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Message: <blockquote data-quote="fuindordm" data-source="post: 2391570" data-attributes="member: 5435">Can other people join in?  You two are getting a little hard to follow.My 2 cents:  you both have points.In our current universe, defined as the extent of everyhing that we can observe, not everything is possible. Even little things like the existence and functioning of stars is highly depended on any number of fundamental constants; tweak these constants, and by extension the laws of the universe, just a little and you end up with stars that can only live a few thousand years, or no stars at all.  If the observations we make of the distant universe can be adequately explained by applying the laws that we've determined through experiments in our own backyard, thenwe can state with confidence that the same laws apply in the distant universe.  If you want infinite variety, then you also have to have an infinite variety of physical laws.This can happen, to some extent, outside our horizon.  Physics demands only that the laws of the universe be coherent on a scale equal to the distance that light could have traveled since the beginning of the universe (the horizon length).  Observations have shown us that the early universe was coherent on much larger scales, but there remains the possibility that if we reach far enough out, we'll find a boundary between our segment of the universe and another segment where the physical constants are different.Such things are common in nature.  The sheets and filaments that you see in ice cubes are the result of crystallization occuring simultaneously in different parts of the water, but with different orientations. The two crystals grow and spread, but when they run into each other they just stop and you get a surface within the ice that is under some tension, and is not clear like the rest of the ice.  Such things are also possible in the substance of space itself, according to Big Bang/inflation theory.We don't know what's doing the crystallizing in the case of the universe (some fundamental particle/field that hasn't yet been identified in laboratories, thought not for lack of trying or theoretical candidates), so we can't really say what the universe would look like on the other side of the boundary.  All the particle masses might be different, or the relative strength of the fundamental forces might be different; or the laws of nature might be even more bizzare.This is all of course, hightly speculative but still within the realm of what physicists today consider possible.  Such 'neighbor universes' might or might not exist.  Then you can try expanding your domain into multiple universes (as I mentioned in my last post), or multiple histories of the same universe coexisting (as some quantum mechanics like to think), or spiritual dimensions to our own universe (which might exist but have not yet been observed with science, which, after all, is only capable of testing repeatable phenomena), and so on.It's not so easy, after all, to define the universe.Is it everything that exists, whether we know about it or not?Is it everything that exists, whether we can affect it or not?Is it everything that might logically exist, whether it does or not?Each version will lead you down a different path, which is why you can get into long arguments about the nature of the universe with no issue--each person has a different idea of what they're including in their definition.Scientists generally restrict themselves to the following:The universe is everything that has a causal relation to us.Meaning they include everything they can detect.  So far all these ideas for multiple universes are undetectable since they all lie outside the maximum travel distance for light; and since the universe is expanding faster than light, they cannot be reached by us, ever, unless we discover something radically new.  But for the present, all these alternative universes are purely speculative.  Fun to think about, but speculative.  And if you want to come to agreement about what could possibly exist, you first have to settle on what sort of alternates you've decided to include in your definition of a universe.Ben</blockquote>

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