In yesterday's post, I neglected to mention why Steven Chu won a Nobel Prize. Chu (along with Claude Cohen-Tannoudji and William D. Phillips) received the 1997 Nobel Prize in physics
"for development of methods to cool and trap atoms with laser light," which has come to be called "laser cooling
At a first reading, this is the sort of remark that baffles laymen like me. Something as hot and fast-moving as a laser being used to cool atoms and trap them?
As far as I've come to understand it (and physicists, feel free to correct me), the short explanation to this is that when photons strike an atom in the right way, they bounce back off and take some of the atom's energy with them. This slows the atom's speed, which means that its temperature falls. As the atom slows and is continually bombarded with photons, it begins to move randomly and thus remains more or less in one place. This allows it to be studied more precisely
"Once you get an atom very cold . . . and cold is really the average speed that an atom moves . . . . Once you get an atom really cold, so it's moving as fast as an ant walks, a fraction of an inch per second, then very, very weak forces can push them around, and you can do what you want with them -- for example, using electric or magnetic fields, or light. You can hold them, you can push them around, you can do things that you simply cannot do when they're whizzing around like supersonic jet airplanes.
The ability to hold onto and control and manipulate these atoms means, for example, you can toss them up; they can turn around due to gravity in a vacuum can where there are no other atoms around, and you can make better atom clocks. You can make what are called, atom interferometers
. You quantum-mechanically split the atom apart, so one part of the atom is the quantum wave going to one region in space; the other part is the quantum wave going to another region of space. That atom interferometer can be used to measure acceleration or gravity or rotations with very high accuracy -- in fact, in terms of acceleration or gravity, better than any other way of doing it. And in terms of rotations, certainly better than any commercial or even laboratory grade laser gyroscope."
As experimental physics goes, this is a pretty neat trick with lots of experimental
applications. But that's not the complete reason that it got the Nobel Prize. According to Alfred Nobel's will
, he intended to bequeath:
"a fund, the interest on which shall be annually distributed in the form of prizes to those who, during the preceding year, shall have conferred the greatest benefit to mankind."
The emphasis upon "greatest benefit" suggests that Nobel Prizes will be awarded to those whose work has had profound practical
So, what are the practical
benefits of laser cooling to mankind?
"So all of a sudden, you can measure changes in gravity so accurately that it's going to become competitive with the current ways of measuring changes in gravity, which is useful in all [oil?
] exploration. You can probably put it on an airplane or a helicopter. And with global positioning satellites to tell you the height and changes in distance, and inertial sensing systems, and something that measures change of gravity over distances on a scaled meter, it opens up the opportunity to do map gravity drains and pockets of oil, diamonds, things of that nature, minerals, on a very fast-moving platform like a slow-moving plane or helicopter. So there are real practical implications."
These sorts of applications factor into the calculations of the Nobel Committee. Interestingly, they are not the sort of things that Chu or others were thinking about
while they were doing their research:
"The atom interferometer was totally unexpected. It just popped out. People, even the researchers in the field, [find it] hard to think about what you can do with it, even if you force yourself, until you have it in hand, and you can then begin to see the abilities of this new method or technique. It's only after we had it . . . and then not only me, my group, but the world in general. No one was talking about any of the applications that came out until we actually had it and we saw how powerful it was, and then began to appreciate it. You can force yourself to think of what might come about, and you can write down a few things, but you're going to get only a small fraction of them. That's the wonderful thing about science."
I suppose that Chu means that the applications of scientific discoveries go far beyond what one could ever imagine, which is a pretty wonderful thing (or perhaps alarming, if one is pessimistic). But might he have also meant that it's wonderful that one need not think about such things during the process of scientific discovery?
I ask this because he has repeatedly emphasized the wonderful experience of workng for Bell Laboratories, which for him was a time of pure freedom -- scientific inquiry untrammeled
by practical considerations (oddly enough, given that he was employed by Bell Lab):
"So I joined Bell Laboratories. My department head said, 'Steve, you can do whatever you want. It doesn't even have to be physics. All we ask is that you don't go to a high-energy accelerator and do high-energy physics, because that would be hard on the stockholders.' (My thesis project, and when I was working as a post-doc, addressed a high-energy physics problem.) He said, 'And by the way, don't do anything immediately. Spend six months. Talk to the people around the labs, and just keep an open mind.' This was a devastating experience for me, because of the freedom to do whatever you want and being told, 'Don't do what you think you want to do now, but explore.' So I spent some time exploring and thinking. And there, I really felt pressure, because he would say, 'We expect great things out of you.' I didn't want to hear that. It's much nicer to have a little problem to work on; it's very cozy.
But it did have a real influence on me, because it got me in that mode of going and talking to people outside of my field. When I finally started doing things at Bell Laboratories . . . and I started, first, in an area that was in condensed matter physics that I knew nothing about, but using techniques in my old field, atomic physics and laser physics. But it got me into the mode of, 'I've got this crazy idea.' I'd go to some colleague in Bell Laboratories and say, 'How does this sound?' And they would tell me, 'No, this is the stupidest thing I've heard,' or 'Yeah, maybe you have something there.' It set the tone for what I've done for the rest of my life -- collaborating with people, especially outside my local expertise. It was a wonderful experience.
I also should say, in the years I was there, '78 to '87 -- there was an economic slump in the mid-seventies; Bell Labs just started hiring people -- and there were a group of us, maybe a few dozen, two or three dozen, and we all were young, energetic, bright-eyed, bushy-tailed. We were all being put in this position: 'Do something important. Here are the resources of American Telephone and Telegraph System. We expect you to do something wonderful.' We were there at night. We were there on the weekends. We knew what each other's cars looked like, so we knew who was in there, let's say, on a Saturday or Sunday. We would party together. [Looking back,] I think either five or six of us [later] got Nobel Prizes. Over a dozen are in the National Academy of Sciences. It's like this: we all were growing up together. And we had these really wonderful senior scientists there as well.
It was a remarkable period of time. Everything was exciting, and something would come along that was not in my field, and I would say, 'Wow, this is really interesting.' We'd go in, we'd discuss it. People would jump fields, or jump areas. There was this feeling of the excitement of the science, that even though we were doing this, it was all right to move and do that. You wouldn't be considered a failure because you gave up this, because something else even more exciting came along, either from your own laboratory or from a colleague's lab, or from the outside world."
Significant here is Chu's emphasis upon the importance of thinking broadly and taking intellectual risks by leaping over the barriers between fields. This willingness to "jump fields" requires an ability to think analogically
, i.e., approaching problems in other fields by applying an angle that he's already used in his own field. Chu himself often alludes to analogies. Referring to the laser cooling method of catching atoms as a kind of "optical molasses" (itself an analogy), Chu makes an explicit analogy to Brownian motion:
"When I was making a back-of-the-envelope calculation of how long the molasses would keep the atoms in this region, I was thinking of a way to simulate this by computer, and I thought, 'Well, you really don't need a computer simulation, because you can make an analogy to Brownian motion.' The situation is very similar to Brownian motion where you have a dust particle and you put it in a fluid. As the atoms hit against this dust particle it starts to jostle around, and the fluctuations in the number of atoms that hit from the left and the right actually make the dust particle move. But the fluid dampens its motion; once it starts to move it hits viscosity in the fluid and wants to slow down. It's exactly the same in optical molasses, only it's a fluid of photons from the laser that creates the dampening. If the atoms want to move in the fluid they slow down, and it looks exactly like Brownian motion.
So after scratching around for a half hour or so I said, 'Hey! I know about this, I learned this in elementary physics!' In fact, Einstein was the first guy to figure out Brownian motion; it's a lesson that everybody learns. Doing the calculation, this random-walk motion meant that if you had a region about a centimeter in diameter you could keep the atoms corralled for about a second . . . . [I]f you arrange laser beams in a certain way, amazing things should happen; namely, you should create a soup of photons that would damp any motion of the atoms, so if the atom wants to go any particular way it can't, it just sits there."
This is a pretty basic analogy to make since Chu learned about Brownian motion in elementary physics, but how does he manage to apply analogical thinking to other areas outside of his expertise? I think that this requires two parallel processes:
1. Concentrating on a few areas of intense interest as one's specialization (which necessitates attention to a lot of details).
2. Reading broadly even in fields somewhat distantly related to one's primary interests (which necessitates attention to a more general understanding of issues).
To see this, let's look again at yesterday's posting of Chu's views on this process of thinking:
" So I would look around, and I had some [knowledge] from reading newspapers and magazines such as Science
, Science Times
, The New York Times
, Scientific American
, things of that nature. I had an interest in these biological problems, and I would pick something that I was interested in. But, of course, since I wasn't an expert in biology, I didn't know, 'Is this a stupid question? Is this a deep question? What?' I would say, 'Well, I think I can do something here and I have some interest.' So I'd trot over to the biology department or medical school and say, 'Is this something we're studying? I think I want to do this.' And they would tell me sometimes, 'No, no, it's silly,' or 'It's been done before.' Or sometimes they'd say, 'This is a central problem in biology.'"
Note that Chu's interest in these other fields shows the same pattern of approaching problems as already exhibited in his earlier, Bell Lab days. As then, he here begins from the specialized field in which he is an expert and brings his expert knowledge to his more general reading in biology and science. This means that he can approach problems in other fields from perspectives unavailable to the experts in those fields.
Analogical thinking is only one aspect of the creative-thinking process, of course. There's also lateral thinking
, i.e., "problem solving by approaching problems indirectly at diverse angles," which Chu surely must also do a lot of. Thinking by analogy, however, seems to play a very important, perhaps major role in Chu's approach.
Perhaps I should ask him about this tomorrow.