Could the speed of light be different in different universes?

[Sebastiaan]

Assuming there is a multiverse, has the speed of light (or casuality) to be the same for all universes?

 

[Ssnow]

If there exist a multiverse yes it is possible, there are kind of multiverse where also the mathematical structures can be differents ...
But personally I am skeptical on this topic...

ref. https://en.wikipedia.org/wiki/Multiverse

 

[Nugatory]

Assuming there is a multiverse, has the speed of light (or casuality) to be the same for all universes?

There's no good answer to that question. The problem is that we have no coherent theory that says that there might be such a thing as a "multiverse" (whatever that might be), and hence no clear description of one. Thus, the question you're asking is basically "What are the hypothetical properties of some hypothetical thing that, if it exists, will obey laws of physics that haven't been discovered yet?" and the answer to that question is "Who can say?".

One side note though: People sometimes confuse the altogether speculative multiverse idea withe the Many Worlds Interpretation of quantum mechanics. MWI is a different thing, and if it's what you mean when you say "multiverse", the answer your question about the speed of light would be "The same, and by the way these multiple worlds aren't what you're thinking they are".

 

[GeorgeDishman]

Would it be fair to say that, if the geometry of GR applies in other universes, then scientists there could also use units in which c=1 and therefore there would be no difference?

 

[Orodruin]

Would it be fair to say that, if the geometry of GR applies in other universes, then scientists there could also use units in which c=1 and therefore there would be no difference?

Yes.

 

[Nugatory]

Would it be fair to say that, if the geometry of GR applies in other universes, then scientists there could also use units in which c=1 and therefore there would be no difference?

Yes.

But that's tantamount to saying that if this completely speculative and hypothetical other universe just happens to have a particular property (and there's no reason to think that it does or doesn't because it's completely hypothetical and speculative so we can speculate that it has whatever properties we find amusing to speculate about) than it will act as if it has that property.

This isn't science.

 

[Orodruin]

This isn't science.

... and, as a consequence, the question of whether the speed of light has a different value is also not scientific.

 

[Delta Kilo]

Assuming we are talking about multiverse in Everett's Many Worlds sense, different "worlds"/"branches" are basically different solutions to the same set of equations. As far as I understand they all have the same laws of physics (give or take). Some physical constants like particle masses may have been set due to symmetry breaking in the early universe and so might be different in other branches, but c is not one of them.

All of it is of course unobservable and therefore pure speculation.

 

[GeorgeDishman]

Assuming we are talking about multiverse in Everett's Many Worlds sense

I was thinking in terms of Guth's bubble universes from inflation theory.

 

[Nugatory]

OK, now that we've demonstrated to everyone's satisfaction that the term "multiverse" is not well-defined, we can close the thread.