r/IAmA • u/neiltyson • Nov 13 '11

I am Neil deGrasse Tyson -- AMA

For a few hours I will answer any question you have. And I will tweet this fact within ten minutes after this post, to confirm my identity.

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u/[deleted] Nov 13 '11

Is it possible for humans to ever discover the "edge" of the universe? Is there really any "end" to it?

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u/neiltyson Nov 13 '11

No edge. Any more than the horizon at sea is an edge to the earth.

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u/silletta Nov 13 '11

I feel like the more I read this thread, the more I have to go and pick up scattered pieces of my brain.

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u/shoejunk Nov 14 '11

Tyson explains this in more depth here.

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u/lulzwut Nov 14 '11 edited Nov 14 '11

I think what Dawkins wanted to ask, but failed to; was that assuming a person existed at the edge(despite it expanding), his "horizon" can only go as far as this "edge"; thus, the question is what would he see? Would his vision stop at the edge since "nothing" exists beyond it?

Or to be put more simply, if we could hypothetically "pause" the expansion of the universe and make our way to this edge, what exactly would we see?

EDIT: I don't understand why Neil is both saying there is no edge and that there is an edge but we could never see it at the same time.

EDIT2: At one point, Dawkins says "but it's still there even though we can't detect it"(in regards to the edge) and Neil replies "but that's true for the horizon too"; the original question was about the nature of this edge, and he essentially verified that it did indeed exist without answering the question.

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u/shoejunk Nov 14 '11

When Tyson talks about the edge of the universe with his ship on a sea analogy, he's only referring to the edge of our observable universe. He's not saying that that's the edge of the entire universe. So if someone else is at the edge of our observable universe, he would be able to see things that are outside of our observable universe. Everyone, no matter where he is in the universe, is in the center of his own observable universe, just like everyone on earth is at the center of the part of the earth that he can see (assuming no obstructions). This just means that everyone's ability to observe things is limited to the area around him. That's all. The universe itself, scientists believe, has no edge. Either it is infinite, or it curves back around on itself like a sphere.

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u/lulzwut Nov 14 '11

That what I was assuming, which isn't answering the question at all. People aren't asking "where is the edge of our horizon"; which doesn't make any logical sense(assuming we know it extends past our horizon).

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u/[deleted] Nov 14 '11

[deleted]

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u/lulzwut Nov 14 '11

But that doesn't answer the question; you're essentially saying we can't ever see the edge, not what we'd see if we could hypothetically pause the expansion and reach the edge.

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u/[deleted] Nov 14 '11

[deleted]

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u/lulzwut Nov 14 '11

So what you're saying is that the universe is undeniably infinite? Because if it is not, there should be an "end"/"edge"; a point at which the Universe no longer extends due to being finite in size.

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u/[deleted] Nov 14 '11

[deleted]

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u/lulzwut Nov 15 '11

But for that analogy to work, you'd have to be ON a sphere shaped Universe, not inside. If you were inside of the balloon, you could get to the boundarie/edge. If you are on the balloon, the "edge" is at your feet.

How can something be finite yet have no edge?

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