Yesterday evening, I was sitting with the local knitting group and reading the last few pages of Guth's book. "Should I actually believe
this?" I bemusedly asked the two CERN physicists sitting on either side of me. "HELL NO!" said T, after glancing at the cover. "Inflation?? I HATE IT!!! It's why I gave up cosmology and went into nuclear physics! That's real science!" But A had a more positive opinion. "Well," she shrugged, "it's part of the standard Big Bang model. How else are you going to make sense of the observational data?" Then they both hastened to add that I shouldn't take seriously anything they'd said, they weren't experts, not their field. In fact, they didn't know. I wondered if they thought that would be a typical reaction, were I to ask other professional scientists. Would everyone say they didn't know, unless the question concerned the tiny area where they were an acknowledged world-class expert? A thought about it. "Probably," she said. So, ah, to summarise, no one except a handful of experts understands our current theories about the origins of the universe well enough to say whether they make sense, but Alan Guth, the guy who kicked it off, has written a book about how we got here. I personally found it very helpful and feel I grasp the idea of "inflation" far better than I did a week ago: the brief summaries I'd seen elsewhere had left me cold, but seeing how the ideas developed over time put them into perspective and made them less outlandish.
Though I still have real trouble believing this stuff; it seems impossibly speculative, even if it does "explain" important things, in particular the flatness and uniformity of the universe, and the slight unevenness in the Cosmic Microwave Background Radiation (CMBR) that later turned into galaxies. Guth describes his key insight from 1980 and the developments following on from it. You project the history of the universe backwards in time, and it gets hotter and denser the further back you go. At some point, about 10^-35 seconds after the beginning of time, things are so hot that the three non-gravitational forces - electromagnetism, and the strong and weak nuclear forces - all become the same force. But then, winding the clock forwards again, the universe cools down, and they split up into the three forces we see today. In the process of doing so, there could have been an intermediate state, a "false vacuum", where the universe was filled with the enormous energy released by the splitting up of the three forces. This energy would have caused it to expand exponentially, making it uniform and flat; quantum fluctuations would account for the minor unevennesses we have found in the CMBR.
This is indeed the standard story, but I am shocked to see how many assumptions you need in order to make it work. There is a bunch of "Grand Unified Theories" explaining how the three forces can be unified into one, but the energies needed to test them are over a billion times higher than anything we can create in our current accelerators. The potential curve which determines how the energy level falls during the splitting of the forces needs to have a very specific shape in order to get results that match the data. Originally, the idea was that the field mediating the energy was going to be the Higgs field, which we know something about; but in fact the Higgs field turns out not to have the right properties, so a new field was required. (By the way, this seems to be why the Higgs is often called "the God Particle"; people thought for a while that it had created the universe, but they later changed their minds). The universe has to be locally flat enough before inflation started, which involves some kind of theory of quantum gravity. All these theories are speculative.
I can't help being reminded of medieval cosmologies. Back then, astronomers tweaked systems of cycles and epicycles to make them fit the observed notions of the planets. Now, they tweak the potential curves of the inflaton field to make it fit the patterns found in the CMBR. No one had ever seen a crystal sphere, and no one has ever seen an inflaton; perhaps they are equally mythical. But careful analysis of the crystal spheres eventually produced better theories, and I'm guessing the same thing will happen here, given time. Why is there never a Newton around when you need one?
People who have read this book might want to look carefully at Appendix B and compare it with this paper by J.D. Norton
. It certainly seems to me that the 1895 result from Seeliger quoted by Norton completely invalidates Guth's argument, and in fact leaves him looking rather silly. But see if you agree.