There is perhaps little that has held the attention of humankind for so long as the nature of the cosmos and the motion of the sun and the stars. Over centuries of contemplation through long nights undisturbed by city lights, the ancients saw people, animals and gods in the heavens and wove theories and fables around them, and these were the first cosmologies
It was natural to think of the earth as the centre of the action and to imagine the circle as the suitable path of these wonders of creation. The Ptolemaic system traced the movement of the sun and stars as circles around the earth and the paths of the planets as circles within circles. The method was quite accurate in predicting the position of planets and seasons and there was little reason, astronomical or philosophical, to doubt the model.
That the earth could be going around the sun became a serious possibility only after the discovery of the telescope and Galileo’s discovery of the moons of Saturn. And yet, for many years, the old system was the more accurate in predicting the paths of the planets!
But after the discovery of the telescope and the formulation of Newton’s laws of gravitation and motion, more extensive and accurate data about the night sky became available. The solar system was studied in detail and the nature and distribution of the fainter, ‘stellar’ heavens was analysed. The great bulk of stars were found to lie along a bright belt in the sky, called the Milky Way. This, we now understand, is because the earth is on the outside of a disk-shaped collection of stars, or galaxy. When we look along the plane of the disk, we see the vast number of stars that belong to the galaxy.
The Milky Way is known to be a galaxy because there are methods of measuring the distance to a star and it is found that this multitude of stars lie together, in a collection, while other stars are many times more distant. Painstaking plotting of the positions of stars shows that our galaxy has a bulge in the middle, which may happen if the galaxy were spinning round. And painstaking measurements of the motion of the stars in the Milky Way show that this is also true!
Distant stars were found to consist of groups of stars, or galaxies in their own right. Groups of galaxies were found to form clusters and groups of clusters to form greater clusters. The scale of distance was in millions of light years, or the distance light travels in millions of years. Light, at 3,00,000 kilometres a second, takes about a second to reach us from the moon, some eight minutes to come from the sun, and about five hours for the distance from Pluto. In comparison, Proxima Centauri, our nearest star after the sun, is 4.3 light years away and the Milky Way is 100,000 light years across. The farthest stars are over 10 billion light years away and this serves as an estimate of the age of the universe itself.
The last century was rich in theorizing about the dynamics of this vast universe. How did the different parts affect each other? What were the processes going on? How far did the universe extend? In the time scale of millions of years, was the universe changeless or turbulent? Physics and Mathematics revealed much about the birth, flourishing and death of stars, the nuclear fires that warmed and lit them, mysteries of supernovae, neutron stars and black holes.
An astonishing discovery was that the universe appears to be expanding, with the farthest parts receding the fastest! Distances to star clusters were estimated with the help of Cepheids, a class of stars which have a ‘cycle of brightness’. It is found that the intrinsic brightness, or how the star looks before the brightness dims due to distance, rises and falls, in a ‘cycle of brightness’. And then, that the cycle is slowest with the Cepeids that have the greatest intrinsic brightness. Once we have this rule in hand, observing how long it takes for the Cepheid to rise, fall and rise again becomes a measure of the intrinsic brightness. But because the star is a distance, it actually appears much dimmer, and by measuring how much dimmer, compared to the intrinsic brightness, how far away the star is can be worked out.
Another feature the the light from stars is that their spectrum contains special bright or dark lines of light corresponding to common elements, like hydrogen, in the atmosphere of the stars. Now if the star is moving away from the observer, then, the position of these ‘marked’ lines shift towards the red side of the spectrum, just like the whistle of a railway engine moving away from us gets less shrill. This effect, the so called ‘redshift’, is then a measure to work out how fast the star is moving away from us.
Using these two measuring rods, the Americl astronomer, Edwin Hubble, in 1929, was able to show that all distant stars were receding, and also that the speed of recession was greated for stars that were further away. This was a remarkable observatoin and is now the rule by which the distance to the most far away stars is worked out, by measuring the red shift. But more important is the consequence, that the universe itself is expanding!
Explaining the many startling features of the universe has long been the quest of cosmologists. The ‘big bang’ theory, that the universe set out some 15 billion years ago as a point that appeared from nowhere, is successful in explaining much of what has been observed and is currently the accepted way to think about the cosmos. But a ‘rival’ theory, the ‘steady state’, now less in favour, also has an important place in the recent history of cosmology.
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Professor Jayant V Narlikar, later Director of the Inter University Centre for Astronomy and Astrophysics at Pune, in India, was an important participant in the work done in the last few decades in this field and was one of the leading architects and proponents of the ‘steady state’ theory. |
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In the early 1960s, when the big bang was not considered a ‘foregone thing’, as most view it today, Narlikar had become knwon in the field for his work in formalizing the steady state theory. Recent discoveries of previously unknown forms of matter in the universe, like ‘dark matter’, which can be detected only by its gravity, or proposed kinds of matter where the force of gravity is ‘repulsive’, may even draw the ‘steady state’ nearer centrestage.
Modern cosmology started in the early 20th century, which saw two revolutions in scientific thought. These were the quantum theory and the theory of relativity. The quantum theory is the new way of thinking about matter at very small dimensions, like in atoms and atomic nuclei. At this minute scale, our everyday experience of ‘smooth’ changes needs to give way to changes in ‘packets’ or ‘steps’. Even the conservation of energy is found not to hold for short durations and nature is found to behave more ‘statistically’ than according to clear rules.
The theory of relativity had its origin in a strange discovery about the speed of light. Our usual experience is that if we are in a car that is moving at 100 kmph and we throw a stone backwards at 60 kmph, the stone will strike the ground at 100 – 60 = 40 kmph. But if a beam of light were shone from a speeding meteor, this speed would be the same both when measured by the meteor as well as on the ground!
Einstein solved the mystery with a new way of calculating speeds, which gave the correct, though unfamiliar results when things were moving at speeds near the speed of light. This new way of working things out was equally valid at ordinary speeds too, because the strange effects that showed up at high speeds reduced to normal experience at lower speeds. What Einstein showed was that measurements of lengths and time differed when measured by observers in motion with respect to each other. In our usual way of looking at things, we refer to an event by the place where it happened, for instance by the latitude, longitude and the distance above the earth, and the time, say in GMT. Another event, seen by another observer, would have its own position, and time, also by GMT, and we can usually compare the two events, say how far apart they occurred and which one took place first.
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But Einstein showed that place and time, in fact, depend on the speed with which the second observer is moving with respect to the first. If this speed were comparable with that of light, then the distance between the events would perceptibly shrink, in the view of the moving observer. The time between their occurrences would also increase or reduce, and, unless the events were so close together in position and time, that a signal from one could have caused the other, their order of occurrence could reverse! An event, generally, is thus located not by three dimensions of space and an independent dimension of time, but by four dimensions of space and time, in a new space called space-time. This four dimensional space is found to be the correct way to calculate when speeds are high. This fourth dimension smoothly reduces to the usual, independent time dimension as we slow down to our usual pace. |
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The stretching out of time when things move fast gets neatly tested in the case of radioactive particles that come in as cosmic rays, at velocities near that of light. When these particles are produced in reactors it is seen that a given percentage of the particles decay in a certain interval of time. But the particles streaming in as cosmic rays are seen to take much longer to decay to the same extent. The meaning is clearly that time seems to pass slower for these high speed particles.
Another consequence of the theory of relativity is that energy and mass are equivalent, by the famous E = mc2 relation (c, the speed of light is such a large number that even a small mass is found to be equivalent to huge energy. This is the idea behind nuclear fuel and the atom bomb).
Einstein generalized the theory by taking into account the effect of gravity as well. As an isolated observer cannot distinguish acceleration due to a force from the effect of gravity, Einstein considered that gravity and acceleration were the same thing. With this basis, he rewrote the equations of motion, with the time dimension taken as just one more dimension, like the three measures of position, and in the working, he included the equivalence of mass and energy. This, in general, was the correct method to use when speeds were high and masses huge, so that gravity became important. A remarkable thing about this representation was that the presence of a mass got translated into a curve in the four dimensional space, which then affected the motion of bodies, just like gravity would have!
This new view, the General Theory of Relativity, was soon verified with incredible accuracy, in explaining the eccentric motion of Pluto, something that had defied Newtonian mechanics. That mass caused space to curve was also verified when starlight was seen to bend when passing the sun during a solar eclipse.
Einstein then applied his new equations to analyse the dynamics of the universe. As a first simplification, the suns and galaxies were not considered individually, but only ‘on the average’, as if the total mass of the universe were evenly spread, without ‘lumpiness’. Another assumption he made was that the universe was essentially static, which is to say, not evolving or changing in any basic way.
But the approach did not lead to solutions that made good sense. An implication of the solutions was that the universe should contain a form of matter that had a quality that was the opposite of gravity – it repelled, with the force of repulsion increasing with distance! The Russian physicist and mathematician, Alexander Friedmann then suggested that these problems arose because of thinking the universe was static. If this condition were removed, the theory seemed to behave itself! This was an answer, to consider the universe not as static, but as expanding! Even Einstein granted that ‘he had been a fool(!)’ to think otherwise!
This was the start of the theories of the expanding universe. The equations of Einstein were not in three dimensions, like the space we are used to, but were in ‘space-time’. The expansion, then, was not the kind that we can visualize, in three dimensions, like an expanding balloon, but was an expansion of space itself. The example of the balloon can illustrate the expansion of space in two dimensions. Take two points on the balloon. As the balloon expands, the distance between the two points would increase. A two dimensional being on the surface of the balloon would then experience an ‘expanding’ of space. If the being were spotting stars in a two dimensional sky, it would detect the recession of galaxies!
The image of an expanding universe implies that in the past the universe was smaller and at some time it must have been of zero dimensions. In the 1940s, George Gamov proposed that the universe may have set out as a primeval atom that suddenly exploded, with tremendous density and heat, and simultaneously become the origin of all matter and space. As this infernal entity expanded, with particles and energy moving outwards, it would pass through stages of being just photons, then free electrons and then, neutral hydrogen atoms. And thus, over millions of years, the hydrogen would spread out into space, form collections as clouds that collapse into stars, then galaxies, and so on.
The theory has now been greatly refined and has passed many tests and has been able to account for many things about the universe. But at the time, it sounded so fantastic, that the renowned astrophysicist Sir Fred Hoyle mockingly dubbed the theory the ‘Big Bang’, a name that has stuck. One of the problems with the theory, at the time, was that calculations based on parameters then available put the age of the universe at some two billion years. This was far short of even geological evidence on the earth, of four to five billion years, and it was known that some galaxies were over ten billion years old. The figure now computed by the big bang theory is in much better agreement, but in the 1940s, this was a serious snag.
Gamov had also proposed that the early universe, being intensely hot, would have emitted radiation like any hot body. Gamov said that some traces of this emission should exist, in the form of uniform background radiation. This would be the ‘smoking gun’ or clinching evidence that there had been indeed a blazing fireball at the start of it all. In the 1940s no such radiation had been detected.
In 1948, Hoyle, with Herman Bondi and Thomas Gold, proposed an alternate theory. The theories till then had been based on a ‘cosmological principle’, that the universe was homogenous and the same in all directions. Hoyle et al suggested going one step further, to say that the universe was also the same at all times, or in a steady state.
This is not to say that the there are no processes in the universe. By all means, stars would be born, collapse to cores of fiendish temperatures, synthesise the elements, explode as supernovae, crush into black holes… but the totality of the heavens would remain unchanged like a street scene is much the same through the afternoon, though hundreds come and go!
But the expansion of the universe, the receding of the farthest stars, how does that fit into the steady state? If the stars continued to recede beyond some 10,000 million light years, when they would start receding at the speed of light, and disappear from view, could we say the universe is in a steady state? Hoyle, Bondi and Gold said that this would be compensated by spontaneous ‘creation’ of matter everywhere in the universe. Would this not violate the principle of conservation of matter, that matter could neither be destroyed, nor created? And if matter were being continuously created, would we not have seen evidence of the fact?
The objections were countered by evidence of spontaneous creation of matter by gamma rays and other phenomena that allow violations of conservation, in small quantities. In any case, the theory does not attempt to describe the process of creation. It only says that such creation is a property of matter, just like mass or charge or gravity. And as for evidence, the universe consists of such vast spaces of near vacuum that the rate of production of matter needs to be only one atom of hydrogen per litre of space every billion years! Surely, we have no experimental competence to measure anything as meager as that!
The stand taken, in fact, is not as arbitrary as it seems, if we consider the possible hypotheses about matter in the universe:
i. that all matter has always existed
ii. that all matter was created at some definite time, the moment of creation
iii. that matter is being continuously created.
The first possibility implies that infinite time has elapsed since matter was created. If this be the case, all free hydrogen in the universe would have formed stars and got converted to helium, lithium and the higher elements. But there is still so much hydrogen in the universe that this possibility gets ruled out.
The second possibility is nothing but the big bang theory. At the time the steady state was proposed, the big bang had serious flaws. The third possibility, the steady state, was hence a totally reasonable alternative. But still the steady state theory was pilloried and battered, mainly because it relied not on observation or deduction but leaned on the ‘perfect cosmological principle’. Was this not like the Ptolemaic reliance on the ‘perfection’ of the circle to justify a picture of the cosmos?
This was when Jayant V Narlikar, a young research scholar at Cambridge got active and collaborated with Hoyle to develop a rigorous basis for the steady state theory. Narlikar was born in Kohlapur, Maharashtra in 1938 and was educated at the Banaras Hindu University. He continued his studies in Mathematics and astronomy at Fitzwilliam House, Cambridge, to be selected as a research scholar by Sir Fred Hoyle, in 1960.
During the early 1960s, Narlikar and Holye developed an efficient theory for the continuous creation of matter in the setting of Einstein’s General Relativity Theory. Historically, what Newton’s theory of gravitation did was to link two bodies ‘at a distance’, with no apparent connection between them. Einstein had replaced this ‘action at a distance’ or the idea of a ‘field’ with the force of gravity being due to the structure of space-time. This was so successful that attempts were made to connect the electromagnetic and nuclear forces as well with such a geometric approach. These, unfortunately just made no headway. But meanwhile, even electromagnetism, the showpiece of the ‘field’ approach had been elegantly formulated through the ‘particle’ approach.
Hoyle and Narlikar now attempted a new theory of gravitation to support the creation hypothesis. The insight of relativity also clears ‘action at a distance’ objection by showing that distance itself shrinks to ‘no distance’ in the four-dimensional space-time continuum. With the action at a distance difficulty out of the way, Hoyle and Narlikar brought in an idea that mass and inertia of matter was not an intrinsic property but arose from interaction with distant bodies. In fact, they have developed an equation that relates the mass of any object with the total mass of the observable universe. The equation also implies the creation of new matter quite naturally, and not by the ad hoc insertion of new terms, like Hoyle had done earlier. The theory, in fact uses the energy of the universe’s expansion itself to create the new matter!
Around the same time, independent researchers stumbled upon a uniform microwave radiation background in all space. This was the clear proof of the big bang theory, which had not been there so far. It was a momentous discovery and so revived the big bang school that the steady state hypothesis began to sound like heresy! The ‘age of the universe’ problem with the big bang theory had also been resolved and now the rasion d’être of an alternate theory evaporated.
The steady state theory also suffered the disadvantage of not having made any specific assertion that could be established by experiment. At the time, the background microwave radiation, furthermore, had no explanation in the steady state theory. For all its intellectual validity and its contribution to objectivity in science, the steady state theory began to be viewed at best as a pursuit of academic interest.
But Hoyle and Narlikar persisted and soon came out with a modified steady state theory, which permitted ‘mini bangs’ in localized ‘bubbles’ where the universe may expand and contract without creation. While the explanation has been viewed as ‘contrived’, Hoyle and Narlikar and Narlikar with others, have persisted with revisions and alternates, in keeping alive a line of research which cannot be abandoned just based on elimination of some questions about a theory which still bristles with problems. This is all the more important in a field, where as one thinker said, we are like the fruit fly, who, based on a glimpse of humans during its brief hours of life, is trying to work out the nature of human genetics!
Narlikar went on be elected Fellow of King’s College and then worked as a staffer in the Instiiute of Theoretical Astrophysics at Cambridge. In 1972, he returned to India and managed the Theoretical Group for Astrophysics at the Tata Institute of Fundamental Research, Mumbai.
Narlikar is now active in promoting the popularization of science, in teaching and research and in managing the Inter University Centre for Astronomy and Astrophysics, at Pune. He is married to Mangala Rajwade and they have three daughters.
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