I’m just back from a couple of days up in Edinburgh, one of my favorite cities in the UK. London is bigger, more intense, but Edinburgh is more beautiful, dominated by its landscape—London is New York to Edinburgh’s San Francisco.
I was up there to give the Edinburgh University Physics “General Interest Seminar”. Mostly, I talked about the physical theory behind and observations of the Cosmic Microwave Background, but I was also encouraged to make some philosophical excursions. Needless to say, I talked about Bayesian Probability, and this in turn gave me an excuse to talk about David Hume, my favorite philosopher, and son of Edinburgh. Hume was the first to pose the “problem of induction”: how can we justify our prediction of the future based on past events? How can we logically justify our idea that there is a set of principles that govern the workings of the Universe? The canonical version of this asks: how can we be sure that the sun will rise tomorrow? Yes, it’s done so every day up until now, but tomorrow’s sunrise doesn’t logically follow from that. One possible argument is that induction has always worked up until now, so we can expect it to work again in this case. But this seems to be a vicious circle (rather than a virtuous spiral). As I discussed a few weeks ago, I think this whole problem just grows out of a category error: one cannot make logical proofs of physical theories.
I also went down the dangerous road of discussing anthropic arguments in cosmology, to some extent rehashing the discussion in my review of Paul Davies’ “Goldilocks Enigma”.
But in between I talked about the current state of CMB data, our own efforts to constrain the topology of the Universe, and the satellites, balloons and telescopes that we hope will improve our knowledge even further over the coming few years.
Next up, a more general talk on the topology of the Universe at next week’s Outstanding questions for the standard cosmological model meeting, and then a more general review of the CMB at the Institute of Physics Nuclear and Particle Physics Divisional Conference.