The history of mankind is full of instances where important sections of society expressed views that we humans on the Earth are the most important part of this universe. Time and again such beliefs are expressed and eventually they are shown to be wrong. But they resurface in a different form and eventually meet the same fate.
The longest surviving belief of this kind is the so-called geocentric theory of the universe. It may have been around even earlier, but it was really popularised by the Greek philosopher Aristotle. A distinguished philosopher and teacher, Aristotle counted among his distinguished pupils, Alexander the Great. Alexander engaged in several battles which he won and thus expanded his empire. However, even though he thought that he had more or less conquered the world, his empire did not last more than a century. In contrast, Aristotle’s teachings lasted nearly two millennia. In particular, his view that the earth is fixed and the whole universe revolves round it was the dogma that prevailed not only in his local region, but in Europe, Arabia and the Indian subcontinent.
Thus, when in the fifth century, Aryabhata, a distinguished scholar in mathematics and astronomy made the statement that the Earth revolves round an axis against the background of fixed stars the reaction to this “counter-view” was threefold. His peers and followers like, for example, Brahmagupta were scathing in their criticism. There were others who tried to take advantage of the flexibility of Sanskrit language to reinterpret his verse to mean the exact opposite. And there were others who simply ignored the statement saying that it was not his own but inserted later by somebody else. (There are several such examples in our ancient literature.)
In Europe of the 15th-17th centuries we have examples of Giordano Bruno, Nicolaus Copernicus and Galileo Galilei — all of whom had to suffer for daring to oppose the geocentric theory. But after observational tests finally demolished the geocentric theory, the human prejudice switched its focus on a different aspect. Sure, human ego was hurt to learn that the Earth is not the centre of the universe: But the Sun which was the centrepiece of the planetary system was seen to be important enough to be at the centre of the Milky Way. For as better telescopes became available, the astronomers began to get a large-scale view of the vast collection of stars that seem to be part of the Milky Way. The British astronomer William Herschel made a map of this system and it showed the Sun to be at the centre of the Milky Way. This view dating from the 19th century went some way towards pleasing human ego, which had suffered a blow with the downfall of the Earth.
However, the early 20th century saw new telescopes with better observing technology leading to a major revision of Herschel’s map. The revised Milky Way did not have the Sun at its centre. Rather, with a disc-like shape the Milky Way had the Sun at about two-thirds of the radius away from the centre. Thus gone was another “special status” that man aspired to in the universe. However, an even greater shock lay ahead.
Any astronomy textbook at the beginning of the 20th century would proudly announce that the Milky Way was the sole galaxy of stars in our universe. Having lost the battle for the Sun’s pre-eminence the stress now was on the Milky Way — a galaxy of some hundred billion stars. That it was unique in the universe seemed to restore the human ego somewhat. But that was not to be! Astronomers were finding small cloud-like patches around the Milky Way: What were they The majority believed that they were nebulae, that is, cloud-like structures in our Milky Way. But a small minority felt that they were galaxies like our own but very far away. At first this interpretation was ridiculed but in the face of evidence, gradually but surely coming from observations, it had to be accepted. So the sum total was that a perfect democracy prevails in our universe and no galaxy has any special status.
However, human ego does not rest. Today, it seems that there is a resistance to accepting the possibility of extraterrestrial life. Taking all numbers together, we can argue that there are some thousand billion, billion stars in our observational range, of which the Sun is one ordinary member. Can we argue that life exists only on one star out of this vast number The astronomers having so many stars to play with would tend to argue in the negative. However, the biologists often take the cautious and opposite stand to say that life is a very complicated phenomenon and it may be so complicated that it could materialise only in one case, namely here!
In recent times, positive evidence that is evidence in favour of life is coming from two sources. There are complex organic molecules seen in space in giant clouds spanning several light years in our galaxy and beyond. Some of these molecules are seen as part of the DNA which is basic to life on Earth. Also we are finding many stars with planets like the Earth and some have atmospheres like that on the Earth. So there is the material that makes living systems and there are locations that may be friendly to life. These two basic factors suggest that life may not be all that rare.
Of course, the enthusiasts for advanced life have already started sending radio signals to prospective ETs and are looking for tiny signals among the noise that comes through the radio telescopes. On a more modest level in India, efforts are on to collect microorganisms in the Earth’s atmosphere. Some bacteria have indeed been found at heights of over 40 km. Are these from outside or are they tossed up from the Earth Again one notices a tendency to deny the extraterrestrial option. Is this a new version of the geocentric thinking
The writer, a renowned astrophysicist, is professor emeritus at Inter-University Centre for Astronomy and Astrophysics, Pune University Campus. He was Cambridge University’s Senior Wrangler in Maths in 1959.
