Our strange universe

It is generally assumed that the subject of astronomy has grown to its present form by a systematic process of theorising by a few visionaries and finding by keen observers. The reality is otherwise. While astronomy has grown by systematic additions to its database, the most remarkable contributions have come from the realm of the unexpected.

Nobel laureate Subrahmanyan Chandrasekhar expressed this aspect of astronomy in an interview where he narrated the episode of the press conference where two distinguished physicists, Arthur Stanley Eddington and Edwin Hubble, announced the approval for building the (then) biggest telescope on Palomar Mountain in southern California. Hubble played a major role in discovering the remarkable feature of the universe that it is expanding. Eddington provided the theoretical modelling of this finding based on Einstein’s general theory of relativity. The media asked these doyens of astronomy what they expected to find with the proposed big telescope. They replied: “If we knew the answer, there would be no need to build the instrument!”

Indeed, one can cite many examples of this aspect of astronomy. British astronomer William H. McCrea once said: “The astronomer’s view of the cosmos may be influenced to a great and almost unknowable extent by a combination of lucky and unlucky circumstances...” The example of the discovery of planet Neptune is a case in point. In the 19th century two young theoreticians had independently argued that the then observed discrepancy in the motion of planet Uranus indicated another, hitherto unknown planet not too far from Uranus was perturbing its orbit. The calculation was based on Newton’s laws of motion and gravitation. Of these, the first to complete his calculation was John Couch Adams from Cambridge, England. He sent his calculations to the Astronomer Royal Airy and to Challis, director of Cambridge Observatory, with the request that they look in the direction indicated by the calculation and discover the new planet. But these senior astronomers took the suggestion (from a young theoretician) lightly, and didn’t act. Later U.J.J. Le Verrier from Paris did the same calculations and sent his results to leading French astronomers. He too faced the same apathy. But being persistent, he sent his results to the Berlin Observatory too.

As luck would have it, the observatory’s director was away on leave, celebrating his birthday. In his absence a young astronomer, Galle, who was holding charge, saw the letter from Le Verrier. He took the result seriously and looked for the planet. It was there as predicted. This only tells us not to ignore young astronomers! However, it underscores the fortuitous circumstance that the director of the observatory wasn’t on duty. Who knows Had he been present, he may have ignored the letter from France.

Some astronomical events also depend on the chance element in location and timing. Take the phenomenon of total solar eclipse. It is a spectacular event, that earlier led to many superstitious beliefs. But the eclipse’s scientific explanation is simple: it is a shadow-effect. When the Moon comes exactly between the Earth and the Sun, it blocks the view of the Sun as seen from certain regions of the Earth. But if we think a little deeper, we notice this “blocking” of the Sun by the Moon depends on a coincidence. The diameter of the Sun is around 400 times the diameter of the Moon. The reasons why the Moon is able to block a body 400 times its size is because it is closer to the Earth compared to the distance of the Moon from the Earth. (If we hold our thumb at arm’s length it can block the view to a tree trunk about a hundred metres away.) If we have not forgotten our school geometry we can say the Sun is within the angle subtended by the Moon at our eye. But the remarkable part of the story is that the Sun is just within that angle. This happens as the distance of the Sun is around 400 times the distance of the Moon from us. We thus encounter the same factor 400. What does this signify It means the totality of the eclipse is only just achieved. Had the Sun been slightly bigger in size, say, 410 times the Moon, the latter would not have been able to block it out of our view. Had the Sun been slightly smaller, say 390 times the Moon, a total solar eclipse would have been more common and lasted longer. Thus it is a chance effect that makes the total solar eclipse just possible, but so rare.

While the Sun, Moon, planets and stars are commonly seen, the cosmos contains so many other objects, far more intriguing than these. There are the pulsars which send out pulses of radiation with so much regularity that the best manmade clocks fail to match them. Then there are quasars, that are such powerful radiators that a typical one sends out energy equivalent to what is radiated by a galaxy containing a hundred billion stars, that too from a volume of the size of our solar system. There are huge radio sources extending to sizes of several million light years and very powerful but shortlived bursts of gamma rays. But the remarkable thing about each and every new discovery has been that it was unexpected! Usually it so happens that a new and more powerful observational facility results in the discovery of some new type of object. It very well justifies the statement by biologist J.B.S. Haldane — that the universe isn’t only queerer than we suppose, but it is queerer than what we can suppose.

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.