the block universe

[roosh]

Hi guys,

 

I'm just trying to get an idea of the status of the block universe concept within the field of physics. On the one hand, the impression that is created in the mainstream, through TV series such as NOVAs the Fabric of the Universe, as well as through other sources, is that the block universe concept is the logical conclusion of Einsteinian relativity. The distinct impression that is created is that, if the mathematics of Minkowski spacetime represent an underlying physical structure of the universe, then the block universe is the embodiment of that physical structure. On the other hand, some people simply dismiss it as a philosophical concept which makes no testable assumptions, and so, has no place in physics.

 

 

I am interested to hear peoples opinions on this; is it a logical necessity of Einsteinian relativity or is it just a philosophical concept which has no place in the field of physics; is the view that is propagated in the general mainstream reflective of the thinking within the mainstream of the field of physics?

[md65536]

Models have a place in physics. I think it's important to separate a model's physically measurable predictions from any sort of metaphysical guess of what those measurements represent (the "underlying physical structure" that you mention). Then the value of any model begins and ends with its predictions, and not any extra implied meaning.

[Bel Gio]

Relativity of Simultaneity means Block universe. I cannot see any other interpretation. Can you?

[roosh]

Relativity of Simultaneity means Block universe. I cannot see any other interpretation. Can you?

It does seem to necessitate it.

[JonG]

Minkowski's four-dimensional spacetime, which is what underpins the idea of a block universe, is something which Einstein initially regarded with some contempt, dismissing it as "superfluous learnedness". I don't think it could be described as a "logical consequence" of relativity. It isn't necessary in Special Relativity, but it was an invaluable tool in the formulation of General Relativity.

 

I suspect that whilst all physicists would know what is meant by "spacetime", a few would scratch their heads when "block universe" is mentioned, despite the fact that they refer to the same thing.

Edited November 12, 2013 by JonG

[roosh]

Minkowski's four-dimensional spacetime, which is what underpins the idea of a block universe, is something which Einstein initially regarded with some contempt, dismissing it as "superfluous learnedness". I don't think it could be described as a "logical consequence" of relativity. It isn't necessary in Special Relativity, but it was an invaluable tool in the formulation of General Relativity.

 

I suspect that whilst all physicists would know what is meant by "spacetime", a few would scratch their heads when "block universe" is mentioned, despite the fact that they refer to the same thing.

that does seem to be the case alright. In discussions elsewhere I spoke about it assuming it was widely known, but a good few people had never heard of it.

 

Einsteinian relativity does seem to necessitate that "past" and "future", to some extent exist or persist. If you picture a spacetime diagram where a bullet is fired towards a house and two observers are moving relative to each other, at the moment when the observers cross paths each will disagree with the location of the bullet, with one saying it is close to the house than the other. For observer A (to label them) the bullet will be located at a tree, for arguments sake, while observer B will say that it has passed the tree. For observer A, the location of the bullet according to B will represent a location the bullet will occupy in the future while, for observer B, the location of the bullet according to A will represent a location occupied by the bullet in the past.

 

 

Apologies for not posting the diagram, but someone else drew it. I can dig it out if necessary.

[md65536]

Einsteinian relativity does seem to necessitate that "past" and "future", to some extent exist or persist. If you picture a spacetime diagram where a bullet is fired towards a house and two observers are moving relative to each other, at the moment when the observers cross paths each will disagree with the location of the bullet, with one saying it is close to the house than the other. For observer A (to label them) the bullet will be located at a tree, for arguments sake, while observer B will say that it has passed the tree. For observer A, the location of the bullet according to B will represent a location the bullet will occupy in the future while, for observer B, the location of the bullet according to A will represent a location occupied by the bullet in the past.

That's simply "relativity of simultaneity".

 

Personally I don't think that that on its own requires a block universe, however it does seem that relativity of simultaneity together with an assumption of standard simultaneity (aka Einstein simultaneity) seems to.

 

 

 

Just as an example of what I'm trying to say: Say you're far from Earth and suddenly change velocity relative to it, and there is a change in relative simultaneity with respect to Earth. You might have a situation where you consider it December 2013 on Earth, and the next moment you consider it November 2013 on Earth. You haven't (necessarily) reversed time or anything... all the events can be considered the same on Earth, just differently lining up with your current time... a block universe.

 

However, the Earth is so far away and nothing of whether it is Nov or Dec there can be observed by you yet. There is no physically measurable effect of the change in simultaneity from Dec on Earth to Nov on Earth. Furthermore, you receive light from the various events on Earth in order, so you will never observe any backward change in time. The only thing you have to be certain of the change in simultaneity is the knowledge that incoming photons travel at c, allowing you to define standard simultaneity, and only according to that definition and SR, can it be Dec on Earth one moment and Nov the next, according to you.

 

Without the assumption of standard simultaneity, you can still have relativity of simultaneity, but might not need the block universe.

Edited November 13, 2013 by md65536

[md65536]

Addendum:

Say you're far from Earth and vibrate back and forth at a high fraction of c. According to standard simultaneity, moments on Earth that are simultaneous with moments where you are can vary back and forth through time on Earth. But even this does not require a block universe; the block universe is just one of the simpler interpretations.

 

Perhaps you're having the Earth merely cycle back and forth through the same set of events, with each event having only one existence --- a block universe.

 

Perhaps these events don't actually happen unless you can later measure them --- some sort of delayed causality or an alternative physical simultaneity perhaps. Then whatever may happen on Earth but is "undone" via changes to relative simultaneity, didn't really happen.

 

Perhaps each time you vibrate the Earth goes through different sets of events from a superposition of all possible events --- some sort of multi-world interpretation.

 

And it can get worse... perhaps you're "spawning new realities" by vibrating or doing any action. I think the more complicated interpretations are ridiculous, but the block universe isn't required, it is just an interpretation that doesn't assume any extra complications.

Edited November 14, 2013 by md65536

[JonG]

 

Einsteinian relativity does seem to necessitate that "past" and "future", to some extent exist or persist.

 

 

It's difficult to express this notion because the past clearly doesn't exist "now" .Einstein himself appears to have seen the past and future in that way. When his friend Besso died, he wrote to Besso's family ,"Now Besso has departed from this strange world a little ahead of me. That means nothing. People like us, who believe in physics, know that the distinction between past, present and future is only a stubbornly persistent illusion". (source here: https://en.wikipedia.org/wiki/Michele_Besso)

He was almost certainly thinking of the idea of time you have mentioned - events don't cease to exist as they slip into the past - it's just that we can no longer access them.

[michel123456]

IMHO the block universe is the result of a wrong interpretation of time.

 

To me, all objects are traveling in time, meaning that objects change coordinate in time. And not that object somehow "persist" in time.

 

The commonly accepted view is that an object in spacetime is a line: IOW the object occupies in spacetime more than one set of coordinates.

 

In my view (speculating here) an object can occupy only one set of coordinates because each set is mutually exclusive. If you are here (in spacetime) you are not there (in spacetime). You cannot be both.

 

If you consider time the way I do then the block universe stops to exist, changing nothing to Relativity.