Is a clock in one universe of any use to someone in a different universe? Supposing the multiverse model is correct, it posits the existence of several distinct universes that exist independently of each other. I understand how two separate universes can be independent in terms of their space: just imagine each universe as being different buildings on a street. But how does time fit into the theory? Does the passage of time through a universe only apply to objects that are contained within its own confines?

This seems paradoxical to me since if you were in a separate universe, you would have no meaningful way to speak of time in any universe other than your own and I find that difficult to comprehend. Thus, it would make sense to speak of the passage of time between universes in the same sense that we speak of the passage of time between observers in the theory of relativity.


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    $\begingroup$ Since relativity, you have different local times within a single universe. $\endgroup$ – Mitchell Porter Jul 16 '18 at 7:08
  • $\begingroup$ @MitchellPorter I thought relativity was only a refutation of simultaneity as predicted by Newtonian models $\endgroup$ – Alex S Jul 16 '18 at 7:12
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    $\begingroup$ Can you define what flavour multiverse you are considering. From the context I'm guessing you mean something like the bubble universes we get in eternal inflation. $\endgroup$ – John Rennie Jul 16 '18 at 7:51
  • $\begingroup$ @John Rennie I'd rather not make any assumptions about the type of multiverse under consideration. What are some of the more trendy ones? $\endgroup$ – Alex S Jul 16 '18 at 8:04
  • $\begingroup$ It's a different universe, so applying "any" carry over concepts from ours in a big assumption , in my opinion. For example, if physical constants are different, which they will be in a different universe,otherwise how would you distinguish it, how would that affect the measurement of time. $\endgroup$ – user198207 Jul 16 '18 at 8:26

"time should not depend on any universe in particular and it would make sense to speak of a kind of universal time that applies to all universes"

Since Einstein, there hasn't been universal time in physical theory, even within a single universe. So your premise is violated by modern physical theory, before multiple universes are even considered.

  • $\begingroup$ Okay, I understand; I should be more clear of what I mean. Would it make sense to speak of the passage of time between universes, or are they completely distinct from one another? $\endgroup$ – Alex S Jul 16 '18 at 9:59
  • $\begingroup$ It depends on the theoretical framework. In inflation you can have a tree of "universes" sprouting from each other, so there should be a local time that connects parent universe to child. If they were never connected then they should have independent times - though I cannot think of serious physics in which a "multiverse of totally separate universes" is the main concept. It seems more of a philosophical possibility than a physics idea. $\endgroup$ – Mitchell Porter Jul 16 '18 at 13:18

0kay, I understand; I should be more clear of what I mean. Would it make sense to speak of the passage of time between universes, or are they completely distinct from one another?

if they were not completely distinct, it would be the same universe as ours.

From: Wikipedia Multiverse

The multiverse (or metaverse) is a hypothetical group of multiple separate universes including the universe in which humans live. Together, these universes comprise everything that exists: the entirety of space, time, matter, energy, the physical laws and the constants that describe them. The different universes within the multiverse are called the "parallel universes", "other universes" or "alternative universes

As they are thefore. completely distinct (if the multiverse is a viable idea in the first place), then they will have "something" different from our universe and those somethings are the physical constants.

Although our measurement of time in this universe is a definiton:

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.

this definition relies on a physical constant, or a combination of them.

In the hypothetical other universes, this definitition of time will not be the same, so the "character" of time (apologies, I have no other word to describe a very nebulous concept) in any other universe will be different.


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