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two more seminars

I think my journal is turning into a seminar journal. But that's okay, they're usually the most interesting part of my week.

This week I went to a philosophy colloquium on Tues by Bas van Fraassen on "Appearances versus Reality as A Scientific Problem", and a physics colloquium on Thurs "Cosmology on the String Theory Landscape" by Shamit Kachru. The former was the first real philosophy talk I've been to, as far as I can remember. It was followed by an hour-long discussion period which was pretty neat. Physics lectures don't usually have discussions afterwards that last more than ten minutes or so. I don't think I learned all that much new from this particular philosophy lecture (being mostly a historical account of the development of science's changing ideology), but it was neat to see the differences between how philosophers think of science and how scientists think of science. (But also frustrating.) Abstract for both behind the cut, plus more on the

Bas van Fraassen
Department of Philosophy,
Princeton University

"Appearance versus Reality
as a Scientific Problem"

Science is a representation of nature, but what precisely does it
represent, and how paintings and photos depict things as they appear
to us in perception. In contrast, a scientific theory may be claimed
to depict things as they really are. The differences between the
appearances and this postulated reality can be striking. So even if a
scientific theory or model represents how things really are, its task
is not complete unless it accounts for how things look to us in
observation or measurement.

Even if we see completeness as only an ideal, we must have criteria
for what it would take to have a complete world picture. But the
criteria of Galileo, Descartes, and Newton are no longer ours. Past
criteria were challenged during revolutionary changes in science.
That challenge was posed dramatically for our time by Einstein in the
famous paper "Can quantum-mechanical description of physical reality
be considered complete?". I will argue that in fact, we have
experienced a radical change in our conception of what science is to

Speaker: Shamit Kachru
Stanford University

Title: Cosmology on the string theory landscape


String theory is our leading candidate for a unified theory of particle
physics and gravity. However, it is becoming increasingly clear that it
accomodates an astonishingly diverse range of possible 4d worlds, all
arising at different points in a "landscape" of possible vacuum states.
We explain how this landscape seems to contain valleys with positive
cosmological constant (which could be related to the observed cosmic
acceleration), and how string theory also suggests simple and
distinctively stringy models of early universe inflation.

Although I didn't understand everything Shamit was talking about, I think I picked up a lot more about how slow-roll inflation works and how it relates to string/M theory. He put up a really beautiful slide of a Calabi-Yau manifold projected down onto 3-dimensions. I've seen little diagrams of this before, but this one really captured the complexity of it. (I can't imagine how these people can integrate over such manifolds, it must require some incredibly abstract techniques!) The most interesting thing he said in the lecture, I think, is that our world--which has a postive cosmological constant and broken supersymmetry--may only be metastable with respect to its so-called fundamental properties. On the "string theory landscape"--which he depicted by analogy on another pretty slide of a landscape of mountains, valleys, and seas--our world is up in the mountains (even if it's a local valley), and can therefore decay via quantum tunnelling into something with lower energy: a perfect supersymmetric "sea". Pretty wild.


( 3 comments — Leave a comment )
May. 7th, 2004 10:56 pm (UTC)
The string theory talk sounds pretty cool. Though I must say, between Feynman ("I do feel strongly that this is nonsense!") and Finkelstein, I'm pretty biased against string theory as "our leading candidate for a unified theory..."
May. 8th, 2004 03:09 pm (UTC)
It's the leading candidate in the sense that: if you were to have all the physicists in the world today who are working on unified field theories vote on the most likely candidate... string theory would win by a landslide. Of course, popularity contests don't prove that it really is the most likely story, but I think it's fairly safe to say "leading" candidate (since that's not really saying much). About 50% of current particle theory research is directed towards string theory or closely related subjects like supersymmetry. Most of the other 50% is phenomenology (which usually means trying to iron out the few remaining unsettled kinks in the gravityless Standard Model). And then you've got a handful of people like Finkelstein working on their own ideas for unifying gravity with QFT. And actually, I heard him say one day that he thought M-theory was a big improvement over strings; and that despite his commitment to his own ideas, it might be going somewhere too. I'd be very curious to hear what he said to you if anything about it. I only heard him mention it once or twice.
May. 9th, 2004 08:01 am (UTC)
I'll bet the Calabi-Yau manifolds are much simpler when expressed mathematically, and so might not be so bad to work with. The Klein Bottle, for example, looks fairly complicated when viewed, but is not much worse than a torus when you work with it.
( 3 comments — Leave a comment )


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