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Tuesday, December 09, 2008
We Know So Much, Yet So Little
By John Fleck
Journal Staff Writer
It is hard to know whether to be encouraged by Carlton Caves' thoughts on the future of humanity and the timing of our impending doom. You might categorize the University of New Mexico theoretical physicist's ideas this way: Some things it's better not to know.
Or perhaps, to be more precise: It is important to distinguish what you know from what you don't.
For about 15 years, physicists, journalists and those inclined to look for a scientific foundation for their apocalyptic fears have played a mathematical parlor game, calculating the odds of humanity's demise.
"Our extinction as a species is a very real possibility," Princeton physicist J. Richard Gott III wrote in New Scientist magazine 11 years ago. "We had better take steps to improve our survival prospects before it's too late." With a 95 percent certainty level, Gott argued that humanity should last at least another 5,100 years, and at most 7.8 million years.
Worst case scenario 5,100 years? Whatever. I'm off to lunch. Burrito or teriyaki?
But Caves doesn't dismiss the question so easily.
Carl Caves (no one calls him "Carlton") is the smartest person I know.
My wife laughs when I say that, pointing out that I often describe someone as "the smartest person I know." She is right. As the Journal's science writer, I have the privilege of talking to a lot of awfully smart people.
But only a few get the label "smartest person I know." Caves is one.
They share an important characteristic. In addition to knowing a lot, understanding it deeply and explaining it well, they are especially careful about understanding what they don't know.
Given the 58-year-old Caves' chosen profession the strange world of theoretical quantum physics that is a good thing. Serious conversation with members of his tribe eventually runs aground on the shoals of the things we don't know.
Caves meant to go into molecular biology until he sat through Harold Rorschach's physics lectures as a Rice University freshman. "It just seemed spectacular," Caves told me, "that you could take the laws of physics and figure out what was going on."
Caves got his doctorate at Caltech, studying under the legendary Kip Thorne. (Physics fans at this point are saying "Thorne? Wow!")
Today, Caves studies the weird world of the extraordinarily tiny, where fuzzy quantum strangeness takes over and the comfortable solidity of things like tables and basketballs disappears.
In the quantum world, you never quite know where the tiny equivalent of a basketball is or which direction it is spinning. This isn't because of a lack of information but because in some strange sense it really is spinning both ways at the same time, and it really is in this basket and at the other end of the court at the same time.
"We don't know what's actually happening," Caves said, "and we're not going to know. That's the lesson of quantum mechanics."
Caves' dust-up with Gott over the odds of humanity's impending doom, which has been going on for the better part of a decade, has achieved that small measure of postmodern fame that comes from showing up in Wikipedia. It is a sideshow to Caves' quantum gig, but it nicely illustrates his care in distinguishing what we know from what we don't.
Gott offers an alluringly simple argument, which is why his work has made such a popular parlor game. A couple of assumptions, a simple equation, and presto: 5,100 to 7.8 million years.
It's a fun game. You can use Gott's math to calculate the odds of nearly anything: the future life span of the venerable science journal Nature (which Gott did, in the pages of Nature no less, estimating in 1993 that it would last between 3.5 and 4,800 years, a prediction that has thus far held up) or the chances that the long-suffering Chicago White Sox would eventually win the World Series. Gott did that in 1996, nine years before the Sox won.
The problem, Caves says, is that one of Gott's key assumptions is wrong, and the probabilities that result are useless. You'd have had much better luck, Caves pointed out, making the simple assumption that the Sox, as one of baseball's 30 major league teams, had a 1-in-30 chance of winning the Series every year.
In the case of humanity's future, you are better off ignoring Gott and thinking, for example, about what we know and don't about the impending decline of Earth's supply of fossil fuels (another interest Caves and I share).
If you're interested in the details, go to the home of all things physics, www.arxiv.org, and type "Carlton Caves" in the search box. You'll find "Predicting future duration from present age: Revisiting a critical assessment of Gott's rule," along with some neat discussions of quantum teleportation and nonlinear quantum metrology.
I hope you come away with an appreciation for the value of the distinction between what we know and what we don't.
Contact Journal science writer John Fleck at 823-3916 or e-mail him at firstname.lastname@example.org.