# Questions tagged [gravity]

Gravity is an attractive force that affects and is effected by all mass and - in general relativity - energy, pressure and stress. Prefer newtonian-gravity or general-relativity if sensible.

605 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
0answers
212 views

### Criteria for being able to work with gravity in quantum mechanics, without a full theory of quantum gravity?

It's common to see people oversimplify by saying that physics currently lacks the tools to describe any situation involving both quantum mechanics and gravity. Clearly this is not the case. For ...
0answers
558 views

### What are Galileons good for?

Lately I've seen many papers (for example "The galileon as a local modification of gravity"; 292 total hits on the arXiv) on types of field theories known as Galileons, and I'm wondering what the ...
0answers
1k views

### Variation of the Einstein-Hilbert action in D dimensions without the Gibbons-Hawking-York term

Consider the standard Einstein-Hilbert action in $D \ne 2$ dimensions spacetimes : \begin{equation} S_{EH} = \frac{1}{2 \kappa} \int_{\Omega} R \; \sqrt{- g} \; d^D x, \end{equation} where $\Omega$ is ...
0answers
123 views

### Does the Gibbons-Hawking boundary action have an anomaly inflow interpretation?

The Einstein-Hilbert action on a manifold $M$ with boundary is $$\frac{-1}{16\pi G}\int_M d^n x \sqrt{-g} R +\frac{1}{8\pi G} \int_{\partial M} d^{n-1}x \sqrt{|h|} K$$ where $K$ is the extrinsic ...
0answers
63 views

### Different features of Gravity and Yang-Mills

I am reading a famous paper by S.Hawking - "Quantum gravity and path integrals" https://doi.org/10.1103/PhysRevD.18.1747. On the third page left column there is a statement, after the ...
0answers
109 views

### Entropy and equilibrium concepts at astronomic scales

I am always puzzled to read here and there discussions dealing with thermodynamic concepts applied to astronomic scales where gravity matters. To my opinion, there is a certain carelessness to go into ...
0answers
185 views

0answers
63 views

### Why is the Weyl tensor square gravity non-unitary?

I want to understand constraints of unitarity in quantum field theory. There is quite folklore statement: gravity with a Weyl tensor square term is non-unitary How to understand this? (I think that ...
0answers
117 views