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  • "The Universe," informally, means "everything there is" - mountains and oceans and the moon

  • and hot nuclear balls of hydrogen and a whole lot more.

  • But if the Universe is "everything", does that mean it includes the things that we don't

  • know that we don't know exist? Or even the things that we believe exist but haven't yet

  • seen or observed? For example, is the future a part of the universe?

  • In physics, we usually distinguish between these two notions of universe as 1) the "observable

  • universe," which is everything whose existence we've thus far been able to confirm or observe, or could in principle observe if we point our telescopes at it

  • and 2) "The Universe" with a capital U, or, "The Whole Universe," which is everything

  • that exists, has existed, or will exist, any time, anywhere, regardless of whether or not

  • we're aware of it yet (or ever will be).

  • Of course, the main reason for this distinction is so that we can talk scientifically about

  • parts of the universe we haven't yet been able to observe, and the two biggest reasons

  • we might not have been able to observe a piece of the universe yet are either it's in the

  • future or it's so far away that light from it hasn't had time to reach us - yet. To explain:

  • as far as we know, the universe had a beginning and is now around 13.8 billion years old.

  • Light takes time to travel through space, so anywhere too far away from us just isn't

  • visible yet in the same way that thunder from a distant lightning strike isn't audible - until

  • you wait long enough. If you were blind, the thunder would be the first sign you have of

  • the storm's existence, though once you hear it, you can infer that the storm must have

  • existed all along.

  • So within the observable universe, what do we know "exists"? Pretty much just three things:

  • spacetime, particles, and the physical laws that describe how spacetime and those particles

  • interact to give rise to gravity and matter and forces and everything else. It's open

  • for debate whether or not mathematics is a part of the universe or if it exists "outside"

  • the universe in some sort of mathematical heavens - but if you think that mathematics

  • exists and if The Universe is everything that exists, then, well... I'll leave that up to you.

  • There's one other thing, though - you may have heard of parallel universes, or "Multiverses,"

  • an idea proposed by researchers or sci-fi fanatics that perhaps what we think of as

  • The Universe is actually just a small piece of a larger thing which is really "everything

  • there is"... but that's another verse in the story.

  • (Gazzlle介紹)

"The Universe," informally, means "everything there is" - mountains and oceans and the moon

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B1 universe exists observe spacetime observable universe observable

What Is The Universe?

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    drsueec posted on 2013/08/24
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