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In which Hank explains how and why phycisists think that the univers has no edge.


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A Bunny
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Green: Good morning, John! Today I would like to talk to you and-- Edgy

Hank: NO EDGE.

Hank: Yes, today's video is going to be about the fact that the universe does not have an edge, and we're going to start with the observable universe. We often use 'universe' interchangeably with 'observable universe', which is the universe that we can conceivably see given that photons have to travel from the edge of it to us before we can see them. The observable universe is a sphere, and it centers upon the observer, meaning that each and every one of us looking out at the night sky, we are the center of the observable universe. The observable universe is like the observable ocean if you're sitting on the beach, there's a horizon out there, but of course, what that doesn't mean is that there isn't more stuff out there beyond what we see as the edge of the universe. Edgy

Hank: NO EDGE.

Hank: The universe can also be defined as just everything there is, and of course it's impossible to say that there is something outside of everything. Edgy


Hank: That one was creepy. But that's not actually a very good definition of the universe, what the universe really is, is this evenly dense, ever-expanding mass of stuff that we can study and we've learned many fascinating things about. Now a lot of people say to me, Hank, the universe is expanding, it has to be expanding into something, if it's expanding into something, there has to be an edge. There's nothing here and there's universe here, right, 'cause it's expanding? NO. It's actually not expanding into something, it's just expanding. I'm going to try to explain that. The Big Bang was not an explosion the way that we think about explosions, with things shooting off and you know, more stuff in the middle. The Big Bang was not like that, and the universe is not like that. Just like there is no edge, there is no center. After that cosmological moment of The Big Bang, everything existed and was evenly spaced and remains that way, though gravity like, makes little clumps, but overall, the universe is evenly dense. When we say that the universe is expanding, we don't mean that individual galaxies and planets are shooting out away from one another, what we mean is that the fabric that they exist in is stretching. In order to freak you out just a tiny bit more, if you wanted to find the physical geographical place where The Big Bang started, it would be...everywhere. We're not actually sure whether the universe's infinite current data suggests that it is, so apparently, it's perfectly possible that the universe is infinite, and also expanding, which, bwaagh! Edgy

Hank: NO EDGE.

Hank: I know! I'm right there with you, dude. So yes, it may just be that some infinities are larger than other infinities (holds up copy of TFIOS). The universe also, on the other hand, might be finite, somewhere out beyond where we can see, there might be an edge. Edgy

Hank: Wait.

Hank: Are--are you gonna be okay? Edgy

Hank: Edge?

Hank: Yeah, I know, maybe, probab--, maybe, I-- But nevertheless, beyond what we can see, there is certainly more, and if there is an edge, we will never see it and we will never know it. Now there are also a lot of other reasons why this is fascinating, I'm not going to get into all of those reasons, maybe I will write a blog post about it. By the way, speaking of blog post, my Tumblr died, it's complicated, but if you were following me on Tumblr, you'll have to go follow me on Tumblr again, I'm sorry, please do that, 'cause I'll miss you otherwise. Also, there's a very limited quantity of these still existing, if you would like to get one, it's the Tour de Nerdfighting CD which, uh, I had at the Tour de Nerdfighting, but we had extras and I don't want to throw them away. John, even though it seems that you don't think that the universe is appropriately interesting, I still like you a lot, and I will see you on Tuesday, NO EDGE. Hello, endscreen, if you're wondering, basically this video is what SciShow is all the time, except SciShow has nicer production value, so you may want to go to and subscribe. (singing) I'm on the edge of glory, and I'm hanging on a moment with you-- Edgy

Hank: NO EDGE!