Jonathon Davis is a final year PhD student at University College London working in particle astrophysics. Jonathon works on the ARA experiment deployed at the South Pole which is designed to detect high energy neutrinos using radio signals.
You can be the cleverest guy in the world but if the theory doesn’t match experiment then it’s wrong.
On becoming interested in science
One thing that comes to mind is sitting in a lesson in my secondary school and we were being taught the physics GCSE and I really enjoyed learning about how the world worked. And my teacher…well, I’d covered all the work already, I was a bit of a nerd and was quite good at science back then, and he introduced me to the concept of special relativity, which is one of the theories that Einstein is most famous for. And that just kind of blew my mind, trying to work out this kind of weird – almost illogical from the point of view of our every day experience – way of looking at the world and the geometry within the universe. And I just thought that was really neat. I thought it was really cool that you could describe things in this kind of, really, almost abstract way but be able to predict things and make a sort of self-consistent theory that described nature really elegantly.
On choosing astrophysics as a career
I’m interested in the fundamental forces in nature and why the world works the way it does and so particle physics is concerned with those things. Astrophysics is also concerned with the fascinating universe that we live in so I kind of fell into the area because I was offered a PhD on a specific project that fulfilled both of those things. So the experiment that I work on is in a kind of weird place. Physics experiments should be, I mean, there’s a kind of romanticism where people try weird and wacky things and maybe you see something really interesting. Maybe you don’t but part of the fun is trying to do physics in a kind of extreme environment or a weird way.
So I work on an experiment called the Askaryan Radio Array, which is an experiment where we are trying to build a neutrino telescope in the deep, radio transparent ice at the South Pole in Antarctica, which is a fun place to do physics. The idea there is we’re trying to see, um…neutrinos are these kind of fun particles, they’re almost ghost-like, so travel through matter, through you or I, or the ceiling in this room, or the floor, unimpeded without us ever knowing they were there. And the only way we are ever really able to see that particles exist is if they sort of bump into something or produce some radiation. So if they travel through stuff there’s no way of seeing them. So the idea is to produce a massive block of stuff that hopefully a neutrino will knock into something there. You know, the bigger your net, I guess, like a fishing net fishing for neutrinos in some sense, the more the chance there is of a neutrino hitting something and you being able to observe it.
The idea for the experiment was originally conceived by a Russian-Armenian, a guy called Askaryan, who predicted that you could observe neutrinos interacting in all sorts of interesting materials and his examples were ice, sand and salt. And in these materials you could see some radio waves that are produced when the neutrinos slammed into this material and hit a nucleus in there and everyone at the time thought this was a weird and wacky idea and no one really paid any attention to it until about twenty years ago when people were interested in the flux of neutrinos. So, neutrinos arriving from places other than our solar system, so from very different places in the universe, some of the most extreme objects in the universe like the supermassive black holes at the centre of galaxies and things like this, and there was an interest in that. In order to see them, they’re very rare and they don’t really interact with much, so the current method, at the time, of detecting neutrinos was using these water detectors where you look for a flash of light in water as the neutrino hits something, were just too small to be able to see at this very, very low flux so some pioneering guys tried to develop techniques to detect neutrinos in ice because there’s so much ice in Antarctica. And this kind of led to a series of efforts in Antarctica to try and use these radio techniques to try and detect neutrinos. And ARA is kind of the modern day front runner in terms of trying to detect this neutrino flux.
So we’re in the process of building the experiment at the moment, so you go from the theory of working out whether or not it’s conceivable, or feasible, to detect these neutrinos, how big your detector would need to be, ah, so you do all sorts of simulations as to how likely a neutrino would be to interact in the ice and also how many of them are there arriving at earth and then you begin to work out whether or not it’s an engineering challenge that you can overcome. You know, it’s very difficult to do the things that we want to do, like get to the South Pole, get instrumentation there, drill holes in the ice and deploy our detection equipment. And the things I personally work on are working out a way of recording interesting information, so recording what we call events, which are little snap shots in time that are likely to have a neutrino interaction in them. The way I describe it to my friends is, we have these radio antennas which are like our ears, which are listening to, for example, any noise, but our brain is able to pick out conversations going on. So if you’re in a busy café you’re able to hear what people are saying to each other and, more specifically, your brain can pick out an interesting conversation, like the conversation you’re having with a friend, so what I’ve been working on, in that analogy, we have a thing called a DAQ, which is some whizzy electronics which is our experiment’s brain and it decides from all this noise, is this an interesting conversation or is this a kind of neutrino and should I record it for a scientist to look at later and decide, or make some more interesting decision about whether or not it’s a neutrino or whether or not the conversation was interesting.
On the goals of physics
For me, physics is about trying to explain phenomena in nature in a coherent and elegant way and the current goals, say, for example, particle physics or astro particle physics, are to explain nature in regimes that we’ve not been able to observe before. So it’s kind of pushing the boundary of what we know. So, for example, we all know what happens when you throw a tennis ball at a speed that your arm can throw it through this room, you know, you can imagine it will travel along, it’ll hit someone and it’ll hurt and it’ll drop down as it travels because of gravity. But, you know, what happens if you throw the tennis ball faster than you can throw it with your arm? And then you ask the question what happens if you can throw it faster than that and is there some new physical phenomenon that you could observe in that condition. So I feel that that’s the kind of goal for particle physics at the moment. So at CERN they’re trying to look at collisions between protons at energies that’ve never been observed in these quantities before and try to understand physics at the associated increased energy level that’s available in this collision that we’ve never been able to explore before and it’s a fundamental understanding of how our universe works.
On the limits of special relativity
Special relativity is concerned with the geometry of space and it basically says that instead of thinking of the world as being a 3D world in which we have three dimensions, so forwards and backwards, left and right, and up and down, we need to incorporate time into that description as well. So we move into a kind of 4D view of the world. One of the upshots of that is that there’s a fundamental limit to which objects can move in that world and that’s the speed of light in a vacuum and so nothing can travel faster than that speed in special relativity and any object that has a mass that is greater than zero cannot get to that speed. So there’s a kind of fundamental limit. You can give something a kick, you can give it as many kicks forward and increase its speed as much as you want, but it will never actually reach the speed of light.
Now, one of the things that could happen [if we went beyond it] would be a lot of press coverage. It was last year, or maybe the year before, the OPERA experiment in the Gran Sasso Laboratory in Italy, made an announcement about the measurements they’d been making about the speed of a fundamental particle called the neutrino. And they announced that they thought they’d seen neutrinos that were faster than the speed of light and the whole scientific community erupted, you know, it was a really big deal because it’s very difficult to produce a theory that is consistent with all the measurements we’ve made in nature and that is the fundamental benchmark for whether or not for whether or not…you can have the cleverest theory in the world, right, you can be the cleverest guy in the world, but if the theory doesn’t match experiment then it’s wrong. It’s very difficult to be able to make theories that allow for that to happen. But, if we were able to travel faster than the speed of light we would essentially be able to go backwards in time which is a kind of cool, and weird, thing. And remember how much I said learning about the theory of special relativity seemed like a kind of abstract concept to me as a fifteen year old boy in secondary school, the idea of being able to travel faster than the speed of light, and the implications in terms of causalities, the causation of events, so, you know, what came first, did I kick the ball and it disappeared off or, you know, that is even more mind-blowing, which I guess is part of the reason why the scientific community kind of erupted when those results were announced because that kind of thing is earth shattering in terms of the physics world and that’s when fun stuff happens because people get to postulate all sorts of weird and wonderful things to try and describe this new phenomena.
It shows how difficult these modern particle physics experiments are to do. It involves hundreds, if not thousands of scientists trying to build enormous machines that look like something from a 1960s version of the future. Yeah, it’s very difficult to make these kind of measurements and it kind of shows the kind of rigour that people need to use in making announcements and probing science. But it also gives you a fantastic respect for people who are able to do things like observe the Higgs Boson in an enormously complicated pair of experiments at CERN and they’ve managed to do it in a consistent and coherent way which is just, you know, astonishing.