Rising Stars - Alternative Universes
This week's Rising Star is physicist Andrew Pontzen...
If you've heard a recent video or television discussion about cosmology you might have heard mentioned that we live around the sun: a single star in a galaxy of 100,000,000,000,000; that a galaxy in turn is just one of billions of other galaxies visible to us and that the vast spaces between these galaxies are constantly expanding. You may also have heard that to fully explain measurements of all this we need to invoke little understood and mysterious ideas like dark matter and dark energy. Most cosmologists work on ideas like these which is understandable given how much there is still to comprehend but to introduce you to my own research we need to gloss over these problems and think about things differently.
It's often pointed out that if the laws of physics differed in the most minute way we, as humans, simply couldn't exist. But even give a certain set of physical laws our existence in the universe is only assured by the initial conditions. Let me explain what I mean by that. Let's say you have a pendulum. If you pull back the bob a long distance and then let go it's going to swing back and forth. On the other hand if you carefully put the bob right in the centre of the swing and then let go it just sits there, stationary. It's the same physical system but we see a different behaviour depending on how you start it. The entire universe is similar. It seems possible for it to start in different ways and only if it starts the right way does it produce life like humans later on.
As it turns out this means that shortly after the beginning of time the universe has to be highly uniform. One part has to look much like any other except for tiny ripples which eventually grow into galaxies. But what would have made it look like that and what dictates exactly how big those ripples are and what form they take? These are questions to which there are no known definite answers, only possible explanations which themselves are riddled with further difficulties. My own current work looks at types of ripples that might not be ruled out in all of these possible theories. We know from observations these ripples were not present. So I'm working on universes which are never going to agree with what we actually see. The idea is that this may shed light on why the universe is like it is and isn't like it isn't. It's a small part of a large jigsaw but in optimistic moments I hope it will help us fit other pieces around it.