Have there been aliens? Will there be aliens?
The fact we are alive and pondering a vast Universe from spaceship Earth raises a number of fascinating questions. Astrophysicist are now asking why “here” and why “now”. What is the chance of life emerging around a star like the Sun, about 12-13 billion years after our Universe was born?
A recent work looked at the past, and set a lower bound on the probability that one or more technological species have evolved anywhere and at any time in the history of the observable Universe (Frank 2016). The authors conclude that is very likely that humanity is not the first technological intelligence that has evolved, so far, in the Universe. “Yes, There have been aliens” seems to be the conclusion of this work, although the Fermi paradox seems to point out that either intelligence is a very rare avenue of life and/or alien civilizations do not last very long, or that aliens like to play hide-and-seek with us.
But let’s forget intelligence for a second and just focus on the likelihood of Life1 in the Universe. In a paper just posted on the arXiv and submitted to the Journal of Cosmology and AstroParticle Physics, Avi Loeb (Harvard), Rafael Batista and David Sloan (Oxford), discussed the relative probability of Life emergence in the Universe as function of time. This is, in a sense, similar to asking the question “What is the likelihood of being born on Earth on a certain year?” assuming some knowledge of the number of humans alive as function of time across the full history of our planet.
Life as we know it, that is life involving carbon-based chemistry in liquid water↩