Gravitational Constant Alternative To Dark Matter: The Cosmological Crisis

2 Mar, 2018 18:24 IST|Sakshi
Gravitational Constant Alternative To Dark Matter: The Cosmological Crisis

On the occassion of the National Science Day, Dr B G Sidharth, Director of BM Birla Science Centre Hyderabad delivered the CV Raman lecture on “Crisis in Cosmology”. Sidharth has argued that an alternative candidate to dark matter would be a gravitational constant G that is very slowly decreasing with time. This was not an ad hoc conclusion but rather based on Sidharth’s cosmological model.

It is well known that the concept of dark matter was born around 1930 because Fred Zwicky and others noticed that the rotation curves of galaxies displayed a slight anomaly: Normally one would expect that as we went away from the centre of the galaxies the rotation curves would die down as per Kepler’s laws. In contrast they appeared to flatten out, reaching out a constant velocity at about 300 kilometers per second. It was hypothesized that some additional unseen matter within the galaxies was responsible for this strange behavior: This additional or dark matter would speed up the slowing stars at the edges of galaxies.

Unfortunately for the past nearly nine decades we have not been able to get a fix on what exactly this hypothesized dark matter is. Could it be some exotic new type of particles like supersymmetric particles or sterile neutrinos or even the recently discovered pentaquarks and so on? Other speculations have attributed to dark matter such objects as low luminosity brown dwarf stars. Yet others have forwarded the idea that the centre of galaxies are dominated by gravitational black hole which carries the extra gravitation. Unfortunately the debate and speculation is still on.

On the contrary latest observations throw up an even bigger puzzle. The Planck satellite indicates on the one hand that dark matter comprised 34% of the universe in its early days whereas the Dark Energy Survey (DES) indicates a present content of only 26% throwing up the question, is dark matter, whatever it is, decreasing? In this context the team for Max Planck Institute for Experimental Physics has found an even more intriguing observation, using the 8.2 metre very large telescope in Chile. The older galaxies of about ten billion years ago did not display the flattening rotation discs which are a hallmark of dark matter. This indicates that dark matter appeared only later in the universe.

On top of all this have come the latest observations by Adam Riess and his team. Riess shared the 2011 Nobel Prize for observing dark energy in 2008. The team found in 2015 that the universe was accelerating some 8% faster than what the cosmological models and observations indicate. This result was again reconfirmed by Riess a year later. It must be mentioned that Sidharth and Das had pointed out that if there were no dark matter (or much less of it) then this 8% surfeit of acceleration could be explained.

It may be mentioned that in 1997 astronomers stitched up like now a standard cosmological model with dark matter dominating the universe and only about 4% of ordinary matter. This meant that the universe though expanding would halt and collapse. In 1997 Sidharth came up with his model which claimed that on the contrary the universe was predominantly made up of dark energy, rather than dark matter. This would lead to not a deceleration, but rather a small acceleration of the universe. This was observed by Perlmutter, Schmidt and Riess independently the very next year. Perhaps we are facing a similar situation now when the new standard cosmological model would need a further revision.

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