Superluminous Signalling 101?

[Yablon]

Dear Friends,

Over many months I have watched from the sidelines with bemusement the many passionate arguments here about Bell's theorem, etc. In part -- and intending no offense to anybody involved in the debates -- this is because I am struck by the impression that much of the discussion is sophistry, tenuously if at all rooted in clear empirical observation. Also, while as much as anyone I recognize scientific development as a creative enterprise which can spawn great debates during the birthing of new science, sooner or later things do tend to get settled into a quiescent state of mainstream acceptance. So it is further bemusing to me that after decades of debate these discussions still appear to be highly contested and unsettled. I take this as a sign that something is missing. And what is usually missing in these situations are some simple, foundational insights that can at last settle the debates. So, I have a request I would like to have answered as best as anybody can, with the intention if seeing whether there is some way to steer these discussions into a reasonably safe and uncontested harbor:

Please lay out in the simplest and most direct form possible, the direct experimental evidence that that is interpreted by at least some people in the physics establishment to require superluminal communication / signalling which defies the special relativistic requirement that no material signal may travel faster than the speed of light. That is, please lay out in this space, the coursework "101" evidence for superluminal signalling. Of course, as there seem to be arguments against these interpretations, please lay those contra positions out too.

Let me be clear that I am looking for the experimental sources of the views that there is something superluminal going on, and I would like to see the connection made as directly as possible. I am not interested in hearing about simulations or gedankens. I am issuing a challenge for folks to clearly draw the direct line to real experimentation in the physical world, or, at least as direct a line as can be drawn.

Thanks,

Jay

[harry]

Dear Friends,

Over many months I have watched from the sidelines with bemusement the many passionate arguments here about Bell's theorem, etc. In part -- and intending no offense to anybody involved in the debates -- this is because I am struck by the impression that much of the discussion is sophistry, tenuously if at all rooted in clear empirical observation. [..]

Please lay out in the simplest and most direct form possible, the direct experimental evidence that that is interpreted by at least some people in the physics establishment to require superluminal communication / signalling which defies the special relativistic requirement that no material signal may travel faster than the speed of light. That is, please lay out in this space, the coursework "101" evidence for superluminal signalling. [..]

Let me be clear that I am looking for the experimental sources of the views that there is something superluminal going on, and I would like to see the connection made as directly as possible. [..]

Thanks,

Jay

Hi Jay,

I won't answer directly but instead I will lay the ground for a fruitful discussion as your questions contain some misunderstandings already.

First of all, it's perhaps good to clarify that there are no experimental sources for the views that there is something superluminal going on. And no real signalling is thought to be possible either! Nobody makes any claim about a clear empirical observation of superluminous signalling. The view that something superluminal is going on is based on inference from theory. Of course, that is often the case with increased sophistication of theory and experiments.

Experiments only come in play insofar experiments confirm predictions from theory: "Bell's theorem" is the claim that some predictions from QM cannot be explained without resorting to superluminal explanations (or, by expansion, some other weird alternative explanations). Experiments that try to test those predictions without leaving much room for "common sense" interpretations are interpreted by many people in the physics establishment to require superluminal "influences" which themselves cannot be directly detected. And SR has been modified to comply with that interpretation of QM; it is said to be compatible with QM because no superluminous signals can be detected.

As there is only such very indirect experimental evidence, are you still interested to hear the details?

[Mikko]

Please lay out in the simplest and most direct form possible, the direct experimental evidence that that is interpreted by at least some people in the physics establishment to require superluminal communication / signalling which defies the special relativistic requirement that no material signal may travel faster than the speed of light.

There is none, and not for non-material signals, either. Some phenomena need superluminal signalling (but not necessarily material) if they are explained with certain kinds of theories but not when explained with conventional theories.

[Yablon]

I won't answer directly but instead I will lay the ground for a fruitful discussion as your questions contain some misunderstandings already.

Hi Harry,

I am not misunderstanding, and in fact expected a reply of the sort you gave. And I am glad you did...

First of all, it's perhaps good to clarify that there are no experimental sources for the views that there is something superluminal going on. And no real signalling is thought to be possible either! Nobody makes any claim about a clear empirical observation of superluminous signalling. The view that something superluminal is going on is based on inference from theory. Of course, that is often the case with increased sophistication of theory and experiments.

Experiments only come in play insofar experiments confirm predictions from theory: "Bell's theorem" is the claim that some predictions from QM cannot be explained without resorting to superluminal explanations (or, by expansion, some other weird alternative explanations). Experiments that try to test those predictions without leaving much room for "common sense" interpretations are interpreted by many people in the physics establishment to require superluminal "influences" which themselves cannot be directly detected. And SR has been modified to comply with that interpretation of QM; it is said to be compatible with QM because no superluminous signals can be detected.

What I am trying to do is force some scientific discipline on a debate which often strikes me as a free-floating craps game. (I am dating myself with that "Guys and Dolls" reference. ) We use theory in science to explain and tie together that which we empirically observe. If we are good at it, the theory we use to explain one type of phenomenon turns out to also explain a seemingly-different phenomenon, and then we have unified some things and perhaps even predicted some things. But at the end of the day, we use theory to explain and tie together a range of observations.

So, in the case at hand, there are quantum theories we use to explain what we observe, and what is very clear, is that some folks have concluded that some of the things we observe cannot be explained unless one employs a theory in which "something" superliminous and / or non-local is occurring. I am trying to get people as a matter of discipline and clear thinking (rather than more endless inconclusive arguing) to draw the connection from what we observe to the felt-need to use some resort to superluminosity in some form (which form should be precise and not just words) as crisply and cleanly and directly as possible. Clear away the debris and make the line as apparent and straight as possible without sophistry. And I would like to hear from the skeptics who think there is no such need and why.

So I am not saying "show we where we have observed superluminosity." I am showing "show me what has been observed that causes people to believe that we have to theoretically resort to some type of superluminosity, be clear about what the superluminosity really means, and if you disbelieve that this resort is necessary, then make that case as well. And sift out the superfluous stuff that gets in the way of clear thinking.

As there is only such very indirect experimental evidence, are you still interested to hear the details?

Absolutely!

Thanks,

Jay

[minkwe]

Good questions Yablon,
Unfortunately, you will find the opinions are divided even as concerns experimental evidence. Perhaps there should be an intense psychological study of this topic to understands why these of "scientists" fancy in inventing things from thin air, or how we found ourselves in a "quiescent state of mainstream acceptance" of the absurd which we must then be convinced out of. Perhaps the difficulty is due to the fact willingness to accept the absurd without any ounce of skepticism could very well be proportional to inability to carefully evaluate and ponder on evidence. Needless to say, there is a lot here for psychologists.

There is a much larger problem in Foundations of Physics that is only dimly revealed in the Bell debates and dates back to the Einstein and Bohr debates and probably even back to the debates on Fermat's principle. It is a problem of the use of language. I'll give you an example from Bell's work.

Bell says in his 1964 paper that: "Consider a pair of spin-half particles in the singlet state".

That statement is an embodiment of the problem. If you measure "a pair of spin-half particles" using Bell's own prescription of outcomes {+1, -1}. You can never have any paired product results other than +1 or -1. No matter the angles at which you measure them, whether you have superluminal signalling between the particles or not. So it seems what Bell is actually interested in considering is not "a pair of spin-half particles in the singlet state" but something else entirely. Whatever it is, that should be the context of the claimed "signalling". And, any such signaling may then require not just superluminouslity but backwards in time features to be consistent. For the Bell believers, I will add a question here:

How on earth does "a pair of spin-half particles" produce a cosine correlation. [Hint: don't ignore the underline.]

You find similar gobbledygook in QM where many "scientists" write of "a single particle" or " a pair of particles" when clearly their descriptions could never apply to individual particles or individual pairs. Worse, they apply statistics and probability to such talk. Nothing other than paradoxes are guaranteed to result from such thinking. They mix discussions of "a single particle" with discussions of multiple particles and create a mess that can not be disentangled without bleaching all their brains and sending them to kindergarden for a full do-over.

And I forgot one other question:

Signaling between what and what?
I bet you those suggesting superluminal signalling don't even know what the parties of the claimed signalling are supposed to be.

[minkwe]

One other thing, I can bet that you are not going to see any experimental evidence presented here that will be different from the following story line:

1. An inequality derived in "single-particle/single pair of particles"-land.
2. Experiments performed on multiple particle pairs
3. Violation --> therefore single particles do not exist, OR --> therefore some features of single particles are untenable.
4. Profit.

[gill1109]

Minkwe talks about pairs of particles. However we should forget all about particles and pairs of particles. Listen to Bell (1981) in "Bertlmann’s socks and the nature of reality", Chapter 16 of "Speakable and Unspeakable":

You might suspect that there is something specially peculiar about spin-1/2 particles. In fact there are many other ways of creating the troublesome correlations. So the following argument makes no reference to spin-1/2 particles, or any other particular particles.

Finally you might suspect that the very notion of particle, and particle orbit, freely used above in introducing the problem, has somehow led us astray. Indeed did not Einstein think that fields rather than particles are at the bottom of everything? So the following argument will not mention particles, nor indeed fields, nor any other particular picture of what goes on at the microscopic level. Nor will it involve any use of the words ‘quantum mechanical system’, which can have an unfortunate effect on the discussion. The difficulty is not created by any such picture or any such terminology. It is created by the predictions about the correlations in the visible outputs of certain conceivable experimental set-ups.

Consider the general experimental set-up of Fig. 7. To avoid inessential details it is represented just as a long box of unspecified equipment, with three inputs and three outputs.

Here is the figure in question:

The text continues:

Consider the general experimental set-up of Fig. 7. To avoid inessential details it is represented just as a long box of unspecified equipment, with three inputs and three outputs. The outputs, above in the figure, can be three pieces of paper, each with either ‘yes’ or ‘no’ printed on it. The central input is just a ‘go’ signal which sets the experiment off at time t_1. Shortly after that the central output says ‘yes’ or ‘no’. We are only interested in the ‘yes’s, which confirm that everything has got off to a good start (e.g., there are no ‘particles’ going in the wrong directions, and so on). At time t_1 + T the other outputs appear, each with ‘yes’ or ‘no’ (depending for example on whether or not a signal has appeared on the ‘up’ side of a detecting screen behind a local Stern–Gerlach magnet). The apparatus then rests and recovers internally in preparation for a subsequent repetition of the experiment. But just before time t_1 + T, say at time t_1 + T – δ, signals a and b are injected at the two ends. (They might for example dictate that Stern–Gerlach magnets be rotated by angles a and b away from some standard position). We can arrange that cδ << L, where c is the velocity of light and L the length of the box; we would not then expect the signal at one end to have any influence on the output at the other, for lack of time, whatever hidden connections there might be between the two ends.
Sufficiently many repetitions of the experiment will allow tests of hypotheses about the joint conditional probability distribution

P(A,B|a, b)

for results A and B at the two ends for given signals a and b.

Yablon asks: "where is the evidence"? Evidence can be of two kinds: experimental, theoretical.

On the experimental side the answer is that there is no proof, the good experiment still hasn't been done. Possibly it might be done within a year from now, the experimentalists are getting close.

On the theoretical side the answer is just the old QM story which everyone here knows. According to QM it seems that that good experiment ought to be feasible. The experimentalists have been trying hard for 50 years and still haven't managed to do it.

Yablon talks about superluminal signalling as being what is at issue. However in the just mentioned paper by Bell, the author lists four possible metaphysical conclusions. Only one of them involves effects spreading faster than the speed of light, and this only happens in a "hidden" layer not directly accessible to observations. Since this hidden layer is purely theoretical, saying that it "exists" is pretty meaningless.

Bell's list of four positions to take is not exhaustive. Some writers consider the 50 years of failure to perform the desired experiment as strong experimental proof that it can never be done, because quantum mechanics itself prevents it from being done: uncertainty relations preventing the required state to be created and measured under the needed spatial and temporal constraints.

Quantum mechanics itself prevents superluminal signalling between observable experimental inputs and outputs. Whether or not superluminal signalling is needed to create the cosine correlations, then, even if they could be created in the interesting context of a loophole-free experiment, you couldn't use them to signal.

So whatever the Bell discussion is all about, it is not about superluminal signalling.

Michel asks, how on earth can a spin-half pair of particles produce a cosine correlation? Well one pair just produces one outcome pair, but the outcomes of many pairs create what we call a correlation. But how can that be done? The answer is, nobody knows. It can't be done in a local realistic way, it can't be done in a simulation of a local hidden variables model by a network of computers in the arrangement of a loophole-free experiment. (Fast, rapid, local, random selection of measurement settings; no non-detections; rigorous enforced time-space separations as in Bell's story). Bell's theorem says it can't be done that way, and Bell's theorem is so incredibly elementary there can be no doubt about it. But if you don't trust elementary calculus and logic, then there is the experimental evidence: there have been 50 years for inventors of local hidden variables theories to come up with a computer simulation model which is a counterexample to Bell's theorem ... they haven't done it (and they won't, ever). And plenty have tried!

[harry]

[..]
I am looking for the experimental sources of the views that there is something superluminal going on, and I would like to see the connection made as directly as possible. [..]

Well here are a few for starters, although, as mentioned above, taken by themselves they are not so convincing. However, combined with each other and with other experiments, such experiments were sufficient to convince many people:

http://journals.aps.org/prl/abstract/10 ... tt.81.3563
At first sight here a correlation occurred that looks like immediate action at a distance.

http://www.nature.com/nature/journal/v4 ... 791a0.html
At first sight here we are dealing with "real objects" that were correlated in an unexplainable way, if one also adheres to the concept of "locality". Remember that "locality" concept is about more than just the speed; it's negation was called "spooky action at a distance".