Edge: HOW FAST, HOW SMALL, AND HOW POWERFUL?


The
Third Culture
 
Edge 87
 
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"Something else has happened with computers. What's happened with society is that we have created these devices, computers, which already can register and process huge amounts of information, which is a significant fraction of the amount of information that human beings themselves, as a species, can process. When I think of all the information being processed there, all the information being communicated back and forth over the Internet, or even just all the information that you and I can communicate back and forth by talking, I start to look at the total amount of information being processed by human beings — and their artifacts — we are at a very interesting point of human history, which is at the stage where our artifacts will soon be processing more information than we physically will be able to process."

SETH LLOYD — HOW FAST, HOW SMALL, AND HOW POWERFUL?: MOORE'S LAW AND THE ULTIMATE LAPTOP
[7.23.01]



THE REALITY CLUB: Joseph Traub, Jaron Lanier, John McCarthy, Lee Smolin, Philip W. Anderson, Antony Valentini, Stuart Hameroff and Paola Zizzi respond to Seth Lloyd

Introduction

"Lloyd's Hypothesis" states that everything that's worth understanding about a complex system, can be understood in terms of how it processes information. This is a new revolution that's occurring in science.

Part of this revolution is being driven by the work and ideas of Seth Lloyd, a Professor of Mechanical Engineering at MIT. Last year, Lloyd published an article in the journal Nature — "Ultimate Physical Limits to Computation" (vol. 406, no. 6788, 31 August 2000, pp. 1047-1054) — in which he sought to determine the limits the laws of physics place on the power of computers. "Over the past half century," he wrote, "the amount of information that computers are capable of processing and the rate at which they process it has doubled every 18 months, a phenomenon known as Moore's law. A variety of technologies — most recently, integrated circuits — have enabled this exponential increase in information processing power. But there is no particular reason why Moore's law should continue to hold: it is a law of human ingenuity, not of nature. At some point, Moore's law will break down. The question is, when?"

His stunning conclusion?

"The amount of information that can be stored by the ultimate laptop, 10 to the 31st bits, is much higher than the 10 to the 10th bits stored on current laptops. This is because conventional laptops use many degrees of freedom to store a bit whereas the ultimate laptop uses just one. There are considerable advantages to using many degrees of freedom to store information, stability and controllability being perhaps the most important. Indeed, as the above calculation indicates, to take full advantage of the memory space available, the ultimate laptop must turn all its matter into energy. A typical state of the ultimate laptop's memory looks like a plasma at a billion degrees Kelvin — like a thermonuclear explosion or a little piece of the Big Bang! Clearly, packaging issues alone make it unlikely that this limit can be obtained, even setting aside the difficulties of stability and control."

Ask Lloyd why he is interested in building quantum computers and you will get a two part answer. The first, and obvious one, he says, is "because we can, and because it's a cool thing to do." The second concerns some interesting scientific implications. "First," he says, "there are implications in pure mathematics, which are really quite surprising, that is that you can use quantum mechanics to solve problems in pure math that are simply intractable on ordinary computers." The second scientific implication is a use for quantum computers was first suggested by Richard Feynman in 1982, that one quantum system could simulate another quantum system. Lloyd points out that "if you've ever tried to calculate Feynman diagrams and do quantum dynamics, simulating quantum systems is hard. It's hard for a good reason, which is that classical computers aren't good at simulating quantum systems."

Lloyd notes that Feynman suggested the possibility of making one quantum system simulate another. He conjectured that it might be possible to do this using something like a quantum computer. In 90s Lloyd showed that in fact Feynman's conjecture was correct, and that not only could you simulate virtually any other quantum system if you had a quantum computer, but you could do so remarkably efficiently. So by using quantum computers, even quite simple ones, once again you surpass the limits of classical computers when you get down to, say, 30 or 40 bits in your quantum computer. You don't need a large quantum computer to get a big huge speedup over classical simulations of physical systems.

"A salt crystal has around 10 to the 17 possible bits in it," he points out. "As an example, let's take your own brain. If I were to use every one of those spins, the nuclear spins, in your brain that are currently being wasted and not being used to store useful information, we could probably get about 10 to the 28 bits there."

Sitting with Lloyd in the Ritz Carlton Hotel in Boston, overlooking the tranquil Boston Public Gardens, I am suddenly flooded with fantasies of licensing arrangements regarding the nuclear spins of my brain. No doubt this would be a first in distributed computing

"You've got a heck of a lot of nuclear spins in your brain," Lloyd says. "If you've ever had magnetic resonance imaging, MRI, done on your brain, then they were in fact tickling those spins. What we're talking about in terms of quantum computing, is just sophisticated 'spin tickling'."

This leads me to wonder how "spin tickling" fits into intellectual property law. How about remote access? Can you in theory designate and exploit people who would have no idea that their brains were being used for quantum computation?

Lloyd points out that so far as we know, our brains don't pay any attention to these nuclear spins. "You could have a whole parallel computational universe going on inside your brain. This is, of course, fantasy. But hey, it might happen."

"But it's not a fantasy to explore this question about making computers that are much, much, more powerful than the kind that we have sitting around now — in which a grain of salt has all the computational powers of all the computers in the world. Having the spins in your brain have all the computational power of all the computers in a billion worlds like ours raises another question which is related to the other part of the research that I do."

In the '80s, Lloyd began working on how large complex systems process information. How things process information at a very small scale, and how to make ordinary stuff, like a grain of salt or a cube of sugar, process information, relates to the complex systems work in his thesis that he did with the late physicist Heinz Pagels, his advisor at Rockefeller University. "Understanding how very large complex systems process information is the key to understanding how they behave, how they break down, how they work, what goes right and what goes wrong with them," he says.

Science is being done in new an different ways, and the changes accelerates the exchange of ideas and the development of new ideas. Until a few years ago, it was very important for a young scientist to be to "in the know" — that is, to know the right people, because results were distributed primarily by pre prints, and if you weren't on the right mailing list, then you weren't going to get the information, and you wouldn't be able to keep up with the field.

"Certainly in my field, and fundamental physics, and quantum mechanics, and physics of information," Lloyd notes, "results are distributed electronically, the electronic pre-print servers, and they're available to everybody via the World Wide Web. Anybody who wants to find out what's happening right now in the field can go to http://xxx.lanl.gov and find out. So this is an amazing democratization of knowledge which I think most people aren't aware of, and its effects are only beginning to be felt."

"At the same time," he continues, "a more obvious way in which science has become public is that major newspapers such as The New York Times have all introduced weekly science sections in the last ten years. Now it's hard to find a newspaper that doesn't have a weekly section on science. People are becoming more and more interested in science, and that's because they realize that science impacts their daily lives in important ways."

A big change in science is taking place, and that's that science is becoming more public — that is, belonging to the people. In some sense, it's a realization of the capacity of science. Science in some sense is fundamentally public.

"A scientific result is a result that can be duplicated by anybody who has the right background and the right equipment, be they a professor at M.I.T. like me," he points out, "or be they from an underdeveloped country, or be they an alien from another planet, or a robot, or an intelligent rat. Science consists exactly of those forms of knowledge that can be verified and duplicated by anybody. So science is basically, at it most fundamental level, a public form of knowledge, a form of knowledge that is in principle accessible to everybody. Of course, not everybody's willing to go out and do the experiments, but for the people who are willing to go out and do that, — if the experiments don't work, then it means it's not science.

"This democratization of science, this making it public, is in a sense the realization of a promise that science has held for a long time. Instead of having to be a member of the Royal Society to do science, the way you had to be in England in the 17th, 18th, centuries today pretty much anybody who wants to do it can, and the information that they need to do it is there. This is a great thing about science. That's why ideas about the third culture are particularly apropos right now, as you are concentrating on scientists trying to take their case directly to the public. Certainly, now is the time to do it."

—JB

SETH LLOYD is an Associate Professor of Mechanical Engineering at MIT and a principal investigator at the Research Laboratory of Electronics. He is also adjunct assistant professor at the Santa Fe Institute. He works on problems having to do with information and complex systems from the very small — how do atoms process information, how can you make them compute, to the very large — how does society process information? And how can we understand society in terms of its ability to process information?

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