# Implications of quantum foundations on interpretations of relativity

Gold Member
4) is a bit strange, but not and interpretation. It just adds something additional, that is completely unnecessary.
Maybe it's unnecessary within classical physics, but it appears in some versions of relativistic Bohmian mechanics.

You say "If the Bell theorem is interpreted as nonlocality of nature...", well what if it isn’t?
Then 1. is the most natural formulation of relativity.

Gold Member
For me the fact that space-time has the structure of Minkowski space is not an interpretation but a consequence.
What about block universe? Is that a consequence or an interpretation?

martinbn
Maybe it's unnecessary within classical physics, but it appears in some versions of relativistic Bohmian mechanics.
Then it is unrelated. In celestial mechanics it may be convenient to choose coordinates centered at the sun, but that is not an interpretation of classical mechanics.
Then 1. is the most natural formulation of relativity.
I don't understand this.

weirdoguy
martinbn
What about block universe? Is that a consequence or an interpretation?
I've seen different people to mean different things by block universe. What do you take it to mean?

Gold Member
I've seen different people to mean different things by block universe. What do you take it to mean?
The past, presence and future exist on an equal footing.

Michael Price
Gold Member
I don't understand this.
See the second paragraph in #3.

A. Neumaier
2019 Award
For me the fact that space-time has the structure of Minkowski space is not an interpretation but a consequence.
But this alleged fact is already false in general relativity.....

Gold Member
But this alleged fact is already false in general relativity.....
He said consequence of special relativity.

Summary: If the Bell theorem is interpreted as nonlocality of nature, then what does it tell us about the meaning of Einstein theory of relativity?
According to ether theories, there are absolute space and absolute time, but under certain approximations some physical phenomena obey effective laws of motion that look as if absolute space and time did not exist. The original Lorentz version of ether theory was ruled out by the Michelson-Morley experiment, but some more sophisticated versions of ether theory are still alive.
Sorry, but what is known as the Lorentz ether is simply equivalent to SR (and therefore an interpretation of SR) and therefore not ruled out by the Michelson-Morley experiment. And which versions you think about?
4. Spacetime+foliation interpretation. This interpretation posits that in addition to spacetime, there is some timelike vector field nμ(x)nμ(x) that defines a preferred foliation of spacetime, such that nμ(x)nμ(x) is orthogonal to the spacelike hypersurfaces of the foliation. This preferred foliation defines a preferred notion of simultaneity.
The Lorentz ether is here only a particular case, where the foliation is defined by a preferred inertial frame.
What different interpretations of QM can tell us about those interpretations of relativity? Which interpretations of relativity seem natural from the perspective of which interpretations of QM?
There is a quite simple general answer: All realistic as well as all causal interpretations require a preferred foliation. Here, "realistic" means that the EPR criterion of reality holds, and "causal" means a notion of causality which includes Reichenbach's common cause principle. This follows from variants of Bell's theorem, which use, beyond Einstein causality, only EPR realism resp. Reichenbach's common cause principle.

martinbn
The past, presence and future exist on an equal footing.
How is that specific to relativity? It seems like a general philosophical position. In fact it seems very non-relativistic in spirit. What is present in relativity? A choice of simultaneity convention? Which one?

What about block universe? Is that a consequence or an interpretation?
An interpretation. In interpretations with a preferred frame, that preferred frame also defines the presence objectively, and the relativity of simultaneity is reduced to an impossibility to identify the preferred frame by local observations.
How is that specific to relativity? It seems like a general philosophical position. In fact it seems very non-relativistic in spirit. What is present in relativity? A choice of simultaneity convention? Which one?
A philosophical position that assumes a block universe exists too, it is named fatalism. In fatalism, the future is predefined, thus, already existing in the same way as the present. In what I would simply name common sense, the future, as well as the past, have a different status, only what is present exists.

This difference is an objective one, a property of the world, not of observations of the world. Once the preferred frame cannot be identified by observation, it cannot be a choice by an observer. The observer can only guess which is the correct preferred frame (and the CMBR frame gives a quite plausible guess).

The preferred frame interpretations are, indeed, very non-relativistic in spirit. Relativistic symmetry holds only for some observable effects, it is not a fundamental symmetry, and in particular not a symmetry of space and time. This is what makes them much better compatible with similarly non-relativistic interpretations of quantum theory.

A class of interpretations of QT which depends on a preferred frame for extensions into the relativistic domain can be easily identified: If we look at the Schrödinger equation in the configuration space, it gives a continuity equation for the density ##\rho(q)##:
$$\partial_t \rho(q,t) + \partial_i ( \rho(q,t)v^i(q,t)) = 0.$$

All one needs is to give the corresponding ##\rho(q,t)v^i(q,t)## a physical interpretation, as a probability flow.

What about block universe? Is that a consequence or an interpretation?
A consequence. The block universe has always seemed, to me, a consequence of pre-Minkowski classical physics, which describes time as a fourth dimension. Nothing in SR (or GR) changes this.

I don't get your point 4, though. There is no preferred foliation for time after Einstein and Minkowski, and no preferred foliation problem, just as there is no preferred basis problem in quantum mechanics.

How is that specific to relativity? It seems like a general philosophical position. In fact it seems very non-relativistic in spirit. What is present in relativity? A choice of simultaneity convention? Which one?
Just as there is no preferred position, so there is no preferred time. Seems entirely relativistic to me.