Research Fellows Directory
Dr Andrew Pontzen
University College London
The universe today (the part of it which we can actually see) contains hundreds of billions of galaxies – each of these is a clump of gas and perhaps hundreds of billions of stars. But rewind 13.75 billion years to the big bang, and the universe was much smoother: there weren’t any stars, and the gas was spread out almost uniformly. The ‘cosmic microwave background’, light left over from those early times, lets us see this directly.
So what happened to the universe? Why did the gas clump into galaxies? And where did the stars come from?
We think we have a partial answer to these questions. Gravity, a force which pulls every piece of matter towards every other piece of matter, is the key. It dictates that all things tend to clump together given enough time. Any regions of the early Universe which were slightly denser than their surroundings end up being very much denser. This makes big clumps of matter – in other words, galaxies. On smaller scales within the new galaxies, the same process creates stars, balls of gas which are dense enough to ignite nuclear fusion.
However creating galaxies and keeping them glued together requires a certain strength of gravity. When we calculate the expected gravity generated by the matter we see, it’s simply not enough. So either Einstein’s laws of gravity are wrong or there must be more matter than we can see directly. In a remarkable leap over the last few decades, astronomers invented the idea of ‘dark matter’, extra mass which keeps galaxies glued together through gravity – but which cannot currently be seen or detected directly.
My work focuses on understanding dark matter, and how the visible universe helps us to understand it. This is essential if we are to connect what our expanding knowledge of the night sky to fundamental physics experiments performed here on Earth. Ultimately it points us to a fuller understanding of the basic building blocks of reality.
Interests and expertise (Subject groups)