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A 9-line summary of textbook physics

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Re: A 9-line summary of textbook physics

#141

Post by abdullahkhalids »

Reventlov wrote: post #6

I opened a volume of the books linked in the page, and found this: « Learning allows us to discover what kind of person we can be. Learning widens knowledge, improves intelligence and provides a sense of achievement. Therefore, learning from a book, especially one about nature, should be efficient and enjoyable. Avoid bad learning methods like the plague! Do not use a marker, a pen or a pencil to highlight or underli…

If you steelman the author's claim, the unsaid interpretation is, the optimal way of learning Physics is to solve questions. Lots of them. On the order of thousands for an undergrad Physics curriculum.

Reading the textbook and getting some concepts out is only a precursor to real understanding which is when you apply those concepts to scenarios in questions. Far too many people get stuck thinking reading the book and highlighting is sufficient, but it is only the foreplay not real sex.

Re: A 9-line summary of textbook physics

#142

Post by sockaddr »

tvanantwerp wrote: post #36
Reventlov wrote: post #6

I opened a volume of the books linked in the page, and found this: « Learning allows us to discover what kind of person we can be. Learning widens knowledge, improves intelligence and provides a sense of achievement. Therefore, learning from a book, especially one about nature, should be efficient and enjoyable. Avoid bad learning methods like the plague! Do not use a marker, a pen or a pencil to highlight or underli…

I can't say what the author's intent was, but I see two ways to parse this: one I disagree with, one I agree with. The disagreeable interpretation is that the only way to learn is from a pristine book. This is so obviously stupid that I see no reason to discuss it further. The other interpretation, which I think is more useful but unclear from the text, is that _passive activities are subpar learning activities_. Fro…

> The disagreeable interpretation is that the only way to learn is from a pristine book. This is so obviously stupid that I see no reason to discuss it further.

Agreed. I actually prefer to see markings in used books I'm reading. Not only does it provide possibly useful context into how another person is thinking about the topic, but it even makes it feel like there's a bit of friendship or community in the book.

Re: A 9-line summary of textbook physics

#143

Post by lisper »

knzhou wrote: post #124
spekcular wrote: post #100

The author is a well-known crank. See post #10 here, for instance: https://www.physicsforums.com/threads/strand-model-published... Proceed with caution.

Indeed, the author's 2000-page online textbook, heavily promoted on the internet, is a classic trap for unwary students. It looks alright at first: volume I is light on math, but full of neat examples. But it's full of intuitively plausible but slightly wrong statements which fall apart in more general situations, reflecting the author's lack of technical expertise. This problem steadily gets worse: volume IV is an o…

> the standard textbooks are excellent

Sorry, I have to disagree with this, at least with respect to quantum mechanics. The pedagogy of QM is atrocious because it generally focuses on the single-particle case and relegates entanglement to the sidelines while making a big deal out of the mystery of the measurement problem. This leaves students hopelessly confused. At least, it left me hopelessly confused for about ten years. Even today one hears physicists speak un-ironically of "quantum erasers changing the past" and other associated nonsense. If there's a standard text that inoculates against that, I have not seen it.

Re: A 9-line summary of textbook physics

#144

Post by sacrosancty »

supernova87a wrote: post #139

I'm a former physics/astro person, and honestly I had never seen a factor like c^4 power in my life...

Huh? It appears in the basic relativistic energy/momentum equation at the bottom of here http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/relmom.ht...

Re: A 9-line summary of textbook physics

#145

Post by blablabla123 »

_Nat_ wrote: post #108
PrettyPebble wrote: post #104

Earlier quoted context omitted.

Of course the 9 lines imply all of physics. Just mention a part of physics that is missing, and I'll buy you a beer. "Zero entropy" is indeed against the laws of physics - in this universe. It may be different in other universes. Line 2 does not speak about locality, but about the speed of light. Entanglement does not violate the speed of light - in this universe. It may be different in other universes. If you know w…

There's no Lagrangian in those 9-lines. Nor is there Quantum-Theory, nor the Standard-Model, nor General-Relativity. Nor is science there, really. Which is kinda my point -- those 9-lines aren't all of science.. unless, I guess, if you assume that all of science is a given. But then, why even have 9-lines when 0-lines could do? Then it's hard to avoid critiques because there're obvious flaws. For example, yes, there'…

I can see how this is almost offensive to the whole subject of Experimental Physics since it ignores all of it - and for that matter Solid State Physics as well. But for Theoretical Physics (minus Mathematical Physics) it seemed to me almost like a sport where professors tried to boil the theory down to a minimal set of assumptions while taking symmetry arguments to the extreme. Obviously this doesn't contain any QM postulates but OTOH for practical purposes QFT is what many people use to compare theory with predictions. IMHO Theoretical Physics without Experimental Physics is useless and vice-versa. And there isn't much research going on with QM (despite plenty of open questions)

Re: A 9-line summary of textbook physics

#146

Post by eutropia »

didericis wrote: post #110
gus_massa wrote: post #55

> Lines 1, 2 and 3, together, uniquely determine special and general relativity, cosmology, the Hilbert Lagrangian and Einstein's field equations, as told here. This is a huge exaggeration. For example 1 says "W=∫L" but L is never defined. The definition of L hides a lot of details, in particular that each point of the universe is equivalent, so there is translation invariance that using the Noether's theorem implies…

These kinds of comments block me from doing a physics dive; I don’t know where to start/am worried about starting from a bad point. I don’t know whether to follow some of the trails the linked author has laid out if I want to learn more, whether you’re nitpicking, or whether you’re advocating for a much better approach that starts with the details you say this obfuscates. When I was younger and had more time I’d be w…

If you can find a copy of “Understanding Physics” by Isaac Asimov, that is an excellent place to start.

Re: A 9-line summary of textbook physics

#147

Post by raydiatian »

didericis wrote: post #110
gus_massa wrote: post #55

> Lines 1, 2 and 3, together, uniquely determine special and general relativity, cosmology, the Hilbert Lagrangian and Einstein's field equations, as told here. This is a huge exaggeration. For example 1 says "W=∫L" but L is never defined. The definition of L hides a lot of details, in particular that each point of the universe is equivalent, so there is translation invariance that using the Noether's theorem implies…

These kinds of comments block me from doing a physics dive; I don’t know where to start/am worried about starting from a bad point. I don’t know whether to follow some of the trails the linked author has laid out if I want to learn more, whether you’re nitpicking, or whether you’re advocating for a much better approach that starts with the details you say this obfuscates. When I was younger and had more time I’d be w…

Step 1. Download a university physics textbook

Step 2. Read said textbook

Step 3. Refer to internet to give relief and contrast to your mental model.

Step 4. Take notes

Step 5. When you finish that textbook, use your knowledge as a foundation to select and consume the next.

Repeat from step 1.

There’s a self-learning approach absent of any dependence on ycombinator comments. And it’s plenty efficient—there aren’t even exams if you don’t want to take them!

Re: A 9-line summary of textbook physics

#148

Post by ephimetheus »

didericis wrote: post #110
gus_massa wrote: post #55

> Lines 1, 2 and 3, together, uniquely determine special and general relativity, cosmology, the Hilbert Lagrangian and Einstein's field equations, as told here. This is a huge exaggeration. For example 1 says "W=∫L" but L is never defined. The definition of L hides a lot of details, in particular that each point of the universe is equivalent, so there is translation invariance that using the Noether's theorem implies…

These kinds of comments block me from doing a physics dive; I don’t know where to start/am worried about starting from a bad point. I don’t know whether to follow some of the trails the linked author has laid out if I want to learn more, whether you’re nitpicking, or whether you’re advocating for a much better approach that starts with the details you say this obfuscates. When I was younger and had more time I’d be w…

I know that is not really what your comment is about, but symmetries, conserved quantities and Noether’s theorem are some of the neatest bits of fundamental physics.

Basically you observe that stuff stays the same if you move around (not true on earth, but like, in space, generally speaking). The physics is invariant under translation. That’s what we call a symmetry.

Now Emmy Noether came up with a relationship and formulae that connects each such fundamental symmetry with a conserved quantity. For translation the quantity turns out to be momentum. Conservation of momentum is one of the most fundamental building blocks of classical mechanics. And we can derive that it is in fact conserved from something as simple as a symmetry.

And it doesn’t stop there: next in line: invariance under rotation: angular momentum conservation, which is equally important as momentum conservation. If angular momentum wasn’t conserved, our universe would look entirely different.

Ages later people figured out that this symmetry business goes way deeper than initially thought. These U(1), SU(2) and SU(3) from the posted link are notation for other, less intuitive, symmetries. Here they don’t apply to space itself anymore but to quantum fields. With that and Noethers theorem (and some admittedly kind of involved maths) you can derive theories describing all electromagnetic and nuclear interactions.

So basically, these symmetries are effectively at the heart of the world (and physics) and I think that’s amazing.

Re: A 9-line summary of textbook physics

#149

Post by mananaysiempre »

amluto wrote: post #131
gus_massa wrote: post #55

> Lines 1, 2 and 3, together, uniquely determine special and general relativity, cosmology, the Hilbert Lagrangian and Einstein's field equations, as told here. This is a huge exaggeration. For example 1 says "W=∫L" but L is never defined. The definition of L hides a lot of details, in particular that each point of the universe is equivalent, so there is translation invariance that using the Noether's theorem implies…

Oof. I don’t see how you recover any of thermodynamics. S ≥ k is a really odd axiom to start with. It certainly doesn’t superficially imply the second law. It’s also rather at odds with the usual statistical formulation in which the entropy of a system in its unique ground state (or simply a system without meaningful microscopic states) is zero. Imagine trying to describe the behavior of a single (idealized) particle…

> The quality of the average thermodynamics textbook doesn’t help.

The very beginning of Huang’s statistical mechanics text is a really good, really short summary of axiomatic thermodynamics. The bulk of the book is 60s-era stat mech models, but the first couple dozen pages contain a surprisingly lucid exposition of the classic story of Clausius, Thompson, and Carnot. Rumer and Ryvkin is also a good book that explores things purely from a perspective of phenomenological axiomatics before plunging into statistics, and includes for example a discussion of how the potentials determine the equilibrium state under various conditions.

Unfortunately, neither of these subsumes the other, and I wouldn’t really recommend either as a first-time introduction, so that mental spot is still empty for me. But as a way to demystify thermodynamics (which I find myself reaching for every few years with disturbing regularity) they serve well.

(I also have a stack of various people’s notes that finally made the Legendre transform click for me lying around here somewhere, if anybody wants them.)

Re: A 9-line summary of textbook physics

#150

Post by 7373737373 »

gus_massa wrote: post #55

> Lines 1, 2 and 3, together, uniquely determine special and general relativity, cosmology, the Hilbert Lagrangian and Einstein's field equations, as told here. This is a huge exaggeration. For example 1 says "W=∫L" but L is never defined. The definition of L hides a lot of details, in particular that each point of the universe is equivalent, so there is translation invariance that using the Noether's theorem implies…

Kind of the same as positing that a Lisp meta-circular evaluator or Smalltalk (syntax) fits on the postcard. There are so many more elaborations on semantics and further definitions missing
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