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September 2, 2004, Thursday


Sorry, E.T., but Parcel Post May Beat Phoning Home

Correction Appended

Ever since 1960, when a Cornell astronomer named Frank Drake pointed a radio telescope at a pair of nearby stars on the chance that he might hear a cosmic ''howdy'' from extraterrestrial beings, astronomers have persevered in the notion that radio or light waves could bridge the unbridgeable gulfs marooning civilizations in space and time.

So far there has been only silence, but in their wildest, most romantic moments, astronomers dream of tapping into a kind of galactic library in which the knowledge and records of long-dead civilizations are beamed across the galaxy.

Now, however, it appears that E.T. might be better off using snail mail.

According to new calculations being published by a physicist and an electrical engineer today in the journal Nature, it is enormously more efficient to send a long message as a physical package, a cosmic FedEx, than as radio wave or laser pulse. As a result, say the authors, Dr. Christopher Rose, a professor of electrical engineering and computer science at Rutgers, and Dr. Gregory Wright, a physicist at Antipodes Associates in Fair Haven, N.J., searchers for extraterrestrial intelligence should pay more attention to how messages could be inscribed and delivered and where they might be found.

''Our results suggest that carefully searching our own planetary backyard may be as likely to reveal evidence of extraterrestrial civilizations as studying distant stars through telescopes,'' they wrote.

In an accompanying commentary, Dr. Woodruff T. Sullivan of the University of Washington said that although this was not a new idea, the new paper was the first quantitative analysis of the comparative costs of the ways of delivering information between the stars. He compared the notion of a message in a bottle to the monolith left as a calling card by aliens in ''2001: A Space Odyssey,'' adding, ''If astroarchaeologists were to find such, it would hardly be the first time that science fiction had become science fact.''

Although the result sounds counterintuitive, the problem will be familiar to anyone who ever spent time shrinking a digital photograph before trying to send it over the Internet through a dial-up connection. It would be much easier to drive a truck of photo albums across town or put them in an overnight-mail box than to go through the process of scanning and shrinking each photo.

The paper, Nature's cover article, is being received with bemusement by veterans of the Search for Extraterrestrial Intelligence, or SETI.

Dr. Paul Horowitz, a Harvard physicist and SETI expert, called it ''a fun and an enjoyable read, but I wouldn't turn off my radio telescope and go out with my butterfly net.''

The new argument is based on a simple observation. The farther a light beam or radio wave is sent, the more it spreads out, and the smaller fraction of its energy is recaptured at the other end. Moreover, if the recipients are not looking in the right direction at the right frequency when the signal arrives, it will shoot past and be lost. A letter, by contrast, does not disperse in transit, and waits at its destination until it is read.

And with modern nanotechnology, the authors point out, that letter can contain quite a lot. Some 1022 bits of information -- much more than the sum of all the written and electronic information on Earth -- can be encoded into a cube weighing about 2.2 pounds, Dr. Rose and Dr. Wright say.

Even allowing for thousands of pounds of lead to protect the message from cosmic rays and the weight of fuel, they calculated that it would take 100 million times as much energy to radiate those bits from the world's largest radio telescope to an antenna 10,000 light-years away as to send it them in a ''letter.''

The hitch is that the package could not travel as fast as radio waves. At only one-thousandth the speed of light, it could take 20 million or 30 million years to reach distant stars, but that is still a blink compared with the galaxy's age, 10 billion years.

The main advantage of radio waves, the authors argue, is the possibility of two-way communication. But other beings could be so far away -- hundreds or thousands of light-years -- that even at the speed of light a reply would be impossible.

''If you're simply trying to say, 'Here we are,' a radio wave is the best way to do it,'' Dr. Rose said in an interview. But he added that any detailed information would require a long message. Still, he acknowledged that someone out there might be trying to communicate that way.

''We'd be goofy not to keep looking for radio waves,'' he said.

Dr. Jill Tarter, an astronomer at the SETI Institute, intends to keep on doing just that. ''We've always reserved the right to get smarter and add new search strategies to our arsenals,'' she said. ''For me personally, I'm sticking with radio.''

Correction: September 6, 2004, Monday An article on Thursday about the prospects for receiving messages from distant planets misstated the affiliation of Dr. Frank Drake, the first astronomer to search for radio signals from aliens, in 1960. He did the search at the National Radio Astronomy Observatory in Green Bank, W.Va., not at Cornell.


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