High School Questions on QFT & QM: Is QM or QFT Absolute Time?

[Lynch101]

Please give a reference. I'm not aware of any such derivation.

Poincaré anticipated the seminal work of Herman Minkowski on the four-dimensional formulation of special relativity. However, unlike relativity in four-dimensional space-time, in the ether theory these properties represent mere mathematical niceties that do not have a physical meaning.

Pablo Acuña L. On the Empirical Equivalence between Special Relativity and Lorentz’s Ether Theory.

his achievements in this area were largely mathematical: formulating the notion of the Lorentz group andfinding its invariants, formulating the notion of a four-vector andfinding quantities that transform like four-vectors, interpreting the Lorentz transformations as rotations in four-dimensional space. These are results that follow from the mathematical structure of the equations, not from any physical understanding of their significance; they paved the way for the powerful mathematical formalism developed by later workers in the field, but did not provide the essential physical insight that provides the formalism with its application.

And PhysicsForums own policy on LET and Block Universe suggests the predictive equivalence between the two interpretations.

 

[Lynch101]

Since it's built in relativity, it's also built in any mathematical formulation of it.

I don't understand what you mean and why is there any "absolute time" involved in the discussion of relativity.

Does it form part of the minimal interpretation of the mathematics, or is it part of the Einsteinian interpretation.

As I mentioned in this post Poincaré [appears to have] derived the mathematics of Minkowski spacetime from a foundation of absolute time, which is why I would question the idea that relativity of simultaneity is baked into the mathemaical formalism.

 

[Lynch101]

Smolin's discussion is basically about background independence in Quantum Gravity and a hidden variable theory of sorts. As @PeterDonis has said trying to learn about QM and QFT from such advanced subjects is not a good idea. Inferring things as "pertinent" is not valid as he is discussing a subject way beyond what you are talking about.

I appreciate that but not all the quotes are from Smolin and some of them are taken from literature aimed at the lay audience. The quotes taken from the perimeter roundtable are perhaps not meant for a lay audience and may presuppose a level of background knowledge, but the statement about "time which is absolute" is so explicit and it's juxtaposition with the "relative and dynamical" time of GR so intentional that I struggle to see how any level of background knowledge could alter the meaning.

Even if it is made in the context of QG, the question would remain as to why it is raised as an issue at all.

 

[weirdoguy]

As I mentioned in this post Poincaré [appears to have] derived the mathematics of Minkowski spacetime from a foundation of absolute time

And I see no justification of such claims in what you've quoted. Mathematics of Minkowski spacetime is internally inconsistent with the notion of absolute time, period.

 

[weirdoguy]

and some of them are taken from literature aimed at the lay audience

Which, per PF rules, is not a suitable source for a discussion. The main issue is not absolute time, because there is none in QFT, it's the 'background dependence' of the theory.

 

[Lynch101]

If the $t$ in the Schrodinger equation can be transformed into the $t$ in a different coordinate system with a different notion of simultaneity then time isn't absolute in the Newtonian sense.

I'll try to clarify my own misunderstanding.

How I'm interpreting it is that you have the quantum system under consideration, with time 't' being provided by a clock outside the system. You're saying this can be transformed into the 't' of another frame.

I'm imagining a system of two relatively moving observers where the time is given by a clock outside the system i.e. common time for both observers and this 't' can be transformed to the 't' of another frame.

 

[DarMM]

The quotes taken from the perimeter roundtable are perhaps not meant for a lay audience and may presuppose a level of background knowledge, but the statement about "time which is absolute" is so explicit and it's juxtaposition with the "relative and dynamical" time of GR so intentional that I struggle to see how any level of background knowledge could alter the meaning

And yet you have read it wrong. As @weirdoguy has said they are discussing background dependence, not time being absolute in the Newtonian sense. The contrast is between the background dependence of QM and the background independence (i.e. dynamic background) of GR.

Again it's not about absolute time in the Newtonian sense.

 

[DarMM]

I'm imagining a system of two relatively moving observers where the time is given by a clock outside the system i.e. common time for both observers and this 't' can be transformed to the 't' of another frame.

Yes and can be done so in a way that is Lorentz invariant.

 

[Lynch101]

And I see no justification of such claims in what you've quoted. Mathematics of Minkowski spacetime is internally inconsistent with the notion of absolute time, period.

I'm basing it on Poincaré's derivation of the mathematics. Did he not derive the mathematics of Minkowski independently of him? That is why I ask if they are "baked" into the mathematics.

 

[Lynch101]

Which, per PF rules, is not a suitable source for a discussion. The main issue is not absolute time, because there is none in QFT, it's the 'background dependence' of the theory.

apologies, we can limit it to the statement from the perimeter roundtable

 

[Lynch101]

And yet you have read it wrong. As @weirdoguy has said they are discussing background dependence, not time being absolute in the Newtonian sense. The contrast is between the background dependence of QM and the background independence (i.e. dynamic background) of GR.

Again it's not about absolute time in the Newtonian sense.

ah, OK. I've read a bit about the background dependence vs independence problem. I'll go back and have a look at that. Thanks

 

[weirdoguy]

Did he not derive the mathematics of Minkowski independently of him? That is why I ask if they are "baked" into the mathematics.

Apparently he did, but if he only focused on mathematics he could not base it on the notion of absolute time since time is not a mathematical concept. It sais in your quote that he 'formulated the notion of Lorentz group' and the thing is that the mathematical structure of Lorentz group is inconsistent with absolute time. Actually the structure of Lorentz group leavs barely no room for different physical interpretations.

 

[vanhees71]

Apologies, I've come across the idea of NRQM before but don't fully understand why the likes of Smolin and the others I quoed would talk NRQM when QFT supercedes it.

I fail completely to understand why Smolin talks at all...

 

[Lynch101]

Apparently he did, but if he only focused on mathematics he could not base it on the notion of absolute time since time is not a mathematical concept. It sais in your quote that he 'formulated the notion of Lorentz group' and the thing is that the mathematical structure of Lorentz group is inconsistent with absolute time. Actually the structure of Lorentz group leavs barely no room for different physical interpretations.

I see. Would it be compatible with timelessness?

If time is not a mathematical concept, would that not mean that relativity of simultaneity is not "baked" into the mathematics of Minkowski?

 

[Lynch101]

Yes and can be done so in a way that is Lorentz invariant.

Why isn't that at odds with relativity? I thought that there is a time 't' or each particle in relativity, such that if you were to have a clock outside the system, then that would be a separate reference frame

 

[Lynch101]

I fail completely to understand why Smolin talks at all...

 

[DarMM]

Why isn't that at odds with relativity? I thought that there is a time 't' or each particle in relativity, such that if you were to have a clock outside the system, then that would be a separate reference frame

Lorentz transforming between different $t$ coordinates is directly a part of Relativity, I can't see how it would contradict it. You're free to use any reference frame to anaylse the situation and able to transform among them. That's all in accord with relativity. I don't see the contradiction.

 

[Lynch101]

Lorentz transforming between different $t$ coordinates is directly a part of Relativity, I can't see how it would contradict it. You're free to use any reference frame to anaylse the situation and able to transform among them. That's all in accord with relativity. I don't see the contradiction.

I don't see one myself, it's just that I don't have a clear idea of it.

I'm not sure if the following makes sense, but I'm imagining a system of let's say two particles. How I'm understanding it is that QM uses a common time for both particles, while relativity would have relative, dynamical time for each particle.

EDIT: or maybe it's more a case of there is a common time for the experimenter in the lab and the reatively moving particle? As I say, I'm not entirely clear on it myself

 

[DarMM]

It's just as it is in Relativity the various systems can be analysed in any other frame. $t$ is just the time of the frame in which one performs the analysis.

Do you know the mathematics of Relativity.

 

[Lynch101]

It's just as it is in Relativity the various systems can be analysed in any other frame. $t$ is just the time of the frame in which one performs the analysis.

Do you know the mathematics of Relativity.

Unfortunately not. I wish I knew in high school what I know now. I would have made different choices.

Am I wide of the mark when I think that QM can have a common time for a system of relatively moving particles, while relativity would have relative time for each particle?

 

[DarMM]

Unfortunately not. I wish I knew in high school what I know now. I would have made different choices.

Am I wide of the mark when I think that QM can have a common time for a system of relatively moving particles, while relativity would have relative time for each particle?

QFT would be no different from Relativity in this regard. There's a time for each of the particles and then the time for the frame you are using to analyse these particles.

 

[PeterDonis]

Pablo Acuña L. On the Empirical Equivalence between Special Relativity and Lorentz’s Ether Theory.

As @weirdoguy has already noted, this does not say what you claimed. It says that Poincare derived in detail the mathematical properties of the Lorentz group, which was indeed a very useful mathematical background for later work. But it has nothing whatever to do with "absolute time".

PhysicsForums own policy on LET and Block Universe suggests the predictive equivalence between the two interpretations.

Sure, but that still has nothing to do with what Poincare did.

I would question the idea that relativity of simultaneity is baked into the mathemaical formalism.

This is not only wrong, but egregiously wrong. How much time have you spent working actual problems using the mathematical formalism?

it's confusing as to why these scientists would even consider raising such an issue if QFT completely negated it.

They raise it because they are considering the hypothesis that QFT as we now have it is not a fundamental theory. In other words, they are looking at possible theories that could have QFT as we now have it as an emergent approximation. Those theories might have some kind of "absolute time" in them even if QFT as we now have it does not. They are doing this because that is their current approach to trying to find a theory of quantum gravity.

In other words, when these people talk about "absolute time", they are not talking about anything that has been established by actual measurements or evidence or anything that is claimed by our best current theories at the most fundamental level those theories have. They are talking about a speculative hypothesis that they personally favor. That speculative hypothesis happens to be somewhat similar to how non-relativistic QM works, so they use non-relativistic QM as an analogy to illustrate what their speculative hypothesis is like.

 

[Lynch101]

As @weirdoguy has already noted, this does not say what you claimed. It says that Poincare derived in detail the mathematical properties of the Lorentz group, which was indeed a very useful mathematical background for later work. But it has nothing whatever to do with "absolute time".

Sure, but that still has nothing to do with what Poincare did.
This is not only wrong, but egregiously wrong. How much time have you spent working actual problems using the mathematical formalism?

But he derived it from relatively moving frames, in a manner similar to how Einstein did. But his interpretation of the mathematics included absolute time and simultaneity. How would this be possible if the mathematics necessitates RoS?

They raise it because they are considering the hypothesis that QFT as we now have it is not a fundamental theory. In other words, they are looking at possible theories that could have QFT as we now have it as an emergent approximation. Those theories might have some kind of "absolute time" in them even if QFT as we now have it does not. They are doing this because that is their current approach to trying to find a theory of quantum gravity.

In other words, when these people talk about "absolute time", they are not talking about anything that has been established by actual measurements or evidence or anything that is claimed by our best current theories at the most fundamental level those theories have. They are talking about a speculative hypothesis that they personally favor. That speculative hypothesis happens to be somewhat similar to how non-relativistic QM works, so they use non-relativistic QM as an analogy to illustrate what their speculative hypothesis is like.

The question I had though, was how such an issue could even be raised if QFT already took care of this.

From the thread I started on entanglement it would appear that it comes down to a question of realism/representationalism vs anti-realism.

 

[PeterDonis]

he derived it from relatively moving frames

Basically, yes.

his interpretation of the mathematics included absolute time and simultaneity

His interpretation of the math is not the math. If there is nothing in the math about absolute time and absolute simultaneity, which there isn't, then the math doesn't have those things.

Also, the reference you gave says nothing whatever about his interpretation of the math. Where are you getting his interpretation of the math from?

The question I had though, was how such an issue could even be raised if QFT already took care of this.

Did you read what I said? I'll quote it again:

they are considering the hypothesis that QFT as we now have it is not a fundamental theory

If QFT as we now have it is not a fundamental theory, then it can't "take care of" anything, because it's not fundamental, and a more fundamental theory could have different properties.

 

[Lynch101]

Basically, yes.

His interpretation of the math is not the math. If there is nothing in the math about absolute time and absolute simultaneity, which there isn't, then the math doesn't have those things.

Does that not imply that relativity of simultaneity is also not in the math, but rather an interpretation of it?

Also, the reference you gave says nothing whatever about his interpretation of the math. Where are you getting his interpretation of the math from?

The paper I referenced talks about the Lorentz-Poincaré interpretation and its basis of absolute time and simultaneity.

If QFT as we now have it is not a fundamental theory, then it can't "take care of" anything, because it's not fundamental, and a more fundamental theory could have different properties.

Does it boil down to the realism vs anti-realism debate?

 

[PeterDonis]

Does that not imply that relativity of simultaneity is also not in the math, but rather an interpretation of it?

No. Relativity of simultaneity--the fact that simultaneity is different in different Lorentz frames--is directly in the math. The "interpretation" under which "absolute simultaneity" is claimed simply consists of saying that one particular Lorentz frame (but we can never know which one) is the "absolute" one, and its (relative) notion of simultaneity is called "absolute simultaneity" (and similarly its relative notion of time is called "absolute time"). But there's nothing like that in the math, because there's nothing in the math that picks out anyone particular Lorentz frame as being different from the others; they're all the same in the math.

Does it boil down to the realism vs anti-realism debate?

I don't think so; I think that question is a different question from the question of whether QFT as we currently have it is truly fundamental, or whether it's emergent from some other more fundamental theory.

 

[Lynch101]

No. Relativity of simultaneity--the fact that simultaneity is different in different Lorentz frames--is directly in the math. The "interpretation" under which "absolute simultaneity" is claimed simply consists of saying that one particular Lorentz frame (but we can never know which one) is the "absolute" one, and its (relative) notion of simultaneity is called "absolute simultaneity" (and similarly its relative notion of time is called "absolute time"). But there's nothing like that in the math, because there's nothing in the math that picks out anyone particular Lorentz frame as being different from the others; they're all the same in the math.

But the Lorentz group was derived from the relative motion between the two [absolutely] moving inertial frames. I was thinking that the absolute reference frame could be considered as "scaffolding" and later removed. This would leave just the two relatively movinng frames but with no relativity of simultaneity.

My understanding is that the relativity of simultaneity is derived from the metaphysical assumption of the one-way SoL, as opposed to being a necessary consequence of the mathematics?

I don't think so; I think that question is a different question from the question of whether QFT as we currently have it is truly fundamental, or whether it's emergent from some other more fundamental theory.

Can QFT be considered fundamental if it doesn't explain what happens in individual experiments?

 

[PeterDonis]

the Lorentz group was derived from the relative motion between the two [absolutely] moving inertial frames

This would be a valid description of one way of deriving the Lorentz group if the word "absolutely" were not there. But with the word "absolutely" included, it's wrong. There is nothing whatever in the math that picks out any inertial frame as being different from any other, or that picks out particular frames as being "moving" or "at rest".

How familiar are you with the math of SR? I think you said before that you had never studied it. If you haven't, you should really, really, really take the time to do so before making claims about it.

My understanding is that the relativity of simultaneity is derived from the metaphysical assumption of the one-way SoL, as opposed to being a necessary consequence of the mathematics?

Your understanding is wrong. Go study the math.

Can QFT be considered fundamental if it doesn't explain what happens in individual experiments?

That's a matter of opinion. Some physicists think it can, others think it can't. Smolin and his colleagues appear to be among the latter group.

 

[Lynch101]

This would be a valid description of one way of deriving the Lorentz group if the word "absolutely" were not there. But with the word "absolutely" included, it's wrong. There is nothing whatever in the math that picks out any inertial frame as being different from any other, or that picks out particular frames as being "moving" or "at rest".

I understand that point. Apologies if this is over speculative but I'm just thinking out loud when I say that [I imagine] we could take Poincaré's derivation where he starts with the absolute reference frame and we could treat that absolute reference frame as "scafffolding" which can later be removed. This would leave us with the mathematics of Minkowski but without RoS.

I'm not certain about this, again something that occurred to me as I've been learning more about this; an alternative would be to amend Einstein's derivation with a roundttrip light principle, given that the one-way SoL hasn't been (or possibly can't be) measured. I imagine this should also return the mathematics of Minkowski without RoS "baked" in.

How familiar are you with the math of SR? I think you said before that you had never studied it. If you haven't, you should really, really, really take the time to do so before making claims about it.

Your understanding is wrong. Go study the math.

I'm familiar with the math and others have applied it in discussions and explained how it works, so I haven't formally studied it but I have an understanding of it. The point that RoS comes from the one-way SoL is based on statements made by others who are familiar withh the math. They have stated that the one-way speed of light is encoded in the math and that RoS follows from Einstein's 2 postulates - the 2nd being the one-way SoL.

That's a matter of opinion. Some physicists think it can, others think it can't. Smolin and his colleagues appear to be among the latter group.

ah, I see.

 

[PeterDonis]

we could take Poincaré's derivation where he starts with the absolute reference frame

You're missing the point: Poincare's derivation does not start with an absolute reference frame. There is no absolute reference frame anywhere in the math. The only "absolute reference frame" was in Poincare's personal interpretation.

The point that RoS comes from the one-way SoL is based on statements made by others who are familiar withh the math.

Please give specific references.