Can Exceeding the Speed of Light Really Mean Time Travel?

[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 occurrence 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 ;-)