Today's colloquium speaker was Lawrence M. Krauss, who is somewhat well-known for doing a lot of public outreach and having written several books aimed at the general public. (One of these books was The Physics of Star Trek, which I received from three or four separate people as birthday gifts when it came out in 1995.) He's also done political advocacy, perhaps most notably fighting "intelligent design" creationism in Ohio. Today's colloquium was about neither Star Trek nor politics, however, but about the "dismal future" of the universe.
The talk was basically a series of extrapolations from the fact that cosmological observations show a universe that is not only expanding, but expanding at an exponentially increasing rate. The most direct consequence is that eventually everything that isn't gravitationally bound to our galaxy cluster will be receding away at faster than the speed of light, not only inaccessible but invisible. This won't happen for many billions of years, so it's not of any particular concern to us personally, but will be an issue for the future of life itself. As a result of being isolated to a single cluster, the amount of energy available becomes limited: I think the estimated number was 3x1067 Joules, for what it's worth. Consequently, the amount of information that can be processed also is limited, to on the order of 10120 bits. One of the more interesting numbers quoted was that, if one assumes that Moore's Law will continue to hold on the rate of information processing, civilization would run through this capacity in just 400 years. (Since at the moment we are limited to the amount of energy here on Earth, I expect Moore's Law will fail rather sooner than this, which is why I'm skeptical about Singularity talk.)
Another section of Krauss' talk was devoted to what cosmology would look like to a far-future civilization in one of these "island universes" created by expansion. Since these future scientists would be unable to observe the universe outside the cluster, they would be unable to infer the expanding universe or the Big Bang, and would conclude that the universe was static. (They could, however, estimate the age of the universe from abundance of various elements.)
Finally, on long timescales everything disappears, as dark matter halos evaporate and galaxies dissipate.
Krauss, being a more public figure than most physicists, was a very good speaker who gave an entertaining talk. He was deliberately provocative, declaring at the beginning that he would alienate most of the audience, and particularly targeted advocates of the anthropic principle. I was hoping for more fireworks in the question session, but it was somewhat tame. A video of this talk will appear at some point here on the department website.Tags: Colloquia, Physics