Tag Archives: Trinity College

Cosmic fingerprints at Trinity College Dublin

I was back in my alma mater Trinity College Dublin on Monday evening in order to catch a superb public lecture, ‘ Fingerprinting the Universe’ , by Andrew Liddle, Professor of Astrophysics at the University of Edinburgh. The talk was presented by Astronomy Ireland, Ireland’s largest astronomy club and there was a capacity audience (despite the threat of snow) in the famous Schrödinger lecture theatre in the Fitzgerald Building, Trinity’s physics department.

march2013

Professor Liddle was introduced by David Moore, Chairman of Astronomy Ireland, who also presented an update of the club’s recent activities  (David and I participated in a discussion of the life and science of Sir Isaac Newton on NEWSTALK radio station the evening before, you can hear a podcast of the show here). Anyone with an interest in cosmology will be familiar with Andrew Liddle’s seminal textbook ‘ An Introduction to Modern Cosmology’, (not to mention several other books) and the ensuing lecture certainly didn’t disappoint.

An-Introduction-to-Modern-Cosmology-Liddle-Andrew-9780470848340

Starting with a tribute to the work of both Schrödinger and Fitzgerald, Andrew gave a brief outline of today’s cosmology, showing how it has moved from a rather speculative subject to a mature field of study. He attributed this progress to key advances in three main areas: precision observations by satellite, sophisticated theoretical models and high performance computing for both analysis and simulation.

He then described five specific challenges that any successful model of the cosmos must address –  the expanding universe;  the formation of structure (galaxies etc);  the age of the universe; the composition of the universe (baryonic matter, radiation, neutrinos, dark matter and dark energy);  a consistent description of the very early universe (cosmic inflation or alternatives).

As ever, many in the audience were surprised to hear that, while dark energy is estimated to make up about 73% of the mass-energy content of the universe, we have very little idea of the nature of this phenomenon!

In the second part of the lecture, Andrew focused on the cosmic microwave background (CMB), explaining how the study of this ‘fossil radiation’  gives precious information on the early universe,  and in particular describing how tiny non-uniformities (or anisotropies) imprinted on the radiation formed the seeds of today’s galaxies (‘cosmic finger-printing’). There followed a swift description of results of CMB studies by the COBE and WMAP satellite missions, with a reminder that more recent measurements by the European Space Agency’s   PLANCK Satellite Observatory  will be announced next week. He also reminded us how, amongst other triumphs, the theory of inflation gives a very satisfactory explanation for the origin of the variations in the background radiation terms of quantum fluctuations in the very early universe. This link between inflation and galaxy formation is often under-stated in the popular literature; in answer to a query from me question time, Andrew confirmed that non-inflationary explanations for the origins of the observed variations in the microwave background have not been very successful. It’s pretty impressive that inflation can give an explanation for the origin of structure, given that this was not part of the original motivation for the theory.

ESA's Planck mission

The ESA’s PLANCK Satellite will report new measurements of the cosmic microwave background on March 21st this month

All in all, a fantastic talk, well worth the trip; afterwards, we all repaired to a nearby pub for sandwiches and further discussion of the universe over hot ports and Guinness…

P.S. In his discussion of the discovery of the expanding universe, I was pleased to see Professor Liddle refer to the work of Vesto Slipher; it seems that recent historical work on the important contribution of Slipher is finding its way into the mainstream community.

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Filed under Cosmology (general), History and philosophy of science

The God particle at Trinity College

On Monday evening, I gave a public lecture on the Higgs boson at Trinity College Dublin. The talk was organised by Astronomy Ireland and I think it was quite a success; 200 tickets were sold and quite a few people had to be turned away.

In the Joly lecture theatre at Trinity College Dublin

How to explain the basics of particle physics to a public audience? As always, I presented the material as a short history of discovery: from the atom to the nucleus,  from protons and neutrons to Gell-mann’s quarks. I also included some theory on the fundamental interactions, right up to the Standard Model,  electro-weak unification and the role of the Higgs field in electro-weak symmetry breaking. Not for the first time, I came away with the impression that the Standard Model isn’t as intimidating for the uninitiated as you might expect. As for physics beyond the Standard Model, the audience seemed to take the hypothesis of grand unification in their stride, and the connection between particle experiments and the early universe struck a chord, as always.

The results  It was a pleasure to present the fantastic results of the ATLAS and CMS teams, first announced at CERN last July. Giving such talks is a lot easier now that the data are publicly available in two beautiful papers on the ArXiv here and here. I gave an overview of the main findings in the context of previous experiments at CERN and at the Tevatron,  and I think the audience got a feel for the historic importance of the result. Certainly, there were plenty of questions afterwards, which continued in the pub afterwards.

The famous bumps ( excess decay events) seen by both ATLAS and CMS at around 125 GeV in the di-photon decay channel

Combined signal (all decay channels) for both ATLAS and CMS

So what about that title? Yes, I did agree to the title ‘The God particle at last’? I am aware that most physicists have a major problem with the moniker; it is sensationalist, inaccurate and incurs a completely gratuitous connection with religion. (Some religious folk consider it blasphemous,  while others misunderstand the term as evidence for their beliefs).

A poster for the talk; naughty

All of this is true, yet I must admit I’ve got to like the nickname; it is catchy and just mysterious enough to cause one to think. I imagine a tired lawyer catching sight of the poster as she walks home after work;  ‘God particle’ might cause a moment of reflection, where ‘Higgs boson’ will not. At least the former expression contains the word ‘particle’, giving the reader some chance to guess the subject. Of course the ‘God’ part is hubris, but is hubris so bad if it gets people thinking about science? Also, I disagree with commentators who insist that the Higgs is ‘no more important than any other particle’. Since all massive particles are thought to interact with the Higgs field, finding the particle associated with that quantum field is of great importance.

So is it found?  CERN Director General Rolf Heuer stated in Dublin, “As far as the layman is concerned with have it. As far as the physicist is concerned, we have to characterize it”. Such characterization has been going on since July. Without question, a new particle of integer spin (boson) and mass 125 +- 0.5 GeV has been discovered. So far, the branching ratios (the ratio of various decay channels to lighter particles) match the prediction of a Standard Model Higgs boson very well. So it looks and smells like a Higgs, and we are all getting used to the idea of the Higgs field as reality rather than hypothesis. (That said, there is still the possibility of spin 1 or 2 for the new particle, but this is not very likely).

All in all, a very enjoyable evening. The slides and poster I used for the talk are available here.  No doubt, some Trinity professors may have been none too pleased to see ‘God particle’ posters in the Hamilton building. Me, I’ve decided I can live with the name if that’s what it takes to get the public excited about particle physics…

Update

Some bloke called Zephyr is upset and accuses me of misleading the public (comments). His point is that I refer to the Higgs as a particle, instead of a quantum field. There is a valid point here; what were once thought of as elementary ‘particles’ of matter are now considered to be manifestations of quantum fields. However, in the business of communicating physics to the public, each physicist must find their own balance between what is accurate and what is comprehensible. My own experience is that people grasp the idea of the Standard Model reasonably well if it’s told as a story of particle discovery (phenomenology). A small amount on quantum theory is ok, but too much soon leaves ‘em bewildered. For this reason, I much prefer books like Particle physics: A Very Brief Introduction by Frank Close to books like Higgs: The Invention and Discovery of a Particle  (Jim Baggot)

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Filed under CERN, Particle physics, Public lectures, Uncategorized