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When Bits Bite

Charles Day

Pages: p. 96

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 4 E/ 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 10 32 per human. Mankind as a whole has lost some 10 43 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.


About the Authors

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Charles Day is a senior editor at Physics Today.
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