What I Learnt – “Why are we here?” by Sam Gregson

Last week I went to a talk about one of the universe’s biggest mysteries – why do we exist? Or more specifically in this case, why is there still matter around?

We believe that in the Big Bang equal amounts of matter and anti-matter should have been created, but when matter and anti-matter meet they annihilate each other to produce light. Not long after the start of the universe, all of the matter and anti-matter should have collided again (aided by the fact that each anti-matter particle created would have the opposite charge to the matter particle created with it, and so they would attract each other), leaving the universe filled with light, but not matter. Yet there’s matter all over the observable universe! How did this happen?

Sam Gregson works at the LHCb experiment, part of the Large Hadron Collider at CERN, which is dedicated to trying to answer this question by comparing the decay of some matter and anti-matter particles created by the particle accelerator there, specifically ones containing “bottom” or “beauty” quarks, hence the b in the name. This is a topic I know a fair bit about, and one Sam’s talked about in a few places such as on this radio show (from about 45 minutes in) and will hopefully be talking about again on my online show Sci Cam (he gave a Beginner’s Guide to Particle Physics on a previous episode), so I won’t go into detail here about the main gist of the talk. Instead I’ll mention a few little things that I didn’t actually know before Sam’s talk.

  • Each country involved with CERN pays the same percentage of its GDP towards the costs of CERN.
  • Everyone involved with each of the four experiments at the LHC gets their name on every paper written using data from that experiment, because it would be too hard to work out who was responsible for each bit of code used in the analysis.
  • Half of the data from proton collisions is effectively lost because detectors are only built on one side of where the beams cross and the particles collide, for reasons of cost. The detectors completely surround the beam line, but they are all slightly along the beam line from the collisions.
  • When the researchers are working on coding up their analysis, they have to add a random amount to their final answers until the way that the analysis works has been checked and finalised so that they won’t be able to (consciously or not) bias the results towards their desired result.

It sounds like we’re starting to see some differences between matter and anti-matter in experiments, but we’re not seeing  enough difference to explain the abundance of matter we observe in the universe. There’s still work to do, but at least we can be glad that even if we don’t quite yet know why we are here, we are here and learning more about the universe.


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