What Do UV and IR Mean in the Context of Quantum Gravity Theories?

[inflector]

I keep seeing references to UV and IR in references to string theory and quantum gravity. This seems to come up in discussions of renormalization especially.

Can someone please explicitly explain the term? Google doesn't seem to help here. There are way too many references. I have tried various combinations with other terms as well but haven't found anything useful yet.

I know that UV means ultraviolet and IR means infrared but this does not really help as the meaning clearly has more specificity when used in the context of quantum gravity than just a reference to small bands in the EM spectrum. It seems as if the terms mean the quantum scale and cosmological scale at times based on context. Is this close?

 

[marcus]

I know that UV means ultraviolet and IR means infrared but this does not really help as the meaning clearly has more specificity when used in the context of quantum gravity than just a reference to small bands in the EM spectrum. It seems as if the terms mean the quantum scale and cosmological scale at times based on context. Is this close?

I think that's a good way to put it.
The exact meaning can depend on context. UV usually means small scale and high energy, which makes sense because in particle physics it takes high energies to explore structure and interaction at small scale.

IR has the connotation of lower energy, longer wavelength, larger scale. But not necessarily cosmological. It could simply refer to conditions and scales we experience in the ordinary everyday macroscopic world.

In the case of gravity, the most intensive measurements testing GR have been done on the scale of the Earth and solar system, so I guess the relevant IR regime where QG is supposed to match GR would be solar system or within a few orders of magnitude thereof. But it could also mean cosmological scale.