
Physics Travel Guide – Physics concepts explained in three levels of difficulty - karlicoss
https://physicstravelguide.com
======
magv
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_...](http://frankwilczek.com/Wilczek_Easy_Pieces/172_Unification_of_Couplings.pdf)

[2]
[https://www.quantumfieldtheory.info/](https://www.quantumfieldtheory.info/)

[3] ftp://srdconsulting.com/USB_BackUp/Data/Articles/QFT/StudentFriendlyQFT/

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mhh__
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)

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freetonik
Interesting. I am slowly building a computer science dictionary with a similar
concept: three levels of difficulty
[https://cs.quickref.dev/](https://cs.quickref.dev/)

~~~
kumartarun
Keep doing. Good stuff. Subscribed your youtube channel as well.

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spodek
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
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
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
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.

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monktastic1
I found this section confusing (emphasis mine):

[https://physicstravelguide.com/equations/schroedinger_equati...](https://physicstravelguide.com/equations/schroedinger_equation#tab__concrete)

"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 Ψ(x,t) looks like (sic), namely: Ψ(x,t) = phi(t)ψ(x) =
Ae^(−Et/ℏ)ψ(x). The only thing we then have to do is to solve the stationary
Schrödinger equation Hψ(x) = Eψ(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.

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scythe
>Ψ(x,t) = phi(t)ψ(x) = Ae^(−Et/ℏ)ψ(x)

This equation is missing a sum symbol, also it should be e^(-iEt/ℏ), 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...](https://en.wikipedia.org/w/index.php?title=User:Scythe33/sandbox&oldid=948716529)

~~~
monktastic1
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.

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betageek
This is really great, would love something like this for pure maths.

~~~
abhijat
A few answers from when a similar question was asked last time

[https://news.ycombinator.com/item?id=16373386](https://news.ycombinator.com/item?id=16373386)

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globuous
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 !

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dang
A thread from 2018:
[https://news.ycombinator.com/item?id=16372454](https://news.ycombinator.com/item?id=16372454)

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nobrains
Generally very nice, but I did not find the 3 levels of difficulties. Where
can I see them?

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tiniuclx
They are the tabs just below the title of every subject.

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johndoe42377
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.

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mnky9800n
Is that you jonathan tooker?

~~~
johndoe42377
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.

~~~
Koshkin
> _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.

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m4r35n357
No Special or General Relativity - WTF?

OK found them hidden away under "models" \- WTF again?

~~~
karlicoss
Wikis are intrinsicly hard to organize in a hierarchy. There is a search
though.

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m4r35n357
That is how I found them, estranged from the other "theories" for some reason.

