There are few questions that spark interest as surely as this one: Are we alone in the cosmos?
The idea of a universe replete with alien beings has wide- spread allure and probably derives from our evolutionary history. After all, there’s straightforward survival value in learning about an unseen tribe over the next hill. They could be a threat or, on the brighter side, may offer some novel breeding opportunities.
However, and despite our fascination with extraterrestri- als, researchers have failed to find any compelling evidence for their existence. Not yet, anyway. But this cheerless fact has not dampened hope, and there aren’t many scientists or citizens who would assert that Homo sapiens is the only clever species in our galaxy.
Much of the belief in cosmic intelligence is based on an appeal to large numbers. Two decades of work by astronomers has pegged the number of planets studding the Milky Way at roughly one trillion. That’s a staggering amount of acreage, and it requires industrial-strength chutzpah to argue that all these worlds are sterile, or at best, home to nothing more than insensate beasts.
The effort to find these alien beings is known as SETI, the Search for Extraterrestrial Intelligence. Despite being well known and well regarded, SETI is a niche research activity. The tally of people—worldwide—whose job description is to seek out aliens is approximately a dozen.
The strategy they use is straightforward. Large antennas—radio telescopes—scan the skies in a hunt for trans- missions that are clearly of artificial origin. In other words, the signals must have some narrow-band components to distinguish them from natural radio emitters such as quasars and pulsars. The latter are very broadband and can be “heard” all over the radio dial. In addition, the apparent source of the signals should parade across the sky at the sidereal rate, just as the stars do.
Today’s SETI experiments typically monitor tens to hundreds of millions of simultaneous channels, each only 1 Hz wide. The data are collected, processed, and evaluated entirely by computers running specialized software. This relieves the scientists of the tedium of trying to find E.T. by donning headsets and listening for unusual cosmic static. But of greater importance, it means that the specialized equipment necessary for SETI can be scaled up as funding and technology permit. Because of the close tie between digital electronics and search speed, the pace of explora- tion increases rapidly, and experiments fielded by SETI researchers in a given year can often comb through more data than all previous years combined.
Nonetheless, even after five decades of SETI no confirmed signal has been found. Is there anything to be learned from that?
Commentators outside the field think there is. In particular, they claim that despite the early expectations of many, the sky is not replete with high-powered radio transmitters. These glass-half-empty types will often go further and appeal to an argument known as the Fermi paradox to put this celestial silence into context. Their conclusion is a downer: No one is out there.
That’s a big verdict based on thin evidence. Or rather, on no evidence. The Fermi paradox derives from a remark made in 1950 by the celebrated physicist, Enrico Fermi, who realized that in the very long history of the universe, there’s been more than ample time for an ambitious society to colonize the entire galaxy. Not every civilization has to be so enterprising; if a single species were smitten with the idea of bringing the Milky Way under its wing, then we should expect evidence of its efforts to be visible everywhere, including nearby.
Consequently, more than a few people have stated that SETI’s failure to find E.T.’s radio footprints is important, and strongly suggests that Homo sapiens is the only think- ing species within thousands of light-years or more.
Needless to say, such a conclusion smacks of the self-importance that passed for clear thinking before the time of Copernicus. On that basis alone, it should be suspect. It’s also a sweeping judgment based on a very restricted data set. Yes, there have been SETI efforts to find signals for a long time, but those have been both limited and intermittent. The number of star systems that have been scrutinized over a wide range of frequencies is merely a few thousand. In addition, the sensitivity of even the best of these experiments could detect an omnidirectional galactic transmitter only if it boasted a power level roughly 10,000 times the current energy use of all humanity. That’s a lot of kilowatt-hours. It’s possible that SETI will book success only when we gain the ability to find far weaker signals. It may be that the sky actually is filled with signal sources. But we won’t discover them until our instruments have far greater sensitivity.
Such a massive improvement in sensitivity is difficult to achieve today but might be a trivial effort in the 22nd century. Just as Victorian era astronomers couldn’t have discovered quasars despite the fact that they litter the cosmos, it may be that our quest for E.T. is a bit premature.
While such arguments might give pause, they shouldn’t cause pause. Speculation is never a satisfactory substitute for experimentation when trying to find something new. Given the myriad uncertainties about the activities of extra- terrestrials, the search should continue.
However, there is one aspect of the SETI enterprise that is, to my mind, far more consequential than Fermi’s para- dox. The assumption made since SETI’s inception is that extraterrestrials are most likely to be resident on a planet that’s not only amenable to life but host to complex life. In other words, a world analogous to our own.
While comfortably conservative, this thesis flies in the face of our own experience. Within two centuries of invent- ing radio, it’s likely that humankind will invent and build thinking machines. These devices will be able to expand their own capabilities far faster—and to a far greater extent—than soft, squishy biological intelligence.
It’s a disquieting but simple argument: Biological brains will beget synthetic ones. If this technical evolution is commonplace, then there’s reason to expect that the majority of the intelligence in the universe is nonbiological.
In that case, our hunt for extraterrestrials will require more than just new equipment. We’ll need to rethink the nature of our prey.