There is only one universe that we currently know of. “Uni” means one or whole. In that universe, the speed of light is constant. It does not change.

I am refering to the theory of multible ‘verses’. Theory is a possible thing. An idea based off science and such, not a garantee.

I’m familiar with the idea of the Multiverse or Universe Islands. As you already know it’s still in theory form. As I recall my professor, Miller Grant (part of the astro physics team that recently won the nobel prize in the dept.) said even through black holes all things slow down, because of the intensity of it’s gravity. Or maybe the speed of light stays the same in a black hole, but everything inside the black hole is slowed down s….. never mind, this is all becoming too psychedelic for me to explain at the moment.

I know that physicists continue to debate whether various physical constants, including speed of light, (a) evolve over the lifetime of the universe versus stay constant; and (b) are arbitrary and random versus must be the same in all universes. So probably, nobody knows.

Assuming the multiverse is real, it may be that some universes are “tiny” when first formed, but I’m not sure smaller ones would necessarily grow more slowly. Our universe went through an inflationary period (burst of exponential growth) shortly after the big bang.

Nor am I sure that the speed of light within a universe is somehow connected to its rate of expansion.

It’s been established that light may be slowed down. I don’t think that there’s any way to know specifics about hypothetical ‘verses.

The speed of light is only a constant in a vacuum. It travels more slowly in a transparent medium such as water or glass. In another universe who knows, maybe there is no light there at all.

@Satchafunkilus Theory is a possible thing. An idea based off science and such, not a garantee.

WRONG. Theory is the currently accepted scientific model for how something happens. It is based on data and observation, not speculation. What you’re talking about is a hypothesis, which the multiverse “theory” very much is.

See above. I will join chorus.
Speed of light is a constant.
It is fun to imagine multiple universes, but as far as we know there is only one. . A theory is based on as much knowledge as we have about a phenomenon. It is not wish or hope or sci fi story. And even it’s junior cousin, the hypothesis, has to have some observable basis to have validity.

@flutherother has it: The speed of light varies with the medium. That’s why a prism refracts light, and it’s why a rod stuck into clear water seems not to be straight. The speed is only constant in a vacuum.

As far as we know, the speed of light is max in a vacuum. Our equations and (lack of) experience in other universes and dimensions do not show that it would be different anywhere else.