Ask HN: How to self-study physics? • Hacker News Board

Re: Ask HN: How to self-study physics?

#191

Post by ukj » Sat, Mar 28, 2020, 12:36 PM UTC

ubercow13 wrote: post #153

ukj wrote: post #113

Earlier quoted context omitted.

>Any algorithm can be formalised in e.g. a Turing machine, or any other equivalent universal model of computation Quoting http://math.andrej.com/2006/03/27/sometimes-all-functions-ar... >>The lesson is for those “experts” who “know” that all reasonable models of computation are equivalent to Turing machines. This is true if one looks just at functions from N toN. However, at higher types, such as the type of our func…

What is special about a mutating getter? It operates on the state of the object S and outputs a new state S' and some value x. Some programming languages allow you to write 'functions' without explicitly passing all input state into the function, but does that imply anything fundamental or interesting about mathematics or computation? Is that anything more than a type of syntactic sugar?

What is "special" is that the system has a peculiar property: f(x) != f(x).

If we claim to be subscribed to denotational (Mathematical) semantics then the above contradicts the identity axiom.

And it's not any deep and world-changing insight either - it's obvious to anybody who sees that the LHS and RHS are only evaluated at runtime - they don't have any inherent (denotational) meaning, which is why I keep harping on: programmers use different semantics to mathematicians. We care about things like interaction and control flow structures as first class citizens - those are precisely the things that have no mathematical equivalents. Timeouts, exceptions, retry loops.

It's not "syntactic sugar" - it's necessity for reifying control flow. In the words of the (late) Ed Nelson: The dwelling place of meaning is syntax; semantics is the home of illusion.

https://web.math.princeton.edu/~nelson/papers/rome.pdf

Re: Ask HN: How to self-study physics?

#192

Post by ska » Sun, Mar 29, 2020, 8:11 PM UTC

stared wrote: post #181

ska wrote: post #114

Earlier quoted context omitted.

It's pretty well established now that Feynman is not a good general approach for introductory physics. Plenty of talented teachers have tried it, and moved on to something more effective. This doesn't contradict your point. A particular individual may find them very helpful in learning and understanding the foundational stuff. By all means try, and if it works for you, great. However, it shouldn't be at the top of an…

> It's pretty well established now that Feynman is not a good general approach for introductory physics. Citation needed. For people at the Physics Olympiad level, it is hard to find something as eye-opening and insightful as Feynman Lectures on Physics. For more "general audience", I guess that a more step-by-step is preferred. I know many people (usually not the Olympiad tribe) who preferred Halliday & Resnick.

I don't see how your contention really fits - physics Olympiad types are by definition not general.

For what it's worth, when I was in that position I found some of the Landau and Lifshitz stuff at least as insightful. I'm all for Feynman as a supplement, by the way.

Re: Ask HN: How to self-study physics?

#193

Post by AnthonBerg » Mon, Mar 30, 2020, 12:02 PM UTC

dtornabene wrote: post #183

stared wrote: post #181

Earlier quoted context omitted.

> It's pretty well established now that Feynman is not a good general approach for introductory physics. Citation needed. For people at the Physics Olympiad level, it is hard to find something as eye-opening and insightful as Feynman Lectures on Physics. For more "general audience", I guess that a more step-by-step is preferred. I know many people (usually not the Olympiad tribe) who preferred Halliday & Resnick.

I'm a logician and the Feynman lectures were incomprehensible when I tried to work through them. I for one am glad to see people pushing students toward more approachable texts.

This is very important! It's great to push students towards those texts that are approachable for them.

It would be bad if we were to push students away from texts that are approachable for them, right?

And very important that someone who learns like you is not pushed towards the Feynman lectures because they are not a good cognitive fit.

I promise, we all learn very differently sometimes. I for one found logic as classically presented in CS studies - as symbolic text? - I found it to be very inefficient to acquire. There's a great deal of cognitive transformation that needs to happen. I do much better with wide-ranging abstractions and then then approaching the core logic in a variety of different mechanical approaches – then I "see" the core logic "through" the abstractions and implementations.

And that said, I honestly wish I had easier access to the cognitive style that works "directly" in mathematical symbols and logic and that classical logical training works for. (I don't know if that's you, but I've talked to people that think/function like that.) And I greatly respect that capacity. I.e. I'm definitely not saying mine is better. Only different.

Re: Ask HN: How to self-study physics?

#194

Post by kyuudou » Thu, Apr 02, 2020, 5:59 PM UTC

kyuudou wrote: post #168

jacobolus wrote: post #26

Earlier quoted context omitted.

> (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 scoot…

>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. Paraphrase…

Update: found this link from an ancient blog of mine to a Hebrew Univ study talking about the power of the unconscious: http://www.medicalnewstoday.com/releases/252835.php