graduate research directions

[rockwhj]

I just want to use this post for people to have a discussion and share their opinions. I had a talk with my undergrad advisor today about grad school choice and possible graduate work directions. I am interested in theory in general, cosmology or(and) particle theory, but does not have a very specific target on what i want to do. I like to study theoretical aspects that are fundamental enough. Probably like many of you theorist wannabe here, my personal taste draws me towards doing abstract and fundamental things, like string theory, or quantum gravity, etc. My advisor said something which i think is quite sensible.
He kind of discouraged me to directly pursue topics that are too abstract in graduate work. It is fine to study them after i become a mature physicist later in my career. But for graduate work and possibly postdoc it is advisable to study areas that are more concrete or established and also better experimentally supported. The reason being partly for better chance of yielding something and establishing the status in the academic; but also to me more importantly, it helps build a solid feeling for physics. By feeling i mean better appreciation as well as insights into physics. We are not all genius with inborn insights into physics, we need to foster them by feeling the subject around. After we mature as a physicist, then are are better equipped to study more abstract and fundamental theories.
I never thought about this point before. Before i was always foreseeing myself doing some really cool theoretical research throughout my future. But i think this point is very sensible. On the other hand, i really have an interest in researching on fundamental things.
I'd like to welcome anyone to post their opinion on this, how much do you agree, and what theoretical areas do you think make a good graduate research direction, taking this point into account but not compromising much on the flavor of the work.

Also, right now i have a choice of graduate programs among Caltech, MIT and Stanford. I would like to invite anyone to comment on the strengths of these three schools, as i am not very informative on the academic circle.

Thank you in advance and pardon my English

[dlenmn]

I'm a first year grad student, and we had a series of seminars where professors would come in and tell us about their research. One of the most interesting was when a string theory prof talked to us (I think there are 3 in the department, but the the other 2 were out of town). He addressed how you could get in to such research, and the short story is that you can't really until the very end of your graduate career/a post doc. Before you can do anything, you've got to take a bunch of math classes. After that, a prof can give you what is -- from the professor's point of view -- busywork. It helps you figure out what is going on, but it's not really new research (simulations of already developed theories and the likes -- maybe slight twists on simulations already done elsewhere). Maybe in the last year of your graduate career, you know enough to do something that's really new research. But often it's not until afterwards that you really know enough to do new stuff. He made the point that an advisor in string theory is really doing a labor of love -- you take up a lot of time, and that investment might pay off for part of your last year, but it is never really paid back in full.

That may sound somewhat depressing, but the prof seemed really nice, and I liked it that he was telling it straight -- he went through a similar process and it worked for him. So, I guess what I'm saying is that a good advisor will prepare you by giving you relevant projects that aren't groundbreaking, but will get you up to speed. However, getting up to speed is usually not accomplished in an undergrad degree alone. Kind of what your prof said.

Of course, this isn't my field, so what do I know?

[YF17A]

Hey rockwhj,

I'm in a similar situation...I applied with a stated interest in particle phenomenology, but am interested in how particle physics, astrophysics, cosmology, etc. are all bleeding together as people try to concoct a fundamental theory. I agree with what dlenmn said about string theory, which is why I have tried to take an insane number of math courses so that I can feel like I really understand what I'm doing. However, I've tried to teach myself a bit of string theory on the side, and I've found that it gives you a really good intuition for how physics relates to geometry. Things like the perturbation expansion in QFT (i.e. Feynman diagrams), the number of particle generations, even the Higgs mechanism can be represented in terms of geometry (the Euler characteristic of the string worldsheet, cohomology of various compact manifolds, and separation of several stacked D-branes, respectively), which I find absolutely fascinating.

Now, depending on your interests, you can go one of two ways. If you're more inclined toward the GR side of fundamental physics, you are used to thinking of physics (gravity) in terms of geometry, in which case studying string theory would probably teach you a lot. If, however, you are more inclined toward particle physics, you will probably be put off by the fact that the spectrum of real, physical particles seems to be the least important thing to most string theorists. In particular, I've found that trying to understand most of the particle content of string theory has exposed my lack of knowledge about gauge theories, supersymmetry, and spontaneous symmetry breaking. In that sense, it is much more important to study those things "concretely" in terms of particle phenomenology before attempting to study them "abstractly."

But in the end, string theory is just the quantum mechanics of relativistic 1-dimensional objects - all the higher math comes in when you try to apply it to the real world! Regarding your school choices, MIT has an amazing condensed matter theory group and people in the string community who are trying to apply their work to condensed-matter systems...see http://arxiv.org/abs/0807.1111 for example. They have relatively few people working on phenomenology, though, although they have Alan Guth, who is unbeatable if your interests lie more toward cosmology. Stanford also has a very strong string community, as well as particle phenomenologists like Dimopoulos. Caltech has many string theorists and cosmologists, but not so many particle phenomenologists.

Hope this helps...I think I'm leaning towards MIT myself, but maybe just because Stanford is 15 minutes from my house

[Helio]

I just want to add something along the lines of giving a taste of string theory. I am in that dilemma per se myself at the moment by trying to choose between particle physics (neutrino and/or astroparticle) and stellar spectroscopy as a research subject and since my research background has a bit of both... anyway... how about you just check out the undergrad course on string theory at MIT:

http://ocw.mit.edu/OcwWeb/Physics/8-251 ... /index.htm

To just get an idea of what it is about and what you might be getting yourself into in the long-run. From my experience with string theorists (they make up the "theory" part at my school for the most part) they seem to give a lot of busy work and try to make you comfortable with the mathematics, as one of my friends tried to research with one of the faculty, at the start and do not really let you touch the true stuff until the very end.

[rockwhj]

thanks guys. YF17A, i'll see you in some of the open houses and maybe we can talk more about these then. Yes the geometrical flavor of string theory has a natural appealing to me as my undergraduate training has been quite maths-oriented. But back to what my advisor says, how much do you agree with him? In your opinion, what would be some of the theoretical areas that are interesting enough like string theory but are mature enough and better experimentally supported? I donno if i have managed to get across my ideas

[robertson]

Hey rockwhj,

Another one in the same bout. And it might be even more complicated coming from Spain. Here, there are no professors working on string theory (1 or 2 per school at most) and as we discused a month ago, people trully believe that the USA universities should start to change the point of view and work on less ambitious but more tested theories. Let me tell a few examples:

We know that the strong force seems to be described in terms of quarks and gluons, but one cannot solve QCD from first principles because it is a quantum many-body problem with lots of peculiarities. One can argue that QCD (and the SM in general) is not complete, we must find a better description of nature, one that unifies all the theories and so on. But, we know QCD should describe nature almost perfectly in a wide (and interesting) range of energies, how can we know that there are no clues for a better understanding of nature inside QCD still waiting to be found? I mean, early in the last century, people found the foundations of QM and few years after the jumped into QFT because QM was not complete. At first sight, it seems that the work done in the last 60 years in QFT is far more important that the work done in QM, but will you tell me that entanglement, Quantum information, teleportation are not fundamental things for our understanding of nature? There must be people working on the next step (strings, QLG...) but also working in widening the knowledge that we have in theories that are correct but unsolvable.

Now I go one of the important points of your post, will you just start to work on string theory without knowing how QFT and SM do not perfectly fit in our description of nature? I mean how can you work on a problem that you do not know where it comes from. Of course there are naive arguments to say QFT is wrong like why can't we find a QFT counterpart of gravity, but in my opinion you should really learn hard QFT before working on strings, and that is exactly what most of the great genius of strings did in their time, they were specialists in HEP theory that sudenly jumped to a more theoretical and fascinating theory.

In my personal case, I might decide between Caltech and MIT, but I'll add my knowledge of Stanford because I also applied and I was really interested in their Slac group.

Stanford:
- All the group in the university is working in strings. However, Dimopoulus is known as one of the best specialists in beyond SM, implementing SUSY and such things. You also have the oportunity to work in the SLAC theory group, and there you'll find people like Michael Peskin and few others, that work on phenomenology and LHC related topics.

Caltech:
- Almost all the group works in string theory. However, Mark Wise is as famous as Dimopoulus in similar topics. You have really good people working on theoretical cosmology and astroparticles.

MIT:
- Don't know anyone working on strings, I didn't try to find them (fewer than in the rest of the universities). You have Franck Wilczek, that discovered asymptotic freedom, working on fundamental things of CMT and sometimes in particle theory. Krishna Rajagopal working on QCD superconductors and extreme quark matter. Iaian Stewart working on Effective field theories, a theoretical approach to solve QCD that seems to be the only tool to characterize most of the bound states of the theory (resonances, mesons and etc). Pr. Negele working on Lattice QFT but more related to Nuclear physics. Then you still have Jackiw, Jaffe and some others doing more mathematical stuff.

So for me, it seems that MIT fits better with my needs. Anyway, I'll go to the Caltech's open house and I'll try to find if any of the string theorists is willing to let me understand QFT and SM deeply after more mathetical stuff. That could change my mind and also meeting Mark Wise and talking about his research. But both things are unlikely to happen. Good luck with your decisions, I'll see you in LA and Boston.

[YF17A]

@rockwhj and robertson: this is exactly the kind of discussion I was hoping I would have with classmates in graduate school. I look forward to meeting you guys at the open houses too!

@rockwhj: re. your advisor's opinion, I agree for the most part. I think he's cautioning you against, say, diving straight into string theory research without first understanding all the successes and failures of the standard model. The problem is, the standard model is so successful that there are very few experiments which contradict it. So if you're interested in fundamental physics, i.e. beyond the standard model, your research will necessarily be speculative. No one has a compelling explanation for neutrino masses, CP violation, dark matter, or dark energy yet, and so your choice is between phenomenology, which tries to address these concerns based on direct experimental evidence and model-building, or formal theory, which tries to include them in an over-arching framework like string theory. The LHC data in the next 5-10 years will totally reshape this field depending on what they see (or don't see). A safe bet would definitely be dark matter phenomenology...there's a ton of astrophysical data out there, and a lot of it can be interpreted in the context of dark matter, but you have to live with the fact that your model might be completely ruled out by some collider data in the near future.

@robertson: I think you're absolutely right that we don't understand QCD yet. However, it's interesting that the AdS/CFT correspondence in string theory has shed some light on the behavior of the quark-gluon plasma, so it might be the case that we learn something about QCD from studying string theory! Indeed, the biggest issue with QCD is dealing with the strong-coupling regime, and string theory provides an answer (at least in the limit of a large number of colors) with these gauge/gravity dualities. MIT has very sharp people working on both sides, and I think it will be interesting to see how the fields intersect in the coming years.