Monthly Archives: October 2012

When bits bite

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As the 1995 movie Species begins, space aliens have beamed to Earth information about a new, seemingly endless source of energy. The same transmission includes the codons for alien DNA and instructions for splicing them into the human genome.

The energy source proves bountiful, but the splicing, played out over the movie’s next 100 or so minutes, proves disastrous. Scientists construct the alien DNA, transfect it into a human egg cell, and watch as the egg develops with unnatural speed into a girl they name Sil. Alarmed by Sil’s rapid growth, the scientists plan to kill her, but she escapes and matures into a half-alien/half-human whose drive to mate and lack of inhibition combine in a gory rampage of sex and murder.

Reflecting on the movie one morning on my way to work, I thought, “That’s amazing—malevolent aliens could invade us with pure information!” Just the bits needed to encode DNA are enough to threaten human civilization. But a sequence of alien DNA, expressed as binary signal, is just that: a binary signal. It took unsuspecting humans to make the monster itself.

The idea that information is physical is hardly new. Although we can’t know for sure, marks pressed on wet clay or knots tied in string would have seemed more physical than not to ancient Babylonians and Incas. What’s more recent is the notion that information is intrinsically and inextricably physical. AT&T’s Claude Shannon, IBM’s Rolf Landauer, and others pioneered this viewpoint in the 1940s.

One of Landauer’s successors has shown that the physics of information has theological implications. Carlo Beenakker at the University of Leiden in the Netherlands usually theorizes about electron transport in structures that are just small enough for quantum coherence to play a role. But in a recent article, he tackled a problem raised 40 years ago by Carl Gustav Hempel: Where does physics stop and metaphysics begin?[1]

Beenakker’s analysis tools are limits derived by physicists. Information can’t be transferred faster than the speed of light (Albert Einstein), erased without generating kT log 2 of heat per bit (Landauer), or processed with available energy E faster than 4E/h operations per second (Norman Margolus and Lev Levitin). Beenakker asks three questions, among them, is the immortal soul physical or metaphysical? He answers,

In order to be physical, the immortal soul should contain and process information beyond death, which is the erasure of most information in the organism. Estimates of the amount of information lost upon death are in the order of 1032 per human. Mankind as a whole has lost some 1043 bits of information over the course of 50,000 years. We know of no mechanism by which this amount of information could have survived by physical means, leaving the immortal soul in the metaphysical domain.

Beenakker’s estimate for the duration of mankind comes from science: the age of our most recent chromosomal ancestor “Adam.” But his estimate of a human’s information content comes, indirectly, from science fiction: Lawrence Krauss derived it to conclude that the Star Trek transporters are infeasible.

Which is a relief. Otherwise, malevolent aliens could beam themselves to Earth, rather than just send us information about their DNA.

Reference

  1. C. Beenakker, “Hempel’s dilemma and the physics of computation,” Knowledge in Ferment: Dilemmas in Science, Scholarship and Society, A. Groen et al., eds., Leiden U. Press, Leiden, the Netherlands (2007), p. 65.

This essay by Charles Day first appeared on page 96 of the July/August 2007 issue of Computing in Science & Engineering, a bimonthly magazine published jointly by the American Institute of Physics and IEEE Computer Society.

Quantum computing is exciting and important—really!

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Quantum computing, say its champions, promises prodigious power. Its basic currency, the qubit, exists in an on/off limbo until it’s read out, so if you could operate on k qubits, a potentially vast space of 2k values opens up for computation. The fundamental operation on qubits is a rotation. Combine the rotations, and you have logic gates. Combine the logic gates, and you have algorithms. In principle, these algorithms can perform calculations far beyond classical computing’s conceivable reach.

But to wield that power, you need an actual quantum computer, and building one has proved impossible. Qubits live in small, cold enclaves within the classical macroworld. When heat and other environmental disturbances inevitably intrude, they rob a quantum system of its coherence, its entanglement, and its ability to compute.

So beguiling is the potential of quantum computers that rather than putting people off, the difficulty of building one has assumed the qualities of a mythical quest. Like Jason’s for the Golden Fleece, the quest for a quantum computer is hard and long. To sustain it, the champions of quantum computing appeal not to Olympian gods but to terrestrial funding agencies. Not surprisingly, quantum computing has acquired an aura of hope—and hype. Researchers have made steady progress, though. Physicists have fashioned qubits from superconducting Josephson junctions, trapped ions, semiconducting quantum dots, and other systems. They’ve even built working logic gates.

Still, scaling up a handful of logic gates, whose physical embodiments could require a roomful of lasers, cryopumps, and other finicky equipment, to an actual computer remains out of reach. Rolf Landauer, the IBM physicist who pioneered the notion that information is intrinsically physical, was famously skeptical of quantum computing. All papers on the topic, he said, should come with a disclaimer, and if you didn’t have one, he was happy to offer his own:

This proposal, like all proposals for quantum computation, relies on speculative technology, does not in current form take into account all possible sources of noise, unreliability and manufacturing error, and probably will not work.

Landauer’s skepticism could prove justified in the end, but it would be a pity if research in quantum computing stopped now. Much of it continues to be worthwhile. At NIST’s lab in Boulder, Colorado, for example, David Wineland and his collaborators have applied the techniques they developed for atomic clocks to build logic gates based on trapped ions. Thanks to their work on logic gates, they developed new, entanglement-based clocks of unprecedented precision.

In making qubits out of gallium arsenide quantum dots, Jason Petta, who is now at Princeton University, and his collaborators at Harvard measured the tiny fluctuating magnetic field of 106 gallium and arsenic nuclei inside a quantum dot—a remarkable feat.

Results have been just as impressive on the theoretical front. The work of Microsoft’s Alexei Kitaev and others on topological quantum computation has spawned rich and fruitful explorations of the mathematical similarities of field theory, knots, and the fractional quantum Hall effect. Princeton’s Robert Calderbank has applied the theory of quantum error correction to understand radar polarimetry, and Ignacio Cirac and Frank Verstraete of the Max Planck Institute for Quantum Optics outside Munich have used the entangled states that crop up in quantum information theory to analyze networks of coupled spins.

Do all these advances, and others, represent milestones on a longer, ultimately successful journey or the ends of truncated trips? I don’t know. But they’re exciting and important—really.

This essay by Charles Day first appeared on page 104 of the March/April 2007 issue of Computing in Science & Engineering, a bimonthly magazine published jointly by the American Institute of Physics and IEEE Computer Society.

The death of distance has been exaggerated

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Last April, I went to a meeting at Case Western Reserve University. To get there from Cleveland’s airport, I took a commuter train.

At first, the view from the train was bleakly urban. But as we neared the city center, I expected the industrial outskirts to give way to office and apartment buildings, restaurants, and shops, as in other cities. But no! Through the train windows, right in the center of town, I saw factories, cranes, marshalling yards, piles of gravel, and barges.

I shouldn’t have been surprised—Cleveland is a port. To reduce transport costs, refineries, smelters, and factories are sited as close to rivers and harbors as possible. And in Cleveland, this means the center of town. What’s surprising is that so many other cities have shed their heavy industries and reclaimed their river- and lakefronts.

The Kavli Institute for Theoretical Physics. (Photo by Sarah Vaughan.)

Light industries, including the lightest of all—knowledge-based industries—don’t need to be near harbors. The much-touted death of distance, brought on by the cheapness of telecommunications, means a worker with a modem can be anywhere. Greenwich’s burgeoning hedge-fund industry is based 40 miles from Wall Street, for example, sparing hedge funders a time-consuming commute without disadvantaging their communications.

But is distance really dead? Google, that most 21st-century company, began work earlier this year on a vast data center in Oregon—not in trendy, microbrew-quaffing Portland, but in the modest town of Dalles. At the heart of the center, two buildings the size of football stadiums will house server farms. To cool the servers, the center will draw power from a hydroelectric plant on the nearby Columbia River. Cheap energy brought Google to Dalles.

There’s another sense in which distance remains alive. If you’re a knowledge worker—a computer programmer or an editor, like me—the ability to work anywhere doesn’t mean you’ll set up your broadband wireless computer and work just anywhere. As much as you can, you’ll choose your location. In the 21st century, the best locations might be by rivers and lakes, as they were in the 19th, but this time for recreation rather than transport. You might not set up your laptop in Dalles, Oregon; instead, you might opt for Bend, Oregon, whose pleasant climate and environs have attracted thousands of newcomers in the past decade.

Even theoretical physicists, whose mental abstractions tend to make them indifferent to environment, are succumbing to the pull of place. Twenty-seven years ago, the US National Science Foundation funded a fledgling center for theoretical physics at the University of California’s Santa Barbara campus. At the time, UCSB was hardly at the top of the UC, let alone the US, pecking order. But the campus is on the Pacific Ocean, and the institute is as close to the beach as environmental regulations allow.

The institute is thriving. Its director, David Gross, was lured there from Princeton, and in the institute’s 25th anniversary year, he shared the 2004 Nobel physics prize for his work on quark confinement.

Today, the distance that matters isn’t to a harbor, but to a power plant—or the beach.

This essay by Charles Day first appeared on page 104 of the January/February 2007 issue of Computing in Science & Engineering, a bimonthly magazine published jointly by the American Institute of Physics and IEEE Computer Society.

My computational education

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I peaked as a computational scientist in 1986. At that time, two years from finishing my PhD, I was trying to account for an aspect of the x-ray emission from a pulsar known as Hercules X-1, the first x-ray source discovered in the constellation Hercules. Hercules X-1 consists of a normal star and a rapidly spinning neutron star. So close are the two stars to each other that the neutron star’s gravity grabs material from the normal star’s outer atmosphere. By the time the purloined material reaches the neutron star, it’s a million-degree, x-ray-emitting plasma.

Every 1.7 days—a number I can’t forget!—the two stars orbit their mutual center of mass, and, if you’re watching from Earth, the neutron star is eclipsed by its companion. But just before and just after total eclipse, the neutron star’s x rays pass through the companion’s atmosphere. From a plot of x-ray emission versus time, you can probe and explain the atmosphere’s vertical structure—with the help of a computer model, that is.

Artist’s impression of an x-ray binary system from NASA’s Imagine the Universe!

And so, over several months, I created my longest-ever computer program. Excluding comments, it ran to more than 120 lines of Digital Equipment’s proprietary flavor of Fortran 77. Fortunately, I didn’t have to create a data analysis program from scratch—a postdoc had done that before me—but I did have to incorporate my model into his code. (See Dianne O’Leary’s “Computational software: Writing your legacy,” Computing in Science & Engineering, January/February 2006, page 78, to learn why that exercise builds character.)

How did I become a programmer? When I started graduate school I had no programming—or even computer—experience. To me, computers were toys for the uncool boys. But then my university offered its graduate students a course in scientific programming. And I took it.

The teacher, whose research was in the field of artificial intelligence, displayed impressive loyalty to a single ancient T-shirt. In class and around town, he’d pad about without shoes or socks like a hobbit. His course briefly touched on programming techniques, but only in the abstract. My real teachers were the postdocs in my group. They taught me a sprinkling of practical tricks and, perhaps more useful, some sound principles of programming practice.

Those learning experiences popped into my head when I read Francis Sullivan’s column about Sudoku (“Born to compute,” Computing in Science & Engineering, July/August 2006, page 88). Lacking Francis’s “compute gene,” I have no attraction whatsoever for Sudoku or any other mathematical puzzle. But I do have the physics gene, and its expression, in graduate school, was what compelled me to program.

Having solved the physics for my model, I had to implement it on a computer—which meant I had to read arcane computing manuals, swat the bugs I’d introduced into my program, and struggle with fussy compilers. Every now and again, amid the toil and frustration, would come flashes of inspiration and progress. In the end, I grew to like programming.

So if you teach computational science and your class includes compute-free students like me, give them an interesting science or engineering problem to solve. The poor things might be driven to program despite their genetic inheritance.

This essay by Charles Day first appeared on page 104 of the September/October 2006 issue of Computing in Science & Engineering, a bimonthly magazine published jointly by the American Institute of Physics and IEEE Computer Society.

My Nobel wish list

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My record for predicting the winners of Nobel prizes is mixed. The last time I made a public prediction was two years ago. I correctly picked Konstantin Novoselov and Andre Geim as winners, but I thought their work on graphene—by analogy with the work of Robert Curl, Harold Kroto, and Richard Smalley on buckyballs—would earn the pair the chemistry prize. The only prize I got completely correct was Mario Vargas Llosa’s for literature.

This year, rather than make predictions, I’ve decided to identify who I hope will win the prizes I care about the most: physics, chemistry, physiology or medicine, and literature.

Physics

One of the topics of enduring interest to physicists is the boundary between the realms of quantum and classical behavior. In 2004 I wrote a news story about an ingenious experiment that explored that boundary. Markus Arndt, Anton Zeilinger, and their colleagues at the University of Vienna sent buckyballs through a pair of closely spaced slits.

When the molecules were cold, they behaved like quantum objects and formed interference fringes after passing through the slits. But when the molecules were hot, the coherent fringes disappeared. Evidently, the molecules’ temperature and emission of thermal photons—not their size or mass—demarked the quantum–classical boundary.

That story was my first direct encounter with research on how the environment influences quantum behavior. The second came in 2009 when I wrote about a calculation that resolved a 82-year-old quantum paradox: Why is a chiral molecule found in either its left-handed or right-handed isomeric forms and not in a superposition of the two?

To reach their answer, Klaus Hornberger and Johannes Trost of Ludwig-Maximilians University calculated the most probable states of a deuterated dihydrogen dilsulfide molecule in the presence of helium atoms. At room temperature, once the pressure exerted by the He atoms exceeded 1.6 × 10−5 mbar, the He atoms would kick the D2S2 molecule out of a mix of superpositions and into either its left-handed or right-handed form.

As I noted in my story, that a calculation could precisely locate a quantum–classical boundary is both mundane and profound—mundane, because the calculation made use of standard, unadulterated quantum mechanics; profound, because it demystified the quantum–classical boundary.

The physicist who has done the most to advance the notion that the environment, when fully and properly accounted for, drives the quantum–classical boundary is Los Alamos National Laboratory’s Wojciech Zurek. I hope he’s awarded the physics prize.

Chemistry

The discovery, published in February 2008, of superconductivity in a compound that contains iron and arsenic touched off an explosion of research that continues to this day. Several branches of the family of iron-based superconductors have since been discovered.

Although no family member’s critical temperature can yet match the highest of the cuprates, the iron-based superconductors are significant because their superconductivty, like that of the cuprates, is mediated by electron–electron interactions. Evidence is building that the pairing symmetry is not d-wave, as in the case of the cuprates, but is a form of s-wave.

The iron-based superconductors, therefore, demonstrate that high-temperature superconductivity is not limited either to the cuprates or to the precise form it takes in the cuprates. Other chemical families, as yet undiscovered, could have still higher critical temperatures.

Hideo Hosono of the Tokyo Institute of Technology made the discovery. I hope he is awarded the chemistry prize.

Physiology or medicine

The last time pharmacology was honored with a Nobel Prize was in 1988, when James Black, Gertrude Elion, and George Hitchings shared the award “for their discoveries of important principles for drug treatment.” This year, I hope that Ravinder Maini and Marc Feldmann of Imperial College London are rewarded for identifying tumor necrosis factor as a potential (and now effective) drug target for treating inflammatory diseases, such as rheumatoid arthritis.

Literature

The Wikipedia entry on William Trevor, whose photo appears above, begins like this:

William Trevor, KBE (born 24 May 1928) is an Irish author and playwright. One of the elder statesmen of the Irish literary world, he is widely regarded as one of the greatest contemporary writers of short stories in the English language.

If the Swedish Academy can suspend its habitual political posturing and instead reward sensitivity, sympathy, and skill, then it might just bestow the literature prize on Trevor. Doing so would honor not just him, but two great writers whose work inspired him and who weren’t awarded Nobel prizes: Anton Chekhov and James Joyce.