( I captured the text of this interview because Neil Turok touches on insights that I’ve included in my work on the first principles of the universe that we’ve discovered in physics. )
[INTERVIEW BEGINS]
Hi, Neil Turok.
Thank you so much for joining us on conversations at the perimeter.
My pleasure.
So I have to say I’ve always enjoyed when I’ve had the opportunity to talk to you over the years. And 1 thing that I find particularly impressive about your work is that you have such a deep understanding of the big picture and the goals of fundamental physics. I think this is particularly difficult for researchers like me that can maybe get a bit lost in technical difficulties and calculations.
So I wanna start with a very big picture question.
Okay.
How would you describe the state of theoretical physics research today?
It’s very interesting. It has it has grown into a very large field. There are tens of thousands of researchers around the world. At the same time, I think it’s diversified, enormously.
The part of it which I’m most fascinated in is the fundamental understanding of the universe, be it on very small scales, as in particle physics, or very large scales, as in cosmology. And that part, I would have to say, has been, on the 1 hand, benefiting from incredible observations.
On small scales, we have the Large Hadron Collider, most powerful microscope ever built, showing us what subatomic particles look like. And on the large scales, we have data showing us the whole visible universe, with exquisite precision.
So it’s definitely been a golden age, in that sense, and I but on the more theoretical side, I’d say the picture is more mixed. Since I started in theoretical physics in the early eighties, there have been great hopes about a number of programs of research, grand unified theories, supersymmetric theories, string theory, super gravity, m-theory, and so on.
And I would have to say that, these have not yet panned out. It’s very striking that there is not yet a single prediction, which has, been verified from any of these frameworks.
So from my own point of view, on the 1 hand, you can, you know, wring your hands and say, why hasn’t theory been more successful? In the last 40 years, you know, all the theories we verified are essentially rather old theories, Einstein’s
theory of gravity, the Higgs Higgs theory of the Higgs boson, and the standard model have been verified with more and more precision. But the newer ideas haven’t, panned out. So you can say, you know, feel rather upset and disappointed about that. (But) I don’t.
I think what’s happening is that nature is speaking to us and telling us that, that he or she is, simpler than than than we expected. Because what these observations reveal is a striking minimalism.
You know, we don’t find any more part we have not found any more particles, in probing the universe at very high energies now, at the Large Hadron Collider. And on large scales in the universe, the universe appears to be more or less as simple as it possibly could be, and still give rise to galaxies and stars and and, the structures we observe.
So this is tremendously exciting because I think the the simplicity indicated by the observations is, I believe, pointing us to new principles, and those principles will be, deep and universal, and highly predictive, and highly constraining, and they they will constrain the universe to look something like what we see.
So, whereas you might naively expect the universe to get more and more complicated as you go to bigger scales, the opposite seems to be true. And that I find extremely exciting because it means that maybe indeed we are the the the scales we live on and we operate on are perhaps the, in in some sense, the leading edge of complexity in the universe.
The universe is much simpler on small scales, much simpler on large scales, and, that helps put us in context. And maybe if we understand the big picture, the universe on very large scales, we will somehow understand where we sit, in the universe.
And I’m particularly excited about, our recent work addressing the big bang.
You know, this is the most profound puzzle in all of physics, how everything emerged from a point. And I think in the over the last year or two, we’ve really started to make sense of that.
And again, it indicates our new understanding is that the Big Bang is actually quite simple. It’s not a it’s not a arbitrary or chaotic or random process. It’s a very precise, I mean, if our theoretical ideas are correct, it’s a very precise boundary condition for the universe, and a highly principled boundary condition. And if so, then, you know, the universe becomes much more comprehensible in its entirety.
And as you said, many other researchers work on more complicated theories that are not embracing minimalism as watched. Why do you think others tend to stray away from these simpler ideas? I think, you know, we’re all trying to follow the example set by Maxwell with Maxwell’s equations or Dirac with Dirac’s equation, Einstein with Einstein’s equation.
These are tremendously principled, economical, mathematical equations, which govern a, you know, bewildering variety of phenomena and are extremely predictive.
So we’re all trying to emulate, you know, these highly successful theories, we we
base our current theories on. But I think what happened is that particle theory, over the last 50 years, maybe longer, got into the habit of always postulating new particles.
And to some extent, this was natural, because every time you built a new accelerator, you discovered new particles. And so this just became the norm, is that, you know, we expect once in a while to add a few new particles. And the hope arose that by adding these new particles, at some point we would actually simplify the picture.
So in grand unified theories, for example, you try to make sense of the pattern of particles around us by adding some more particles, and in such a way that the whole unified. And that habit sort of persisted, And so but it generalized. So instead of adding particles, people added extra dimensions of space, and, extra objects.
So there were strings in string theory and membranes and and higher, dimensional structures, which were added to these theories all in the hope
of sort of unifying this in a principle.
However, principles were somewhat lacking.
So string theory, you know, notoriously doesn’t really have a clear conceptual foundation or principle in the same way that Einstein’s theory of gravity had.
You know, in Einstein’s theory, the conception was that you have curved space time and this curved space time tells matter how to move, and in turn, the matter tells the space time how to curve.
That’s that’s how John Wheeler famously described it. And those words, you know, besides being very beautiful, they they capture a concept of how the physical world works, which is very intuitive and very powerful, and when it’s translated into mathematics, it becomes highly predictive.
But, string theory has lacked, such principles.
And it’s more been more a question of sort of follow your nose, and when you come across some phenomenon, you sort of tweak the theory, or you, adjust your interpretation. And in particular, in cosmology, you know, quite a popular endeavor in string theory has been to, try to picture the universe as if it was what’s called an s matrix. An s matrix is something used to the the way the cosmos works seems very, very different to an s matrix.
You know, there was a at least in the part of the universe we we can see there was a starting point. And, you know, there’s this finishing point which is, which is dominated by the energy in empty space, the cosmological constant, sometimes called the dark energy.
And so I think trying to shoehorn the universe into a preconceived picture, which was designed for particle physics experiments, to me seems, you know, a sort of search for a principle but not 1 that’s particularly likely to to work. Mhmm.
So I think people have been trying to find principles, which are economical and powerful and will explain lots of things, but to a large extent those principles don’t seem to be the right ones. Mhmm. And as I say, the the enormous simplicity of nature is hinting that there are principles to be discovered.
And, yeah, I’m hopeful that we’re beginning to get on the right track. I’ve heard you say that a key ingredient in doing this work is having a lot of dialogue between theorists and experimentalists, But this is not always easy to do, and I think That’s right. There tends to be a bit of divide a bit of a divide between these areas of research. So how do you think we can improve this and have more effective collaborations between theorists and experimentalists?
Well, I think it’s difficult because both theory and experiment are very technical.
When I started as a PhD student, you know, it was very noticeable that the theorists were in Imperial College had their own seminars, and the experimentalists had their own seminars, and they generally never went to each other’s seminars.
So , you know, high level of technical complications in both aspects of science mean that people don’t have time to, often to interact much with each other.
And that’s, yeah, that’s very sad, because I do believe that theoretical physics should be, you know, at its most exciting and most effective, should be connected to observations. And there’s been an increasing sort of divergence of so called pure theory from observations.
And even a sort of philosophical justification by saying, oh well, you know, if we know our theories right, for mathematical reasons, we don’t really need to pay attention to the observations. And I am very critical of such point of view, because I think you can really easily go wrong in your mathematical assumptions, and and very quickly just diverge from anything to do with reality. You need to keep an eye 1 eye on the observations.
It may not be in, you know, very much detail. You don’t need to get involved in experiments or data analysis or whatever, but you need to pay very close attention to, you know, major observational results. If you are to actually build a successful theoretical physics, framework. So I think the the the field does need a bit of a reset.
It’s particularly important for students to sort of, appreciate the the wonder, the sort of miracle that theoretical physics is, that when it does connect to reality, it’s quite magical. And I think the students who don’t, pursue that or or aspire to that are really missing out on a lot.
That 1 should, you know, never forget that the real magic in the subject is when it connects to observations. And these observations are extremely fundamental. I mean the universe, you know, we know things about the universe that the fact that empty space seems to have an energy, the cosmological constant, that’s very profound.
There are ideas, again, for interpreting the meaning of that. You know, what is this stuff in empty space? And, then we have the dark matter, very good observations showing us that most of the matter in galaxies is doesn’t interact with light.
We have some very interesting candidates for the dark matter, some of which are very minimal, like, neutrinos. We know neutrinos exist, and it’s a very simple and natural idea that one of the, so called right handed neutrinos is the dark matter. And the exciting thing is that that hypothesis is possible to test, within the next five years or so.
People are projecting that through observations of galaxy clustering, one can actually, detect even very tiny, light neutrino masses. And, if the right handed if one of the right handed neutrinos is the dark matter and if it’s stable, then it follows as a consequence that one of the light neutrinos is massless. And that should be possible to confirm within the next five years.
It’s very, very challenging work, for people doing the observations and modeling, a lot of computational modeling to understand how the light neutrino masses affect the clumping of matter. But so far the predictions are that we we with the with the anticipated accuracy of the measurements, we should be able to tell quite definitively within 5 years or so whether the light neutrinos are massless. And if if that is confirmed, it will be a very strong indication that we’re actually on the road to understanding the dark matter. And then there are other things like the fluctuations coming out of the big bang.
You know, these take the form of quantum fluctuations in the vacuum, which is is a very profound phenomenon. That the quantum fields we observe, like the electron or the photon, all the other fields in the standard model have fluctuations in the vacuum. And these are very paradoxical and strange, have very strange properties. For example, that if you add up all the energy in these vacuum 0 point fluctuations, it’s infinite.
And that doesn’t make any sense because gravity couples to energy, and gravity would see that infinity. So so for decades, we’ve been sweeping this under the rug and pretending it’s not really there, and so called renormalizing it away.
And and this is very … this is not a good state of affairs because it means we do not have a physical picture of what’s going on in the vacuum. And again, these new developments, some of which I’ve been involved in, are pointing to resolution of these questions.
So that by modifying the vacuum of the standard model in a certain very precise way, you can cancel this energy divergence. And in fact, protect some of the deep symmetries in the standard model – one of which is called, local scale symmetry.
So, you know, it’s a it’s a surprising fact that a photon of light is pretty much the same as a photon of x rays or radio waves, and they’re all just, scaled up or down versions of exactly the same thing. That’s a very deep symmetry of Maxwell’s equations, that it’s so called scale invariant, and even more than that, locally scale invariant. So you can change the scale differently in different parts of space and time, and the equations remain the same.
This is why is that such a deep symmetry?
Well, to describe the big bang, where everything came from a point. If all the material in the universe was insensitive to the overall size of the universe, as it is for Maxwell’s theory or actually for Dirac’s theory as well, then the stuff in the universe doesn’t know about the size of the universe at all. So even though from our point of view it all shrank to a point, the stuff of which matter is made doesn’t see, the so called singularity. And this makes the singularity possible to model mathematically and to really understand, and to understand this boundary condition I mentioned at the Big Bang.
So, I think, these principles, in other words, trying to deal with the vacuum energy infinity or divergence, trying to deal with the Big Bang singularity, these are really pointing us to the right principles, which will explain the universe on large scales.
And the most thing I’m most excited about recently is that using these same principles, we’ve been able to calculate the fluctuations we now see in the cosmic microwave background.
And amazingly, the the numbers come out correct. We get the right size of fluctuations. We get the right spectrum, without any free parameters at all. And so, you know, this is early days, but it’s a it’s a very exciting framework, which may end up explaining, the universe and connecting it to the fundamental physics of particles in a in a much more precise way than we ever thought was possible.
And is this something that you have been working towards your whole career, trying to work on these very simple models with very few free parameters? Or would you say this is something that you’ve been exploring more recently? Essentially, I have been working with the same motivation for my whole career. I’ve always chosen to work on testable theories, even when most people don’t.
And so as a student, I was very fascinated by an idea of my professor, Tom Kibble, that, there would be cosmic defects in the universe.
This was actually a consequence of grand unified theories. And what was exciting about it is if these defect if grand unified theories were correct, and if these defects had formed as they predicted, we would be able to see them. And so I spent a lot of time trying to calculate what they would look like, what observations would detect.
And in the end, we disproved, the idea that these defects gave rise to galaxies, which was 1 of the popular theories of the eighties. And I spent a lot of time trying to, you know, calculate precisely what the predictions were. And then when the experiments came along to check, they just proved those theories wrong. So I was very fortunate to work on theories which could be proven wrong.
Then when string theory came along, like most other people, I was very excited.
Maybe this unified framework that really will explain everything is a theory of everything. And I did my best to try to reconcile string theory with cosmology. So we made a model of colliding branes in extra dimensions. And I would say at that point, I was beginning not really to believe.
I don’t I didn’t necessarily believe this framework, but I thought it was, an interesting exercise to create a rival, a competitor to the most popular theory, which was called inflation, And and and hopefully 1 that was less adjustable and more connected to very fundamental physics, you know, as as string theory was,
quantum gravity and so on.
But I think the realization slowly dawned that, you know, this whole framework was too complex. And, especially as the observations have become simpler and simpler, and the kind of signals you would have expected from inflation have progressively gone away.
So 1 of inflation’s predictions was that there should be, very long wave length, gravitational waves, created a sort of aftershock of this burst of expansion, in the beginning of the universe. And you could see these long wavelength gravitational waves through observing the polarization of the micro background sky. And the measurements finally became accurate enough to see this effect.
Initially, they claimed they had seen it, and so all the inflationists were very excited and thought, you know, this is verification, including Stephen Hawking, my my friend Stephen Hawking, bet me in public that or or he he we had a bet.
I had bet they would not see it, and they now claim to see it. And so he wanted me to pay the bet, and I said, you know, all experiments require verification,
and, and there were reasons to doubt this experiment.
In the end, the experiment turned out to be wrong. And, now what’s happened is that the latest experiments see nothing. And within 5 years or so, the upper limit on these gravitational waves is going to get so low that I think most people, most sort of relatively unbiased people will draw the conclusion that inflation
probably isn’t the way to go.
So that’s really exciting. The the precision of the experiments has got to the point where, you know, large numbers of theoretical frame popular theoretical
frameworks are now under severe pressure.
So in the interim, you know, I all these things influenced me a lot. But I think especially when I was working at Perimeter, and I had the responsibility as director sort of deciding which fields were worthwhile to invest in, that made me look very critically at the whole field of theoretical physics and try to assess, you
know, where the best prospects were.
And, of course, that influenced my research. And so when I left as director and I went back to full time research, you know, I was very determined to, to focus on theories which I sort of genuinely believe are promising and have a chance of, of of, you know, providing very large explanatory power.
And so that’s what I’m working on. Mhmm. And I know you’ve said that a lot of
the work you’re doing now relies heavily on some ideas introduced by Stephen Hawking, who you’ve already mentioned.
Can you say a little more on that?
Yes.
I was very fortunate, in many ways to know Stephen Hawking. When I was an undergraduate, I went to his inaugural lecture, called, very provocatively, is the end of theoretical physics in sight? And, it was sort of lecture full of jokes.
And at the end, he concluded it was in sight, and I was worried I’d missed the boat.
They’d sorted everything out. It was super gravity was the answer, and, and that was that.
But, it proved to be overoptimistic. And then later, I went back to Cambridge as a professor and made friends with Stephen, and we wrote, several papers together.
But what’s special about Stephen is he had this, he was extremely adventurous.
You know, at the time he started thinking about quantum gravity and black holes and how they radiate and the the thermodynamics of black holes, You know, that was that was, far ahead of its time.
But his ideas were so deep, they have influenced the whole field for decades.
And the way I you know, I think we’re still struggling to understand what they mean, and he was too.
We still don’t really know what the entropy of a black hole means exactly. We think it’s to do with how many different ways there are to make a black hole, but we we still can’t quite put our finger on it, on exactly what it means and how it’s compatible with all of the rest of physics. But in our very recent work, and this is with, Latham Boyle at Perimeter, we’ve developed, Stephen Hawking’s concept of entropy, gravitational entropy, to, to apply to the universe, the whole universe. And, and that’s been really surprising. And in the course of that study, I’ve
come to the conclusion that Stephen himself underestimated the power of his own ideas.
Okay?
So he developed the idea of entropy, of of gravitational entropy, entropy of black holes, entropy of the universe. He never succeeded in calculating it for the universe, as we now have.
And so he tied his ideas to inflation. You know, inflation, sort of, to put it bluntly, was the sort of rag bag of models, thousands of different models of inflation, all of them sort of tweaked and adjusted and with lots of assumptions to sort of fit
what we see, in the universe.
And my current understanding is you just don’t need it. You don’t need to tie Stevens’ ideas of gravitational entropy to inflation. Just take them as they are, apply them to the real universe without any extra particles or fields or inflation or anything, And they already explain why the universe is big, smooth, and flat, in themselves.
And so that’s been very exciting, is that I think we found that Stephen’s ideas are more powerful than he suspected. And, there are still questions about exactly what it all means, but it looks like they can explain the structure of the universe without any additional input.
And then the other thing in what we’re studying, you see, Stephen’s ideas were
very paradoxical in in many ways. So he said the but a black hole, which only has a mass, an angular momentum, and electric charge, just certain numbers it has, A black and it’s featureless. A black hole is essentially featureless object, like
an elementary particle, but it can be huge. This black hole, can be made in in in in so many ways.
Now the weird thing about that statement is that surely the number of ways you can make a black hole depends on how many different elementary particles there are. You know, if you’ve got particles … If I only got 1 type of particle, I can make a certain black hole. But if I’ve got 2 types of particles, surely I there are more ways to make a black hole. So just assigning an entropy of a
black hole immediately creates a puzzle.
Why are there so many different particles in the standard model? And does the entropy of black hole depend on how many particles there are? So the answer is, in his calculation, it’s just a, a it’s 1 result.
You can’t adjust it. If you if you can’t change the number of particles. You can’t change the entropy by changing the number of particles. It’s it’s whatever it is. That actually implies, I believe, that the number of particles in the standard model is fixed by gravity.
Okay?
And we know there are 3 generations of particles, 16 particles per generation. That number should be forced on you by the fact that the standard model couples to gravity. If it is, then the whole thing is absolutely self contained, and you you just can’t separate these puzzles from each other.
So particle physicists who are trying to understand how many particles there are in nature, that question’s meaningless unless you include gravity. And gravitational theorists trying to understand the entropy of a black hole, that question’s meaningless unless you actually use the real number of particles in the world.
Okay?
So I think that again, the fact that Stephen’s entropy ideas seem to be successful in describing the universe, indicates that physics is truly unified, and and and not adjustable. You know?
And so if all of this works, I would say we will be pretty sure that this is the entirety of physics. Because if you add another particle, you’re gonna spoil all these cancellations and agreements.
So that’s that’s very exciting, that nature may, itself be telling us how things unify, and that all these kind of consistency arguments and arguments about the universe and the big bang and consistency with observations
may, in fact, all come together very beautifully into a coherent, mathematical picture.
[ Snip ]
The real magic of physics is that these
mathematical considerations end up, connecting with reality.
That’s the deep mystery of the field.
Somebody said this to me a few days ago.
You know, mathematicians make their frameworks and
do their calculations, but physicists somehow have
a direct line to God. Okay.
Now I don’t believe in God, I’m not religious, at
least not in any organized sense, but, but I think there’s a kind of element of truth in that, that somehow physicists have uncovered a fundamental feature of existence, which
is this strange ability of our minds to really make
sense of what’s around us.
It’s a very deep puzzle, and I think if you
like, the best way we can appreciate that puzzle and
and further it and, pay it homage almost is to
is to practice that, to make sure we what, you
know, what we do does or to try to relate
the mathematics we do to to the real world. Mhmm.
In many ways, you’re speaking to this idea
that physics needs many different people, including people
who like to make diagrams or Yeah.
Maybe people who might be considered unusual.
Yes. Absolutely.
[Snip]
The rest of the interview consisted of suggestions for students seeking a career direction in physics.
