It’s one of the greatest scientific questions of our time. Are we alone in the universe? Is the rise of an intelligent civilization like our own common across time and space, or such a rarity that we are effectively alone? Scientists have spent more than a half-century trying to resolve this question. SETI, or the search for extraterrestrial intelligence, began in earnest one morning in 1960, when Frank Drake scanned the nearby stars Tau Ceti and Epsilon Eridani with the Green Bank (W.Va.) radio telescope. Years of fruitless searches for extraterrestrial radio waves, conducted by radio astronomy installations around the world, have failed to turn up evidence of life beyond our solar system. That’s led many scientists to ask the obvious question: Are radio telescopes “yesterday’s tech” in searching for ET, the equivalent of looking for smoke signals? Through the years, many alternative search theories have been proposed, and are now being carried out in the search for alien life.
5. Optical SETI: The Search For Laser Pulses From Space
This proposal is currently being conducted by looking for powerful high-speed laser pulses that might be aimed our way by an intelligent species. Studies have already been conducted using the Lick Observatory’s 40-inch telescope to scan target stars looking for laser flashes. The Planetary Society and Harvard University have also conducted an optical SETI campaign using a 72-inch telescope. We’re already capable of sending out such signals using megawatt lasers, and such millisecond bursts could easily outshine a host star. Of course, such a method isn’t omnidirectional like radio, and ET would have to be deliberately aiming it our way. Still, it could be an economical means of hailing us from a low-power perspective, and laser-encoded signals suffer from little interference and would be easy to pinpoint. Large sky surveys such as PanSTARRS and others due to come online in the next decade can scour thousands of stars per night and would be able to detect signs of a laser communication network.
4. Could We Detect ET Via Light Pollution?
Might the nighttime glows of ET’s cities give them (and us) away? One of the unwanted waste products that human civilization generates is the increased illumination of our nighttime skies. In 2011, astronomer Edwin Turner and astrophysicist Abraham Loeb proposed such a search and calculated how the night side of our own planet might appear from a distance. Currently, the daytime side of our planet illuminated by the Sun is about 600,000 times brighter than its nighttime side lit by our cities. Hubble could theoretically see this variation from the edge of our solar system, and you’d need a scope about a hundred times its size to spy this contrast in brightness from Alpha Centauri, the nearest star system. Still, we’ve only been at the light pollution game for about a century, and ET civilizations might be far brighter. Or do emerging civilizations go through a light-polluting adolescence, only to become more mature and energy efficient?
3. Studying Gravitational Waves and Cepheid Variables
With the advent of gravitational detectors such as LIGO, we’re just now achieving the ability to tune in to gravitational waves. Is it possible ET could “vibrate” merging pulsars or black holes to change the amplitude of gravitational waves to communicate? True, it’d be tough to imagine a civilization that would go through such a fuss to do this, and it would set up a curious circumstance where we may soon be able to eavesdrop on the discussion, but not talk back. Perhaps they’re only interested in other advanced civilizations that can do the same? An interesting and exotic possibility also worth looking for has been proposed by researcher Tony Zee. Cepheid variable stars serve as a “standard candle” beacon that have been highly studied by astronomers, and it makes sense ET might find a way to encode a signal in these stars to get our attention. Zee envisions that an advanced civilization may artificially manipulate the timing of a Cepheid by aiming a pulsed neutrino beam at the star, something that no natural source could produce. Such an effort would have an advantage of being omnidirectional, as one can imagine that alien astronomers across the galaxy are scrutinizing Cepheid variable stars.
2. Looking For Dyson Spheres and Geometrical Shapes
In 1960, astrophysicist Freedman Dyson proposed that a truly advanced civilization might build an artificial structure around its host star to harvest its entire energy output. Might it be possible for us to spy such a massive engineering feat from a distance? Such an effort would still emanate waste heat in the infrared, and surveys such as NEOWISE and the James Webb Space Telescope could in theory detect a Dyson Sphere. We’re also currently detecting exoplanets via transits in front of their host stars: is it possible ET would know this and build enormous planet-sized geometrical shapes to get our attention? Or perhaps, large Ringworld-shaped structures straight out of Larry Niven’s 1970 science fiction novel of the same name are a reality. One problem with this method, however, is that the transit of a deliberately placed alien artifact would have to happen to lie directly along our line of sight, which is improbable.
1. Using Spectroscopy to Examine Alien Atmospheres
This is probably the best bet to detect alien life in our lifetimes. The detection of a chemical signature such as chlorophyll in the spectrum of an alien world would be a very strong indicator of life, albeit plant life. Other telltale signs, such as the presence of large quantities of oxygen, don’t stick around long unless something is replenishing it. As with the case of light pollution, we’re just now getting the capability to image planets around other stars directly and obtain a spectrum to see what they’re made of. On the ominous side, we may also detect a synthetic element such as plutonium, which might be a sign of a recent “extraterrestrial nuclear exchange.”
One More: Looking for Alien Artifacts and “Archeological SETI”
We’ve sent out the Pioneer 10 and 11 and the Voyager I and II spacecraft with messages affixed to them … might other species be taking the “message in a bottle” approach? Considering the odds that a derelict “alien spacecraft” is in our galactic neighborhood is a fun thought experiment. We’ve sent five spacecraft — including New Horizons, whizzing past Pluto next year — on trajectories out of the solar system. That’s five missions in just over half a century of being a space-faring civilization, for a rough rate of 1 per every 10 years. One can modify Drake’s famous equation to take a guess at the number of alien artifacts that might be littering the disk of the Milky Way galaxy … though this assumes the rate of production remains constant, the spacecraft of long-dead civilizations would still be intact. Dividing this into the massive volume of the galaxy, however, we still see that it’s very much a needle in a haystack dilemma.