Astrophysicist Paul Sutter explains
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00:00 Do we live in a multiverse?
00:04 No.
00:05 I mean, yes.
00:07 I mean, maybe.
00:09 Look, it's kind of complicated and we're not exactly sure.
00:14 I'm Paul Sutter and this is Paul Explains, the show where I, you know, explain.
00:22 First let's define what we mean by multiverse.
00:25 We have the universe, which is by definition all the things.
00:30 It's all the stars, all the planets, all the people and aliens.
00:34 It's all the bits of fluff just floating around in the void.
00:38 It is the entire thing.
00:40 It's all the stuff.
00:43 So in one sense, there's no such thing as the multiverse because the universe is already
00:48 defined to be all the things.
00:50 But maybe there are patches of the universe that have different physics or different realities.
01:01 They have different forces or different particles.
01:04 And this is what we refer to as the multiverse.
01:09 Now, do we live in a multiverse?
01:12 Maybe, maybe not.
01:15 One of the most promising ways physically to get a multiverse is through something called inflation.
01:24 Inflation is our model of one of the earliest and most momentous events in the history of the universe.
01:32 In the inflation model, when our universe was barely getting started, when it was a
01:38 billionth of a billionth of a billionth of a billionth of a second old, it became very large.
01:45 It went from the size of, say, an atomic nucleus to around the size of a baseball.
01:51 And this event has the possibility of never ending, of inflation of the universe just
02:00 always getting bigger and bigger and bigger all the time.
02:05 And what we call the universe is just one small pocket of that much larger volume of the true universe.
02:15 And in our little pocket, when inflation ended for us, we ended up with one set of physics
02:22 and one set of forces and one set of particles and one set of reality.
02:26 But past the confines of our little bubble, the greater universe is still going, still
02:34 doing its thing, still inflating and different pieces of it pinch off on their own with their own physics.
02:42 Now, it's possible that inflation can lead to a multiverse.
02:48 We don't know if inflation really happened.
02:51 We suspect it did, but we're not entirely sure.
02:54 And we're not sure if inflation demands the existence of a multiverse.
03:00 It's possible that inflation just happened once and did it throughout the universe and that this is it.
03:07 Or not.
03:09 We've looked for evidence for multiverse and have come up short.
03:14 Like if another neighboring universe intersects with the bubble of our universe, we might be able to see signals of that.
03:22 And we haven't seen anything.
03:24 That doesn't rule it out yet, but there's no conclusive evidence for it.
03:30 Even if there were a multiverse, we would never, ever be able to access any of those other universes.
03:37 We wouldn't be able to visit them.
03:39 They wouldn't be able to visit us.
03:41 For all intents and purposes, they wouldn't exist.
03:44 So when it comes to multiverse, whether it exists or not, just focus on our universe
03:51 because really, it's the only one we got.
03:55 [cheers and applause]
03:57 (audience cheering)