## Wednesday, March 2, 2011

### Dark Energy at Berkeley

"Are we from Stanford?" asks Alex Fillipenko, referring to the apparent repulsion of other galaxies from the Milky Way. "Are we lactose intolerant? - Get it - milky...way," he quips. Impressively self confident, the frequent tennis player and skier is also well known for being the best professor on campus and probably the best astronomy prof in the world. Working in competition with Saul Perlmutter (also a Berkeley prof.), Fillipenko found out in the late 90s that the universe was not only expanding, but that this expansion was accelerating in time.

On the Wednesday compass talk, he talked about Dark Energy and the runaway universe. He started with an apple: throw it up, and it comes back down. As Fillipenko mentioned, "may the net force be with you). Now if we look at the universe at large, the gravitational attraction between the massive galaxies should eventually slow down the expansion. Or should it? Theory should say that it depends on the matter density of the universe - there's some critical density below which the universe expands forever. It's a lot like the escape velocity of a rocket from the Earth. If we define $\Omega_m =\rho/\rho_{c}$, where $\rho_{c}$ is that critical density, then $\Omega_m = 1$ represents a continually expanding universe that asymptotically reaches an 'infinite' maximum. Now bring in experimental data - collected from meticulous observations on supernovae visible currently to telescopes. By calibrating these titanic explosions, it turns out that $\Omega_m$ is negative (!) and there is something pushing the universe apart.

The idea of the cosmological constant comes into play here - opposing the gravitational force at incredibly large distance scales. Initially designed by Einstein as a fudge factor to ensure a steady state universe, it's currently what theorists believe is the cause of this crazy universe.

I was about to ask about the connection between this dark energy and inflation, but he covered that in his talk. It's possibly the only problem about the best teachers - they anticipate and answer your questions before you can ask them.

At one point, while describing the idea of using 'standard candles' to estimate these (literally) astronomic distances, he goes "Let's say we have a very large red giant in this galaxy called Charlie - we know it's it's really powerful, so we can compare it to Betelgeuse." Umm... Charlie Townes was in the row in front of me, so that was probably a token of respect for the incredibly important nobel laureate. But still - did he just call Charlie a big fat red giant?? OBJECTION!! Let's see you that fit when you're 95.

Apart from that, it was an excellent talk - and got me thinking about a number of topics that I might think about and post here.

At the end of the Q&A: "And so if we look on this side of the line, we know precisely how much dark energy we've go...Oh shit! I have to pick my kids up from school."

#### 1 comment:

1. I do hate it when I cant write math properly somewhere. If any of you intrepid readers know how to incorporate LaTeX into Blogger, send me an email.