Was the universe made for us? | Sabine Hossenfelder

when it comes to the constants of nature we don't have any probability distribution so if someone makes a statement like it seems to be very unlikely that the constants of nature would just have exactly the values that we do have that's a completely meaningless statement because we can't quantify this probability [Music] so we'll continue with the question was the universe made for us to which I think the answer is no for we currently know so first I think I have to put this question into a context physicists as I said we don't really like to talk about life and so on but in cosmology we often talk about the preconditions for life for example a carbon is often used as a precondition for life but some of you may think maybe this is already too specific at the very least you'd need something like a sufficiently complex chemistry or indeed the possibilities for any structures form in the universe uh and this is all not life in and by itself but it's something that we believe to be necessary for life to ever come into being and um so the reason um physicists talk about this uh this question like was the universe especially made for us like do we have a special place in this universe comes from the observation that um for some slight changes to the constants of nature um it would not be possible for structures to even form it would not be possible to form a carbon or any kind of sufficiently large molecule the most famous example uh may be the structure of the carbon nucleus which is a prediction that was made by Fred Hoyle so he figured out that for carbon to be produced in Stars the carbon nucleus had to have a particular structure it had to have a particular resonance and that was later actually discovered um so I think one way to look at this kind of prediction is to say that the observation that we ourselves exist is also an observation and that is good for some things for example for the observation that it must be possible for stars to produce carbon there are some other examples where some changes to properties of the constants of nature or nuclear and so on would eradicate Life as we know it a particularly simple to understand example is the cosmological constant so the cosmological constant is that thing which makes the universe expand and actually makes the expansion of the universe accelerate so if the cosmological constant was very large then it basically immediately rip apart all the structures in the universe so stars and galaxies could never form this is if the value is positive if the values are large and negative so the absolute value is large but the sign is negative then the universe would immediately recollapse after the big bang so again there's no way that structures could have formed um so again we we see that just the observation that we exist or else this sounds tells us something about the cosmological constant it's a similar story for Newton's constants the Newton's constant sets the strength of gravity uh If gravity is too strong then Stars burn out too quickly and so on and so forth um there are lots of books that have been written about this I'm not going to go through the entire list of examples they all basically work the same way you take a particular concept of nature you make a small change to it you figure out what happens to all the physical processes that we know of and then you figure out that some of the preconditions for life are no longer fulfilled which brings up the question can this possibly be a coincidence it looks as though making these small changes makes it appear very unlikely that our universe would have had just exactly the right values for the constants of nature so that life can exist so there's a big problem with this argument which is that if you're talking about the probability of something you have to quantify this probability so normally when we talk about the probability of say throwing throwing dye we have a probability distribution that in principle we can either derive from a model for the die or we can just collect it by throwing dire many times and collecting the data so we know it's 1 6 for each of the different phases to come up but when it comes to the constants of nature we don't have any probability distribution so if someone makes a statement like it seems to be very unlikely that the constants of nature would just have exactly the values that we do have that's a completely meaningless statement because we can't quantify this probability so it's not a scientific argument you know you could certainly say and people have made this argument based on Bayesian probabilities I find it surprising that the values of the constants are so as to allow for the existence of life and that's fine you know you're free to find surprising whatever you want but it's not a scientific argument there is another issue with this argument which is uh for one it's just wrong and that may be it it may cause someone else a surprise because some of those topics that we talk about in the foundational physics it seems that nothing ever changes you know we've been talking about some of those things uh for hundreds of years like determinism in determinism nature of time uh and so on but this is this is an example where people have actually um come up with new arguments uh for example um they figured out that they're actually other combinations of the constants of nature that do seem to allow for the preconditions of life in some form and those are not the same as in our universe one example as I just said um Hoyle figured out that the carbon nucleus should have a particular resonance uh so as to for carbon to be produced in stars but there are other possibilities uh other ways you can make this uh happen and uh recently someone have has come up with a different way to do it where the concepts of nature are not the ones that we have in our universe there are also people who have argued that we actually don't really need What's called the weak nuclear force so the weak nuclear force is one of the fundamental interactions that we know of it's responsible for example for radioactive decay and some people have argued that we actually don't need it to create all those structures that we see in the universe they call this universe without the weak uh without the weak force and they say in such a universe you'd still be able to to produce sufficiently complex chemical structures so it just seems that it's just not the case that there's only one particular combination of those constants I also think that part of the reason why physicists fall for this kind of argument like the universe is really really special and we need this exact combination of constants is that they tend to think that complexity is rare you know it takes something to create it whereas I think it's exactly the opposite like complexity is the thing that we generically get if we combine all those physical processes and this is actually an argument which was made beautifully in Stuart Kaufman in his book at home in the universe he basically says if you if you combine sufficiently many things and you just give it time and complexity uh will come out of it I think that physicists kind of they're not familiar talking about complexity at all so for them this kind of thinking is a little bit alien but I believe if we understand better how complexity comes about and how chaos works and all that kind of thing we'll probably find there are many other examples of combinations of constants of nature that would also give rise to preconditions for life so I really think it's more likely to be the rule than the exception so was the universe made for us for we currently know no so let me come to these two copies of us exist so this is really a question about the Multiverse and I would say that's an example of a question which is a scientific um to use the word from my friend Palmer which he brought this up in an interview that I did with him and I just took it and ran away with it okay so um again I think I first have to explain why would someone even come up with this idea that copies of us exist that sounds certainly a little bit weird but that's because Infinity is weird so in this standard model of the universe that we currently use for cosmology the universe is infinitely large um this by the way is also the case at the big bang I know that a lot of people have this idea at the Big Bang the universe was kind of like a small ball but that's not quite right so these are not cosmology the universe is always infinitely large what happens at the Big Bang is really that the energy density becomes uh infinitely large so but the thing with infinity is that if you have some kind of density fluctuations in this in this early universe and you just go out all the way to Infinity then any kind of fluctuation will happen somewhere with probability one that's what Infinity does to you now our solar system our galaxy and you and I everything we know um grew out of this early hot Plasma in the universe with those small density fluctuations in them so if you have an infinitely large Universe then those density fluctuations they will repeat with arbitrarily small changes to them so there would be a version of Earth that's exactly the same as ours in every detail except that there was maybe one cosmic ray that didn't come down exactly the same way and it didn't damage someone's DNA and your neighbor is still alive or something like this so all those variations should actually exist in an infinitely large universe um but the problem is the speed of light is finite and we cannot communicate uh with anything that's outside what's called our cosmological Horizon that's basically anything we can reach uh by sending signals with the speed of light or below the problem being that since the expansion of the universe actually speeds up it becomes more and more difficult to reach other galaxies so they're basically they're receding faster than from us than we can possibly communicate with them um to make a long story short the the universe may be infinite and it may have all those copies of us but we'll never be able to find out because we can never interact with them so there are no observations that can refute or confirm that these copies exist this is one of the simplest version of what's sometimes called a Multiverse the one equivalent of whether those are actually other multiverses another example is what's called Eternal inflation so inflation is one of those theories for the early universe that I was talking about the idea is that there is a new field which fills the universe this field is called the inflaton field so and this is the only thing that exists in the early universe and the quantum fluctuations in that field and from those Quantum fluctuations um there are bubbles created and those bubbles expand and give rise to the universe um around us now the thing is that in this infinitely large space there are lots of those fluctuations again and those bubbles keep on popping out forever so there's an infinite number of big Banks going on in this eternal inflation scenario and they'll keep on going on into all eternity there are several variations of of this idea of Eternal inflation for example in some of those little bubbles that pop out and grow into universes the constants of nature could be a little bit different from the one that we have here they could also be the same if if they are different this is often called the landscape you may have heard of this as the string theory landscape so this is actually where the idea comes from String Theory seems to tell you that um the concepts of nature should come with our possible values so you can combine this with this idea of Eternal inflation basically by Distributing the different values of the constants over the different big Banks this is called the Multiverse though again one can debate whether this is a particularly good term of course if you take the word Universe to mean all that exists then by definition the Multiverse doesn't exist which is probably not what the people who use the term intended but that's the way that it goes with nomenclature it doesn't really always make sense so also in this version of the Multiverse there should be copies of us in all those other big bearings again the problem is though there are no observations that can recruit to confirm that these copies exist because we can't interact with them again you you'd have to be able to send signals faster than the speed of light or to transport yourself faster than the speed of light to get into one of those other universes there's a final version of this copy argument that I want to mention which you may have heard of that's the many words interpretation of quantum mechanics so as I said earlier in quantum mechanics we have two different ingredients to the time Evolution we have the Sharia Evolution and then we have the measurement update and the measurement update is indeterministic in the standard interpretation of quantum mechanics now in the many worlds interpretation uh people say well actually making a measurement does not collapse the wave function instead what happens is that the Universe splits each time you make a measurement so if you measure the particle say let's take a simple example where a particle goes on a screen and you want to know does it go left or does it go right in a standard interpretation you would say well I've measured it the notes on the left side and that's the end of the story in the many words interpretation you would say well now I have two universes one in which the particle one to the left side and the detector says it's on the left side and one in which it went to the right side and the cactus has its on the right side so now we have two universes and this happens all the time everywhere like every time some kind of photon bumps into the wall the universe splits so there are lots of those universes and there are copies of us in them because all those Quantum events happen around us they even happen in your brain you know they have every time you turn on a lamp it's not a rare event so um though in the many words interpretation copies of us are all over the place and our lives pan out in in all possible ways that they can pan out um and there are a lot of people in physics who actually really believe that this is what's going on again the problem is though there are no observations that can refute to confirm that these copies exist because uh it's one thing to say okay the universe splits and all possible outcomes of a measurement actually do happen in some universe in our universe we only see one outcome and that's what we know and so there's no way to ever figure out if those other outcomes are actually real or what it might it doesn't even really make sense to speak of something being real if you can't observe it the reason physicists at least some of them believe that these copies actually do exist is the same in all cases they basically believe that because there are equations for it it also has to be real so they have a set of equations they have some reason to believe that those equations are correct because they describe something that we observe but then uh they jump one step further and say therefore I believe that everything which is in those equations is also real even if I can't even if I can't observe it now the problem is um that's not a notion of real anyone ever uses you know it doesn't really mean anything to say something is real if if you can't interact with it if you if you can't observe it you can just assume that those mathematical structures are real but this is an unnecessary hypothesis you don't need it to describe anything we observe because it pertains those parts of the theory that we do not observe and as I said earlier we shouldn't use unnecessary unnecessary hypotheses in our theories that's just not allowed in science so I think these Multiverse arguments are not proper science um we can't tell if those copies are real so we shouldn't assume that they are but this doesn't mean that those copies are not real because science also can tell you that they do not exist science doesn't really say anything about it so if you want to believe that there are copies of you out there somewhere in the Multiverse you can believe in this there's nothing in science that speaks against it this brings me to the last question can particles think and you won't be surprised to hear that I think the answer is no so again I first have to explain why would someone have this idea to begin with so this I have to say is uh maybe not so surprisingly not an idea that's particularly popular among particle physicists it enjoys a certain popularity among philosophers so they have this idea of pan psychism everything is a little bit conscious because it contains something that they call proto-consciousness and the idea is that it explains where Consciousness comes from because you can combine all those little bits very much like particle physics and they inform bigger things like us and at some point the proto-consciousness combines to what we normally call Consciousness now there are different variants of this argument one is that this proto-consciousness isn't a physically real thing so this is very much like dualism and it doesn't have any observable consequences to just like you can say well the mind and the body is really to separate things um and this is fine you know it's not in conflict with science um this idea of proto-consciousness without observable consequences um is also not in conflict with science but then of course you can't use it to actually explain what we observe because it doesn't have any observable consequences so that that's really I would say a purely philosophical thing but there are also some of those pan psychists or whatever you want to call them who think that this Consciousness stuff is actually physically real so they want to actually use it to explain Consciousness in the old-fashioned scientific way now the problem is that what you're doing then if you're talking about the properties of the fundamental constituents of nature you're actually doing physics and then you talk about proto-consciousness better Greece with what we know about the fundamental laws of nature so I have to look at this in a little bit more detail this is what we know about the fundamental particles in the world this is basically what everything is made of um called the standard model of particle physics you don't have to count them there are 25 of them contains good old friends like the electron and the photon and the Higgs boson um the standard mode of particle physics does not contain composite particles like protons and neutrons those are made up of quarks each of them of three quarts so um the way that the standard model Works um is that each of those particles um has a set of so-called quantum numbers of the quantum numbers Define exactly what the properties of the particles are quantum numbers one that you're probably familiar with is the electric charge some of those particles have an electric charge some sometimes it's negative sometimes positive sometimes it's zero the particles can also have a spin they have a property that's called the weak hypercharge it's basically a more complicated version of the electric charge the quarks also have a color and so on and so forth so there's this set of quantum numbers and now the way that the standard model works is that you you take all those quantum numbers for the particles and then typically what you want to do is you want to calculate the results of some particle collision and what you see in this picture here this is what happens if you slam two protons into each other so this is an image from Atlas at CERN so the the beams go into to the screen basically and they run into each other and then you create a lot of new particles basically from the energy in the beams and they go out and go into different kinds of detectors and then what they do is they take the measurements and they detectors and they reconstruct where the particles came from and what kind of particles there were and you compare this with predictions so you get you have your data and you make a calculation for what you expect with the standard model and that's where the quantum numbers go in and now the thing is if there were any other quantum numbers that those particles had then the results would just be different Loosely speaking it's because in quantum mechanics everything that can happen does happen so if there were more quantum numbers than all those different possible values for the quantum numbers would also be produced and there'd be more particles and we don't see that so if Elementary particles had any other internal States and the quantum numbers that just wouldn't agree with observation so you can't just say well I believe that particles have an additional new property which I call a proto-consciousness it doesn't really matter what you call it there isn't any such property so project Consciousness can only exist if it has no physical properties whatsoever in which case it does not explain any observations so parent psychism is popular among some philosophers so I should probably add that I'm not opposed to philosophy in fact I think physicists are not paying enough attention to philosophy in some aspects it'll be really really important for example when it comes to the question are those are the universes real this is really a question where you have to pay attention to what you actually mean by something being real but the idea that particles have additional physical properties whether you call these additional Properties proto-consciousness or something else is a statement about physics so when philosophers start doing physics then they actually have to pay attention to what the physics says this is also by the way why I'm not a fan of the simulation hypothesis this is another section in my new book It suffers from the same problem it makes big statements about um the fundamental laws of nature without actually paying attention to what we know about the fundamental laws of nature so do particles think no I think the overall story that I want to tell with my book is that I think sign and religion aren't at War there are a lot of people who try to play those two out against each other but if you look at what's actually going on in the foundations of physics that then many of the ideas that physicists consider there especially about um the question how the universe began they're basically extensions of some of those originally religious or spiritual ideas that just formulated uh in the form of mathematics and there are many of those religious ideas which are still compatible with with all we currently know there are also some things that may forever remain unknown I already said I believe that ultimately we probably won't be able to figure out how the universe began because it seems to me that this is just a way that science is fundamentally limited that we we aren't allowed to make a story more complicated though that may not be wrong like there may have been a more complicated Universe before ours it's just that the way that science works we would never be able um to say whether it was actually correct another question to which we may never found find an answer is if there's actually a theory of everything so this isn't something which I talked about here in any length again that's something that I talk about in my book um but to make a long story short the problem is there will always remain the question for any Theory why this Theory we know that the Universe has to be in some particular way I mean we know that it is some particular way and not any other so we need a theory that agrees with what what we observe but then there will always be questions in this Theory which we can only answer by saying because it describes what we observe so I think this is another way um that science is fundamentally Limited um scientists don't always mind this Gap I think some of the examples that I gave you show this very clearly that sometimes they stray over into a room where actually the methods of science fail and they don't always notice okay so this brings me back to my book so I'm pretty much done I hope you enjoyed this little talk there are more questions in my book and you can find more information on my website existentialphysics.com thank you for your attention thank you for more debates talks and interviews subscribe today to The Institute of Arts and ideas at IAI TV

Channel: The Institute of Art and Ideas

Views: 19,252

Keywords: learning, education, debate, lecture, IAItv, institute of art and ideas, IAI, philosophy, Sabine Hossenfelder, Theoretical Physics, Quantum Mechanics, Big Bang, Cosmology, Density Fluctuations, Infinite Universe, Cosmological Horizon, Multiverse, Eternal Inflation, Inflaton Field, String Theory, Landscape, Constants of Nature, Quantum Fluctuations, Many Worlds Interpretation, Wave Function, Schrödinger's Evolution, Measurement Update, Photon Interaction, Quantum Events

Id: V45ABEM-7m0

Length: 29min 45sec (1785 seconds)

Published: Sat Jun 10 2023