On Monday evening, I gave a big bang talk to the Harvard Graduate School of Arts and Sciences. I really like the way there is a single graduate school for both arts and science at Harvard, what a great interdisciplinary mix. The school has its own activity center, Dudley House ; the house is non-residential but modeled on the residential houses at Harvard, with its own building (Lehman Hall) complete with coffee shop, canteen, senior common room, games room, and a beautiful and quiet library with a fantastic view of Harvard Square. It is served by two faculty masters, an administrative staff and graduate student fellows who organize activities for the School’s 4,000 Masters and PhD candidates. In truth, I spend a good deal of time at Dudley House – perhaps it’s the wide variety of disciplines that makes for such interesting conversations.
Dudley House, home of the Harvard Graduate School of Arts and Sciences
The talk was titled The Big Bang; Is It True? and it was great fun, with a drinks reception, a really nice dinner, a 40-min spiel from me and then almost an hour of questions from the audience. There were postgrads there from history, literature, psychology, philosophy, astronomy and other fields. Apparently, tickets sold out within hours of the posters going up, it shows the interest in the subject.
Of course, no scientist can give a definitive answer to the question I posed. Instead, I laid out a brief history of the discovery of the evidence supporting the big bang model (the expanding universe, the composition of the elements and the cosmic microwave background), followed by an outline of recent puzzles that have arisen from modern studies of the microwave background. I like a quasi-chronological approach to such talks, I think it makes the discoveries and concepts easier to understand, and at the same time it gives the audience a great feel for the surprises nature has in store for scientists. As for truth, the audience can decide for themselves.
You can see the full slideshow at http://coraifeartaigh.wordpress.com/my-seminars/
I really enjoyed the questions and discussion afterward; not for the first time, it struck me that you get very interesting questions and comments from a wide interdisciplinary audience (it doesn’t hurt if they are Harvard PhD candidates). There was also plenty of time to touch on one of my favourite themes; that a great many scientific discoveries come as a complete surprise to the discoverers. Far from being ‘constructed’ in order to support pet theories, scientific findings are often undesirable, unexpected data that no-one knows what to make of at first – an aspect of science that proponents of the social construction of scientific knowledge often fail to address, in my view.
All in all, it was great to interact with postgrads from so many different disciplines, I wish I could do this more often.
One of the most challenging questions came from Prof Sam Schweber, a well-known Harvard physicist and historian of science. Sam couldn’t make the talk, but he emailed me his question: What happened before the bang?
I think the answer is twofold:
1. The standard answer is that the big bang model is situated within the context of general relativity, the modern theory of gravity. Since relativity predicts that space and time form part of the universe (and are affected by motion and by mass for example), we expect that time is born at the bang along with everything else – there is no ‘before’ just as there is no north of the north pole.
2. However, cosmologists are less cocksure of this answer nowadays. This is because fundamental problems in describing the moment of the bang (the singularity) have, far from going away, got worse. The problem is due to the inapplicability of the modern theory of gravity to phenomena on the atomic or quantum scale i.e. due to the absence of a successful theory of quantum gravity. Since we have no real way of modeling the singularity, we cannot rule out the prospect of exotic phenomena such as multiple bangs. The problem is compounded by the fact that, while recent observational evidence offers support for some type of cosmic inflation close to the birth of the universe, there is (so far) no way of selecting a particular model of inflation – which leaves the door open for models such as the cyclic universe. In other words, we cannot rule out the possibility of a ‘before’ until we have a clearer picture of what happened at the bang itself.