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Ask HN: How to self-study physics?

451 points by hsikka ↗ HN
Hey HN,

I'm a CS graduate student, and I do a lot of Deep Learning Research. I've always wanted to get a strong foundation in Physics, and while on lockdown because of COVID, I thought it would be a great opportunity.

I've run across this incredible guide https://www.susanjfowler.com/blog/2016/8/13/so-you-want-to-l... and I was also thinking about going through MIT Open Courseware following their bachelor's curriculum.

Do you all have any suggestions or tips? I really appreciate it!

193 comments

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Areading314
Some tips:

* Don't get discouraged. Physics is hard!

* Work on problems, and don't let yourself look at the solutions too soon. Sometimes it takes a few days of thinking to solve a problem.

* When reading through equations, go really slow. Make sure you fully understand each step and don't let yourself skim.

Edit: +1 for the guide you linked, it looks excellent.

fyp
Your link is already a great resource, thanks for that! I didn't know Susan Fowler was a physics major at UPenn.

The tl;dr; seems to be get "University Physics with Modern Physics" and go from there?

greattsclerouse
I'd recommend starting here: https://ocw.mit.edu/courses/audio-video-courses/#physics

In my experience these are some of the best online courses you can watch to learn physics. Personally, I would look into the trying to watch the lectures from Walter Lewin--Walter is a fantastic orator and has a really great mad-scientist persona that is really captivating. Some additional archived lectures can be found here: http://dspace.mit.edu/handle/1721.1/34001 and here: https://ocw.mit.edu/courses/physics/archived-physics-courses...

I got my minor in physics from NYU many many moons ago (yes I'm getting old), but I found that the MIT lectures and OCW materials went way beyond the NYU coursework in both breadth and depth. I watched these lectures and worked through the lecture notes & assignments for Physics I, II, III, Quantum I, II, and several others in addition to digging into the Mathematics lectures / content. I found this material to be the most helpful out there. I'll also point out that I emailed the professors (Lewin, and others) and was pleased to receive a warm and helpful response on several occasions. I hope these are as helpful for your learning as they were for mine.

Once, you are able to complete the video lectures here, OCW has a massive amount of content for some of the more advanced courses that aren't in video format. In my experience, going through these video lectures and some of the mathematics lectures should set you up well to be able to comprehend even the most advanced content across field theory and string theory.

Cheers!

8bitsrule
For a 'strong foundation', you'll want to look at a first-year textbook and make sure your math skills are up to it. Use something with an eraser on it.

Old joke from Anonymous: "Theoretical physicists aren't very expensive -- they only need a blackboard and an eraser. Compare that to a philosopher -- much the same but without the eraser."

yummypaint
There are some general concepts that make frequent appearances, it's worth looking out for them because they can help form connections between different areas. Some examples: 1. the harmonic oscillator and associated quadratic potential. 2. Wave-like phenomena and the wave equation. This comes up in all kinds of mechanical and em systems, plus the schroedinger equation itself. 3. Decomposition of functions into orthogonal sets of other functions, its not just a mathematical trick, but a powerful way of reconceptualizing things. 4. Approximations and expansions are everywhere. Always keep in mind what it is youre solving for and look at its sensitivity to other properties of the system.
FuckButtons
Start by brushing up on your math, there’s not much you can really get into without first getting into the calculus of variations, which you probably haven’t covered. From that you can get into Hamiltonian mechanics and from there you can start to really grapple with quantum mechanics.

After dealing with the more technical side, you should read Paul Dirac’s book “the principles of quantum mechanics”

gjstein
I was a physicist for a time and I learned physics via numerical simulation: I would find problems I could solve by hand and code them up---solving integrals, derivatives, systems of equations all numerically and comparing the results. Only a handful of physics problems have closed-form solutions, and being able to turn an interesting problem into code and "play around with it" was enormous fun for me and helped me build intuition as well. This advice strongly depends on your mathematics background, but with some basic calculus you can already start playing around.
kkaranth
This sounds interesting! Could you talk a bit more about what sources you used to find problems and learn from that translated well to this approach?
op03
Math for Game Programmers - Jorge Rodriguez. There is a playlist on youtube.

Game programming is an underrated/underused tool to teach math, physics and programming.

jmiskovic
Game engine implements only a tiny slice of physics science, and even that in very distorted smoke-and-mirrors way in order to make it run in realtime. You learn more about computational optimizations, numerical methods and linear algebra, while physics is mostly elementary level. For example, all of optics is stuffed into highly optimized and simplified rendering pipeline and "physically based rendering" is anything but.
qchris
Just to add my own two cents here: while I absolutely agree that numerical simulation is a great approach for understanding physics, the canonical closed-form solutions really are a necessary step for building an intuitive understanding of principles like symmetry and the importance of choosing useful reference frames. These are things that are very well complemented by building numerical models (and I think it would be tough to build those models without that understanding of concepts like that in the first place), but it's important to recognize that it's very difficult to skip directly to the numerical models stage.

As I said, I think the parent covered that, but just wanted to try to make it a little more explicit.

dave_sullivan
I've been taking a similar approach and pursuing this topic by getting into Computational Fluid Dynamics and understanding physics in code first, then trying to bridge the code to the more rigorous mathematical representation.

This is after I tried reading a bunch of physics books and, while interesting, I couldn't really get my head around "Ok, so how would I program something like that?"

But then there's this, you might find it interesting, it helped me understand how everything fits together a lot more: https://github.com/barbagroup/CFDPython

Also, physics is a big area, so this is just one part, specifically the physics of fluid simulation. But there's a big market behind CFD too, so you could do worse in picking something with some directly practical application.

codebolt
I highly recommend Road to Reality by Roger Penrose. Takes you all the way from classical through modern physics, and introduces all the necessary math. Gives you a good overview of the territory, but you might want to supplement with some extra literature/lectures to go more in-depth certain places.
madaxe_again
Roger Penrose

Kip Thorne

Michio Kaku

Douglas Hofstadter

Isaac Asimov (non-fiction/essays)

All have written numerous excellent books on various physics topics, and each explains the concepts they wish to convey clearly, with as much or as little mathematics as you like.

Before I went to university to read physics, I devoured their (and others) popular science books, and had a pretty good understanding of the majority of the material on my degree course before I started it - the degree filled in the blanks, annealed the maths in my mind - but there’s little as good as a book written by an expert on a topic to imbue knowledge.

pdonis
In general I think actual textbooks or course materials (the OP mentioned MIT Open Courseware, which I think is a good set of course materials--full disclosure: I'm an MIT alum) are better for learning physics, or any scientific field, than pop science books, however high quality.

That said, if you are going to read pop science books, I don't think Michio Kaku is a good choice. He is much too prone to treat way-out speculations as though they were established physics.

Koshkin
Penrose's is a terrible book for a beginner to try to learn from. It's a weird mix of relatively simple stuff and one you can't possibly appreciate if you do not have a degree in math or physics. It has a tendency to dwell on simple and familiar things and then rush through rather involved topics that are no doubt something a beginner would not have a chance to be prepared for.
knzhou
I don't know of anybody who's ever learned new stuff from that book. It literally zooms from addition and subtraction to fiber bundles in a few hundred pages. That's simply not enough to pick up anything but the bare intuition, and certainly not enough to do any nontrivial calculations. The only people I know who enjoyed the book at all were those who already knew the stuff in it, but in that case the book was pointless!
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perczel
I thought I would also add my two cents, though there have been many excellent responses already. I recently defended my PhD in Physics (MIT '18).

First of all - great idea! It is never too late to learn math and physics! In fact, with hard work and commitment, anybody can muster them to a high level.

(1) Reading =/= understanding in math and physics. You understand a topic only if you can solve the problems.

(2) Work through the solved problems you encounter in textbooks carefully.

(3) Most people around me have never read any physics textbook cover to cover. E.g. reading Halliday, Resnick & Walker completely might take you years! Not all topics are equally important. Focus on the important parts.

(4) You need guidance on what is important and what is not. Online courses, college material (especially problem sets!), teaching webpages could be a helpful guide. MIT OCW is an excellent resource, once you are ready for it.

(5) Finding someone to talk to is really useful. You will likely have questions. Cultivating some relationship that allows you to ask questions is invaluable.

(4) College courses in math and physics have a very definitive order. It is really difficult to skip any step along the way. E.g. to understand special relativity, you must first understand classical physics and electrodynamics.

(5) Be prepared that the timescales in physics are long. Often, what turns people off is that they do not get things quickly (e.g. in 15-30 minutes). If you find yourself thinking hours about seemingly simple problems, do not despair! That is normal in physics.

(6) You have to 'soak in' physics. It takes time. Initially, you might feel like you do not make a lot of progress, but the more you know, the quicker it will get. Give yourself time and be patient and persistent.

(7) Often, just writing things down helps a lot with making things stick. It is a way of developing 'muscle memory'. So try and take notes while reading. Copying out solved problems from textbooks is also a good technique.

(8) Counterintuitive: If you get completely stuck, move on! Learning often happens in non-linear ways. If you hit an insurmountable roadblock, just keep going. When you return in a few days/weeks, things will almost certainly be clearer.

indutny
In addition to said here:

* https://www.susanjfowler.com/blog/2016/8/13/so-you-want-to-l...

There are plenty of textbooks and lecture notes available online and that article links to most of the popular choices. Make sure to choose correct order of topics to avoid getting stuck!

chongli
Wow, thanks for the link! What an incredible resource! It’s really a shame that she had to become famous for being mistreated, rather than for writing such a helpful post as this.
jacobolus
> (8) Counterintuitive: If you get completely stuck, move on! Learning often happens in non-linear ways. If you hit an insurmountable roadblock, just keep going. When you return in a few days/weeks, things will almost certainly be clearer.

This is something our education system does a poor job at.

My observation from watching a 3.5-year-old all the time is that bootstrapping most skills (e.g. riding a 2-wheeled scooter, solving simple logic puzzles, drawing, cutting with scissors, building structures out of construction toys) does not require frequent or extensive practice per se, but only practice spaced out in time, combined with a positive emotional outlook. The student can try something with limited success for a little while (maybe 15–30 minutes), go away for a few weeks, come try again and fail again, go away for another few weeks, etc., and after a few months there are sudden leaps in ability as the brain has apparently been churning away at the problem in the background without any obvious deliberate effort in between.

I think we should be organizing education to expose concepts and tools early before people are “ready”, but not putting any particular pressure on repeated failure/struggle, and then trying again intermittently.

Instead we try to organize instruction so that each idea, tool, or method is taught once, with students encountering something new for the first time and being expected to understand it through short-term brute effort and punished if they fail, and then often a concept or idea is subsequently left aside and not revisited.

jimhefferon
> being expected to understand it through short-term brute effort

Very true, very true. But I have to give grades.

Sure there are things you can do, like quizzes they take as many times as they want and where you only take the final value. But then people don't complete the work. I can't pass them along to Calc II without knowing 70% of Calc I.

It's a tough question in psychology. I had hoped tech would help with it, but I've not had luck in that direction.

kyuudou
>as the brain has apparently been churning away at the problem in the background without any obvious deliberate effort in between.

This is so fundamental. I picked up a similar concept from a passionate english teacher in 7th grade. He said, after a certain point you've done all that you can do, so let your subconscious work on it, sleep on it and the next day or week you'll find your idea coming together. Paraphrased of course.

Sleep is a very important component of this IMO. It doesn't work as well if you are in poor health and sleep-deprived.

It's like some kind of garbage collection and backend processing happens that we just don't fully understand yet as part of the learning process.

Similarly, I found back in college that concepts processed and stored in short-term memory needed to be "slept on" to fully and solidly store into long-term memory and "stick".

Control the input, carefully imagine and focus on the desired output and your brain will take care of much of the rest. Let it.

petargyurov
An excellent list. Pretty much hits the nail on the head. The only thing I would is this:

Often times, well known phenomena and concepts are NOT explained well specifically because they are well known. Whether it's a lecturer or a YouTube video, lots of sources tend to skimp out on the fundamentals. Having said that, don't let it discourage you. It took me forever to discover what the Uncertainty Principle actually means and how it manifests itself in real life. This is related to point 5) I guess.

commandersaki
Isn't an important aspect of learning Physics is being able to conduct experiments in a lab?
petargyurov
I'm not the original commenter but here's my thoughts.

For reference, I studied theoretical physics up to a bachelor level in university. Despite the "theory" focus I still had to do the same amount of lab work as everyone else. I did not enjoy it. I didn't learn much about the concepts from it.

I did however learn about the importance of visualising and representing data, statistics and so on.

We all learn differently I guess - for me lab work was a chore and that mental barrier probably didn't help me learn what the experiments were designed to teach.

abdullahkhalids
Absolutely. How can you claim to model something if you haven't at least looked at the thing with your own eyes, played with it with your (metaphoric) hands?

Experiments teach you, that reality is complicated and models have to be simple, but with judicious choices of assumptions, one can still get accurate and precise prediction out of simple models. I am a theoretical physicist, but I would say the experimental courses I have taken were the most important courses in understanding the limitation of theory.

jhrmnn
I disagree. Perhaps in some areas, like electromagnetism or optics, but there are large fields in physics where it's not necessary (statistical mechanics, quantum mechanics, gravity, high-energy physics)
abdullahkhalids
I am not saying that you should to do experiments in every area. Just that experiments in a few areas (usually mechanics/EM/optics/basic QM targeted by undergrad labs) is sufficient to give you the necessary intuition about the limitations of theory in all areas.
h91wka
Short answer: not every physicist works in a lab. Theoretical & mathematical physics are entirely about working with mathematical models of phenomena that other people observed in a lab. It's enough to understand that any theory is rooted in the experimental, and should be falsifiable by it.
hyperpallium
I think it's essential to have a strong grasp of high school mathematics, not just high marks, but actually understand it. Gaps here are very serious. What do you think?
jhrmnn
(not parent) Agreed. But I would also say that physics can actually help you a lot with understanding math. I learned both physics and math very organically at high school, going way ahead the curriculum, and to me it was more like a single subject. For a physicist, math is just such an essential tool. I cannot imagine having the understanding of calculus that I have without physics. (But then again that's why I'm not a mathematician.)
stared
A lot of good pieces of advice (especially on problem-solving, timescale, and moving on).

However, some points are IMHO superfluous, for example:

> Not all topics are equally important. Focus on the important parts.

These statements are correct and general, and most people would agree with (even having no idea the topic), but are rarely actionable (or even: make sense for a newcomer). Vide most of the motivational quotations.

In short: hard to disagree. But how the heck a newcomer knows what is important and what is not?

CBLT
The introduction or author's foreword usually covers that in my experience. They'll say which chapters you can skip, and sometimes lay out a map of the key milestone chapters.
longtermd
Read the Feynman Lectures https://www.feynmanlectures.caltech.edu/
indutny
Fantastic material! That being said I'd recommend to have several alternative textbooks for every subject at hand. Whenever stuck - one should switch to another and try a different take.
funklute
It's perhaps worth being aware that when Feynman initially gave his course at Caltech, most of the students either did extremely well or completely bombed the exam. The middle ground kinda disappeared. So if you read the Feynman lectures and struggle to understand his perspective from the first few chapters, it may be best to give up sooner than later (and move onto other sources).
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occamschainsaw
I second Feynman lectures! It is a delightful introduction to physics. Susskind's theoretical minimum series is also a good starting point: http://theoreticalminimum.com/courses
rex_lupi
The Feynman lextures are must if someone wants to develop intuitions in physics. Volume 3 (quantum mechanics) is a bit difficult for new learners or undergraduates, but I absolutely recommend reading vol.1 & 2.
lidHanteyk
Everybody recommending Feynman would do well to remember his attitude towards women. Instead, here's a few hours of Susskind on general relativity [0], string theory [1], and quantum mechanics [2].

[0] https://www.youtube.com/playlist?list=PLD9DDFBDC338226CA

[1] https://www.youtube.com/playlist?list=PLA2FDCCBC7956448F

[2] https://www.youtube.com/playlist?list=PLA27CEA1B8B27EB67

fsloth
Please stop demanding dead people to be absolute saints and please cherish their good qualities.

Most of the top scientists I can name were very failed humans in other ways. If you demand absolute totalitarian compliance with modern ethical dogma you will not find many people, I'm afraid.

Feynman was also obviously socially very insecure given his double jeopardy background (blue collar parents and a jew). Rampant antisemitism was very much a thing in Feynmans day. I think this affected his obvious need to pose as the cool rebel and the alpha intellectual. But he was also ruthlessly honest. And loved physics and loved explaining things.

Please remember him for the things he loved. Not for his failures.

Simon_says
Poppycock! A person's art is separable from their other beliefs and actions, and Feynman was among the best both in individual contributions and communication to laymen. In any case, I'm unaware of any attitude he had about women aside from wanting to have sex with most of them.
timwaagh
I wouldn't recommend either because i find it to be impossible to learn physics or other complex ideas from an audio stream. But i don't think feynmann was at his core disrespectful towards women, regardless of his intermittent usage of swear words. Not from the accounts I read anyways. so that kind of criticism is ultimately more of the old social conservative critique against the bachelor lifestyle.
Quiark
People can have different opinion on whether Feynman needs to be condemned or not

BUT I can stand behind recommending Susskind!

cameronperot
I have a list of resources [1] I found to be helpful when I was doing my physics undergrad. I can highly recommend MIT's courses.

Learning physics can be tough at times if you're doing it alone as it's common to get stuck on a hard problem and need to talk it through with someone else. If you ever want to discuss any problems feel free to reach out to me (see the contact page on my website).

[1] https://cameronperot.com/resources/

hsikka
This is amazing, thank you! I will most definitely take you up on your offer!
[dead] throwawaybumeer
You can take your Nordic feminist radical views and shove them up your ass. Do well to remember that.
buzzkillington
I have a bunch of letters before my name that have something to do with physics and what you're asking is far to open.

If you want a general grounding have a look at Fundamentals of Physics any addition and work through some of the problems.

You will need calculus, which CS doesn't use at all.

If you want something better: http://www.goodtheorist.science/ It will take you 10 years or so.

thecleaner
Anyone knows of a good reference for numerical methods for quantum mechanics ?
steerablesafe
Hi, I'm a physicist and former IPhO contestant from Hungary. Unfortunately most of the books I could suggest are Hungarian, but there are some resources in English for hard physics problems.

KoMaL [1] is a high school competition, students have one month to solve five physics problems (they can solve more, but only the five best is counted each month). Unfortunately older archives are only in Hungarian, but this is an endless resource, you can come back for new problems each month.

Ortvay [2] is a yearly take-home, one week long problem solving competition for University students. These problems are _very_ hard, so don't be discouraged by not being able to solve them right away.

[3] and [4] are some of my favorite books with Physics problems from Hungarian authors. The problems have varying difficulty, but they are clearly marked in this regard. There are separate hints and full solutions.

[1] https://www.komal.hu/verseny/feladatok.e.shtml [2] https://ortvay.elte.hu/main.html [3] https://www.cambridge.org/gb/academic/subjects/physics/gener... [4] https://www.cambridge.org/gb/academic/subjects/physics/gener...

stared
I self-studied physics when I was a high-school student. I read The Feynman Lectures of Physics, and it was a great introduction (especially Vol 1 and 2; Vol 3 gives interesting insights but I wouldn't treat is like a canon of quantum physics). It is accessible online, https://www.feynmanlectures.caltech.edu/, so go there and read chapter by chapter the pace you like. AFTER there are plenty of ways to go, but for an overview, it is a masterpiece.

However, make sure you practice your skills. It is very easy to get the impression that one understands something, yet not being able to solve a basic exercise (no matter if it is programming or physics).

For an intro to quantum physics, I gathered some materials "Quantum mechanics for high-school students": https://p.migdal.pl/2016/08/15/quantum-mechanics-for-high-sc...

As you come from a programming background, I really encourage you to write small simulations of some pieces. For problems, it is easy to find books with problems for Olympiad preparation (I have a long list of them but in Polish). Or something like: https://physics.stackexchange.com/questions/20832/is-there-a...

jhrmnn
Second this. Vol 1 was the most influential physics book at high school for me. Though be prepared to go through it repeatedly. At least as a teenager with still developing abstract thinking, I had to think things through over and over again.