Meaning of Spacetime Foliations [Archive]

stglyde

Dec17-11, 08:56 PM

We know that we didn't go from Galilian Invariance to Lorentz Invariance by just adding lenght contraction and time dilation. We also added the speed limit of light as c. So Lorentz Spacetime is a completely new foundation than Galilian Spacetime. And Spacetime foliation as I understood it being a slice of different nows and lengths giving rise to relativity of simultaneity. However, I can't understand what Tim Maudlin was talking about in the article "Non-Local Correlations in Quantum Theory: How the Trick Might Be Done" when he tried to make compatible Bohmian mechanics non-local nature by adding a new "Spacetime Foliation". Maudlin said:

If we begin with a non-Relativistic theory that makes essential use of absolute simultaneity, the most obvious (or perhaps crude and flat-footed) way to adapt the theory to a Relativistic space-time is to add a foliation to the space-time, a foliation that divides the space-time into a stack of space-like hyperplanes. One then employs these hyperplanes in place of absolute simultaneity in the original theory. If no attempt is made to produce a further account of the foliation, and it is accepted as intrinsic space-time structure, then such a theory will clearly fail, in the sense described above, to be Relativistic. But the way it fails is worthy of note: no positive part of the Relativistic account of space-time is being rejected: rather, in addition to the Lorentzian metric, a new structure is being added.

How does it differs to the normal Spacetime foliations in Lorentz Spacetime? Is Mauldin describing about adding Spacetime foliations to Newtonian absolute space and time. Or is it adding additional structure to Lorentz Spacetime? But why did he refer to it as spacetime foliations (which has generic meaning in SR as slicing of spacetime in relativity of simultaneity)? Also wouldn't this end up the same as Lorentz Spacetime? I just can't imagine how the two differs and want to know how their spacetime diagrams differ.

The following is prior to the above paragraph to give the context of what Maudlin was describing:

So for the purposes of this paper, we will adhere to two conditions for the physical theories we consider: first, each theory must have some local beables, and second, the physics must predict violations of Bell’s inequality for some possible experimental situations involving experiments performed on the localized objects at space-like separation. Bell’s result proves that this can occur only if the physics is irreducibly non-local, in the sense that the physics governing a beable at a particular space-time point cannot be exhausted by considering only the physical state in the past light-cone of that point. Even once we have conditionalized on the past light-cone, there must be further predictive improvements to be made by conditionalizing on events at space-like separation.

The central physical question, then, is which events at space-like separation must be taken into account and how they must be taken into account.

Until very recently, the only available fully articulated theories took a particular line of the “which?” question, a line that put the theories in tension with Relativity. These theories proceed in the most straightforward way to adapt non-local non-Relativistic theories to the Relativistic space-time, but in doing so, they are forced to add space-time structure, or the equivalent, to the physical picture. So if one interprets Relativity as demanding that the Lorentzian metric be all the space-time structure there is, these theories are not fully Relativistic. The theories need not reject the physical significance of the Lorentzian metric, but they do need to appeal to further space-time structure to formulate their laws. We will examine two examples of such theories first, and then turn to a recently discovered alternative theory, which is completely Relativistic. Our goal will be to assess, as far as we can, the advantages and demerits of these theories.

stglyde

Dec18-11, 05:45 PM

To those familiar with Mauldlin article. Is he talking about putting a preferred frame in SR to define the Bohmian frame of absolute simultaneity? If not. What is he talking about?

haushofer

Dec19-11, 04:06 AM

I don't understand

no positive part of the Relativistic account of space-time is being rejected: rather, in addition to the Lorentzian metric, a new structure is being added.

If you have a 1-dim spacetime foliation (a vector indicating the "time" direction and a 3-dim. spatial metric on the hypersurface), an absolute time will prevent you from constructing the "total metric" from these ingredients; there is no 4-dim. invariant spacetime interval. I would say there is no "Lorentz metric" to start with.

stglyde

Dec19-11, 08:11 AM

Say, are all preferred frames in SR automatically aether frame? If not. What are the preferred frames that don't use aether in SR? Bohmian mechanics are one of the intensively researched interpretations in Arxiv more than Many world Interpretation. And back to back with it is search for spacetime structure that can allow non-locality with beables.

ghwellsjr

Dec19-11, 11:48 AM

stglyde

Dec19-11, 01:35 PM

Any inertial frame in SR will be exactly like the presumed single aether rest state of LET. Any and all characteristics attributable to aether will also be applicable to any other inertial frame moving with respect to the aether that you want to choose. Can you think of any characteristic of the aether rest state for which this is not true?

What do you mean by "preferred frames in SR"? There is only one "preferred frame" and it's in LET, not SR, and nobody knows how to identify it.

In Bohmian mechanics, the wave function is sensitive to all configuration changes instantaneously throughout the universe. Any idea how to model this nonlocality in Special Relativity? I mentioned BM because in Copenhagen, since the wave function is not physical but just in the equations. There's nothing there to be non-local. But in BM, non-locality is its middle name. Let's avoid LET for now.

ghwellsjr

Dec20-11, 10:21 AM

Do you agree or disagree with my statement?
Any and all characteristics attributable to aether will also be applicable to any other inertial frame moving with respect to the aether that you want to choose.

stglyde

Dec20-11, 04:27 PM

Do you agree or disagree with my statement?

I agree but in Bohmian Mechanics, somehow the wave function can use the preferred frame, that is undetectable by us. So how does it do it?

ghwellsjr

Dec20-11, 04:51 PM

stglyde

Dec20-11, 05:07 PM

It does it the same way light propagates at c only in the aether frame and yet it also propagates at c in any other inertial frame moving with respect to the aether that you want to choose. Since you said you ageed with my statement, why are you asking about other specific examples?

It can't just propagate at c. This is because in Bohmian Mechanics, the wave function is sensitive to any configuration changes throughout the universe instantaneously. For example. The wave function of any object on earth can feel the configuration of any object say 20 billion light years away and instantaneously. So how does it do it?

ghwellsjr

Dec21-11, 02:24 AM

Are you saying that in Bohmian Mechanics, light does not propagate at c in the aether frame but rather instantaneously?

stglyde

Dec21-11, 05:56 AM

Are you saying that in Bohmian Mechanics, light does not propagate at c in the aether frame but rather instantaneously?

In BM. Light propagates at c but the wave function propagates instantaneously.

harrylin

Dec21-11, 06:58 AM

ghwellsjr

Dec21-11, 09:17 AM

Are you saying that in Bohmian Mechanics, light does not propagate at c in the aether frame but rather instantaneously?In BM. Light propagates at c but the wave function propagates instantaneously.
Are you saying that in Bohmian Mechanics, the wave function propagates instantaneously in the aether frame?

stglyde

Dec21-11, 09:34 AM

Are you saying that in Bohmian Mechanics, the wave function propagates instantaneously in the aether frame?

They used different languages like foliating spacetime specially such that absolute simultaneity can be arranged. I'm still reading on Maudlin book. But for the purpose of this message. Yup. One can say (for purpose of discussion) that in Bohmian Mechanics, the wave function propagates instantaneously in the aether frame. What's the problem with that?

ghwellsjr

Dec21-11, 01:23 PM

They used different languages like foliating spacetime specially such that absolute simultaneity can be arranged. I'm still reading on Maudlin book. But for the purpose of this message. Yup. One can say (for purpose of discussion) that in Bohmian Mechanics, the wave function propagates instantaneously in the aether frame. What's the problem with that?
I'm not saying it's a problem. I'm just saying that if it's true in the aether frame then it is also true in any other inertial frame moving with respect to the aether frame. What's the problem with that?

stglyde

Dec21-11, 04:19 PM

I'm not saying it's a problem. I'm just saying that if it's true in the aether frame then it is also true in any other inertial frame moving with respect to the aether frame. What's the problem with that?

I was thinking that only FTL with aether can avoid causality problem by the BM wave function always in instantaneous speed in the aether frame. So you are saying we can use plain SR and FTL and no causality problem by making the FTL true in every inertial frame?? Hmm....

harrylin

Dec22-11, 04:31 AM

I'm not saying it's a problem. I'm just saying that if it's true in the aether frame then it is also true in any other inertial frame moving with respect to the aether frame. What's the problem with that?
To hold that an influence can also be instantaneous in any other inertial frame creates a self contradiction: except for one specific direction, an instantaneous influence in one standard inertial reference system (the "ether frame") is determined (or defined) as an influence forward or backward in time in other such systems that are in uniform motion relative to the first one.

PS: But certainly you know that, so I guess that you meant something else than what you appeared to say. :smile:

TrickyDicky

Dec22-11, 04:59 AM

I think one significative property such a frame has is that it seems a way (the only one I know) of reconciling Quantum nonlocality and local realism. Something that is usually considered as impossible. Then again we don't seem to have empirical evidence of such frame (though this is debatable), and it is also apparently incompatible with GR cosmological models (also a moot point IMO).

ghwellsjr

Dec22-11, 11:46 AM

I'm not saying it's a problem. I'm just saying that if it's true in the aether frame then it is also true in any other inertial frame moving with respect to the aether frame. What's the problem with that?To hold that an influence can also be instantaneous in any other inertial frame creates a self contradiction: except for one specific direction, an instantaneous influence in one standard inertial reference system (the "ether frame") is determined (or defined) as an influence forward or backward in time in other such systems that are in uniform motion relative to the first one.

PS: But certainly you know that, so I guess that you meant something else than what you appeared to say. :smile:
I'm saying that any inertial frame you want to pick will have all the attributes of a presumed aether frame, otherwise, we would have a way to identify the rest state of the aether and that would make headlines and since it hasn't made any headlines, it must not be the case.

ghwellsjr

Dec22-11, 03:02 PM

Or to put it another way--let's suppose that instead of Michelson and Morley proposing MMX to detect aether wind, they proposed an experiment to detect the rest state of the aether by seeing if the speed of light was the same in all directions. It would be exactly the same experiment but with a different stated goal. Then, the very first time they performed their experiment they would have declared success--they had found the absolute rest state of the aether.

So whatever experiment Bohmian Mechanics wants to propose to detect the absolute preferred rest state of the aether will yield a positive result the first time it is performed.

Qzit

Dec22-11, 08:47 PM

What if the rest state is "C" and mass is a reduction of "c"?

harrylin

Dec23-11, 04:07 AM

I'm saying that any inertial frame you want to pick will have all the attributes of a presumed aether frame, otherwise, we would have a way to identify the rest state of the aether and that would make headlines and since it hasn't made any headlines, it must not be the case.

Yes - obviously that would break the symmetry of the phenomena! :smile:

stglyde

Dec23-11, 07:49 AM

Before we get to very complicated spacetime diagrams. Let's first review some basic.

In SR between two inertial frames moving with respect to each other for example in the Twin Paradox. The home twin will measure the travelling twin light mirror lightspeed as travelling at c all the time, right.

In LET between two inertial frames moving with respect to each other for example in the Twin Paradox. The home twin will measure the travelling twin light mirror lightspeed as varying depending on the motion with respect to each other, right?

But according to ghwellsjr "I'm saying that any inertial frame you want to pick will have all the attributes of a presumed aether frame"... how do you apply this to the above? In the Twin Paradox, what is the aether frame?

harrylin

Dec23-11, 08:19 AM

Before we get to very complicated spacetime diagrams. Let's first review some basic.

[1] In SR between two inertial frames moving with respect to each other for example in the Twin Paradox. The home twin will measure the travelling twin light mirror lightspeed as travelling at c all the time, right.

[2] In LET between two inertial frames moving with respect to each other for example in the Twin Paradox. The home twin will measure the travelling twin light mirror lightspeed as varying depending on the motion with respect to each other, right?

But according to ghwellsjr "I'm saying that any inertial frame you want to pick will have all the attributes of a presumed aether frame"... how do you apply this to the above? In the Twin Paradox, what is the aether frame?

There can be no difference between [1] and [2]: the exact same measurements are performed, and no model to explain the measurements can affect those measurements.

According to SR it is not possible to track our motion relatively to such a frame, if it exists; and it is not part of the theory. According to Langevin, his thought experiment therefore merely detects the existence of such an ether frame. Here's his summary statement preceding that thought experiment:

In all the above, the employed reference systems are supposed to possess uniform translational motion: for only such systems, observers associated with them cannot experimentally detect their collective motion, only for such systems the equations of physics must hold their shape when switching from one to another. For such systems it is thus, as if they were stationary relative to the aether: a uniform translation in the aether has no experimental sense.

But because of this it should not be concluded, as has sometimes happened prematurely, that the concept of aether must be abandoned, that the aether is non-existent and inaccessible to experiment. Only a uniform velocity relative to it cannot be detected, but any change of velocity, or any acceleration has an absolute sense.
- p.47 of http://en.wikisource.org/wiki/The_Evolution_of_Space_and_Time

That I understand; however, as is the topic here, now Maudlin suggests something like that as well as two(?) other possible explanations. Is there anyone here who understands those other ones? :uhh:

stglyde

Dec23-11, 08:43 AM

There can be no difference between [1] and [2]: the exact same measurements are performed, and no model to explain the measurements can affect those measurements.

According to SR it is not possible to track our motion relatively to such a frame, if it exists; and it is not part of the theory. According to Langevin, his thought experiment therefore merely detects the existence of such an ether frame. Here's his summary statement preceding that thought experiment:

- p.47 of http://en.wikisource.org/wiki/The_Evolution_of_Space_and_Time

That I understand; however, as is the topic here, now Maudlin suggests something like that as well as two(?) other possible explanations. Is there anyone here who understands those other ones? :uhh:

Have you not read Maudlin article called "Non-Local Correlations in Quantum Theory: How the Trick Might Be Done". Anyway. Tumulka stuff was a topic in Scientific American March 2009 edition called "Was Einstein Wrong?: A Quantum Threat to Special Relativity"

http://www.scientificamerican.com/article.cfm?id=was-einstein-wrong-about-relativity

Here's sample of what's being said:

"Hope for Special Relativity?

Two new results—pulling in curiously different directions—have emerged from this discussion in just the past few years. The first suggests a way
that quantum-mechanical nonlocality could be compatible with special relativity; the other reveals a new blow that the combination of quantum mechanics and special relativity strikes against our deepest intuitions of the world.

The first result appeared in an astonishing 2006 paper by Roderich Tumulka, a young German mathematician now at Rutgers. Tumulka showed how all the empirical predictions of quantum mechanics for entangled pairs of particles could be reproduced by a clever modification of the GRW theory (recall that this theory proposes a philosophically realist way to get the predictions of quantum mechanics under many circumstances). The modification is nonlocal, and yet it is fully compatible with the spacetime geometry of special relativity.

This work is still very much in its infancy. No one has yet been able to write down a satisfactory
version of Tumulka’s theory that can be applied to particles that attract or repel one another.
Moreover, his theory introduces a new variety of nonlocality into the laws of nature—a nonlocality not merely in space but in time! To use his theory to determine the probabilities of what happens next, one must plug in not only the world’s current complete physical state (as is customary in a physical theory) but also certain facts about the past. That feature and some others are worrying, but Tumulka has certainly taken away some of the grounds for Maudlin’s fear that quantum-mechanical nonlocality cannot be made to peacefully coexist with special relativity.

Just read the rest from Sci-Am. I don't like Tumulka's theory. If it can't even describe particles that attract or repel. I'd say it's such a long way.. much worse than Bohmian Mechanics.

ghwellsjr

Dec23-11, 09:39 AM

stglyde

Dec23-11, 05:31 PM

I'm afraid I don't understand what you mean by "The home twin will measure the travelling twin light mirror lightspeed as..." What exactly is the measurement you are describing here?

In SR, Home Twin would measure Travelling Twin time as dilated and length as contracted. But it would still measure the light travelling in Travelling Twin inertial frame as c. But in LET, the Home Twin would measure the light traveling in Travelling Twin inertial frame as varying depending on the velocity. I got this from PeterDonis where he mentioned about Frame-dependent thing in message #7 in the thread SR, LET, FTL & Causality Violation where he mentioned in the following:

There actually is one other assumption required in this scenario: that the spacelike curve the tachyon fired from the pistol follows is frame-dependent; the usual assumption appears to be that the tachyon velocity v is fixed relative to the emitter (the pistol in this case). For example, if you look at a typical scenario that uses tachyons to create closed loops, where A sends a message to B and then receives B's reply *before* he sent the original message, in order for the reasoning to go through, it has to be the case that tachyons emitted by B travel along spacelike curves that are not parallel to the curves followed by tachyons emitted by A--put another way, B's tachyons travel at some fixed v > c relative to B, while A's tachyons travel at the same v > c relative to A; but B's tachyons do *not* travel at v relative to A. (If they did, they would not be going backwards in time relative to A, so A could never receive B's reply before he sent his message.)

Peterdonis above mentioned that "B's tachyons do *not* travel at v relative to A", this means even light do not travel at c relative to each other in LET. Do you believe this?

ghwellsjr

Dec23-11, 07:16 PM

In SR, Home Twin would measure Travelling Twin time as dilated and length as contracted.
Measurements are made without regard to any theory and only theories that explain all measurements will survive. But it would still measure the light travelling in Travelling Twin inertial frame as c. But in LET, the Home Twin would measure the light traveling in Travelling Twin inertial frame as varying depending on the velocity.
No theory allows for you to measure how light travels. SR and LET have different definitions of how light travels and there is no measurement that favors one theory over the other.
I got this from PeterDonis where he mentioned about Frame-dependent thing in message #7 in the thread SR, LET, FTL & Causality Violation where he mentioned in the following:

Peterdonis above mentioned that "B's tachyons do *not* travel at v relative to A", this means even light do not travel at c relative to each other in LET. Do you believe this?
I believe anything Peter says but I don't see where he said anything different than what I'm saying.

stglyde

Dec23-11, 07:47 PM

Measurements are made without regard to any theory and only theories that explain all measurements will survive.
No theory allows for you to measure how light travels. SR and LET have different definitions of how light travels and there is no measurement that favors one theory over the other.

I believe anything Peter says but I don't see where he said anything different than what I'm saying.

For there to be paradox, the following needs to be the case:

B's tachyons travel at some fixed v > c relative to B,
while A's tachyons travel at the same v > c relative to A;
but B's tachyons do *not* travel at v relative to A.

However, in Bohmian non-locality, the tachyon equavalent is instantaneous, then how does one make a version of the above, like:

B's insta-tachyons travel at some fixed instantaneous velocity relative to B,
while A's tachyons travel at the same fixed instantaneous velocity relative to A;
but B's instantaneous tachyons do *not* travel at v relative to A??

It should because it's instantaneous. But yet paradox still occurs as our Tachyon pistol example.

ghwellsjr, you may not understand the subtlety of what I'm describing here.

This problem has been consuming me for 5 days already. I wrote Peterdonis a private message asking it 5 days ago and no replies yet. Maybe he misses it, so hope he can address it here as it's what preventing me from fully comprehending the spacetime diagrams of Mauldin article.

ghwellsjr

Dec23-11, 08:36 PM

What experiment involving tachyons are you proposing that gives different measurements in different frames?

stglyde

Dec23-11, 09:00 PM

What experiment involving tachyons are you proposing that gives different measurements in different frames?

I don't know. I just want to understand for now what Peterdonis was describing. I know LET and SR is the same, and I try to understand LET so one become more conversant with SR. Going back to the following. For there to be paradox (in LET), the following needs to be the case:

B's tachyons travel at some fixed v > c relative to B,
while A's tachyons travel at the same v > c relative to A;
but B's tachyons do *not* travel at v relative to A."

In plain old SR. Can you give an example where something has to travel at a fixed velocity relative to A and B and not common to both (frame dependent)?

stglyde

Dec23-11, 09:44 PM

What experiment involving tachyons are you proposing that gives different measurements in different frames?

After rereading again and again the other thread esp. messages by Peterdonis. I think I am seeing what he is describing. In the tachyon pistol duel scenerio we discussed. If the ether frame is used, then when A shoot the pistol at 8 seconds.. instead of B being hit at 4 seconds (due to time dilation factor of 2), B would also be hit in 8 seconds also.. because in the ether frame, both frames can be seen to be ticking at the same time. Right?! I know this is lorentz violation for at least the tachyon velocity. I know you'd say that in SR and LET, they are equivalent in that what happens in one frame in LET happens to all the frames in SR. So we can say the Bohmian Mechanics Wave functions instantaneous velocity is a lorentz violation and it uses the Ether frame only. Since our world is only composed of particles, then no problem with BM wave function having lorentz violations. Maybe this is what Mauldlin meant by foliation of spacetime in BM, isn't it. Now do you see any problem with BM wave functions having lorentz violations? Any conflict with other stuff like Quantum Field Theory or none at all?

DaleSpam

Dec23-11, 10:27 PM

In plain old SR. Can you give an example where something has to travel at a fixed velocity relative to A and B and not common to both (frame dependent)?A standard pistol. The muzzle velocity is relative to the pistol, in other frames it may not travel at the muzzle velocity.

stglyde

Dec23-11, 10:43 PM

A standard pistol. The muzzle velocity is relative to the pistol, in other frames it may not travel at the muzzle velocity.

Oh. Of course, the famous relativity of simultaneity. I remembered the train example. What changed due to the observer's velocity relative to the train is the relationship between measuring instrument and train.

PeterDonis

Dec23-11, 11:47 PM

If the ether frame is used, then when A shoot the pistol at 8 seconds.. instead of B being hit at 4 seconds (due to time dilation factor of 2), B would also be hit in 8 seconds also.. because in the ether frame, both frames can be seen to be ticking at the same time. Right?!

If the frame in which the diagram for that scenario was drawn is the ether frame, and if tachyons were assumed to be "instantaneous" in the ether frame, then yes, A and B would both fire their tachyon pistols at t = 8 sec in the ether frame, and both pistol shots would hit at t = 8 sec in the ether frame.

Of course, in any other frame, the shots would not travel "instantaneously"; in any other frame, one would appear to travel forward in time and one would appear to travel backward in time. So the term "instantaneous" is not an invariant; even in an ether theory, a tachyon can only travel between two points "instantaneously" as seen in one specific frame. That wouldn't change the result of the duel because the motion of A and B would also look different in any other frame, so it would still turn out that A's shot hit B just as B was firing, and vice versa. But the tachyons would no longer travel "instantaneously".

I know this is lorentz violation for at least the tachyon velocity. I know you'd say that in SR and LET, they are equivalent in that what happens in one frame in LET happens to all the frames in SR.

I think you're misunderstanding ghwellsjr's comments on this. SR and LET use the same mathematics; they just put different interpretations on it. So if LET says some particular equation applies "in the ether frame", and that equation is expressed in covariant form, then that equation will apply in all frames, whether you use SR or LET to interpret the equation.

But if you explicitly violate covariance, for example by specifying that tachyon velocity is always some specific v > c relative to a specific frame, which you call the "ether frame", then the tachyon velocity will be different in some other frame, because you specified that this particular phenomenon violates covariance. (The case of "instantaneous" tachyons is just the case v = infinity relative to the ether frame.)

So we can say the Bohmian Mechanics Wave functions instantaneous velocity is a lorentz violation and it uses the Ether frame only.

Bohmian Mechanics is explicitly non-relativistic; AFAIK nobody has ever succeeded in making a relativistic version. So Bohmian Mechanics doesn't even address this question; it simply can't be applied to relativistic phenomena at all.

PeterDonis

Dec23-11, 11:53 PM

Peterdonis above mentioned that "B's tachyons do *not* travel at v relative to A", this means even light do not travel at c relative to each other in LET. Do you believe this?

I should add to my previous post the important qualification that light still travels at c in all frames, even if we start considering possibilities like tachyons. Both SR and LET use the same math, as I said, including the Lorentz transformations; and the Lorentz transformations ensure that anything that moves at c in one frame, moves at c in all frames. So the stuff I was saying about tachyons does *not* apply to light.

(Of course, if you're willing to allow tachyons to explicitly violate Lorentz covariance, you could try to concoct a theory where light did too; but at that point you'd basically be starting from scratch, since if you can't rely on the Lorentz transformations being right you've basically gotten rid of all the math of SR/LET anyway, so you're on your own. I've been assuming that we aren't going to go there.)

stglyde

Dec24-11, 12:09 AM

If the frame in which the diagram for that scenario was drawn is the ether frame, and if tachyons were assumed to be "instantaneous" in the ether frame, then yes, A and B would both fire their tachyon pistols at t = 8 sec in the ether frame, and both pistol shots would hit at t = 8 sec in the ether frame.

Of course, in any other frame, the shots would not travel "instantaneously"; in any other frame, one would appear to travel forward in time and one would appear to travel backward in time. So the term "instantaneous" is not an invariant; even in an ether theory, a tachyon can only travel between two points "instantaneously" as seen in one specific frame. That wouldn't change the result of the duel because the motion of A and B would also look different in any other frame, so it would still turn out that A's shot hit B just as B was firing, and vice versa. But the tachyons would no longer travel "instantaneously".

Thanks for your explanation. It's much clearer now. For many nights, these thoughts have consumed me.

But why is "in any other frame, the shots would not travel "instantaneously"? What principle prohibits that? Maybe because c is still the limit and tachyons just special? But if c and all particles are instantaneous. Then everything would look instantaneous in every frame, agree?
And we are back to Galilean spacetime where even gravity travels instantaneously.

I think you're misunderstanding ghwellsjr's comments on this. SR and LET use the same mathematics; they just put different interpretations on it. So if LET says some particular equation applies "in the ether frame", and that equation is expressed in covariant form, then that equation will apply in all frames, whether you use SR or LET to interpret the equation.

But if you explicitly violate covariance, for example by specifying that tachyon velocity is always some specific v > c relative to a specific frame, which you call the "ether frame", then the tachyon velocity will be different in some other frame, because you specified that this particular phenomenon violates covariance. (The case of "instantaneous" tachyons is just the case v = infinity relative to the ether frame.)

Bohmian Mechanics is explicitly non-relativistic; AFAIK nobody has ever succeeded in making a relativistic version. So Bohmian Mechanics doesn't even address this question; it simply can't be applied to relativistic phenomena at all.

PeterDonis

Dec24-11, 01:46 AM

But why is "in any other frame, the shots would not travel "instantaneously"? What principle prohibits that?

The Lorentz transformation. As I said, I was assuming that the only violation of Lorentz invariance being proposed was the specific violation of the tachyon itself, and that everything else was still to remain as it is in SR. If you get rid of the Lorentz transformation in general, you're basically on your own.

Maybe because c is still the limit and tachyons just special? But if c and all particles are instantaneous. Then everything would look instantaneous in every frame, agree? And we are back to Galilean spacetime where even gravity travels instantaneously.

And we are also in gross violation of many, many experiments, so that's not a viable option. That's another reason why I assumed that the *only* violation of Lorentz invariance was the specific violation of the tachyon velocity being fixed relative to a particular frame.

stglyde

Dec24-11, 02:30 AM

The Lorentz transformation. As I said, I was assuming that the only violation of Lorentz invariance being proposed was the specific violation of the tachyon itself, and that everything else was still to remain as it is in SR. If you get rid of the Lorentz transformation in general, you're basically on your own.

And we are also in gross violation of many, many experiments, so that's not a viable option. That's another reason why I assumed that the *only* violation of Lorentz invariance was the specific violation of the tachyon velocity being fixed relative to a particular frame.

Presently. Quantum non-locality has 3 explanations:

1. Many Worlds where there is really no non-locally but just a result of matching up.
2. Copenhagen where the wave functions don't exist physically.. so since there is no beables in spacetime.. then there is nothing to be non-local about. Everything is just wave function, spacetime manifolds and equations and one must simply hide it under the rug.
3. Bohmian version where the wave function is a beable existing in spacetime and non-local and has instantaneous velocity and it moving fixed relative to a particular frame.

The last is identical to the situation we were discussing about "tachyon velocity being fixed relative to a particular frame" or wave function being fixed relative to a particular frame, agree? In other words, can you equate tachyons velocity with BM wave function velocity?. And if this not viable, then only possibility 1 and 2 exist. Are you saying #3 is not viable? And why?

stglyde

Dec24-11, 03:56 AM

I don't understand

If you have a 1-dim spacetime foliation (a vector indicating the "time" direction and a 3-dim. spatial metric on the hypersurface), an absolute time will prevent you from constructing the "total metric" from these ingredients; there is no 4-dim. invariant spacetime interval. I would say there is no "Lorentz metric" to start with.

Haushofer, have you not yet understand what Maudlin was describing? In another article "Space-Time in the Quantum World" I saw at google, he described it in other words (see if you can pick up what he was referring to):

"What Bohm's theory and the collapse theories seem to need is something like the classical notion of absolute simultaneity: a fundamental physical relation between events at space-like separation. In effect, such a relation would induce a foliation (italics) of the space-time, a division of the spacetime manifold into a stack of space-like hyperplanes. Putting a measure over those hyperplanes yields an absolute time-function in terms of which the Bohmian dynamics or the collapse dynamics can be framed."

PeterDonis, any idea what Mauldlin was talking about? See thread message #1 for his other statements. Many of us are at a loss what he Mauldin was describing. Maybe you know what and can assist us.

stglyde

Dec24-11, 08:06 AM

Interesting!
I didn't know that article (although I now had a quick look at it); but I do have (and read) his book "Quantum Non-Locality and Relativity". One of the possible options that he mentions in view of Bell's theorem (which he takes for granted) and relating to Bohm's explanation is the existence of what he calls a "preferred frame", with which he obviously does not really mean a preferred but an "absolute" frame - just as Bell did before him.

So, perhaps he means with "further space-time structure" simply the addition of a Lorentz-Einstein ether, in which, as he mentions, "absolute simultaneity" exists although we cannot detect it ("not empirically accessible"). However, he calls such an interpretation of relativity not "completely relativistic" and presents another interpretation by Tumulka which he does hold to be completely relativistic - but which I do not understand (and neither do I understand the one by Ghirardi).
Anyone else?

Harald

Harald.. why don't you read this Tumulka paper http://arxiv.org/abs/quant-ph/0406094 about "A Relativistic Version of the Ghirardi-Rimini-Weber Model". Many physicists are interested in it because it is completely relativistic formulation of non-locality with beables (collapse model). Can you find any flaw with it that can kill the theory?

Btw.. I also owned Maudlin 2nd edition Quantum Non-Locality and Relativity. It's now in its third edition (May, 2011) which includes Tumulka relativistic GRW. I'll review the book.

PeterDonis

Dec24-11, 11:44 AM

3. Bohmian version where the wave function is a beable existing in spacetime and non-local and has instantaneous velocity and it moving fixed relative to a particular frame.

As I said before, this is *not* Bohmian Mechanics, which is explicitly non-relativistic and does not even deal with the matter of changing reference frames at all. Bohmian Mechanics uses the Schrodinger Equation, which is explicitly non-relativistic and can't be transformed from frame to frame, at least not without making predictions that grossly contradict experiments. So the same is true for Bohmian Mechanics.

Another way of putting this is that we know the Schrodinger Equation is not correct; it is only an approximation that is valid if everything is moving slowly compared to the speed of light. As soon as you start talking about "instantaneous" wavefunction collapse over a significant spatial distance, you are violating that restriction. For experiments confined to a single lab, you can get away with this, but it won't work in general.

The last is identical to the situation we were discussing about "tachyon velocity being fixed relative to a particular frame" or wave function being fixed relative to a particular frame, agree? In other words, can you equate tachyons velocity with BM wave function velocity?. And if this not viable, then only possibility 1 and 2 exist. Are you saying #3 is not viable? And why?

I'm saying nobody has an actual theory corresponding to #3; the theory of Bohmian Mechanics is not it because it does not deal with changing reference frames at all. AFAIK nobody has actually come up with a consistent relativistic version of Bohmian Mechanics. So there's no way to tell what the "instantaneous wavefunction velocity" would become in a version of Bohmian Mechanics that could actually deal with more than one reference frame.

PeterDonis

Dec24-11, 12:04 PM

PeterDonis, any idea what Mauldlin was talking about? See thread message #1 for his other statements. Many of us are at a loss what he Mauldin was describing. Maybe you know what and can assist us.

I can't say for sure since I haven't read the book or article you are taking these quotes from. so I don't know if he's talking about just something speculative or if he's actually referring to a paper or papers making a serious attempt to extend Bohmian Mechanics or something similar to a relativistic theory. In the quote at the end of the OP there is a reference to a "recently discovered alternative theory", but no link or paper title is given. But I can speculate based on the quotes given.

The general meaning of the term "foliation" is clear, of course: it's a slicing of spacetime into a "stack" of 3-D spacelike hypersurfaces, each of which is viewed as a "surface of constant time" according to some family of observers. The family of observers is the described by a congruence of timelike worldlines such that each worldline passes through one and only one point of each hypersurface. Each worldline then can be viewed as labeling a "point in space" occupied by the observer traveling along it.

In general, any given spacetime will have an infinite number of different possible foliations, so it looks like what Mauldin is proposing is to label one such foliation as "preferred" with respect to wavefunction collapse. In other words, any given wavefunction collapse would have to occur "instantaneously" with respect to that particular foliation only. For example, suppose I am traveling along one particular worldline A picked from the congruence of worldlines described above; in other words, I am at rest at "spatial point A" with respect to the preferred foliation. I receive one of a pair of entangled particles, the other of which is sent off in the opposite direction. When I receive my particle, I measure it in a way that collapses the joint wavefunction of both particles; this measurement takes place at time t0 with respect to the preferred foliation, i.e., it takes place at the event where my worldline A intersects the hypersurface marked t = t0. Then, according to the type of theory Mauldin is proposing, the wavefunction of the other particle in the entangled pair also collapses at the event where its worldline intersects the t = t0 hypersurface.

Of course this violates Lorentz invariance in a way similar to the tachyon pistol when we specified that its velocity was fixed relative to the ether frame, instead of relative to the pistol. In both cases, there is an obvious question: what, physically, picks out *that* particular frame, that particular foliation, as being "special"? Just saying "it's the ether frame", or "it's the foliation my theory picks out", won't do; there should be some *physical* property that picks out one foliation over another.

stglyde

Dec24-11, 01:09 PM

I can't say for sure since I haven't read the book or article you are taking these quotes from. so I don't know if he's talking about just something speculative or if he's actually referring to a paper or papers making a serious attempt to extend Bohmian Mechanics or something similar to a relativistic theory. In the quote at the end of the OP there is a reference to a "recently discovered alternative theory", but no link or paper title is given. But I can speculate based on the quotes given.

Oh, the recently discovered alternative theory Maudlin is referring to is the paper by Tumulka at http://arxiv.org/abs/quant-ph/0406094 about "A Relativistic Version of the Ghirardi-Rimini-Weber Model". Many physicists are interested in it because it is completely relativistic formulation of non-locality with beables (collapse model or even BM). Can you find any flaw with it that can kill the theory?

The general meaning of the term "foliation" is clear, of course: it's a slicing of spacetime into a "stack" of 3-D spacelike hypersurfaces, each of which is viewed as a "surface of constant time" according to some family of observers. The family of observers is the described by a congruence of timelike worldlines such that each worldline passes through one and only one point of each hypersurface. Each worldline then can be viewed as labeling a "point in space" occupied by the observer traveling along it.

In general, any given spacetime will have an infinite number of different possible foliations, so it looks like what Mauldin is proposing is to label one such foliation as "preferred" with respect to wavefunction collapse. In other words, any given wavefunction collapse would have to occur "instantaneously" with respect to that particular foliation only. For example, suppose I am traveling along one particular worldline A picked from the congruence of worldlines described above; in other words, I am at rest at "spatial point A" with respect to the preferred foliation. I receive one of a pair of entangled particles, the other of which is sent off in the opposite direction. When I receive my particle, I measure it in a way that collapses the joint wavefunction of both particles; this measurement takes place at time t0 with respect to the preferred foliation, i.e., it takes place at the event where my worldline A intersects the hypersurface marked t = t0. Then, according to the type of theory Mauldin is proposing, the wavefunction of the other particle in the entangled pair also collapses at the event where its worldline intersects the t = t0 hypersurface.

Of course this violates Lorentz invariance in a way similar to the tachyon pistol when we specified that its velocity was fixed relative to the ether frame, instead of relative to the pistol. In both cases, there is an obvious question: what, physically, picks out *that* particular frame, that particular foliation, as being "special"? Just saying "it's the ether frame", or "it's the foliation my theory picks out", won't do; there should be some *physical* property that picks out one foliation over another.

Thanks. I'll think about it.

stglyde

Dec24-11, 08:22 PM

I can't say for sure since I haven't read the book or article you are taking these quotes from. so I don't know if he's talking about just something speculative or if he's actually referring to a paper or papers making a serious attempt to extend Bohmian Mechanics or something similar to a relativistic theory. In the quote at the end of the OP there is a reference to a "recently discovered alternative theory", but no link or paper title is given. But I can speculate based on the quotes given.

The general meaning of the term "foliation" is clear, of course: it's a slicing of spacetime into a "stack" of 3-D spacelike hypersurfaces, each of which is viewed as a "surface of constant time" according to some family of observers. The family of observers is the described by a congruence of timelike worldlines such that each worldline passes through one and only one point of each hypersurface. Each worldline then can be viewed as labeling a "point in space" occupied by the observer traveling along it.

In general, any given spacetime will have an infinite number of different possible foliations, so it looks like what Mauldin is proposing is to label one such foliation as "preferred" with respect to wavefunction collapse. In other words, any given wavefunction collapse would have to occur "instantaneously" with respect to that particular foliation only. For example, suppose I am traveling along one particular worldline A picked from the congruence of worldlines described above; in other words, I am at rest at "spatial point A" with respect to the preferred foliation. I receive one of a pair of entangled particles, the other of which is sent off in the opposite direction. When I receive my particle, I measure it in a way that collapses the joint wavefunction of both particles; this measurement takes place at time t0 with respect to the preferred foliation, i.e., it takes place at the event where my worldline A intersects the hypersurface marked t = t0. Then, according to the type of theory Mauldin is proposing, the wavefunction of the other particle in the entangled pair also collapses at the event where its worldline intersects the t = t0 hypersurface.

Of course this violates Lorentz invariance in a way similar to the tachyon pistol when we specified that its velocity was fixed relative to the ether frame, instead of relative to the pistol. In both cases, there is an obvious question: what, physically, picks out *that* particular frame, that particular foliation, as being "special"? Just saying "it's the ether frame", or "it's the foliation my theory picks out", won't do; there should be some *physical* property that picks out one foliation over another.

I think this is what Maudlin meant. So you are saying that instead of referring to LET and its ether frame. One can just speak of Preferred Foliation to refer to the same idea without mentioning a word about LET?? In other words, Preferred Foliation is the same Ether frame in LET? In our examples. We use tachyons moving at v>c relative to the aether frame. Translating this to language of Preferred Foliation. One can say the tachyons moving at v>c relative to the Preferred Foliation (which doesn't necessarily involve the aether frame)? If the two are different. Then what is the Preferred Foliation equivalent in LET that is in addition to the aether frame?

PeterDonis

Dec24-11, 08:59 PM

So you are saying that instead of referring to LET and its ether frame. One can just speak of Preferred Foliation to refer to the same idea without mentioning a word about LET??

I'm not sure they're the same idea. LET does claim that there is some Lorentz frame that is an "ether frame", but it doesn't claim that the existence of this frame has any physically detectable consequences. The kind of "preferred foliation" that Mauldin is talking about would have physically detectable consequences; you could in principle detect the "preferred frame" defined by the preferred foliation by accurately timing wavefunction collapses using detectors in different states of motion.

In our examples. We use tachyons moving at v>c relative to the aether frame. Translating this to language of Preferred Foliation. One can say the tachyons moving at v>c relative to the Preferred Foliation (which doesn't necessarily involve the aether frame)?

If we specify that tachyons always move at some fixed v > c relative to the aether frame, then the aether frame is physically detectable (just fire tachyon pistols in different states of motion); so it would count as a "preferred foliation" in Mauldin's terminology (if I have correctly captured what he intended by that term).

stglyde

Dec24-11, 09:30 PM

I'm not sure they're the same idea. LET does claim that there is some Lorentz frame that is an "ether frame", but it doesn't claim that the existence of this frame has any physically detectable consequences. The kind of "preferred foliation" that Mauldin is talking about would have physically detectable consequences; you could in principle detect the "preferred frame" defined by the preferred foliation by accurately timing wavefunction collapses using detectors in different states of motion.

If we specify that tachyons always move at some fixed v > c relative to the aether frame, then the aether frame is physically detectable (just fire tachyon pistols in different states of motion); so it would count as a "preferred foliation" in Mauldin's terminology (if I have correctly captured what he intended by that term).

Uhm. We commonly use the term "Preferred Frame" and "Preferred Foliation" is not commonly use. So Is "Preferred Frame" and "Preferred Foliation" exactly the same meaning or is there any subtle difference between them?

PeterDonis

Dec24-11, 09:35 PM

Uhm. We commonly use the term "Preferred Frame" and "Preferred Foliation" is not commonly use. So Is "Preferred Frame" and "Preferred Foliation" exactly the same meaning or is there any subtle difference between them?

I don't know that "preferred foliation" has a commonly accepted meaning; as you say, it's not in common use. The term "preferred frame" is used fairly often, but people seem to mean different things by its use; some use it to indicate a frame that is in principle physically detectable, others use it to indicate a frame like the LET aether frame that can't be physically detected even in principle. The best advice I can give is to ask for clarification whenever you see either of these terms used.

stglyde

Dec24-11, 10:56 PM

I don't know that "preferred foliation" has a commonly accepted meaning; as you say, it's not in common use. The term "preferred frame" is used fairly often, but people seem to mean different things by its use; some use it to indicate a frame that is in principle physically detectable, others use it to indicate a frame like the LET aether frame that can't be physically detected even in principle. The best advice I can give is to ask for clarification whenever you see either of these terms used.

But foliation has same meaning has frame as when you mentioned in message #76 in the other thread:

a "frame" is a particular way of *describing* the 4-D spacetime by slicing it up (in Gardner's terminology) into 3-D slices (which are then called "surfaces of simultaneity" or "slices of constant time" or something like that) such that (a) each 3-D slice is labeled by a unique value of a fourth coordinate, "time" ("fourth" because it takes three coordinates to specify a point in each 3-D slice), and (b) each event in the spacetime appears in one and only one 3-D slice. Particular objects are then 4-D subregions of the whole 4-D spacetime, and different ways of slicing will "cut" the subregions at different angles, so the shapes of the slices of the objects will be different.

So it is also right that "a "foliation" is a particular way of *describing* the 4-D spacetime by slicing it up (in Gardner's terminology) into 3-D slices (which are then called "surfaces of simultaneity" or "slices of constant time" or something like that)..."??

So frame and foliation has same meaning... but why do the word "foliation" is not used much?

About LET ether being undetectable and the Preferred Foliation being detectable. First read the following by John Bell:

" I think it’s a deep dilemma, and the resolution of it will not be trivial; it will require a substantial change in the way we look at things. But I would say that the cheapest resolution is something like going back to relativity as it was before Einstein, when people like Lorentz and Poincare ´ thought that there was an aether – a preferred frame of reference – but that our measuring instruments were distorted by motion in such a way that we could not detect motion through the aether. . . . that is certainly the cheapest solution. Behind the apparent Lorentz invariance of the phenomena, there is a deeper level which is not Lorentz invariant. . . . what is not sufficiently emphasized in textbooks, in my opinion, is that the pre-Einstein position of Lorentz and Poincare´, Larmor and Fitzgerald was perfectly coherent, and is not inconsistent with relativity theory. The idea that there is an aether, and these Fitzgerald contractions and Larmor dilations occur, and that as a result the instruments do not detect motion through the aether – that is a perfectly coherent point of view. . . . The reason I want to go back to the idea of an aether here is because in these EPR experiments there is the suggestion that behind the scenes something is going faster than light. Now if all Lorentz frames are equivalent, that also means that things can go backward in time. . . . [this] introduces great problems, paradoxes of causality, and so on. And so it is precisely to avoid these that I want to say there is a real causal sequence which is defined in the aether. (‘‘John Bell,’’ (1986) interview in Davies and Brown; cf. Bell 1987: 279; see also Bell 1984: 66–76)

Now the LET ether is said to be undetectable. But can't we say that Entanglement experiments make it detectable because it uses the LET ether frame as Bell wanted to suggest?

In other words. Particles like fermions and bosons are ruled by SR and don't use the aether frame, while only wave function use the aether frame. Is this not possible?

Well. I know gauge theory which says locality and gauge principle is what created the gauge bosons in the first place (when you have to add cheating terms to the wave function to make it vary from place to place.. i got this very clear from Schumm book Deep Down Things). So this gauge principle is what make it impossible that the wave function use the aether frame right?

This is the reason Maudlin is so excited about the completely relativistic GRW with flash (in the paper shared a few message prior to this). But I think it is very much in infancy.

So right now the safest bet is Copenhagen where since the wave function is just in the equations, there is nothing to be non-local about. This means one must only see Spacetime as equations and wave functions and spacetimes are models about reality and we only have models to reality and nothing further that can be know... end of story. We must not think of any physical sense to them or we may not be able to reconcile non-local equations. Is this what you also believe?

bohm2

Dec24-11, 11:23 PM

".Bohmian Mechanics is explicitly non-relativistic; AFAIK nobody has ever succeeded in making a relativistic version. So Bohmian Mechanics doesn't even address this question; it simply can't be applied to relativistic phenomena at all.

I think there is one by a member in this forum:

It is often argued that hypothetic nonlocal reality responsible for nonlocal quantum correlations between entangled particles cannot be consistent with relativity. I review the most frequent arguments of that sort, explain how they can all be circumvented, and present an explicit Bohmian model of nonlocal reality (compatible with quantum phenomena) that fully obeys the principle of relativistic covariance and does not involve a preferred Lorentz frame.

Making nonlocal reality compatible with relativity
http://xxx.lanl.gov/abs/1002.3226

PeterDonis

Dec24-11, 11:26 PM

But foliation has same meaning has frame as when you mentioned in message #76 in the other thread:

You're right, "foliation" does mean pretty much the same thing as "frame" the way I defined it. But putting the word "preferred" in front changes the meaning; there are lots of different possible frames/foliations, but saying that one of them is "preferred" is giving that one a special status that needs justification.

why do the word "foliation" is not used much?

"Foliation" is used a lot in the technical literature of GR when talking about the global structure of spacetime and various theorems about it. Being able to find a global foliation of the spacetime with the properties we've been assuming is actually a pretty strict condition on the spacetime, if "spacetime" is considered simply as a mathematically valid solution to the Einstein Field Equations.

Now the LET ether is said to be undetectable. But can't we say that Entanglement experiments make it detectable because it uses the LET ether frame as Bell wanted to suggest?

No, because the entanglement experiments don't pick out any particular frame as the ether frame. Bell was suggesting that the viewpoint that there is an ether frame even though it's physically undetectable was "coherent"; he wasn't suggesting (at least not as I understand him) that the ether frame was actually detectable.

In other words. Particles like fermions and bosons are ruled by SR and don't use the aether frame, while only wave function use the aether frame. Is this not possible?

I don't think this is what Bell was trying to say. If by "wave function" you mean the standard wave function as defined in standard quantum mechanics, it is not something separate from the particles, and it has to obey the same rules as the particles do. If you are talking about the "wave function" as it is used in Bohmian Mechanics, remember that that theory is explicitly non-relativistic, as I said before, so the question of whether it selects a "preferred frame" can't really even be asked, since relativistic phenomena are outside the theory's domain to begin with.

Well. I know gauge theory which says locality and gauge principle is what created the gauge bosons in the first place (when you have to add cheating terms to the wave function to make it vary from place to place.. i got this very clear from Schumm book Deep Down Things). So this gauge principle is what make it impossible that the wave function use the aether frame right?

I don't see a connection here. Can you give some more specfics about what the book says about gauge theory?

This is the reason Maudlin is so excited about the completely relativistic GRW with flash (in the paper shared a few message prior to this).

I've only skimmed the paper so I can't say much about it at this point.

So right now the safest bet is Copenhagen where since the wave function is just in the equations, there is nothing to be non-local about. This means one must only see Spacetime as equations and wave functions and spacetimes are models about reality and we only have models to reality and nothing further that can be know... end of story. We must not think of any physical sense to them or we may not be able to reconcile non-local equations. Is this what you also believe?

I think the Copenhagen interpretation is obviously incomplete; the fact that it works well in practice may just be because we haven't gotten sophisticated enough yet in running experiments that reveal its limitations.

I think that EPR-type experiments show that reality does not work the way our classical intuitions say it "should" work, but I don't see this as a problem, since I don't expect our classical intuitions to accurately tell us how reality works outside of the limited domain in which those intuitions evolved. Our brains are not built to understand quantum phenomena or relativistic phenomena intuitively the way we understand classical non-relativistic phenomena like thrown baseballs intuitively.

I don't think the observed violations of the Bell inequalities in EPR-type experiments indicate any violation of causality or Lorentz invariance, even "behind the scenes". I think it just indicates that we are still learning how to understand causality and Lorentz invariance. If you look at the actual math of quantum field theory, it does not place any restrictions on how spacelike-separated measurements can be correlated; the only thing actually required for causality and Lorentz invariance to be maintained is that spacelike-separated measurements must commute; that is, the results can't depend on which one happens first. The EPR-type results satisfy this criterion. So again, I don't think these results indicate anything "mysterious"; they just indicate that we don't yet fully understand how reality works.

stglyde

Dec25-11, 12:14 AM

You're right, "foliation" does mean pretty much the same thing as "frame" the way I defined it. But putting the word "preferred" in front changes the meaning; there are lots of different possible frames/foliations, but saying that one of them is "preferred" is giving that one a special status that needs justification.

"Foliation" is used a lot in the technical literature of GR when talking about the global structure of spacetime and various theorems about it. Being able to find a global foliation of the spacetime with the properties we've been assuming is actually a pretty strict condition on the spacetime, if "spacetime" is considered simply as a mathematically valid solution to the Einstein Field Equations.

You said earlier that "In general, any given spacetime will have an infinite number of different possible foliations, so it looks like what Mauldin is proposing is to label one such foliation as "preferred" with respect to wavefunction collapse." But Maudlin appears to be referring to label all foliations as preferred. Maybe the following passages in his article "Non-Local Correlations in Quantum Theory: How the Trick Might Be Done" will hold the key to what he meant:

Since the exact outcome of the experiment depends on which x-spin measurement is made first, the notion of “first” and “second” has an ineliminable physical role in Bohm’s theory. In the non-Relativistic theory, which measurement comes first and which second is determined by absolute simultaneity. And if one is to transfer the Bohmian dynamics to a space-time with a Lorenzian structure, one needs for there to be something fit to play the same dynamical role. Since no such structure is determined by the Lorentzian metric, the simplest thing to do is to add the required structure: to add a foliation relative to which the relevant sense of “first” and “second” (or “before” and “after”) is defined. The foliation would then be invoked in the statement of the fundamental dynamical law governing the particles.

So is Maudlin referring to label one such foliation as "preferred" with respect to wavefunction collapse or referring to label all the foliations or using all of them in the wavefunction collapse? The argument perhaps being that since there is nothing that chooses just one of them as special... may as well choose all of them. In all his attributions of "foliation". He never mention about labelling one of them as preferred, but just mentioned it like doing it to all foliations (refer to message #1 again to get the context of what I mean he refer to a singular and general 'foliation'). Is this what he was saying all along. You can know perhaps by the context of what he described above.

Let's settle this first as it is the most vague and focus of this thread "Meaning of Spacetime Foliation".

I'll address the other points below in another post.

No, because the entanglement experiments don't pick out any particular frame as the ether frame. Bell was suggesting that the viewpoint that there is an ether frame even though it's physically undetectable was "coherent"; he wasn't suggesting (at least not as I understand him) that the ether frame was actually detectable.

I don't think this is what Bell was trying to say. If by "wave function" you mean the standard wave function as defined in standard quantum mechanics, it is not something separate from the particles, and it has to obey the same rules as the particles do. If you are talking about the "wave function" as it is used in Bohmian Mechanics, remember that that theory is explicitly non-relativistic, as I said before, so the question of whether it selects a "preferred frame" can't really even be asked, since relativistic phenomena are outside the theory's domain to begin with.

I don't see a connection here. Can you give some more specfics about what the book says about gauge theory?

I've only skimmed the paper so I can't say much about it at this point.

I think the Copenhagen interpretation is obviously incomplete; the fact that it works well in practice may just be because we haven't gotten sophisticated enough yet in running experiments that reveal its limitations.

I think that EPR-type experiments show that reality does not work the way our classical intuitions say it "should" work, but I don't see this as a problem, since I don't expect our classical intuitions to accurately tell us how reality works outside of the limited domain in which those intuitions evolved. Our brains are not built to understand quantum phenomena or relativistic phenomena intuitively the way we understand classical non-relativistic phenomena like thrown baseballs intuitively.

I don't think the observed violations of the Bell inequalities in EPR-type experiments indicate any violation of causality or Lorentz invariance, even "behind the scenes". I think it just indicates that we are still learning how to understand causality and Lorentz invariance. If you look at the actual math of quantum field theory, it does not place any restrictions on how spacelike-separated measurements can be correlated; the only thing actually required for causality and Lorentz invariance to be maintained is that spacelike-separated measurements must commute; that is, the results can't depend on which one happens first. The EPR-type results satisfy this criterion. So again, I don't think these results indicate anything "mysterious"; they just indicate that we don't yet fully understand how reality works.

PeterDonis

Dec25-11, 12:28 AM

So is Maudlin referring to label one such foliation as "preferred" with respect to wavefunction collapse

Yes; he has to be, because he needs to make the time ordering of the measurements determinate, and that can only be done for spacelike-separated measurements by picking a particular simultaneity, which means picking a particular preferred foliation.

stglyde

Dec25-11, 12:47 AM

I don't see a connection here. Can you give some more specfics about what the book says about gauge theory?

What I learnt from the book is that Quantum Mechanics as originally formulated is phase invariant... meaning changes in phase won't affect it... that is global gauge invariance. However, "locally" it's not invariant so one has to add a cheating function or factor to the equation to make it invariant under local changes of phase. By adding a "cheat" factor. It surprisingly describes the field of the photon, the quantum of the electromagnetic field and so the QED U(1) and explaining why the charge is conserved.

Now the weak force. From the doublets (muon, antimuon thing for example). They consider something like weak isospin orientation as well as the qm-phase. Now to compensate
for the problems caused by the derivator operator that vary from point to point, "cheating" terms must be added. This time, one is not enough. 3 cheating terms must be added (to make it invariant). And bingo, this creates the force carriers of the weak force, the +W, -W and Z.

This also works fo the SU(3) strong force with the Lie Group having 8 generators.

So gauge theory has to do with the fact that the wave function is local. Therefore making it non-local may undo everything gauge theory teaches us. If you don't agree, then how do you make the wave function non-local?

I think the Copenhagen interpretation is obviously incomplete; the fact that it works well in practice may just be because we haven't gotten sophisticated enough yet in running experiments that reveal its limitations.

I think that EPR-type experiments show that reality does not work the way our classical intuitions say it "should" work, but I don't see this as a problem, since I don't expect our classical intuitions to accurately tell us how reality works outside of the limited domain in which those intuitions evolved. Our brains are not built to understand quantum phenomena or relativistic phenomena intuitively the way we understand classical non-relativistic phenomena like thrown baseballs intuitively.

I don't think the observed violations of the Bell inequalities in EPR-type experiments indicate any violation of causality or Lorentz invariance, even "behind the scenes". I think it just indicates that we are still learning how to understand causality and Lorentz invariance. If you look at the actual math of quantum field theory, it does not place any restrictions on how spacelike-separated measurements can be correlated; the only thing actually required for causality and Lorentz invariance to be maintained is that spacelike-separated measurements must commute; that is, the results can't depend on which one happens first. The EPR-type results satisfy this criterion. So again, I don't think these results indicate anything "mysterious"; they just indicate that we don't yet fully understand how reality works.

Yes, quantum entanglement doesnt violate causality or lorentz invariance but we don't have physical picture of it. The wave function is in the equation, the spacetime manifold is also in the equation.. yet when you walk down or up the stairs, you feel physicality.. our physics doesn't explain how the transition from equations to reality work. "Shut up and calculate" kind of physicists just accept it is so. Bohmians and Many Worlders and those not satisfied with simply shutting up and calculate (dumb down mode).

PeterDonis

Dec25-11, 01:29 AM

What I learnt from the book is that Quantum Mechanics as originally formulated is phase invariant... meaning changes in phase won't affect it... that is global gauge invariance. However, "locally" it's not invariant so one has to add a cheating function or factor to the equation to make it invariant under local changes of phase. By adding a "cheat" factor. It surprisingly describes the field of the photon, the quantum of the electromagnetic field and so the QED U(1) and explaining why the charge is conserved.

...

So gauge theory has to do with the fact that the wave function is local. Therefore making it non-local may undo everything gauge theory teaches us. If you don't agree, then how do you make the wave function non-local?

The "global" and "local" here don't refer to the wave function; they refer to the gauge transformations. A "global" gauge transformation is one that is the same at every point in spacetime. A "local" gauge transformation can vary from point to point in spacetime. So having the laws of physics be invariant under "local" gauge transformations is a much stricter condition than just having them be invariant under "global" gauge transformations; and it turns out that, as you say, we have to add gauge fields ("cheating" is a bit strong a term to use to describe what they do) to make the laws of physics meet the stricter condition.

The terms "global" and "local" to describe the transformations are rather unfortunate since they invite confusion about what is being referred to, but those are the standard terms and we're stuck with them.

Yes, quantum entanglement doesnt violate causality or lorentz invariance but we don't have physical picture of it.

Yes, we do. What we don't have is a physical picture *that matches our "classical" intuitions.* My view is that this is a problem with our intuitions, not with the physical picture. A good expression of this viewpoint is in the article "Think Like Reality" by Eliezer Yudkowsky, here:

http://lesswrong.com/lw/hs/think_like_reality/

He says:

The universe was propagating complex amplitudes through configuration space for ten billion years before life ever emerged on Earth. Quantum physics is not "weird". You are weird. You have the absolutely bizarre idea that reality ought to consist of little billiard balls bopping around, when in fact reality is a perfectly normal cloud of complex amplitude in configuration space. This is your problem, not reality's, and you are the one who needs to change.

We should not expect the "physical picture" of quantum reality to look like our intuitive picture of everyday reality.

The wave function is in the equation, the spacetime manifold is also in the equation.. yet when you walk down or up the stairs, you feel physicality.. our physics doesn't explain how the transition from equations to reality work.

Physics is not a science of consciousness, it's a science of fundamentals way below the level of consciousness. When you ask for an explanation of why you "feel physicality" when you walk down or up the stairs, you should not be asking physics; you should be asking the theory of consciousness, which is hardly in a state to give a coherent reply at this stage of our knowledge, true, but that's not the fault of physics.

stglyde

Dec25-11, 03:47 AM

The "global" and "local" here don't refer to the wave function; they refer to the gauge transformations. A "global" gauge transformation is one that is the same at every point in spacetime. A "local" gauge transformation can vary from point to point in spacetime. So having the laws of physics be invariant under "local" gauge transformations is a much stricter condition than just having them be invariant under "global" gauge transformations; and it turns out that, as you say, we have to add gauge fields ("cheating" is a bit strong a term to use to describe what they do) to make the laws of physics meet the stricter condition.

The terms "global" and "local" to describe the transformations are rather unfortunate since they invite confusion about what is being referred to, but those are the standard terms and we're stuck with them.

But the wave function is related to the gauge transformations. The best book with 44 Full 5 Star "Deep Down Things" by Bruce Schumm mentions the following for example (he used the words "cheating terms" for fancy since his audience are laymen):

http://www.amazon.com/Deep-Down-Things-Breathtaking-Particle/dp/080187971X/ref=sr_1_1?ie=UTF8&qid=1324805331&sr=8-1#_

"Again, the gauge fields, or interactions, Ac(x) need to be introduced into the free-particle wave equation to patch up the damage caused by color-space rotations that swap the quark colors among one another by amounts that differ as you move from point to point in space-time. Over there, you rotate or transform, a blue quark into half-green, half-red quark, while over here, you transform a blue quark into a pure red quark (and maybe change the quantum-mechanical phase of the resulting wave function by some amount also). These differing transformations alter the way the wave function changes from point to point in space. This, in turn, destroys the delicate balance, required by the wave equation, between the rate of change in the wave function around any point in space and the energy of the object described by that wave function. We thus find it necessary to introduce gauge field (interaction) terms of the form gsAc(x)psi(x) as "cheating terms" that act to restore this delicate balance and thus make the wave equation and its wave function solution invariant with respect to local SU(3) color space rotations."

You see he mentioned "These differing transformations alter the way the wave function changes from point to point in space" so its local and global is related to the wave function as he emphasized numerous times in the book. Yet you emphasized it is the gauge transformation that is local and globe.. but gauge transformation involves wave function!

stglyde

Dec25-11, 06:13 AM

I think there is one by a member in this forum:

Making nonlocal reality compatible with relativity
http://xxx.lanl.gov/abs/1002.3226

I read the paper entirely. There is one part which if debunked would debunk the entire idea. It is the following claim:

"By 2) I mean that time and space should be treated on an equal footing. Note that in
the usual formulation of QM, time and space are not treated on an equal footing. First,
for one particle described by the wave function psi(x,t), the infinitesimal probability in
the usual formulation is |psi|^2d^3 x, while from a symmetric treatment of time and space
one expects |psi|^2 d^3 x dt. Second, for n particles the wave function in the usual formulation
takes the form (x1, . . . , xn, t), while from a symmetric treatment of time and space one
expects (x1, t1, . . . , xn, tn). I formulate QM such that fundamental axioms involve the
expressions above in which time and space are treated symmetrically, and show that the
usual formulation corresponds to a special case."

Any seasoned Relativists can debunk this? PeterDonis?

bohm2

Dec25-11, 11:14 AM

I read the paper entirely. There is one part which if debunked would debunk the entire idea. It is the following claim:...Any seasoned Relativists can debunk this? PeterDonis?

Actually, some physicists who favour the pilot-wave interpretation find that such models trying to find lorentz-invariant de Broglie-Bohmian models are misconceived for other reasons:

A number of authors insist that a realistic quantum physics should be ‘seriously Lorentz invariant’, in the sense that Lorentz invariance should be fundamental, and not merely phenomenological or emerging in some limit. This contrast is remarkable, because it is precisely in quantum foundations that there is arguably the strongest motivation of all for abandoning fundamental Lorentz invariance: the experimental detection of quantum nonlocality, through the observed violations of Bell’s inequalities. As emphasised by Bell, quantum theory is incompatible with locality, independently of any assumption about the existence of hidden variables...

Note that, in the specific hidden-variables theory given by pilot-wave dynamics, even leaving nonlocality aside, the natural kinematics of the theory is arguably that of Aristotelian spacetime E × E3, with a preferred state of rest (Valentini 1997). This is essentially because the dynamics is first order in time, so that rest is the only reasonable definition of ‘natural’ or ‘unforced’ motion. Pilot-wave theory then has a remarkable internal logic: both the structure of the dynamics, and the operational possibility of nonlocal signalling out of equilibrium, independently point to the existence of a natural preferred state of rest.

Hidden Variables and the Large-Scale Structure of Spacetime
http://lanl.arxiv.org/PS_cache/quant-ph/pdf/0504/0504011v2.pdf

To impose Galilean invariance on the pilot-wave theory is like imposing, on Newtonian mechanics, an invariance under transformations to uniformly accelerated frames. The Galilean transformation of ψ amounts to the introduction of fictitious inertial (Aristotelian) forces. Despite appearances, then, Galilean invariance is not a fundamental symmetry of the low-energy pilot-wave theory. There is then no reason to impose Lorentz invariance in the high-energy domain. Some authors, following Bell, have portrayed the current situation as a sort of two-horse race for fundamental Lorentz invariance, the contestants being the pilot-wave and dynamical-reduction theories. From the above perspective, this is quite misguided. For in the pilot-wave theory, uniform motion is not relative–so the ‘problem’ of finding a Lorentz-invariant extension simply does not arise. Whether the theory of dynamical reduction is also able to circumvent this problem remains to be seen. (Perhaps the reduction mechanism could be shown to single out a natural state of rest.)

On Galilean and Lorentz invariance in pilot-wave dynamics
http://lanl.arxiv.org/PS_cache/arxiv/pdf/0812/0812.4941v1.pdf

PeterDonis

Dec25-11, 11:30 AM

You see he mentioned "These differing transformations alter the way the wave function changes from point to point in space" so its local and global is related to the wave function as he emphasized numerous times in the book. Yet you emphasized it is the gauge transformation that is local and globe.. but gauge transformation involves wave function!

Yes, the gauge transformations alter the wave function, but only in the mathematics, not in the physics. Saying that a theory is "gauge invariant" is actually saying that there are multiple mathematical expressions that describe the same physical state; a "gauge transformation" is a transformation that switches from one expression to another without changing the actual physical state. For example, the states that he is calling "blue quark", "red quark", etc. are not physical states per se; they are descriptions of physical states in a particular basis. The gauge transformation that changes, for example, "blue quarks" into "red quarks" is actually a change of basis, like a change of coordinate frames in SR; it doesn't change the physical states at all, it just changes the "coordinates" in which they are described. So when he says the gauge transformations are "changing the wave function", he's only talking about changing the basis; he's not talking about changing any actual physical observables.

As far as "local" and "global", read my description of what those terms mean as applied to gauge transformations again. They have nothing to do with the type of function that the transformations act on. Classical electrodynamics, which doesn't have wave functions at all (only the classical potential and fields) has the same property of gauge invariance.

Whether a wave function is "local" or "nonlocal" depends on what parameters it is a function of. If it's a function of a single spacetime point, it's local; if it's a function of multiple spacetime points, it's nonlocal. So, for example, a wave function describing a single particle in quantum mechanics is local; it's just a regular function that assigns an amplitude to every point in space (or spacetime, in the relativistic version). But a wave function describing two particles is nonlocal: it assigns amplitudes to *pairs* of points, which may be separated. If the two particles are not correlated, we can factor the wave function into a product of two local ones, one for each particle; but if the particles are entangled (e.g., if they are in an EPR-type experiment), we can't do this and the wave function is fundamentally nonlocal. But all this has nothing to do with whether our theory is gauge invariant or not.

PeterDonis

Dec25-11, 11:47 AM

"By 2) I mean that time and space should be treated on an equal footing. Note that in the usual formulation of QM, time and space are not treated on an equal footing.

Here he's talking about ordinary non-relativistic quantum mechanics, not quantum field theory. I'm not sure why, since elsewhere in the paper he talks about QFT and says it's relativistically covariant. I'm still reading through the paper so I won't comment more until I'm finished, but this is one thing that jumped out at me.

stglyde

Dec25-11, 06:14 PM

Yes, we do. What we don't have is a physical picture *that matches our "classical" intuitions.* My view is that this is a problem with our intuitions, not with the physical picture. A good expression of this viewpoint is in the article "Think Like Reality" by Eliezer Yudkowsky, here:

http://lesswrong.com/lw/hs/think_like_reality/

He says:

The universe was propagating complex amplitudes through configuration space for ten billion years before life ever emerged on Earth. Quantum physics is not "weird". You are weird. You have the absolutely bizarre idea that reality ought to consist of little billiard balls bopping around, when in fact reality is a perfectly normal cloud of complex amplitude in configuration space. This is your problem, not reality's, and you are the one who needs to change.

We should not expect the "physical picture" of quantum reality to look like our intuitive picture of everyday reality.

The article "Think Like Reality" is only about quantum. I'd like to create a relativistic version for those some newtonian fellows I know who still can't accept the concept of relativity of simultaneity. They reasoned the world being physical shouldn't be based on perspective.

So what is the counterpart of complex amplitudes in GR and also configuration space. I guess differential manifold is counterpart of configuration space and lorentzian metric tensors as counterpart for complex amplitudes? If so, then the paragraph would be relativistically changed to:

"The universe was propagating lorentzian metric tensors through differential manifolds for ten billion years before life ever emerged on Earth. Special & General Relativity are not "weird". You are weird. You have the absolutely bizarre idea that reality ought to consist of absolute space and time as background when in fact reality is a perfectly normal array of lorentzian metric tensors in differential manifold. This is your problem, not reality's, and you are the one who needs to change."

But the terms lorentzian metric tensors may be awkward. So what is the GR counterpart for complex amplitudes in QM? I know the Einstein Fields Equations have changing parameters just like QM complex amplitudes. What are they exactly?

stglyde

Dec25-11, 07:06 PM

Yes, the gauge transformations alter the wave function, but only in the mathematics, not in the physics. Saying that a theory is "gauge invariant" is actually saying that there are multiple mathematical expressions that describe the same physical state; a "gauge transformation" is a transformation that switches from one expression to another without changing the actual physical state. For example, the states that he is calling "blue quark", "red quark", etc. are not physical states per se; they are descriptions of physical states in a particular basis. The gauge transformation that changes, for example, "blue quarks" into "red quarks" is actually a change of basis, like a change of coordinate frames in SR; it doesn't change the physical states at all, it just changes the "coordinates" in which they are described. So when he says the gauge transformations are "changing the wave function", he's only talking about changing the basis; he's not talking about changing any actual physical observables.

As far as "local" and "global", read my description of what those terms mean as applied to gauge transformations again. They have nothing to do with the type of function that the transformations act on. Classical electrodynamics, which doesn't have wave functions at all (only the classical potential and fields) has the same property of gauge invariance.

Whether a wave function is "local" or "nonlocal" depends on what parameters it is a function of. If it's a function of a single spacetime point, it's local; if it's a function of multiple spacetime points, it's nonlocal. So, for example, a wave function describing a single particle in quantum mechanics is local; it's just a regular function that assigns an amplitude to every point in space (or spacetime, in the relativistic version). But a wave function describing two particles is nonlocal: it assigns amplitudes to *pairs* of points, which may be separated. If the two particles are not correlated, we can factor the wave function into a product of two local ones, one for each particle; but if the particles are entangled (e.g., if they are in an EPR-type experiment), we can't do this and the wave function is fundamentally nonlocal. But all this has nothing to do with whether our theory is gauge invariant or not.

Well, even if gauge transformations alter the wave function, but only in the mathematics, not in the physics, as you emphasize, it's still related to Special Relativity as Bruce Schumm mentioned in the following:

We know that phase is irrelevant. The choice of the phase of an object's - or a system of objects' - or the universe's wave function is arbitrary. One the one hand, the hallowed wave equation tells us that the arbitrary choice of phase must be consistent from point to point in space and time or all hell breaks loose. On the other hand, as Yang and Mills point out, this requirement appears to be incompatible with Einstein's well-supported notions of the nature of space and time. The contradiction is direct and demands a resolution, so something has to give. And, as has so often been the case in modern science, in reconciling these apparently incompatible points of views, Yang and Mills were led down a path that profoundly and fundamentally augmented the way physicists view the operating principles of the natural world (note 8.2).

So because of Einstein's well-supported notions of the nature of space and time, or Special Relativity, the equations have to conform to SR and be altered, which results in the existence of the gauge fields.. even if gauge transformation is in the equations and not in physical space.

PeterDonis

Dec26-11, 12:47 AM

So because of Einstein's well-supported notions of the nature of space and time, or Special Relativity, the equations have to conform to SR and be altered, which results in the existence of the gauge fields.. even if gauge transformation is in the equations and not in physical space.

Do you have an online reference for the source from which this quote was taken? Since he mentions Yang and Mills, it appears that he is talking about non-abelian gauge theory, but I'm not sure about the context.

In general terms, you're correct, making quantum theory consistent with relativity appears to require gauge fields. But that may be as much a matter of the mathematical form we choose to write our physical laws in as anything else. As I said in a previous post, gauge transformations don't change any physical observables; they only change the particular "basis" we write the laws in, similar to a change of coordinates. It may be that we will someday find a better way of writing the laws, that naturally expresses relativistic quantum processes without requiring the "redundancy" of gauge fields to compensate for the fact that multiple mathematical states represent the same physical state.

PeterDonis

Dec26-11, 12:54 AM

The article "Think Like Reality" is only about quantum. I'd like to create a relativistic version for those some newtonian fellows I know who still can't accept the concept of relativity of simultaneity. They reasoned the world being physical shouldn't be based on perspective.

The article is using quantum mechanics to make a general point, but the point applies to relativity as well.

So what is the counterpart of complex amplitudes in GR and also configuration space.

There isn't, really, since GR is a classical theory, not a quantum theory. But your relativistic version is not a bad "translation", I think, except that metric tensors aren't usually thought of as "propagating". I would use spacetime curvature instead, perhaps something like this:

"The universe was generating spacetime curvature from stress-energy in a locally Lorentzian differential manifold for ten billion years before life ever emerged on Earth. Special & General Relativity are not "weird". You are weird. You have the absolutely bizarre idea that reality ought to consist of absolute space and time and Newtonian forces, when in fact reality is a perfectly normal curved manifold with local Lorentz symmetry. This is your problem, not reality's, and you are the one who needs to change."

bohm2

Dec26-11, 10:13 AM

I'm not sure if what you guys are looking for is a model that's both lorentz-invariant and narrative (as discussed by D. Albert):

Albert calls a theory narratable if specifying a system’s state at all times is sufficient to specify all properties of a system. Poincare-covariant quantum mechanics is not narratable: if we give the state at all times on a given foliation, we have given something less than the complete description of the system.

http://philosophyfaculty.ucsd.edu/faculty/wuthrich/PhilPhys/AlbertDavid2008Man_PhysicsNarrative.pdf

I believe there are only 2 such models:

1. Tumulka’s GRWf ("flash") model:
The flash ontology is an unusual choice of ontology; a more normal choice would be particle world lines, or fields in space-time. The motivation for this choice lies in the fact that the GRWmodel with flashes can be made Lorentz invariant (by suitable corrections in the equations), whereas the GRW model with the matter density m(r, t) cannot in any known way.

Collapse and Relativity
http://www.maphy.uni-tuebingen.de/members/rotu/papers/losinj.pdf

A Relativistic Version of the Ghirardi–Rimini–Weber Model
http://arxiv.org/PS_cache/quant-ph/pdf/0406/0406094v2.pdf

2. The more recent Bedingham model:
Mathematical models for the stochastic evolution of wave functions that combine the unitary evolution according to the Schrodinger equation and the collapse postulate of quantum theory are well understood for non-relativistic quantum mechanics. Recently, there has been progress in making these models relativistic. But even with a fully relativistic law for the wave function evolution, a problem with relativity remains: Different Lorentz frames may yield conflicting values for the matter density at a space-time point. One solution to this problem is provided by Tumulka’s “flash” model. Another solution is presented here. We propose a relativistic version of the law for the matter density function. According to our proposal, the matter density function at a space-time point x is obtained from the wave function ψ on the past light cone of x by setting the i-th particle position in |ψ|2 equal to x, integrating over the other particle positions, and averaging over i. We show that the predictions that follow from this proposal agree with all known experimental facts.

Matter Density and Relativistic Models of Wave Function Collapse
http://arxiv.org/PS_cache/arxiv/pdf/1111/1111.1425v1.pdf

See this thread for more detail:

Albert's narrative argument against Everett-type theories
http://www.physicsforums.com/showthread.php?t=535980

stglyde

Dec27-11, 12:04 AM

Do you have an online reference for the source from which this quote was taken? Since he mentions Yang and Mills, it appears that he is talking about non-abelian gauge theory, but I'm not sure about the context.

In general terms, you're correct, making quantum theory consistent with relativity appears to require gauge fields. But that may be as much a matter of the mathematical form we choose to write our physical laws in as anything else. As I said in a previous post, gauge transformations don't change any physical observables; they only change the particular "basis" we write the laws in, similar to a change of coordinates. It may be that we will someday find a better way of writing the laws, that naturally expresses relativistic quantum processes without requiring the "redundancy" of gauge fields to compensate for the fact that multiple mathematical states represent the same physical state.

The author has many refereces in the book without being specific to it. Try to check out the book "Deep Down Things: The Breathtaking Beauty of Particle Physics" (as I mentioned earlier). It may be the best particle physics book for laymen on earth because it didn't dumb down things like other popular science books. But I'm concerned about this SR law within gauge theory that works in the equations. If true. I wonder how to write a gauge theory of preferred foliations. But then the author seems to be describing spacetime points in the following (Try to go to Amazon and they have a 25 page free book preview of any pages. Just go to page 217- 330. The following is where he introduced Yang Mills predicament. Pls. comment on this:

In the mid-1950s, two physicists, C.N. Yang of the Institute of Advanced Study at Princeton University, and R.L. Mills of Brookhaven National Laborator, became deeply interested in the quesiton of the phase invariance of quantum mechanics. What intrigued them most was that, on reflection, the idea of global phase invariance didn't quite wash with Einsten's notions of the nature of space-time. Yang and Mills were perfectly happy with the idea that the observable properties of a quantum-mechanical system should be independent of the phase of the wave function, as discussed at length above. What bothered them was that, to exhibit this independence of phase, one had to change the phase globally, by the same amount everywhere in space-time. We haven't yet demonstrated that changing the phase locally- by an amount that differs from point to point in space and time- disrupts the delicate balance of the Schrodinger equation, but we will in due course. In any regard, the need to require that quantum-mechanical systems be unaltered only by global changes of phase seemed to Yang and Mills to be very unnatural"

<skipping 7 paragraphs>

But now, Yang and Mills admonish us that we shouldn't really talk about global phase invariance because not all points in space-time are causally connected. So, it makes no sense to require that the choice of change of the wave function's phase be the same everywhere in space-time. Instead, we must consider local changes of phase, that is, changes in the phase of the electron's wave function by an amount that varies from point to point.

<skipping 18 paragraphs>

Whenever the phase of the wave function changes locally (by an amount that varies from point to point in space), the result of the derivative (rate of change) operation changes, introducing some "mistake" that cause the new wavefunction to no longer satisfy the wave equation. The thing - the only thing - we require of this new term we're going to add is that it commit precisely the same mistake, but with a negative sign, so that when the mistake from the term with the derivative is added to the mistake from the new term, they exactly cancel out, and everything is OK. In other words, Yang and Mills cheated; when nobody was looking, they added another term that got rid of the problem caused by the effect of the rate of change operation"

<skipping 12 paragraphs more include mathematical arguments>

You can read the skipped paragraphs at Amazon free preview. But from the above it is clear the author was talking about changes in spacetime points and not just in the equations in gauge transformation (as you claimed). What do you think?

PeterDonis

Dec27-11, 12:28 AM

But from the above it is clear the author was talking about changes in spacetime points and not just in the equations in gauge transformation (as you claimed). What do you think?

I think you're reading too much into the author's attempt to describe a highly technical issue in non-technical terms. Every time a Brian Greene physics special airs again on one of the science channels, we get a spate of threads asking about things he said that sound a lot more colorful than the actual physics is. The author's use of the term "cheating" and describing what Yang and Mills did as "when nobody was looking, they added another term" strikes me as similar to the colorful ways in which Greene describes aspects of quantum mechanics; it sounds good and sells books and videos, but it can easily lead to misunderstandings.

Take a look at the Wikipedia page giving an introduction to gauge theory:

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

Note one thing in particular, which I have mentioned before: the fact that general relativity is invariant under arbitrary continuous transformations of the coordinates is an example of gauge invariance! So if Yang and Mills were "cheating" by adding terms involving gauge fields, then Einstein was also "cheating" when he added terms related to spacetime curvature to coordinate transformations in order to make the laws of physics look the same in all coordinate systems when gravity was present.

stglyde

Dec27-11, 12:54 AM

I think you're reading too much into the author's attempt to describe a highly technical issue in non-technical terms. Every time a Brian Greene physics special airs again on one of the science channels, we get a spate of threads asking about things he said that sound a lot more colorful than the actual physics is. The author's use of the term "cheating" and describing what Yang and Mills did as "when nobody was looking, they added another term" strikes me as similar to the colorful ways in which Greene describes aspects of quantum mechanics; it sounds good and sells books and videos, but it can easily lead to misunderstandings.

Take a look at the Wikipedia page giving an introduction to gauge theory:

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

Note one thing in particular, which I have mentioned before: the fact that general relativity is invariant under arbitrary continuous transformations of the coordinates is an example of gauge invariance! So if Yang and Mills were "cheating" by adding terms involving gauge fields, then Einstein was also "cheating" when he added terms related to spacetime curvature to coordinate transformations in order to make the laws of physics look the same in all coordinate systems when gravity was present.

Forgive the author using the term "cheating". Of course he meant Yang and Mills well and we know they are honest people. The "cheating terms" were just used for sake of illustration.

Anyway. So what you were saying was that the phase of the wave function is not really located in space time but in internal space of the equations like isospin. Maybe the author use PUN too much. But then.. in Bohmian Mechanics, the phase of the wave function is really propagating in space and time!

PeterDonis

Dec27-11, 09:14 AM

But then.. in Bohmian Mechanics, the phase of the wave function is really propagating in space and time!

Only in the simplest case of a single particle. When multiple particles are present, the space the wave function "lives" in is a tensor product of multiple copies of spacetime, one for each particle. So realistically, you can't think of a wave function even in Bohmian Mechanics as propagating in the actual spacetime we perceive.

(Actually, for standard Bohmian Mechanics, which is non-relativistic, even the single-particle wave function isn't a function on spacetime, it's a function on space that evolves in time; time is a parameter, not a coordinate. Multiple-particle wave functions are functions on a tensor product of N copies of space, one for each particle, which evolve in time. I'm assuming that a relativistic version of Bohmian Mechanics would work as I said above, since otherwise it wouldn't be able to match the predictions of standard quantum field theory; I haven't read through the paper linked to earlier that claims to develop such a relativistic version.)

stglyde

Dec27-11, 11:18 AM

Only in the simplest case of a single particle. When multiple particles are present, the space the wave function "lives" in is a tensor product of multiple copies of spacetime, one for each particle. So realistically, you can't think of a wave function even in Bohmian Mechanics as propagating in the actual spacetime we perceive.

(Actually, for standard Bohmian Mechanics, which is non-relativistic, even the single-particle wave function isn't a function on spacetime, it's a function on space that evolves in time; time is a parameter, not a coordinate. Multiple-particle wave functions are functions on a tensor product of N copies of space, one for each particle, which evolve in time. I'm assuming that a relativistic version of Bohmian Mechanics would work as I said above, since otherwise it wouldn't be able to match the predictions of standard quantum field theory; I haven't read through the paper linked to earlier that claims to develop such a relativistic version.)

If you have time. Please try to read through the paper which is only 10 pages long and half of it is in simple question and answer and the following is the last paragraph of half of it:

"O: Isn’t it shown that the Bohmian interpretation requires a preferred Lorentz frame?
R: That is true in the usual formulation of the Bohmian interpretation based on the
usual formulation of QM in which time and space are not treated on an equal footing.
When QM is generalized as outlined in 2) above, then the corresponding Bohmian inter-
pretation does not longer require a preferred Lorentz frame.
O: I think I’ve got a general idea now. But I’ll not be convinced until I see the technical
details."

The technical details are summary of what are presented in peer reviewed Physics Review Journal. It's written by he who called himself Demystifier who is here to defend himself.

The contents are radical.. It's perhaps like when Minkowski changed the world when he said "The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality". Demystifier attempted to change the shadows into actual, and even more radical and deserves a Nobel (if he were right).

Anyway if you still don't have time to read it. What do you make of the following where he said time and space should be treated on an equal footing? Don't we treat space and time as equal footing now? Time is in imaginary axis while space is in real axis. Perhaps what he did is make time another space too? (what don't we and if not why do we not do it in the first place?)

"By 2) I mean that time and space should be treated on an equal footing. Note that in the usual formulation of QM, time and space are not treated on an equal footing. First, for one particle described by the wave function psi(x,t), the infinitesimal probability in the usual formulation is |psi|^2d^3 x, while from a symmetric treatment of time and space one expects |psi|^2 d^3 x dt. Second, for n particles the wave function in the usual formulation takes the form (x1, . . . , xn, t), while from a symmetric treatment of time and space one expects (x1, t1, . . . , xn, tn). I formulate QM such that fundamental axioms involve the
expressions above in which time and space are treated symmetrically, and show that the usual formulation corresponds to a special case."

http://xxx.lanl.gov/abs/1002.3226

harrylin

Dec28-11, 07:35 AM

Have you not read Maudlin article called "Non-Local Correlations in Quantum Theory: How the Trick Might Be Done".
? That's the article of this thread to which I referred after I read it; I don't understand the new interpretations that are mentioned there.

Anyway. Tumulka stuff was a topic in Scientific American March 2009 edition called "Was Einstein Wrong?: A Quantum Threat to Special Relativity"

http://www.scientificamerican.com/article.cfm?id=was-einstein-wrong-about-relativity
Here's sample of what's being said: [..] Just read the rest from Sci-Am. I don't like Tumulka's theory. If it can't even describe particles that attract or repel. I'd say it's such a long way.. much worse than Bohmian Mechanics.
Thanks for the sample; I don't have access to that article. Note that I can understand why my university dropped SciAm. Maybe that article is OK, but maybe not... Do you understand Tumulka's theory? [Edit] I see that now in post #66 more links are provided - will have a look at those. :smile:

stglyde

Dec28-11, 08:34 AM

? That's the article of this thread to which I referred after I read it; I don't understand the new interpretations that are mentioned there.

Thanks for the sample; I don't have access to that article. Note that I can understand why my university dropped SciAm. Maybe that article is OK, but maybe not... Do you understand Tumulka's theory? [Edit] I see that now in post #66 more links are provided - will have a look at those. :smile:

It's easy to understand.

Maudlin said Bohmian Mechanics needs Preferred Foliation
Original GRW with wave function needs Preferred Foliation too.

But Tumulka GRW with flash doesn't need Preferred Foliation anymore. Somehow Alice and Bob or Entangled Pair doesn't have the correlations occuring at the same time.. the flash or beable wave function collapse (which is physical compared to Copenhagen version) is not simultaneous... but choreographed by the wave function. Something like that.

Maudlin was very interested in Tumulka because it was the only non-local theory he encountered that doesn't require Preferred Foliation and needs only the lorentz metric. Maybe he missed Demystifier's paper on "Making nonlocal reality compatible with relativity" at http://xxx.lanl.gov/abs/1002.3226

Anyway. Maudlin ended his "Non-Local Correlations in Quantum Theory: How the Trick Might Be Done" with the following observations:

"It has been a constant complaint against Bohmian mechanics, from its inception, that it “has no Relativistic version”. The reason that the theory is hard to reconcile with Relativity is clear: it is because of the way the non-locality of theory is implemented. In fact, the easiest way to extend that implementation to a space-time with a Lorentzian metric is to add a foliation, as we have seen. There may be some other way, but no one has discovered it yet.

But the non-locality of Bohm’s theory is not a peculiar feature of that theory: it is instead a feature of the world. Any theory adequate to explain the phenomena will have to have some non-locality. As we have seen, Ghirardi’s version of GRW, which takes a rather different approach to the non-locality than Bohmian mechanics, also is most easily adapted to a Lorentzian space-time by adding a foliation. One can create a fully Relativistic version of GRW, as Tumulka has shown, but only by a very different choice of local beable than Ghirardi made. So these are real, physical problems, with implications for the physical ontology, not merely matters of rewriting a theory in one way or another.

I guess Maudlin was wrong when he mentioned above "There may be some other way, but no one has discovered it yet.". He may not have known about Demystifier paper on "Making nonlocal reality compatible with relativity" at http://xxx.lanl.gov/abs/1002.3226 which is based on peer reviewed Physical Review Journal paper. If Peterdonis or others have read the paper shared in the link, please let us know if it is Viable, or Not Even Wrong. Thanks.

PeterDonis

Dec28-11, 09:13 AM

He may not have known about Demystifier paper on "Making nonlocal reality compatible with relativity" at http://xxx.lanl.gov/abs/1002.3226 which is based on peer reviewed Physical Review Journal paper.

I still haven't read through the papers completely, but from skimming them I certainly don't think they are in the "Not Even Wrong" category.

One item I think is missing from the paper linked to above is that there are no specific references given for this statement on p. 1: "it is often argued that no model of nonlocal reality can be compatible with relativity". I'm not sure this is right; what I understand to be "often argued" is that no *local* model of reality can be compatible with quantum mechanics. I also have seen it said that nonlocality *appears* to be incompatible with the "spirit" of relativity, but that is clearly not a rigorous claim as it stands; and AFAIK nobody has actually tried to make such an argument rigorously (which would be very difficult since standard quantum field theory predicts correct results for EPR experiments but is explicitly relativistically covariant).

The statement is not central to the paper, which is mainly about giving a relativistically covariant version of Bohmian mechanics, so it's not a crucial point, but I would still be interested to see specific references in relation to it.

stglyde

Dec30-11, 02:25 AM

? That's the article of this thread to which I referred after I read it; I don't understand the new interpretations that are mentioned there.

Thanks for the sample; I don't have access to that article. Note that I can understand why my university dropped SciAm. Maybe that article is OK, but maybe not... Do you understand Tumulka's theory? [Edit] I see that now in post #66 more links are provided - will have a look at those. :smile:

Searching for GRW and Tumulka stuff in the net. I found out this blog by physicist Lubos Motl, an extreme Copenhagenist who considers Bohmian Mechanics, Many Worlds Interpretation as Pseudo-science. He also considers Collapse Theories like GRW as pseudo-science. In the following, he is describing the essence of GRW and it may give an good introduction to you or others who don't have idea what it is.

http://motls.blogspot.com/2011/06/ghirardi-rimini-weber-collapsed.html

Ghirardi, Rimini, Weber: a real collapse

But I want to discuss another approach that hasn't been described on this blog yet: the GRW approach. The basic 1986 paper in PRD has 1217 citations as of today which is just gigantic if you realize that the paper is complete crackpottery:

Much like in the other anti-quantum approaches, this approach is trying to make some "classical reality". Unlike the Bohmian pseudoscience, it doesn't add any sharp positions of the particles. Instead, it keeps Schrödinger's equation only and adds some nonlinear "flashes" into the evolution that are meant to squeeze the state vector in the mantinels that the authors consider "appropriate".

It's very easy to describe what their proposal is - even though you may have a hard time to extract this basic point from the dozens of useless pages of the paper above. Imagine Schrödinger's equation for N non-relativistic particles - like the Bohmian pseudoscience, the formalism is linked to particles of the non-relativistic type, so all attempts to apply it to fields are inevitably awkward.

It is evolving according to Schrödinger's equation but GRW don't like that it's spreading because they want to imagine that the wave function is a "real object" and "real macroscopic objects" are not spreading - a classical misinterpretation of the wave function by all the anti-quantum "thinkers". Well, it obviously is spreading and there are many outcomes that have various probabilities - which doesn't hurt - but GRW just don't like it. So they decide that the wave function shouldn't freely spread! How do they ban the spreading? Well, that's easy for GRW.

They say that every 10^{15} seconds, which is a randomly chosen new bureaucratic constant of Nature (whose value is of course completely fabricated and has nothing to do with any justifiable laws of physics or any observations) each particle is obliged to prove to the census officials that it has a rather well-defined location. So there is a Poisson process running for each particle that once per 10^{15} seconds in average, it says "flash" to each particle. The more particles you have, the more flashes you obtain.

So what do or others think about this? Motl didn't mention about Tumulka which is a newer addition (I think Tumulka paper is like Lisa Randall RS1 and RS2 paper in popularity in the physics community) but it has the same GRW essence.

It seems that by trying to do away with Preferred Foliation. They have to de-linearized Quantum Mechanics and violate the superposition principle. So what's the lesser of the two evil?

bohm2

Dec30-11, 09:35 AM

It is evolving according to Schrödinger's equation but GRW don't like that it's spreading because they want to imagine that the wave function is a "real object" and "real macroscopic objects" are not spreading - a classical misinterpretation of the wave function by all the anti-quantum "thinkers".

But the new PBR theorem suggests (or so it is claimed), that if one wants to take a scientific realist stance then the wave function must be ontological and not epistemic/statistical; unless you want to take a purely instrumental approach with respect to the wave function. In that case it is irrelevant.

Papers:
The quantum state cannot be interpreted statistically (this is the original paper)
http://lanl.arxiv.org/abs/1111.3328
Generalisations of the recent Pusey-Barrett-Rudolph theorem for statistical models of quantum phenomena
http://xxx.lanl.gov/abs/1111.6304
Completeness of quantum theory implies that wave functions are physical properties
http://arxiv.org/PS_cache/arxiv/pdf/1111/1111.6597v1.pdf

Popular:
Quantum theorem shakes foundations
http://www.nature.com/news/quantum-theorem-shakes-foundations-1.9392

Blogs:
http://mattleifer.info/2011/11/20/can-the-quantum-state-be-interpreted-statistically/
http://www.scottaaronson.com/blog/?p=822
http://www.fqxi.org/community/forum/topic/999

The first blog above by Matt Leifer does a real good descriptive job of hi-liting which interpretations of QM have been eliminated as a result of this new theorem. The second one is Scott Aronson's and in there Lubos Motl gives his take on it and he appears to have misinterprated it accoring to Leifer.

From that blog in the comments section (with respect to the PBR), Lubos Motl writes:
You couldn’t have possibly read the paper or you’re unfamiliar with basic facts about QM or basic terminology used by those who want to replace QM by something else, if I avoid the term crackpot. Quantum mechanics is definitely probabilistic. It means that it can only make probabilistic predictions of measurements which can’t be made more unambiguous, not even in principle, and it says nothing about the “real state” of a system prior to the measurement. These are completely basic and universal properties of any quantum mechanical theory that are not open to any interpretation. The probabilistic framework of quantum mechanics is undoubtedly valid. Even the very abstract of the Pusey paper presents these things very clearly and argues – totally absurdly – that the statistical interpretation (by Max Born) is wrong. On the other hand, when you say that the paper is trying to resolve the battle between the “ontic” and “epistemic” camps, what you fail to understand is that, as you can see in the first paragraph of e.g.

http://arxiv.org/abs/0706.2661
both of these two camps are composed of advocates of hidden-variable models, if I avoid the term crackpots for the second time. To say the least, the hidden variable models have been falsified for more than 40 years and they are by definition incompatible with the basic principle of quantum mechanics: both of these adjectives are anti-quantum-mechanics. So the paper surely can’t prove that ontists or epistemists are right because both of these groups have been known to be wrong for 40+ years (and I would really say for 85+ years).

But Leifer writes:
First up, I would like to say that I find the use of the word “Statistically” in the title to be a rather unfortunate choice. It is liable to make people think that the authors are arguing against the Born rule (Lubos Motl has fallen into this trap in particular), whereas in fact the opposite is true. The result is all about reproducing the Born rule within a realist theory. The question is whether a scientific realist can interpret the quantum state as an epistemic state (state of knowledge) or whether it must be an ontic state (state of reality). It seems to show that only the ontic interpretation is viable, but, in my view, this is a bit too quick.

stglyde

Dec30-11, 05:58 PM

As the year draw to a close, I realize I learn more things in these few weeks here than I had the last years.. especially key conceptual stuff. I wonder what life would be like without Physicsforums and the quality advices that we get. I learnt everything about LET and FTL and Causality. I learnt about Preferred Foliations and realized something about Gauge Transformation which I hadn't consider before. So I can understand papers better now than before. Thanks to Peterdonis and Dalespam and others. I learnt that without bringing out what's bothering one. It couldn't be resolved. So before we all forgot about this thread and since this thread is about Preferred Foliation. Let me inquire something more about it before we all forgot about Maudlin stuff.

In Tumulka theory, instead of Preferred Foliation. Tumulka used another device that can produce non-locality but without any Preferred Foliation and it is relativistic. Peterdonis, do you understand the following? Hope you can rephrase them in your own words because I'm not exactly sure how it occurs or how to picture it in my mind (refer to Lubos Motl intro about "flashy GRW" but let's just focus on the Foliation thing (which is independent of the flash GRW):

When we turn to Tumulka’s theory, we find that the punctate ontology permits definition of a surrogate for the foliation theory’s universal clock. Given a point in a relativistic space-time, there are well-defined regions of constant invariant relativistic intervals from the point. The loci of zero intervals are, of course, the light cones, and regions of fixed time-like intervals form hyperbolae that foliate the interiors of the light cones. Since the ‘‘particles’’ are not allowed to reappear at space-like intervals from their previous location, these hyperbolae can serve the role of the universal time function for this particle: the likelihood of the next flash being at a certain location is a function of the time-like interval between the last flash and that location. Such a ‘‘flash-centered clock’’ can be defined using only the Lorentzian metric.

Furthermore, given a locus of constant time-like intervals from a given flash, the Lorentzian metric on space-time will induce a pure spatial metric on that locus (which will be a space-like hypersurface). This pure spatial metric can in turn be used to define the Gaussian used to specify the GRW collapse of the wave function, conditional on the next flash occurring at a specified location on the hypersurface. So the basic tools used in the original GRW theory can be adapted to this milieu using only the Lorentzian metric and the location of the last flash. In the multi-time formalism, the spatio- temporal structures needed to calculate both the conditional probability of the next flash and the new (post-collapse) wave function can be constructed using only the Lorentzian metric and the location of the last flash.

Since only the relativistic metric has been used in the construction, we have a completely relativistic theory.

Note when he referred to "flash", just replace it with "physical wavefunction collapse"
So without Preferred Foliation, he can produce the same effect of non-locality by replacing Preferred Foliation with something else that produced the same effect, do you understand what he is doing Peterdonis?

PeterDonis

Dec30-11, 09:39 PM

Note when he referred to "flash", just replace it with "physical wavefunction collapse" So without Preferred Foliation, he can produce the same effect of non-locality by replacing Preferred Foliation with something else that produced the same effect, do you understand what he is doing Peterdonis?

What you quoted seems pretty clear, yes. Instead of foliating the entire spacetime with lines of constant t, he's foliating the future light cone of a given event with hyperbolas of constant t^2 - x^2, i.e., constant timelike interval from the chosen event. Since those hyperbolas are taken into themselves by a Lorentz transformation (unlike lines of constant t), I can see how this would allow a Lorentz covariant description of the dynamics of a single particle.

What the quote doesn't describe (but maybe it's elsewhere in one of the papers that are still on my list to read) is how this scheme is extended to the case of multiple particles. The problem is that a wavefunction for N particles is not just N copies of a single-particle wavefunction with some interactions thrown in; it's a single wavefunction of N variables, one for each particle. In non-relativistic mechanics, where time is a parameter, not a coordinate, the single time parameter is "shared" by all the particles, i.e., the multi-particle wavefunction evolves in "time" the same way the single-particle one does. But for a relativistic theory this doesn't work; you can't just have a separate "copy" of 4-D spacetime for every particle because they have to interact, but you also can't just have a "shared" time coordinate among all of them because they may be in relative motion. So I'm not sure how you would come up with a Lorentz-covariant analogue of the above hyperbolas of constant t^2 - x^2 for a multi-particle wavefunction.

The reason this is important is that nonlocality is not an issue for a single particle; it only becomes an issue at all if at least two particles are involved, so an EPR-type experiment can take place.

stglyde

Dec30-11, 11:55 PM

What you quoted seems pretty clear, yes. Instead of foliating the entire spacetime with lines of constant t, he's foliating the future light cone of a given event with hyperbolas of constant t^2 - x^2, i.e., constant timelike interval from the chosen event. Since those hyperbolas are taken into themselves by a Lorentz transformation (unlike lines of constant t), I can see how this would allow a Lorentz covariant description of the dynamics of a single particle.

Hyperbolas? Honestly.. I'm not so verse in spacetime diagram to know what hyperbolas are. But I have this book Spacetime Physics by Edwin Taylor in one of the boxes of books in the attic. I'll try to find it tomorrow and read again. But if you think it's as dumb down as Brian Greene books, let me know.

I http://www.amazon.com/Spacetime-Physics-Edwin-F-Taylor/dp/0716723271/ref=pd_sim_sbs_b_1

I'm sure there are software where one can input some parameters and the spacetime diagrams and hyperbolas can be shown in the screen. Do you know such program? There ought to be one given how useful spacetime diagram is.

What the quote doesn't describe (but maybe it's elsewhere in one of the papers that are still on my list to read) is how this scheme is extended to the case of multiple particles. The problem is that a wavefunction for N particles is not just N copies of a single-particle wavefunction with some interactions thrown in; it's a single wavefunction of N variables, one for each particle. In non-relativistic mechanics, where time is a parameter, not a coordinate, the single time parameter is "shared" by all the particles, i.e., the multi-particle wavefunction evolves in "time" the same way the single-particle one does. But for a relativistic theory this doesn't work; you can't just have a separate "copy" of 4-D spacetime for every particle because they have to interact, but you also can't just have a "shared" time coordinate among all of them because they may be in relative motion. So I'm not sure how you would come up with a Lorentz-covariant analogue of the above hyperbolas of constant t^2 - x^2 for a multi-particle wavefunction.

The reason this is important is that nonlocality is not an issue for a single particle; it only becomes an issue at all if at least two particles are involved, so an EPR-type experiment can take place.

Is "extended to the case of multiple particles" related to "interaction Hamiltonian" of some kind "between the various families" or is the latter a separate problem? (see context below) But then it is mentioned "The multi-time wavefunction is defined for a fixed collection of “particles”.. it means Tumulka has solved your issues above? The following is the context of what I'm saying in Mauldin description:

What are the essentials of Tumulka’s theory that allow it to live within the narrow means of the Lorentz metric? It seems essential that the local beable be point-like: the point is a locus that privileges no reference frame. The point also has the virtue of determining, in conjunction with the Lorentz metric, a set of hyperplanes that can be used in place of an imposed foliation. It seems essential that the dynamics be stochastic: we have seen how the determinism of Bohmian mechanics forces a distinction between the two sides of the singlet experiment: one measurement or the other must “come first”. And it seems essential that the local beable be intermittent, or flashy, so that experiments done on one side need not immediately register on the local beables on the other side, as they do in Ghirardi’s theory. Perhaps some of these features can be eliminated, but it is not obvious to me how this could be done.

There are some technical shortcomings of Tumulka’s theory at this point. The multi-time formalism can only be employed when there is no interaction Hamiltonian between the various families, so a lot of existant physics cannot be done in this form. The multi-time wavefunction is defined for a fixed collection of “particles”, so particle creation and annihilation phenomena are not covered. And there seems to be an initiation problem: the calculation of probabilities depends on specifying the “most recent” flash for each “particle”, but presumably right after the Big Bang most of the “particles”had had no flashes at all. It is not clear to me how to get the whole calculation of probabilities off the ground in this circumstance.

But these shortcomings are vastly overshadowed by Tumulka’s accomplishment: he has figured out how to construct a theory that displays quantum non-locality without invoking anything but the Lorentz metric. For years it has been known that no one has proven that the trick can’t be done, and many people suspected that somehow or other it could be done, but Tumulka has shown at least one way to do it."

If you have time in the weekend holidays. The following is Tumulka full paper about it:

A Relativistic Version of the Ghirardi–Rimini–Weber Model

http://arxiv.org/PS_cache/quant-ph/pdf/0406/0406094v2.pdf

stglyde

Dec31-11, 12:29 AM

Hyperbolas? Honestly.. I'm not so verse in spacetime diagram to know what hyperbolas are. But I have this book Spacetime Physics by Edwin Taylor in one of the boxes of books in the attic. I'll try to find it tomorrow and read again. But if you think it's as dumb down as Brian Greene books, let me know.

I http://www.amazon.com/Spacetime-Physics-Edwin-F-Taylor/dp/0716723271/ref=pd_sim_sbs_b_1

I'm sure there are software where one can input some parameters and the spacetime diagrams and hyperbolas can be shown in the screen. Do you know such program? There ought to be one given how useful spacetime diagram is.

Is "extended to the case of multiple particles" related to "interaction Hamiltonian" of some kind "between the various families" or is the latter a separate problem? (see context below) But then it is mentioned "The multi-time wavefunction is defined for a fixed collection of “particles”.. it means Tumulka has solved your issues above? The following is the context of what I'm saying in Mauldin description:

If you have time in the weekend holidays. The following is Tumulka full paper about it:

A Relativistic Version of the Ghirardi–Rimini–Weber Model

http://arxiv.org/PS_cache/quant-ph/pdf/0406/0406094v2.pdf

Reflecting on what you were saying that it can't work on multiple particles. Slowly the "multi-time wave function" came ringing. I guess Tumulka was proposing some kind of multiple Spacetimes as when he said that: (??)

"The technical apparatus Tumulka uses is a bit unfamiliar- for example, he uses a multi-time wavefunction defined over N copies of space-time (for N families of flashes), and he models the “collapse of the wavefunction” as a change from one multi-time wavefunction defined over the whole multi-time space to a different wavefunction defined over that whole space- but these refinements need not detain us. What we can already see is how Tumulka’s choice of local beable aids in rendering the theory completely Relativistic."

So it's like saying one particle uses an entire separate Spacetime? And the wave function is for a collection of them? Do you think this is as outrageous as Many Worlds? Any problems it produced?

I know. If it's true. I think we must not be serious with Tumulka because it is far behind Bohmian Mechanics.

stglyde

Dec31-11, 10:27 AM

stglyde

Dec31-11, 09:26 PM

PeterDonis

Dec31-11, 10:12 PM

I think what you meant is that for non-relativistic wave function. It is N copies of spacetime for each particle.

No. I probably should have given more details before; here they are.

In non-relativistic QM, there is no "spacetime". Time is a parameter, not a coordinate, and there is only one time parameter. Wave functions are functions in a 3N-dimensional space, where N is the number of particles. You can sort of think of this space as N "copies" of a 3-dimensional space, one per particle, but you have to be careful. For one thing, this 3N-dimensional space has different representations; the "configuration space" representation, in which the coordinates in the space are related to spatial positions, is only one such representation. (Another is the "momentum space" representation, where the coordinates in the space are related to spatial momenta.) For another, most wave functions are not "separable", meaning you can't interpret them as saying something like "one particle is at spatial point A and another is at spatial point B"; the factors attached to the different particles mix together in a way that has no straightforward interpretation in terms of "particles at spatial points".

Wave functions on the 3N-dimensional space at one time then evolve into wave functions on the same 3N-dimensional space at another time according to the Schrodinger Equation, for non-relativistic QM.

stglyde

Dec31-11, 10:29 PM

No. I probably should have given more details before; here they are.

In non-relativistic QM, there is no "spacetime". Time is a parameter, not a coordinate, and there is only one time parameter. Wave functions are functions in a 3N-dimensional space, where N is the number of particles. You can sort of think of this space as N "copies" of a 3-dimensional space, one per particle, but you have to be careful. For one thing, this 3N-dimensional space has different representations; the "configuration space" representation, in which the coordinates in the space are related to spatial positions, is only one such representation.

I guess you are just describing Hilbert Space above.. so why didn't you mention Hilbert Space. Unless things can be explained in non-relativistic QM without referring to Hilbert Space?

(Another is the "momentum space" representation, where the coordinates in the space are related to spatial momenta.) For another, most wave functions are not "separable", meaning you can't interpret them as saying something like "one particle is at spatial point A and another is at spatial point B"; the factors attached to the different particles mix together in a way that has no straightforward interpretation in terms of "particles at spatial points".

Wave functions on the 3N-dimensional space at one time then evolve into wave functions on the same 3N-dimensional space at another time according to the Schrodinger Equation, for non-relativistic QM.

PeterDonis

Dec31-11, 10:31 PM

I guess you are just describing Hilbert Space above.. so why didn't you mention Hilbert Space. Unless things can be explained in non-relativistic QM without referring to Hilbert Space?

"Hilbert space" is a general term for a type of abstract vector space in mathematics. The 3N-dimensional space I was describing for the wave function is a Hilbert space, yes.

stglyde

Dec31-11, 10:52 PM

No. I probably should have given more details before; here they are.

In non-relativistic QM, there is no "spacetime". Time is a parameter, not a coordinate, and there is only one time parameter. Wave functions are functions in a 3N-dimensional space, where N is the number of particles. You can sort of think of this space as N "copies" of a 3-dimensional space, one per particle, but you have to be careful. For one thing, this 3N-dimensional space has different representations; the "configuration space" representation, in which the coordinates in the space are related to spatial positions, is only one such representation. (Another is the "momentum space" representation, where the coordinates in the space are related to spatial momenta.) For another, most wave functions are not "separable", meaning you can't interpret them as saying something like "one particle is at spatial point A and another is at spatial point B"; the factors attached to the different particles mix together in a way that has no straightforward interpretation in terms of "particles at spatial points".

Wave functions on the 3N-dimensional space at one time then evolve into wave functions on the same 3N-dimensional space at another time according to the Schrodinger Equation, for non-relativistic QM.

Earlier you wrote "But for a relativistic theory this doesn't work; you can't just have a separate "copy" of 4-D spacetime for every particle because they have to interact". You sounded as if in non-relativistic theory, one can have separate "copy" of 4-D spacetime. But then, spacetime doesn't exist in non-relativistic theory. So what is the scenerio where one can have "a separate "copy" of 4-D spacetime for every particle"? I guess none. Anyway. How does relativistic quantum field theory implement it all? But Smolin mentioned particles still move in fixed background even in QFT.. so you agree that we still don't have a true and pure relativistic formulation even in relativistic QFT?

stglyde

Jan1-12, 12:16 AM

Earlier you wrote "But for a relativistic theory this doesn't work; you can't just have a separate "copy" of 4-D spacetime for every particle because they have to interact". You sounded as if in non-relativistic theory, one can have separate "copy" of 4-D spacetime. But then, spacetime doesn't exist in non-relativistic theory. So what is the scenerio where one can have "a separate "copy" of 4-D spacetime for every particle"? I guess none. Anyway. How does relativistic quantum field theory implement it all? But Smolin mentioned particles still move in fixed background even in QFT.. so you agree that we still don't have a true and pure relativistic formulation even in relativistic QFT?

Mulling it. I think what Smolin was saying was our QFT was not background independent (GR metric) although it uses the Minkowski metric (SR). And we know the Dirac Equation is the equation of relativistic QM. The following passage in the Tumulka paper we saw before would have many good food for thoughts:

http://arxiv.org/PS_cache/quant-ph/pdf/0406/0406094v2.pdf

A Relativistic Version of the Ghirardi–Rimini–Weber Model

The wavefunction is a multi-time wavefunction, i.e., it is defined on the Cartesian
product of N copies of space-time. We use the Dirac equation as the relativistic version
of the Schr¨odinger equation determining the evolution of the wavefunction apart
from the collapses (but we will mostly not worry whether the wavefunction lies in the
positive energy subspace, except in Section 3.7). More precisely, we use the multi-time
formalism with N Dirac equations. For the consistency of this set of equations, we
cannot have interaction potentials. To avoid discussing the question of interaction in
relativistic quantum mechanics, we will assume non-interacting particles. Interaction
can presumably be included by allowing for particle creation and annihilation, which
however is beyond the scope of this paper. In any case, the difficulty of including interaction
that we encounter here does not stem from the spontaneous collapses but rather
from the mathematics of multi-time equations, and is thus encountered by every kind
of relativistic quantum mechanics.

You mentioned that non-relativistic QM doesn't have spacetime. Since the paper mentioned it has "N copies of space-time", then it is relativistic after all. It uses the Dirac equation which is completely relativistic. However, there is something I can't quite completely understand. It avoided "interaction potentials" to avoid inconsistency of equations. And in the last sentence, it mentioned that relativistic quantum mechanics has difficulty with interactions. Maybe it's referring to QFT as being a theory where interactions occur and QM having no interactions, and since it uses the latter, interactions are temporarily avoided? But I still can't understand how it is able to use relativistic equations for the hyperbolas of t^2-x^2 as you mentioned earlier. Anyway. For those who do. Please let us know how. Thanks.

stglyde

Jan1-12, 01:57 AM

harrylin

Jan1-12, 05:46 AM

I just realized something silly. We have been discussing about Spacetime Foliations for more than a week. All along I was thinking it was for Bohmian Mechanics. But Peterdonis emphasized there was not even spacetime for nonrelativistic theory. And since the BM as we knew it is nonrelativistic. Then it doesn't even need spacetime foliations. It simply needs newtonian absolute simultaneity. So our spacetime foliations are for other theories with Beable like features. But since Tumulka flashing GRW is relativistic, and so is Demystifier BM, then there is no use of the spacetime foliations. And considering Copenhagen doesn't need any foliations because it's nonlocality is in the equations and no way to send signal. Then there is absolutely few or use of the preferred foliations.

I have to write this down so I can refer to this thread in the future for review and as note. Journey entry New Year's Day: Worrying about foliations and non-existent spacetime in nonrelativistic theory. Gee.
I'm now far behind with looking at the interesting references of this thread, that's for later. Consequently I can't really comment on your conclusions. My first impression is that those "flashing" foliation theories are pseudo science, and I think that the Copenhagen interpretation is a pseudo interpretation (effectively a physical non-interpretation). :tongue2: Anyway, the subtle thing about "spacetime" is that of course space-time is (and has been from the start) an important part of classical mechanics. Only Minkowskian (as well as post-Minkowskian) Spacetime is a new concept that corresponds to a popular interpretation of relativistic mechanics.

stglyde

Jan1-12, 06:23 AM

I still haven't read through the papers completely, but from skimming them I certainly don't think they are in the "Not Even Wrong" category.

One item I think is missing from the paper linked to above is that there are no specific references given for this statement on p. 1: "it is often argued that no model of nonlocal reality can be compatible with relativity". I'm not sure this is right; what I understand to be "often argued" is that no *local* model of reality can be compatible with quantum mechanics. I also have seen it said that nonlocality *appears* to be incompatible with the "spirit" of relativity, but that is clearly not a rigorous claim as it stands; and AFAIK nobody has actually tried to make such an argument rigorously (which would be very difficult since standard quantum field theory predicts correct results for EPR experiments but is explicitly relativistically covariant).

The statement is not central to the paper, which is mainly about giving a relativistically covariant version of Bohmian mechanics, so it's not a crucial point, but I would still be interested to see specific references in relation to it.

Peter, I searched Demystifier paper at Physicsforum archives and there are many hits but only few comments. The most is the one by Maaneli in the thread http://www.physicsforums.com/showthread.php?t=366994&page=6 where I learnt quite a few things and in one of the papers referenced there. I found out the following which is Nikolic claiming time as parameter in newtonian space is somehow carried to relativistic coordinate time! Yes. So before I start a new thread on this. Hope to get your comment on the following since it's related to our recent discussions about parameter vs coordinate time (and in the following Nikolic said the former is retained in the latter explaining non-locality??!):

http://xxx.lanl.gov/PS_cache/arxiv/pdf/1007/1007.4946v1.pdf

sec 2.1

For nonrelativistic particle systems with conserved energy, the forces do not have an explicit dependence on time t. The only quantities that have a dependence on t are particle trajectories Xia (t), i = 1, 2, 3. Thus, the parameter t has a physical meaning only along trajectories; time without trajectories does not exist! In this sense, t is only an auxiliary parameter that serves to parameterize the trajectories in 3-dimensional space, not a fundamental physical quantity by its own. Yet, a “clock” can measure time indirectly. Namely, a “clock” is nothing but a physical process described by a function Xia (t) periodic in t. One actually observes the number of periods, and then interprets it as a measure of elapsed time.

The theory of relativity revolutionized the concept of time by replacing the parameter t with a coordinate x0 treated as a 4th dimension not much different from other 3 space dimensions. Yet, it does not mean that an auxiliary Newton-like time parameter is completely eliminated from relativistic mechanics. Such a parameter can still be introduced to parameterize relativistic spacetime particle trajectories in a manifestly covariant manner. This parameter, denoted by s, can be identified with a generalized proper time defined along particle trajectories of many-particle systems [23]. The parameter s can even be measured indirectly by a “clock” corresponding to a physical process periodic in s, in complete analogy with measurement of t in nonrelativistic mechanics. As discussed in more detail in [23], this makes the parameter s appearing in (6) a physical quantity, very much analogous to Newton time
t. With this physical insight, the relativistic-covariant equation (7) is to be interpreted as physical probability conservation during the evolution parameterized by the evolution-parameter s"

Comment anyone? Could it be true?

stglyde

Jan1-12, 07:56 AM

The following are important exchanges between Demystifier (Nikolic) and Physicforums only challenger (Maaneli). The contents are important because what is at stake is the soul of physics and the great debate about non-locality.

Selected vital quotes from the thread "Re: Pilot wave theory, fundamental forces":

Maaneli: the relativity of simultaneity is nevertheless a consequence of the metrical structure of Minkowski spacetime

Demystifier: No, this is not true. What is true is that the metrical structure of Minkowski spacetime implies relativity of simultaneity IF THERE IS NO ANY OTHER STRUCTURE. But in the case we are considering there is another structure. And this additional structure is not the parameter s (as you might naively think), but the non-local wave function. (Or the scalar potential in the classical setting discussed in http://xxx.lanl.gov/abs/1006.1986.)

And yet, you can see that this nonlocal wave function (or the scalar potential) is compatible with the metrical structure of Minkowski spacetime and does not introduce a foliation-like structure.

So, does it mean that you agree that WITH example of my theory there IS a known dynamical structure that is consistent with the metrical structure of Minkowski spacetime, and yet violates the relativity of simultaneity?

By the way, one can introduce such a structure even in classical local relativistic mechanics. Consider two twins who initially have the same velocity and same position, and their clocks show the same time. After that, they split apart, and each has a different trajectory, independent of each other. Yet, one can consider pairs of points on two trajectories which have THE SAME VALUE OF PROPER TIME (showed by a local clock on each trajectory). Such a structure (defined at least mathematically, if not experimentally) also can be said to violate relativity of simultaneity, in a way very similar to that of my theory. Of course, there is a difference, but the similarity may be illuminating too.

Demystifier: Or let me use an analogy with nonrelativistic BM. A point is space is denoted as r=(x,y,z). Consider two particles with space positions {\bf r}_1 and {\bf r}_2 at a given time t. There is a Cartesian frame (given by a rotation of the original Cartesian frame) in which {\bf r}_1 and {\bf r}_2 have the same value of z. In this frame, we say that the interaction between these two particles is z-taneous. Does it lead to any paradoxes? Does it mean there is a preferred z-coordinate? Does it mean there is a preferred foliation of space into 2-surfaces? Whatever your answer is, the same answer applies to analogous questions in relativistic-covariant BM. And if you still don't get it, then look at the equations of relativistic-covariant BM again.

Maaneli: ... by virtue of the fact that you have to synchronize the initial (spacetime) positions of the particles at a common time s,

Demystifier: The parameter s is not time.

Maaneli: But as a "joint parameter", it plays precisely the role of a universal time parameter for the evolution of the particle spacetime coordinates. Yes, I realize that the wavefunction on configuration spacetime doesn't depend on s, but that doesn't mean that s cannot also be interpreted as a time parameter (even if it is a fictitious one).

Demystifier: You are right. The parameter s can be interpreted as a sort of time. However, this is more like Newton absolute time, note like Einstein relativistic time [which I already implied by saying it is a UNIVERSAL time parameter]. OK, that's clear enough. And you are right, nonlocal signaling violates the relativity of simultaneity. Yet, in the next post I explain why it is NOT in contradiction with metrical structure of Minkowski spacetime.

(Maaneli in other message mentioned Nikolic theory has foliation like structure)

Demystifer: No, there is no foliation-like structure. The synchronization parameter is NOT something additional to the SR metrical structure, just as time in nonrelativistic BM is NOT something additional to the 3-space rotational-symmetry structure.

My point is that relativistic-covariant BM in 4-dimensional spacetime is ANALOGOUS to nonrelativistic BM in 3-dimensional space. I am just trying to make you understand this ANALOGY, because when you do, you will suddenly say: "Oh, THAT is what you meant. Now I get it. In fact, it is trivial." But it is essential that you see this analogy by yourself, while I can only guide you in the right direction. And at the moment, it seems to me that you don't have a clue what I am talking about, because you are not able to see the analogy. And that is probably because you are unable to think of time as just another "space" coordinate.

To help you think in the correct way, let me suggest you a mental trick. For a moment, FORGET that the spacetime metric has the form (+---). Instead , think of metric as just any metric, which can be (++++), (++--), or whatever. In fact, simply don't think about metric at all. Just pretend that you have a 4-dimensional space with some unspecified metric. Or if it is easier for you, just pretend that the metric is (++++). And forget that one of the coordinates is called "time". (Who cares about names, anyway?) And NOW try to understand again what equations of relativistic-covariant BM are actually saying. This trick works for many physicists, so it could work for you as well.

(Note: the last exchange between Demystifer and Maaneli occured in Jun 22, 2010)

Maaneli: Of course, by covariant, you must mean "fundamentally covariant", because anyone can construct a covariant particle dynamics on a preferred foliation. I think it might be best for us to resume our discussion on the old thread, "Pilot waves, fundamental forces, etc.", regarding whether your proposal of using a synchronization parameter and treating time and space on equal footing is truly fundamentally covariant or not, and whether or not it does have the condition of equivariance. We never got to finish that discussion, mainly because I became too overwhelmed with deadlines and work and kept forgetting to reply to the thread. My apologies about that.

Demystifier: I would like to continue the discussion there. But I will wait for your first step.

(But they never continued. And since June, 2010. There is no other challenger to Demystifier. And he continued to share his papers which are referenced in peer reviewed journals but unfortunately, no one read it much. Therefore let us continue and settle it once and for all whether Demystifier is fundamentally correct. Before I make a new thread out of this. Just want some comment from you PeterDonis on what you think about all this. Thanks)