This Fall, I had to take one last physics core course to fulfil the requirements of my PhD degree. There weren’t many options available and I had long felt uneasy about my insufficient knowledge of quantum field theory, so the choice was made: My last graduate physics course would be ‘Introduction to Quantum Field Theory’. The only problem was that, in 2013, the University of Waterloo would not be offering the course at all! Alas, the only available option was to take the Perimeter Scholars International (PSI) courses for credit. Students undertaking PSI’s masters program are usually called ‘PSIons’ and so it is my experience as a temporary PSIon that I want to share with you in this post.
First let me say one thing: the PSI program is INTENSE. It is not intense, it is capitalized-bold intense! Here’s how it works: Students have to take two courses at a time, and each course is three weeks long with one hour and a half lectures every day plus an assignment at the end of each week. For each of the two courses, there are also three ‘tutorials’ per week: 90-minute-long problem-solving sessions where students work in groups. To cap it off, every course has a 30 minute ‘interview’ in which the students are asked questions concerning the topics covered and they must answer orally in front of a blackboard. Mind you, these courses are not the type to be easily digested, this is ‘Condensed Matter Physics’, ‘Relativity’ and ‘Statistical Mechanics’ we are talking about! So, while the average graduate student usually has an entire term to deal with these monsters, a PSIon has to master them in three weeks; not an easy task. In fact, I once read that a former PSIon accurately referred to the program as ‘drinking water from a firehose’.
Of course, the intensity of the program is one of its many virtues. There is something about totally immersing into a subject that really gets the gears of learning working at their full potential. Intensity is also necessary for the program to achieve another of its merits: immense exposure to different areas of physics. During my year-long course-based Masters at the University of Toronto, I took a total of six courses that I freely chose according to my research interests. In the first half of their program, PSIons have already taken six core courses plus some ‘front-end’ courses on mathematical methods, computational methods and preliminary quantum mechanics. The PSI program is ideal for someone who is either undecided about what research topic to undertake for their PhD or for someone who is genuinely interested in all aspects of theoretical physics. It is not really suited for someone, like me, who is looking to be quickly specialized in a particular subject and who enjoys contact with experimental physics.
Having said that, let me get one thing straight: The PSI program is extraordinary. Instructors are absolutely world-class researchers and lecturers, the facilities of Perimeter Institute are awe-inspiring, students are the smartest and most interesting I have seen in any other place, and the amount of learning that takes place in PSI is, to the best of my knowledge, unrivalled. PSI is amazing.
So what lessons do I take with me from this experience (besides some knowledge of QFT)?
Quantum information is not really physics.
In the beginning of the first lecture of Fredy Cachazo’s (perhaps the best South-American scientist I have ever met) QFT 1 course, we discussed Maxwell’s classical field theory of electromagnetism, carefully choosing units of c=1 and deriving the equations of motion from the relativistically-invariant Lagrangian of the electromagnetic field. The last time I encountered relativity, the need to choose units, Lagrangians and equations of motion in my research was… never. Quantum information and computation is concerned with the consequences and possibilities of understanding information and information-processing in terms of the mathematical formulation of quantum mechanics. It is inspired from physical law, but it is not really physics (unless you are dealing with implementations). We could endlessly argue about what it means to ‘be physics’, but the lesson I learnt is that the expertise I have gained during my PhD is heavily disconnected from that of most working physicists. I admit, I like this!
The fundamental laws of nature are not simple.
Don’t let others fool you into thinking otherwise. Just because you can write the relevant equations in a t-shirt, it doesn’t make a theory simple! Just to understand the formulation of the standard model, even the smartest people need years of preparation (and a collection of headaches). Performing the simplest calculation requires formidable mathematical and computational dexterity. The rules of Reversi are simple, the rules of Conway’s Game of Life are simple, but the fundamental rules of the universe are not. Perhaps this is partly what makes the universe so incredibly interesting.
Part of a typical QFT calculation.
I prefer discrete over continuous.
Give me a sum, not an integral. Give me countable, not uncountable. Give me differences, not differentials. I just like it better that way.
Grassmann variables are awesome.
They are. Also, imaginary numbers rock!
Recorded lectures are a phenomenal learning tool.
I often feel frustrated that I cannot remember everything that was said in a lecture. Sure, taking notes and having available lecture notes are extremely helpful, but they are a poor substitute for the lecture itself. Perimeter records pretty much everything that happens in the institute, including the PSI lectures. I went back many times to the recordings to clarify certain points I was dealing with, to re-experience a crucial explanation or to fill in a hole in my notes, all the time thinking how much I wished this had been possible in all the courses I ever took. Recorded lectures also come in very handy when despite your best intentions, a snowstorm prevents you from actually attending the lecture!
There are intelligent people in every corner of the world.
The ‘I’ in PSI stands for ‘International’. It is a policy of the program to accept students from all around the world and the diversity of PSIons is immediately evident: North and South America, Europe, Asia, Africa and Australia/NZ all have representatives and they are all remarkably bright and talented people. I’ve never felt that my intellect was more mundane than in a room full of PSIons: what a privilege! Looking at a PSI classroom can make anyone dream of a world where the shape of the world is constructed equally by everyone, not just a privileged few.
I have many friends who were former PSI students, so I have always felt some closeness to the experience of being a PSIon. Something that always struck me about it was the strength of the bond that was formed between them. Virtually all PSIons arrive to Waterloo without knowing anyone living there. PSIons all live in the same floor of the same building, they attend lectures and tutorials together, they have breakfast, lunch and dinner in the same place. They form an almost inseparable group. That amount of collective experiencing creates a connection that truly lasts a lifetime and which is rare amongst physicists. I feel fortunate to have shared in this experience by being a temporary PSIon and most of all, I am honoured to be able to count many of the people I met amongst my friends.
Last lecture of QFT 2 with François David.
Now back to research!
Qonaom 
I liked this post, Juan Miguel! I do feel, however, that I have to rebut this idea that Quantum Information is not “really” physics. It’s so easy to believe that the only real Physics out there is Quantum Field Theory, since it plays such a fundamental role in our understanding of Nature. Easy, but wrong.
First, I don’t consider Quantum Field Theory to be consistent. QFT does not include gravity, so there is something fundamentally wrong with it — gravity, after all, is an intrinsic property of energy. That fundamental problem is encapsulated by Haag’s Theorem, which I do not understand very well but consider to be fairly damning evidence that we must accept QFT only with a great deal of skepticism. If we are to accept QFT as Physics, we must be cautious to realize that it is far from complete as a theory.
Second, I think “fundamentalism” in Physics is a dangerous tendency of the last fifty years. Physics is larger than the reductionist mentality, and subjects such as Statistical Mechanics are honest Physics without being so reductionist. A comprehensive discussion of Statistical Mechanics would include very little of what you and others might describe as Physics. I consider Quantum Information to be Physics in the way that Statistical Mechanics is Physics. Physics is about the behaviour of the world, not just its constituents.
Finally, Physics is intrinsically informational. Though there is a lot of discussion in Waterloo about founding Physics on various ontological positions, I think all these discussions are moot. Despite Einstein’s rather famous objections to this way of thinking, I do not think good Physics requires any ontological commitments at all. Physics is a set of rules about predicting the outcome of any given experiment, which naturally and fundamentally requires a theory of the information processing capacity of the measurement process in said experiment. This is a modern interpretation of the Principle of Complementarity, which is a statement about epistemology rather than ontology.
In short, Quantum Information is good Physics. I claim that anyone who says otherwise is taking an unacceptably narrow view of Physics that does not stand up to scrutiny.
Hey Yuval!
Thank you for your dedicated comment. I make a deliberate effort of NOT being too meticulous with these blog posts because I want them to remain light to read and provocative.
Deciding whether a certain subject is ‘physics’ or not is largely a matter of determining what we mean by ‘physics’, which will lead to endless discussion. I didn’t intend to enter that discussion but to make a simple point: What we learn and do in quantum information (not implementations) is quite far removed from what most working physicists learn and do, a point in which I imagine you will agree with me.
Of course, information is ultimately physical. Of course, we care not only about constituents and fundamental laws but about their mathematical structure and consequences. But then again, there is a good reason why there are more mathematicians and computer scientists working in quantum information theory than there are physicists!
Hi Miguel,
I found your blog while self-studying QFT 1 and 2, given by Freddy and Francois, from PIRSA video recordings. I am wondering whether you have the tutorial/assignment from that time so that I can do some exercise and improve my understanding of the subject. That would be a great help for me.
My email is same as in comment.
Thanks.