New theory of gravity might explain dark matter

A new theory of gravity might explain the curious motions of stars in galaxies. Emergent gravity, as the new theory is called, predicts the exact same deviation of motions that is usually explained by inserting dark matter in the theory.

More…

CrazyNeutrino said:

New theory of gravity might explain dark matter

A new theory of gravity might explain the curious motions of stars in galaxies. Emergent gravity, as the new theory is called, predicts the exact same deviation of motions that is usually explained by inserting dark matter in the theory.

More…

From https://en.wikipedia.org/wiki/Induced_gravity

Induced gravity (or emergent gravity) is an idea in quantum gravity that space-time curvature and its dynamics emerge as a mean field approximation of underlying microscopic degrees of freedom, similar to the fluid mechanics approximation of Bose–Einstein condensates. The concept was originally proposed by Andrei Sakharov in 1967.

Sakharov observed that many condensed matter systems give rise to emergent phenomena that are analogous to general relativity. For example, crystal defects can look like curvature and torsion in an Einstein–Cartan spacetime. This allows one to create a theory of gravity with torsion from a World Crystal model of spacetime in which the lattice spacing is of the order of a Planck length. Sakharov’s idea was to start with an arbitrary background pseudo-Riemannian manifold (in modern treatments, possibly with torsion) and introduce quantum fields (matter) on it but not introduce any gravitational dynamics explicitly. This gives rise to an effective action which to one-loop order contains the Einstein–Hilbert action with a cosmological constant. In other words, general relativity arises as an emergent property of matter fields and is not put in by hand. On the other hand, such models typically predict huge cosmological constants.

Some argue that the particular models proposed by Sakharov and others have been proven impossible by the Weinberg–Witten theorem. However, models with emergent gravity are possible as long as other things, such as spacetime dimensions, emerge together with gravity. Developments in AdS/CFT correspondence after 1997 suggest that the microphysical degrees of freedom in induced gravity might be radically different. The bulk space-time arises as an emergent phenomenon of the quantum degrees of freedom that live in the boundary of the space-time.

Anyone want to place bets?

mollwollfumble said:

CrazyNeutrino said:

New theory of gravity might explain dark matter

A new theory of gravity might explain the curious motions of stars in galaxies. Emergent gravity, as the new theory is called, predicts the exact same deviation of motions that is usually explained by inserting dark matter in the theory.

More…

From https://en.wikipedia.org/wiki/Induced_gravity

Induced gravity (or emergent gravity) is an idea in quantum gravity that space-time curvature and its dynamics emerge as a mean field approximation of underlying microscopic degrees of freedom, similar to the fluid mechanics approximation of Bose–Einstein condensates. The concept was originally proposed by Andrei Sakharov in 1967.

Sakharov observed that many condensed matter systems give rise to emergent phenomena that are analogous to general relativity. For example, crystal defects can look like curvature and torsion in an Einstein–Cartan spacetime. This allows one to create a theory of gravity with torsion from a World Crystal model of spacetime in which the lattice spacing is of the order of a Planck length. Sakharov’s idea was to start with an arbitrary background pseudo-Riemannian manifold (in modern treatments, possibly with torsion) and introduce quantum fields (matter) on it but not introduce any gravitational dynamics explicitly. This gives rise to an effective action which to one-loop order contains the Einstein–Hilbert action with a cosmological constant. In other words, general relativity arises as an emergent property of matter fields and is not put in by hand. On the other hand, such models typically predict huge cosmological constants.

Some argue that the particular models proposed by Sakharov and others have been proven impossible by the Weinberg–Witten theorem. However, models with emergent gravity are possible as long as other things, such as spacetime dimensions, emerge together with gravity. Developments in AdS/CFT correspondence after 1997 suggest that the microphysical degrees of freedom in induced gravity might be radically different. The bulk space-time arises as an emergent phenomenon of the quantum degrees of freedom that live in the boundary of the space-time.

Anyone want to place bets?

“At first glance, Verlinde’s theory has features similar to modified theories of gravity like MOND (Modified Newtonian Dynamics, Mordehai Milgrom 1983). However, where MOND tunes the theory to match the observations, Verlinde’s theory starts from first principles. A totally different starting point”

That’s how I read it, too. Note that MOND now goes by the name “f® theory”.

Let’s have a look at the paper. https://arxiv.org/pdf/1611.02269v2.pdf

I can’t rule it out from a quick look at the paper. It relies on so much, including the ER = EPR proposal that we discussed recently on the forum. It’s sort of like it takes a bit from everywhere, from string theory, from the CFT-AdS correspondence, from the old Emergent Gravity theory of Sakharov, from MOND, from the black hole information paradox and its relationship to holographic theory, from Postpocalypse’s mad ideas, from the QM graviton, from Shannon entropy, from an analogy between gravity and elasticity.

Interestingly, given the range of concepts it’s built from, it doesn’t rely on Unruh radiation, which is a good sign. Also interestingly, although string theory is used, the number of time-space dimensions is set firmly to 4, not 10 (superstrings) or 11 (supergravity), also a good sign.

I sort of understand that the dark matter component comes from the ER = EPR “quantum entanglement = wormhole” correspondence. It appears in the equations through “To obtain this result as a genuine entanglement entropy one has to extend the microscopic Hilbert space by associating to each AdS region a tensor factor … C(L) quantum mechanical degrees of freedom … We interpret the positive dark energy in de Sitter space as the excitation energy that lifts the vacuum energy from its ground state value”.

Slight mathematical inconsistency in that we have r = L, l < L, l = r, which implies r < r, but I don’t think that that would have a major effect on the results.

PS. What the heck is “quiver quantum mechanics”? Whatever it is, it hasn’t made it onto Wikipedia yet.

We may just be looking at a future Nobel prize here.

The author does give this word of warning in the conclusions, “ an immediate question that comes to mind is whether this relation continues to hold throughout the cosmological evolution of the universe. We have worked exclusively in a static situation near the center of the static patch of a dark energy dominated universe. Any questions regarding the cosmological evolution of the universe are beyond the scope of this paper.”

mollwollfumble said:

“At first glance, Verlinde’s theory has features similar to modified theories of gravity like MOND (Modified Newtonian Dynamics, Mordehai Milgrom 1983). However, where MOND tunes the theory to match the observations, Verlinde’s theory starts from first principles. A totally different starting point”

That’s how I read it, too. Note that MOND now goes by the name “f® theory”.

Let’s have a look at the paper. https://arxiv.org/pdf/1611.02269v2.pdf

I can’t rule it out from a quick look at the paper. It relies on so much, including the ER = EPR proposal that we discussed recently on the forum. It’s sort of like it takes a bit from everywhere, from string theory, from the CFT-AdS correspondence, from the old Emergent Gravity theory of Sakharov, from MOND, from the black hole information paradox and its relationship to holographic theory, from Postpocalypse’s mad ideas, from the QM graviton, from Shannon entropy, from an analogy between gravity and elasticity.

Interestingly, given the range of concepts it’s built from, it doesn’t rely on Unruh radiation, which is a good sign. Also interestingly, although string theory is used, the number of time-space dimensions is set firmly to 4, not 10 (superstrings) or 11 (supergravity), also a good sign.

I sort of understand that the dark matter component comes from the ER = EPR “quantum entanglement = wormhole” correspondence. It appears in the equations through “To obtain this result as a genuine entanglement entropy one has to extend the microscopic Hilbert space by associating to each AdS region a tensor factor … C(L) quantum mechanical degrees of freedom … We interpret the positive dark energy in de Sitter space as the excitation energy that lifts the vacuum energy from its ground state value”.

Slight mathematical inconsistency in that we have r = L, l < L, l = r, which implies r < r, but I don’t think that that would have a major effect on the results.

PS. What the heck is “quiver quantum mechanics”? Whatever it is, it hasn’t made it onto Wikipedia yet.

We may just be looking at a future Nobel prize here.

The author does give this word of warning in the conclusions, “ an immediate question that comes to mind is whether this relation continues to hold throughout the cosmological evolution of the universe. We have worked exclusively in a static situation near the center of the static patch of a dark energy dominated universe. Any questions regarding the cosmological evolution of the universe are beyond the scope of this paper.”

Another positive sign is the insistence of applying this theory in “de Sitter space” as opposed to say, anti-de-Sitter or Freidmann space. Only an old crazy like mollwollfumble would know that “de Sitter space”, invented in 1932, is exactly and uniquely what is required here. De Sitter solved the equations of General Relativity in the complete absence of matter (and hence no gravitational curvature) to develop a consistent mathematical expanding cosmology. If the gravitational effect of matter emerges naturally from space-time then that space-time can only be de Sitter space.

CrazyNeutrino said:

New theory of gravity might explain dark matter

A new theory of gravity might explain the curious motions of stars in galaxies. Emergent gravity, as the new theory is called, predicts the exact same deviation of motions that is usually explained by inserting dark matter in the theory.

More…

Today’s xkcd is directly relevant.

http://xkcd.com/1758/