What We Know, and Don't, and Why

By Sean Carroll | December 19, 2006 5:33 am

Yeah, I already used this title once before. It’s a good title, okay? Cut me a little holiday slack here.

By way of slightly-warmed-over blogging, I present to you the slides from a talk I gave a few weeks ago at Villanova, my undergrad alma mater. The original mandate was to talk about scientific literacy to a collection of undergrads, but I didn’t know how to make that fascinating. So I took it to the next level and went a bit meta, talking about the way science works. It was at a fairly abstract level — I didn’t go into building detectors, and error bars, or anything like that — but not too highbrow philosophy-of-sciencey — I didn’t get into Kuhn vs. Popper, much less Feyerabend or the Strong Programme, although you’ll find touches here and there.

To bring things down to earth (relatively speaking), most of the talk consisted of an extended look at the battle between “dark matter” and “modified gravity.” It goes all the way back to Leverrier and the discovery of Neptune, whose existence was inferred via its gravitational tug on the orbit of Uranus. Neptune was the first successful prediction of dark matter — some unseen substance whose existence is revealed by its gravitational influence. Leverrier tried again with the similarly-discrepant orbit of Mercury, positing a planet called Vulcan; but this time it turned out that gravity itself was the culprit, after Einstein showed that general relativity correctly accounted for the precession of Mercury’s orbit. So the lesson from history is — different ideas work in different circumstances. Keep an open mind until the data come down on one side or another. (And once they do, admit it.)

Today, of course, we’re dealing with an analogous problem, given that 25% of the universe is apparently some kind of dark matter that doesn’t fit into the Standard Model of particle physics, and 70% is some kind of dark energy that is even more mysterious. Modified gravity might be at work here as well, and I talked about the prospects.

Along the way, I drew out some of the lessons about how science works that these various investigations have taught us. I intentionally did not try to wrap it all up with a neat bow into a catch-all philosophy of science, as I think the reality is kind of messy, and it’s worth admitting that. The closest I came was the famous quote from Professor Rumsfeld, previously shared. This led to a series of cautionary homilies warning against misuse of the hypothesis-testing nature of scientific inquiry. The truth is, scientific knowledge is inevitably tentative, not metaphysically certain. But that doesn’t mean that anything goes — some things we really do understand! So I cautioned against various mistakes, using perpetual-motion machines, Intelligent Design, and What the Bleep Do We Know as good examples of what not to do.


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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .


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