95% of the Universe is missing

Professor Malcolm Fairbairn is a member of the Theoretical Particle Physics and Cosmology Research Group, Kings College London. His research lies at the boundary between cosmology, particle physics and astrophysics. In particular, he is interested in dark matter, dark energy, cosmological inflation and particle astrophysics. He has been awarded an ERC consolidator grant running from 2015-2020 to study dark matter and particle physics in the early Universe.

Richard Bright: Can we begin by you saying something about your background?

Malcom Fairbairn: I am originally from Wigan in the northwest of England, I did my UG and PhD at Birmingham, Cambridge and Sussex then I did postdocs in Brussels, Stockholm and at CERN before coming to King’s College London just over a decade ago. I am a theoretical physicist (so I do calculations rather than experiments), and I work at the intersection of Particle Physics, Astrophysics and Cosmology. I spend a lot of time thinking about the nature of dark matter and how we might learn more about it or even better, discover what it is precisely.

RB: You are involved in a season of events, ‘Dark Matter: 95% of the Universe is missing’, taking place at the Science Gallery, London. Can you say more about your involvement in this and what this season is hoping to achieve?

MF: I had two main roles.  The first was as curatorial advisor to the curators who were putting the exhibition together. The team has evolved a lot because of maternity leave and changes in personnel. When we started the core was myself, Jen Wong, and the main curator Sandra Ross. The old director of Science Gallery London, Daniel Glaser, was also involved in the motivation for this season. There was also a bigger advisory pool of artists but in the early days, Sandra and myself formed the core of putting the exhibition together under moderation by Jen. My main job, the guess the role my personality drove me towards, was to be open minded to the different kinds of artistic interpretations that Sandra would try to discuss and develop, the different threads and kinds of ideas she wanted to develop. However, when I felt she was moving too far away from anything even remotely related to the science that we do, I expressed myself quite clearly. Sometimes we had quite deep differences of opinion. It was not easy for me to work with Sandra and it was not easy for her to work with me, but I am proud of what emerged and I am proud to now call Sandra a friend.

RB: What is dark matter and how is its existence and properties inferred?

MF: We think Dark Matter is some mysterious particle which we think is zooming around, through the earth, through rooms, through the air, through whatever environment you are reading this. I say “zooming” because we think it is moving at several hundred kilometres per second. We think it is there because when we look at the motion of objects such as stars and galaxies, we can only explain how fast they are moving due to some extra gravitational acceleration created by some matter which must be there but which we cannot see.

From a physicist’s point of view, dark matter is rather simple, actually much simpler than normal matter. Normal matter is governed by several forces, gravitational force, electromagnetic forces and the nuclear forces, so it sticks together to form different elements and molecules and emits radiation to cool down and stuff like that.

The only force that dark matter appears to obey is gravity. In particular, it doesn’t emit any light and you can’t bounce light off it, so it’s transparent. Perhaps we should have called it invisible matter, but because we deduced its existence by looking into the night sky and because it doesn’t emit any light, we ended up calling it dark matter.

We can tell it doesn’t stick together or emit any invisible light or even collide with itself by mapping out its distribution in space due to its gravitational effects.

RB: Are there differing theories that aim to provide an explanation for dark matter?

MF: There are lots of different kinds of ideas as to what kind of particle the dark matter could be, and lots of different experiments trying to find the dark matter. Some of physicists favourite theories are the kinds of particles that explain some other complicated problems in physics, such as why there is more matter than anti-matter, but there isn’t really any reason why dark matter should do this. Some physicists think that there is no particle at all, but rather that we have misunderstood the force of gravity on huge scales, but most physicists, including myself, think that some particle which emits no light is the culprit.

RB: Dark Energy is pushing the universe to expand faster and faster. What is dark energy?

MF: Haha! What is dark energy? Well, this is the trillion dollar question. In some sense dark matter is quite boring in comparison, dark matter is just like normal matter that you can’t see, and as the Universe expands it gets spread out. Dark energy is an energy field which doesn’t get spread more thinly as the Universe expands, as if it is being constantly created from nothing. This sounds impossible but we think such exotic forms of matter and energy could exist in the Universe. It turns out we seem to require both dark matter and dark energy to explain the Universe, which is very unsatisfactory for science, but honestly, if you try to live without either it is very difficult to explain the observations.

RB: You collaborated with artists, Carey Young, Agnieszka Kurant and Aura Satz, who are taking part in the Science Gallery, London exhibition. Can you say something about your involvement in these collaborations?

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