Opinion How renowned cosmologist Jayant Narlikar helped build the steady-state theory of the universe

The steady-state theory, mainstream in the 1950s and the 1960s, has become less popular over time, mainly because of the emergence of new evidence that better supports the Big Bang theory.

(Express archives)

Narlikar’s contribution

Born in 1938 in Kolhapur, Maharashtra, Narlikar was a young PhD student at Cambridge University in the early 1960s, when he produced a series of influential works in cosmology. He did so under the guidance of Hoyle, who had come up with the steady-state theory of the universe in collaboration with Hermann Bondi and Thomas Gold.

Incidentally, Hoyle is also the one who coined the term ‘Big Bang’, referring to that theory in a rather dismissive manner in a radio interview in 1948.

Narlikar entered the picture at a time when fresh experimental data produced by radio astronomer Martin Ryle, at the Cambridge University’s Cavendish Laboratory, seemed to support the Big Bang theory, and provided new energy to the debate. Narlikar and Hoyle used some of Ryle’s own data to show that Ryle’s results were limited, and not conclusive evidence of the Big Bang theory.

The two developed their work further, and produced their famous Hoyle-Narlikar theory that promised to alter several other established theories, including gravity. Their main motivation for an alternative theory seemed to stem from a few major shortcomings of the Big Bang theory that continue to puzzle scientists even today. The Big Bang theory says the universe came into being in one single instant about 13.8 billion years ago. All matter and energy in the universe were created in that single instant, and all subsequent events are only transformations of this pre-existing matter and energy.

The Big Bang theory is unable to explain, even today, where the matter and energy produced in that instant came from, or what happened before that. That sudden creation of the universe out of nothing has been an uncomfortable issue for a lot of scientists.

Hoyle and Narlikar instead worked to explain the steady-state theory. One of their key ideas in their hypotheses was the constant creation of new matter in the universe. This was important for the model of the universe that they proposed.

In building this model, they also sought to modify Einstein’s general relativity. In general relativity, gravity arises out of local curvature of spacetime caused by heavy objects. Hoyle and Narlikar proposed that gravity at any location in the universe could also be affected by far-away objects. In a way, all the matter everywhere in the universe contributes to gravity at any given place.

In an expanding universe, the distribution of matter in the universe would change, and that would affect gravity at any given location. To keep gravity unchanged, Hoyle and Narlikar had to introduce the idea of constant creation of matter.

In his autobiography, My Tale of Four Cities, Narlikar himself explains how the universe can be seen as expanding steadily, while maintaining a constant density.

“To understand this concept better, think of capital invested in a bank which offers a fixed rate of compound interest. That is, the interest accrued is constantly added to the capital, which therefore grows too, along with the interest. The universe expands like the capital with compound interest. However, as the name ‘steady state’ implies, the universe always presents the same appearance to any observer. Such an observer, for example, can measure the density of the universe from time to time. He or she should find the universe to have the same density at all times. How is this possible, when we know that anything that expands becomes diluted and less and less dense? To answer this question, Bondi, Gold and Hoyle had to conclude that there is new matter created to make up for the diminishing density of existing matter,” Narlikar wrote.

That was the reason why the steady-state theory proposed that the density of matter in the universe was constant. “It was the same, say a few billion years ago, as it is now, and as it will be a few billion years in the future. In this respect, the theory differed from its rival, the big bang theory which assumed that the entire universe that we see today came into existence in one go, through a primordial explosive creation event,” Narlikar wrote.

His major contribution was in modifying Einstein’s general relativity equations in a way that was consistent with the creation of new matter in the universe.

(Express archives)

Decline of the theory

Despite the elegant mathematics that Narlikar had produced, the steady-state theory slowly lost out, with the emergence of new observations that fit the Big Bang model better. One of the most prominent discoveries in this regard was that of cosmic microwave background (CMB) radiation in 1965.

Discovered accidentally, CMB refers to the microwave radiation that fills the universe and is considered to be remnants of the Big Bang event. The Big Bang theory predicts the existence of this kind of background radiation. It also proposes that this radiation would have a uniform temperature everywhere. The accidentally discovered CMB has properties that are well aligned  with the predictions.

Some other observations made later, including evidence to show that galaxies evolve, and that distant galaxies are younger and more chaotic, and some of the work of Stephen Hawking and Roger Penrose on singularities, piled more evidence in support of the Big Bang theory. They also challenged the steady-state theory.

Narlikar and Hoyle tried to address some of these challenges, but by the 1980s, Big Bang theory had emerged as the dominant explanation for the origin of the universe.

Narlikar, while acknowledging the growing evidence in favour of the Big Bang, maintained that the evidence was still not unambiguous, and was based on several unproven assumptions that were open for challenge. He considered himself amongst the minority that believed that sufficient evidence existed to re-examine the situation.

Although their big ideas have largely become out of fashion now, the work of Narlikar and Hoyle has not been discarded. The underlying mathematics was based on very sound foundations, and many of the frameworks and methods developed by them continue to be useful in different situations.