I was at a very interesting event in Dublin yesterday evening; an informal panel discussion for the public on ‘Angels, Demons and Antimatter’ hosted by the Royal Irish Academy and The Irish Times. It’s great to see the Academy hosting this sort of event as it helps to bridge the gap between science and the humanities (the ‘two cultures’ famously described by C.P. Snow).
The event was ably chaired by Dick Ahlstrom, veteran science editor ofThe Irish Times, and the panel boasted four heavy hitters from the world of particles physics: Alex Montwill, Ireland’s best-known particle physicist and renowned communicator of science: Ronan Mc Nulty, leader of the experimental particle physics group at UCD, a group that have a major involvement with the LHCb antimatter experiment at CERN: Tara Shears, lecturer in physics at Liverpool University, also heavily involved in the LHCb experiment: and Paul Bowe, the Irish physicist who is technical director of ALPHA, the anti-Hydrogen experiment at CERN.
In his introduction to the event, Dick Ahlstrom sensibly asked the audience how many had seen the film – only about a third, which confirmed my view that people are interested in particle physics for its own sake, film or no film. Tara Shears then kicked off with a pithy summary of the film, explaining that a ticking bomb made of antimatter provides the timeline of the unfolding story. Then it was over to Alex to give a brief introduction to the phenomenon of antimatter. He did this in exemplary fashion, starting with the prediction of antimatter from the Dirac equation (…“Dirac was not the sort of scientist to brush extra solutions that seemed to have no corresponding physical reality under the carpet“) and proceeding to the experimental discovery of the positron in 1932 (if you want details on the discovery of antimatter, see post here). The discussion then honed in on the nature of antimatter, how it occurs in nature and how it is produced in minicscule amounts in high-energy accelerators.
The panel then turned to one of the great mysteries of physics – why is our universe primarily made of matter and not antimatter? Ronan gave a brief overview of charge symmetry, parity symmetry, charge-parity (CP) violation and the Sakharov conditions ; these are three conditions that theory predicts must have existed in the early universe for the current asymmetry of matter and antimatter to develop.
Charge and parity operations: note that the final quadrant is not identical to the first
This led nicely to a discussion of the relevance of high-energy physics to cosmology. I was very pleased this came up, as it is not always obvious to the public that, as well as studying the fudamental nature of matter, high energy accelerators offer a direct glimpse of the very early universe by recreating the energy conditions that existed shortly after the big bang (a point that is often missed by critics of the big bang model).
Paul Bowe then discussed the production of anti-hydrogen at CERN (an atom of anti-hydrogen simply comprises an anti-electron orbiting an antiproton, see previous post on this). He gave a brief overview of the ALPHA experiment – the production of positrons, the production of antiprotons, the mixing trap etc.
Schematic of hydrogen and anti-hydrogen atom
A picture of the experiment reminded me that while I find the discoveries of particle physics fascinating, I’m happy to leave the experiments to others!
Image of ALPHA experiment
Paul also addressed a question I was asked a while ago – Do we expect the spectrum of anti-H to be the same as that of H? If I have understood correctly, the answer is yes (since the electromagnetic interaction between the anti-proton and the positron should mirror that between the proton and the electron). If not, the spectrum of anti-H will have major implications for our understanding of CP violation.
The second part of the discussion dealt with Hollywood’s take on antimatter in Angels and Demons. It started with a clip from the film, the scene where Dr Vetra tries to explain to the destructive potential of the antimatter bomb to the authorities, advising that they evacuate the Vatican city forthwith.
Of course, the panel were quick to point out the unfeasability of the bomb, as mentioned in the post below: because of the difficulties of creating even a few atoms of antimatter in particle accelerators, it is simply not possible to create a bomb made of antimatter (or to use it as an energy source). And if such a bomb could be made, the trap container would be gigantic, not the little package portrayed in the film. However, I was pleased to hear that Tara (and I think the panel as a whole) felt Brown’s plot was acceptable cinematic license and made for a good story.
A small container for an antimatter bomb?
In keeping with the informal nature of the event, there was a lengthy question and answer session after the panel discussion. Some interesting questions were;
1. Is it possible there is plenty of antimatter in our universe today, in the form of distant galaxies made of antimatter?
I think the answer was that this is a real possibilty, but a basic asymmetry between matter and antimatter is still implied.
2. Does the neutron have an antiparticle?
Yes, because the neutron is a composite particle – the anti-neutron is made up of anti-quarks etc). Ronan pointed out that the question Does the neutrino has an antiparticle? is much more interesting and the subject of much debate.
3. What is the relation between antimatter and dark matter?
None – dark matter is the name we give to matter that has a gravitational effect but does not interact with the electromagnetic force. However, whatever particles make up dark matter presumably have anti-particle counterparts!
4. My question: Why did Dan Brown choose to introduce the topic of antimatter to the story at all, wouldn’t TNT have done?
My own view is that he was anxious to include cutting edge science, as the relation between religion and emerging science is a major theme of the novel. However, Tara had a better answer: novelists write about what they find interesting and Brown happens to be interested in particle physics! Apparently, he even visited CERN in 1990. QED.
All in all, this was a very interesting an informative event, a treat for anyone interested in particle physics or indeed are the public perception of physics. If there was one sour note during the evening, it was Dick Ahlstrom’s observation that “ the UCD contribution to the LHCb experiment really occurs through the back door” as Ireland is not a member of CERN. This is a sad situation that we have touched on many times before, so I’ll leave it for now. As for Dan Brown, long may he continue to include science in his bestselling novels.