Thursday, April 12, 2007

Stephen Hawking, still fascinating

MSNBC's Cosmic Log column carries a very interesting piece about Stephen Hawking, who is physically degenerating due to ALS ("Lou Gehrig's disease") but ever more fascinating as an intellectual figure, both in science and on the wider public stage. Hawking, in a talk in Seattle discussed in the piece, recounted the changes in his own views -- an admirable subject to address.

Hawking has gone back and forth about what happens to the things that are sucked into a black hole. At one time, he held that the "information" falling into the black hole is lost forever, but recently he has said that the contents of a black hole would leak out in the form of "Hawking radiation," until the black hole itself dissipates.

"Information is not lost, but it is not returned in a useful way," he said. "It is like burning an encyclopedia. Information is not lost, but it is very hard to read."

That's a good line. Hawking noted one consequence of his change of mind:

Speaking of encyclopedias, Hawking noted that his reversal caused him to lose a bet to a fellow physicist, with the payoff coming in the form of a baseball encyclopedia. "Maybe I should have just given him the ashes," Hawking joked.

Hawking also discussed his "backwards" or top-down approach to his subject. Without knowing a thing about the science, I like his comments:

We don't really know how the human brain works. I find women's brains a particular mystery. But it is reasonable to assume that humans remember the same direction of time as computers do.... We understand how computers work, unlike humans. And one can show that when a computer records an item in its memory, the total amount of disorder goes up. So computers and humans remember the past, and not the future. That is, because of the Second Law [of Thermodynamics], we usually recount history forward.

We say that later events are caused by earlier events, but not that earlier events happen in order to lead to the later. This "bottom-up" approach, as I call it, works well in situations in which we can choose the initial state and observe the outcome. But the bottom-up approach does not work in cosmology.

We do not know what the initial state of the universe was, and we currently can't try out different initial states and see what kinds of universes they would produce."

Wow, I think I even get it.

Posted by Evan Hughes at 03:13 PM

Print | E-mail to a friend | Permalink | Subscribe via rss