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Tomorrow is the first journal club meeting this year. Topic looks reminiscent of Shamit Kachru's string theory landscape talk, but with a different twist. An exploration of cosmologies based on tunnelling between false vacuum states (down to either another more insidious false vacuum, or perhaps the "true" vacuum (if there is a such thing)... the bottom rung, so to speak). This can apparently lead to a rapidly expanding bubble of spacetime, similar to the one we see around us. More details, perhaps, after tomorrow. But here's the teaser...

(from email invite)
To kick off journal club for the year, I will be presenting something on false vacuum decay. Imagine that there are two vacuum states of a scalar
field which permiates the universe. This can be represented by constructing a potential for the scalar field with two local minima, where
one minimum is lower than the other. Now, one defines a boundary condition for the universe: at some point in the distant past (older than the age
of the universe in the big bang picture) the region of space that our universe now occupies was in the higher energy vacuum state (false
vacuum). Since the scalar field is a quantum field, there is some probability that a region of space will tunnel to the true vacuum. To obey
energy conservation, this region must be a bubble of a minimum radius (depends on the potential chosen, but that radius would be on the order
of kilometers). Once the bubble is formed, it will expand until eventually the false vacuum region is replaced by a true vacuum region.
The exciting part happens when you include gravity (the zero point energy of the scalar field acts as a cosmological constant) in this
picture. The region inside the bubble looks like our universe - undergoing accelerated expansion which started at some finite time in the past. So,
the "Big Bang" could have been the formation of a true vacuum region. This scenario has spawned a number of cosmologies, and I will talk about a few.


( 2 comments — Leave a comment )
Oct. 1st, 2004 02:32 am (UTC)
Topological cosmology! Something I am interested in.
Oct. 2nd, 2004 10:28 am (UTC)
Update: turns out, it wasn't terribly enlightening. Mostly stuff I knew or had guessed before, pretty basic. I do understand inflation a bit better now, but nothing too surprising to report. It started kinda late, so I never got to drill him on what the real motivation for these cosmologies are. It seems to be a trick to "get the ball rolling" for slow roll inflation, but I don't see why you couldn't do that in countless other ways, or just say "at some point it started rolling" without getting into false vacuu stuff. Ah well, I'll finish learning about this eventually.
( 2 comments — Leave a comment )


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