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Professor Fay Dowker


 

Fay Dowker is a cosmologist and professor of Theoretical Physics at Imperial College London.  As a student she studied wormholes, was awarded the Tyson Medal and completed her PhD under the supervision of none other than Professor Stephen Hawking.  She is currently conducting research in the areas of quantum gravity and casual set theory.

So, quantum gravity is my day job, that’s what I do.

On getting interested in science

I wasn’t interested in science at all when I was a kid.  I had a strange kind of monomania.  I just liked maths.  And, apart from reading books, which I also liked, I just wanted to do maths and more maths.  In fact, I did double maths and physics A Levels and I was kind of irritated I had to do the physics.  If there had been triple maths I would’ve done that.  And then I did maths as an undergraduate and while I was…during my undergraduate degree I kind of became more interested in the applied maths and theoretical physics courses and I found that the pure maths was kind of too hard for me so I moved in the theoretical physics direction and did a theoretical PhD.  So I’m really not a proper scientist at all!  I’m just a sort of failed mathematician in disguise!

On being a skeptic of inflation theory

There is a scientific judgment and there is my wishful thinking, so let me give you the wishful thinking first.

Inflation is…the idea is that it’s an epoch in the history of the universe that took place before our current epoch, so it set up the hot dense conditions of our current epoch but took place during a time in the universe when we can approximate, or describe, spacetime as a smooth fabric.  So inflation doesn’t…or rather it assumes that space-time is described by Einstein’s theory of general relativity, that’s the basic assumption, one of the basic assumptions that goes into inflationary theory.  And the whole idea of inflation is that whatever was around at the beginning of inflation is inflated away.  Everything becomes very, very dilute and so it blows away the physics that was around at the very beginning of the universe. So, what it means is we can’t see back beyond inflation, before inflation, to that earlier epoch.  And the earliest epoch is when space-time itself breaks down, when the conditions in the universe are such that we can’t describe space-time as a nice smooth fabric anymore and we have to use a theory of quantum gravity.  So, quantum gravity is my day job, that’s what I do: I’m trying to find a theory that incorporates and extends Einstein’s theory of gravity and the quantum description of the matter in the universe.  And the beginning of the universe is exactly the epoch when that theory is important.  When we need that theory to describe what’s going on.

You don’t need it for intense for inflation.  And inflation is a blockage to seeing back to a period in the universe when those effects could show themselves.  That’s the wishful thinking.  I hope that inflation is not right, because if it were then it hides the quantum gravity era from us and as a… because that’s what I work on, I want to see back to those earliest times.

Then the scientific judgment is that…it’s something that’s a personal thing, to me as a scientist, and other scientists obviously disagree, when I look at the theory of inflation and the predictions it has made and the evidence for it, I don’t think that that evidence is strong enough to say, ‘Yes, I am sure that inflation took place’.  It’s a very interesting idea, it’s a good idea and the more it’s tested and the more predictions it makes that are verified the better, and the stronger, the evidence will be.  But at the moment it’s simply that I don’t consider the evidence to be strong enough. 

On evidence for or against inflation

Well, one of the problems with inflation is that there are very few alternatives to inflation in explaining those initial conditions, that initial state, that hot dense state and the fact that space seems to be so very flat.  So those are very unusual and surprising initial conditions.  So, at the moment, there are not that many competitor theories to inflation and so…I think our job as scientists is to come up with more ideas that could compete with inflation for explaining that.  So I think one of the reasons that inflation has been sort of taken up by many cosmologists and they really think that it did happen is because they haven’t seen anything better, anything that could be more powerful, anything more explanatory.  And for that you need this theory of quantum gravity, something that’s going to explain why the initial conditions arose from a more fundamental dynamic of space-time in which the dynamic is inherently quantum mechanical.  So I think what we would need truly to be able to judge inflation and say yes or no to it would be competitive theories which are…or really do take quantum effects into account when discussing gravitational physics.

On the concept of space-time

That’s a very good question, and I can give you the answer that current physics gives us and then I can give you my speculations about the future, about what our deeper understanding of it is.

So our best theory of space-time is Einstein’s theory of general relativity and that’s both a theory of space-time and a theory of gravity.  And space-time is an entity, it’s a material and it’s very different from the kinds of materials we were used to in physics up until the beginning of the 20th century.  So most materials in physics we thought of being, of existing in space, so they have a three dimensional quality to them.  So, um, the matter has extent in three dimensions.  But space-time is an entity that doesn’t have extent in three dimensions but is four dimensional in extent.

Now, it’s true that that is a difficult concept but in physics you always bootstrap up your understanding.  So you understand a simpler situation first but then you say, ‘Ah, but this situation is like that but just one more’ or ‘Like that, but ten times bigger’, but the intuition that is required to conceive a four dimensional thing is difficult and it’s not something that I can personally claim to hold in my head, that I actually see four dimensional things in my head, but I just bootstrap up my understanding from, well, I know what a two dimensional thing is, a surface which has two dimensions, it means it has…you can draw onto a coordinate grid onto a two dimensional surface and to locate any particular point in that surface I need two coordinates.   

A three dimensional thing, I could imagine drawing a three dimensional grid and to locate any point in it I would need three numbers.  You know, I’d need the three dimensional coordinates to locate where it is.  So a four dimensional thing is like that.  It’s something which you need four sets of…four coordinates to locate it.  And I can’t point to it on a piece of paper and no-one can, but you just say, well, it’s like that but I just add one dimension.  So it’s a four dimensional substance and the amazing thing is that we, you and I, are also four dimensional substances.  In general relativity that’s the picture of the world we have.  It’s not just that space-time is four dimensional but everything is four dimensional.  Everything that exists exists, along with space-time, in a four dimensional way.

So you are not just a three dimensional thing that exists at different moments of time, evolving into the future, you actually are a four dimensional world tube or world volume, sweeping out your history, and that’s you.  The basic, most fundamental current description we have, according to our best science, agreed upon science, is that you’re a fully four dimensional thing.  You don’t have an existence in space, with time ticking away, you’re actually a four dimensional world tube and that raises an immediate question of why you experience time passing.  So if you’re just this world tube, why is there this special moment of now?  And I think that is one of the questions we don’t…I mean, at the moment, we have no particular answer to that question.  It’s one of the questions that may be answerable in the future.  So, which brings me on to my particular approach, my work, which is to try to understand space-time at a deeper, more fundamental level and the hypothesis that my research is based upon is that space-time, this four dimensional fabric, is actually not smooth and continuous, but is composed of individual atomic units.  So, space-time itself is granular.  It’s made of grains of space-time, or atoms of space-time, and the smoothness and the continuity that we experience is just because we’re very large and the scale of the granularity of the atomicity is so very small.  Like, you experience water as a fluid, it seems continuous and you don’t see any evidence of its discreteness, that’s because we’re large and we’re looking at it at a large scale, but when you probe its microscopic structure then it’s actually made of atoms and molecules.  So it’s the same kind of concept, yeah.

On testing space-time theory

This granularity is on incredibly tiny scales.  Much smaller scales than we can probe in any conceivable – or at the moment conceivable – experiment that we could do on Earth.  But the universe is a very large place so one idea of testing, this idea of testing atomic space-time is to see what kind of effects this underlying granularity of space-time would have on matter that’s propagating in space-time because even though the effects could be very tiny, they could build up over a long trajectory.  So something that comes from the edge of the universe could be affected by the granularity in such a way that we could actually detect its effects because it’s come through so much space-time that these really minuscule effects could build up. So that’s one idea that we’re working on.  We have some models that propose different effects that space-time granularity could have on propagating particles, on physical entities like the polarisation of photons.  We have models which describe effects that this granularity might have on these quantities and then you can look at the data and see if they show themselves.  So, so far the data is consistent with there being no effect but we can look harder, we can try harder to get more detailed data.

And then the other success that this theory of granular space-time has had was that it was actually used to make a prediction of what people call the effect of dark energy, so the accelerated expansion of the universe was actually predicted using a heuristic argument from this theory of granular space-time in the late eighties and early nineties, so before the supernovae experiments which confirmed it in 1998.  So this idea of atomic space-time has actually had one success in terms of making predictions that were verified.

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