Evidence for Parallel Universes – Max Tegmark

In recent years we humans have figured out a great deal about our universe but that begs another question which is very interesting and very controversial could there also be other universes and do we have any evidence for this before we talk about other universes parallel universes let’s remind ourselves what we mean by our universe first our universe is does not mean everything that exists it simply means the part of space from which light has had time to reach us so far during the billion years since our Big Bang so this is our universe if space is bigger than that then there are other universes other regions of the same size farther away if you want to know what’s happening in the galaxies over here you have to wait billions of years more for light to reach us so we cannot see anything outside of our universe one of the reasons this is so controversial is because many people say oh this is just stupid philosophical nonsense you know we if we can never by definition see parallel universes then it must mean it’s not science it’s like talking about ghosts or something else that you know you can’t see but it’s actually more interesting in this because this parallel universes are not a theory they’re a prediction from certain theories which we can in turn test and various other ways so to explain what I mean by this let’s look at another theory first Einstein’s theory of gravity general relativity it predicts a whole bunch of stuff which we can test and observe like the motion of mercury around the Sun the bending of light by stars the time-dilation that you can measure with your GPS in your phone etc and because of this we take general relativity very seriously as a scientific theory which means we have to take seriously everything it predicts even things that it predicts that we cannot actually observe like what happens when you fall into a black hole Einstein’s theory of general to predict exactly what happens inside black holes but I cannot go observe it and then come and publish the results and a scientific journal here on earth it’s impossible right but if one of my colleagues says much so I don’t like I don’t like black holes you know they can’t just opt out of black holes it’s predicted by the theory if they want to get rid of the black holes they actually have to invent a different theory of gravity another mathematical theory that’s different from Einstein’s which doesn’t have black holes but which can explain everything else that Einstein did and that has proven very hard so hard that after a hundred years or so of trying many of the smartest people on the planet have failed to do that the point here is that for a theory to be scientific you don’t have to be able to observe everything it predicts you just have to be able to observe at least one thing that it predicts and if if that convinces you to believe in the theory you have to also take seriously their other stuff it says now what does this have to do with parallel universes well first of all we have a different theory the theory of inflation in cosmology it’s also a scientific theory it predicts a whole bunch of things we have tested and observed very carefully in the cosmic microwave background radiation and three-dimensional galaxy maps it’s right now the most popular theory in my field for what put the bang into our Big Bang it was pioneered by Alan Guth and Andrei Linde and others it’s a beautiful mathematical theory and it also predicts parallel universes in particularly predicted it predicts that space itself isn’t just really big but that the space is actually bigger than our universe maybe even infinitely big so the logic is that if inflation theory is correct and we take it seriously we have to take seriously the idea that space is bigger than our universe that there are parallel universes other regions of space that are just too far away from it for us to see I call these parallel universes the level one parallel universes because they’re not that different from our universe the only difference is that over there yep the particle started out in different places so the galaxies formed different ways and if there are people over there they will still learn the same things in physics class but they might learn different things in history class because King started out differently in history unfolded differently a fascinating thing about parallel universes is it the most interesting question now really to me isn’t whether there are any but how many different kinds there are this is the least controversial kind the first level then there’s level two and that’s something that you end up with if you combine the theory of inflation with one more idea if it turns out that string theory or loop quantum gravity or whatever the ultimate correct theory is going to be that unifies all the physics if it turns out that that theory has more than one solution with a homogeneous space in it kind of like the equations for water and I have three different solutions liquid water ice and steam then this theory of inflation actually will create not just a big space but it’ll create a big space with each of these solutions actually happening so the theory of inflation actually converts potentiality into reality it’ll make a universe with this kind of space with that kind of space with a third counter space some string theorists think that there is ten to the power five hundred different kinds of space even and what does it feel like to live in one of those parallel universes if they exist well more interesting and diverse than in the level one kind because they wouldn’t only learn different things in history class they would actually learn different things in physics class they might learn for example that there are not six kind of quarks which is what I learned in physics class but that there are ten kinds of quarks or two kinds of quarks many of the properties that we that we thought were fundamental properties of physics according to string theory are just telling you which particular solution of string theory you’re in do these exist we don’t know of course how can we test it well we by testing inflation more am i studying strength anymore to see if it seems to make any sense or not if it does make sense though it actually would help answer another big mystery we have in physics which is when you look around us in the world our universe has all these numbers bill into it we call constants of physics for example there’s a number that tells us that the men how much dark energy there is the value of the number is about 10 to the power minus 120 30.000 bla bla bla bla one with under 23 zeros and if you imagine that you could make your own universe you could have a little dial a little knob that could change each of these numbers that would recommend don’t touch those knobs because it turns out almost anything you change by a little bit will kill all life if you put in more dark energy than we have by a lot you destroy all the galaxies dark energy prevents them from forming for example if you change another number to do with the Higgs particle suddenly you can’t have any atoms and this is a deep mystery in physics why is it that our universe has these numbers which seem to be fine-tuned for life is this this luck there’s it some kind of miracle or or what well the level 2 parallel universe is actually give a scientific explanation for this Steven Weinberg made a famous argument many years ago where he said that suppose the level two multiverse exists and the amount of dark energy is different in different parts of space then you predict something like the Sahara Desert you know most of it is dead no life no galaxies but there will be still you know some places where just happened where the dark energy has exactly the right value to allow galaxies and that’s of course where we should expect to find ourselves if I if I would know that I’m a Bedouin and I live in the Sahara Desert I’m not going to be surprised to know that I live in an oasis that’s the only places there are people really living it and they paint this picture where the same thing is happening on a larger scale in our cosmos after this prediction was made dark energy was discovered with death and the Nobel Prize was given for it and this has made people take this idea quite a bit more seriously it’s still fair to say that it’s very controversial we’d no but it’s certainly a scientific question we can discuss whether a reality is this big we should also be mindful that we humans have again and again made this mistake of under estimating the size of our cosmos first we thought earth was the center of everything right then we discovered that our solar system existed only generally see in the universe so it might very well happen again there’s no guarantee in the laws of physics that we humans should be able to see everything that exists and if we cannot by definition there are parallel universes well and if there’s even more there’s a third kind of parallel universes which have become I’ve come into the scientific discussion from studying not the biggest things but from studying the smallest things by studying quantum mechanics the rules that govern how atoms and elementary particles behave this is arguably the most successful theory in all of science it’s given us transistors computers cell phones lasers etc but at the cost of some weird ideas the quantum mechanics tells us that little particles can be in several places at once if the particles can be in several places the ones well I’m made of these particles I should be able to be in several places at once as well and in 1957 a young graduate student named you Evert work this out really carefully and argue that what it really means is that there is a third kind of parallel universes where when you make certain decisions effectively our world splits into several parallel tracks if I get a parking ticket there is a parallel universe maybe where I didn’t but there’s another parallel universe maybe where my car was stolen instead so yeah wait time you lose some this sounds very philosophical but it’s the way this test this again is not by speculating but by studying quantum mechanics more and particularly we should try to build quantum computers which is a kind of machine which takes advantage of parallel computation and effectively using these parallel worlds if we try to build them and there are millions and millions of dollars spent right now to try to do so if it fails because we notice that the basic equation of quantum mechanics is wrong then we can figure about all these parallel universes but if they succeed and they can calculate something in five minutes that would take longer than the age of our universe to do what a normal computer I think that will make many scientists take these parallel universes more seriously you

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