I'm just wondering what the generally accepted status of Minkowski spacetime is, as represented by the "block universe" concept, within the field of physics?

From discussing the idea with some people they make it seem like it's the block universe or nothing, but some people regard it simply as a philosophical idea and treat it as almost non-scientific. While it seems to be a philosophical concept, it also gets painted as a necessary consequence of Einsteinian relativity, such that, if Einsteinian relativity is correct then, by extension, some variation of the block universe is a necessary consequence. The impression that seems to be given is that if the mathematics of relativity represents the physical universe, then the the physical embodiment of the mathematics comes in the form of the block universe, or some variation on it, for example the growing block theory.

Given that Einsteinian relativity has the concept of relativity of simultaneity as a necessary component, it would seem that some variation of the block universe is a necessary consequence, although the size of the block, in terms of the timespan, is not necessarily defined.



I'm just wondering how Minkowski spacetime, as represented by the block universe, is generally viewed in the field of phyiscs; by physicists, philosophers of science, or whoever?

I must confess I'm not particularly familiar with the block universe. Does it make any physical predictions that standard relativity does not?

twistor59: Don't some of the mathematical physicist types just like chasing elegant reformulations of theories for their own sake? I kind of thought that's what Minkowski spacetime is: a really elegant reformulation of relativity. I thought it was supposed to be similar to what Noether did in interpreting conservation laws in terms of invariances. If so, then it's not about making predictions, but perhaps giving a much more elegant and deeper understanding of something.

I'd also like to know about its "status", because the picture painted by the block-universe gives me the willies (in a cool way).

???

@JHendrix wrote an excellent post on related matters. If you scroll down to "The Kalam’s serious problems with modern science", there is a discussion about the block universe theory versus something called the "Neo-Lorenzian" view.

It risks letting a physics thread get bogged down in wibble, but I'd like to hear more stuff about this, in order to preserve my willies.

twistor59 wrote:I must confess I'm not particularly familiar with the block universe. Does it make any physical predictions that standard relativity does not?

I'm not a physicist, and unfortunately have never studied it, so I can only offer a laypersons perspective, based on discussions I've had and the information I've encountered; but as far as I know, it doesn't necessarily make any testable predictions that standard relativity doesn't make, although it may imply certain physical consequences.

I'm not sure if it would be considered representative of the mainstream thinking, but scientific documentaries such as NOVAs "the Fabric of the Cosmos" and other documentaries appear to paint "the block universe" as being the logical consequence of Einstein's relativity. It seems that the idea is that, if the universe has an overall, macroscopic, physical structure, then the block universe is it i.e that is how the universe has to exist. The suggestion appears to be that the mathematics of relativity point to this "block universe" model, where "past", "present", and "future" co-exist within the spacetime continuum. That would represent the physical consequences of the model, which would appear to be untestable.

Essentially, the impression I get is that, if the mathematics represents the physical world then the block universe is the embodiment of the mathematics of Einsteinian relativity. Again, I'm not sure if that is representative of mainstream thinking within the field of physics, but it is certainly the idea that seems to be in the public mainstream - which, of course, can be two completely different things.

VazScep wrote:@[color=#CC0000][b]JHendrix[/b][/color] wrote an excellent post on related matters. If you scroll down to "The Kalam’s serious problems with modern science", there is a discussion about the block universe theory versus something called the "Neo-Lorenzian" view.

It risks letting a physics thread get bogged down in wibble, but I'd like to hear more stuff about this, in order to preserve my willies.

Cheers VazScep, I'll check that out.

VazScep wrote:twistor59: Don't some of the mathematical physicist types just like chasing elegant reformulations of theories for their own sake? I kind of thought that's what Minkowski spacetime is: a really elegant reformulation of relativity. I thought it was supposed to be similar to what Noether did in interpreting conservation laws in terms of invariances. If so, then it's not about making predictions, but perhaps giving a much more elegant and deeper understanding of something.

I'd also like to know about its "status", because the picture painted by the block-universe gives me the willies (in a cool way).

???

Yes, this is what's confusing me - for me, Minkowski space IS relativity (special anyway). I don't think of it as a reformulation, but rather as the most natural formulation imaginable. I don't see what the block universe does that's different to Minkowski space. Block universe just seems like some sort of philosophical statement, whose content I don't really get.

I hear things like "well it means that the past, present and future are equally real". But I haven't a clue what "real" means.

mangaroosh wrote:

twistor59 wrote:I must confess I'm not particularly familiar with the block universe. Does it make any physical predictions that standard relativity does not?

I'm not a physicist, and unfortunately have never studied it, so I can only offer a laypersons perspective, based on discussions I've had and the information I've encountered; but as far as I know, it doesn't necessarily make any testable predictions that standard relativity doesn't make, although it may imply certain physical consequences.

I'm not sure if it would be considered representative of the mainstream thinking, but scientific documentaries such as NOVAs "the Fabric of the Cosmos" and other documentaries appear to paint "the block universe" as being the logical consequence of Einstein's relativity. It seems that the idea is that, if the universe has an overall, macroscopic, physical structure, then the block universe is it i.e that is how the universe has to exist. The suggestion appears to be that the mathematics of relativity point to this "block universe" model, where "past", "present", and "future" co-exist within the spacetime continuum. That would represent the physical consequences of the model, which would appear to be untestable.

Essentially, the impression I get is that, if the mathematics represents the physical world then the block universe is the embodiment of the mathematics of Einsteinian relativity. Again, I'm not sure if that is representative of mainstream thinking within the field of physics, but it is certainly the idea that seems to be in the public mainstream - which, of course, can be two completely different things.

Yes, that's my impression too. As soon as you're dealing with a 4 dimensional spacetime, presumably you've got yourself a block universe?

Background information: http://plato.stanford.edu/entries/spacetime-bebecome/

And some more in section 2 here:

http://arxiv.org/ftp/quant-ph/papers/0605/0605039.pdf

- although it just sounds like the wow factor that we first had when we learned special relativity for the first time. Nothing additonal.

twistor59 wrote:

Yes, that's my impression too. As soon as you're dealing with a 4 dimensional spacetime, presumably you've got yourself a block universe?

Twistor, take a second look at that paper. It's full of nonsense. Here's one statement that got me jumped off the floor: "The received view has it that Schrödinger’s equation is Galilean invariant, so it is generally understood that NRQM resides in Galilean spacetime and therefore respects absolute simultaneity."

No, in QM, the quantum states are vectors in a hilbert space, not in configuration space. Secondly, QFT contains SR because it requires that its lagrangian, written as 4-vectors, satisfy lorentzian invariance. It also respects causality by requiring that the commutation relationship between compatible operators are to be written at equal times.

A few paragraph down, and it says: "Therefore, we realize that the spacetime structure for NRQM, while not M4 in that
it lacks time dilation and length contraction, nonetheless contains a “footprint of relativity” due to the relativity of simultaneity."

Where do they get that is mind boggling. Again there is a basic (mis)understanding on the part of the authors. We don't have a theory in configuration space. QM is based on a hilbert space in which the square of the amplitude of normalized vectors allows us to calculate probabilities, certainly not time dilation nor space contraction.

zaybu wrote:Twistor, take a second look at that paper. It's full of nonsense.

Pffttt...compared to your own post, it is, at best, the wrong kind of nonsense.

The quantum invariance replacement operators are galilean invariant up to causality respecting space time null vectors.

zaybu wrote:

twistor59 wrote:

Yes, that's my impression too. As soon as you're dealing with a 4 dimensional spacetime, presumably you've got yourself a block universe?

Twistor, take a second look at that paper. It's full of nonsense. Here's one statement that got me jumped off the floor: "The received view has it that Schrödinger’s equation is Galilean invariant, so it is generally understood that NRQM resides in Galilean spacetime and therefore respects absolute simultaneity."

Well, I posted it because section 2 contains a description of the blockworld, which was the subject of this thread.

But anyway, when they write "NRQM resides in Galilean spacetime" I would interpret that to mean "the Hilbert space of NRQM carries a unitary representation of the Galilean group". However, Galilean invariance of the Schroedinger equation is a bit awkward, since if you perform Galilean transformations on the wavefunctions, you have to fuck about with their phases to retain covariance:

http://redshift.vif.com/JournalFiles/V13NO4PDF/V13N4OST.pdf

Maybe it means that quantum mechanics was invented on the shores of the sea of Galilee?

Cheers guys, I think I've got a relatively decent understanding of what the block universe is, but the purpose of this thread was to see what it's status within the field of physics is. Is it generally accepted, in the mainstream, as being the "preferred" [for want of a better word] model?


Twistor, two of your posts above somewhat threw me, but it might just be the pre-conceptions I have. On the one hand you say that you don't understand what the block universe does, or how it is different from Minkowski space, but on the other you say that if you've got a 4 dimensional spacetime you've presumably got a block universe.

Would you differentiate between the 4 dimensional spacetime and the traditional model of the block universe, where an observers past and future co-exist with their present?


Also, just a further qustion on the block universe; is it generally accepted that objects exist as worldlines, or worldtubes, in the 4 dimensional spacetime; that is, they are spatially and temporally extended through spacetime such that they form a line, or a tube, through spacetime?

mangaroosh wrote:

Twistor, two of your posts above somewhat threw me, but it might just be the pre-conceptions I have. On the one hand you say that you don't understand what the block universe does, or how it is different from Minkowski space, but on the other you say that if you've got a 4 dimensional spacetime you've presumably got a block universe.

When I first read this thread, I hadn't read anything about the block universe, was vaguely aware of the name but that was about it, hence my plea of ignorance. Subsequently, having read a bit about it, I don't see anything different to the usual picture of Minkowski space and relativity of simultaneity that's taught in relativity101 courses.

mangaroosh wrote:
Would you differentiate between the 4 dimensional spacetime and the traditional model of the block universe, where an observers past and future co-exist with their present?

I think the term "coexist" belongs to philosophy and doesn't really mean anything concrete.

mangaroosh wrote:
Also, just a further qustion on the block universe; is it generally accepted that objects exist as worldlines, or worldtubes, in the 4 dimensional spacetime; that is, they are spatially and temporally extended through spacetime such that they form a line, or a tube, through spacetime?

It's accepted that objects trace out worldlines, yes.

twistor59 wrote:

zaybu wrote:

twistor59 wrote:

Yes, that's my impression too. As soon as you're dealing with a 4 dimensional spacetime, presumably you've got yourself a block universe?

Twistor, take a second look at that paper. It's full of nonsense. Here's one statement that got me jumped off the floor: "The received view has it that Schrödinger’s equation is Galilean invariant, so it is generally understood that NRQM resides in Galilean spacetime and therefore respects absolute simultaneity."

Well, I posted it because section 2 contains a description of the blockworld, which was the subject of this thread.

But anyway, when they write "NRQM resides in Galilean spacetime" I would interpret that to mean "the Hilbert space of NRQM carries a unitary representation of the Galilean group". However, Galilean invariance of the Schroedinger equation is a bit awkward, since if you perform Galilean transformations on the wavefunctions, you have to fuck about with their phases to retain covariance:

http://redshift.vif.com/JournalFiles/V13NO4PDF/V13N4OST.pdf

Maybe it means that quantum mechanics was invented on the shores of the sea of Galilee?

If the theory is invariant under a symmetry, it is with the Lagrangian that we must work it out. In the case of lorentzian symmetry, you perform the transformation:

(1) xμ → x'μ= Λμνxν , where Λμν is part of the Lorentz group.

For a scalar field, this means,

(2) ϕ(x) → ϕ'(x) = ϕ(Λ-1 x)

Substitute (1) and (2) into the Langrangian,

L = 1/2 Nμν ∂μϕ∂νϕ − 1/2 m2ϕ2, where Nμν is the Minkowski metric.

If you can show that L = L', then you have an invariance, which for the Lorentz transformation, this turns out to be true.

But the paper talks about the invariance of the Schroedinger equation. I know of no textbooks that ever did that.

twistor59 wrote:I think the term "coexist" belongs to philosophy and doesn't really mean anything concrete.

I'd have thought that if this stuff wants to stay technical, we (and by that, I mean you) might talk about things such as Neo-Lorentzian relativity, where there is a preferred frame of reference. Wiki backs up JHendrix on what seems to be the salient point:

"in LET the existence of an undetectable ether is assumed and the validity of the relativity principle seems to be only coincidental, which is one reason why SR is commonly preferred over LET. "

I'd want to know a few more things: like, is it possible to understand the relativity of simultaneity as just some sort of limitation in making observations, or do you hit contradictions if you try to do things like that. I'd have hoped it would be similar to the hidden variables problem, which I thought physicists had basically ruled out.

twistor59 wrote:When I first read this thread, I hadn't read anything about the block universe, was vaguely aware of the name but that was about it, hence my plea of ignorance. Subsequently, having read a bit about it, I don't see anything different to the usual picture of Minkowski space and relativity of simultaneity that's taught in relativity101 courses.

Ah, I see.

You are probably right in that there is no difference between the block universe and Minkowski spacetime, that is partly the reason I use them interchangeably, because the impression that is given in the mainstream is that the block universe is the embodiment of Minkowski spacetime and a logical necessity of Einsteinian relativity.

twistor59 wrote:I think the term "coexist" belongs to philosophy and doesn't really mean anything concrete.

While it might be a philosophical term, it seems as though it is a necessary one to describe relativity of simultaneity. RoS would seem to necessitate that an observers past continues to be observable, in a given reference frame, in a manner other than simply being an image resulting from light reaching a second observer in that reference frame. While we might say the light reaching a distant observer represents an image of a given scene, while the scene itself is no longer current, or no longer exists [whatever the nature of its existence]; RoS, on the other hand would seem to require that the distant observer doesn't simply observe an image, indeed, they may not actually observe an event that forms part of their "present", given the distance between them. However, it seems to require that what is "the past" for one observer is still current for another, relatively moving observer; that is, it continues to exist and is theoretically observable by someone local to the event - your "past self" for example.

twistor59 wrote:It's accepted that objects trace out worldlines, yes.

I think there might be the need to make a distinction between the mapping of an object in a spacetime diagram and the existence of an object in 4 dimensional spacetime. The block universe would seem to necessitate that the absolute nature of an object is that of a line in 4 dimensional spacetime, or the block universe, where all the states of an object exist in spacetime and are extended temporally as well as spatially. It seems to necessitate the idea that objects are physically connected through time, such that they form a worldline, or worldtube, in 4 dimensional spacetime.


That is the impression that I get anyway, I was just wondering if that is generally accepted in the field of physics.

VazScep wrote:I'd have thought that if this stuff wants to stay technical, we (and by that, I mean you) might talk about things such as Neo-Lorentzian relativity, where there is a preferred frame of reference. Wiki backs up JHendrix on what seems to be the salient point:

"in LET the existence of an undetectable ether is assumed and the validity of the relativity principle seems to be only coincidental, which is one reason why SR is commonly preferred over LET. "

I'd want to know a few more things: like, is it possible to understand the relativity of simultaneity as just some sort of limitation in making observations, or do you hit contradictions if you try to do things like that. I'd have hoped it would be similar to the hidden variables problem, which I thought physicists had basically ruled out.

The wiki page also states "the last vestiges of a substantial ether had been eliminated from Lorentz's "ether" theory, and it became both empirically and deductively equivalent to special relativity. The only difference was the metaphysical[C 7] postulate of a unique absolute rest frame, which was empirically undetectable and played no role in the physical predictions of the theory".
LET current status
Unfortunately it lacks a citation, but it is a point others have made in discussions on another forum; those "others" would not have been proponents of LET.

Are you familiar with that idea?

mangaroosh wrote:

twistor59 wrote:I think the term "coexist" belongs to philosophy and doesn't really mean anything concrete.

While it might be a philosophical term, it seems as though it is a necessary one to describe relativity of simultaneity. RoS would seem to necessitate that an observers past continues to be observable, in a given reference frame, in a manner other than simply being an image resulting from light reaching a second observer in that reference frame. While we might say the light reaching a distant observer represents an image of a given scene, while the scene itself is no longer current, or no longer exists [whatever the nature of its existence]; RoS, on the other hand would seem to require that the distant observer doesn't simply observe an image, indeed, they may not actually observe an event that forms part of their "present", given the distance between them. However, it seems to require that what is "the past" for one observer is still current for another, relatively moving observer; that is, it continues to exist and is theoretically observable by someone local to the event - your "past self" for example.

Yes, that's exactly right, the term "coexist" has no absolute significance. This is the essence of RoS. You can say a set of events coexist relative to an observer - he defines a time slicing of Minkowski space and the events on his slice "coexist" for him. But this notion of coexistence is observer dependent, so it doesn't really mean anything to say the whole of Minkowski space, past, present and future, coexists. RoS is the striking part of SR and is precisely what excited many of those who've studied it as part of their courses.

mangaroosh wrote:

twistor59 wrote:It's accepted that objects trace out worldlines, yes.

I think there might be the need to make a distinction between the mapping of an object in a spacetime diagram and the existence of an object in 4 dimensional spacetime. The block universe would seem to necessitate that the absolute nature of an object is that of a line in 4 dimensional spacetime, or the block universe, where all the states of an object exist in spacetime and are extended temporally as well as spatially. It seems to necessitate the idea that objects are physically connected through time, such that they form a worldline, or worldtube, in 4 dimensional spacetime.


That is the impression that I get anyway, I was just wondering if that is generally accepted in the field of physics.

I don't see any distinction in physics terms between the your two descriptions that I highlighted. Maybe someone else can?