Distant Wanderers

Finding life on other planets (Aliens!) is a tantalising prospect that occupies our daydreams. And yet with the constant onslaught of new technology are we fast approaching a time when it could become a reality?

To humans, the idea of being alone in a Universe at least 10 to 13 billion light years across is disconcerting. The philosophical ramifications of being alone in such an overwhelming expanse of spacetime cannot be overstated. Given everything we know about the current rate of star and planetary formation, however, it would seem illogical that we should be the only sentient beings in the Universe. And given what we do know about the structure of life here on Earth and of molecules found thus far in the interstellar medium, it would appear that carbon could be the key to life's development anywhere in the Universe.

While we can only continue to speculate about the extraterrestrial development of life and intelligence, we do know that carbon production is based on the rate of star formation. Estimates by the Hubble Space Telescope strongly suggest that carbon production peaked almost 7 billion years ago. Given the time span necessary for biological evolution as we know it, some theorists now believe that it is highly unlikely that the Universe could have seen the first carbon-based intelligent life any sooner than 3 billion years ago, or when the Universe was already more than 10 billion years old. In other words, the evolution of extraterrestrial intelligent life could be a very "recent" cosmic phenomenon. In fact, as Mario Livio from the Space Telescope Science Institute and Charles Lineweaver from the University of New South Wales in Sydney have both pointed out, the Universe may only just be awakening to an epoch of intelligent life. As Lineweaver has noted, at this stage in our own development, it is impossible to know whether we have come late or early to the cosmic party, but in the long history of our Universe, we might be relative newcomers.

If there are extraterrestrial civilizations capable of communicating as we do, shouldn't it follow that the same basic physics also held for their evolution? Life as we know it, has its best chance of developing on an Earth-like, fast-rotating planet in orbit around a Sun-like star, which has a hydrogen-burning phase that would provide a stable environment for life to evolve. And even with those parameters in place, ETs would likely emerge only after their home world had developed some sort of genetic code. They would also have to become cognizant enough to communicate with each other. Yet in order to communicate over interstellar distances, extraterrestrials would first have to overcome the gravity of their own planet. In order to communicate with us, as Seth Shostak of the SETI Institute frequently points out, they would have to develop the dexterity to build technology and telescopes.