[HN Gopher] Physics Travel Guide - Physics concepts explained in...
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Physics Travel Guide - Physics concepts explained in three levels
of difficulty
Author : karlicoss
Score : 339 points
Date : 2020-04-02 09:42 UTC (13 hours ago)
(HTM) web link (physicstravelguide.com)
(TXT) w3m dump (physicstravelguide.com)
| SeanFerree wrote:
| Cool article!
| magv wrote:
| From just glancing at a few articles, this site is a treasure
| trove of references to highly readable explanations on a variety
| of fairly advanced topics. In fact, just the links to Wilczek's
| grand unification overview [1], and Klauber's Student Friendly
| QFT book [2,3] made this site worth visiting for me.
|
| Resources that explain physics in (relatively) simple language
| without requiring books worth of prior knowledge seem to always
| be targeted at school-level physics; this one is different.
|
| Of course, this is no substitute for a university curriculum, but
| as a way to plug holes in one's understanding, the site seems
| genuinely high quality.
|
| [1]
| http://frankwilczek.com/Wilczek_Easy_Pieces/172_Unification_...
|
| [2] https://www.quantumfieldtheory.info/
|
| [3] ftp://srdconsulting.com/USB_BackUp/Data/Articles/QFT/StudentF
| riendlyQFT/
| mhh__ wrote:
| I haven't read it in full but Klauber's book is supposedly
| loaded with errors and also (in my view) needs re-typesetting
| (it's written in word)
| nobrains wrote:
| Generally very nice, but I did not find the 3 levels of
| difficulties. Where can I see them?
| tiniuclx wrote:
| They are the tabs just below the title of every subject.
| betageek wrote:
| This is really great, would love something like this for pure
| maths.
| abhijat wrote:
| A few answers from when a similar question was asked last time
|
| https://news.ycombinator.com/item?id=16373386
| dang wrote:
| A thread from 2018: https://news.ycombinator.com/item?id=16372454
| johndoe42377 wrote:
| Some of those articles are just a modern Tantra - no one is
| seriously trying to refute these models because lots of people
| have a comfortable, high social status living out of it, just
| like modern theologians or tibetologists - they know the mantras
| and it's current interpretations, and the question of "How real
| it is" is frowned upon.
|
| Generalisations aside (however valid and useful) most of this
| theoretical physics is nothing but a socially constructed models,
| agreed upon.
|
| And yes, I have read a few of Bohm's books before forming an
| opinion.
| mnky9800n wrote:
| Is that you jonathan tooker?
| johndoe42377 wrote:
| Before Hegel and his abstract bullshit, the main question of
| philosophy was "What is real", not what a mind can imagine.
|
| Similarly, the main question of physics used to be "how
| everything is", not how do we think everything might be.
|
| A map is not a territory, a model is not what is. It is that
| simple and infallible.
| abdullahkhalids wrote:
| > Similarly, the main question of physics used to be "how
| everything is", not how do we think everything might be.
|
| I assure you, philosophy of physics is much more
| complicated than that, and a lot of senior physicists and
| leaders in the community are aware of these subtleties, and
| constantly argue about it.
| Koshkin wrote:
| > _the main question of philosophy_
|
| Well, philosophy is known to ask questions for which there
| are no answers. As to (theoretical) physics, I think we
| should look at it first and foremost as a computational
| tool (similar to applied mathematics) which is the way it
| has been since Newton, then it becomes clear that physics
| does indeed help understand "how everything is" - in the
| sense that it helps us predict the results of experiments,
| and I am not sure if it even makes sense to talk about a
| "higher level of understanding" than that. A map is
| definitely not a territory, but it can indeed be (and will
| always remain to be) both "true" and "false" to a certain
| degree; similarly, no one in their right mind would say
| that physics is, should, or can be equivalent to the
| reality (aspects of) which it merely reflects.
| PTOB wrote:
| So, are you a model of Jonathan Tooker, or are we
| encountering the real deal here?
| madhadron wrote:
| > Some of those articles are just a modern Tantra
|
| Would you care to provide concrete examples?
|
| > Generalisations aside (however valid and useful) most of this
| theoretical physics is nothing but a socially constructed
| models, agreed upon.
|
| Well, of course. Theories are formal systems that we construct
| to be a "looking glass" of the results of observations and
| experiments.
| benreesman wrote:
| I don't endorse the tonality of the comment, it's rambling and
| sort of bitter (I've been guilty of worse on "the Internet").
|
| With that said it's at least possible that the commenter is
| alluding to a trend in physics research that is so concerning
| to practicing physicists and mathematicians that books called
| things like "The Trouble with Physics" and "Not Even Wrong" are
| being written and published.
|
| I'm little better than a layman as concerns physics, but I've
| been around the block with organizational dysfunction amongst a
| group of super smart people, and I don't find it at all
| implausible that String Theory is the "Docker-First" of physics
| funding.
| monktastic1 wrote:
| I found this section confusing (emphasis mine):
|
| https://physicstravelguide.com/equations/schroedinger_equati...
|
| "This means that for _all_ systems where the Hamiltonian does not
| explicitly depend on the time, we known (sic) immediately how the
| time-dependence of the total wave function Ps(x,t) looks like
| (sic), namely: Ps(x,t) = phi(t)ps(x) = Ae^(-Et /)ps(x). The only
| thing we then have to do is to solve the stationary Schrodinger
| equation Hps(x) = Eps(x)."
|
| It sounds like they're saying that _all_ systems with a time-
| independent Hamiltonian are stationary, which is obviously wrong.
| This would have confused the hell out of me while learning QM,
| and dissuades me from learning more on this site.
|
| Have I misread? I can infer what they're trying to say from
| context and previous knowledge, but that's of little help for
| someone new.
| scythe wrote:
| >Ps(x,t) = phi(t)ps(x) = Ae^(-Et/)ps(x)
|
| This equation is missing a sum symbol, also it should be
| e^(-iEt/), where in the correct case the amplitude does not
| change. What you get is a sum of products of each occupied
| stationary state and a time-dependent phase. So the general
| solution looks like this:
|
| https://en.wikipedia.org/w/index.php?title=User:Scythe33/san...
| monktastic1 wrote:
| Indeed. But as another commenter points out, what I _think_
| they wanted was to solve only for eigenstates here.
| Apparently I 'm not the only one this confused.
| contravariant wrote:
| You have misread slightly I fear. Note that he says:
|
| >the stationary Schrodinger equation Hps(x) = Eps(x)."
|
| which is _not_ the original Schrodinger equation, but _a_
| Schrodinger equation which is stationary and which forms part
| of the solution of the original Schrodinger equation.
| monktastic1 wrote:
| Thanks. That's the context I was referring to. Reading the
| whole thing again twice more, I can still confidently say it
| would have confused me more than helped me when I was first
| learning.
| globuous wrote:
| Just looking around, but this looks like a gold mine ! Definitely
| going to be my go to site when I'm bored ! I love how each
| concepts are explained at high school, college, and grad school
| levels !
| m4r35n357 wrote:
| No Special or General Relativity - WTF?
|
| OK found them hidden away under "models" - WTF again?
| evanb wrote:
| General relativity is (sort of) a classical field theory; it
| isn't crazy to put it under models, in the same way that QFT is
| under 'theory' but the standard model is under 'models'.
| karlicoss wrote:
| Wikis are intrinsicly hard to organize in a hierarchy. There is
| a search though.
| m4r35n357 wrote:
| That is how I found them, estranged from the other "theories"
| for some reason.
| freetonik wrote:
| Interesting. I am slowly building a computer science dictionary
| with a similar concept: three levels of difficulty
| https://cs.quickref.dev/
| zeusly wrote:
| That's very cool!
| spodek wrote:
| Almost nothing about experiments. Physics is an experimental
| science, based on observation of nature.
|
| Its treatments of experiments is as if they were mere side notes
| to the real thing. The Tools section might include something like
| a ruler, clock, or basic physical tools used to observe nature
| with.
| nabla9 wrote:
| I strongly disagree "Physics concepts explained" has no need to
| add anything about experiments. The focus of the site is
| learning concepts.
|
| Criticizing focused educational site for not being
| comprehensive enough is not valid.
| duckmysick wrote:
| I strongly disagree. Experiencing concepts first-hand through
| experiments improves learning and understanding, excites
| curiosity, and teaches practices that can be used in other
| disciplines.
|
| I learned about many physics concepts with simple experiments
| in elementary school. They can certainly be extended and
| adapted for an adult audience.
| nabla9 wrote:
| What you say is true about learning physics. Not valid
| criticism against this site.
|
| It's not meant to be the only source for learning physics.
| It is focused reference site for concepts. Having focus and
| focusing on just one viewpoint is a good thing.
| madhadron wrote:
| Huh. The first thing I opened was Aharanov-Bohm which
| immediately describes an experimental setup.
| pretendscholar wrote:
| Might be a good idea to understand the concept in general and
| then take a look at the experiment to prove it.
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