Lamp shines on 'dark energy' bet

Physicist wins Einstein wager

By G.S. Mudur
  • Published 2.12.16
Thanu Padmanabhan next to the lamp he won in the wager. It is a special lamp whose colour output can be altered at will using a mobile app. For logistic reasons, he bought the lamp in Pune, after Wiltshire sent him the $200.

New Delhi, Dec. 1: An Indian physicist who has extended Albert Einstein's theory of gravitation to explain a mysterious, all-pervading energy across the universe has won a 10-year-old bet with a physicist from New Zealand who had challenged his ideas.

David Wiltshire at the University of Canterbury, New Zealand, today announced that he had conceded the wager to India's Thanu Padmanabhan on the nature of the so-called "dark energy" and - under the written terms of the wager - gifted an "objet d'art" to Padmanabhan.

The object is a $200 decorative lamp that Padmanabhan, a professor at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, has now placed in his living room.

At the centre of the wager is one of the biggest mysteries of modern physics - dark energy, a repulsive force discovered in the late 1990s through observations of distant supernovae (exploding stars) that pushes everything in the universe away from everything else.

Dark energy makes up about 72 per cent of all the matter-energy in the universe, while all visible matter in the universe such as planets, stars and galaxies make up only about 4 per cent. The balance is also equally mysterious so-called dark matter, experienced only through its gravitational tugs.

Padmanabhan, through pen-on-paper calculations over the past decade, tweaked Einstein's theory of gravitation, also called the general theory of relativity, to suggest that dark energy is a mathematical term called the "cosmological constant" that Einstein had initially proposed in his equations and then abandoned.

In a talk at an international physics symposium in Australia in 2006, Padmanabhan claimed that over the next decade, there will be no evidence whatsoever to contradict the hypothesis that dark energy is the cosmological constant.

While most physicists appeared unwilling to accept the wager, Wiltshire took up the challenge.

Padmanabhan and Wiltshire drew up a formal agreement, with two fellow physicists as witnesses, under which Wiltshire agreed to purchase for Padmanabhan a lamp to "help him better illuminate his calculations of the darkness of the universe". And Padmanabhan, if proved wrong, would buy Wiltshire a clock to "help him keep better track of the lack of constancy of cosmological ideas".

Over the past decade, Padmanabhan persisted with his calculations, according to which the cosmological constant defines the observed acceleration of the expansion of the universe attributed to dark energy.

"The cosmological constant is an extraordinarily tiny number - it is one divided by one followed by 123 zeroes," Padmanabhan told The Telegraph, minutes after Wiltshire conceded the bet at a similar physics symposium in Australia, about two weeks after sending an email to Padmanabhan, offering him the lamp.

Padmanabhan, working with his astrophysicist daughter Hamsa Padmanabhan, a fellow at the Institute of Astronomy, Zurich, has also predicted the cosmological constant's value through calculations that IUCAA says are in agreement with observations of the accelerated expansion of the universe.

The predictions relate the cosmological constant to an event called inflationary expansion at the beginning of the universe as well as to the amount of matter and radiation observed in the universe today.

Padmanabhan's ideas are consistent with Einstein's theory of gravitation, but extend it to build what some physicists are calling a revised and improved understanding of gravity.

At the end of the 10-year wager term, no other physicist has moved to renew Padmanabhan's bet on fresh terms.

"I don't think I'm going to make any more money from the cosmological constant," he said in a media release issued by IUCAA.