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

Indian Express

20-05-2025

Prof Jayant Narlikar, one of India's best-known scientists, passed away in Pune on Tuesday morning (May 21).
A cosmologist, Narlikar is best known for developing an alternative to the Big Bang theory of the origin of the universe, in collaboration with his PhD guide Fred Hoyle, who was among the prominent figures of 20th-century astrophysics.
The Hoyle-Narlikar theory produced evidence to support what is known as the steady-state theory of the universe. Unlike the Big Bang theory that suggests a definite beginning, and possibly an end, to the universe, the steady state theory maintains that the universe has always been, and would continue to be, the way it is – infinite in extent, without a beginning or an end.
It acknowledges an expanding universe, which was experimentally verifiable, but adds that the universe is able to maintain a constant density by continuously creating new matter.
The steady-state theory, a powerful challenger to the Big Bang in the 1950s and 1960s, has become less popular over time, mainly because of the emergence of new evidence that is explained better by the Big Bang theory.
Narlikar's contributions
Born in 1938 in Kolhapur, Maharashtra, Narlikar was a young PhD student at Cambridge University in the early 1960s, when he produced his seminal work. He collaborated with Hoyle, the originator of the steady-state theory, alongside Hermann Bondi and Thomas Gold. Incidentally, it was Hoyle who coined the term 'Big Bang' while discussing the subject during a radio interview in 1948.
Narlikar entered the picture at a time when radio astronomer Martin Ryle produced fresh experimental data at the Cambridge University's Cavendish Laboratory. That information seemed to support the Big Bang theory and provided new energy to the debate. Narlikar and Hoyle used some of Ryle's data to show that his results were limited and not conclusive evidence of Bthe ig Bang theory.
The two went on to further develop the work and produce the famous Hoyle-Narlikar theory, which modified Albert Einstein's general relativity and proposed an alternative mechanism for gravity. The key idea in this was the suggestion that gravity behaved the same even if spacetime was stretched or contracted in any way. Narlikar worked out the rigorous mathematical framework for this theory. The Hoyle-Narlikar theory specifically supported the steady-state concept and allowed for the constant creation of new matter in the universe, which is an essential part of that concept.
In his autobiography, My Tale of Four Cities, Narlikar 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.
'So, the steady state theory predicted that the density of matter in the universe would always remain the same. 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,' he wrote.
Narlikar's main contribution was in modifying Einstein's general relativity equations in a manner consistent with the creation of new matter in the universe.
However, 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 the 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, which says that the universe originated at a particular moment about 13.8 billion years ago, predicts the existence of this kind of background radiation. It also predicts that this radiation would have a uniform temperature everywhere. The accidentally discovered CMB has properties that are 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 also some of the work of Stephen Hawking and Roger Penrose on singularities, piled more evidence in support of the Big Bang, and challenged the steady state theory.
Narlikar and Hoyle tried to address some of these challenges, but by the 1980s, Big Bang had emerged as the dominant explanation for the origin of the universe.
Narlikar, while acknowledging the growing evidence in favour of Big Bang, maintained that the evidence was still not unambiguous, and 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.