Search for Extraterrestrial Intelligence (SETI)
SETI’s outcome has profound implications for our future here on Earth.
SETI involves detecting electromagnetic signals from beyond the Solar system and trying to decipher if there are signs of intelligence in these signals.
To best understand SETI, it may be helpful first to examine Earth in this context. After being quiet for more than 4 billion years, Earth, starting somewhere in the 1940-s, produced the kind of electromagnetic signals that penetrated the interstellar space. We are generating such signals ever since. By now, there is an electromagnetic bubble centered on Earth with a radius of about 80 light-years, the distance those first signals of the 1940-s traveled, and this bubble is expanding at the speed of light, reaching an ever-increasing number of stars. An alien intelligence inside this bubble, assuming this intelligence has at least similar technological and scientific capabilities to our own, could detect intelligent life on Earth.
The SETI program is trying to detect such bubbles from those other civilizations. A much older civilization would have a much larger bubble than ours, possibly encompassing the whole Milky Way galaxy.
So far, SETI has seen no signs of intelligence “out there.” This is not good news.
Of course, we may be the only intelligence that has ever appeared in our galaxy. However, this does not seem likely. One cannot do statistics based only on a single occurrence, but looking at life’s history on Earth, one must marvel at its tenacity. Life emerged very early and then remade the planet to more of its liking. And, since at least the Cambrian explosion, more than 500 million years ago, life seems to be steadily progressing toward complexity, an obvious requirement for intelligence. Accordingly, we would tend to discard the “alone since ever” as a viable hypothesis.
It is also possible that civilizations more advanced than ours emit signals that to us look like having a natural source. But this too is not likely. We are advancing, and we probably would not fail in detecting an intelligence even if their signals were not as obvious as the ones we are emitting right now. Thus, one can assume that if there are intelligences “out there,” and we are inside their bubbles, we would detect their existence.
However, the longevity (L) of alien civilizations may be a worrisome clue in the deafening silence that we are exposed to. The famous Drake conjecture, which guides the estimates of the number of civilizations that we can expect to detect signals from (N), does contain this longevity factor, L. Since the time that we are listening is only a few decades, which is zero on a cosmic time scale, we would only detect another civilization if the period of their existence overlaps (shifted, of course, by the time it takes for light to travel) with the moment of our listening. Because of this, N is proportional to the longevity, L, divided by a Sun-like star’s lifetime, which is several billion years. This ratio would be a small number even if a typical civilization were to last a few million years. However, with other factors such as the number of stars, stars likely to have planets suitable for life, etc., if L is about a million, we could reasonably expect to observe a sign of a civilization “out there.” But if the lifetime of civilizations is, let’s say, only a few hundred or even a few thousand years from the moment of their coming to technological prowess, then N, the expected number of detectable civilizations, would be essentially zero.
Hence, SETI is not an academic exercise but something having implications for us all. There could be no better news for humanity than a positive SETI detection. It would mean somebody “out there” made it! This would imply that we, too, have a fighting chance to cross our scientific adolescence without extinguishing ourselves. On the other hand, the longer SETI yields zero, the darker its meaning is. Combining such silence “out there” with what we observe here on our planet gives more credence to the likelihood that our civilization would disappear in a blink of an eye.
An earlier version published at http://www.infinitetime.org.
