Life has arisen on the earth due to certain climatic conditions that are conducive to its formation and multiplication. Life on earth started as unicellular organisms which became more complex with the passage of millions of ears till the mammals originated in the Tertiary period of the Cenozoic era 75 million years ago followed by man in the Quaternary period of the same era a mere 1 million years ago.
Our galaxy, the Milky Way consists of 10,000 crore stars (10 raised to the power of 11) and the known universe consists of 10,000 crore galaxies. This means the total number of stars in the known universe is 10 raised to the power of 22 which is a mind boggling figure.
Astronomers have determined that 15% of the stars in the universe have solar systems. This translates to a figure of over 10 raised to the power of 21 for stars having solar systems.
Now for life to evolve the planets have to possess certain conditions. They are
1. Moderate temperature---If the planet is too close or too far away from the star, then the conditions of life prevailing on them is nil.
2. Presence of water---The presence of water on the planet is a must for the existence of life as we know.
3. Presence of Oxygen---Presence of Oxygen too is essential for life.
4. Presence of atmosphere---The planet has to be covered by atmosphere so that harmful cosmic rays do not get through and destroy life.
5. Moderate mass---If the planet is too heavy then life may evolve but that would prevent the evolution of higher and complex forms of life.
Let us now assume that point number 1 would be met only by 1 out of each 1000 planets. This would reduce the possible number of planets that support life to 10 raised to the power of 18.
Similarly if we consider each of the other conditions would have a chance of 1 in a 1000, the figure of the planets that can support life gets reduced by another 12 zeroes.
Even after this severe reduction, still we would be left with a figure of 10 raised to the power of 6 or a million planets that can support life.
If there are a million planets in the Universe that can support life, then some of them would have life forms that would have evolved less than us and some of them would be more evolved than us. If we consider that the evolution of life on earth is in the top 10% of the planets, then there should be at least some 100,000 planets where life has progressed more than us.
Of these 100,000 planets if we consider that only 1 in a 1000 has achieved a civilization that can crack the light barrier, then the figure of such planets get reduced to just 100.
100 is not a big figure from the Universe, but how is it that not a single civilization has tried to contact us? Even with our limited development we are desperately seeking to contact other civilizations in the universe, so they would have also done the same if they exist.
These assumptions points to the following 3 possibilities:
1. There is no other planet in the Universe that is as advanced as our own.
2. The barrier of light cannot be breached.
3. We are the only civilization in the Universe.
Now, the above deductions have been done taking into account life as we know. There is no reason to believe that there may not be life forms that are totally different from the principles that are known to us.
I am no professional astronomer but just a person interested in Astronomy and the mysteries of the Universe. I faintly remember reading a book in my native language Telugu over 30 years ago which has similarly deduced about intelligent life forms in the universe. I do not exactly recollect what the book has said in its conclusion, but it has proceeded on similar lines.
I have arrived at the above from the knowledge I have and it may look fallacious to a professional who is researching in the field of life in the universe yet I feel very interested on the matter and am posting this.
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