Leonard Susskind - How Many Universes Exist?

Lenard the concept of multiple universes pocket universes bubble universes developed by Alan Guth Andre Linda others have really revolutionized our understanding of how big reality can possibly be from the standpoint of a string theorist someone who is deeply concerned about explaining reality how have you incorporated those ideas into your worldview yeah well if I understand correctly these ideas that that you've mentioned by people who are other than me the idea of multiple universes how they come out of inflation is basically that inflation is a mechanism for creating all the diversity in different places in the universe that is possible everything that is possible within the framework of the equations of the theory will appear someplace so if the theory has a solution with this property or with that property or with some other property someplace it will appear and not just once many many many many times over so those ideas will lead to a universe which is populated by many many bubbles but the question is how many different kinds of bubbles are there you can imagine that there are only two different kinds of bubbles a universe of this type a or that type B what string theory brings to it is something about the number of possibilities it's not just a and B it's not just a through Z but the number of possible kinds of universes the number of possibilities that are inherent in the equations is nobody knows how big but it's numbers which are far far bigger than the number of atoms in the universe far far bigger than anything you can think of the number 10 to the 500 gets bandied about a lot 10 to the 500 not 10 to the 500 different little pocket universes but 10 to the 500 types of them each one being repeated over and over again now the reason that that is or at least one of the reasons why we find that important is because it provides a possible natural explanation as opposed to supernatural explanation for this anthropic idea namely the idea is that the universe is so diverse so big so diverse that there will be pockets in it no matter how unlikely those pockets may be there will be pockets where the conditions happen to be right for life to exist most likely if this view is correct almost all of this multiverse is sterile is not full of life is dead it's inflating too fast all sorts of the bad things are happening it doesn't have electronic constants of physics are the physics are moving the wrong direction right but just like here and there there's a planet that you can live on here and there there's an environment or a pocket universe which is at the right spot on the landscape for all of the things to come together which are required for life so according to this view we are a very very rare phenomena the universe was not created than just the uniformly be able to describe life everywhere so to have life in it everywhere is it was just a big random thing that had so much randomness to it that here and there conditions were right okay let's take the situation of these multiple universes being generated chaotically by inflation and in virtually an infinite way and these 10 to the 500th approximately of possibilities that string theory can have as you say these vacua that string theory can exist there what is that what is the relationship between between these two both are talked about very much most of the time independently occasionally as you've done bringing trying to bring them together here what which generates the other which is the primal force and which is the result as they work together I don't think it's a question of cause and effect of one of the other they're two separate things yes ah the space of possibilities in other words the collection of all possible kinds of universes that can exist it is very similar in a way to the space of all possible kinds of creatures that can exist they're necessary being that string theory that's string that's okay and but you get that strengthener 500 approximately by geometrically that's right by rotating that's right by studying the various ways that you can combine microscopic geometries together and at least 10 to the 500 have been counted so that's the estimate right that's correct so on the one hand string theory gives you the analog of the different number of ways of rearranging a DNA molecule what inflation brings to it is the other side of the coin how do you bring these different universes with different DNA have you bring them into existence so it's much much more like the way the biosphere formed from a bunch of carbon a bunch of oxygen some Darwinian evolution various survival of the fittest all these kind of things came together and created all of these different patterns which were inherent in the theory of DNA in the same way eternal inflation populates creates more and more space more and more space and that space simply just fills up all of the different possibilities that are inherent in the equation let me try this metaphor see if you see if it works that the the string theory is with if you have a deck of 52 cards all the different ways that 52 cards can be arranged and inflation shuffles the deck and deals them out no no inflation makes more and more decks each one ship shuffled differently okay sure inflation doesn't inflation doesn't take one deck and reshuffle it it makes it just creates more and more and more index of card but each one shuffled differently okay great that's the right so we have this the possibilities of how the cards are ordered in in a deck right inflation just makes lots and lots of these in each one shuffles them differently it's a fight for more than fifty two cars factory but the cards come out in each each time they created they created different different order right right and of course there's much more than 52 in the analogy and this much more okay okay so actually with just 52 cards you can get a hell of a lot of arrangements there factorial and so as you see these two fairly powerful theories in today's world how do you see progress being made you do you see next no boy you know that yeah that so there are two kinds of progress that you can imagine one is at the theoretical level and one is at observational experimental level theoretically I think we will simply learn to explore this landscape better and better find out what's there and eventually perhaps find our own place in that landscape which means like finding out exactly not perhaps exactly but approximately what combinations of base pairs in the DNA add up to a human being we may be able to figure out which combination of these elements put together in various ways create a universe like our own and check that there is such a possibility so that's an entirely theoretical enterprise we may also be able to better understand the mathematics of this eternal inflation and convince ourselves or convinced it's not a question convincing ourselves it's convincing the the opponents that the mathematics holds together that that the theory holds together and makes good sense now that is a long ways to go but the critics and I must say the credits of course correct that it's not enough you have to find some way of confirming this by observation by experimental and that's where the hard stuff is it is the answer I am afraid is nobody really knows we have we are rapidly coming to the end of the possibility of doing experiments within a human lifetime current experiments in particle physics that's a very small from inception the completion is 2530 years it involves building an accelerator that 50 miles big and so forth incidentally an accelerator that could probe the scales that were really interested in would have to be as big as the galaxy and it would have to use trillion barrels of oil a second to fuel it so we're coming to the end of where we can really directly probe these kind of things and that's very frightening I mean frightening for somebody who has invested that much of their life in these things on the on the observational in Cosmo a cosmological where that we're beginning to see things as big as the horizon we know that we cannot see things bigger than the horizon and so again we're coming to the end of observation there are two ways to make progress one way is entirely theoretical mathematical and that entails understanding this landscape much better finding our own place in it understanding the mathematics of eternal inflation much better and convincing ourselves that it's a mathematically correct theory that's on the theoretical side that will not be entirely satisfactory to most people they will want to see experimental and observational comes our confirmation we're not going to see other pocket universes they're outside the horizon the too far away they're outside our experience what we may be able to do is to look into the past and by looking into the past discover that our universe was born from one of these bubble nucleation x' this is possible that we will be able to look into the past and see the event which gave rise to our universe being in nuclei from another point in the landscape that is possible but quite frankly the possibilities the experimental possibilities are very limited and very very hard so I am NOT optimistic that we will see a great deal of experimental evidence in this direction at least in the short term

Channel: Closer To Truth

Views: 207,661

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Keywords: Leonard Susskind, Closer To Truth, universe, multiverse, physics, science

Id: AuWDzQ-tiZ8

Length: 11min 28sec (688 seconds)

Published: Wed Dec 23 2015