“Should I choose to study theoretical high energy physics?”

“Should I join this research group?”

This article is written for the students who may have those questions.

Why this article

Well, they are always difficult decisions. I am sharing my opinion because of two reasons:

My experience might be of some help.
You can see if my opinion fits yours. There is no standard answer for such hard questions. But if we converge in those opinions, we are more likely to work together smoothly.

I will focus on theoretical high energy physics. Applied physics and/or experiments are different. The career there can be easier because of their much stronger connection with industry.

The difficulties

Before the exciting things, the sad parts first:

Theoretical physics is not an efficient way to make money.
It takes long before one can settle down as a physicist.
One may not be able to end up being a physicist even he/she tries to.

The first point is obvious. Let me explain the last two points a bit more.

The below is the track that one usually follow to become a theoretical high energy physicist:


UG	4 years
PG	4-6 years
1st postdoc	2-3 years
2nd postdoc	2-3 years
assistant, associate, full prof.

This has also been shown in a cartoon by Iván D. Flórez:

At each transition point, a considerable number of people quit.

The people who quit often get good jobs because of their training on physics, math and programming, and in general, the scientific way of thinking. Elon Musk says

Well, I do think there is a good framework of thinking. It’s physics. You know, the sort of first principles reasoning.

However, to train the skills of another job through theoretical physics is for sure not the most efficient way.

So in my opinion, one is advised to choose theoretical high energy physics if he/she

considers exploring the unknowns more attractive than money. I am not saying physicists should be poor. It is not bad to have better living condition and make more money. I also do try to provide more comfortable conditions for my students. But that does not change the fact.
One (and had better both) of the following
- is confident against the pressure to quit.
- loves physics so much that the time spent on physics is considered to be valuable even if having to quit.

To conclude, one needs to be strongly interested!

Is theoretical high energy physics hard?

I did mentioned a number of difficulties above. But I did not say it is intellectually hard. So is it hard?

For sure, different people are talented in different things. It is a good idea to choose your career coinciding with your talent, unless you have so strong interest to balance your choice.

But we can still ask the question in general. As an analogy, singing is extremely hard to me. But that does not hurt to say that singing is in general not hard (in a limited sense that I will come back to).

So is theoretical high energy physics hard?

Yes or no.

It is hard if one thinks about how much one has to learn before being able to do research. I will expand the necessary background knowledge later.

However, it is not particularly hard compared to anything else if one wants to do it well. Fine, singing seems not hard. But how many people in the world can be great singer? I don’t think the number is more than great theoretical physicists.

A crosstalk comedian Degang Guo says, crosstalk (and doing research) is like mountain climbing. Let’s say we have to go through an entrance (certificate of being able to do it) during climbing. Some mountains has the entrance built at the bottom, some mountains has the entrance built near the top. But that does not make a difference if our aim is to be on the top.

To put in numbers, Gladwell estimates that

”… the key to achieving world class expertise in any skill, is, to a large extent, a matter of practicing the correct way, for a total of around 10,000 hours.” – Ourliers, quotes from Wikipedia

Our aim to do theoretical physics is not barely be able to do research, but rather to do good research. Thus theoretical physics is not more difficult compared to anything else in this sense.

The exciting part

I am not sure it excites everybody. But I am excited. I am kind of person that the most exciting thing in my life is to understand more about how the world operates. That is also true for lots of my colleagues.

Learning is exciting. For example, one of my most memorable moment is the moment when I understood renormalization group. Some other comparable moments include when I understood that heat is actually internal motion of small particles, and topological defects.

Whitehead says that learning begins with romance. Later I found that I misunderstood his meaning but nevertheless I do feel the romance of learning, and things become increasingly romantic as I grow older.

Doing research is another level of great things. For most of the time, the research one does is not as great as the knowledge that one learns from classes. My ultimate dream on my research is that one day my research can be written in standard textbooks, but I am as far from my dream as I can ever imagine. Nevertheless, I have the chance to understand a tiny little thing that people never ever understood.

Actually, even if the achievement is small, it still feels great. It’s like playing a video game that after lots of combats, eventually we conquered the big boss. The video game could be Star Wars, it could either be the King of Fighters. The excitement does not depend on the scale of the game very much – interstellar or indoor. But it comes from that you made it, and after overcoming so many difficulties and you made it yourself.

Also, there are many first-time experiences in one’s life which are special. For example, first time to meet, first time to read a novel, and so on. The second time it may be less exciting. But for your own research, it is always new as long as you are making progress. A life of research realizes the dream that a Chinese poet had hoped: May life be like the first-time experiences (人生若只如初見).

Oh, I may have been saying all the nonsense in this section. But I cannot help writing it down. Sorry…Feeling is always subjective (and there is a debate whether beauty is objective or subjective). Also, one should be reminded that not everybody loves research more than learning. You may do some research projects to find out if you are one of them.

The trajectory of learning

One is expected to have learnt quantum field theory (QFT) before being able to do research. One can take a look at Zee to get some general ideas about quantum field theory. To learn the techniques, Srednicki and Peskin & Schroeder are great. The latter fits best for a prospective particle physicist and the former fits best for mastering the general principles of quantum field theory, aiming at applying them in a theoretical way.

Basic knowledge of general relativity (GR) is also crucial if one wants to work on gravitation or cosmology. General relativity uncovers the nature of gravitation, which is the curved space and time. My favorite book on GR is Hartle. Some other books also look amazing and I hope to have a chance to read them, including Carroll and Zee.

There are a lot of online resources also. For example, the PSI lectures, the MIT open course and the theoretical minimum look great. People also love Coleman videos a lot (which seems to be the counterpart of Feynman lectures for high energy physicists).

For HKUSTers, the good news is that I teach both courses, and the bad news is that I teach them every other year. See C15 (will be extended to include GR in the future) and QFT16.

It is noticed that QFT and GR are not the end point of learning, but actually the starting point. After a number of further courses (if offered), we end up with learning from review articles and eventually research papers, for the bleeding edge knowledge that has not been ever written in a book.

Factors of being excellent

Einstein says,

If A is success in life, then A = x + y + z. Work is x, play is y and z is keeping your mouth shut.

Nowadays, probably we have to modify the formula into A = x + y - z (this looks easier than modifying his theory of gravity).

Work. People often complain that they are not born smart. But the truth is that for most cases, they have not worked hard enough that intelligence ever become the crucial factor in the competition. It is, actually, extremely difficult to work hard enough, even if one strongly wants to. The sad thing is that the best people in the field indeed work harder than others. But the good aspect is that, the effort that one has made is truly something to be proud of oneself, instead of the intellectual smartness which was given by one’s parents. (Well, it is another debate if you don’t believe in freewill.)

To work hard does not mean sitting there and pretend to be learning/working. It has to be efficient training of our brain. Otherwise, as Ms. Rong Huang commented, there is a danger that one’s ages live onto the body of dogs.

This article is not about “Science of Success”. But I do want to have one more comment on motivating oneself to work. Self control is like our muscles. If we use them too much, we are tired and can no longer control ourselves well. The trick is use our limit self control on forming good habits.

Play. Yes, play, seriously. The worst time I have is the time that I am so busy that I don’t have time to play with science comfortably with trial and fail. When one become extremely busy, one may hope to make sure that the time spent is valuable, i.e. some achievements are guaranteed. But another way to say it is that, one is doing small things without the courage and creativity to try bigger ideas.

The small things are the ones that even AI may soon be able to do but the bigger ones are not before it is smart enough to pretend it cannot do it.

Let’s see what Mr. Feynman says about this aspect:

I was in the cafeteria and some guy, fooling around, throws a plate in the air. As the plate went up in the air I saw it wobble, and I noticed the red medallion of Cornell on the plate going around. It was pretty obvious to me that the medallion went around faster than the wobbling. I had nothing to do, so I start figuring out the motion of the rotating plate. I discovered that when the angle is very slight, the medallion rotates twice as fast as the wobble rate—two to one. It came out of a complicated equation! I went on to work out equations for wobbles. Then I thought about how the electron orbits start to move in relativity. Then there’s the Dirac equation in electrodynamics. And then quantum electrodynamics. And before I knew it… the whole business that I got the Nobel prize for came from that piddling around with the wobbling plate.

Not keeping your mouth shut. Nowadays is not the era that one fights physics by his/her effort alone. The biggest thing that one can fight with alone is the windmill. One has to talk! People don’t know your excellence if you don’t talk to them. Catch the heroes of the field at lunch and show them how great you are. This is often the starting point of your next level of excellence. Also, talk to the group members before you try to join a group. It’s much better to know in advance whether it is likely to work out well.

For prospective graduate students

If you agree with most of the above, talk to me and show me your excellence.

The PhD program can be 4 years at HKUST. This is good and bad. Good because it feels nice to get a degree faster, and bad because when applying postdoc positions, you have to compete with those who can work 5 or 6 years for their thesis. Remember that you will apply postdoc at the beginning of the 4th year. So be careful with the 3 years of time (and don’t forget the importance of playing).

The requirements and procedure for application can be found here.

For students seeking for UG projects

There are three things for undergraduate students to consider about research – to enjoy research, to try out and see whether one fits for research and to have some publications which will be a big advantage for applying graduate schools.

Again recall that one has to apply at the beginning of the 4th year. It takes sometime to work something out and write a paper. So it is very challenging to publish something before application. But excellence students can do that. For example, a visiting student published 4 papers before his application, on 3 different areas in theoretical physics (cosmology, scattering amplitude and black hole physics) and has quite a few works in preparation. Focusing on one area and having one publication is much easier than that!

From previous experiences of successes and failures, I will recommend the students to learn at least either QFT (preferably) or GR before starting to do any research. The easiest way is to take either of my courses on those topics. The best students (as far as I met and I look forward to new surprises) can take them and learn them very well at their second year. That’s good timing if one wants to try to have some publications in this field before applying for graduate schools.

You are to make a hard decision

Sure. It will be a hard decision. But hard decisions define your trajectory and make you who you are. If all decisions in one’s life are straightforward, i.e. it is stupid to choose otherwise, then he or she is effectively either stupid or has no freewill.

So make a careful decision, but never be afraid to do so.

Beyond the end

I don’t believe that you are so patient that you actually reached here! But if you are, and you happen to understand Chinese, then there is an Easter egg – an article that I wrote 10 years ago when I was a first year graduate student. You can see that although I was so simple, young and naïve at that time (fortunately not much better now, and the proof is having written this article) the fundamental things did not change.

You are welcome to leave a comment below if you’d like to.