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What Is The Name Of That Which Exists Beyond The Universe?

If by definition Universe is "totality of everything that exists", then what do physicists mean by multiple universes?

  • Seems to be a question of definitions, but I think it goes slightly beyond that. Because we define the Universe we live in (U) as "everything that exists", the definition implies that we can, theoretically, directly or indirectly observe any object, particle or wave that exists. Everything is in interaction with everything else. Now let's say there exists some other universe (U'), that has no relation whatsoever to our own Universe. It means we have no chance of observing or even receiving information from U', because if it was possible, it would mean some type of interaction exists between U and U', which in turn makes them part of one, i.e. U. On the other hand, if information exchange is not possible between U and U', then a simple "down-to-earth" question can be asked: why bother hypothesizing about other universes if their existence has no influence on us and our Universe, let alone there is no practical or theoretical way of verifying it?

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    Unfortunately these days the term universe doesn't always mean "totality of everything that exists".  We thought thats what the universe was, and it was about 15b light years across.  Then we decided due to recent developments in cosmology that the universe may be much larger (see theories of inflation, multiverse).  So now the "observable universe" is the 15b light years across thing, but sometimes depending on context is just "the universe", sometimes also called a "pocket universe" in the context of other cosmological theories.  The whole enchilada is sometimes thought to be a set of parallel universes, or a multiverse.  For more on these mind bending ideas, check out Max Tegmark's breakdown of the 4 levels of parallel universes: http://space.mit.edu/home/tegmark/crazy.html. To your question of "why bother hypothesizing other universes which may have no impact on us," the answer is because theories which predict those other universes also predict certain aspects of our current universe (again, see Inflation).  In other words theories that explain observable properties of our universe (flat, smooth) also predict such other universes. And for the record, I am not a cosmologist, nor do I play one on TV.  I am hardly qualified to read the relevant Wikipedia pages.

Garrick Toubassi at Quora Visit the source

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The term "universe" has almost lost any useful meaning. It used to mean everything that exists that we can see. As more dimensions have been added and removed (time, for example, and now all dimensions above and beyond that, depending on which theory you subscribe to), the term "universe" has been expanded or contracted almost constantly over the years. To the point where when you see the word now you can't confidently say how many dimensions you're talking about about, which means you almost always have to quantify the number of dimensions any time you use the term. My take, anyway.

Jason Kolb

I wonder the same thing. I found this questions by typing in this question and finding yours instead. One thing I noticed about physics and other technical fields is that just because you're a master of some technical field, doesn't qualify you as a master of describing it. I know that even the physicist that use these terminologies are smart enough to realize the contradiction, but why continue to use this terminology is beyond me. But, perhaps at one time "the world" meant everything, but now we can say we have many worlds. Finally, the answer is that they are referring to a universe as something that contains a whole system of galaxies.... and since there are more than one (according to some theories), then we end up with universes. In a sense it's a natural progression... we thought we had one universe, but now we have discovered many. In one sort of fucked up way, multiple universes does a good job of describing a lot of current theories in physics. Since we "thought" we lived in one universe, when we actually lived in many. It reminds me of the Matryoska dolls, the little wooden dolls inside of dolls. We live in a doll inside of a doll inside of a doll. So we just call them all "doll", although depending on your perspective, there are "multiple dolls". Perhaps, a long time ago "galaxy" meant what "universe" meant at one time, as in, it was singular. "Galaxy" actually existed when there was no knowledge of a second galaxy, so this may be a evolution of terminologies to draw from. Perhaps there were linguistic debates about galaxy back in the day too.

Kurt Braget

Many times it's necessary to infer functions and properties of other demensions to help explain what we see here. For instance, it can make sense to talk about other universes in the "multiverse?" if for instance it's true that the weak forces are weak because they originate outside our universe.  I'm not qualified to answer anything beyond that generalization.

Jason Bogovich

We need a word that refers to everything that exists, and since the universe no longer does that job, I currently use cosmos for the purpose.

Mark Beronte

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