Four Types of Multiverse - Sixty Symbols

since there are so many different notions of what is a multiverse I think it it's a it's quite useful to sort of categorize them and that has been done yeah yeah different there's a hierarchy of a multiverses and a guy called max tegmark very well-known physicist he's err classified into four levels so varying levels of controversy so well they say we'll begin with level one multiverse so what tegmark cause a level one multiverse and this is basically the idea that there is stuff beyond the observable universe so we think of it we talk about the observable universe which is basically it's around 10 to the think 26 meters distance something like that that order of magnitude so big distance scales that's as far as the eye can see essentially that's the farthest away you can go that light could have reached us from in principle since the beginning of the universe so pretty big distance scale but what's beyond that that's a legitimate question and this is the notion of a level 1 multiverse the universe is if you like the existence beyond that that strike me is still being a universe well I would agree but in a sense they're completely disconnected from us so in a sense that they are distinct I think that region beyond the the observable horizon that we call in the cosmological horizon is not very big but it could be enormous the universe could be absolutely gianormous one of the reasons that you can make it big is due to something called its eternal inflation so we know that why our universe around as our core of the universe we we think it got big because at some point it just grew very quickly due to something called an influence on expanded out very very fast got very very big and and what the influence on the funny thing about this in flat on field is what it does is is it generically it won't do this ok generically it will appear and it won't cause a universe to expand very quickly it won't have the right kind of conditions for that to happen but every so often it will okay so what this in flat on field does it takes a little random walk in the beginning of the universe and eventually it finds itself in just the right conditions to suddenly make that little pocket of the universe expand very quickly okay so if you like I like to think about this as our friend ed at Copeland he's a pretty chilled out guy right I mean we would agree with that very chilled out but a thing about Ed is is they every soft and I've known him for quite a few years now and every so often something will rile him doesn't happen very often but it can happen and then he'll explode and he'll explode the universe around it right it doesn't have a very often but it can happen so you could imagine ed going on a little random walk through town okay most things keep them nice and serene but every so often something rouse them in it and it blows up okay that's like the inflow Tom field so that's kind of how you explain how these quite unlikely scenarios suddenly made our pocket the universe big but the thing is the in flatten or ed doesn't stop doing its little random walks okay in different regions of space it can do its little random walks here and there and eventually sometimes it can be it can jump up back into the right region where it's going to cause this explosion again or maybe it never stopped exploding okay so ad for example might calm down but some in some regions of space he's being maintained annoyed because of these quantum fluctuations likely keeping them annoyed okay well like the inflow town it's being kept maintaining this expansion of space so you have this eternal process where regions of space are just continue to expand our region has stopped expanding at such a huge rate okay the expansion is slowing down someone but and but other reasons it doesn't it just gives it accelerated expansion blowing up at a crazy rate and so this is making those regions of space enormous and generally you expect that some regions of space will be behaving like this and are eternally inflating this is why we call it a tail inflation it and so whilst our region of space of might have slowed down that's not true generically now of course we now know that our region is places it's starting to speed up again but another story but what this means is is that those regions of space outside of our observable units could be truly gargantuan and this is where you get all the sort of crazy sort of notions that we talked about in the in the Googleplex video arising there's also the idea of Boltzmann brains as well it can arise from this but that's probably another video so one of the important things to realize about level one universe is that the laws of physics the values of the fundamental constants they're the same here in our corner as they are in those far reaches level two is subtly different to that a level two universe well you've got to imagine now is is that there are bubbles the universe is made up of bubbles our corner is living inside of one bubble where the physical constants are what they are and so on and so forth there are other bubbles where the physical constants might be different where the laws of physics look different there are Planck's constant you know the Newton's constant and you know fine-structure constant all these constants that underline you know physics okay these can change from from Bubble to bubble now why might this happen well we believe this could happen because of string theory string theory tells us that there aren't just one possible universe ones possible vacuum for the universe that you can have there's an entire plethora of them ten to the five hundred of them a huge number okay this is drink theory when it was first introduced it was hoped that it would come up with some sort of a unique and vacuum solution unique sort of set of circumstances which coincided with the universe we see and that's not what happened it was the exact opposite it came up with a huge number of possibilities now of course our corner of the universe is just one of those but generically there's many more and what will happen is you'll find these bubbles forming so within one one bubble you can have true quantum tunneling you can have a bubble of another unit another type of universe form with different physical constants and different yeah this can happen within the bubble through quantum fluctuations and so but then that expansion will occur with it inside that bubble and the bubble outside it can expand and the whole thing sort of you know proliferate you get percolation effects and you know the whole universe just gets filled with these with these bubbles of different vacua of different where the physical constants are different are they because I'm thinking of bubbles in a bubble bath or like you know stacked up against each other but what you're talking about there sounds more like Russian dolls well no I mean yeah but bokes okay it's both actually so the bubbles can happen you know you could have a bubble nucleate here there's a universe inside it where the laws are that they are everything's expanding so your bubble might get bigger and so you don't really notice you know or maybe that bubble will overtake take the other one there's dynamics involved in the whole process some bubbles may have an even even experience different dimensionality different numbers of dimensions so if you're in one bubble you might not experience a four-dimensional universe you might feel a five or six or seven dimension or what what's it the interface between bubbles can I Drive my car from one bubble to another well that would be quite destructive because of course the the laws there you know the things that's holding your car together the atomic forces that are holding the horn electromagnetic forces that are holding your car together the physical constants that are controlling that are going to change as you traverse the edge of one of these bubbles and enter another bubble okay so what your car looks like if you get to the other side might be something extremely different and you know who knows I don't want to speculate what it's going to look like right and so I mean the edges of these bubble walls are going to be sort of you know highly energetic regions where basically you're going to get sharp gradients in the in the in how things that you know things have changed it because you know Planck's constant you know it's going to perhaps change as you cross one of these walls that's going to create a strong gravitational effect in principle and so these are the sort of things that are happening so but the walls themselves don't have to be sort of you know they can be wide walls they don't have to be sort of particularly thin they'll be thin compared to the bubble as a whole but you know it said there's a there's a transition as you go from one to the other and one of the things we're actually looking for in the Cosmic Microwave Background is evidence of these bubbles evidence of bubble collisions so they're looking for circles in the sky that's what the core it's because you know you might see two bubbles colliding the imprint it would have on the Cosmic Microwave Background would be like a circle some sort of circular shape within the temperature fluctuations so we're actually looking for these things but this is a level two multiverse and I would say level one's not particularly controversial level two a little more controversial but still I mean if you believe in string theory probably by that level three on the other hand is I would say controversial and this is the idea that we've already done a video about this is the idea that you know in quantum mechanics you know you have this sort of a idea of probabilities so and whenever there's a chance that ever there's any probability ever there's any uncertainty for example in a coin toss if we're going to sort of try to picture it classically you know picture it sort of microscopically it doesn't really make sense to do that but if you were to try to do that you might think that whenever you toss a coin that the universe splits in two and it um in one way it there the coin came up heads and me and the other way the coin came up tails and that both happen what physical space at two different universes occupy the same space like like right now as we continually fork and split and split and split and split and split and split you know where are these new universes exist well I think the idea is that we'll be right on top of each other essentially but you can't interfere from one to the other there's no way of communicating that I don't think that's really necessary though this is this is I mean there's a few things I don't like about this firstly you know your kink whenever you have a split well when does the split occur which point does the split occurred precisely when is that I mean there's already time uncertainty in this so in quantum mechanics so when does the splits occur that's not really clearly answered secondly and you can't just if you do these splits then you're increasing through the split it's either slit you're increasing the number of states suddenly you're increasing the size of the space that describes a quantum system and that doesn't seem satisfactory either and but the problem I have is is that this was originally introduced or people like to think about it because they're uncomfortable with the idea of collapse of the wavefunction the idea when you open the box the cat is out of dead or alive and not this mixture but we actually understand why that is now it's to do with a process called decoherence where they the large environment outside of the box starts to mix up with the cat in such a way that the overlap region between cat dead and cat alive because of the large environmental system outside just get made very small so if we're okay with wavefunction collapse because we understand it through this decoherence I don't think that we need a what's wrong with the idea that the nature is probabilistic why do we have to have that every possibility is realized it's a quantum mechanics is probabilistic that's the way nature make sure what is and just because and you know our classical sort of intuition tells us that and you know we enjoy a deterministic existence that doesn't mean quantum mechanics has to behave light doesn't mean nature's behavior I just means that day to day that's how it seems to behave but truly it's probabilistic and that's fine ok doesn't mean every possibility has to be realized so that's level three so the last of these is the level four and this is the last one true the last one there is no level five so the idea of a level four this is very much tegmark thing and very much controversial so the idea of a level four multiverse is the following we look at our universe we look at of physical existence and we say it's described by a mathematical structure that seems reasonable that I can build build up general relativity from the rules of mathematics and they can and they can describe the universe that I see for example or I can build a standard model from both math m and I have this mathematical structure which is the standard model plus general activity plus all these things that describes the universe I see and then you say okay but there are other mathematical structures then fact there are many more mathematical structures that you can think of there's math the Wiis is just that we use to describe you know the standard model of generality it's just one corner of the possible huge realm of mathematical structures that you could imagine you're saying if I just gave you a blank piece of paper and said can Tonys make up some new mathematics exactly and this this is known as the subject of formal systems that this it actually exists you know you just need certain operations you know does your mathematical structure include multiplication for example it doesn't have to ours does that we use to describe the universe that we see but in principle you could imagine a mathematical structure that doesn't have multiplication in it that's just as good as any other okay so so there are other mathematical structures and then you have to ask the question well which ones correspond to physical reality is it just the one that we speak of or is it all of them or is it none of them well clearly not none of them but you know it's like so what so mark says he says well I can't really answer that question unless I have mathematical democracy so he says I exploit this notion of mathematical democracy it says that all mathematical structures are physically real so all of them so they have a physical reality to them so this is the ultimate multiverse now that all mathematical structures not just general tivity not just string theory all these things but anything any kind of operation you can create in a formal system anything that constitutes a mathematical strut it is physically real okay and this is quite a dramatic thing and that's are you saying each one has its own universe it is physically real I mean the notion of a universe may not even exist in some of them but it's physically real so you see what I mean it says it's like it may not even contain gravity it may not even it's kind of hard for us to imagine what what they are because we're so used to thinking about that you know the one in which we're familiar with but you know anything that is basically it's saying that maths is reality hey now why is this why does tegmark like this well on one hand he likes it because it's kind of final in a sense that the set of all mathematical structures is itself a mathematical structure so it's the it's the end of the road it sort of completes itself and it also answers or appears to answer a question at wheel oppose which is why why of all the possible mathematics that we could have to describe the universe why this you know what's special about this one is there anything special about it and well it seems to answer that well no there's nothing special about it that all structures are real is this like the bubbles is this saying that next door to us is a bubble where multiplication and I have a store I mean I wouldn't say the bubbles nest because the notion of a bubble line I even exist with some mathematical structures so I mean it's it's so abstract it's kind of it is bordering on the well it is bordering on the absurd right but I mean let's think about it it even makes sense I mean on one level it's not clear that the set of my all mathematical structures is well defined so that's a problem there's also this is challenged by girdle's incompleteness theorem which says that there are some things which are which are true but but can't be proven to be true and you know is that if you have a universe where that's the case if we have a mathematical structure which is like that cannot properly describe a universe it there seems to be some sort of weakness there and in fact ten markers there lesson his statement to suggest that actually only girdled complete mathematical structures are physically real and but again I think it comes back to for me it comes back to the same debate that one would have with the with the level three multiverses just because and they can exist and just because you can still have mathematical democracy but why why do they have to exist can't we just have the exist with a certain probability can we just build that into it why is it and and maybe we could have some sort of measure amongst the the multiverse of possible mathematical structures and just say an odd happens to be the one that was picked out with a certain probability that's fine doesn't mean all the others have to actually physically exist so that's level four so I as I said I think level one pretty uncontroversial level two not too controversial and level three and four well make them what you will but you know it's sometimes just fun thinking about these things it's just such a nice idea it's almost like it's science fiction but serious science fiction because the game reality to me at least means that it has some testable consequences you know something for something to be real you have to be able to interact with it in some way

Channel: Sixty Symbols

Views: 398,034

Rating: 4.940506 out of 5

Keywords: sixtysymbols, Multiverse, Physics (Field Of Study)

Id: w3TDO1AA1Sw

Length: 17min 16sec (1036 seconds)

Published: Thu Feb 05 2015

Reddit Comments

[u/ijmacd]

I would like some suggestions for further reading on the topic. Recent work in this area. I found Tegmark's introduction where he himself acknowledges not all theory are completely sane.

Personally I think it'd be pretty neat to find the accelerated expansion of our universe from dark energy was actually another (possibly not limited to one) bubble universe expanding inside our universe, currently undetectable to us.

[u/BlazeOrangeDeer]

I find it odd that both of his objections to Many Worlds are actually answered by the same concept, and it's the one he mentions right away (decoherence). The splitting process is just entanglement between the system and its environment that reduces the overlap between them in the Hilbert space (he described this), and obviously the size of the state of the system doesn't increase because it's all happening in the same Hilbert space with the same time evolution rules. So maybe he just hasn't heard very much about Many Worlds and hasn't connected the dots.

[u/[deleted]]

in those kind of topics, people often mix up "theory" and "speculation".

[u/squamosal]

Where do these expanding corners of the universe expand into? Do they push what's around them? The actual physical objects can't get bigger or smaller so how does just one spot expand without affecting the rest of the universe (or at least the immediate surroundings)?

[u/aakksshhaayy]

I subscribe to the mathematical multiverse (type 4 in this video). Also, postulating the properties of the transition region between multiverse bubbles, talk about theoretical lol.