Where Did The Universe Come From? With Prof. Geraint F. Lewis

[Music] you have fallen into event horizon with john michael godier [Music] in today's episode john is joined by garange lewis born in old south wales grant lewis is a professor of astrophysics at the sydney institute for astronomy part of the university of sydney's school of physics his research focuses on the dark side of the universe the matter and energy that shapes our cosmos dr lewis is a teacher an author and science communicator as well as two books on cosmology he has published more than 400 papers in international referee journals dr lewis's new book co-authored with very chris is titled where did the universe come from and other cosmic questions our universe from the quantum to the cosmos event horizon and my channel are now available as a podcast on apple podcasts spotify and youtube memberships early ad free episodes bonus episodes and sleep focused content sign up now by clicking the links below to your platform of choice professor garrett lewis welcome to the program hello now professor you are from south wales the original and you have moved to new south wales in australia does this evoke thoughts of parallel universes in in your mind not the fact that i'm in new south wales because new south wales is actually very different old south wales i mean where i grew up in britain uh is uh definitely not as sunny as a lot rainier than here so it's it's it is a very different place and parallel universes in my mind though are something which i do think about a lot in terms of cosmology i think that these are possible things that are out there but like all good cosmological ideas this is somewhat in the realm of speculation and hard science at the moment do you think we'll ever be able to test these various ideas of parallel universes of which we have the idea of the many worlds interpretation of quantum mechanics but we also have this idea of multiverse so there are two different ways to have parallel universes do you think any of this is testable well well firstly i think there's more than just two ways of having parallel universes even with the multiverse idea there are different kinds of multiverse we have of course the potential that our universe itself a single universe is infinite in extent and there are chunks of universe out there that we may never have causal contact with where the laws of physics could be very different to the laws of physics here so that is one kind of multiverse but there is another kind of multiverse above that where there's not just our universes but there's other universes out there that might even have a similar structure now the question of whether this is testable is an interesting one because the problem we have is that we can naively imagine this picture of parallel universes and we can say oh that we're causally disconnected so therefore they're always beyond the reach of experimentation but until a multiverse idea becomes a scientific theory in the sense that there is a strong mathematical basis that no i mean that's what a physicist needs to interrogate an idea is the mathematics of the situation we just don't know we just do not know what the influence of one universe on another universe might be we i said we have we have this picture that they could be causally disconnected but there could be ways that universes do interact and there have been speculations claims that our cosmic microwave background may have a bit of a pattern in it which indicates that our universe was born in a collision with another universe sometime in the past i mean i think these are these are not very well supported ideas but people are thinking about could other universes influence this universe but until we have a i said a robust mathematical theory it's it's speculation more than anything so we don't know now in regards to the anthropic principle of which you have worked with the anthropic principle sort of almost implies a multiverse because if this universe is moderately fine-tuned for life it can happen although there are some that have worked out that it could be better but if this universe is fine-tuned for life then we simply won the lottery and we're in the right universe with the right laws of physics to support life and intelligence but that would imply there are many universes that are not and we just simply won the lottery so if there's only one universe it looks really strange but if there are many not so strange right yeah so so as you said this is something that i've i thought about quite a bit and i wrote a book on this this very topic uh this notion that our universe can host life and of course we we should expect ourselves to to find ourselves in such a universe the question in my mind is not really about life though this is because this is where the argument sometimes goes off the rails when people take the anthropic principle to mean people for me the question is complexity right the universe hosting complexity so in our universe right we have 92 natural elements and we can use those uh to build molecules and molecules have different shapes and structures and we are basically molecular machines where molecules interact in and the question is where does that complexity come from okay so why do we have a periodic table with 92 natural elements in there you can you can work out that that the existence of the periodic table is a something that's implied by the relative strengths of the fundamental forces right to to have an atom you've got to have a nucleus which is held together and that nucleus has a strong force which is pulling together an electromagnetism which is forcing it apart and you've got to have electromagnetism to hold the electrons in place and you've also got the weak force which causes you know aspects of radioactive decays so to have a stable long-lived periodic table is a balance between those forces and if you start to mess around with those forces then you find that you can rapidly wipe out that complexity so if you have a universe where molecules can't form say we only add helium in the universe helium is a an element that just doesn't form molecules because it's just no very stable atom then there's no prospect for complexity and then there's no prospect for life right so so it's a question of complexity and as you mentioned when we look at the laws of physics it's very easy to think of ways of building a universe without the required complexity for life and the question is why why would we find ourselves in a universe that has allowed this complexity to be here and you can either just sort of go shrug my shoulders and say that's just the way it is but personally i find that as a you know particularly unsatisfying kind of answer and so you you have to delve into the possibilities and the one of the possibilities and in my mind the the most scientific of the possibilities is this notion that our universe is not the only universe in the sense that our universe is generated by some mechanism that generates universes and each universe gets stamped by with its laws of physics as it's created and we were the ones as you said won the lottery we got the mix of physics that allows us to be here but that as also implied that means that there must be many many other universes that have been created which are basically dead and sterile and so you know this is a hard question to answer about you know what fraction of universes can host complexity but looking at the laws of physics it would seem that we would be exceedingly rare in that ensemble of possible universes to have universes that have complexity in life so yeah what we do with that information now is i i think is it is a is an interesting one some people don't even like to think of this notion of the multiverse because they said they have this idea in their mind that it's untestable therefore you know it's just speculation but you know what we're trying to do is develop theories which are multiverse theories that we want to be able to test down the line somewhere and these theories have to produce universes like our own and and once we have those theories we will sort of know how rare or common complexity and life would be across the the multiverse at the moment we don't really know we think it's exceedingly rare another question which happens to be the title of your new book where did the universe come from and other cosmic questions are universe from the quantum to the cosmos now that's a heck of a question where did the universe come from and do we ever have any hope of understanding what generated the big bang and our universe as we know it well my hope is that we we will we will understand this one day i mean we know why we don't know i mean this is the this is the important part we know where we fall over and this is one of the reasons that we wrote the book in the first place is that modern science or modern physics i should say is built on two pillars right on one hand we have general relativity einstein's vision of gravity and it is a classical theory in the sense that it describes space-time as this continuous thing which can be warped and bent and you get gravity gravity and it it works exceedingly well right relativity is a theory that's been tested to the nth degree on the flip side we have quantum mechanics from quantum mechanics of course you know everybody talks about the weirdness of quantum mechanics but again as a mathematical theory it is highly successful right it makes predictions that those predictions are borne out and written in into our quantum theories these days are the other three fundamental forces electromagnetism weak force and strong force but they are quantum forces and say they are written in the language of probability and particle exchange all this kind of stuff and we therefore have these two highly successful theories gravity quantum mechanics and they are just different mathematics okay so you know you've got classical sort of maths over here of fields etc and on the other side you've got the quantum maths and probability and that kind of stuff and what we don't know is how we get those two forces to uh two theories to play together nicely it's where we think gravity and the other forces are essentially vying for dominance are the interesting places where we have questions yet to answer so that you know for a cosmologist there is that question about where did the universe come from and we know that as we run the clock backwards the universe gets hotter and hotter and denser and denser we see that in the very very early universe you have gravity and you have the other forces and they are they are essentially fighting for dominance in the early universe and we don't have the mathematics to explain exactly how the universe behaves in that kind of situation what we're looking for you know and this has been a search for uh you know as long as i can remember uh you know this this either the quantum theory of gravity or this theory of everything grand unified theory we can write everything in a single mathematical framework because without that maths that then all we can sort of do is guess right we can sort of say right i'm going to take this theory and i'm going to take this data i'm going to sort of stick them together it kind of works but i don't know if i really trust it but my hope is is that once that nut is cracked once somebody somewhere sorts out how you make the four fundamental forces work within a single mathematical framework then that door which is preventing a scene where the universe came from will be opened we will understand and i'm not saying that we will understand everything but we will understand a lot more about the the very birth of our universe and what came before right was it truly the birth of a universe from nothing which you know lawrence krauss has written about or is it that our universe branched off from some other space-time structure that occurred before us so i i do hope that we can work that out one day but you know we are still facing the challenge that we've been facing for 50 60 70 years on how you can unify gravity with the other forces this also holds something that is pretty exciting because and and you'll you'll as a physicist you'll you'll appreciate this this tells us that there exists new physics that we really just don't know yet there is a missing puzzle piece that every time we find new physics and this happened with both quantum theory and relativity it makes all sorts of predictions and things that you know we you know wormholes and you know quantum non-locality and all these all these weird aspects of the universe and there could be examples of that within this hidden physics that we have no idea what it what what's going to come out of it right if we do figure it out absolutely i mean i think this is one of the the areas of science that that doesn't get portrayed to the public well enough is that physicists want to throw their textbooks in the bin right i mean physicists love it when you can either unify previous ideas into a single idea or you could open up a new avenue in terms of direction to go with with regards to physics because it just means that there are so many more problems that we can we can solve so this is you know this is one of these great hopes for searching for the the theory of everything grand unified theories etc is that there will be just so many more things that physics will be able to encompass and there'll be so many more things we'll be able to understand and where we're at at the moment is that we are in a very frustrating situation in the sense that i said we have these two pillars and they both work exceedingly well right so you know on the quantum mechanical side we're talking about predictions being born out for like 11 decimal places right it works in cosmology we have a very similar kind of problem in that the the cosmological equations that come out of einstein's general theory of relativity they work they explain expanding universes it's incredible how well they work they also explain you know gps and and for me you know the the discovery back in that is it 2016 i think it must be now or maybe a little bit earlier no the first gravitational waves right that you know predictions that were made essentially a century before all born out and the stuff that relatively predicts we see the stuff that quantum mechanics predict we see and we just know that these two theories are not the final answer they cannot be complete because they just sort of avoid each other and so um physicists are desperate for clues to which direction to go in right because if you can imagine i've got my my mathematics for either quantum mechanics or relativity and i'm saying right this is not the complete story there must be some way to either extend these ideas such that they'll come together one one day right but if i give you some mathematics there's a there's an infinite number of ways you can expand that mathematics right if it's just a an addition you can just add more terms you can multiply or you can add more dimensions to your problem and all this kind of stuff so people are trying all these different mathematical extensions to these theories and seeing what the predictions are but what you really need for your scientific theory of course is right i've now got my my extended version of the mathematics how can i tell if i'm on the right path and you tell if you're on the right path by comparing your predictions to what's observed and what we're finding is that again you know it's just the bare old relativity and quantum mechanics works this is why people get very excited every time there's you know the the buzzword right anomaly when something looks like it might not quite fit with the standard model of particle physics or with with the gravitational wave signatures the physicists get very very excited is this is this the direction of course as you said the catch cry is is new physics is this the direction we should be going in and you know as of yet most anomalies sort of die away when we get more more data but it's it's it's our big hope in that we can that something won't fit and we will get an idea of the direction in which to go and of course we we have many things we want to explain birth of the universe center of black holes but there are other things which in our cosmological model the equations work that's great but why does the universe have so much dark matter in it particle physics doesn't tell us and what the heck is dark energy right i mean the equations work but where do these things fit into our fundamental theories and that's one of the things we would hope that theories of everything could tell us now this evokes history the history of science because we once relied entirely upon newtonian mechanics you know the physics of isaac newton but over the course of that people started noticing little discrepancies and things were a little bit off even though to this day we still use newtonian mechanics to launch rockets and do all this stuff but it was incomplete as you said and that led to general relativity which i mean that's one way to say okay we have an incomplete theory it's mostly right but there's little discrepancies but within those discrepancies was general relativity and out pops this gigantic predictive theory that keeps turning out right correct over and over and over and the discrepancy with quantum mechanics where general relativity sort of breaks down the world of the small now if you had to characterize these two theories which is the stronger one is quantum mechanics stronger or is general relativity stronger it depends what you mean by stronger here right because there are realms where these theories dominate right in that no matter what i do with general relativity it's not going to tell me how one electron talks to another electron right so you know so quantum mechanics electrons talking to each other that's what we use but quantum theory can't tell me anything about the expansion of the universe right so it can't tell me how the universe is expanding it can't tell me how gravitational fields are working so there are regimes where we apply these theories and so in those regimes they are the dominant theory right when i in my everyday cosmology when i want to talk about the expanded universe i don't really worry that much about quantum mechanics unless i want to add it on as an extra process say i'm looking at nuclear synthesis the formation of the elements so then i've got my quantum mechanics doing all the particle stuff in a background of the expanding universe so i can make those two sort of work together but they are are different regimes the the i mean i guess the you could ask the question of in terms of strongest which one is do i think is the direction that we should be going i.e should quantum mechanics look more like relativity or should relativity look more like quantum mechanics and there's a lot of people that think that what we need to do is quantize gravity i we have to bring gravity in to the language of quantum mechanics so you know this is various quantum theories that people are trying string theory is is again one of those ones where you want to try and quantize everything but not everybody agrees that that's the right route okay it there are some that think that maybe it's quantum mechanics is it's peculiar in certain ways but it's but the it may be the mathematics that we have written quantum mechanics in is is some sort of approximation of some other kind of mathematics which matches more nicely with relativity and i said that at the moment i wouldn't want to put a bet in it which one is the more correct theory if i had to i would sort of suggest that maybe both need to be modified in that the mathematics is i would say somewhere in between but it's maybe some sort of mathematical structures we haven't even thought of yet that encapsulates both relativity and quantum mechanics but i don't think anybody really knows now one of the major developments within physics developing as we speak is the possibility of a fifth force of nature which is extraordinary now the existence of a fifth force should it be proven that there is one would that lead to insight or could that lead to insight on the nature of gravity and the discrepancies between the two theories possibly possibly so you remember so the the this fifth force idea as i said this has come from measurements of uh like the the muon gyromagnetic ratio and those kind of experiments so the question is if there is a fifth force right what does it look like now if i if i was sitting here and i put my quantum mechanics hat on right i would say well this fifth force i'm seeing it to do with muons which are like heavy electrons i could i can add that fifth force into my quantum mechanical description of forces right there is a particular language in which you write down the forces and at some level that language always looks the same so you can you can add any number of forces you wanted to by just adding the appropriate terms the question is though it does that fifth force agree with that mathematics right is it gonna just go you know toe the party line and look like all the other quantum forces which would suggest that it's got nothing to do with gravity or is there something peculiar about this force in that it won't obey the mathematics of quantum mechanics and suggests that it's related to something else going on in the universe at the moment the problem that we have of course is that the the fifth force at some level it's like a ghost force right what we're not seeing is the fifth force in action in the same way as you see electromagnetism and the strong force in the nuclear force we are seeing the influence of the struck of this new fifth force potentially on a measurement of the spin of of a particle which is to do with you know the background universe of which the particle finds itself so we we really need to firstly identify whether or not the fifth force exists and if it does exist exactly what is its mechanism what is the fifth force mediating what is what is it acting between what's its effect and only when we get to that point are we going to be able to then ask the bigger questions well does it fit neatly into the quantum mechanics bucket or is it telling us something else about the universe back to the beginnings of the universe when we look classically at forces they unify or we think they unify some of them certainly do and at very high energies we think they they all unify including gravity but is there a model where gravity is not forced per se rather it's something else and doesn't unify and that the reason that we're having trouble figuring gravity out is because it isn't a classical force it's something else now what are the theories regarding that this this notion of unification of the forces you're you're you're correct that we already know that the weak force and electromagnetism two sides of the same coin that unification has been shown and the strong force looks like it's it's playing ball as well gravity however the idea that gravity unifies with the other forces that's more of a wish than a an idea a theory or anything right because without that mathematical framework we just don't know what happens to gravity in the high energy energy regimes there is the possibility of course that we do live in a universe where gravity is just separate no matter how hard we try we are never going to come up with a quantum theory of gravity and so that unification picture you you're talking about it may be that gravity just stays over here and does what gravity does okay and as i said because there's this there is a worry with relativity as with with quantum mechanics right is that what we're looking at in terms of the mathematics is the approximation or the low energy version of some higher theory right so so that relativity would look different at higher energies which is kind of it's kind of harder to formulate that because energy and and relativity go together in a really strange kind of fashion it's it's not easy to talk about relativity in a high energy regime but there is this possibility that yeah the the mathematics when we if we can solve it if we did have an idea of how gravity behaved in the very early universe it might look quite different to the picture we have about curved space-time it might be something else to do with i mean their idea ideas that gravity has something to do with a force across multiple dimensions and all this kind of stuff we just don't really know i mean there are there are many many ideas but again we're in that state of you know you wouldn't be willing to bet your house on any particular one of them being correct maybe you bet your car but not your house i mean it's it's all a bit open now gravity being so mysterious is it possible that gravity is a phenomenon of another universe leaking into ours and that's why it's sitting apart this is this has been suggested right so as i mentioned people have talked about gravity acting across multiple dimensions so and some people have said right maybe what you've got is you've got gravity basically being shared between two universes and this is why it's overall a weak force because if you could look at it in the ensemble of universes it would be strong but it dilutes itself it's impossible right again it's impossible it and it you know it's one of those nice kind of speculative ideas and people have actually proposed tests of course what you want to ask is how does gravity behave on small scales where you know these dimensions might be very close to each other and people have asked the question about you know if i take neutrons and i drop them how do they accelerate under gravity and maybe you will see that there's deviations from what you'd expect from relativity on these very small scales the problem is of course is that you're you're trying to do an experiment on gravity in the realm where quantum mechanics dominates and what we know about you know at that small scale is that it's very hard to come up with an isolated scenario where you could consider things like neutrons dropping and measuring their acceleration due to gravity because everything then would be influenced in the neutron right there might be photons bouncing off it or it might be in a you know a magnetic field which is affecting its internal spins and all this kind of stuff so it's very very hard to do these experiments and but but people are trying yeah that's that's the real trick is experimentation and you know we have these ideas like string theory that might link the two disparate theories and the problem is is that good luck testing string theory you know this is where where we get into a problem because any theory we come up with linking the two may be completely untestable and all we will ever know is that it mathematically predicts correct right yes well i'll give you a slight personal story here um i i started my undergraduate degree in 1987 at the university of london and one of my tutors there was michael green who is considered one of the the fathers of of string theory we were told that you know any minute now any minute now string theory is going to solve it all any minute and here we are sitting you know what is it like 40 years or so later and we don't seem to have moved that far and as you said the real problem that we have well there's a couple of problems number one is that is that string theory itself has morphed right the mathematics of strings here is morphed and it's morphed into this thing called m theory and my understand is that nobody really knows what the m stands for but m theory is not a single theory m theory is a collection of mathematical extensions that people are trying to bring together to come up with an overall overarching theorem and as and the real problem is is that the the places where you would get predictions that would tell you whether or not string theory slash m theory are correct i just beyond our sort of um experiments here on earth right the energies involved for uh string theory and m theory to reveal themselves much greater than the energies that we can produce but this is why you know this notion of particle cosmology particle astrophysics etc has gained a lot of traction because people have realized that you know the greatest particle accelerators the places where energies are the greatest are out there in the universe especially in the early universe and so people are asking the question of well maybe is the signature of m3 written into the big bang and then what would that mean for observations as of yet of course there's been no no clean signal that anybody could point to and say look this proves that m theory is correct but people are still trying to search for potential observational evidence but i'd say we might just have to say that this is always going to be beyond our experiments speaking of the beyond our experiments maybe the big bang itself is a kind of experiment in the framework of brain theory now what are your thoughts of this idea of colliding membranes other universes colliding and causing big bangs again i i think it's it's an interesting kind of question the entire picture again you you rapidly step from robust theory into speculation right when you talk about these other universes being out there and colliding but it's it's not completely off the books right it it it fits into this notion that maybe our true multiverse or whatever you want to call it uber universe is many dimensions maybe it's 11 or 23 or whatever the number is in a particular theory and that would mean that our uni our universe would be effectively a sheet in there and why not more right and then you can come up with pictures about what happens when these these sheets collide and you know you get the creation of potentially the creation of new universes but you know it's it you always have to be very careful of just you you have to remember that this is still more speculation than robust theory it has as i mentioned earlier on people have suggested that there are patterns in the cosmic microwave background that might indicate such collisions with other universes but you know the statistical significance of these patterns you know most people sort of go no you know you're doing the usual thing that humans do you're seeing patterns in the noise um and so yeah it none of it jumps out as being look this says that there are other universes floating around in a multi-dimensional brain out there but it's impossible it does have something going for it in that it there is a sort of elegant simplicity to the idea that the multiverse is basically a bunch of parallel clothes lines with sheets pinned to them that occasionally in the wind hit each other now where does time come into this because time is a property of this universe it begins at the begin the big bang and we see you know time integra you know it's in integral to space so much so einstein when the term space time can there be an analog of time in the multiverse absolutely i mean the question of where did time begin right so i i'm going to take one slight step sideways here physicists don't like talking about time most of the most of the time they leave it to the philosophers to argue about the what is time but you know physicists have come up with ideas about is time you know as you said did time begin at the birth of the universe or is is time emergent in that is it is it time constantly being produced and then the question of whether or not there is time across the larger space-time structure and i'm going to put spacetime in quotes there because um you know it might not look like what we call time in the in the overall picture again it's a possible we we could imagine that there is something like what we would call time across the multiverse but the weird thing is is that when you when you come down to it and you even look at time in our universe it really starts to hurt your head quite a bit right because let's just say that einstein was correct right and uh that the universe can be described purely in terms of general relativity and you immediately hit this problem which is which is called the block universe is that that in relativity the future exists as much as the past exists right it's a it's already there it's a full four-dimensional structure and all we are doing is we're winding our way through this block universe in the same ways that a map is already drawn and you can just do your path across the map etc so in einstein's picture of the universe you already run into problems that people you know really keep people up at night is that you lose the notion of free will right if the future is already written then and we're just you know falling apart threat so where does free will come into any of this which is why then people say well well we need to bring in the quantum mechanical nature of time and we have this this notion that um you know carlo revelli is written about this time being these like little little seeds and grains that continuously pop up and the universe sort of builds itself into the future but again i i'm i actually think most physicists are not comfortable with most of these ideas that you know i you know if you sat down a room full of physicists and asked does the future already exist at some sense they wouldn't really know how to vote so understanding time in this universe is difficult enough understanding time across the multiverse is going to be even more complicated and in fact there's there was a nice bit of work by uh max tegmark it must be pushing more than 20 years ago now because we can write down our equations of relativity right easily enough you can write in multiple dimensions of time we know how to do that and it becomes a very very complicated universe if you could imagine that you've got a universe where there are two time dimensions then you can you can play all sorts of tricks right you can hide in one time dimension and do stuff like before going over to the other time dimension then and what actually happens is the entire notion of physics as being a predictive topic that's something that you can make predictions goes out the window it only really works when we have one dimension of time and so we're they're now left here sitting well why is there one dimension of time why was that written into the universe not two or none and that comes back that entire fine-tuning question that we we almost started with a while ago so if we entertain ideas like gravity being a force that leaks into this this universe from another could time be in the same boat in in that time leaks into our universe from the multiverse and does that give us an insight on why the arrow of time is pointing the direction it is because it could point backwards you know things could go either way so would this would this provide some sort of moderating force to explain the arrow of time question oh again you know where this is this is something that keeps the philosophers in in employment for a long long long periods of time possibly right again it it is one of those ideas but you you then still have to ask yourself what is time in our universe right in the relativistic picture time is already there it exists past present and future is already there it doesn't leak in from anywhere else so you'd need to think about how does that time sort of flow in and build the universe and again maybe that's sort of related to the pictures like uh ravelli have put forward about you know this constant build-up of the universe the entire question of the arrow of time though is is is an immense and actually worrying question right because uh we we definitely we know that our laws of physics in general are time symmetric they work equally backwards and forwards yet we experience time in a certain direction right time always points towards the future what whatever points towards the future mean but we know that means things decay things get older etc we never see it in reverse and we have this entire topic of of thermodynamics and entropy which sort of talks about you know this increasing disorder to the universe but nobody knows why time points in the direction it does for us and and just to to clarify what i mean by that right so let's just take einstein's picture again of the universe okay and i said that you know we are making our way through the university et cetera and we we're following what's known as our world line and we go from the past to the future why do we travel that way it's because i wrote down in my mathematical equations that i'm going to start traveling this way and i'm going to go and travel into the future there is nothing to stop me making a mathematical choice which is completely valid that i start in the future and i make my way towards the past right and in that that if i was doing that i would basically see the universe running backwards so so the question that we sort of have is is what why then are all our paths started in the past and heading towards the future why why haven't we got future people objects moving towards the past and this is a question that's really bothered a lot of physicists and philosophers and i think the the sort of hand-wavy general kind of solution is that our universe unlike the laws of physics our universe is not symmetric in time right in the sense that it has a start point the big bang and there may have been stuff before there but we won't worry about that but there's a start point and the universe has been expanded and into the future it's going to continue expanding and continue expanding there is not going to be an end like there was a start and that asymmetry in the overall history of the universe is the thing that wrote the arrow of time into the universe now what that means again there's lots of argument about why the why the universe was born in a in a low entropy state right so to just just to clarify right if our universe had been born instead of there being atoms of hydrogen and helium it had been born and it just created huge black holes everywhere so no normal matter but just black holes that would mean that our universe was born in what's known as a high entropy or highly disordered state there would not be no useful energy to do anything right so you couldn't have life in those kinds of universes our universe was born in a state where matter was simple right so if you start off with simple matter you can make more complicated matter and that's what stars do so you can produce energy and it started off with mata being smoothly distributed right so that meant things could collapse so you could release gravitational energy but why was the universe born in that state of of low entropy right why was it born in that special configuration and people like roger penrose have tried to calculate the the chances that the universe was born in this kind of state by accident you get numbers like 10 to the power of 10 to the power of i don't know there's some huge factor it doesn't really matter when you get to those kind of numbers chance that that that was just a like a random state that the universe found itself in so again look for me a lot of these questions come back to this fine-tuning issue about that the initial conditions of our universe meant that it was low entropy it meant it had the potential to go and do stuff and that somehow is related to the arrow of time but exactly what this means in terms of other universes and how time behaves and if time flows between universes i i think it's that's a question that we are nowhere near answering at the moment but there was seemingly at the very moment of the big bang there was something was not quite uniform meaning that when you look at the cosmic microwave background radiation you see variations in temperature very tiny ones and had those not been there the universe could have been entirely homogeneous basically atoms spaced equally from each other and nothing ever clumps so there was a slight tune there that not not not even getting into life but matter itself this could have been a universe of atoms forever oh yeah yet it wasn't so we're not just talking about the existence to hammer home your point here we're not just talking about life existing it's matter itself stars galaxies everything else the universe is fine-tuned for matter to exist right that's right so so the so those lumps in the cosmic microwave background they are thought to come from that this period at around 10 to the minus 35 seconds which is known as inflation right so this is the universe has this sort of like hiccup where it increases by like 80 orders of magnitude in size it takes a tiny fraction of a second and some sort of quantum pattern gets written into the universe right due to inflation you're right that that pattern if that pattern had come out and it was too smooth then mata would never collapsed into uh stars and galaxies so it would just be a wash with dilute gas throughout the universe but the flip side as well is that if that pattern had been stronger it's of order one part in 10 to the five if that pattern had been stronger then after the big bang you would have started off again with atoms but things would have collapsed very very quickly and you would have basically formed black holes so you would have rapidly gone from this situation where you have almost dilute material into black holes very very quickly so again we we seem to have come out with this this inhomogeneity in the early universe at a nice level for the creation of stars and galaxies and for there to at least be a span of the universe before mata gets turned into black holes where the universe can host complexity in life so again yeah i said uh i'm one of those that you know everywhere you look you start to see there are fine-tuning issues that that lead to complexity and life in the universe that we don't know the answer to right because if inflation had gone on for longer then you would have gotten a very different outcome and if it happened a lot shorter as well you'd have gotten a very different outcome to the one that we we actually have in our universe today so without the existence of a multiverse and that this is a true universe meaning it is all that is was and ever will be as the classical description of it goes in a one universe model the anthropic principle starts looking very spooky and to evoke the philosophers again the idea of it being a simulation do you think that has legs oh yeah yes look i'm i i i i'm gonna say i like and i'm going to put air quotes around the word like i like the notion of the simulation hypothesis right so this is this notion that we are actually a computer simulation one of one of the things i do in my day job with my students is that we generate synthetic universes right so we study the evolution of flow of matter in universes with computer simulations and this notion of the simulation hypothesis that as our computers get bigger and faster our simulations get better that you know what if our simulations get to the point where we can actually have consciousness within our simulations although exactly how we would know is is another question altogether so does sort of fit in the philosophical kind of picture that this universe could be a simulation now one of the things that i think is kind of interesting is is what what was the simulation being run for right so you know there are people that say oh the simulation hypothesis that's they're simulating us right we are in the matrix or whatever you want to put it but if you think about it it could be that the the great simulator in the universe above is just exploring different kinds of physics right so whatever the physics they've got in their universe they are saying right well what if i consider universities that have only three dimensions of space and one of time and they've looked through and they said oh well if i have this mix of physics and that mix of physics that's going to be a boring simulation why would i do that i'm going to simulate interesting universes where i can get complexity et cetera and maybe we are not the sort of central aspect of the simulation right we are a byproduct of the simulation that the great simulator in the sky doesn't care about us doesn't even know about us we are just part of the simulation and they are more interested in just looking at you know how many giant stars are there how many m dwarf stars or whatever their view is and so the the the motives behind the simulation and we of course may never imagine what the that mind may be like anyway it might have nothing to do with this which i i think is not the way a lot of people look at the simulation hypothesis and of course there's the prospect then as well as is if it is a simulation what if they get bored right you know and they've just flicked the switch then that's you know the end of the end of the the universe is because now they thought oh i've got enough for my homework assignment i i'm going to go off and do something else now now let's go forward trillions and trillions of years and i think the the the uh my favorite scenario that i've come up with just pondering the idea of simulated universes is the idea of a boltzmann brain you know in a an infinitely aging universe that's gone black but all of a sudden just out of out of the ether comes this thinking something you know maybe a quantum supercomputer existing just briefly and it looks around at that black universe that dead universe and it asks itself what was this once like so it sparks off a simulation and you know you could never you could never prove anything like that but it's a fun science fiction scenario but going into the very very far future do you think that we just live in an infinite universe that's just gonna age forever in blackness eventually cold and blackness or do you favor any of the theories like the big rip or big freeze or anything like that what do you think will end this okay so if we take our cosmological picture as we understand it right which is currently 70 dark energy 30 mata of which dark matter is the big dominant component and we can run our universe into the future we we know essentially what's going to happen based upon the laws of physics as we understand them right so we know that stars are going to shine for roughly uh 100 trillion years okay and that's when eventually the stars will go out then after that things become slightly more speculative because you've got this entire question about proton stable and if you have proton decay then around 10 to the 40 years that's when mata sort of melts away and then if hawking was right about hawking radiation about 10 to the 100 years that's when black holes were finally evaporated you're left with that infinite universe which is filled with nothing but electrons positrons and photons but it's diluting and deleting and diluting so in terms of the universe as we understand it that it's heading for that that that heat death as it's called right the the ultimate high entropy version of the universe no potential to do anything whatsoever but there are some big caveats in that right now so number one is is that dark energy right has particular properties to it we know that it's causing the expansion of the universe to accelerate and that's because there's a particular you know it's we call it the equation of state it's it's energy density versus its sort of tension now what if on the huge time scales of the universe that the dark energy changes its spots in the sense that you know given uncountable number of years into the future dark energy stops being what it is now and transforms into something else now again i can write down the equations for that but i don't know if they apply to dark energy that we have in our universe but it's a possible thing there are there are other and if that happens then you could get as you said a big rip scenario but that would just basically end the universe and it would just eventually become a dead heat-death universe sooner if you have a big rip i think that one of the more interesting things though is dark energy is a is a certain amount of energy for every cubic meter and it's an energy field in the universe right so we know it's there and some people have speculated maybe again on immense time scales right remember it's a field in the universe it's governed by the laws of quantum mechanics and quantum mechanics allows energy levels to spontaneously change from one to another through through quantum tunneling right that allows you to go from one state to another and there is the potential that dark energy could do this again on an immense time scale 10 to the 10 to the whatever number of years the dark energy could undergo a transition and go from one energy state to another and if it does that then that would mean that that that transition could kick off effectively another version of the inflation that we had in our early universe so you could get this bout of energy being released rapid expansion then that energy being released back into the universe and it's no longer in the form of dark energy anymore that energy gets transformed through a process in our universe called reheating into matter and radiation so you you could imagine that um in the far future of the universe instead of the universe just cooling to infinity that there's this transition a burst of inflation and the universe or universes are born again right there's new universes that are formed out of this transition of energy and that you know who knows exactly what will be in them whether it be matter and radiation like in ours etc and there are some that have speculated that that may be where our universe came from right that the universe has already been through this cycle of birth almost eternal life to some sort of heat death and then rebirth again and off you go so again it's it's impossible and i like i like to try and be an optimist in the in the sense that you know you wouldn't want to think that the ultimate future is just a cold and dead universe and that there is a prospect whereby there will be this cosmic rebirth some point in the future all right doctor it's been a fascinating discussion and we are out of time but oh uh your new book where did the universe come from where can everybody get that from your online bookstores that it is available more or less everywhere i believe as well in in the us uh there's copies in every in the uh what's in what's the name of your big bookstore there i've forgotten the name oh that we still have them yeah yeah yeah yeah i think there's uh barnes and noble i think is it barnes and noble that's the word i was looking for yes i believe that they they actually are going to have physical copies uh uh there as well right doctor thanks for joining us and i hope we can do this again sometime thank you for having me and would love to come back on the show [Music] thanks for listening i am futurist and science fiction author wrong channel no it's not thanks for listening i am futurist and science fiction author john michael gautier currently hosting event horizon and wondering where anna actually came from one day i had a tablet computer the next i had a boss very disturbing and be sure and that's enough of that youtuber forever like subscribe and hit the bell sell out what [Music] [Applause] [Music] you

Channel: Event Horizon

Views: 177,757

Keywords: event horizon, john michael godier, event horizon john michael godier, universe, multiverse, where did our universe come from?, a universe before ours?, geraint lewis, astrophysics, astronomy, quantum, cosmology

Id: 5BnljyQ1sak

Length: 58min 4sec (3484 seconds)

Published: Thu Dec 09 2021