Massive Gravity (modified GR)

[Philip Thrift]

https://futurism.com/massive-gravity-theory-universes-biggest-paradox

@philipthrift

[Alan Grayson]

On Wednesday, January 29, 2020 at 10:20:36 PM UTC-7, Philip Thrift wrote:

https://futurism.com/massive-gravity-theory-universes-biggest-paradox

@philipthrift

Did Einstein really posit a graviton (with or without zero mass)? How is this possible if the existence of the graviton depends on the quantization of gravity? AG

[Lawrence Crowell]

This has been making the pop-sci rounds of late. It is best to wait and see what happens here, for there is a long history of various alternate theories that have been popular that are now on the trash heap. The near coincidence of gravitational waves and EM radiation from neutron star collisions puts a very small bound on any possible graviton mass. The correspondence

(∂^2 - m^2)φ → G(k, k') =  ∫dk∫dω(k)/((k - k')^2 - m^2)

means the m^2 term is a dispersion, and if the graviton had mass this would act to slow the propagation of the graviton. Linearized gravitational waves in the weak limit do obey a very linearized wave equation similar to that of photons.

I have not read the paper yet, but massive gravitons are not entirely impossible. However, they are likely a manifestation of heterotic or SO(32) supergravity with two graviton states. The massive graviton is then an additional quantum gravitational state. The questions though is whether this is stable. It is not entirely clear how to adjust the mass, say a mass due to a Higgsian-like process, that is not close to the Planck mass and unstable. 

LC