The h Bar

Anonymous

12:04 AM

@JohnRennie Happy Birthday! Hope you will keep sharing food pics with us (and remain 13 years old). ;)

6

bolbteppa

@user222141 this

Course of Theoretical Physics

The Course of Theoretical Physics is a ten-volume series of books covering theoretical physics that was initiated by Lev Landau and written in collaboration with his student Evgeny Lifshitz starting in the late 1930s. It is said that Landau composed much of the series in his head while in an NKVD prison in 1938-1939. However, almost all of the actual writing of the early volumes was done by Lifshitz, giving rise to the witticism, "not a word of Landau and not a thought of Lifshitz". The first eight volumes were finished in the 1950s, written in Russian and translated into English in the late 1950s...

is a good idea to try read if you want to try to start to learn everything, though somewhere around page 20 of volume 1 should reel in expectations ;)

dmckee

I'm TAing at a small private university out here in the western US for this semester.

Just to stay in the classroom, really.

I'm doing recitation and lab for the intro course, which uses OpenStax University Physics for a text.

My impression is that the book lacks a overarching presentation theme and style but it not notably worse than other books in the category ... except that the exercises are poorly stated and the typesetting is spotty at best and runs down to pretty poor indeed.

Still, it's free which has got to be a good thing for the students.

I also don't care for some of the notational choices in the text (I mean, Coulomb's constant is denoted $k_e$), but in the end that's a minor things.

Mo_

second admission USC

:)

dmckee

@Mo_ Congrats. Do you actually want to live in east Los Angeles?

Mo_

@dmckee I've never been in Los Angeles so I have no idea how is the eastern part different from others :)

@dmckee Actually another (still unofficial) admission is CUNY in New York city, where the advisor is much better (one of the leaders of my field) but its ranking is terrible

dmckee

12:17 AM

@Mo_ It has a reputation as a rough area. It is certainly a poor area excepting USC and the students, so there is some friction between the locals and the school/students.

Oh, you have got to be kidding!

In chapter 4 Coulomb's law looks like \$\frac{1}{4 \pi \epsilon_0} \frac{q_1 \, q_2}{r_{12}^2}$.

In chapter 6 the energy of two point charges looks like $k \frac{qQ}{r}$.

::sigh::

Mo_

@dmckee :))

dmckee

(Both in volume 2, BTW).

Yeah. They changed (a) the choice of how to express the constant, (b) the notation for Coulomb's constant, (c) the choice of symbols for the two charges, and (d) the notation for the separation between the two charges.

Nice.

I'm paying attention to this just now because I am re-factoring a document of mine to agree with the text. But at least this means I can pick $k$ for Coulomb's constant without feeling too much guilt.

bolbteppa

12:33 AM

@Mo_ nice, en.wikipedia.org/wiki/Michio_Kaku is there

Mo_

@bolbteppa lol

Is he really a physicist? (like, doing research...)

bolbteppa

"He co-founded string field theory, a subset of string theory. String field theory uses the mathematics of fields to explain string theory"

David Z

@Mo_ Sorry I'm missing context, but presuming this is for grad school, the advisor's reputation matters way more than the university's reputation

Mo_

@DavidZ even if the ranking is that bad?

David Z

Well how bad is it?

If it's on a list of "10 worst graduate physics departments in the US" or something like that, then that might be cause for concern, but otherwise I'm sure it matters less than you think

Mo_

12:40 AM

@DavidZ So bad that you (apparently) haven't heard of it;)

dmckee

^ That. Who, not where.

David Z

@Mo_ Wait what haven't I supposedly heard of?

I thought you were talking about CUNY

Mo_

@DavidZ yeah CUNY

David Z

Yeah, so I'm asking, how bad is it? I.e. what's the ranking you're referring to and its source?

Mo_

I'm referring to the Shanghai ranking (arwu), where it's actually unranked

David Z

12:43 AM

Because I have heard of CUNY; I've met a few people who went there at conferences, and there were a couple of high-profile researchers in my field who hold professorships there

Mo_

the City College is ranked around 500

David Z

Yeah but that's presumably different

Mo_

But couldn't find anything about The Graduate Center in the rankings

dmckee

My impression of CUNY has always been that they don't have big, focused working groups (one does not talk about "the" high energy group at CUNY), but instead individuals doing their own thing.

David Z

@Mo_ ...yeah that means very little.

dmckee

12:44 AM

Presumably because these are people who want to live in NYC and will take a job at the "less prestigious" uni in the area for that big advantage.

Physics Meta

3

Q: Are there guidelines for reopening questions?

Background My closed question originally asked: Why is the sign of gravitational inertial mass chosen to be positive like EM inertial mass? and was put on hold: On hold as unclear what you're asking by Buzz, safesphere, Jon Custer, ZeroTheHero, Chair Feb 3 at 7:50 After reading feedback fr...

0

Q: What depicts the logo of Physics StackExchange?

I am just interested. I guess there is a relation to magnetic fiels or quantum physics but I have no clear idea of it.

discussion

Mo_

@dmckee That's what I thought too. Isn't living in NYC a disadvantage for a phd student (with limited funding!) who just wants to focus on his research?

dmckee

@Mo_ Well, you'd be facing the same trade-off that anyone does starting off in NYC: housing will suck, you will have no practical choice but to use public transportation, and you will have access to simply amazing cultural resources.

Mo_

@dmckee note that my other choice is eastern LA! How do they compare?

David Z

NYC has better food :-P

Mo_

12:50 AM

@DavidZ One of my friends (just graduated from UCSD) told me that going to somewhere with a ranking that bad would be terrible for finding jobs after you graduate

David Z

I just don't think that's accurate.

dmckee

Housing in LA isn't great either, but the transportation thing is flipped: you more or less have to have a car.

It has it's own cultural resources, though one could argue that the flavor is more, well, Holywood.

David Z

For one thing, based on what you're telling me there is no ranking - be very clear that "no ranking" is not a bad ranking - and also, seriously, working for an advisor with a great reputation can absolutely negate any effect of going to a university with a low reputation.

And also, don't confuse reputation and ranking. They're really not the same thing.

Mo_

@DavidZ unranked means no one has bothered to go there and rank it (probably because it wasn't worth the effort)

David Z

Are you sure that's what it means? As opposed to, say, it was evaluated but simply didn't make it into the top 500?

Also, you're making a mistake to assume "not worth the effort" necessarily means "bad"

Mo_

12:58 AM

@DavidZ well, both cases mean a low score!

And what if you didn't want to stay in academia or in your field after graduation? I think in that case (which is very probable for physics majors these days) ranking would matter much more. Am I wrong?

David Z

@Mo_ No, if nobody went out to evaluate the university, that means no score, not a low score

@Mo_ Yes, I believe you're wrong. It depends on who's hiring, of course, but in general if you get a graduate degree from a properly accredited university, the mere fact that you did will be more significant than where it came from.

Physics Meta

2:06 AM

0

Q: Tag cleanups on our meta

I just noticed that a lot of our tags here do not have any wikis/excerpts, and they seem like they're almost identical. Can someone please suggest how they're different and whether or not we should remove them or add descriptions? An excellent example of a question which looks like it has some r...

discussion tags tag-synonyms meta

user222141

2:33 AM

@Blue Well I mean let's say one is going for a physics degree -- what sorts of topics do they normally cover? What might one consider to be a sufficient base?

dmckee

3:07 AM

The standardish curriculum starts with a year course (usually out of a huge tome of a book) that cover basic Newtonian mechanics; a wee bit of thermal physics; introductory electricity and magnetism; ray and wave optics; and (in theory) a scatter-shot introduction to some concepts in relativity, "old" quantum mechanics, and atomic/nuclear physics (though the last one often gets short-shrift or even dropped).

Then students get a course in "modern physics" (meaning everything after 1900), which is a better introduction to relativity and basic "new" quantum mechanics (typically just the Schrödinger picture in the position basis).

Then you launch into the "core" upper division curriculum, with courses (from one semester to one year depending) on Classical Mechanics (Newtonian, Lagrangian, Hamiltonian), Electromagnetism (in much more depth); Thermal Physics (probably including some statistical physics); Quantum Mechanics (moderately seriously). All of which are much deeper and mathier than the previous treatment. And possible a separate course in Math Methods.

And you will be expected to take some electives. Plus, if you are lucky, a demanding upper-division laboratory of some kind.

Get through all that in good standing and you will be ready for advanced studies.

Avnish Kabaj

5:28 AM

@dmckee I believe you didn't open the link

Anonymous

6:58 AM

@user222141 Right, but the point here is that you're not going for a physics degree and you'll probably not be able to devote that much time. I was suggesting discretizing your goals. You could, say, start with Newtonian mechanics and calculus and linear algebra first, and completely forget about learning QM or relativity for the next 6 months or 1 year. Trying to learn everything simultaneously will only leave you in despair.

Anonymous

I don't know what you age is, but even if you live for another say 20 years...that's heck of a lot of time to learn a lot of physics!

Mo_

10:11 AM

@JohnRennie What is accepted upper bound on the mass of a neutron star (that prevents it from collapsing into a black hole)?

I'm finding various numbers, like 3/4, 2, 3-5 (stellar masses), etc.

John Rennie

@Mo_ erm ... there was something about this in the science press just recently because astronomers have just found a neutron star right at the limit. Let me have a quick Google.

@Mo_ aha, it's this article

I forget what the upper limit is, but it's basically the same as that neutron star they've just found i.e. 2.3 ish solar masses. No-one knows exactly because we don't fully understand the equation of state of the degenerate matter. So all these limits are approximate.

Mo_

@JohnRennie Thanks. What about the mass of the original star? The Wikipedia article says $15\odot$ to $20\odot$ but doesn't have any references

John Rennie

Again I'm not sure anyone knows for certain. The neutron star is believed to be formed when a large star goes supernova. As far as I know the large star is expected to be of order 20-30 solar masses but with a large possible spread of masses.

GodotMisogi

11:05 AM

@Blue @user222141 This is extremely true. When I decided to study physics on the side while pursuing aerospace engineering, I wasted my freshman year by fooling myself into thinking I understood a lot of FLP. Luckily, I was able to find a nice circle of friends interested in academia, and that helped develop some critical thinking. Studying formal mathematics also helps clear up some details that you normally would obtain from a professor in a course.

Akash. B

11:18 AM

hi

Anonymous

11:55 AM

@GodotMisogi Yeah, learning the proper mathematical background helps a lot. I was fed up with all the analogies used by physicists (even the MIT prof Allan Adams) to teach QM. Also I found that Griffiths is a terrible textbook with a lot of vague sentences although that's the usual recommendation for beginners.

Anonymous

I mean the sooner one understands that physics is simply the mathematical modeling of reality, the better. Mathematics helps us to communicate those ideas precisely which natural language cannot.

user351417

@Blue Allan Adams is now part of the oceanography department at MIT :P

user351417

No idea how/why I know that though.

GodotMisogi

12:53 PM

@Blue You mean Griffiths' QM, right? I never read that; started with Shankar.

I don't mind his Electrodynamics, though

ACuriousMind

2:18 PM

From the realms of literary question titles, I present to you: My Struggle with Fierz Identity

Anonymous

@Chair ...what's up with the string theorists these days! :P

Jake Rose

2:33 PM

If you know the normal modes of a system can you get its equations of motion just from them?

For example my notes just go from mode to equation of motion

Anonymous

@JakeRose Did you read the corresponding Wikipedia article?

Jake Rose

Nope

will do now though

I see where it goes to give the so,utions

is the way my notes present just getting the equation of motion okay though?

i can’t really understand that?

Anonymous

@JakeRose Seems to be okay although they haven't shown the derivation well. They wrote the equations of motions in the symmetric and anti-symmetric mode, whereas Wikipedia shows the general case.

Anonymous

2:48 PM

The key for the first case is "the central spring is compressed by twice as much as the outer strings are extended" (that's where you get the factor of 3 from).

Jake Rose

Never mind I got it

if you use the normal modes and place them into the $x_1(t)$ equations and the coupled equations on the previous page (I haven’t sent them) it works out well

Anonymous

Nevermind, it's just the physicists being handwavy (in your notes). The intuition is solid though. :P

Jake Rose

i missed a few lectures due to being ill and these lecture notes are horrendous to catch up on

Do you know any good dynamics books?

Considering this is the ‘spec’

Anonymous

@JakeRose Hirsch-Smale is a good text but it might be a bit advanced. Since it's just a few lectures I suggest sticking to your classroom notes (you won't get much time to cover other books). That said, I never took a formal class in classical dynamics...so I'm not really the best person to ask.

Jake Rose

Yeah that’s fair

perhaps use a textbook over vacation to fill in blanks

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