>>3646
If you're worried about joining a saturated field and letting that guide your decision then you're in the wrong mindset completely. Especially if you're looking at long term payouts such as 30 years down the road.
After you study physics long enough you'll grow to be comfortable with the (what I call) academic side of things. Things like stat-mech, quantum, optics, solid state matter, and so on. Your research will hopefully be something you genuinely care about that goes beyond that comfort zone.
The best advice I can give you is to start reading up on topics and research papers that compel you (especially the papers of your professors). You'll find that the topics that interest you may very well interest investors and grant donors, the lifeblood of any scientific discovery.
As for depth in each subject of Physics, here is what I know off the top of my head:
>Quantum Mechanics:
Quantum Computing/encryption
I believe this will bring about the next age in the human chapter. Computers that are capable of multiple calculations in one clock cycle is a huge step towards AI. Quantum encryption also makes it mathematically impossible to break the encryption (think schroedinger's cat).
>Solid State/Condensed Matter:
We all know about solid state drives, so I'll skip over that one. I think the next breakthrough will be graphene superconductors overtaking their silicon brethren. Also anything with the prefix "nano" starts with solid state.
This is your best bet for a lucritive PhD
>Nuclear
I'd argue this is actually the easiest branch of physics. The college I went to is #1 in the world in nuclear physics so a ton of money is being dumped into our rare isotope lab. Outside of doing what CERN essentially does (only at .5c instead of .99c) I'm not sure what Nuclear physics has going for it discovery of the neutrino having a non-zero mass?
>Particle Physics
What everyone thinks of when you say "i'm a physicist". If you're concerned about saturation I'd stay away from this field, plus the amount of original knowledge produced from each test seems to be reaching a peak. This is the best field for generating headlines though.
Your personal preference will differ from mine, who knows you could fucking love Nuclear and go with that. Your biggest mistake would be researching a topic because you thought it would pick up steam in the future. The only thing that should concern you is if a topic is deep and interesting enough to hold your attention for the rest of your professional life. The way my professor put it was the following: Imagine you have to eat one type of food five days a week for 30 years. You'd think long and hard about what you'd want that to be. I chose burritos