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  • The Universe. How big is it? Does it have a center? Does it have an edge?

  • Is it getting bigger, and if so, why?

  • Well, we know that there are two different meanings for "universe" - first, the

  • "observable universe" is everything that we've been

  • able to see, or observe, thus far. And second,

  • "The Universe" (or "the whole universe") means

  • everything that exists or has existed, or will exist.

  • More specifically, the observable universe

  • is the region of space visible to us from earth. And since The Universe is only about

  • 13.8 billion years old and light takes time to travel through space, then regardless of

  • what direction we look, we see light that's been traveling (at most) 13.8 billion years.

  • So it's logical to think that the observable universe must then be 2*13.77 = 27.5 billion

  • light years across - but it's not. That's because over time, space has been expanding,

  • so the distant objects that gave off that light 13.8 billion years ago have since moved

  • even farther away from us. Today, those distant objects are a bit more than 46 billion light

  • years away. Multiply times two and you get 93 billion light years: the diameter of the

  • observable universe.

  • To give you a sense of scale, the size of the earth within the observable universe is

  • roughly equivalent to the size of a virus within the solar system - although that doesn't

  • help much because we can't really appreciate the incomprehensible smallness of a virus

  • nor the bewildering bigness of the solar system, either.

  • \ So let's just say that the observable universe

  • is stupendously big. But The Whole Universe, as far as we can tell, is a lot bigger - space

  • is most likely infinite! Or at least it doesn't have an edge, though the difference between

  • those is another story unto itself.

  • Now, what about the center of the universe? Well the

  • observable universe

  • has a center - Us! We're at the center of

  • the observable universe because the observable universe is just the region of space visible

  • from earth, and kind of like how the view from a very tall tower is a circle centered

  • on the tower, the piece of space we can see from here is naturally centered here. In fact,

  • if you want to be more precise, EACH ONE OF US is the center of our OWN observable universe.

  • But that doesn't mean we're at the center

  • of The Whole Universe, just like the tower isn't the center of the world - it's the center

  • of the piece of the world that it can see - up to the horizon. But just because you

  • can't see beyond the horizon doesn't mean there's nothing there.\

  • And so it is with the observable universe.

  • Looking up at the sky, we see light light that's at most 13.8 billion years old and

  • coming from stuff that's now 46 billion light years away. Anything farther is "beyond the

  • horizon". But each second, we see new, even older light

  • coming from slightly farther away (one light-second

  • farther, to be precise), and so our view of the cosmos is literally getting bigger all

  • the time - all we have to do is wait and watch as the universe ages and light from more distant

  • places has the time to get to us.

  • So here we are, sitting at the center of our observable piece of the Whole Universe.

  • How big is the universe? Well, the observable

  • universe is currently 93 billion light years across. The Whole Universe is

  • probably infinite.

  • Does the universe have an edge? The observable does (it's 46 billion light years away in

  • any direction), and The Whole Universe has a temporal edge (or what we call a beginning)

  • but almost certainly not a spatial one. Does the universe have a center? Again, the

  • observable universe does: YOU! The Universe as a whole? Almost certainly not.

  • And is the universe getting bigger? Yes - space is expanding, which makes both the observable

  • universe and the whole universe bigger - plus, over time, we see older and older light coming

  • from farther and farther away, so our observable universe gets bigger that way, too.

  • And that, in a nutshell, is our view from

  • the tower. You are the center of the universe. And so am I. And so is everyone else. And

  • so is no one.

The Universe. How big is it? Does it have a center? Does it have an edge?

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How Big is the Universe?

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    Why Why posted on 2013/03/29
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