Are we out of aliens' reach?

WRITING IN the Australian recently, astronomer Seth Shostak, visiting Australia for a SETI (search for extraterrestrial intelligence) conference, stated that we should "at least try to make contact if extra-terrestrials exist". His article makes some interesting points but takes a lot for granted. Most obviously, his statement: "There would be little danger ... the tyranny of distance would protect us: the aliens are likely to be hundreds or thousands of light-years away. To bridge such enormous chasms with rockets is a daunting proposition."

It is indeed. But imagine a group of pre-Columbian Americans in 1491 who had some mathematical and astronomical science (as some pre-Columbian cultures did), who knew more-or-less the size and shape of the Earth, and realised there was a high statistical probability of other inhabited countries, who had the technology to fish their own waters, gathered on a headland looking out to sea, speculating on the people living in other lands.

One fearful or imaginative young member of the tribe pipes up that invaders might come from these other countries to take their lands, or worse. The elders and wise men quickly silence these fears: "Obviously, the oceans are too wide and stormy for any canoe to cross. Not only would the waves probably sink it, but it is a mathematical fact that it could not carry enough provisions to last for the distances involved. The cold equations of science state it. We know what canoes can and cannot do. You can relax." In modern management jargon this might be termed a bad call, for it will be seen that embedded in the elders' reply is a mistake.

The mistake is the assumption that the limits of the science and technology which we are familiar with are the limits of science and technology everywhere and always. There is today no proof of any real possibility of faster-than-light travel (except possibly for certain exotic particles), but Newtonian physics is only about 300 years old and Einsteinian physics less than 100 years old. Already there are speculations about odd things that may happen at the edges of black holes. We have less than fifty years' experience of near-Earth space flight. To assume that we know it all is taking a lot for granted indeed.

Only about seventy years ago Robert Goddard was virtually hounded out of the scientific community for suggesting that flight to the moon with liquid-fuel rockets might one day be possible. The New York Times ridiculed the idea on the grounds that there would be no air for a rocket's exhaust to push against. The 1945 Richards Topical Encyclopedia, more daringly progressive, and with about fifteen PhDs on its Board of Editors, forecast such an attempt might be made (unsuccessfully) in 2042, when a then highly-scientific world celebrated the anniversary of Newton's birth.

The "hyperdrive" beloved of science-fiction writers which enables faster-than-light travel is really in story-telling terms a version of magic allowing travel between distant stars with little time lost for the purposes of the story. But can we really be absolutely certain that the Special Theory of Relativity is the last word forever and that cultures which--as Seth Shostak says--may have thousands or millions of years of science and technology behind them have not come up with anything more, or that the rockets we know today are the ultimate and unsurpassable means of space travel?

Even our own theorists have already come up with things that may be better than rockets. The science-fiction story The Mote in God's Eye, by Larry Niven and Jerry Pournelle (both trained scientists who take pains to make their stories scientifically plausible for a readership that also includes many scientists), suggests that interstellar space could be crossed by a sailing ship propelled by beams of coherent light fired at the sail by huge lasers mounted on the ground. Electromagnetic ramscoops, such as the ...