How important is your grad school research to future positions?

[TomServo]

For example, I want to work on quantum gravity and things like Brane cosmology (but not necessarily string theory). I'm really interested in sinking my teeth into differential geometry, general relativity, the shape of the universe, stuff like that. But if I were to go to a grad school that *didn't* study cosmology or quantum gravity but was involved in, say, gravitational wave astrophysics, does that lock me out of ever working on the kind of physics I want to do?

I have a list of seven grad schools I'm applying to. Some explicitly do not-necessarily-string cosmology/quantum gravity/membrane-type-research of the kind I want to do, a few just do gravitational wave stuff and maybe some "mathematical physics" which might or might not scratch my itch but they all do something related to GR. If I went to, say, Certain University, and did gravitational wave astrophysics, does that shut me out of the more cosmological stuff?

I'm fully aware of how rare positions are in that kind of physics anyway. :D Thanks for your time.

 

[Vanadium 50]

As you point out, positions are rare. People who already have a background will be at an advantage over those who do not.