Hacker News Reader

Comment by est31 | Hacker News Reader

Physics is not simple. e=mc^2 might look nice on a t-shirt but it is a cherry picked formula. Newtonian mechanics you learn in high school might seem simple to someone with a MINT degree but they describe a small part of the world, and complicated things like friction are discarded.

General relativity, quantum chromodynamics, etc. They are all incredibly complicated.

View on HN

Even bog standard classical mechanics can be very complicated and unintuitive, once you go to things like Hamiltonian dynamics and many-body problems. Then you have statistical Physics and, as you said, relativity and quantum mechanics. I’ve recently spent some time learning about some quantum gravity theories; these things are hard.

Yes. Chaotic systems arise in classical mechanics. So while often the formalism is easier to write down than for example in general relativity, calculating a solution is often very difficult or practically impossible.

It's probably worth distinguishing between conceptually simple and mechanically simple. A many body problem is easy to understand (relatively), you're just extending existing rules onto more things at once. Now, actually calculating a position at a time given some initial vectors? That's complicated.

You’re right. But many-body can also turn into statistical physics, which is quite complicated conceptually (basically when entropy and ergodicity become important). Then you have the best of analytical Mechanics, statistics, and quantum mechanics if you fancy.

What is a MINT degree?

And e=mc^2 is not a simple formula. Okay, it's simple. But deriving it and understanding why it's like that was what, junior year in college?

I think MINT is the German version of STEM.

Yeah it is. Sorry that a germanism slipped.

"But deriving it"

It was a while back but I think we derived it in school aged 16-17 in first year A level Physics (UK.) Is that roughly "junior year in college" elsewhere?

As I recall, deriving it required a solid grasp of special relativity and calculus. I mean, if you want to say that you did that at 16, I won't argue with you. But if you claim all students did that it seems unlikely.

Edit: Oxford University, since you are from the UK and that's reputable within the country, lists General Relativity (and hence E=MC^2's derivation) as a 3rd year course in the Physics program. So that makes it squarely in the junior year.

E=mc^2 is a result from special relativity. This is usually touched on earlier than general relativity.

Ah, thank you. It's been a while since I had to remember which was which.

No if you take AP physics in the US, yes if you don’t same thing in the UK if you don’t take physics for your A levels you ain’t gonna learn that.

Physicists will tell you that F=ma can get you through virtually all of kinematics and dynamics.

I consider that a big chunk of the world.

Only in terms of spherical cow models. Try to apply pure F=MA kinematics to the real world and deformation is one of many huge issues it’s ignoring.

F = dp/dt

which might not be m*a but usually is.

Reply on news.ycombinator.com