What exactly is the solution for principle of locality and speed of light?

[menniandscience]

how do physicists solve this contradiction (when information moves faster then the speed of light)?
thanks

 

[f95toli]

There is no contradiction because information never travels faster than the speed of light.
Although I am not sure what you are referring to by "principle of locality"?

Note that entaglement etc can NEVER be used to transfer information FTL, no one has ever identified a situation where QM contradicts SR.

 

[zonde]

how do physicists solve this contradiction (when information moves faster then the speed of light)?

I would say that at the present state of things there are several alternative solutions for this contradiction but none of them says that information moves faster then the speed of light.
Good thing is that all the alternatives relay on the same mathematical formalism. So we can expect that there will be some job for Occam's razor in the future.

 

[menniandscience]

so how one particle affect other at the time? (if it does)

 

[zonde]

so how one particle affect other at the time? (if it does)

Obviously they don't as that would involve FTL interaction.
But we can speak how measurements affect each other as they are communicated no faster than light speed.

 

[Orion1]

Günter Nimtz...

no one has ever identified a situation where QM contradicts SR.

A controversial exception has already been identified, Günter Nimtz, a German physicist has already demonstrated that photon particles carrying information can travel at superluminal velocities while quantum tunneling via virtual photons.

1994 Nimtz and Horst Aichmann shown an experiment at the laboratories of Hewlett-Packard using microwaves through a straitened passage of a waveguide. Nimtz says that the Frequency modulated (FM) signals transports the 40th symphony of Wolfgang Amadeus Mozart 4.7 times faster than light due to the effect of quantum tunneling.

This experiment is video demonstrated in reference 2, the differential signals arrive on an oscilloscope detector that demonstrates the tunneling photon signals arrive faster than vacuum photon signals, also while carrying information, however the received information is attenuated.

I have also corresponded with a professor at the University of Cologne that has studied Nimtz scientific papers and concluded that the superluminal quantum tunneling effect is also possible with particles with mass.

Although theoretical, I have never seen an experiment that demonstrated a superluminal quantum tunneling virtual mass particle.

Reference:
http://en.wikipedia.org/wiki/G%C3%BCnter_Nimtz"
http://www.youtube.com/watch?v=UI7nPmlgBEk"
http://en.wikipedia.org/wiki/Quantum_tunnelling"

 

[Dmitry67]

The understanding of Nimtz and Stahlhoven is that tunneling is the one and only observed violation of special relativity[5] but according to them, that is not a violation of causality: due to the temporal extent of every signal it is impossible to transport information into the past. They claim that tunneling can be explained with virtual photons like Richard Feynman predicted.[6]

Criticism sound not very convincing at wavelength was 33mm and gap was 1 meter wide, while GPS in my smartphone have a precision of 5 meters measuring the ‘arrival times’ of the satellite signals. I believe such intervals can be measured very accurately.

 

[Cthugha]

A controversial exception has already been identified, Günter Nimtz, a German physicist has already demonstrated that photon particles carrying information can travel at superluminal velocities while quantum tunneling via virtual photons.
[...]
This experiment is video demonstrated in reference 2, the differential signals arrive on an oscilloscope detector that demonstrates the tunneling photon signals arrive faster than vacuum photon signals, also while carrying information.

Not that crap again. This has been discussed in these forums several dozen times and it is pretty clear that the tunneling photon do NOT travel faster than c. Nimtz uses the speed of the pulse peak for measuring signal propagation, which is nonsense, especially if the shape of the pulse changes like in Nimtz' experiments. The speed of the peak is not the speed at which information is transmitted and it is also not the speed of particles.

This is like trying to measure the speed of a moving train and taking the position of the passengers as the measure of the speed of the train. If all of the passengers move from the back to the front of the train you will measure a faster train according to your definition although the speed of the train is constant all the time.

 

[Dmitry67]

What if there is only one peak (delta function)? Only one very short pulse?

 

[Cthugha]

Nimtz' experiments rely on the fact that his tunnel barriers cause nonlinear pulse damping. The "front part" of the wave is less damped and the "back part" gets damped heavily. If you just have a delta peak, you will only see a damped peak coming out without any shift in time. He uses just a clever version of pulse shaping using anomalous dispersion.

 

[Orion1]

A photon tunneling through the barrier is therefore most likely to arrive before a photon traveling unimpeded at the speed of light. Our experiment confirmed this prediction. But we do not believe that any individual part of the wave packet moves faster than light. Rather the wave packet gets "reshaped" as it travels, until the peak that emerges consists primarily of what was originally in front. At no point does the tunneling-photon wave packet travel faster than the free-travelling photon.

In 1982 Steven Chu of Stanford University and Stephen Wong, then at AT&T Bell Laboratories, observed a similar reshaping effect. They experimented with laser pulses consisting of many photons and found that the few photons that made it through an obstacle arrived sooner than those that could move freely. One might suppose that only the first few photons of each pulse were 'allowed' through and thus dismiss the reshaping effect. But this interpretation is not possible in our case, because we study one photon at a time. At the moment of detection, the entire photon 'jumps" instantly into the transmitted portion of the wave packet, beating its twin to the finish more than half the time. Although reshaping seems to account for our observations, the question still lingers as to why reshaping should occur in the first place. No one yet has any physical explanation for the rapid tunneling.

Although reshaping does occur especially for quantum tunneling multi-photons, it does not account for superluminal quantum tunneling single-photons.

I also refuse to accept the argument that Stanford University and AT&T Bell Laboratories professors that are aware of the reshaping effect are incapable of measuring the velocity of quantum tunneling photons.

Reference:
http://www.dhushara.com/book/quantcos/qnonloc/qnonloc.htm"

 

[Cthugha]

Although reshaping does occur especially for quantum tunneling multi-photons, it does not account for superluminal quantum tunneling single-photons.

I also refuse to accept the argument that Stanford University and AT&T Bell Laboratories professors that are aware of the reshaping effect are incapable of measuring the velocity of quantum tunneling photons.

Reference:
http://www.dhushara.com/book/quantcos/qnonloc/qnonloc.htm"

A reference constantly misspelling Paul Kwiat as Paul Kwait is pretty suspect. Fortunately there are the original publications of the authors to check, what they really intended to say. Check for example:

A. M. Steinberg, P. G. Kwiat, and R. Y. Chiao
Measurement of the single-photon tunneling time
Phys. Rev. Lett. 71, 708 - 711 (1993)

Where they conclude:
"Our measurements indicate that the peak of the undistorted (but attenuated) single-photon wave packet appears on the far side of a tunnel barrier earlier than it would were it to propagate at c. There is, however, no genuine violation of Einstein causality, as explained above."

As explained in the paper this is a result of postselection combined with low probabilities. You only select the transmitted photons and the transmission probability is indeed low. See references 22 and 23 in the paper I quoted for further discussion on that topic.

So in conclusion: The authors do not draw the conclusion you would like them to draw. There is no information transfer at superluminal velocities according to the authors you mentioned.

 

[Orion1]

Although the apparent tunneling velocity (1.7c) is superluminal, this is not a genuine signal velocity.

If the tunneling photon (virtual photon) is not a genuine signal then virtual photons could not relay quantum information and also frequency modulated photons could not traverse the barrier, that is the photons that leave the barrier would still be attenuated but not frequency modulated.

If the tunneling photon (virtual photon) is not a genuine signal, then polarized photons (quantum information) that enters the barrier would leave the barrier as non-polarized photons.

The tunneling velocity is too high for 'pulse reshaping' because the wave packet distribution for photons are extremely small and this would violate the Heisenberg Uncertainty Principle.

The paper claims that the tunneling time differential is due to 'pulse reshaping', however it does not state a theorem that proves it.

Reference:
"www.ino.it/~azavatta/References/PRL71p708.pdf"[/URL]
[PLAIN]http://en.wikipedia.org/wiki/Uncertainty_principle"
http://en.wikipedia.org/wiki/Pulse_shaping"

 

[Cthugha]

You are completely misinterpreting the paper.

If the tunneling photon is not a genuine signal then virtual photons could not relay quantum information and also frequency modulated photons could not traverse the barrier, that is the photons that leave the barrier would still be attenuated but not frequency modulated.

If the tunneling photon (virtual photon) is not a genuine signal, then polarized photons (quantum information) that enters the barrier would leave the barrier as non-polarized photons.

The paper does not say that the tunneling photons are not genuine signals. It says that the tunneling times are not the times, which it takes to transmit information.

The tunneling velocity is too high for 'pulse reshaping' because the wave packet distribution for photons are extremely small and this would violate the Heisenberg Uncertainty Principle.

As you can see in the HOM-dip in figure 3 of the quoted paper the wave packets are indeed pretty broad and long compared to the time difference of 1.47 fs between free space propagation and barrier propagation. Pulse reshaping does not violate the HUP in this case.

The paper claims that the tunneling time differential is due to 'pulse reshaping', however it does not state a theorem that proves it.

The paper does not even claim that directly. It claims that pulse reshaping is the cause of the tunneling time differential in classical optics and says that the mechanism is a bit different for single photons. However, the mechanism in this case is in fact pretty similar. As you see in figure 3 there is still significant destructive interference for time delays as large as +/- 40 fs showing the underlying detection probability density is of the same width as well. It does really not surprise me that the time dependence of the photon detection probability density is "shaped" in the same way a classical pulse will be shaped. If the peak shift was larger than the HOM-dip this would be a good indication for FTL-information transfer. In this case, it is not.

 

[menniandscience]

people, concentrate, i was talking about EPR paradox, is there a solution?

 

[Dmitry67]

Is there a problem? :)

 

[f95toli]

As Dmitry67 has already: Is thera a problem?
It is important to remember that what Einstein and co ASSUMED was a paradox in QM is actually not.
The starting point of their argument is basically that a certain type of experiments will "obviously" yield a result X (because information can not travel FTL); i.e. they ASSUMED a certain outcome.
However, when people actually started doing these experiments many years alter this was NOT what was seen meaning the whole line of reasoning leading up to the paradox is actually incorrect.

And yes; I am simplifying this quite a bit here (both the physics and the history) but the main point is that there IS no paradox; QM is consistent (at least mathematically; that many people enjoy spending ages discussing various intepretations related to the EPR is another story.


Also, I would like to stress that I am in no way trying to say that the EPR paper was not important because it was -it stimulated an enourmous amount of important work- but that does not change the fact that what they were trying to show in the paper (that QM was inconsistent) turned out to be incorrect.

 

[DrChinese]

As Dmitry67 has already: Is thera a problem?
It is important to remember that what Einstein and co ASSUMED was a paradox in QM is actually not.
The starting point of their argument is basically that a certain type of experiments will "obviously" yield a result X (because information can not travel FTL); i.e. they ASSUMED a certain outcome.
However, when people actually started doing these experiments many years alter this was NOT what was seen meaning the whole line of reasoning leading up to the paradox is actually incorrect.

And yes; I am simplifying this quite a bit here (both the physics and the history) but the main point is that there IS no paradox; QM is consistent (at least mathematically; that many people enjoy spending ages discussing various intepretations related to the EPR is another story.


Also, I would like to stress that I am in no way trying to say that the EPR paper was not important because it was -it stimulated an enourmous amount of important work- but that does not change the fact that what they were trying to show in the paper (that QM was inconsistent) turned out to be incorrect.

To add to the above, with which I agree entirely:

The QM answer is: "This makes the reality of P[position] and Q[momentum] depend upon the process of measurement carried out on the first system..." These words are from the EPR paper itself, although they rejected this idea because they thought it was not a "reasonable definition of reality".

 

[zonde]

how do physicists solve this contradiction (when information moves faster then the speed of light)?

Somehow solve, one way or another ;)
... without any information moving faster then the speed of light.

people, concentrate, i was talking about EPR paradox, is there a solution?

If you want solution for you I can recommend deterministic viewpoint involving hidden variables. You can imagine that hidden variables does not hold (yet) any known physical meaning - it is just sophisticated way of numbering particles :)
With that view in mind you should draw some analogy between wave function collapse and discarding of some particles (subsampling). That way you pick the part of sample that show required correlations in postselection process that does not require any faster than light information transfer.
There might arise small problem if you afterwards will consider Malus' law. That's because implied explanation for Malus' law is that photons have hidden variable of polarization.
So it turns out that this way EPR experiments conflict with intuitive understanding of Malus' law.
However this can be solved if you assume that polarization is not hidden variable of single photon but rather property of sample of photons e.g. their configuration relative to one another plus certain strange arrangement between polarizers that might not seem so strange if you like Bomian interpretation of QM or even have heard about The Invariant Set Postulate hypothesis.

 

[zonde]

Thought that I might add this link as it seems relevant to what I said about Malus' law (not completely sure however)
http://www.springerlink.com/content/0136072643546224/"
It's Hnilo et al "Low Dimension Dynamics in the EPRB Experiment with Random Variable Analyzers"

 

[haushofer]

Ok, it has been a long time since I've thought about this EPR-stuff, but basically I always thought the problem was the following:

Both particles are in a superposition. If I measure one particle's spin, it's wavefunction will collapse to a spin eigenfunction. But the other particle's wavefunction will also collapse to the other spin eigenfunction. I always considered this to be some sort of "information exchange", because the wavefunction is collapsed by the measurement.

In the classical case, I let a red and a white ball travel in opposite directions, without knowing which one goes where. If I measure one ball's colour, I also know the other colour. But in this case, I don't have any "information exchange", because classically there isn't a superposition and the ball was already in the "colour eigenfunction" before I measured.

I didn't read all the posts here, so maybe I'm repeating things, but this point of view on "information exchange" is wrong? Apparently I never really understood the meaning of "information exchange" and the EPR-situation.

 

[zenith8]

I didn't read all the posts here, so maybe I'm repeating things, but this point of view on "information exchange" is wrong? Apparently I never really understood the meaning of "information exchange" and the EPR-situation.

Actually you are quite right. What the EPR experiments show is that there is a superluminal causal connection and superluminal information transmission in a single measurement. What is not seen is superluminal matter or energy transport, or any possibility of superluminal controllable signalling.

The latter signalling thing is what people confuse with 'information transmission' - signalling refers to what happens when you repeat the experiment many times. It would be something like transmitting a message in Morse code by going 'up-up-up down-down-down up-down-up' - there is no possibility of this because the quantum randomness washes out the controllability.

I haven't read the previous posts either, so I apologize if someone has already made this point.

 

[zonde]

Both particles are in a superposition. If I measure one particle's spin, it's wavefunction will collapse to a spin eigenfunction. But the other particle's wavefunction will also collapse to the other spin eigenfunction. I always considered this to be some sort of "information exchange", because the wavefunction is collapsed by the measurement.

Well but entanglement measurement happens when you correlate measurements from both sites. So if you say that measurement collapses wavefunction then correlation of spin measurements from both sites collapses wavefunction to "entanglement eigenfunction" if this can be said this way.

That's without sarcasm of the other answer

 

[zenith8]

That's without sarcasm of the other answer

Sorry, why is my answer (which I presume is what you're referring to) sarcastic?

 

[zonde]

Sorry, why is my answer (which I presume is what you're referring to) sarcastic?

transmitting a message in Morse code by going 'up-up-up down-down-down up-down-up'

I found this funny
Do you say that I missed your point?

 

[zenith8]

I found this funny
Do you say that I missed your point?

Given that you can apparently instantly transmit information to the other side of the universe (something like 'since here is up, over there it must be down') then - if only you could control what happens at your end - you could transmit a message in Morse code instantaneously to Alpha Centauri (a controllable signal) with ups and downs replacing dots and dashes. With the universe as it apparently is, then all you would actually get is random noise.

It's a bit silly certainly, but it isn't sarcastic.

 

[zonde]

Given that you can apparently instantly transmit information to the other side of the universe (something like 'since here is up, over there it must be down') then - if only you could control what happens at your end - you could transmit a message in Morse code instantaneously to Alpha Centauri (a controllable signal) with ups and downs replacing dots and dashes. With the universe as it apparently is, then all you would actually get is random noise.

It's a bit silly certainly, but it isn't sarcastic.

Ups, I didn't realized
Then maybe consider other a bit more scientific option that each separate spin measurement actually IS wavefunction of entanglement? And it collapses when by perfectly classical information transfer it is transferred to coincidence counter and is correlated with other side?

 

[RUTA]

Actually you are quite right. What the EPR experiments show is that there is a superluminal causal connection and superluminal information transmission in a single measurement. What is not seen is superluminal matter or energy transport, or any possibility of superluminal controllable signalling.

There is another possibility -- nonseparability. The EPR-Bell experiments imply nonlocality and/or nonseparability.

 

[zenith8]

There is another possibility -- nonseparability. The EPR-Bell experiments imply nonlocality and/or nonseparability.

Indeed it is a possibility. But sadly one that doesn't appear to make any sense - I have never seen this explained in words that a bear of little brain like myself can actually understand. Go on, try me. And remember, I really am very stupid.

 

[RUTA]

Indeed it is a possibility. But sadly one that doesn't appear to make any sense - I have never seen this explained in words that a bear of little brain like myself can actually understand. Go on, try me. And remember, I really am very stupid.

Ok We have an explanation of our particular method using the famous "face-vase" illusion. It's a paragraph in the Conclusion (section 6) of arXiv 0908.4348, the paragraph begins with "We have already presented a mathematically detailed account of our approach so here we supply a caricature ... ." That paragraph should provide a picture of a nonseparable ontology.

 

[zonde]

Ruta,
If I understand correctly this nonseparability relays on blockworld that in everyday language we would call destiny. Is it right?
What would you say about such mind experiment:
Three entangled photons with the same polarizations are sent to three sites where one photon stream is analyzed with polarization beam splitter (PBS) at angle 0° relative to common reference other with PBS at angle 45° and third with PBS at angle 22.5°.
What we would see if we correlate results each with each?

 

[RUTA]

Ruta,
If I understand correctly this nonseparability relays on blockworld that in everyday language we would call destiny. Is it right?

In a blockworld, the future, past and present are equally "real." So, yes, your future is "determined" in a blockworld.

What would you say about such mind experiment:
Three entangled photons with the same polarizations are sent to three sites where one photon stream is analyzed with polarization beam splitter (PBS) at angle 0° relative to common reference other with PBS at angle 45° and third with PBS at angle 22.5°.
What we would see if we correlate results each with each?

Photon 1 (and 2 and 3) is in the |1> eigenstate of operator 1 (representing the polarizer set at 0 deg), so it will always pass (call that eigenvalue 1, not pass eignevalue is 0) and correlated results will require outcomes at polarizers 2 & 3 are also 1. The initial state is |1,1,1> where each |1> is in the eigenbasis of operator 1. To find the probability of correlated results (1,1,1 outcomes), you just find the projection of the |1> state in eigenbasis of operator 1 on the |1> state of each of the other operators' eigenbases. Multiply and square for the probability of a 1,1,1 outcome. The angle of the polarizer is the angle of the eigenbasis for photons, (whereas it's cut in half for spin) so that when your polarizer is at 90 deg relative to the polarization state you get 0 (not pass), which means the |1> eigenstate of the 90 deg operator is |0> in the eigenbasis of the 0 deg operator. Experimentally you don't measure 0, so if you wanted info on outcomes for the |0> state you have to measure 1 at 90 deg from the angle in question and infer 0 for the angle in question.

There is a good paper showing all the theory for an entangled pair plus experimental data and equipment, “Entangled photons, nonlocality, and Bell inequalities in the undergraduate laboratory,” D. Dehlinger and M.W. Mitchell, Am. J. Phys. 70, Sep 2002, 903-910. I have the following typos: RHS of Eq (15) should be inverted (and I get theta = 44 deg instead of 46 deg); either a = 45 deg or b' = -22.5 deg for polarizer angles in deriving Eq (23). They don't provide the individual values of E for computing S immediately after Eq (25). I obtain E(a,b) = .49661, E(a, b') = -.58742, E(a', b) = .68861, and E(a', b') = .52468 so that S = 2.297 (they obtain 2.307, less than 1% difference fm rounding).

If you have questions about this, you should probably contact me directly. I think we're getting a bit off topic for this thread.

 

[WaveJumper]

There is another possibility -- nonseparability. The EPR-Bell experiments imply nonlocality and/or nonseparability.

There is one more - realism. Though one could argue that locality contains an implicit form of realism.

There is also the 'option' of giving up the arrow of time. Either way, it apears impossible to maintain the classical notion of realism without sacrificing one or more of the intuitive notions.

 

[zonde]

If you have questions about this, you should probably contact me directly. I think we're getting a bit off topic for this thread.

I will slowly read trough what you wrote but a quick question. If I understood you correctly you considered only cases where all three photons are detected. But my question was more about cases where there are two photons detected at two locations. So we have 3 interdependent entanglement measurements.

 

[RUTA]

I will slowly read trough what you wrote but a quick question. If I understood you correctly you considered only cases where all three photons are detected. But my question was more about cases where there are two photons detected at two locations. So we have 3 interdependent entanglement measurements.

I thought you were talking about coincidence counts at three detectors, so of course you'd need three photons. In any event, if you read that AJP paper, you'll see how to do the math for two photons easy enough. And, you'll see how the experiments are actually carried out, e.g., how coincidence counts involving the |0> state are obtained when |0> means the photon didn't get through the polarizer.