between points. Absolute simultaneity of events at separate locations.

Assuming teleportation to a distant location in the same frame; How do you calculate the proper time at the point of arrival?? Given t=0 at point of departure.

BTW Congrats.

 

[yuiop]

Looking at events E and F, although F seems to happen "first", it is the burn on Cindy's arm produced by the firing of the gun at E by the remains of Alex, so the effect precedes the cause.

Of course that's the point, the gun was fired by the corpse unless we insist that the timelike loop must be self-consistent.

Well it is not clear that Cindy's arm would be burnt as we go forward in time again, because Alex, perhaps along with his tachyon gun, has been destroyed so he is not in a position to do anything. In this case it looks like "evil" Alex is killed in a single unprovoked attack by "nice" Cindy.

As mentioned in #18, the first time around the loop, Alex is alive between events E and H and the second time around he is dead between those same two events. This requirement for different histories probably requires the concept of parallel universes to make sense. Can we say FTL interaction not only implies traveling backward in time, but also implies parallel universes?

 

[yuiop]

An energy paradox involving time travel.

Let us say we have one very large uncharged lead battery and a small solar panel to charge the battery. We follow these steps:

1)We connect the solar panel to the uncharged battery.
2)We put a note on the uncharged battery saying "When this battery is charged please send it back to time 1"
3)Our future self obliges and sends the charged battery back in time.

The first time a battery is sent back fully charged, we still have the initial uncharged battery. the second time a charged battery is sent back, we have the initial uncharged battery and two fully charged batteries. Repeat as often as required. We could in principle end up with more batteries than there is lead on the Earth to make them with and with a greater energy store than the total energy impinging on the Earth from the Sun between times 1 and 3.

 

[Sean Pan]

Have we adequately clarified the connection between the two in your original question?

Thanks a lot and I have a clearer understand of this problem now. I actually knew that if there were FTL particles, causality would be violated. My opinion is that FTL observers can never actually traveling backwards. And thanks for all above that I now understand what other physicsts mean when they are saying 'returing to the past', it's just an illusion caused by the limited speed of information-carrier. But still, to an FTL particle, γ is no longer real, so I think lorentz boost can't be applied directly here. For example, how can time dilation effect being discussed here?

 

[GeorgeDishman]

Ok, so if the lorentz transformation is correct and the limiting speed is c, then any hypothetical tachyon would go back in time in certain frames? Thus there cannot be faster than light travel?

Exactly, FTL and time travel in this sense are synonymous. Whether that makes them impossible or not is another question.

 

[GeorgeDishman]

Well it is not clear that Cindy's arm would be burnt as we go forward in time again, because Alex, perhaps along with his tachyon gun, has been destroyed so he is not in a position to do anything. In this case it looks like "evil" Alex is killed in a single unprovoked attack by "nice" Cindy.

As mentioned in #18, the first time around the loop, Alex is alive between events E and H and the second time around he is dead between those same two events.

Hence he didn't shoot, Cindy didn't respond and the third time round Albert is alive. What you have built is the same as an electrical logic circuit with an inverter in a feedback loop, it creates an oscillator switching between two states.

This requirement for different histories probably requires the concept of parallel universes to make sense.

Possibly, that's one way out in sci-fi stories. The other is "cosmic censure" which would require the history round the loop to be consistent, for example forcing a misfire of one of the guns or a non-fatal injury to Albert allowing him to fire (though he could die immediately thereafter).

If you think of the quantum wavefunction going round the loop and Young's Slits as an analogy, we could surmise that non-consistent outcomes lie in the dark bands of destructive interference when calculating their probabilities using the sum over histories method.

Can we say FTL interaction not only implies traveling backward in time, but also implies parallel universes?

Personally, I think they are independent. Albert's shot has an infinite number of points on which it might graze Cindy's arm so alone generates an infinite number of universes and the same is true of every other particle interaction throughout the period. IMHO, anyone universe either sees a paradox or a consistent outcome hence you need something more than parallel universes which acts in each. That said, it won't stop the sci-fi authors using it though ;-)

 

[GeorgeDishman]

Thanks a lot and I have a clearer understand of this problem now. I actually knew that if there were FTL particles, causality would be violated. My opinion is that FTL observers can never actually traveling backwards.

That is an opinion most share as you can see from the replies.

And thanks for all above that I now understand what other physicsts mean when they are saying 'returing to the past', it's just an illusion caused by the limited speed of information-carrier.

No, that is exactly the opposite of what everyone has said here! What Cindy or Albert can see is on a cone into the past at 45 degrees to the vertical from each event. They never see the tachyons coming but the shots still travel into the past in the frames of both. Albert is killed at event H before he even picks up his gun to start the fight at event E.

It sounds as though you are disregarding what has been said so that you can believe in FTL without dealing with its consequences.

But still, to an FTL particle, γ is no longer real, so I think lorentz boost can't be applied directly here. For example, how can time dilation effect being discussed here?

The time dilation factor simply becomes negative. A Lorentz boost is nothing more than a geometric rotation so still applies perfectly to tachyonic particles. For example it would have applied to the reported FTL neutrinos last year (which turned out to be a faulty connection to a clock).

 

[Fredrik]

Hi Fredrik
Teleportation came up in another similar thread.
Instantaneous translation between points. Absolute simultaneity of events at separate locations.

Assuming teleportation to a distant location in the same frame; How do you calculate the proper time at the point of arrival?? Given t=0 at point of departure.

BTW Congrats.

Hi Austin0.

I don't think I understand the question. Since you mentioned absolute simultaneity, you seem to be asking about instantaneous messages in Galilean spacetime. If there's absolute simultaneity, the question of "simultaneous in what coordinate system?" doesn't even arise. So if t=0 at the departure, then isn't t=0 at the arival too, by definition of "instantaneous".

"Proper time" is a property of a curve in Minkowski spacetime, not a point. The concept of proper time isn't needed in Galilean spacetime. (We would have to define it as the coordinate time difference between the endpoints).

The post I linked to in #6 deals with instantaneous messages in Minkowski spacetime.

 

[DrGreg]

Teleportation came up in another similar thread.
Instantaneous translation between points. Absolute simultaneity of events at separate locations.

Assuming teleportation to a distant location in the same frame; How do you calculate the proper time at the point of arrival?? Given t=0 at point of departure.

Within the theory of relativity, if two events are simultaneous in some frame then the proper time between those events is an undefined concept.

 

[Austin0]

Within the theory of relativity, if two events are simultaneous in some frame then the proper time between those events is an undefined concept.

Hi DrGreg I was using the term proper time in it's common usage as simply meaning the clock reading at the location and time of arrival, not as a proper time interval. Sorry for my possible misuse.
Does this clarify my question??

Thanks

 

[Austin0]

Hi Austin0.

I don't think I understand the question. Since you mentioned absolute simultaneity, you seem to be asking about instantaneous messages in Galilean spacetime. If there's absolute simultaneity, the question of "simultaneous in what coordinate system?" doesn't even arise. So if t=0 at the departure, then isn't t=0 at the arival too, by definition of "instantaneous".

"Proper time" is a property of a curve in Minkowski spacetime, not a point. The concept of proper time isn't needed in Galilean spacetime. (We would have to define it as the coordinate time difference between the endpoints).

The post I linked to in #6 deals with instantaneous messages in Minkowski spacetime.

Hi The question is purely in the context of SR It seems to me that the term proper time is frequently used to mean the observed reading on the local clock and not necessarily an interval. If this is technically incorrect then it's commonly incorrect and I will curb the habit.

So the absolutely instantaneous definition is applied to the phenomenon of teleportation.

So are you saying here that in a SR context the arrival time would be t=0 ??

Thanks

 

[Nysgjerrig]

Is there anyone who have looked into this mysterious particle called bosson singlet? According to some scientist it should be possible to use those particles as tool to send message back in time with LHC (CERN). I find that interessting in terms of particles that can exceeding the speed of ligth or at least find "a loop hole" so it outmatch the speed of ligth.

 

[Fredrik]

Hi The question is purely in the context of SR It seems to me that the term proper time is frequently used to mean the observed reading on the local clock and not necessarily an interval. If this is technically incorrect then it's commonly incorrect and I will curb the habit.

So the absolutely instantaneous definition is applied to the phenomenon of teleportation.

So are you saying here that in a SR context the arrival time would be t=0 ??

Thanks

Many people define proper time as what a clock measures. I don't like that actually. I prefer to define the term only as referring to a mathematical property of the curve that represents the motion of the clock. The statement that clocks display proper time is then a correspondence rule, i.e. an assumption that tells us how to interpret a piece of mathematics as predictions about results of experiments.

I still don't quite understand your teleportation question. If you are talking about messages that are instantaneous in the coordinate system in which the emitter is stationary, then this is covered by the post I linked to in #6.

 

[GeorgeDishman]

So the absolutely instantaneous definition is applied to the phenomenon of teleportation.

So are you saying here that in a SR context the arrival time would be t=0 ??

The definition I understand of "teleportation" is moving from one location to another without passing through intervening locations, for example in quantum tunneling.

In SR, there is no such thing as absolute simultaneity so if your form of teleportation existed, SR would not be applicable, you would need to discard SR for some other theory that supported absolute simultaneity.

 

[Austin0]

The definition I understand of "teleportation" is moving from one location to another without passing through intervening locations, for example in quantum tunneling.

In SR, there is no such thing as absolute simultaneity so if your form of teleportation existed, SR would not be applicable, you would need to discard SR for some other theory that supported absolute simultaneity.

Hi Thank you .I am in complete agreement. That is exatly the point.
I have the same understanding of what is meant by teleportation. I also don't consider it a very plausible possible reality but in an imaginary thought experiment it can be well defined so the same conditions pertain as if it was a reality. Which, as you say would mean that SR was not applicable.
That to simply assign the time according to coordinate simultaneity, isotropically to its arrival anywhere within a frame, is to implement an implicit assumption of absolute synchronization of the clocks in that system. Which we know is not a valid assumption in SR.

Without this initial assumption and the consequent spacetime location of its arrival or hypothetical arrival, in the initial frame, there is no basis whatsoever for any prediction of where or when it might arrive in another frame.
WOuld you agree?

I agree the idea of a universal simultaneity according to Galilean clocks was actually eliminated by SR but the idea of restricted absolute simultaneity as, for exsample EPR , is not mentioned or excluded.
As far as my understanding of the QM concept and the current state of experimentation it appears to be (or at least promise) a means of establishing absolute simultaneity between two locations. I myself, don't see this as a problem or a detraction from SR as the phenomenon doesn't entail motion per se , through spacetime, so is outside the domain of SR or perhaps more correctly would simply be a physical phenomenon within SR but would not necessarily change the structure.
Thanks

 

[harrylin]

[..] As far as my understanding of the QM concept and the current state of experimentation it appears to be (or at least promise) a means of establishing absolute simultaneity between two locations. [..]

That is inexact, and here it is necessary to be exact. From Bell's theorem and the current status of experiments one may infer the existence of an absolute simultaneity, but other explanations have been given. And the main point here: if it would be possible to determine absolute simultaneity, that would break the relativity principle. According to all the currently discussed explanations it will not be possible to determine absolute simultaneity.

 

[GeorgeDishman]

The definition I understand of "teleportation" is moving from one location to another without passing through intervening locations, for example in quantum tunneling.

Hi Thank you .I am in complete agreement. That is exatly the point.
I have the same understanding of what is meant by teleportation. I also don't consider it a very plausible possible reality but in an imaginary thought experiment it can be well defined so the same conditions pertain as if it was a reality.

Let me give a crude sci-fi example of what I mean. Suppose a human could be frozen in liquid helium and later thawed as the cryonics industry is attempting. The frozen person could be dismantled atom by atom here with the relative location of each particle noted. That data could be emailed to Mars and the person reassembled using locally sourced atoms. When thawed, they would have traveled between the planets without passing through the space between them in physical form. That technique could be extended to distant stars if unmanned probes could be sent there to build the receiver. That would essentially provide "teleportation" at the speed of light.

In SR, there is no such thing as absolute simultaneity so if your form of teleportation existed, SR would not be applicable, you would need to discard SR for some other theory that supported absolute simultaneity.

Which, as you say would mean that SR was not applicable.

The assumption of absolute time would mean SR is philosophically wrong (IMHO) though still mathematically valid, the assumption of teleportation does not.

That to simply assign the time according to coordinate simultaneity, isotropically to its arrival anywhere within a frame, is to implement an implicit assumption of absolute synchronization of the clocks in that system. Which we know is not a valid assumption in SR.

Without this initial assumption and the consequent spacetime location of its arrival or hypothetical arrival, in the initial frame, there is no basis whatsoever for any prediction of where or when it might arrive in another frame.
WOuld you agree?

Not quite. The question of "where" is easy, you arrive wherever the receiver is located. If the teleport works at or below the speed of light, normal physics applies. If it is FTL then the actual speed in any frame tells you when and the where/when coordinates can be transformed by Lorentz as usual, you just get an FTL result in all frames, but as has been discussed, you also get the ability to move back to your own past.

I agree the idea of a universal simultaneity according to Galilean clocks was actually eliminated by SR but the idea of restricted absolute simultaneity as, for exsample EPR , is not mentioned or excluded.
As far as my understanding of the QM concept and the current state of experimentation it appears to be (or at least promise) a means of establishing absolute simultaneity between two locations.

From Bell's theorem and the current status of experiments one may infer the existence of an absolute simultaneity, but other explanations have been given.

I don't follow that. For example, you can measure the state of two entangled particles at spacelike separated events and find they are correlated but that doesn't define a surface of simultaneity. You know when you measure a particle but you cannot distinguish between (a) whether you are the first or second to make a measurement and (b) whether the value was determined by your measurement or had already been forced some time earlier. This means that although it appears to imply there is a linkage which is FTL, all FTL values are equally valid, and since no information is passed, SR is not invalidated that way either.

Obviously, an absolute frame is one approach to understanding the behaviour of entangled systems but I don't think it can be "inferred", only postulated.

I myself, don't see this as a problem or a detraction from SR as the phenomenon doesn't entail motion per se , through spacetime, so is outside the domain of SR or perhaps more correctly would simply be a physical phenomenon within SR but would not necessarily change the structure.
Thanks

If an absolute frame defines the rate of physical processes, then SR becomes only an emergent description of something else IMHO, but nothing I've seen so far provides any evidence for that.

Incidentally, this experiment looks as though it could send data into the past (by binary modulation of Victor's decision measured by correlation of Alice and Bob's results) which, combined with the "teleportation" method outlined above would allow us to visit the past any time after the first receiver is built:

http://www.sciencedaily.com/releases/2012/04/120423131902.htm

The preprint is available here:

http://arxiv.org/abs/1203.4834

 

[harrylin]

[about Bell theorem]
I don't follow that. For example, you can measure the state of two entangled particles at spacelike separated events and find they are correlated but that doesn't define a surface of simultaneity. [..] SR is not invalidated [..]

Yes, you elaborated on what I stated in the part that you snipped.

[..] Obviously, an absolute frame is one approach to understanding the behaviour of entangled systems but I don't think it can be "inferred", only postulated.

Such a postulation is not based on nothing. Again: that is one of a few possible explanations that may be inferred (http://dictionary.reference.com/browse/infer?s=t ) from observations; other proposed explanations are conspiracy, non-reality or many worlds. Elaborating would be off-topic both in this forum and in this thread, but see the last part of http://cdsweb.cern.ch/record/142461?ln=en

 

[GeorgeDishman]

Yes, you elaborated on what I stated in the part that you snipped.

Such a postulation is not based on nothing. Again: that is one of a few possible explanations that may be inferred (http://dictionary.reference.com/browse/infer?s=t ) from observations; other proposed explanations are conspiracy, non-reality or many worlds. Elaborating would be off-topic both in this forum and in this thread, but see the last part of http://cdsweb.cern.ch/record/142461?ln=en

OK, I think I was reading too much into your use of "infer", no problem.

 

[Austin0]

[

As far as my understanding of the QM concept and the current state of experimentation it appears to be (or at least promise) a means of establishing absolute simultaneity between two locations.

That is inexact, and here it is necessary to be exact. From Bell's theorem and the current status of experiments one may infer the existence of an absolute simultaneity, but other explanations have been given. And the main point here: if it would be possible to determine absolute simultaneity, that would break the relativity principle. According to all the currently discussed explanations it will not be possible to determine absolute simultaneity.

Certainly I have drawn no conclusions. And the current state of the technology and implementation don't seem to allow for any determination as they all seem to be essentially fuzzy, timewise. Not discrete events but statistical aggregates of events over some interval.
But it is early days and based on the concept it still appears to hold the possibility of eventual definite determination. As for that occurence breaking the relativity principle I am not sure how to interpret your point:

It is safe to assume it won't happen because of RoS?

If it did happen SR would be less valid??

Other??

As I interpret it, RoS said nothing about the possible actuallity of absolute simultaneity or even its possible future determination.
It said that our past conception and assumption of universal clock synchronization and determinate simultaneity where false. That at the time there was no method of real determination and no valid assumption of actual simultaneity between disparate events.

So even if determination was possible through later science and technology it could not invalidate a claim that was never made. And it would certainly not invalidate conventional clock synchronization.

 

[harrylin]

[..] But it is early days and based on the concept it still appears to hold the possibility of eventual definite determination.

The correlations can only be established afterwards, by means of signalling at <=c. There is no proposal of how the PoR could be broken in principle.

It is safe to assume it won't happen because of RoS?
If it did happen SR would be less valid?? [..]
As I interpret it RoS said nothing about the possible actuallity of absolute simultaneity or even its possible future determination.

Special relativity says that absolute simultaneity cannot be determined. A recent, very elaborate discussion about RoS is here:
https://www.physicsforums.com/showthread.php?t=575332

 

[Austin0]

That to simply assign the time according to coordinate simultaneity, isotropically to its arrival anywhere within a frame, is to implement an implicit assumption of absolute synchronization of the clocks in that system. Which we know is not a valid assumption in SR.

Without this initial assumption and the consequent spacetime location of its arrival or hypothetical arrival, in the initial frame, there is no basis whatsoever for any prediction of where or when it might arrive in another frame.
WOuld you agree?

Not quite. The question of "where" is easy, you arrive wherever the receiver is located. If the teleport works at or below the speed of light, normal physics applies. If it is FTL then the actual speed in any frame tells you when and the where/when coordinates can be transformed by Lorentz as usual,

yes the where in the other frame is decided but the spacetime location of that point in the other frame at the exact instant you teleport is not. The normal procedure is to calculate the spatial coordinate in the initial frame (with the same time reading) that is proximate to the destination coordinate in the other frame. But the site on the other frame could only actually be there at that absolute instant if your system clocks were absolutely simultaneous.
If the clocks are not absolutely simultaneous there is no basis to assign a location or a local time to the arrival event of a absolutely simultaneous translation.
I am picturing something along the lines of electron tunneling. A quantum device that manipulates the probability of your waveform being detected at some distant location. ;-).

 

[GeorgeDishman]

yes the where in the other frame is decided but the spacetime location of that point in the other frame at the exact instant you teleport is not. The normal procedure is to calculate the spatial coordinate in the initial frame (with the same time reading) that is proximate to the destination coordinate in the other frame.

No, you would normally add a delay dependent on the speed of your teleporter communication channel to the time at the source to find the time at the destination in your original frame. (In fact if the distance between the source and destination is constant, you don't even need to change frames.)

But the site on the other frame could only actually be there at that absolute instant if your system clocks were absolutely simultaneous.
If the clocks are not absolutely simultaneous there is no basis to assign a location or a local time to the arrival event of a absolutely simultaneous translation.
I am picturing something along the lines of electron tunneling. A quantum device that manipulates the probability of your waveform being detected at some distant location. ;-).

There is no such thing as absolute simultaneity in quantum tunneling phenomena, they can be described by QED which is entirely relativistic. However, if you tunnelled to Alpha Centauri, you might find the particles of your body randomly strewn over ±4 years, even if they're all at the same location ;-)