Saturday, April 09, 2011

Lemaitre Conference Pt 1

At conference organised in memory of Georges Lemaitre. I was only able to join from Sat am so missed the earlier talks, including (sadly) one by Martin Rees, but I was able to catch up with him and congratulate him in person.  Key points for me:
  • Paul Shellard spoke on recent advances in "Big-Bang' cosmology.  He is rightly very excited about the extent to which observational data are enabling rigorous scientific tests of cosmological models like inflation, constraining the many different flavours on offer.  But there are plenty of enigmas remaining (he listed 9, many to do with fine-tuning) and he's understandably very sceptical of String/M-theory.  He thinks it is essential to distinguish between cosmology and what he calls meta-cosmology, and that many popular accounts, even by eminent scientsts who should certainly know better, fail to do so.
  • John Barrow then addressed Lemaitre's legacy, (with a capital Lambda!)  John's old colleague Bill McCrea had known him and thought he was the most brilliant of the old masters, with a deep physical intutiion that enabled him to use just the right amount of mathematics.  Lemaitre discovered the Hubble Constant 2 years before Hubble, and could have predicted inflation.  John also metioned his paper with Shaw that proposes that Lambda is in fact a slowly varying scalar field and which gives a very interesting an soon-testable prediction (Discussion in Nature here)
  • Don Page spoke up for the Multiverse view, and rather pleasingly gave a plug for QoT and for E[HELP]. It's increasingly clear to me that some variational principle is the best chance of "explaining" the value of the parameters, but Martin says that we are too far away from being able to do the calculations. I also think Don needs to take confidence intervals more seriously: prior probabilites and likelhoods cannot, ITRW, be given as single numbers.
  • George Ellis then warned hard against taking Mulitverse ideas too seriously. They were legitimate hypotheses but it is grossly misleading to suggest (as Martin certainly doesn't but Brian Greene and others do) that they or indeed string/M-theory are known reality. We go from Known Physics to Hypthetical Physics and only the latter requires any form of Multiverse. As for the idea that "we are all in a computer simulation" - this is completely ridiculous. No conceivable computer could do this, and anyway who built the computer etc.. I suggested that this was part of the extreme left-brain thinking that was so dysfunctional, plugging The Master and His Emmissary. George is in my view over-impressed with Lee Smolin's Cosmic Natural Selection and I'll send him my paper that debunks it.
  • Bernard Carr then emphasied the "cosmic omphalos" in which the largest scales (c10^33 cm) arise from the smallest scales (c 10^-30 cm) if a quantum fluctuation gives rise to the Big Bang. There are a whole wealth of anthropic coincidences and we seem to be at the centre of length scales. He is inclined towards the Multiverse view, but also is very clear that mind, consciousness and mind and spirit are fundamental realities in the universe.
An interesting panel discussion followed, and now for the drinks reception.

1 comment:

Crude said...

The position I've seen George Ellis take is that there are good philosophical reasons for considering a multiverse, but that these reasons do not add up to scientific reason. This is what I took away from his recent review of Brian Greene's book.

That, I think, is an important point to drive home. One worry I have is that what anyone else would call philosophy and metaphysics if only some other person was saying it, gets viewed as "science" if a scientist says it.