April 10, 2007 at 10:34 PM ET
World-famous cosmologist Stephen Hawking was in the Seattle spotlight Monday night to explain the big questions: Why does time seem to move always forward but never backward? Why does he think running time backwards the only way to solve the universe's biggest mystery? But the small questions can be just as intriguing: For example, how does Hawking “autograph” a book? When he composes a sentence on his gesture-controlled computer, does he blink or does he sneer?
Here are some insights into those questions, great and small, gleaned during a close encounter with Cambridge University's frail genius:
Kimberly Wright / Reuters file
|Physicist Stephen Hawking uses an infrared sensor |
mounted on his eyeglasses as part of a
computerized writing/speaking system.
The title of Hawking's advertised talk was "The History of the Universe Backwards," but he actually delivered two lectures - one looking back at his own career in physics, and another focusing on his latest theories about a "top-down" approach to cosmology.
The first talk touched on the milestones of his career: how he went into cosmology rather than particle physics, the subdiscipline du jour, because he marched to the beat of a different scientific drummer ... how he was diagnosed with a neurodegenerative disease, known as amyotrophic lateral sclerosis or ALS, while he was in graduate school ... and how, despite his increasing disability, he went on to plumb the theoretical depths of black holes and the big bang.
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."
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.
It was the second talk that really spurred my interest. Hawking and a colleague from CERN, Thomas Hertog, recently declared that the best way to understand how the universe arose was to look at our current cosmic conditions, then work back through "the sum of all histories" to figure out which theory would produce those conditions.
Hawking calls it a "top-down" approach to what he has long considered the biggest cosmic question: What was the initial state of the universe? Did God just create the universe the way it was, and that's it? Or is there a scientific reason for why the cosmos is just so ... why, for instance, it could lead to the conditions for intelligent beings like us?
Hawking's top-down vs. bottom-up approach goes to the heart of the issue covered in his best-known bestseller: "A Brief History of Time." During his Seattle talk, Hawking contended that cosmologists essentially had to look at time in reverse.
If time is a definite dimension like up-down, left-right and forward-back, why does time only move forward? Hawking said the answer to that question might lie in the Second Law of Thermodynamics - the idea that an enclosed system must move from a more ordered to a less ordered state:
"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, 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."
General relativity alone can't solve the problem, so quantum mechanics has to come into play to figure out what's the likeliest backward history for our universe, Hawking said.
As we've mentioned before, the twists in mathematics that link up general relativity and quantum mechanics seem to imply that we live in an 10- or 11-dimensional universe, perhaps with up to seven dimensions somehow rolled up into immeasurably small loops. The math also implies that there is a virtually immeasurable number of ways that our universe could have developed - nearly driving theoreticians to despair.
Hawking, however, isn't the despairing type: He said physicists should focus just on the scenarios that have three large spatial dimensions, like ours. It may sound like the anthropic principle - that is, the view that the universe is the way it is simply because there would be no intelligent life around to observe it if things were much different. But Hawking preferred to use another term - "the selection principle" - because the selection "doesn't depend on intelligent life."
That's not to say the loop dimensions don't count. Hawking said those other dimensions, which he called "internal space," may well determine the fundamental characteristics of our cosmos, such as the charge of an electron or the nature of subatomic interactions.
So how can physicists work their way backwards and map out that internal space? Strangely enough, Hawking endorsed the same approach favored by Columbia physicist Brian Greene, an earlier speaker in the Seattle lecture series: looking closely at irregularities in the "fingerprint" of the early universe, as seen in the background radiation left behind by the big bang. Those irregularities, which could soon be mapped in greater precision by probes such as the Planck spacecraft, may reveal the imprint of our own internal space.
Hawking said that the universe may represent just one "bubble" in a cosmic froth - perhaps longer-lasting than some other blips. Rather than dwelling so much on how many other unseeable bubbles there could be, Hawking advised concentrating on what makes our bubble the way it is.
"There seems to be a vast landscape of possible 'internal spaces,'" he said, setting up for a final joke. "We live in the anthropically allowed region, in which life is possible. But I think we might have chosen a better location."
I met Hawking at a reception after the talk, and here are some impressions on those smaller questions at the beginning: