Theoretical Physics vs Theoretical Cosmology

[flyingpig]

What exactly is the difference? The latter does not seem so popular to me? On average how much does the latter earn?

 

[fasterthanjoao]

Sigh, I wrote out a giant reply and the computer crashed - lost it all.

In brief:

Physicists can generally be described as theoretical or experimental. Within these terms there are the area in which the physicist works to consider. e.g. Theoretical Particle physics, or experimental particle physics.

Cosmology is the subject area (though it is astronomy..)
http://en.wikipedia.org/wiki/Physical_cosmology

It is really not a question of 'popularity' as much as practicallity. In the UK, where I live, for example - universities have a banding system to pay their academics. The longer you have spent at the institution and depending on your duties, your pay will increase. It does not depend on the subject in which you work.

The issue, then, is how easy it is for the university to secure funding for your subject area (after all, they need to convince other people that your subject is worth giving money to - so they can pay you to work on it.). Something like, say, nuclear physics has many practical applications; medical and power are obvious ones. These can be used as in-routes to obtain funding. With something like cosmology the interest might be seen as purely academic, with practical implications less obvious.

This means that it is more a question of how many people there are working in the field. The number of people working in something like cosmology world-wide will be much smaller than those working in many other areas of physics (there are of course institutions that have large groups which specialize in cosmology but overall there are less than other areas). And so, it will be more difficult to secure a future working in this field - many students will take this at graduate level (since many of the projects are highly computational, it is a good skill to gain) and if they all try to make a career of it, they'll find there aren't enough jobs to go around: there is also a lot of cross-over with particle physicists wanting to work on cosmology, making it even more competitive.