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doi:10.1038/nindia.2012.181 Published online 4 December 2012

New research published today has cast doubts on some of the crucial hypotheses of the standard 'Big Bang' cosmology^{1}.

The research by Abhas Mitra of the Astrophysics Sciences Division of Bhabha Atomic Research Centre in Mumbai has, for the first time raised doubts over the physical realization of key concepts like 'dark energy' and 'cosmic inflation' that are basic to mainstream cosmology. This envisages that the universe was born out of nothingness in an infinitely powerful explosion (Big Bang) some 13.7 billion years ago.

Mitra argues that that the 'Cosmological Constant', the fundamental ingredient behind all concepts such as dark energy and cosmic inflation should actually be non-existent — meaning zero — and cannot have a finite value as currently believed.

Modern Big Bang cosmology has in its foundation a feature called 'inflation'. As per this inflationary big bang theory, the universe went through a momentary phase of an exponential expansion almost immediately after its birth. It was hypothesized that the new-born universe developed a positive Cosmological Constant — representing a fairly large repulsive vacuum energy —that gave rise to this runaway expansion.

Further, from 1998 onwards, the mainstream cosmology believes that the universe is just not expanding, but undergoing an accelerated expansion. This extra push for faster expansion too is believed to result again from a repulsive Cosmological Constant, and is termed as 'dark energy'. Physically speaking, the Cosmological Constant is equivalent to an underlying background energy (dark energy) that traditional cosmologists believe exists in space even when it is devoid of matter.

Historically, such an exponential expansion driven by a 'repulsive' Cosmological Constant is known as a 'de-Sitter phase' in the name of the famous Dutch physicist Williem de-Sitter (1872-1934). "But the supposed de-Sitter expansion has a very perplexing aspect in that while some observers do perceive the explosion, there are others who do not at all see the explosion," Mitra told *Nature India*.

"On the other hand, in physics, and in Einstein's General Relativity, a genuine physical effect must be perceived by all." The bottom line of Mitra's highly mathematical paper is that, a quantity called 'Expansion Scalar' must objectively decide whether there is any genuine expansion or not.

However, the fact that the de-Sitter phase appears standstill to some observers means that this scalar is inherently zero, and which in turn implies that Cosmological Constant is actually zero, Mitra explains.

Therefore according to him, the de-Sitter explosion picture obtained by assuming a finite Cosmological Constant is only a 'mathematical mirage'. Mitra argues that, accordingly, the 'dark energy' and apparent acceleration of the cosmos too could be fictitious, an artifact of explaining a complex inhomogeneous universe in terms of an over-simplified Big Bang model.

Interestingly, String Theory, which purports to unify fundamental interactions like electromagnetic and nuclear forces with gravity, also invokes an attractive (instead of repulsive) 'Anti-de-Sitter'(Ads) feature. "It invokes this AdS/Conformal Field Theory correspondence in order to connect itself to quantum field theories of electromagnetism and nuclear interactions," says Mitra and adds that this 'correspondence' is "basically a profound conjecture."

Mitra says that the self-contradictions in standard cosmology can be removed only by considering the Cosmological Constant as zero in conformity with Einstein's alleged comment that the introduction of the 'Cosmological Constant' in his general theory of relativity was the "biggest blunder" of his scientific life.

The BARC physicist says he is specially happy that his work has fundamental importance not only in cosmology but also in physics.

- Mitra, A. Interpretational conflicts between the static and non-static forms of the de Sitter Metric. Sci. Rep. doi: 10.1038/srep00923 (2012)

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