Universe not dominated by dark energy?

The universe is expanding at a constant rate, and is not dominated by "dark energy", according to a new study led by an Indian-origin researcher, which casts doubt on the Nobel Prize winning discovery stating that the cosmos is undergoing accelerating expansion.
Five years ago, the Nobel Prize in Physics was awarded to three astronomers for their discovery that the universe is expanding at an accelerating pace.
Their conclusions were based on analysis of Type Ia supernovae - the spectacular thermonuclear explosion of dying stars - picked up by the Hubble space telescope and large ground-based telescopes.
It led to the widespread acceptance of the idea that the universe is dominated by a mysterious substance named 'dark energy' that drives this accelerating expansion.

Scientists led by Subir Sarkar of Oxford University in the UK have cast doubt on this standard cosmological concept.
Making use of a vastly increased data set - a catalogue of 740 Type Ia supernovae, more than ten times the original sample size - the researchers have found that the evidence for acceleration may be flimsier than previously thought, with the data being consistent with a constant rate of expansion.

"The discovery of the accelerating expansion of the universe won the Nobel Prize, the Gruber Cosmology Prize, and the Breakthrough Prize in Fundamental Physics," said Sarkar, who also holds a position at the Niels Bohr Institute in Copenhagen.

"It led to the widespread acceptance of the idea that the universe is dominated by "dark energy" that behaves like a cosmological constant - this is now the "standard model" of cosmology," he said.
"However, there now exists a much bigger database of supernovae on which to perform rigorous and detailed statistical analyses," Sarkar said.
There is data that appears to support the idea of an accelerating universe, such as information on the cosmic microwave background - the faint afterglow of the Big Bang - from the Planck satellite.
"All of these tests are indirect, carried out in the framework of an assumed model, and the cosmic microwave background is not directly affected by dark energy," said Sarkar.

"So it is quite possible that we are being misled and that the apparent manifestation of dark energy is a consequence of analysing the data in an oversimplified theoretical model - one that was in fact constructed in the 1930s, long before there was any real data," he said.
"A more sophisticated theoretical framework accounting for the observation that the universe is not exactly homogeneous and that its matter content may not behave as an ideal gas - two key assumptions of standard cosmology - may well be able to account for all observations without requiring dark energy," he added.

"Indeed, vacuum energy is something of which we have absolutely no understanding in fundamental theory," he said.
The study is published in the journal Scientific Reports.