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Physics + MathPhysics & Math

Controversial ‘Entropic Gravity’ Clears Hurdle on Path to Eliminating Dark Matter

ByTim De ChantNOVA NextNOVA Next

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Using the way light bends around dense galactic cores, a team of physicists has shown that the universe may not need dark matter after all, at least if a controversial theory of gravity proves true.

Margot Brouwer and her colleagues used existing troves of data on distant galaxies to study dark matter using gravitational lensing, or how gravity bends light around them. Dark matter is thought to make up 27% of the universe and significantly increase the mass of galaxies. But when Brouwer and her team plugged their results into a typical model of gravity—including dark matter—and one without, they received the same results. What’s more, the model without dark matter required fewer tweaks.

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It’s just the first test of what are likely to be many, but if future studies find similar results, it could upend one of the fundamental tenets of physics.

A merger of galaxy clusters about 5.2 billion light years from Earth.
The Musket Ball galaxy cluster, shown here, reveals the possible existence of dark matter (in blue).

Here’s Mark Anderson, reporting for New Scientist:

Brouwer’s study takes advantage of catalogues of distant galaxies released in 2011 and 2015 and looks at regions close to the visible disc of each galaxy. These regions are where gravitational lensing should be bending light from distant galaxies beyond.

Using statistical algorithms that consider the shape and color of the background galaxies, the researchers inferred a lensing profile for the foreground galaxy. It’s a bit like projecting an image onto a warped and uneven sheet of glass and then, knowing what the original image looks like, figuring out the optical properties of the glass sheet from what we see on the far side.

The researchers compared the gravitational distortions for each galaxy based on Verlinde’s new model and, separately, on a more conventional dark matter approach. Verlinde’s model was a better match, but it defies the Newton’s and Einstein’s well-established laws of gravitation. The set of equations on which Verlinde’s model is based, known as “modified Newtonian dynamics” (or MOND) has been contested for as many as 30 years. But the man behind MOND, Mordehai Milgrom, says that Brouwer’s study is consistent with his own 2013 analysis of gravitational lensing data.

Verlinde’s theory and Brouwer’s results still face obstacles within the scientific community. Verlinde’s premise is that on large scales, dark matter is just an illusion—and that both spacetime and matter arise from a network of quantum bits. If Verlinde and others can account for the perception of dark matter in the universe (including in the cosmic microwave background, or CMB), then they could stand a chance of capsizing the great vessel called gravitation.