Where does word universe originate from?

Chalnoth

Well, I would go a little bit further than that, though. It is conceivable, for instance, that we can build experimental tests based upon these properties of other regions of our universe.

Here's an example (about quantum mechanics, not cosmology, but about a common 'multiverse' idea):
http://arxiv.org/abs/0809.4422

The proposal is that we obtain a very specific prediction of convergence rates based upon assuming the many worlds interpretation, a prediction that can be experimentally tested.

TalonD

if indeed we find that there are other spacetimes like ours and the definition of universe is expanded to include those, what would we then call our little piece of it?

Chronos

Think observational evidence. None currently available compells us to believe anything exists 'outside' our 'universe'.

Chalnoth

That depends upon what you mean by "our universe". If you just mean the totality of what we can observe, then this isn't true: the fact that the universe is obscenely homogeneous on large scales indicates very strongly that the universe extends quite far out in space.

Furthermore, our theories of high energy physics seem to point to spontaneous symmetry breaking events in the past, events which, by their very nature, vary from place to place. We would therefore expect that if you go far enough out, the universe will start to appear quite different based upon different outcomes of this spontaneous symmetry breaking.

So I would say that even right now, there are strong reasons to believe that there exists more stuff out there beyond that which we can see, and that some of that stuff is very, very different from what we see here.

marcus

It is hard to predict how language will evolve but we have historical precedents suggesting that we will find something to call it.

What we once called the universe we now call the milkyway galaxy.

Earlier, what was called the universe was mainly the solar system (surrounded by a sphere of stars).

Historically, the word universe (and synonyms like cosmos, mundus) have been for the whole thing and we make up new words for subassemblies as we discover that they aren't the whole thing.

Of course that historical pattern could break down at the very next opportunity! We can't foresee future linguistic choices at that level of detail.

But suppose it doesn't break down, and the practice continues of calling the whole works the universe, then your question is asking us to guess what word might be adopted
(for the local connected spacetime region governed by a uniform set of laws and physical constants.)

The vision being evoked now is of disconnected regions governed by different laws or by different accidental choices of physical constants.

In my personal language sense, the word for a continguous territory governed by a uniform code of law is Land. That is how I picture it. A universe made of several or many Lands, and the laws of physics are possibly different in other lands, from what they are in our land. Maybe a different ratio of the masses of proton and electron. A fine structure constant different from our 1/137. A different cosmological constant. Like having different money in different lands (remember the franc, deutschmark, lira, kroner?)

Right now we can't say whether these other lands exist or not. Lee Smolin has proposed a falsifiable conjecture involving their existence (and so far observations have not ruled it out.) Essentially the speculation about other parts of the universe is a concrete question about LAW ITSELF. Where does physical law come from? What determines it? Could it be different somewhere else? Or is there only one consistent system, no other choice so to speak? Can Law evolve. If matter falls down a black hole and emerges in a big bang will that new spacetime region have different physics constants, or will it have exactly the same? Does the vacuum, or the geometry of space, contain all the information about what particles can appear in it? Or if you pass the geometry thru a wringer---thru a collapse and re-expansion---can it come out slightly different from how it went in?

Multiverse talk is, in some sense, simply a pictorial way of wondering about the Laws of Nature. Anyway that is how I see it. And I think inquiring directly about physical law is actually a tougher and more interesting approach than the pictorial fantasy.

It is significant that Smolin's conjecture is basically one where you examine the laws themselves to determine if they could have evolved by the black hole wringer mechanism. Falsifiable predictions and tests can be made. The laws are then the observational data. It is like having a new kind of telescope or microscope to examine nature with---instead of looking at quasars or microbes you look at the values of the parameters for signs of their having evolved by some possible mechanism---having been selected for reproductive fitness.

If some idea like that gains currency then it will force some slight adjustment in language. The linguistic choice might depend on how you visualize the particular scenario. If it an idea like Smolin's you might call the part we live in a "branch" of the universe. Because his evolutionary picture is like a branch of a tree that keeps on branching.

Thats all I can say about your question Talon. We won't have to decide that semantic issue for quite a while, I think, so no need to try to settle it yet.