6
$\begingroup$

Let me introduce this question by noting that my training is in condensed matter physics, and my familiarity with gravity is superficial at best. Hence, this question may be somewhat naive.

In addition to the usual Einstein gravity that apparently governs our universe at long wavelengths, I have seen several different gravity theories discussed in literature. For example, I have heard of supergravity, topological gravity, bimetric gravity, W gravity, and maybe others. My question is: what makes a theory gravitational? It seems obvious to me that any theory that wants to call itself gravity better have a dynamical spacetime metric (correct me if I'm wrong). Is there any other ingredient that is essential to gravity?

Some corollary questions: Do all gravity theories have black holes? If so do they behave like black holes in Einstein gravity (e.g., obey the Bekenstein-Hawking formula)? Can all gravity theories be realized as string theories?

$\endgroup$
  • $\begingroup$ A theory of gravity is a special case of a theory of acceleration. For example, GR is a theory, in which not only distance and speed are relative, but acceleration is relative is well. Thus it is unclear what exactly you mean by gravity in your question (e.g. is the Rindler metric gravity?). $\endgroup$ – safesphere Nov 10 '18 at 5:25
7
$\begingroup$

As an operational definition, a theory of gravity is a theory that reduces to the known working descriptions of gravity (Newtonian gravity, General Relativity) in some limit.

(If you think this is a pithy answer, try to come up with anything more specific that applies to e.g. MOND, String theory and Loop quantum gravity at the same time.)

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.