Is dark matter all just a big mistake?

Hubble image captures what dark matter is supposed to be.

Asks Anil Ananthaswamy at Nautilus:

For his theory of emergent gravity, Verlinde takes the bold leap that the entropy of spacetime has an additional component that scales with volume. His thinking is that our universe, which approximates a spatiotemporal geometry called de Sitter space, is expanding at an accelerated rate, and so has a cosmological horizon—a distance beyond which we cannot see, because galaxies are receding faster than their light can reach us. Such a horizon is very similar to the boundary of a black hole and, by Bekenstein’s and Hawking’s arguments, implies an entropy. This entropy must be counted in addition to the entropy that physicists already ascribe to spacetime, and—crucially, according to Verlinde—it is not localized at the horizon. “The entropy that we normally associate with the horizon should be thought of as entropy that is distributed throughout the de Sitter space,” he says.

To justify his assumptions about entropy, Verlinde appeals to the nature of the spacetime microstructure. The microstructure is highly patterned, so that its parts are mutually correlated. Normally physicists assume that these correlations extend over only very short distances; the properties of two nearby points are very similar, while the properties of two distant points are unrelated. This patterning leads to an area scaling law for entropy. But in de Sitter space, Verlinde argues that the microstructure also has correlations that span large distances. Two distant points may be very similar. Such a patterning implies a volume scaling law.

Sprinkling entropy throughout the volume is tantamount to adding energy to the vacuum of spacetime and raising its temperature. “That energy is dark energy,” says Verlinde. And just like that, the problem of dark energy goes away.More.

These are interesting speculations, clouds in our coffee. But one has the haunting sense that current cosmology is in worse shape than they imply.

See also: Dark matter: Skeptics wanted

Anti-dark energy theories are burnt toast?

and

How do dark energy and dark matter relate to ID?

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