Martin Rees - How Many Universes Exist?

Barton throughout my life as I've wondered about existence I've always been fascinated with cosmology and astronomy and just when I thought I was sort of getting my arms around it suddenly we now have multiple universes which just takes your breath away in terms of what the potential is I can't think of a better way to really understand what it's all about than to discuss it is this just fiction or could there really be multiple universes well it's speculation but I would say it's speculative science and not just metaphysics and I think we may be in for a conceptual leap rather like early leaps in the past because we've gone over history from a view of the geocentric universe politican universe the idea that we have a Milky Way galaxy and then the idea since the 1920s in that galaxy is one of billions but we may be led to the idea there's far more to physical reality than the vast domain that we can see through our telescopes we can see through our telescopes a region extending at least ten billion light-years away from us the expanding universe which started in the so-called Big Bang but we have every reason to expect that there's a lot of space and time beyond the horizon and our observations there's a limit to how far we can see with our telescope set by essentially how far light's been able to get since the Big Bang and there's every reason to expect that there are many many galaxies beyond that that we never see and it's rather like if you imagine being in the middle of an ocean on the ship you climb up the mast you see a horizon around you but there's no reason to think that the ocean ends just beyond your horizon and if you climb up the mast a bit higher you can see a bit more but the question is what lies beyond is it just more more the same are you on an infinite ocean or is there something very different far beyond I think most of us would say that it's very likely that the universe in the form that we see within the domain of our telescopes extends thousands of times further we'd be surprised if it didn't extend the reason for that is that if we look as far as we can in that direction of thousand the other direction we see no difference with a precision of one part in 100,000 so the gradient across that domain is so tiny it would be amazing if the universe didn't extend thousands of times beyond what we can see but maybe goes much further still in fact you could imagine it going on infinitely if that were the case then we have the fascinating possibility that there may be somewhere a universe exactly resembling ours a galaxy exactly resembling ours and there could be an earth with replicas of us because all combinatorial options will be repeated if you have enough space and enough time and so it could be that our domain of space and time the aftermath of our Big Bang is vast enough to encompass every possible option got to be fascinating but even that is not all because I've talked so far about just the aftermath of our Big Bang some people think that our Big Bang is just one of many and that there could be other big bangs which would be in Kapiti disjoint regions of space and time maybe even embedded in some higher dimension and they could lead to different cosmoses a lot of ideas on this one is an idea called eternal inflation that this is sort of substratum it's expanding exponentially and big bangs pop off in it another idea is that there may be different domains of space and time embedded in some higher dimension just as we can imagine two two-dimensional surfaces each with an scurrying around on them and one is not aware of the other so there could be another universe just a millimeter away from ours but we're not aware of it because that millimeter is meshed in some fourth spatial dimension and we imprisoned in r3 so there could be other domains of space and time the other question is if there are these other domains are they like ours are they governed by the same physics do they contain the same sort of atoms are they governed by the same force of gravity etc and again that's another separate question and that's a very important question the fascinating option is that there are these other universes and they're governed by different physical laws space may be different gravity may be different atoms may be different and so we would then have all these universes government laws and only some tiny subset of them would be governed by laws that allowed complexity to evolve most would be sort of sterile because gravity was too strong to allow complex structures because hoffman's weren't stable over some other reason so there are two fundamental questions which were among the greatest challenges I think the 21st century science the first is was our Big Bang the only one we don't know the answer to that and the second is if there were many big bangs were they all replicas of each other or did they end up governed by different laws the most fascinating option of course is the idea of many big bangs displaying an immense variety of physical laws because then science fiction is the only limit to what might happen and we can regard our universe as being in some sense selected as the one in which complexity could evolve but those two challenges I think are among the greatest for science in the 21st century and maybe far beyond because it may be that they involve physics which is beyond what we can grasp even in the 21st century is there any hope of getting experimental data to support theory for either one multiple Big Bang's or what the laws might be if there were I think there is because there are lots of fundamental physical experiments which we can do which may give clues to what the fundamental laws are and so if we had a theory which explained things in our present-day universe to be can observe like why the three kinds of neutrinos why protons and electrons exist etc then that too would have gained credibility and we would then take seriously its implications for cosmology and if that theory says something about the Big Bang and if so many big bangs then we take it seriously to give an example we believe that we can talk about the first few seconds of the Big Bang when hydrogen helium were made because the laws of nuclear physics that apply then can be tested here on earth simply we believe we can understand what happens inside the Sun that we can't go there because we could test the laws on earth and so it could be that we'll be able to corroborate the theories there's relevant to the Big Bang in other ways and the other possibility is we may have a theory which makes some predictions about our Big Bang and that's refuted and so we have ways of refuting ideas of the multiverse if they make predictions about this particular manifestation of it that we live in and so for that reason I would regard this subject as part of science in that it is potentially testable it links into laboratory physics even and it's potentially falsifiable so it's not purely metaphysics although the clay does have metaphysical implications it is just so astonishing I mean can one conceive of even nesting these multiple universes so if there were universes and extra dimensions those universes can generate their own chaotic inflation or their own activity so you have a nesting of of infinities of universes I mean if it seems so incredible well people have speculated about that ideas and it could be that's the way it'll work out because one particular option is that there could be all kinds of possibilities for the physical laws and for the nature of space and the physical reality as a whole could be just as complicated any biological structure biological organism we just as much varieties that's one possibility some physicists don't like that they'd like to think that the laws of nature are clear-cut and we can understand them but it may be that the underlying laws which govern the whole of physical reality are very complicated and what we observed within our astronomical universe is just some tiny special case of this immense variety and in that context what we call the laws of nature would just be local bylaws in our cosmic patch as it were they apply in the reason we can observe which is a vast region extending ten billion light years away but still in this enlarged perspective if you've made this extra Copernican leap from a university or multiverse then these will just be bylaws and there may indeed be some underlying laws but they be still more general and it's up an entire new concept because we're used to the idea of realizing that what we thought was something special is just an example Kepler thought our solar system was something very special look for exact laws where we now know that is just one of many planetary systems we don't look for special laws governing our solar system and likewise we may have a deeper level of laws which apply more broadly than what we've traditionally called our universe I find that absolutely astonishing that if we have multiple universes each with its own set of laws similar to ours that they would all be different in all jaring really almost all possibilities which would would come out of that well is it certainly conceivable and indeed there are some theorists with a straight face talk about mortals like that but to achieve that if we have multiple universes all generating different laws there has to be at some deeper level some series of laws or law at the multi-universe level in order to generate all the multiple universes that have different laws does that make sense Oh indeed there would be us at the fundamental law but what we have thought to be valid our laws are just just sort of secondary parochial questions it was specific expressions of some general law so there would have to be a universe generating law that generates different universes with different laws but they'd have to be a some sort of a general universe generating law indeed and if we had that fundamental law it would tell us what variety was possible in the local bylaws what numbers the dimensions were possible etc and what range of possible laws governing atomic physics etc and we don't know and the question is how far we will get in meeting that challenge in this century but that's one of the fundamental questions what is your instinctive feeling well I feel the only appropriate stance is agnosticism because we just don't know but I would say that there are some physicists who I believe conflate what they would like to be the case with what actually is likely to be they can easy to do indeed and many people would like to be able to write on their t-shirt the equations that determine exactly the laws of physics that we observe here on earth that's a worthy goal it's wonderful people are searching for this but they may fail it could be that the laws as we understand them traditionally are just these local environmental accidents of the aftermath of our particular Big Bang and that there are laws at a much deeper level I find that a rather grand and fascinating concept even though it means we are further from being able to grasp the final laws but as to which way to pan out then I think we have to ask these two questions first is our Big Bang the only one and secondly if there are many big bangs are they all governed by the same laws or do they display events variety

Channel: Closer To Truth

Views: 38,877

Rating: 4.9024391 out of 5

Keywords: Martin Rees, Closer To Truth, physics, universe, multiverse, General Relativity

Id: 47YBtGC1Omg

Length: 13min 6sec (786 seconds)

Published: Wed Dec 23 2015