The big unanswered questions in particle physics

Chris - Do these other entities like dark matter and dark energy, are they using the Standard Model for their existence or are there bolt-ons that go with our Standard Model, which then explain them? So when we say the Standard Model is complete, is it complete but there are extra bits that can be bolted on the side? Or are they just using what we already know about and it's just we need to find out how they use what we already know about, but in a novel way.

Lyn - The Standard Model is complete in understanding the particles and their interactions that we have. But for instance, gravity doesn't fit into the standard model. Gravity is the oldest force that we know about, but the least that we know, the most mysterious. It's 23 orders of magnitude weaker than the strong forces of the Standard Model. There have been many attempts to make a theory of what's called quantum gravity, which would then integrate gravity into the Standard Model. So that's one thing. Dark matter and dark energy are totally mysterious. We don't have a clue what they are. One theory for dark matter was a very elegant one where, just like we have a mirror world of of matter and antimatter that was predicted, there should be a mirror world of supersymmetry that each of the particles that we know would have a mirror world of particles with similar properties, which we could create in our accelerator. And the lowest mass particle in that supersymmetry could be the dark matter. Now the LHC has discounted that, so it's not only discovered the Higgs boson, it's made one contribution to eliminate what was a very attractive explanation of dark matter. So we are back to square one with dark matter. Dark energy is even more mysterious. It looks like at very large distances there is anti-gravity. And dark matter and dark energy make up about 90, 95% of our universe, we understand 5%, there is 95%, which is a complete mystery to us today. And that's a pretty sobering thought.

Chris - It is indeed. Now, when you are not thinking about these sorts of challenges, which are going to keep physicists very busy for a very long time, what do you like doing to unwind?

Lyn - To unwind <laugh>? Well, when I was younger, I did a lot of sport, of course, I played a lot of rugby, which is a subject, which I do not wish to talk about at the moment. Now, of course, I'm my age, I can't play rugby or squash or anything like that. I play golf which is good in this region. You can only play golf for about eight months of the year because of weather conditions. I've stopped skiing now, but I was skiing for 40 years, which was great. So mostly I sport, but also, I read a lot, I chair committees. One of the most interesting committees that I chair is in the European Southern Observatory, where the headquarters are in Munich, but the telescopes are in Chile, and are building a thing called the Extremely Large Telescope. And I chair their advisory committee. This telescope, you know, any normal telescope we'd have a mirror. The biggest mirror on a telescope is eight metres or something like that. The Hubble has got an even smaller mirror of I think six or even smaller. This telescope has a mirror 38 metres in diameter. Not a single mirror, but a composite thing. So, I do things like that and there's a few other projects as well that I help with. So, I try to stay active and I quite enjoy it. It's good to be able to give advice without having the responsibility on your shoulders.

Chris - A bit like grandchildren. Then people often say they like grandchildren because you can give 'em back. But <laugh> in closing, Lyn, what scientific question would you really like to see answered if one could be answered in your lifetime?

Lyn - Well, for me it's very clear: what is dark matter? I mean, it's absolutely sure that it's there, that there are several different ways of observing its existence, but nobody has got the slightest clue what it is. That's the one, that's the first question that I would like to see answered.