From the beginning the spark of life is everywhere, longing to spring up in the universe.

*The Human Phenomenon – Pierre Teilhard de Chardin* ( 1881 – 1955 ).

On May 10^{th} **NASA’s Kepler mission** announced the discovery of the largest collection of planets ever to be found, a staggering 1,284. Launched in March 2009, Kepler is the first NASA mission to have detected earth – size planets orbiting stars in or near the habitable zone – the orbital region around a star in which liquid water may pool on a planet’s surface.

We have been learning more and more about the origin and structure of the universe, whilst yet remaining in complete ignorance as to whether or not mankind remains the only living system.

Some time before the launch of the Kepler telescope the mathematician Amir Aczel in his book *Probability 1 *went to great pains to demonstrate the existence of other intelligent life in the universe simply by applying the Drake equation. In fact, according to the astronomer Frank Drake ( 1930 – ) the number ( N ) of possible extra-terrestrial civilisations depends on the product of seven factors, or variables: i) N_{*, }the number of stars in our galaxy; ii) f_{p , }the fraction of those stars with planetary systems; iii) n_{e }, the number of planets per star with environments favourable to the formation of life; iv) f_{l }, the fraction of suitable planets on which life actually appears; v) f_{i} , the fraction of planets on which intelligent life evolves; vi) f_{c} , the fraction of planets with civilizations able to communicate; vii) L, the length of time such civilizations release detectible signs into space.

When seven dice are tossed the probability of achieving a number seven is given by the product of getting a number one from each die, i.e. 1/6 ·1/6 · 1/6 · 1/6 ·1/6 · 1/6 ·1/6, or ( 1/6 ) ^{7 }, where the symbol (·) as used in mathematical equations means multiply. In similar fashion, the probability of getting (N ) intelligent civilisations in our galaxy is given by N_{*} · f_{p }· n_{e }· f_{l }· f_{i} · f_{c }· L.

The conclusion arrived at by Drake and Aczel was that the existence of intelligent life in the Milky Way was a certainty. Let us now tackle the Drake equation once more, this time using a more prudent approach.

If we estimate the number of stars in the Milky Way to be 300 billion, then ( N_{* }) where only 5% ( f_{p }) are sun-like would be N_{* }· f_{p} = 300 billion _{ }· 0.05 = 15 billion.

According to the astronomer **Mayor**, who discovered the first extra solar planet, every sun-like star possesses at least one planet. This assumption the Kepler mission has now validated. In addition, if the research community is to believed, there could be many more planets than sun-like stars. Thus, if we seek to determine which planets are orbiting a distant star in the habitable zone, there should be at least 15 billion planets for us to investigate. Several scientists interviewed by Aczel are of the opinion that the fraction of planets with chemistry suitable for triggering the lottery of life should be in the region of 10%. Using a far more conservative estimate we might say it could be in the region of 0.1%, or 0.001 ( n_{e} ).

Thus, N_{* }· f_{p }· n_{e} = 15 million.

Even though a statistically based estimate of the fraction of planets with the right environmental factors for life is not possible, scientists involved in Drake’s equation have conjectured that the value of the factor, or variable, f_{l}, should be 10%, or 0,1. By adopting a rather more conservative approach, dividing 0,1 by 100, f_{l} becomes equal to 0,001. Thus, N_{* }· f_{p }· n_{e} · f_{l} = 15,000.

While it remains arguable whether intelligence is not just a fluke in the genetic development of life, there is a considerable difference between life and intelligent life. According to the scientists discussing Drake’s equation, of all planets supporting life the proportion of those supporting intelligent life, f_{i}, could be in the region of 10%. Again dividing by 100 in pursuit of a more prudent approach, we obtain f_{i} = 0.001.

Thus, by multiplying: N_{* }· f_{p }· n_{e} · f_{l} · f_{i} , we find 15 intelligent planets in the Milky Way.

The Greek, Roman, Egyptian or Mayan civilisations did not have the means to communicate with other extra-terrestrial worlds, thus the factor f_{c} of Drake’s equation can be considered as a sort of technological index, whilst the factor L marks the longevity of a civilisation, given that intelligent civilisations may eventually destroy themselves. An estimate of L might be the distance in time between Marconi inventing the radio and the destruction of Hiroshima.

Several scientists have attributed a probability ratio of about 3 % to both factors f_{c } and L. By once again dividing both percentages by 100 for prudence sake, we could complete the Drake equation as follows,

N = 15 · 0.03^{2}/100^{2} = 0.00000135. In this way we arrive not at the certainty promulgated by Drake and Aczel, but at the evanescent 1.35 / 1,000,000 probability of the existence of other intelligent planets in the Milky Way.

According to the latest estimates by astrophysicists there are at least 100 billion galaxies in the Universe.

By applying the above evanescent probability to each and every galaxy, we would then have, according to the Law of Large Numbers, 0.00000135 · 100,000,000,000 = 135,000 overall intelligent planets.

In order to determine the probability of Earth being the most intelligent planet, given the complete dearth of information, the principle of symmetry has to be applied, namely that all planets have the same probability of securing first prize. This probability is equal to 1/135,000, or 0,0000074074.

The diameter of the Milky Way spans over 200,000 light-years of space and it takes 50,000 years for the light from its centre to reach the Earth. Bearing in mind that light travels at a speed of 186,000 miles per second, in one earth year light travels almost six trillion miles.

The closest star to Earth is Alpha Centauri, situated at a distance of 4.3 light-years. A hypothetical phone conversation with inhabitants of a planet orbiting this star would last several dozen years, since one would have to wait no less than nine years to get an answer to any question one might wish to pose. In short, should we receive a signal of whatever kind from another intergalactic civilisation, it is quite possible that by the time we receive the signal that civilisation may have disappeared.

Stellar distances preserve Earth’s future from extra-terrestrial aggressors, but not from internal ones.

Ennio Falabella London, 3^{rd} August 2016