How improbable is a universe that contains intelligent life? How ‘finely-tuned’ do the laws of physics have to be?
Ard: Could you explain to us the concept of fine-tuning in cosmology?
GE: Okay. Well as a cosmologist one imagines imaginary universes, counter-factuals, and tries to see if you can learn anything. And if you imagine other universes, not only will they be bigger or smaller, expanding faster or slower and so on, but they can have different laws of physics. Because one of the things as a cosmologist one wonders about is, why are the laws of physics as they are?
So if you imagine the other laws of physics, you can ask how different can the laws of physics be and still enable life to exist. And it turns out there are a great many ways in which if you vary physics, pretty soon life cannot exist. And so there’s what’s called fine-tuning, namely that physics has to lie in a very restricted range in order that we, living beings, can come into existence. And it focusses, in particular, on something called the fine-structure constant, which is basically the strength of the electro-magnetic force, and the cosmological constant, which is how fast the universe is accelerating at the present time. And in either case you can show if they lie outside of a rather restricted range, in the one case, atoms won’t exist and therefore we won’t exist, and in the other case galaxies, and therefore planets won’t exist, and therefore we won’t exist.
David: I once heard you talk about Fred Hoyle in this. Could you tell me that story?
GE: The famous story about Fred Hoyle is he was one of the early people trying to work out how the elements out of which we are made come into existence, and he was particularly concerned about carbon.
In order that carbon exists, there has to be this excited state in the carbon atom. Now it turns out that the existence of that state depends on the fine-structure constant, and so there’s a link from the fine-structure constant through to this excited state, through to the fact that carbon is created in stars and thereby enables us to come into existence.
So if you imagine universes scattered around with all sorts of values of these constants, almost none of them will allow life: you have to lie in this very narrow band.
David: And how do you account for that then?
GE: How do you account for it? Okay, there are popular and unpopular versions. You can do it in three ways. One is to say it’s just chance: the universe just happens. Now, by chance I don’t mean it’s probable: it’s not probable or improbable, it’s just the way it happened. Now that’s a philosophically impeccable solution, but people don’t like it because it doesn’t get you anywhere.
David: It’s not much of an explanation is it?
GE: It’s philosophically impregnable.
Ard: You say it just happened, and that’s it. If it didn’t happen then we wouldn’t be around.
GE: The second one is to try to say it’s probable. Now how do you try to say it’s probable? Your problem is there’s only one universe with one value. So if you can imagine an ensemble of universes which actually exist, they don’t exist in your mind but they physically exist, in some of them life will be able to come into existence.
David: Is that what people call the multiverse?
GE: That’s the multiverse and this is the scientifically preferred version of Martin Rees, Steven Weinberg. A lot of people prefer this.
Ard: So there would be just many, many universes?
Ard: So most of those universes would not have life, but if you have enough of them, eventually one of them will have life.
GE: I have a problem with this because if there is that multiverse out there, the question is, can you prove it exists? And in my view you basically can’t. So I think this is a philosophical but not a scientific solution to the problem.
Ard: So if you had the multiverse, if you had many different universes, enough universes that one of them would have life, do you think that would still need some kind of fine-tuning?
GE: Yes, because the problem just recurs at the next level. I can construct you a multiverse in which none of the universes exist. The multiverse, if it’s going to be sensible, has to have laws which create the multiverse. That’s going to have constants of nature in them, and some of those constants will allow the multiverse to allow it.
David: Otherwise you get the wrong multiverse?
GE: Yes, and so then, if you follow this up, you get multiverses of multiverses of multiverses.
David: As you say, it’s not getting you anywhere. You’re just pushing the problem back.
GE: Philosophically it doesn’t solve a thing, it just pushes you one step back. And then, of course, the final one is that the reason that the constants are what they are is that something, or some purpose, or some principle, or something, intended life to exist, which of course relates to the religious world view in some sense. It’s very unpopular in scientific terms, but again, philosophically, this is a perfectly viable position.
Ard: So you’re saying basically that the three possibilities are: happenstance, it just happens, just blind luck; or some kind of multiverse, or maybe some kind of providence?
GE: Yep, that’s correct.
Ard: So what did Fred Hoyle think when he came up with his…?
GE: Hoyle originally developed the Big Bang model as a way of avoiding a start to the universe which he thought had religious significance.
Ard: So the word ‘Big Bang’ comes from Fred Hoyle?
GE: The word Big Bang comes from Fred Hoyle, as a derogatory term. He developed a steady-state model which didn’t have a start because it was disproved by observations. But he then got in to thinking about these probabilities of life and all the rest of it, and eventually he made the statement that life was so improbable that it looked like a put-up job. And he used that kind of phrase, which was just a statement that life is very, very improbable. The universe has to be really fine-tuned for life to come into existence, and so from a scientific viewpoint there is something to be explained.
But let me just clarify something: when I say there is something to be explained, it doesn’t contradict any experiment; when I say there is something to be explained, it’s a philosophical thing that needs to be explained. Fine-tuning is a philosophical problem. It’s not a scientific problem in the sense that there’s an experiment which gives a result.
David: Because you’ve said there’s no way of testing the philosophy.
Ard: In some sense the science everyone agrees on. Everyone agrees that these constants are fine-tuned. It’s what that means that they disagree on.
GE: Correct. It’s what that means which is a philosophical issue. And so it’s a meta-scientific question.
Ard: But that’s an important thing to talk about.
GE: It is. The problem is that some of my colleagues are writing about it as if it can be solved on a purely scientific basis, and I think this is very misleading to the public, and I think it’s very misleading within the scientific community. I think it’s a problem when scientists present a philosophical statement and claim it can be tested or proved scientifically.
David: Can you please tell us just what the fine-tuning argument and problem has been in physics.
MG: Right, so fine-tuning: imagine the old radios that you had to tune in to the station, and if you didn’t quite get it right, you wouldn’t hear the music. So fine-tuning is somewhat like that. Imagine that the way we understand nature is through this alphabet: the alphabet of constants – the constants that physicists like to call the Constants of Nature. So you have the electron mass, the electron charge, the proton mass, the proton charge. There are quite a few of those, and the point is this: those constants have been measured through the ages to have certain values which are very specific, and had they been otherwise, meaning if those values were different, nature would have worked in a very different way than it does. And if nature worked in a very different way than it does, we wouldn’t be here.
So the fine tuning essentially means that the Constants of Nature have the value that they do have and because of that we are possible. So the question becomes, why those values?
MG: If they were different, we wouldn’t be here.
Ard: So why would we not be here? Would there be no life?
MG: If you tweak just a little bit of the proton mass, stars would not be possible. If you tweak the proton mass, if you tweak the neutron mass just a tiny bit – less than a percent – stars would behave differently. They would burn much faster. They would not produce the heavier elements – like calcium, iron – that we need.
Ard: So what would happen if the stars were different?
MG: Without fine-tuning, the stars would not behave the way they do. They would not produce the chemical elements that they do, and life as we know it, which depends on a whole set of different chemical elements, would not be possible.
So when people jokingly say, ‘We’re all stardust’, it’s not a joke. It is actually beautiful. It’s true: we definitely are stardust, and, in fact, all the chemical elements that we have in our bodies – the calcium in your bones, the iron in your blood – they belonged to stars, billions of years ago before the solar system existed.
David: So what have been the responses to that problem over the last 30 years?
MG: So one of the responses is, who cares? You know, it just happened to be that way. It’s an accident, and the fact that it’s an accident doesn’t make it special at all. So that’s one possibility: it’s all random, and because of that there is no reason to try to explain it, which is quite appealing, actually, in many ways.
The other one is to say there is a reason for this: everything has a reason, and the goal of science is to explain why things are the way they are. Hence, the fact that the electron has this mass etc. must have a causal explanation. And so what would that be? Then it becomes not so much a fine-tuning, but a search for an explanation for the fine-tuning.
MG: There have been a few out there, but the most popular one nowadays comes from something called String Theory, which is a very bold attempt to understand nature in a completely different way than we usually understand, which is that instead of things being made of little bits called elementary particles, they are actually made of vibrating wiggly things called strings. And the same way that when you play a violin or a guitar you pluck a string, and if you change where your finger is, you’re going to get a different sound, a different frequency or vibration, those strings can vibrate in different ways, and depending how they vibrate, they actually emulate the properties of all the different particles of nature. So it’s a very cool idea, and it’s an idea that, in principle, could bring together all different forces of nature: so the big, grand unifying theory.
The problem is, on these string theories, that you would hope, originally, when they were proposed in the, early 80s – they were called Super Strings – they would say, ‘We’re going to solve these equations, and the solution is going to be the universe as we know it!’ You know, everything is in there. And, people tried and tried and tried.
Ard: Did you try?
MG: I tried, yes. And one of the problems with these theories is that you have ten dimensions: nine spatial and one time. And then you look around, you’re like, ‘Wait a second, I only see three.’ You know, is it north, south, east, west, up, down? Right, three? Where are the other six?
David: So the other dimensions are here, they’re just curled up really small and we can’t see them?
MG: That’s right. They’re really so small that you cannot see them.
David: So they’re all around us?
MG: Imagine each point of space has a little six-dimensional blob, or sphere, associated with it, and that’s what it is. And it’s not so crazy because if you look at this. [Holds up a stick] This is a stick. If you look at it from very, very far away, it’s going to look like a line, and a line is a one-dimensional thing. You can only go this way or that way. But you look closer and you realise it’s not really a line because you can also go around. So this is more like a cylinder. But from far away it looks like it has one dimension, because this circular dimension around it is too tiny compared to the length of the stick.
The idea is exactly the same. Every point in space has this six-dimensional sphere hidden in it, and it’s just so tiny, we don’t see it. And so the question is, why are they so tiny?
So, back to strings. Strings, to exist, have to vibrate in this nine-dimensional space, and the point is those extra six dimensions, they can be folded up in many different ways – just like if you get a balloon you can twist it, you can make holes in it. These are different topologies. So the six-dimensional extra space has different topologies. When people start to calculate how many of these could be around, instead of ‘the universe’ coming out, they came up with a ridiculously huge number, which is a ten with 500 zeros on top: so, one with 500 zeros afterwards.
David: Isn’t that many more particles than we have in the universe?
MG: Oh, pfft! Yeah, many, many, many, many more particles.
David: That’s a big number.
MG: It is a ridiculous number, which means, now what? So the goal, the dream, of finding ‘the universe’ became, ‘What do we do with all this stuff?’ That’s where the multiverse came up. So each solution, each folding of this extra-dimensional space, is, potentially, a different kind of universe.
David: So we’re going to have 10 to the power 500 different universes to explain this one?
MG: Yes, exactly.
David: But instead of having the difficulty of explaining how one universe comes into being, now we’ve got to explain how 10 to the 500 universes came into being.
David: And since we can’t explain this one, it seems to me we’ve just made the problem a whole lot worse, not better!
Ard: Yeah, but I think the argument would be that now you’ve got a mathematical theory, at least, a beautiful theory which explains that.
David: I don't know. It doesn’t seem that beautiful to me. We used to have the one universe we needed to explain, now we’ve got loads.
MG: Exactly. It’s like the universe now becomes a data point in a vast manifold of possible points, and are you really explaining something with that? Did you gain any knowledge from this?
Ard: And there’s a question maybe about can you do experiments on…?
MG: That, to me, is the fundamental question. Physics is supposed to be an empirically validated science. You come up with some hypothesis, doesn’t matter how crazy it is, but it has to be empirically tested. You’ve got to make an experiment, an observation, and say, ‘Yeah it’s okay’, or ‘It’s not okay’. In practice, it’s not so black and white. There are many, many subtleties to this argument, but at the end of the day you need to be able to prove your idea, otherwise it’s not physics, it’s something else.
Ard: Prove it by experiments.
MG: You prove it by experiments, and that’s why there is the rift, right? Because… It’s something else because it’s a different way of doing science. Because what you’re trying to do now is you’re bringing up an idea that is based on a-posteriori reasoning, which is, ‘We’re here’. We start from that, and usually the explanation is, ‘How did we get here?’ You go from beginning to end. Now, it’s starting from the end and you want to create an argument based on our existence. And the point is, is that good enough as an explanatory tool, or are we just throwing in the towel and pretending we are smart?
Ard: So wouldn’t you also say that this method of trying to find out about other universes is like the method Dirac used to predict antimatter? He used the tools of mathematics: he tried to make something consistent and out of it pops antimatter. You do it again and you get the Higgs boson. You do it again, and out pops other universes. Isn’t that…?
MG: Yeah. That would be beautiful if I could go and do an experiment to see the multiverse the same way I see the Higgs or the positron, but I can’t. So it…
Ard: That’s where it’s different?
MG: Yeah, so the mathematics is compelling. But being compelling doesn’t mean it’s right. And that’s very important.
Ard: Do you think that because, in the past, that compelling mathematics has turned out to be true, that physicists feel that it must be true about the multiverse?
MG: Well, you have to be careful. It has been true a few times, sometimes, not always.
MG: And of course, when it is true, it’s so mind-bogglingly spectacular that you go, ‘Whoa! There is something going on here.’ But you can’t make that into a rule.
Ard: I was wanting to jump to something closer to science, which is that the elements in our body – the whole series of elements – where did those come from?
PA: In what we term the Big Bang.
PA: At least the simple elements were, but happily they got roasted in stars.
PA: And once you start roasting things you get tastier meals like carbon and oxygen and nitrogen.
Ard: Okay. And so these elements in our body come from stars.
PA: Yes. We are stardust.
Ard: We are stardust.
PA: You are the child of some distant and now extinct star.
Ard: Which has exploded?
PA: And scattered its ashes. And you are ash.
Ard: I’m ash. That’s a kind of poetic...
PA: I think it’s lovely.
Ard: So do you think that gives us some kind of meaning?
PA: It gives us a certain humility insofar as humility is meaning. I think it’s a fantastic vision, really that through the processes of physical law, we have emerged and are able to have conversations of this kind. I think it’s quite an extraordinary vision of the grandeur of the universe.
Ard: Sure. Philosophers have tried for millennia to solve the problem of the meaning of life. Do you think that problem should be handed on to scientists now?
PA: Well philosophers haven’t made much of a fist of it, have they?
Ard: Okay. A classic kind of philosophical question is: why is there something rather than nothing? So, where did the universe come from?
Ard: Do you think science can answer that question?
PA: Well, nothing else can.
Ard: Okay. Do you think we’ve…?
PA: Obviously, theology thinks it can, by saying it was the workings of the finger of God which stirred up nothing and out of it came the universe. This is not, to my mind, very satisfying as an explanation.
Ard: And when you say ‘nothing’, what do you mean by ‘nothing’? Do you mean…?
PA: I mean what everyone means by nothing. It means absolutely nothing.
Ard: So it’s not like Lawrence Krauss says the laws of physics out of which…?
PA: No, no, that’s the laws of physics. It’s a meta-nothing.
Ard: Okay. It’s a meta-nothing. So nothing means nothing. There are no laws of physics. There is…
PA: I mean absolutely nothing. Not even a void.
Ard: Not even a void. So where did the voids and the laws of physics come from then?
PA: God knows!
Ard: God knows! Okay.
David: Very good!
Ard: Do you think that’s a deep mystery?
PA: When I say that God knows, I’m using that, of course, allegorically. I must say this.
Ard: There’s no doubt about that!
PA: I think the extraordinary thing is that we humans, we products of the creation, are on the track of giving a real answer to that extraordinary question.
Ard: Do you think we’ve got some ways we could answer that question?
PA: Oh, yes. Science is an extraordinarily powerful instrument of discovery that wherever it touches, the rocks give way.
Ard: Do you think it could be that we’re just the product of an accident? A cosmic accident?
PA: Well, yes, kind of. For an accident to occur, you need a kind of substratum for the accident to occur in. But even though it’s a difficult concept, it may be one that we ultimately find our way to understand. So I think it’s a real challenge for science, but we’re edging towards it. That’s the extraordinary thing. Science is edging towards understanding the deepest possible questions: it’s not rushing in. Sometimes it rushes in and then it gets rebuffed, but it is cautiously edging towards discovering the deep fabric of the universe and the events that took place in its inception.
Ard: But wouldn’t you say that science is based on the rules of physics and chemistry, etc.? But the question of where those rules came from, you think that’s also a scientific question?
PA: Oh, absolutely. I mean the ultimate level of the rules of science must be some kind of intrinsic logic to the universe.
Ard: And where did that logic come from?
PA: It might be that… This is pure speculation, of course.
PA: Many kinds of universes can bubble into existence but immediately evaporate, vaporise, because they don’t have a logical structure that causes them to cohere. But then you get a universe suddenly that, quite at random, bubbles out of absolutely nothing, which by chance has a logical structure that enables it to persist.
Ard: But what makes those universes bubble out of nothing?
PA: Who knows? I mean, it would be unwise… I don’t think it’s the finger of God saying, ‘Bubble, bubble’. But, once we know that these universes have bubbled out of absolutely nothing, then we can start to understand why they did.
PA: Perhaps they didn’t. Perhaps it’s all an illusion.
Ard: But they would have to be uncaused somehow, right?
PA: Of course.
Ard: Definitely uncaused?
PA: Although even causality might take a knock because it could… The kind of deep causality that we’re talking about might be retrospective causality, because something comes into existence, causality exists, and so it bootstrapped it into existence. Who knows?
David: A bit like time?
David: It would be the same? Time wasn’t ticking away waiting for the universe, but once the universe is here, it has time.
PA: But, you know, these very deep questions are extraordinarily important questions. But they are… Such is the plasticity and power of the human brain. I don’t think we should say that they are beyond human ability to elucidate. But it might take time, and we might be astounded by the answer. Who knows? We might have to say, ‘There’s a God!’
David: I take it you would reject out of hand the notion of people who say we should talk about the purpose of the universe?
PA: I dismiss that because there’s no evidence.
PA: It may be true, because with my puny understanding of cosmic history, who knows? There might be a God out there that is completely invisible to me in all his actions. But, you know, who knows? It might be true, in which case there would be a reason for the universe. But because I see no evidence for it, I’ve no reason to accept it. And if I could…
Ard: So because you see no evidence for God, there is therefore no purpose?
PA: I think I think that.