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.

David: Okay.

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?

GE: Yes.

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.