[HN Gopher] A 9-line summary of textbook physics
___________________________________________________________________
A 9-line summary of textbook physics
Author : PrettyPebble
Score : 226 points
Date : 2022-03-19 13:47 UTC (9 hours ago)
(HTM) web link (www.motionmountain.net)
(TXT) w3m dump (www.motionmountain.net)
| gpvos wrote:
| _> This pdf file is licensed under the Creative Commons
| Attribution-Noncommercial-No Derivative Works 3.0 Germany
| Licence, whose full text can be found on the website
| creativecommons.org /licenses/by-nc-nd/3.0/de, with the
| additional restriction that reproduction, distribution and use,
| in whole or in part, in any product or service, be it commercial
| or not, is not allowed without the written consent of the
| copyright owner. The pdf file was and remains free for everybody
| to read, store and print for personal use, and to distribute
| electronically, but only in unmodified form and only at no
| charge._
|
| Doesn't that "additional restriction" negate the CC-BY-NC-ND
| license? What does it even mean?
| humanistbot wrote:
| Yes it does.
| mouzogu wrote:
| nice. the funny thing is that each of those 9 lines probably
| requires at least 9 years to fully understand :)
| PrettyPebble wrote:
| No - just a few weeks each, during your physics studies. And
| several lines can be learned in parallel.
| gus_massa wrote:
| > _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 the
| conservation of momentum.
|
| There are many definitions of L, for example if you are analyzing
| bead that locked to a circular wire, it's usual to define L with
| a coordinate that follows the shape of the wire. There are also
| definitions of L in spherical coordinates, where each coordinate
| is different. Anyone with a Major in Physic has nightmares about
| the posibilites to define L.
|
| For example in 2 "v <= c" can be true in a stupid universe where
| the force is bounded and there is enough friction everywhere.
| Imagine a universe that is full of "water" or "aether" or other
| magical thing with magical friction. And for some reason the
| force is bounded, for example like the post says in 3 "F <=
| c4/4G"
|
| Also, I can't imagine how it is possible to rediscover all
| thermodynamics from "S >= k" in item 5.
| 7373737373 wrote:
| 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
| PrettyPebble wrote:
| For deriving special and general relativity, see
| https://www.motionmountain.net/maximumforce.html The page also
| cites the papers proving the statement.
| user-the-name wrote:
| That page has zero words about actually _deriving_ anything.
| PrettyPebble wrote:
| See Physical Review D 104 (2021) 124079. Html page is
| updated.
| amluto wrote:
| 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 in a box
| using this law -- you would get very confused very quickly.
|
| For non-physicists: you can model a gas as a bunch of almost
| entirely non-interacting particles in a box. You can assume
| that there is some way for them to exchange energy, but you
| don't need any details at all of how that works. With some care
| (and IMO a really fascinating series of arguments) you can
| derive the ideal gas law and a whole lot of useful
| thermodynamics. As a first hack at reducing it to one sentence,
| I might try "at equilibrium, each unit of phase space (or each
| discrete microstate in a discrete system) is equally likely."
|
| (I personally find statistical mechanics much more intuitive
| than classical thermodynamics. I have always felt like E, H, F,
| and G are mathematically correct quantities that come from
| manipulating partial derivatives but that they mostly lack
| intuitive value. The quality of the average thermodynamics
| textbook doesn't help.)
| mananaysiempre wrote:
| > The quality of the average thermodynamics textbook doesn't
| help.
|
| The very beginning of Huang's statistical mechanics text
| constitutes 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.)
| noobermin wrote:
| As a recovering theoretical physicist, things like this which
| is primarily an attitude are tiresome. I'll even go further
| down the line, just because you can write down the "equations
| of motion" often doesn't give you anything but another starting
| point.
|
| I will always be amused when people who study particle physics
| do everything after 2nd quantization and thus assume that
| literally understanding _plane wave interactions_ explain all
| physics, rather than such methods are actually reductionist and
| have their own attendant assumptions that fail at certain
| points (like the UV limit for QED), but that means you really
| don 't "understand" all physics just by writing down the
| Lagrangian for SM, it's just a starting point. "Understand" for
| a scientist shouldn't be abstract, it should be "given x
| equations/model I can predict y output" which is very hard for
| a lot of physics, otherwise there wouldn't millions of
| scientists doing things other that just doing string theory
| derivations everyday.
|
| Equations of motion is not understanding.
| didericis wrote:
| 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 willing
| to eat the inefficiency, and the bigger reason for not doing a
| deep dive is the difficulty, my own laziness, and lack of
| practical need, so take what I'm saying with a grain of salt,
| but the time needed to parse criticism like this to see whats
| legitimate and whats not drives me a bit nuts.
|
| I've done enough self learning to know that there is no perfect
| starting point/backtracking is inevitable, but something about
| the modern intellectual landscape feels very noisy/jargony and
| particularly prone to inefficient learning.
|
| When you say "there is translation invariance that using the
| Noether's theorem implies the conservation of momentum", I have
| no idea what that means. It sounds like a description of a
| turbo encabulator. I'm sure its not, and that your description
| is much more efficient than spelling it out from the ground
| level, but it annoys me how difficult it is to distinguish
| between a legitimate domain expert jargon meant to condense
| complexity and unnecessarily obfuscatory jargon that works more
| like a status/club membership symbol.
|
| Maybe its always been like this somewhat and that problem is
| inevitable, idk.
| pas wrote:
| Start from conservation laws, get a feel for the typical
| mechanics problems. Acceleration, forces, work, energy,
| momentum. (At first don't try to understand WTF all that has
| to do with symmetries/invariants.) Then a bit of EM. (Circuit
| analysis, RLC circuits.)
|
| Eventually you'll need some undergrad level math. To get a
| few very concrete (hehe) examples maybe look into a bit of
| structural dynamics (resonant frequency, tuned mass damper,
| mass distribution described by a matrix).
|
| Then eventually you need to be able to solve simple
| differential equations and know what Fourier has to do with
| radios, and how mechanics depends on calculus of variations.
|
| The more examples you work through the more you'll know what
| you want to learn about.
|
| My recommendation is don't try to deep dive into one topic,
| instead start to look for similarities in other topics,
| basically do a breadth-first search.
| eutropia wrote:
| If you can find a copy of "Understanding Physics" by Isaac
| Asimov, that is an excellent place to start.
| whatshisface wrote:
| > _I don't know where to start /am worried about starting
| from a bad point._
|
| Start from the basics. You will get plenty of ability to
| analyze real-world problems from learning Newton's laws.
| Lagrangian mechanics rarely even applies in engineering
| contexts because it can't do friction, air resistance or
| other dissipative terms.
| raydiatian wrote:
| 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!
| ephimetheus wrote:
| 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.
| analog31 wrote:
| One thing about the traditional sequence of physics topics,
| is that it progresses (more or less) in parallel with the
| traditional math sequence. So you can get yourself up to
| speed on both simultaneously.
|
| Also, you don't need to get all the way to the whiz-bang
| stuff, for it to be both enjoyable and useful. Granted, my
| degree was 30+ years ago, but today I specialize in designing
| measurement equipment. If all you end up learning is calculus
| plus how some mundane things work like circuits and optics,
| it would hardly be a loss. I don't even claim to understand
| fundamental stuff like field theory.
|
| There's also a problem with explaining physics: Most of us
| who claim to understand it (I have a physics degree) have
| never attempted to explain it or even think about it without
| math. There's the commonly shared anecdote about physicists
| trying to grasp the "non calculus based" college physics
| course, and finding it too complex and baffling to proceed.
| amluto wrote:
| If you want to dive in to physics on your own, a textbook can
| be a decent starting point. Griffiths is pretty good,
| although if you're starting from zero, it'll be a challenge.
| amelius wrote:
| Exercise: derive from these 9 lines that we have 3 spatial
| dimensions and 1 time dimension.
| PrettyPebble wrote:
| Number of dimensions is one of the 25 numbers of line 9.
|
| But reducing the nine lines to fewer lines is an open problem,
| indeed.
| arcbyte wrote:
| I think the future of physics is in Energy Wave Theory. Maybe not
| that theory exactly, but a similar theory going back to the idea
| of _some_ kind of ether in which waves propagate.
| neonate wrote:
| https://web.archive.org/web/20220319135620/https://www.motio...
| humanistbot wrote:
| Physics maybe, but all sciences? This is is some serious physics
| determinism --- obligatory XKCD: https://xkcd.com/435/
| PrettyPebble wrote:
| You are right - The text should say all "natural sciences".
| IgorPartola wrote:
| The unnatural sciences are where the fun really begins.
| PrettyPebble wrote:
| True!
| MauranKilom wrote:
| Funny enough, there's an even more related xkcd for this page:
| https://xkcd.com/2034/
| PrettyPebble wrote:
| Good one!
| nayuki wrote:
| > The nine lines contain physics, chemistry, material science,
| biology, medicine, geology, astronomy, engineering and computer
| science.
|
| I have doubts that these 9 lines describe computer science. As
| I interpret it, computer science is founded on pure mathematics
| and is not a physical or empirical science. Computer science
| deals with perfect abstract mathematical objects like numbers,
| sets, quantification, recursion, infinities, etc.
| ravi-delia wrote:
| Considering that these lines specify our laws of physics only
| if you grant that math is a thing, you could argue that all
| of mathematics gets in for free ;). Sort of like how ZFC
| can't encode basic logic, but you still need it for axioms to
| make sense
| PrettyPebble wrote:
| Good point - but it needs computers...
| ianbooker wrote:
| Strangely not. You can do CS on paper, no need for a single
| bit-flipping device. Turing did half the field in his head
| / a thought experiment.
| PrettyPebble wrote:
| And input and ouput devices ...
| jrockway wrote:
| It's the lowest level. Applying this to, say, medicine is like
| trying to understand a React app in terms of a Turing Machine.
| It's involved, but it doesn't help because of all of the extra
| rules (which are not fundamental properties of the Universe or
| of mathematics) that we add on top. CORS isn't a fundamental
| law of the Universe, but all major browsers enforce it, so you
| have to deal with it.
| jkuria wrote:
| Social 'scientists'? Your turn :)
| humanistbot wrote:
| The natural sciences, the so-called "hard sciences" are really
| the easy ones, because what they study doesn't have free will.
| The truly difficult sciences are of human behavior.
| smoyer wrote:
| You're assuming free will isn't some complex-looking behavior
| driven by quantum uncertainty. In the multiverse, every social
| scientist has many clones who's studies refute their work!
| marginalia_nu wrote:
| Even if that is so, a quantum description of human behavior
| is fairly useless in terms of practical application. How does
| knowledge of the standard model cure the infirm, prevent
| crime, and so forth?
| Itti wrote:
| When we exhibit behaviors. Our context is derived from our
| visual/auditory field processing from birth. Those waves
| implant magnetic field signatures on our neurotransmitter
| morphologies. We are almost explicitly operational in
| quantum activity. Many if not all disabilities or health
| complications are resonant to your mind body homeostasis.
| Challenge the quantum spectral development process of a
| person you solve the aforementioned issues.
| marginalia_nu wrote:
| Right, but how is this fact in any way helpful in dealing
| with the phenomenal world?
| smoyer wrote:
| I'm not sure that we're arguing different positions.
| la64710 wrote:
| Why do the first chapters of all physics textbook ONLY talk about
| Greek philosophers and scientists and NEVER talk about
| contribution to Science from eastern civilization like India and
| China ? These civilizations have a very rich heritage and
| astounding contribution to many underlying scientific
| philosophies. Yet generation after generation of writers ignore
| them and it is sad to see that being true even today. It is time
| that this is changed.
| mhh__ wrote:
| Because we don't care about the real history, it's just a
| euphemism for laying down the basics of things like reference
| frames.
| theduder99 wrote:
| can you recommend me some good books on China and India's
| contributions to Science please?
| WalterGR wrote:
| Do you read a lot about the history of science? Which books
| would you recommend?
| deadbeeves wrote:
| Off the top of my head, I can name three things from either
| China or India that are science-related: the positional
| numbering system (and zero), the Chinese remainder theorem, and
| gunpowder. What am I missing that's very important yet rarely
| mentioned?
| fooker wrote:
| India: quite a bit of astronomy and geometry. Also logic,
| philosophy and linguistics if you want to include them in the
| science list.
|
| China: chemistry and metallurgy.
|
| Indian science took a weird turn towards metaphysics and
| mystical stuff once the priests started playing a fundamental
| role in education.
| PrettyPebble wrote:
| The Indian number system is treated in detail. Indian
| mathematicians are mentioned and cited.
| la64710 wrote:
| Good to know that , I did not go past the first few pages.
| Now some interesting contribution from India that I never
| heard of before
| https://www.manchester.ac.uk/discover/news/indians-
| predated-...
|
| https://www.britannica.com/biography/Aryabhata-I
|
| But I doubt that many conventional physics textbook will not
| even mention these and others. The writers are not to blame ,
| but no doubt the ignorance is an unfortunate reality.
| [deleted]
| PrettyPebble wrote:
| Fun fact: all physics experiments ever made can be described by 9
| lines, without any deviation between theory and observations.
|
| The 9 lines are sufficient to describe quantum physics and
| gravity.
|
| It seems that the 9 lines even contain all (update: natural)
| sciences, not only physics.
|
| Finding an exception to the 9 lines will make you famous.
|
| So will the discovery of a 10th line.
|
| Thousands of researchers work towards these dreams, but none
| succeeded yet.
|
| A few additional fun facts on
| https://www.motionmountain.net/9lines.html
| criticaltinker wrote:
| This is satire right? You might be getting downvotes because
| it's not clear if you're serious, and those claims seem quite
| ridiculous at face value.
| not_kurt_godel wrote:
| It's essentially paraphrased from the OP. Why OP is getting
| upvoted, I do not know.
| PrettyPebble wrote:
| What is ridiculous?
| _Nat_ wrote:
| The 9-lines thing.
|
| May've just drawn a circle and claimed that it describes
| all of science.
| PrettyPebble wrote:
| If the 9 lines are wrong, just show it... Thousands of
| scientists are trying the same since 50 years.
| _Nat_ wrote:
| It's not that they're " _wrong_ " so much as that they're
| incoherent and largely non-sense.
|
| Sorry if that seems harsh, just.. this looks like
| someone's having some sort of crisis. It's worrisome.
| PrettyPebble wrote:
| No, it is fun! The scientists who are looking for
| exceptions to the standard model and to general
| relativity since 50 years are having a crisis at present,
| as often told.
|
| The 9 lines imply all equations of physics. Every
| Lagrangian of physics is included. The lines are also
| coherent: none contradicts another. They are
| complementary: the cover all observations and all fields
| of physics. No field of physics is left out. The lines
| are also correct: every calculation fits with
| observations withing measurement accuracy, since the
| standard model (with neutrino masses and PMNS mixing) and
| general relativity exist.
| _Nat_ wrote:
| Those 9-lines don't imply all of physics. They don't even
| mention most of physics. A lesser problem is that they're
| not correct, either.
|
| For example, Line-5 suggests that entropy is never below
| the Boltzmann-constant. Which simply isn't true; there're
| notions of zero-entropy, where zero is less than the
| Boltzmann-constant.
|
| For another example, Line-2 suggests that nature _itself_
| is local; this would contradict non-local effects, e.g.
| entanglement, and would seem to prohibit faster-than-
| light recession.
|
| Or, maybe those lines were meant in a way that doesn't
| have those problems? But maybe they have different
| problems? Who knows! -- which is the bigger problem.
|
| This is usually described as [" _not even wrong_
| "](https://en.wikipedia.org/wiki/Not_even_wrong ).
| Because, to _be_ wrong, it 'd have to make more sense
| first.
| PrettyPebble wrote:
| 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 what a Lagrangian is - in quantum theory, in
| quantum field theory, in the standard model and in
| general relativity - you also know that there is no
| random interpretation in the 9 lines.
| _Nat_ wrote:
| 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're totally
| productive notions of zero-entropy -- even if not in the
| models you're used to. For another example, macroscale-
| constants haven't been demonstrated to emerge from the
| Standard-Model -- for example, it hasn't been
| demonstrated that astronomical-scale measurements aren't
| influenced by unknown factors, such as many-body forces,
| which might cause results that'd differ from those
| predicted by the Standard-Model. And since we can measure
| some of those things not known to emerge from the
| Standard-Model, the idea that the Standard-Model captures
| everything -- including those things not known to emerge
| from it -- doesn't follow.
|
| But then that seems to be getting off-topic, because
| while there'd seem to be many things off about this, the
| one I'd really stress is that those 9-lines don't contain
| what they claim to.
| blablabla123 wrote:
| 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)
| blablabla123 wrote:
| I mean you have the groups (6. and 7.) from there you get
| all the variables. E.g. from U(1) you get the generator
| and the group item. Then add all combinations of the
| polynomes to L (1.) but skip those that violate
| invariances like Lorentz (2.), U(1), SU(2), SU(3). You
| end up with something like L=-1/2 d phi^2 - m phi^2.
| (Oversimplified) Do the same for SU(2) and SU(3) and you
| end up with
| http://nuclear.ucdavis.edu/~tgutierr/files/sml2.pdf For
| convenience usually some of the variables are then called
| e (Electron), W+ (W+ Boson) etc.
| blablabla123 wrote:
| I would take this with a huge grain of salt. But generally
| it's quite astonishing with how few assumptions such complex
| theories can be derived. Also the mathematical apparatus has
| really all batteries included speaking of Lagrange formalism
| and its Action (point 1)
| erikpukinskis wrote:
| This is just straight wrong. There is no computer in the world
| that can predict the outcome of, say, a drug trial from these
| equations.
|
| If your "science" requires an impossible computer to work then
| it's not science it's faith.
| PrettyPebble wrote:
| The 9 lines do not say this. The lines do say that drugs are
| made of atoms and that the molecules follow quantum theory.
| Jyaif wrote:
| You are saying that we don't have a computer fast enough to
| simulate a drug trial, but you are not actually disagreeing
| with the parent.
| erikpukinskis wrote:
| No, I'm saying no computer will ever simulate it with only
| those equations. Higher level equations are needed which
| cannot be derived from the given ones, they can only be
| discovered through additional science.
| smoyer wrote:
| An impossible computer is different from a computer that
| humankind can not yet build. If our universe is a simulation,
| then some entity has already proven you wrong. If our
| universe isn't a simulation, our limited resources prevent us
| from running (detailed) universe-scale simulations. I'd say
| that we will eventually be able to simulate a drug
| interaction from these rules (it's the interaction between
| these rules that's the key) but I won't predict WHEN that
| might occur.
| erikpukinskis wrote:
| Those are all reasonable beliefs, but still fall in the
| category of "faith".
| spekcular wrote:
| The author is a well-known crank. See post #10 here, for
| instance: https://www.physicsforums.com/threads/strand-model-
| published...
|
| Proceed with caution.
| knzhou wrote:
| 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
| oversimplified introduction to quantum mechanics which contains
| almost no math, and serious conceptual errors on almost every
| page. Volume V covers a bizarre mix of particle physics,
| consciousness, and sexual reproduction. And volume VI is the
| author's almost math-free personal theory of everything.
| Because the change is gradual, a student can get seriously
| misled without noticing, like the proverbial boiling frog.
|
| On HN, people are always asking how to get started self-
| learning topics like physics. The tragedy is that this has been
| a completely solved problem for decades: the standard textbooks
| are excellent. But people don't hear that message because self-
| promoters pollute the discourse.
| hoten wrote:
| What are the standard textbooks? Could I just look at the
| curriculum of any physics program of a respected school and
| go from there?
| spekcular wrote:
| Yes. Whatever MIT uses for their OpenCourseWare is going to
| be fine, for example.
| lisper wrote:
| > 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.
| spekcular wrote:
| Can you point to a standard textbook that does this? The
| ones I'm familiar with definitely don't shortchange multi-
| particle problems.
|
| And is the measurement problem not a mystery? If there's
| convincing explanation, that's news to me.
| lisper wrote:
| > Can you point to a standard textbook that does this?
|
| That does what? Focus on the single-particle case and
| punt on measurement? My two poster children are the
| Feynman lectures and Griffiths.
|
| > The ones I'm familiar with definitely don't shortchange
| multi-particle problems.
|
| What does your reading list look like? Maybe things have
| changed since I last looked.
|
| > the measurement problem not a mystery?
|
| It might be _a_ mystery, but it is not _the_ mystery most
| commonly presented, namely, that particles change their
| behavior "when somebody looks." This is nonsense.
| Measurement has nothing to do with "somebody looking", it
| is just entanglement + decoherence. The only real mystery
| is the origin of the Born probabilities.
|
| See https://flownet.com/ron/QM.pdf for a complete
| discussion.
| [deleted]
| mncharity wrote:
| > the standard textbooks are excellent
|
| A caveat. Some years ago, at a first-tier university, some
| physicists and mathematicians were munching. A physics
| professor described how days earlier he thought he had found
| a case of a well-respected intro physics textbook saying
| something wrong. But, after some hours and days of thought,
| he realized the textbook was very carefully worded so as to
| not be incorrect. Yay. Most everyone smiled and agreed it was
| an excellent textbook.
|
| A bit later, there was a quiet out-of-band question: So... if
| you're already an expert on the topic, and do a close read,
| after thinking about it for days, you will escape being
| misled... and this is a win??
|
| There's an old physics education research joke: If you think
| your lectures are working, your assessment also isn't. I've
| found that to apply to much science education content as
| well.
| PrettyPebble wrote:
| With several recent PRDs.
| knzhou wrote:
| The Physical Review is a gigantic set of journals, and like
| anything of its size, many of its published results are
| wrong. At this very moment I'm writing a rebuttal to a PRD
| paper that arrived at nonsensical conclusions due to some
| basic algebra mistakes.
| spekcular wrote:
| "Several"? Google Scholar shows two, one of which is an
| approximately 1-page comment on a rebuttal to the other one.
| Neither mentions "strand theory," the focus of the criticism
| in that link.
| [deleted]
| Reventlov wrote:
| 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 underline text on paper. It is a waste of
| time, provides false comfort and makes the text unreadable. And
| do not learn from a screen. In particular, never, ever, learn
| from the internet, from videos, from games or from a smartphone.
| Most of the internet, almost all videos and all games are poisons
| and drugs for the brain. Smartphones are dispensers of drugs that
| make people addicted and prevent learning. Nobody putting marks
| on paper or looking at a screen is learning efficiently or is
| enjoying doing so. >>
|
| My sarcasm detector is broken, is that sarcasm ?
| irrational wrote:
| Yeah, this is clearly BS. Recently I changed the turn switch on
| my car. How did I learn how to do that? From the Internet,
| specifically from watching videos. It was easily the most
| efficient way to learn.
| sdoering wrote:
| > Do not use a marker, a pen or a pencil to highlight or
| underline text on paper. It is a waste of time, provides false
| comfort and makes the text unreadable.
|
| What a load of elitist BS (pardon my French). When I was at
| University we were trained early on to cut the notion of a book
| being sacred. We should mark, note, create meaning on the pages
| with pens.
|
| I would not have been able to learn as much in my life if I had
| not taken this advice seriously.
|
| > In particular, never, ever, learn from the internet, from
| videos, from games or from a smartphone.
|
| Yeah. Exactly. OK. So I have not learned new things recently
| about both World Wars through documentaries telling me about
| findings that I did neither learn in school or at university
| studying history (among other subjects).
|
| I know. I am just anecdata. But wow. What a view on learning in
| the quotes book.
| PrettyPebble wrote:
| Writing notes and comments is great - the text only says
| highlight or underline!
| sdoering wrote:
| Even highlighting and marking is essential to help identify
| the core ideas on a page.
| vixen99 wrote:
| I think the author does have a point though it clearly
| doesn't apply to everyone. 'Elitist BS' is rather strong. You
| take a different view but perhaps you've never studied in a
| part of the world where books are in short supply and one
| expensive copy is shared. I underlined passages in books in
| the past and now regret imposing my then partial view via
| permanent marking. Just a thought but a cataclysmic
| extinction event on Earth might well either destroy most
| electronic media or put it beyond general access. Surviving
| physical books might then become generally sacred once more
| as they are in many people's present day collections. We're
| rather too ready to think that the current ease with which we
| can check out almost any topic will be forever a permanent
| fixture. There are days when I doubt it.
| sdoering wrote:
| I have highlighted and marked books and I tended to buy the
| cheapest copies possible (or buy used books) as I was quite
| tight on money when I was at university.
|
| What I discovered was that I could trace my understanding
| and my development towards concepts through the times when
| I returned to a book that I already had worked with before.
| My older notes and highlights were often the starting point
| but with my then current understanding I built on them,
| contradicted them in parts and sometimes laughed about my
| former ideas. It made me more humble towards knowledge
| generation.
|
| To me it were a blessing to have different layers of marks,
| notes & highlights.
| dbsmith83 wrote:
| If a cataclysmic extinction event occurred, I doubt a
| little bit of highlighting or underlining is going to cause
| significant burden on mankind's ability to relearn things.
| I do agree though, that if you don't own the book you
| probably shouldn't mark in it.
| ravi-delia wrote:
| I sort of agree with the book on highlighting and
| underlining. If you don't jot a note down in the margin,
| you'll forget your state of mind and have no idea what made
| some underlined section meaningful. A false comfort.
| dhosek wrote:
| When I taught LaTeX classes, I would often see students
| highlighting whole pages of the class notes I passed out. I
| often said that I should just print them on yellow paper to
| save them the trouble.
| sdoering wrote:
| Marking the essentials (or better essentials based on
| your your current understanding) is different from
| marking whole sections or pages.
|
| I remember one of my teachers saying he needs some books
| like Goethes Faust about every 10 years because of new
| understanding makes him mark different passages (in a
| different color) than on a previous reading. And after
| teaching and using the books for about 10 years he needs
| a fresh page to mark.
| dgellow wrote:
| > What a load of elitist BS (pardon my French)
|
| The actual French word would be "conneries" (in plural here).
| archhn wrote:
| I like it. The author is being real. This is what he sincerely
| thinks. You don't have to agree with everything an author says.
| I for one appreciate the candor.
|
| It's also a proven fact that many smartphone applications are
| effectively dispensers of dopamine at regular intervals. People
| check their social media like smokers take a smoke break. The
| author is right...albeit a bit terse and dramatic.
| Tarq0n wrote:
| Sharing one's thoughts candidly is worth less than good
| epistemology.
| archhn wrote:
| There's always some truth behind genuine expression, even
| it happens to be riddled with lies.
| 323 wrote:
| Author says "In particular, never, ever, learn from the
| internet", but then author makes a website teaching things.
| Hmm
| archhn wrote:
| The site is an advertisement for his books.
|
| I think he's just old fashioned and believes learning from
| physical paper books is superior. He even has a link at the
| bottom of his site that says "Paper book lovers."
| bitexploder wrote:
| But we have studied learning and how memories are formed.
| I hate when people make stuff up because it worked for
| them it must work for everyone. Things like spaced
| repetition and Khan academy are completely valid ways to
| learn.
| tvanantwerp wrote:
| 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_. From what I've read of effective studying
| techniques, things like highlighting text don't help. Active
| recall techniques like spaced repetition are much more useful
| for cementing learned knowledge. Likewise, if you're "learning"
| from a screen by just staring at it, consuming it, then your
| knowledge-to-inputs ratio is going to be low. I've watched
| plenty of YouTube videos on how to do numerous things, but I
| couldn't do any of them on the spot because I've never tried.
| The knowledge went in one ear and out the other. The material
| must be engaged with somehow.
| zaphar wrote:
| highlighting and underlining don't per-se cause you to learn.
| However they do have two useful properties.
|
| 1. The act of looking for and underlining or highlighting
| text helps you to focus on identifying core ideas or concepts
| in the text.
|
| 2. Underlined and highlighted text are useful as hints when
| reviewing a text and reviewing a text _is_ a critical part of
| learning.
|
| These properties are so helpful that many texts actively help
| you to absorb their content by bolding, underlining, or
| otherwise calling attention to core concepts and ideas for
| you.
| sockaddr wrote:
| > 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.
| dr_dshiv wrote:
| Which book?
| Reventlov wrote:
| I was interested in electromagnetism, so
| https://www.motionmountain.net/motionmountain-volume3.pdf, in
| the << Advice for learners >> section of the introduction. I
| reckon this is the same text in every volume.
| dr_dshiv wrote:
| Yeah, not sarcasm. But contradictory for a free online
| downloadable.
|
| I do like the next advice, to be able to say the ideas in
| your own words. Maybe the point (which seems very
| overstated) is that highlighting and videos create the
| sensation of knowing, but not necessarily the knowing.
| micromacrofoot wrote:
| no there are a lot of old academics that think this way, it's
| almost like a form of self-flagellation... if you're having fun
| then you're not learning hard enough
|
| one professor I knew like this (decades ago now) was the type
| of person that would violently throw chalk at students with the
| gall to not hang on every word he was saying
| abdullahkhalids wrote:
| 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.
| emerged wrote:
| None of us can discount the possibility that the universe was
| fine tuned with a specific set of seed parameters which yields a
| specific trajectory including all of the narrative elements of
| one person or everyone's lives.
|
| Most likely the big narrative payoff is somebody winning the claw
| game for once at the local sports bar. But which of us will it be
| for?
| panda-giddiness wrote:
| When Sabine Hossenfelder wins from the toy crane, maybe I'll
| take superdeterminism seriously.
| MauranKilom wrote:
| > About 18 particles
|
| > About 25 numbers
|
| Excellent science here!
| PrettyPebble wrote:
| Improved the first. The second is ok.
| mhh__ wrote:
| Obviously this won't help you find the particles but this
| seriously isn't far off capturing how shocking symmetry groups
| are as a tool for building theories in particle physics. The
| fact that you can reduce so much physics down to some
| invariance is very spooky.
| PrettyPebble wrote:
| Or just beautiful!
| a_e_k wrote:
| I take this to be an acknowledgement that we don't know
| everything.
|
| I.e., "These are the only ones of which the
| news has come to Haaahrvard, And there may be many
| others but they haven't been discohhhvered."
| threatripper wrote:
| You can't contradict this. Nature is perfect.
| rwoerz wrote:
| Sounds like my tax declaration... where they ask for the number
| of my children.
| 7373737373 wrote:
| https://math.ucr.edu/home/baez/constants.html
| the mass of the up quark the mass of the down quark
| the mass of the charmed quark the mass of the strange
| quark the mass of the top quark the mass of the
| bottom quark 4 numbers for the Kobayashi-Maskawa matrix
| the mass of the electron the mass of the electron
| neutrino the mass of the muon the mass of the mu
| neutrino the mass of the tau the mass of the tau
| neutrino 4 numbers for the Pontecorvo-Maki-Nakagawa-
| Sakata matrix the mass of the Higgs boson the
| expectation value of the Higgs field the U(1) coupling
| constant the SU(2) coupling constant the strong
| coupling constant the cosmological constant
| WalterGR wrote:
| ^---- "How Many Fundamental Constants Are There?" by John
| Baez
| Maursault wrote:
| Good to know the speed of light in a vacuum is not a
| fundamental constant.
| analog31 wrote:
| Apparently, even vacuum is not a fundamental constant.
| Maursault wrote:
| The bad news is Nature abhors a vacuum. The good news is
| there's plenty of it.
| 7373737373 wrote:
| Yep, you can just set c=1 and have
| https://en.wikipedia.org/wiki/Natural_units
| BearOso wrote:
| Observation is part of science, but we're also limited by it.
| There's a lot of deeper workings that we just can't get at yet,
| maybe ever.
| 323 wrote:
| I've read a few times that you can derive the Maxwell equations
| from knowing that U(1) exists, as this article implies, that
| every point in space has (among other things) the symmetry of a
| circle.
|
| But I've never seen this derivation. I assume it's either trivial
| or too complicated. Anyone has a link or thoughts on this?
| gus_massa wrote:
| I wrote an ELI25 explanation in a comment a few months ago, and
| I'll copy it here:
|
| In quantum mechanics the wave function Ps is has complex
| values. If you multiply everything in the universe by -1,
| nothing changes because all the physical results use PsPs*
| (where * is the complex conjugation). You can also multiply
| everything by i or -i. Moreover by any other complex number of
| modulo 1 because PsPs* does not change. (The technical term for
| this is U(1) global gauge symmetry.)
|
| But you can be more ambitious and want to multiply each point
| of the universe by a different complex number of modulo 1.
| PsPs* does not change but the derivatives of Ps change and they
| are also important. (When you use the same complex number
| everywhere, the derivatives is just a multiple of the original
| derivative. When you use a different number in each point, it
| changes.)
|
| The only way to fix the problem with the derivative is to add a
| new field A. When you and multiply each point of the universe
| by a different complex number of modulo 1, then A changes in a
| simple to calculate but not obvious way. The change in A fix
| the problem with the derivatives of Ps.
|
| So now the equations of the universe with Ps and A don't change
| when you make this change. (The technical term for this is U(1)
| local gauge symmetry.) When you write carefully how a universe
| like this look like, the new field A is electromagnetism.
| (Actually, you can get the electric field and magnetic field
| using the derivatives of A.)
|
| Too many more details in
| https://en.wikipedia.org/wiki/Quantum_electrodynamics#Mathem...
|
| > _I assume it 's either trivial or too complicated._
|
| It's trivial once you have 3 or 4 years studding Physics, but
| you will never understand how it is related to the magnets in
| your refrigerator. [There are like 5 simplification steps
| between U(1) and magnets in the refrigerator. Each one makes
| sense, but I can't see all of them together in my head.]
| whimsicalism wrote:
| What does it mean to "add a new field A"? Add to what? The
| wave function?
| gus_massa wrote:
| Look at the first formula in https://en.wikipedia.org/wiki/
| Quantum_electrodynamics#Mathem...
|
| If A and B are zero then F is zero and you can forget the
| second part of the right hand part of the equation. Also,
| you must replace D with [?].
|
| Now you have equation of electrons and positrons that move
| in a universe that has no electromagnetism. The important
| part is that in that equation, the only variable is
| ps(t,x,y,z) that appears twice, the rest of the things
| written there are just derivatives, constants or indices.
|
| Now you can turn on B(t,x,y,z) that represents the external
| field, so the electrons and positions move in a more
| interesting patterns, but they don't "see" each other.
| Again, the only variable is ps(t,x,y,z).
|
| Now you do the trick with a local U(1) symmetry, and the
| only way to do the trick is to add a new variable
| A(t,x,y,z). But you must use the complete equation because
| as explained in Wikipedia F(t,x,y,z) is calculated using
| the derivatives of A(t,x,y,z). So now you have two
| variables ps(t,x,y,z) and A(t,x,y,z).
|
| So you " _add a new field A_ " to the list of variables
| that appear in the right hand of the equation, or to be
| more precise, you get a new equation that has one
| additional variable A.
| podiki wrote:
| Add to your theory/model. In order to make the symmetry
| work, you need something to "fix" the discrepancy you would
| otherwise have in the equations. So you add this field
| (variable) to make the whole thing consistent. In the end,
| you see you needed this "gauge field" (for historical
| reasons these are called "gauge symmetries") which is
| electromagnetism.
| B1FF_PSUVM wrote:
| > studding Physics
|
| Typo or rhetoric?
|
| A collectible, either way ;-)
| unicas wrote:
| There are plenty of so called "derivations of Maxwell
| equations", however, I would not claim that they were based on
| U(1) necessarily. IMO ME are just the integrability conditions
| for any conserved quantity (continuity equation): take a
| generic three-form in R^4, then dJ=0 => J=dF. F has six
| components corresponding to two vectofields in R^3 which depend
| on the fourth coordinate and satisfy the div and curl relations
| as in ME ;)
| mhh__ wrote:
| Read the book "Physics from symmetry" by Jacob Schwichtenburg
| podiki wrote:
| In short, if you impose a U(1) symmetry on your Lagrangian, you
| get electromagnetism. Basically you do the action of U(1) and
| enforce that the equation of motion does not change. That gives
| you the electromagnetic force (a photon).
|
| Putting in some of those keywords will find plenty of detailed
| notes online, like
|
| http://www.physics.usu.edu/torre/Classical_Field_Theory/Lect...
|
| or more quick overviews like
|
| https://mugndonut.wordpress.com/2018/03/31/symmetries-yield-...
| kabdib wrote:
| "F equals MA and you can't push a rope" will get you though cow-
| college freshman physics. Not murdering your lab partner helps,
| too. :-)
| lazyant wrote:
| Can somebody with knowledge in biology and/or physics take a look
| at (one of) his book and comment if it's decent as in if the
| science is solid? I browsed
| https://www.motionmountain.net/motionmountain-volume5.pdf and I'm
| intrigued (there are no reviews in Amazon).
| al2o3cr wrote:
| I skimmed the first ~150 pages of that and I'd say it's exactly
| as cranky as you'd think for a 400-page-long self-published
| book about science.
|
| Real equations are introduced without defining any terms or
| notation and then quickly abandoned for discussion of other
| things. For instance, the QED Lagrangian is brought up on page
| 126 without defining any of the highly-specialized notation
| involved (the slashed partial derivatives) and then the
| discussion moves on from it without _doing_ anything with it.
|
| The QED Lagrangian gets only slightly more words than "the
| three lightbulb scams" (p114). The term "spinor" is used
| several times but defined exactly zero times.
|
| The truly "wat"-inducing parts are the "Challenges" sections,
| for instance the first one on p29. An example: "Challenge 12:
| Do birds have a navel?"
| 7373737373 wrote:
| They do seem nicely formatted
| ravi-delia wrote:
| The earlier ones aren't terrible, but yeah they get real bad
| real fast. There are lot's of good introductory resources from
| people that know what they're talking about.
| supernova87a wrote:
| I'm a former physics/astro person, and honestly I had never seen
| a factor like c^4 power in my life...
| sacrosancty wrote:
| 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...
| graderjs wrote:
| s/nature/the simulation/g
|
| 1. Total compute capacity is limited and redistributes toward
| areas of high activity.
|
| 2. Processor speed is limited.
|
| 3. Mutations are sensibly constrained to prevent overflow.
|
| 4. Smallest addressable memory space.
|
| 5. No process is ever fully idle.
|
| 6. IPC is done using circles.
|
| 7. The kernel however operates at the level of spheres, and
| pointers to pointers to pointers to spheres.
|
| 8. There's roughly 18 niceness levels, but rumors are there are a
| couple more.
|
| 9. About 25 programmers worked on the project and at the end each
| one got to pick a nothing-up-my-sleeve number. Some say there are
| Easter eggs hidden there yet to be discovered.
| DangitBobby wrote:
| It makes intuitive sense to me that computers are physically
| constrained in all of the ways (and more) that the universe
| itself is physically constrained. I don't know why the
| inclination is to take these fundamental constraints and then
| say "the universe is in a computer" instead of saying "the
| computer is in a universe".
| KineticLensman wrote:
| Religion: "God did it"
|
| Simulation hypothesis: "God did it, with a computer"
| qiskit wrote:
| Simulation hypothesis: God did the first simulation with a
| computer, everything else is a simulation of a simulation.
| kleene_op wrote:
| Simulation hypothesis: It's simulations all the way down.
| No gods in sight.
| mhh__ wrote:
| The 9 equations aspect is pretty pointless but the chapters on
| the right hand side could be ok.
|
| One of the things that makes physics different to most subjects
| is that we can make an explicit goal of being smug and rederiving
| the laws of physics from the simplest possible principles. I
| think the book seems to do this, but just summarizing like done
| on this webpage is a bit daft.
| ravi-delia wrote:
| I think the way these are phrased do a better job expressing
| the "vibe", for lack of a better word, of our current
| understanding. That the particles and constants are declared by
| fiat, with behavior constrained by simpler laws, is an
| understanding I didn't come to until I took a QFT course. The
| physicist's God is as concerned with forbidding seemingly
| pointless things as the biologist's God is with beetles.
| whimsicalism wrote:
| It is interesting that we humans have so much difficulty
| breaking away from anthropomorphizing.
| ravi-delia wrote:
| And yet the vibe persists! Presumably it's due to low-level
| patterns you subconsciously pick up on, but much of the
| much-discussed physicist-intuition comes from knowing how
| the universe "likes" do do things. There's a similar thing
| in math, with many of the greats having just a few tricks
| they used over and over to great effect in any number of
| fields. I guess we're used to dealing with people, so the
| pattern is expressed as a preference (which does double
| duty encoding that it's not an absolute law).
| roywiggins wrote:
| If large chunks of our brainpower are actually hardwired to
| think in terms of other humans1, anthropomorphism might
| just be a strategy to recruit those hardwired systems into
| helping out with other tasks.
|
| 1 this may not be true
| mhh__ wrote:
| Vibe is not a bad word to use in these situations.
___________________________________________________________________
(page generated 2022-03-19 23:01 UTC)