State of the Universe(s)

October 19, 2009

Last night I had the honor of moderating a fantastic discussion between three leading cosmologists: ASU's Lawrence Krauss (of The Physics of Star Trek fame), University of Michigan's Katie Freese, and Neil Turok, now the director of the Perimeter Institute, which organized the city-wide Quantum 2 Cosmos festival. The Q2C organizers have gone all out with the multimedia: most lectures and panels are available online, streaming live while in progress, along with a Twitter feed.

We covered a lot of ground in 55 minutes, discussing the unprecedented explosion in our scientific knowledge of the universe during the 20th century and looking to the future by exploring the mysteries currently facing cosmologists: dark matter, dark energy, gravitational waves, whether inflationary theory is correct, and what might have existed before the Big Bang? These are deep waters, Watson. Okay, I had to ask Krauss about the whole "red matter" scenario in the latest Star Trek reboot (he liked the movie, had little use for the "science"). But other than that, we stuck to the serious stuff. Mostly.

I always learn something new when I talk to scientists, and this time was no exception, thanks to Katie Freese. She told me about "dark stars": not the precursors of black holes first hypothesized back in the 1700s, but a new kind of star that may have been the first type of star to form in the early universe. Freese and a few colleagues published the seminal paper on dark stars in January 2008 in Physical Review Letters, and she's still uber-excited about the possibilities for the existence of these objects -- as well she should be.

See, if these things turn out to exist, it would significantly change current theoretical models for star formation. Right now, scientists believe the first stars formed inside clouds of dark matter, in which hydrogen and helium cooled down sufficiently to make nuclear fusion possible. The only role dark matter plays in this scenario is to supply the gravity needed for the gases to clump together in the first place.

But if Freese and her colleagues are correct, then the concentrations of dark matter particles would be so high that those particles would collide with each other and annihilate, releasing energy, and keeping the almost-star too hot to collapse down to sufficiently high density for fusion to begin. In short, it's an entirely different fuel source than that which powers "normal" stars. The next step is actually detecting them, and Freese thinks the new James Webb Telescope slated for launch in 2011 will be able to see them, although she cautions that while dark stars may shine, "they will look different than stars that operate by fusion." Emissions of gamma rays, neutrinos or antimatter could all turn out to be "signatures" of dark stars.

Like any new idea, it has its skeptics in the scientific community. Freese et al's model does rely on some necessary assumptions that may turn out to be incorrect. Most notably, their calculations are based on a type of Weakly Interacting Massive Particle (WIMP) called a neutralino -- it's the leading candidate for dark matter particles, but it may not be the right one, or the only one. But it's not an implausible scenario either. Like so much in cutting edge cosmology and astrophysics, the excitement comes from exploring what we don't know, because that inevitably leads to new discoveries.

Anyway, we ran out of time before we could really discuss dark stars in detail during the panel, but we covered lots of other great topics, and we certainly didn't ignore the "dark side of the universe." That's where all the cosmological action is these days. You can watch the whole thing below. (Note: For some reason, the "embed" feature has been giving me grief. If it's not showing up in the post, you can still watch the entire panel discussion here.)