[Music] Newan it's so much bigger than what we can see the question is is it finitely larger or is it infinitely in size on the how how can you be a cosmologist and not wonder about is there a multiv if we have enough time and enough space it's not only likely to happen it's inevitable that there will be a replica of all of us the [Music] [Music] for multiv everywhere all at [Music] [Music] once this universe is only one of an infinite number Spiderman across the spider [Music] [Music] [Music] when I was a kid I always wanted to be an astronaut so that was my dream in another Multiverse if I had a choice I would still want to be a cosmologist I would choose a version of this universe where uh capitalism never existed [Music] [Music] there are observations of the universe around us that are on firm experimental footing they're just observations data or data or data so once you take this data you then follow the logical syllogism to get to the point that it's possible one way to explain why the universe is the way it is is if we do live in a Multiverse [Music] [Music] [Music] G for [Music] people used to think uh in the 15th century that the Earth was flat and had an edge now the universe does not have an edge as far as we can tell what does have an edge is what we call the visible Universe light travels at a certain speed 300,000 kilm per second and the universe has only been around for 13.7 billion years so in 13.7 billion years light has only been able to travel so far and that is how far back we can look we call that the universe's Horizon and we cannot see Beyond the [Music] Horizon so each Observer has their own region of space that they have access to and essentially the space is everywhere and this observable region is around you but it doesn't mean that the whole universe is a [Music] bubble think of ourselves sitting at the center of this roughly spherical object and then any direction we go out and look there's a certain Horizon Beyond which we can't see anything because anything that exists beyond that the light from that object has not had time to ever reach us at the center of the sphere [Music] in fact must be at least something like 250 times larger this is not that but in fact in principle the entire universe could be infinite in size [Music] we don't have a concept of infinity in our head it's not something that the human brain can really wrap itself around our species didn't evolve in anything infinite everything is very finite lifespans resources uh the sunlight you know at the end of the day so we're we're not accustomed to the concept of infinity if the universe is infinite because it's so big Infinity is very very very very being there will be places in the infinite universe or places in the Multiverse when everything is as it is here except that I'm not sitting on this chair I'm actually lying down on a couch and I'm not talking about cosmology I'm talking about genetics well I mean genetics is a fascinating field for sure and uh it's a completely Noble description of life right it up when it was discovered one of the good ways to start to think about uh infinity is so-called you know infinite monkey theorem the idea is roughly that if I have an infinite number of monkeys and I give them typewriters and I let them all start typing uh eventually one of them is going to type Hamlet by Shakespeare they have to if you this is the notion of infinity Cor e [Music] Infinity is not a number it's a thing it's an idea and the concept is so bizarre that it's really hard for us to wrap our heads around par [Music] [Music] [Applause] one of the disturbing facts is that because there are so many examples of universe then anything can happen and anything will happen The Elements of Life are finite we only have about 120 different Atomic nuclei in Mandela's periodic table of the elements so if the universe is infinite or if there's a Multiverse then you're in a bit of a bind Because unless the laws of physics are completely different from what we know here we only have so many building blocks in order to create for example planets or life so it's inevitable that somewhere else because the materials you have are finite that somewhere else you'll end up with a replica of what we have here in our cozy planet on Earth [Music] black so there will be examples where I'm wearing a tie representing the Multiverse whereas in another part of the Multiverse the St Carlos Frank would not be wearing that beautiful tie [Music] etern this is not what the economy is doing right now this is what the universe is doing back in the beginning when the universe was born it was caught in a somewhat uncomfortable state it had an excess of energy that physicist called vacuum energy and the universe didn't like to have this excess of energy so it tried to shake it off just like a dog comes out of a lake and shakes off water in this case the universe tried to shake off this excess vacuum energy by expanding really really seriously fast exponentially fast over a very brief period of time that crucial phase in the story of a universe is known as Cosmic inflation if you have inflation ending it only really ends in one uh part of space in another part of space the universe could be still expanding at this inflating rate [Music] [Music] [Music] [Music] the universe as it inflates can spawn off other universes all the time new universes new Big Bangs popping out uh everywhere and so in the this idea then the outcome the inevitable outcome is that there isn't one Universe there are many instances of universes which we elegantly call the [Music] Multiverse so this is a prediction that can seem very mysterious and and a bit scary and it can make us feel very uncomfortable that there are other universes out there but it is a prediction that we must confront if we actually accept this explanation for what we can see in our own universe I personally find it dissatisfying to accept that an idea like inflation explains all the structure we see in our universe and yet sort of hide away from this this implication which is very generic just a number that we can measure and it's just the way it is there's no mechanism for why that number is the way it is so because of this physicists like me we get frustrated we like what possible mechanism could there be for these magic numbers to be the way they are the gravitational constant represented by the letter G and it measures the strength of gravity now it's a number that we know very precisely and an interesting question is a counterfactual question what would happen if that number was different so imagine you have a dial and um how far would you need to move that dial before we cease to recognize our universe gravity is the architect of our universe and if it was weaker ever so slightly weaker then the galaxies would have never formed and without the galaxies there would never be stars there would never be planets there would never be people now turn the dial the other way make it stronger the universe wouldn't look anything like it does if gravity had been stronger because uh the galaxies just would have not been able to form the way they are most of the m in the universe in a great big lump uh and so which is a great big black hole which is not really the universe in which we live [Music] I doubt you'll hear a nerdier statement said today the universe loves statistical distribution so you know the average resting heart rate of of a bunch of a room of human beings will be distributed among like a gaussian distribution and this just happens naturally uh and you know if you stand on a street corner and you wait for the the rate at which cars will pass you will follow some kind of Wason distribution what if it's possible that our universe just happens to be the one Universe out of a possibly infinite number of other universes in a Multiverse where these other values were taken and those other universes could in principle have these other values that led to very different or very boring or non-existent universes where there's no atoms there's no nothing nothing interesting is happening and ours is the one where everything came together to be able to lead to us to be able to ask the question in the first place that provides a mechanism that provides an explanation as to how and why our universe could get to the way it is today so this is a little bit like Evolution right it's selecting out universes that are hospitable for forming structure and forming life and we can only live in such a universe [Music] you are allowed to have any idea doesn't matter how crazy it is and you will still as a physicist be paid at the end of the month so long as your crazy idea is testable I love my theorist colleagues I'm not a theorist I'm an experimentalist so at the end of the day to be able to demonstrate whether or not this is true we need an experiment we need need a way to be able to test this multi idea imagine this simplest possible thing right I have a portal to another universe and um I'm like okay well I want to just do some very basic tests I want to you know test how long things are in this universe I take a ruler standard ruler that I get from the from the state store and I stick my hand through this portal into the other Universe what if the other Universe has constant of nature such that atoms don't exist carbon doesn't exist hydrogen doesn't exist what's that going to mean for my ruler it it can't exist my hand can't exist this would be there's no way for me to even test what's going on here there's no way we can have any communication of any sort through light through radio waves through gravity with these other elements of the Multiverse and that goes against the some of the basic tenants of physics that for something to be um a part of the body of knowledge that we call physics it must be testable the idea of the Multiverse as such is not testable and that really irritates many of my colleagues [Music] yes just speculating about multiverses is not interesting to me either so I feel driven to try to find a way to test this idea for one of the ways that you can do that possibly and I say possibly because we haven't shown it can be done yet is to take the spooky quantum physics and work out a laboratory system and you can perform the experiment in the laboratory and see whether the prediction of the bubble universes has an analog in terms of making bubbles in a quantum physics system in the lab and so we are gearing up to actually do that which is very exciting [Music] [Music] is clearly science because asking this question in this way and then asking for an experiment to test it at some point that is science this is what the history of physics has done it's constantly destroyed Humanity's hubris that Were Somehow special and this this is just another version of this for because there's no obvious um darwinian evolutionary pressure for us to understand the Universe I mean it doesn't help us um run away from Tigers it doesn't help our species in an obvious way so it must be some side effect of some other um uh tool that humans developed in order to survive but it is an absolutely wonderful gift and um it is one that um I think goes to the essence of what being human is about his ability to ask fundamental questions and in many cases to answer them [Music] h [Music]