Wednesday, June 8, 2016

Earth: One Of The Early Civilizations In The Universe

A paper in Monthly Notices of the Royal Astronomical Society in 2015 (1), based on data collected by NASA's Hubble Space Telescope and the Kepler space observatory, has arrived at some unexpected conclusions. The analysis suggests that earth was quite early in its formation as a habitable planet compared to all the habitable planets the universe will eventually produce.

Kepler's planet survey indicates that there are about 1 billion Earth-sized planets in the Milky Way galaxy at present. If you include the 100 billion galaxies in the observable universe, the number of Earth-like planets becomes exponentially larger. The Hubble volume (the volume of space containing all objects traveling away less than the speed of light due to the expanding universe) is estimated to contain about 10^20 Earth-like planets.

Calculations suggest that our solar system formed after 80% of the existing Earth-like planets in the Universe and the Milky Way had already formed. However, if the existing gas in the Universe continues to condense to form stars and planets, the analysis shows that the Earth formed before 92 per cent of similar Earth-like planets are expected to ever form in the future. In other words, there is less than an 8% chance that we are the only civilization the Universe will ever have.

But if we assume that the Milky Way today contains just one other civilization, calculations show that it is likely that Earth would be at least the ten billionth planet with a civilization in the observable Universe. The observable Universe would eventually contain at least one hundred billion civilizations.

If the calculations are right and most of the Earth-like planets in the Universe will form in the distant future, a civilization a trillion years from now will have a very difficult time in learning how the universe began and formed since most of the evidence for the big bang will have dissipated due to the accelerating expansion of the Universe. We may then consider ourselves lucky in being one of the “early” civilizations to form. 

If we are an early civilization, perhaps the only civilization in the Milky Way until now, though many more will eventually form, it might explain Fermi’s paradox, in which Enrico Fermi famously asked “Where is everybody?” in referring to why signs of extraterrestrial life haven’t yet been found. In the distant future we will be the the ones contacting their early civilizations, our own UFOs to be seen in their skies, and we will be imparting our knowledge of how the Universe formed since they would have no way of knowing.


1.     Peter Behroozi and Molly Peeples. On The History and Future of Cosmic Planet Formation. Monthly Notices of the Royal Astronomical Society, 2015 DOI: 10.1093/mnras/stv1817