Visit With Paul Davies on Block Time

[PeterDonis]

I don't see that SR requires determinism.

Perhaps a better way to put it is that SR, by itself, has no way of modeling non-determinism. See below.

QFT is strictly based on SR as an exact framework and rejects determinism.

QFT in its original form uses flat Minkowski spacetime as its background spacetime, yes. However, you can do QFT in curved spacetime as well. The only treatments I am familiar with for QFT in curved spacetime use Schwarzschild spacetime, which is asymptotically flat; however, I believe quantum cosmology includes models that basically do QFT over a set of Friedmann-like spacetimes. I am not very up to date in this area, though.

Also, the way in which QFT models non-determinism is basically to assign amplitudes to *different* possible spacetimes--that is, different configurations of background spacetime plus quantum fields. (In the original form, the background spacetime is always Minkowski but the field configurations can vary; in the curved spacetime form, the background spacetime can be affected by "back reaction" terms, as in the case of Hawking radiation.) But each individual possible spacetime is "deterministic"; it's a fully determined solution to the appropriate field equations on the appropriate spacetime. So as far as the theory of the underlying spacetime is concerned, there is no indeterminism; each solution to that theory is fully deterministic. The quantum indeterminacy comes from assigning amplitudes to *different* solutions. The classical theory of the underlying spacetime has no way of modeling indeterminism by itself.

Further, there are approaches to treating GR as a gravity theory without curvature (separate and apart from quantum approaches).

Are you referring to the theory of gravity as a spin-2 field on a flat background spacetime? As presented, for example, in the Feynman Lectures on Gravitation? The foreword to that book is now online at Caltech's website:

http://www.theory.caltech.edu/~preskill/pubs/preskill-1995-feynman.pdf

Of course, I agree that however you view gravity, since there is no SR based theory that fully accommodates SM + gravity, SR (at present) can only be used as an accurate local approximation. Yet, I don't consider it established that there cannot be a exist SR based quantum theory that agrees with all verified predictions of SM + GR, and thus can be taken as complete adequate theory of nature.

I'm not sure that an "SR-based" quantum theory, in the sense of a quantum theory that required a fixed flat background spacetime (Minkowski), could be constructed with a classical limit that was, for example, an FRW spacetime. So if predictions about the early universe count as "verified" (which some certainly seem to be), this would count against the possibility of an "SR-based" quantum theory that would be completely adequate.

 

[harrylin]

Some elaboration:

[..] If there are no competing theories, block universe would be required by SR.[..]

Not sure if I read that correctly, but it seems to contain a logical error (or two). If there was only one proposed explanation of why SR works, or even none, that would not mean that SR would require the one that was proposed, or that SR would require no explanation. As it is, there are several competing models and the most popular one (Minkowski's block universe) is often confounded with SR by association.

I gave you a link to a competing model; regretfully it involves going through the rather elaborate presentation in Einstein's 1905 paper if you are not familiar with it. But it's easy to present a much more compact space-time presentation based on that model, as follows (even keeping the historical sequence of development of SR):

1. Postulate a causal, spatial background for physical processes in which light propagates like a wave with speed c (Maxwell-Lorentz).

Define S as a hypothetical reference system that is in rest in that background. Similarly, define S' as a system that is in rectilinear uniform motion with respect to S.

2. From pragmatic considerations, distant clocks are synchronised by assuming that the speed of light dx'/dt' is uniformly c in all directions. However, that is only true with respect to S. Consequently, make a distinction between "local time" t' in S' and "true time" t in S.

3. Based on some experiments, propose that moving objects contract in length:
L'/L = √(1-(v/c)^2)

4. From symmetry (PoR), propose that the natural frequency of moving resonators decreases:
f'/f = √(1-(v/c)^2)

Combining these assumptions yields the following transformation equations for coinciding origins at t'=t=0:

x' = gamma (x -vt)
t' = gamma (t - vx/c^2)

Still one subtle step is needed: so far the meaning of x and t there is not the common one. However, due to the form of these equations, if they are valid for an S in "true rest" then they will also be valid for a system S that is in inertial motion. With that generalisation you obtain the Lorentz transformations for x,x' and t,t' and the related space-time intervals.

As far as SR concerns, the "true time" model is empirically indistinguishable from the "block time" model.

Harald

 

[harrylin]

[..]
3. Based on some experiments, propose that moving objects contract in length:
L'/L = √(1-(v/c)^2)
4. From symmetry (PoR), propose that the natural frequency of moving resonators decreases:
f'/f = √(1-(v/c)^2)
[..]

Oops I see now that I had put the prime sign ' on the wrong side and I should have written "are contracted" and "is decreased". Sorry for that!

The point is that since both models work, it can't be right that Block Time must be the correct one just because it works.

 

[Russell E]

It's easy to present a much more compact space-time presentation based on that model, as follows:
1. Postulate a ... spatial background for physical processes in which light propagates [in time] ... with speed c...
4. From symmetry (PoR) [principle of relativity]...

If your objective is a compact presentation, you already have the complete basis for special relativity with just those two trimmed propositions - properly understood. Note that "like a wave" has been removed from 1, because that is both unnecessary and false, in view of the quantum properties of em radiation, as Einstein had already realized by 1905. Also your items 2, 3, and the rest of 4 are removed because they are consequences of just the above, with the understanding that the "pragmatic considerations" in 2 are simply the choice to use the unique synchronization of standard inertial space-time coordinate systems in terms of which the principle of relativity holds good.

As far as SR concerns, the "true time" model is empirically indistinguishable from the "block time" model.

Empirical indistinguishability is theory-independent (that's why it's called empirical), so the indistinguishability is not limited to "as far as SR concerns".

The "alternate model" you've described is not a different model at all. It's nearly the standard interpretation of the special theory of relativity, albeit presented in an overly convoluted and elaborate way, with many superfluous postulates and assumptions, revealing a lack of understanding of the essence of the theory, which is Lorentz invariance arising from the empirical equivalence between inertia-based and light-based measures of space and time. The only non-standard aspect (setting aside the superfluous meandering) is the pointless metaphysical assignment of the undefined word "true" to one particular (albeit unidentified and unidentifiable) coordinate system.