6 ms·

Shouldn't it be 13 * 2 = 26 across? 13 light years that way, and 13 light years the opposite way? Is there some "relativity trick" I'm missing? Is some space a

Shouldn't it be 13 * 2 = 26 across? 13 light years that way, and 13 light years the opposite way? Is there some "relativity trick" I'm missing? Is some space aliean on the edge of the universe going to see 13 light years in all directions?

ed209 14y ago
that would assume that there is a center to the universe. I'm not sure there is (speaking as the lay-est of laypeople). There are articles on the topic which I won't embarras myself by summarising in a HN comment... http://www.quora.com/The-Universe/Does-the-Universe-have-a-center http://www.quora.com/The-Universe/Does-the-Universe-have-a-c...
- deleted 14y ago
  [deleted]
lifeisstillgood 14y ago
considering I knew even less than I thought I did 20 minutes ago I am going to wait for someone who actually knows to chime in.
goodside 14y ago
This is a misconception. If you just want a satisfying mental image of the Universe: It's really big, it doesn't have any point defined as its center, and it doesn't have any wall-like borders. Aliens living 14.6 billion LY away from us see a Universe that looks just like what we see in all directions. If it is limited in size at all, it's because it wraps around on itself ("if you go straight long enough you end up where you were"). Nobody has firm evidence that it actually does wrap around on itself, and there's reason to believe that if it does, it's on a scale that's much larger than we could ever hope to observe. We will likely never have any sign inconsistent with it being literally infinite regardless of whether or not it is. If you want a better answer than that, you'll need a very firm grasp of special relativity and a basic understanding of general relativity and the metric expansion of spacetime. In which case, read this: http://arxiv.org/pdf/astro-ph/0310808.pdf http://arxiv.org/pdf/astro-ph/0310808.pdf
- wyclif 14y ago
  Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space. ~ Douglas Adams, The Hitchhiker's Guide to the Galaxy
- arikrak 14y ago
  Was it instantly huge after the big bang or did it expand much faster than the speed of light?
  - dhimes 14y ago
    The latter: it went through an inflationary period; the inflationary model supplanted the big-bang theory in the 1980s.
  - sageikosa 14y ago
    The Schwarzschild radius of the observable universe is 10 billion light years. Me thinks that for the mass to be compacted into a smaller space at some point in the past, it would have either had to escape it's own event horizon (since under most current definitions it would be a black hole), or the definition of light-year had to have changed from what it is today. In that regard, the only thing making up the definition of light-year is distance and time; so space-time itself was radically different way back then (from our current perspective of relatively low energy densities).
  - nessus42 14y ago
    Both! If the universe is flat, then it was always infinitely big. And, according to the inflationary universe theory, it expanded faster than the speed of light too. In this case, you have to think of "expanding" as being like stretching. I.e., things within the infinitely big universe rapidly got farther apart from each other.
    - arikrak 14y ago
      How could it have always been infinitely big if there was a big bang where everything was once?
nessus42 14y ago
> Shouldn't it be 13 2 = 26 across?* I guess this depends on how you define "across". Our Hubble sphere is all the space around us for which light has arrived. If the universe is infinitely big, then yes, there are things that we can see that are 26 billion light years from each other. However, they can't see each other, and so they are not causally connected to each other, even though we are causally connected to both. >Is some space aliean on the edge of the universe going to see 13 light years in all directions? An alien at the edge of our Hubble sphere will live in a different, overlapping Hubble sphere, from which they will see 13 light years in all directions around themselves.

ed209 14y ago

that would assume that there is a center to the universe. I'm not sure there is (speaking as the lay-est of laypeople). There are articles on the topic which I won't embarras myself by summarising in a HN comment... http://www.quora.com/The-Universe/Does-the-Universe-have-a-center http://www.quora.com/The-Universe/Does-the-Universe-have-a-c...

deleted 14y ago
[deleted]

lifeisstillgood 14y ago

considering I knew even less than I thought I did 20 minutes ago I am going to wait for someone who actually knows to chime in.

goodside 14y ago

This is a misconception. If you just want a satisfying mental image of the Universe: It's really big, it doesn't have any point defined as its center, and it doesn't have any wall-like borders. Aliens living 14.6 billion LY away from us see a Universe that looks just like what we see in all directions. If it is limited in size at all, it's because it wraps around on itself ("if you go straight long enough you end up where you were"). Nobody has firm evidence that it actually does wrap around on itself, and there's reason to believe that if it does, it's on a scale that's much larger than we could ever hope to observe. We will likely never have any sign inconsistent with it being literally infinite regardless of whether or not it is. If you want a better answer than that, you'll need a very firm grasp of special relativity and a basic understanding of general relativity and the metric expansion of spacetime. In which case, read this: http://arxiv.org/pdf/astro-ph/0310808.pdf http://arxiv.org/pdf/astro-ph/0310808.pdf

wyclif 14y ago
Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space. ~ Douglas Adams, The Hitchhiker's Guide to the Galaxy
arikrak 14y ago
Was it instantly huge after the big bang or did it expand much faster than the speed of light?
- dhimes 14y ago
  The latter: it went through an inflationary period; the inflationary model supplanted the big-bang theory in the 1980s.
- sageikosa 14y ago
  The Schwarzschild radius of the observable universe is 10 billion light years. Me thinks that for the mass to be compacted into a smaller space at some point in the past, it would have either had to escape it's own event horizon (since under most current definitions it would be a black hole), or the definition of light-year had to have changed from what it is today. In that regard, the only thing making up the definition of light-year is distance and time; so space-time itself was radically different way back then (from our current perspective of relatively low energy densities).
- nessus42 14y ago
  Both! If the universe is flat, then it was always infinitely big. And, according to the inflationary universe theory, it expanded faster than the speed of light too. In this case, you have to think of "expanding" as being like stretching. I.e., things within the infinitely big universe rapidly got farther apart from each other.
  - arikrak 14y ago
    How could it have always been infinitely big if there was a big bang where everything was once?

nessus42 14y ago

> Shouldn't it be 13 2 = 26 across?* I guess this depends on how you define "across". Our Hubble sphere is all the space around us for which light has arrived. If the universe is infinitely big, then yes, there are things that we can see that are 26 billion light years from each other. However, they can't see each other, and so they are not causally connected to each other, even though we are causally connected to both. >Is some space aliean on the edge of the universe going to see 13 light years in all directions? An alien at the edge of our Hubble sphere will live in a different, overlapping Hubble sphere, from which they will see 13 light years in all directions around themselves.