Since I cannot comment at Sean's Blog either, I might as well comment here too:)
27. Moshe Says:
October 23rd, 2011 at 5:00 am
Igor, I am not sure I understand. We have an initial value problem, so today’s observations are determined once you specify an initial state at some time in the distant past. If you specify the time to be the beginning of the big bang evolution, with the correct but very contrived initial state (nearly homogeneous with just the right kind of fluctuations) then you get no conflict with observation. By contruction, same applies to inflation, because it reproduces that initial state and all subsequent evolution. The only point of inflation is to make that initial state the outcome of prior evolution. By construction all current observations will then be identical, but the initial state will be more natural and less contrived. As I understand Sean’s statement, quantifying this intuitive notion of naturalness is tricky, and it is not always clear inflation indeed comes ahead. I hope I am not mangling things…
And, for the record, in my mind the notion of “naturalness” is one instance of “algorithmic compression”, which is the whole point of seeking a scientific explanation. Without invoking such criteria, by definition (for example) the particle data group review book would be always the best “theory” of particle physics, and you’d never need to learn about gauge theories and spontaneous symmetry breaking and all that stuff.