# Tag Info

## New answers tagged quantum-gravity

3

Newton's first law does not apply to objects, but to observers. If you are an inertial observer, then you will see everything that is not acted upon by a force travelling in a straight line. There's no qualifier on the everything here - if it is not travelling in a straight line, it has a force acting upon it. Non-Newtonian fluids derive their name almost ...

0

As far as I know, the non-linear behaviour of gravity has nothing to do with getting infinities upon its quantisation (its non-renormalizability). In-fact pure Einstein gravity is 1-loop finite and Einstein gravity coupled to scalar field is 2-loop finite. In contrast, Yang-Mills theory for example (a special case of which lies at the heart of the Standard ...

3

This is the famous back-reaction problem in perturbative gravity. To avoid it, we typically only work to a few orders in a perturbative series (though the PPN people will go farther than seems sane when doing numerical work, but you can't blame them considering that radiation only shows up at 2.5 PPN). It is unclear whether perturbative methods in general ...

5

(1) Well, that's the basic intuition one should have when expanding out the metric as fluctuating about the flat Minkowski metric, i.e., writing $$g_{\mu\nu} = \eta_{\mu\nu}+h_{\mu\nu}$$ where $h_{\mu\nu}$ contains all the information about the curvature, $\eta_{\mu\nu}$ the usual Minkowski metric. What usually happens in most classes is we approximate the ...

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