The quest for quantum gravity: why being wrong is essential to science

Theoretical physicist Fay Dowker says that scientific advances depend on debate.

Einstein's theory of gravity doesn't play nicely with quantum physics. Theoretical physicists such as Professor Fay Dowker are working to create a theory that does: quantum gravity. She tells Amy Barrett why being wrong is a step towards reaching consensus.

I am working on the problem of quantum gravity, and it’s a problem and not a theory because we don’t have a theory of quantum gravity yet. So, the challenge is to find one.

It’s a problem because our current two best fundamental theories in physics are not compatible with each other. It’s a strong statement to say they are contradictory, but I’m not afraid of saying that actually. I think science advances by looking at contradictions between different pieces of our current understanding, and it focuses on those contradictions in order to make progress.

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So, science tolerates contradictions, but not forever. At any particular moment in history, there will always be contradictions between different pieces of our understanding, and those contradictions are exactly where we want to focus on in order to do better. To try to unify our understanding.

The particular approach I’m working on is called causal set theory. Causal set is just the name we give to the mathematical, discrete, atomic object that we’re proposing is the fundamental basis of space-time.

A typical day will involve perhaps a lecture, preparing for a tutorial, talking to my PhD students about their projects, sitting down, reading an interesting paper that’s just come out. So, it’s very varied, and that’s one of the great things about my work. When I’m teaching, I’m interspersing bouts of thinking about research and doing research with my preparation for teaching, meeting students.

I am a theoretical physicist, which means that I’m not tied to a lab, so I can do my research pretty much anywhere. I use a computer a lot, so I’m often sat at a desk reading papers on my computer.

I find it hard to think without a piece of paper in front of me and a pen in my hand, so I’m doing calculations, scribbling notes down on paper.

Professor Dowker © Imperial College London

My colleagues use a lot of computer simulations. Computers are incredibly useful, even though we’re doing theoretical physics. People use computers to simulate the models that they are creating, and also, to solve hard equations: often computers can do what we can’t do.

People use computers to solve differential equations, for example, the equations that govern the geometry and structure of space time: Einstein’s equations. They’re very difficult to solve analytically, just with pencil and paper.

So, we have to use enormous amounts of computing power to solve those equations, to tell us, for example, what the form of the gravitational waves coming from black hole collisions will look like.

It’s a global community of people working on quantum gravity. There are different approaches.

We’re divided into different approaches, so some people will focus on one heuristic motivation, and some others will focus on a different starting point, if you like. And at the moment, the experimental evidence is scarce, and so it’s hard to be guided by actual observations.

The originator of the theory that I’m working on, causal set theory, is a physicist called Rafael Sorkin. He works at the Perimeter Institute in Waterloo in Canada, and he’s the one whose work as progressed the theory more than anyone else.

It’s the epitome of what science is, to try to better our understanding of the Universe. And as I said, science tolerates contradictions, but it doesn’t tolerate them forever. So, science advances by resolving contradictions between different parts of our current understanding.

The scientific drive to understand better is what motivates our attempts to find, our quest to find a theory of quantum gravity. The problem of quantum gravity is so fundamental: space time is the arena in which everything that happens, happens. It is our Universe.

So, understanding that better at a fundamental level is bound to have consequences which we can’t foresee because we don’t know what quantum gravity is yet. It’s bound to have consequences in every part of our lives. Although, as I said, it’s hard to predict what those would be.

If I knew that… [laughs] I just don’t know. I think a lot depends on what happens in cosmology in the future. What sort of new data will come in. At the moment there’s a tension, some people would even now call it a contradiction, between our best theory, the standard model of cosmology, and our observations, in particular our observations of the expansion rate of the Universe.

So, the Universe is expanding, our galaxies are getting further and further away from each other, and we can measure the rate at which that is happening.

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That rate is now in contradiction with our standard model of cosmology. Contradictions are strong, but experimental physicists are very conservative. They don’t want to announce a contradiction until they’re really, really sure, but there’s now a growing tension between our observations and the model we’re currently using.

I think that that is going to show that our standard model of cosmology has to be reformed, and I think that that’s going to be a clue to quantum gravity. But we’ll see. That’s something that may or may not happen in the next few years as more cosmological data is gathered.

When I give public lectures, I am amazed at how well-informed people are. I often get questions from the audience when I give a public lecture that are far more astute and incisive than those that I get asked by my colleagues.

I think it’s because when people are interested they have a much broader perspective. They’re much more questioning. They want to know in general why one is interested in this. Why is one doing this? What are the broader issues here? I enjoy that enormously.

People are very astute: they can spot an inconsistency in your argument.

I really enjoy speaking to non-experts, because their questions are very challenging, and often very well informed, particularly about cosmology.

Quantum mechanics is a different matter, but that’s not the fault of people, of interested non-experts. The confusion, and perhaps misconceptions, about quantum mechanics that abound – and they do abound – are because the community of physicists itself has not come to a consensus about quantum mechanics and how to understand it.

That is a remarkable situation given that quantum mechanics was created in 1925 and has been, in the words of Einstein, our most successful physical theory, but there’s still no consensus on how to understand it. What it means. What does it mean? What picture of the world does it give us?

It’s a different situation from general relativity. There is consensus in the scientific community about the picture of the world that general relativity gives us. There is no consensus on the picture of the world that quantum mechanics gives us. There are different points of view. One point of view is that even asking that question is a waste of time and we shouldn’t bother.

But amongst those who think that it is a genuine, an important physical question, and I include myself in that category, there are different opinions. So, what interested non-experts are picking up is that there is disagreement, there’s controversy, there are different points of view, and there are many I would have to say contradictory statements made by physicists about the nature of quantum mechanics.

I’m surprised that anyone would think that there are no opinions in science. How can anyone get that impression? I mean, science thrives on debate and discussion and disagreement.

Even an individual scientist, if you look at what they say, their work… that develops over time. People’s later work and statements can disagree with their earlier work and statements. So, as a community we’re constantly, constantly debating and arguing with each other.

It’s the way science works, and also, it’s the strength of science. Individuals can always be wrong. In fact, we’re wrong a lot of the time, but the community as a whole advances because we can reach consensus. We have to persuade each other. We have to convince each other that the evidence for something is strong enough that we change our opinion, and that’s the strength of it.

When I was a young girl and young student, I was very interested in maths. I wasn’t too interested in physics at school, and I went to university to study maths. Then, in my third year, I learnt about general relativity, and I loved it.

I’ve loved it ever since, and it’s been the rock on which I’ve rested my intellectual journey. I had the opportunity to teach it to my undergraduate students and it was a joy, a privilege and, yeah, it was my dream teaching experience.

So, I came to physics late in life, I suppose, in the sense that it was only while I was an undergraduate student that I started to be interested in physics.

Quantum gravity always seemed to me to be the most fundamental question that one could ask. I loved general relativity, but I could see that it didn’t accord with our understanding of matter. So, I wanted to know, and still want to know, how to make that work. How to reconcile the quantum nature of the world with our understanding of gravity.

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