When I was young and as yet unformed as a theoretical physicist, cosmology was in a transitional period. We had certainly moved beyond the relatively barren landscape of the 60′s and 70′s, when pretty much the only things one had to hang one’s hat on were very basic features like expansion, rough homogeneity, and the (existence of) the cosmic microwave background. By the late 80′s we were beginning to see the first surveys of large-scale structure, there was good evidence for dark matter, and the inflationary paradigm was somewhat developed. In the 90′s things changed quite rapidly, unbelievably so in retrospect. We detected primordial anisotropies in the CMB and began to study them in detail, large-scale-structure surveys really took off, we discovered the acceleration of the universe, and techniques like gravitational lensing matured into usefulness.
My students and postdocs will readily testify that I am fond of complaining how much harder it is to come up with interesting new ideas that aren’t already ruled out by the data.
In an interesting and provocative post, Peter Coles bemoans a generational shift among cosmologists: “When I was a lad the students and postdocs were a lot more vocal at meetings than they are now.” In particular, Peter is worried that people in the field (young and old) are “willing to believe too much,” and correspondingly unwilling to propose dramatic new ideas that might run counter to received opinion. Or even, presumably, just to express doubt that received opinion is on the right track. After all, even with all we’ve learned, there’s certainly much we don’t yet know.
I’m not sure whether there really has been a shift or not; there’s a big observational bias from the fact that I used to be one of those young folks, and now I am a wise old head. (Old, anyway.) But it’s completely plausible. Is it a bad thing?
There’s an argument to be made that widespread agreement with a basic paradigm is actually a good thing. People agree on what the important questions are and how to go about answering them. Ideas are held to a higher standard. Furthermore, it would be very hard to blame a young scientist who wanted to play by the rules rather than rocking the boat. It’s easy to say “challenge conventional wisdom!”, but the thing about conventional wisdom in a mature field is that it’s usually right. The exceptions are important and memorable (remember when everyone thought the cosmological constant was zero?), but most controversial new ideas are just wrong. Being wrong is an important part of the progress of science, but it’s hard to tell other people that they should be wrong more often.
At the end of the day, though, I agree with the spirit of Peter’s lament. I do think that the discourse within cosmology has become tamer and less willing to try out new ideas. Dark matter is well-established empirically, but we certainly don’t know that it’s WIMPs (or even axions). Inflation has had some successes, but we are very far indeed from knowing that it happened (and the problems with eternal inflation and predictability are extremely real). I have my own prejudices about what’s settled and what are interesting open questions, but the field would be healthier if youngsters would challenge people like me and make up their own minds.
Then again, you gotta eat. People need jobs and all that. I can’t possibly blame anyone who loves science and chooses to research ideas that are established and have a high probability of yielding productive results. The real responsibility shouldn’t be on young people to be bomb-throwers; it should be on the older generation, who need to be willing to occasionally take a bomb to the face, and even thank the bomb-thrower for making the effort. Who knows when an explosion might unearth some unexpected treasure?