Can Quantum Mechanics Explain the Expansion and Contraction of Space-Time?

[TEFLing]

Yes, but this is a fact about human psychology, not about physics. This thread is about physics.
Why? What does it have to do with physics?
This is one way of interpreting what the mathematical model of relativity says, yes. But it could equally well be put forward as an interpretation of non-relativistic physics.
None of this requires relativity. The fact that we are causally connected to our ancestors is perfectly explicable with non-relativistic physics.

Physics must be explained, yes?

So explaining physics requires understanding the audience

And some on this thread seem to prefer popular kinds of explanations

Also, the continuity of world lines is central to Relativity , yes? Einstein called the distinction between past present and future an illusion. I'm trying to explain Relativity using non Relativistic concepts. As long as I choose validly comparable concepts, then I should draw such comparisons, for purposes of explanation, yes?

 

[TEFLing]

I _really_ don't understand this slice business. I thought space was expanding at the rate of the Hubble Constant. If space is not really expanding, what is the explanation of red shift?

Saying that our past selves continue to exist and our future selves already exist is a non-scientific statement. It is all right to make non-scientific statements, but we need to keep in mind that the current existence of the past and future is not subject to observation or experiment, and therefore is not scientific.

Einstein called the distinction between past present and future an illusion. The ontological existence, of the past and future portions, of the worldlines of all particles, is a required and mandatory part of the theory. Space time is a fabric / manifold / membrane of 3+1D

Space like slices of that fabric are bigger and bigger at later and later times ( as measured by clocks inside the fabric )

But no single slice is stretching / growing / expanding

To try to make another analogy, it's like a movie real... Despite the illusion of motion, the movie is really a sequence of still shots... Something exploding in the movie would be a sequence of still shots, each with a bigger fire ball than the frame before...

But the frames aren't changing, and the fireball in a given frame is not changing or growing or anything

So it is not really right to say that one fireball is growing, i.e. that one space is expanding / stretching...

Rather instead there are a sequence of fixed frames, i.e. space like slices of the fabric of space-time, that increase in size from one to the next as defined by a time like coordinate

If you prefer the regular rising raisin bread analogy, then what you should ought to imagine...

Is a sequence of SEPARATE loaves, each flash frozen after a progressively increasing amount of baking time in the oven ... And set out on separate shelves of a tall bakery rack

On the very bottom shelf is a tiny uncooked ball of dough

On the next shelf up is a barely cooked loaf baked for one minute

On the next shelf, a loaf baked for three minutes...

And so on

The fabric of space time is like all of those 3D loaves, stacked on top of each other ( in an orthogonal higher dimension )

If you actually saw such a display in some real bakery, for whatever reason...
Your eyes might scan up the rack, from the bottom shelf to the top...
Your eyes could only focus fully on one shelf at a time...
But all the shelves are always there...
That is like our illusory sense of the present... We focus on now, but past and present are both also part of the 3+1D fabric of space and time

It's not one loaf rising
It's a sequential stack of separate loaves of increasing size
( and for some reason we psychologically single out one loaf at a time for our sense of now)

 

[PeterDonis]

explaining physics requires understanding the audience

And some on this thread seem to prefer popular kinds of explanations

Are you trying to "explain" physics as in "give people an understanding of how the theory actually models things and makes predictions"? Or are you trying to "explain" as in "tell people things that fit in with their intuitions, even if it doesn't help them understand how the theory actually models things and makes predictions"?

I think a lot of people are looking for the latter type of "explanation", but that doesn't mean it should be given to them. If you're not giving people an understanding of how a theory actually models things and makes predictions, then you're not "explaining physics" IMO.

the continuity of world lines is central to Relativity , yes?

Yes. What does that have to do with what we're discussing?

Einstein called the distinction between past present and future an illusion. I'm trying to explain Relativity using non Relativistic concepts.

This seems like an oxymoron to me. Relativity uses relativistic concepts, not non-relativistic concepts.

The ontological existence, of the past and future portions, of the worldlines of all particles, is a required and mandatory part of the theory.

Here's an example of "explaining" in the wrong sense. As you state it, this is simply false: the theory of relativity models the world as a 4-dimensional spacetime continuum, but that does not mean ontological claims about the "existence" of 4-dimensional spacetime are "a required and mandatory part of the theory". But it certainly seems plausible to people's intuitions.

The reason it seems plausible to people's intuitions is that people don't understand that scientific theories are models. The 4-dimensional spacetime used in relativity is a model. Models are not the same as reality. They have to share some features with reality in order to make good predictions, but that does not mean that every feature of the model has to be a feature of reality.

 

[TEFLing]

The theory is a model, yes

According to the model, past present and future are all parts of a single fabric of 3+1D space-time ( and worldlines of particles which occupy portions of that fabric )

Einstein seemed to think that that aspect of the model also reflected reality, calling any distinctions illusory. Insofar as experiments corroborate the predictions of the theory, then judging trees by fruit for want of worthier words, the difficult to describe co existence of past present and future regions of a single fabric of space and time seems the most straight forwardly obvious and natural one ( which Einstein seemed to favor)

 

[TEFLing]

Trying to think of how QM affects the world lines of particles inside of a 3+1D fabric of space-time...

It seems like QM and GR agree that the world lines of particles in the PAST region of space-time are fixed and locked in for want of worthier words...

But GR is a fully deterministic theory , and says the same thing for the future region of space-time as well, i.e. worldlines are fixed and locked in

Whereas QM is probabilistic and says that the future region of space-time harbors wave functions which are UNCOLLAPSED and so diffused and spread out in the ghostly probabilistic sense of QM

I want to ask, what would happen if, from within the framework of GR, you replaced the fixed world lines of non-quantum deterministic ( determined ) particles...

With the quantum probability distributions...

Density ~ mass x <¥|¥>

??