@DIRAC1930 he spends a lot of effort which takes time

i feel like Solipsism has something deep to say about what reality is

the fact that we cant verify if other things exist can be pondered upon

Quantum mechanics refutes solipsism: A proof of the existence of an external world

@user85795 the reasoning given in this paper is incorrect

email the author

the paper argues that, if all quantums systems only exist in the mind, all quantum systems must exist as "hidden variable systems" inside the mind, as the mind cannot be in a superposition

this premise is incorrect

the correct Solipsist premise is that only the results of measurements exist, that the results are only in the mind, and that nothing else exists.

and the quantum mathematical machinery is simply the laws by which the mind behaves... so we do not need to explain anything using hidden variables

@user85795 the author lacks a basic understanding of Solipsism....

@RyderRude Can we at least extend some charity towards other people when discussing opinions here? The author is a professor of philosophy, you have no formal training in it. Disagreeing with someone's statements is one thing, declaring that they lack a "basic understanding" of the topic of their academic paper is another.

Especially when one oneself has a history of being confidently wrong about things one only has a surface-level understanding of, I would expect a bit more restraint when criticizing other people.

ponders changing username to ACriticalMind :P

@ACuriousMind sorry i did not see their designation. my comment is only based on the content of their paper. i may have been wrong about some things in the past, and that is why i mostly just disagree, but this paper is blatantly wrong. at my most charitable, i can only say that the author is re-defining Solipsism and disproving their definition

I have come across a space group symmetry operation that puzzles me. It is supposed to be a mirror reflection in a hexagonal lattice. It says it acts like $(x,y)\rightarrow (-x + y, y)$. I do not understand this mirror reflection. It seems like it does not conserve the length of the vector.

in the latter case, the author is correct. they have disproved one way of defining Solipsism

@SillyGoose fluid mechanics isn't really related to statistical mechanics, at least not the way we usually demarcate these subjects. Sure, the microscopic underpinnings of things like pressure are statistical mechanical, but you don't need one bit of statistical mechanics to start working on Navier-Stokes equations :P

if i was unsure about my own knowledge on the topic, i would not have said that. but it's really a trivial fact that Solipsism cant be disproved

@B.Brekke where did you come across that?

it's as trivial as 1x2=2. so if a math phd argues otherwise, i would charitably only assume that theyre redefining things, which is what the author seems to be doing here

@RyderRude My point is: The correct first response to an expert in a subject making a seemingly incoherent argument is "I must have misunderstood something" not "They don't know what they're talking about". The latter is not impossible, but unlikely.

yeah... i shouldve been more charitable.

For example, in this table. The notation seems to be common in other references as well, but it is beyond me

oh god I hate crystallography notation :P

it always takes me ages to translate it back into standard group theory speech

tbh whether or not Solipsism is "obviously" not disprovable would also depend on one's philosophical school. e.g. i have seen some philosophies reject Descartes and say that the objective reality is immediately accessible before subjective experience is

but ofc, these opinions come completely under philosophy. QM cant prove or disprove solipsism, unless u redefine things

i remember arguing the opposite position in the past : that QM implied one of : many worlds exists, or objective reality doesnt exist

but ofc QM has no jurisdiction over the latter. i ended up realising that i was re-defining objective reality

@B.Brekke So I'm not really sure what's going on here, but many of these operations seem to not preserve vector length

I'm also confused because P6mm seems to be the name of a space group, not a plane group, and also why is the "matrix form" not square?

is the third column the translation part?

@ACuriousMind Yes

I think I figured it out. They use a special set of basis vectors for hexagonal groups that are not perpendicular. It is confusing that they still use $x$ and $y$.

lol

my hate for crystallography notation is renewed :P

"hate" is such a savage word :P

I learned some of it at the beginning of my PhD. At the time it was quite mundane, but it eventually became very useful for understanding "altermagnets".

economist.com/science-and-technology/2024/01/24/…

cool

Sorry guys, are the eigenfunctions of the Hamiltonian of a particle in a box centered at the origin orthonormal? $$\int_{\mathbb{R}}\psi^{\ast}_i(x) \psi_j(x) dx = \delta_{i,j}$$

@ClaudioMenchinelli The eigenfunctions of the Hamiltonian - like of any self-adjoint operator - are always orthogonal

That's what I remember as well

Oh ok hahaha

my domain of integration is not $[-\infty, +\infty]$

I was about to make a terrible mistake :P

Thank god I came to my senses

I mean, your domain of integration might be $[-\infty,\infty]$, you just need to consider all your functions as zero outside the box

(but yes, just integrating over the box is easier)

no no no, I mean I must determine the probability for two fermions constrained inside this 3d asymmetric box to be both in the $x>0$ region

and I was about to use orthonormality hahaha

I have my QM exam in three days so I can't allow myself to make silly mistakes

right, only serious mistakes allowed

hahahha

Last time I failed, but only a mere 11% passed and we were about 300 students

That was more of a massacre than anything else

oof, 11% is more of an indictment of the lecturer than the students

Excluding the fact that the exam is the most difficult of all per se, the biggest problem lies in the amount of time: 3 hours for two exercises, but 1 exercise is usually 12-13 pages long

@ACuriousMind 11% it's not even the worst: the percentage rarely goes above 25% ahahha

???

that doesn't sound like a normal QM course :P

I told you it's the most extreme exam of them all hahaha

the others are much easier when compared to it

I think the worst has been reached last year: 3/92 passed

it was about a weird type of perturbation theory applied to a strange non-anarmonic potential

I heard that the professor who created the exercise actually wanted to make something more interesting, which actually required a deep level of thinking

and you can imagine how that turned out

After that incident, the professors never tried that again :P

@ACuriousMind I think it's not unusual to have a few exams like that in a degree in Italy

the threshold to pass an exam tends to be pretty high. OTOH failing an exam is not as big as a deal as in other countries, there's a lot more flexibility, you can resit many times in a year and failing grades are not recorded

ah, that makes a little bit more sense then

but yeah I would say that such low passing rates are a bad symptom, and some lecturers unfortunately revel in the fact that most students fail

again, the bigger problem most of the times is time

except maybe in the big first year exams, considering that physics is open admission

I agree with what @fqq is saying

the part about lecturers reveling in their students' failure, well I won't comment on that one :P

I consider QM professors to all be really good people

at least the ones I've met

I've heard about far worse carnage of first years students with Analysis I :P

Which is understandable, being the very first course one takes

@ACuriousMind Regarding this, as long as the % is bigger than zero I disagree that the course should be blamed, be it here in Italy or anywhere else

@Mr.Feynman What I mean is that if the percentage of passes is so low, the lecturer either failed to teach their students the course material or they failed in setting an exam that is an appropriate test of the course material. Sure, 100% is unrealistic, especially with the kind of self-directed study we expect from university students, but under normal circumstances, 10% is a failure of the educator - I can't see this any other way.

I do understand your point, I don't agree, though. I'd only blame an educator if they said something wrong, or if they weren't fair in making a test that stands at the same level as the course. In all other cases - as long as it's not niche physics - it's on the students imho

You may argue that you're paying for an education, so my point doesn't stand... and you wouldn't be wrong there

@Mr.Feynman So as a lecturer you think I can just incoherently ramble about the topic instead of preparing careful lectures actually designed to teach people, then fail all the students in my exam, and it's their fault as long as my rambling technically contained the correct course material?

No, sure. The lecturer must do his job, lecturing about the correct material. What I'm saying is that if he's good at conveying stuff, that's a plus, if he's not, but still he says correct things (sticking to the program), I wouldn't consider them guilty

If you ask me, I think that it is not possible to understand something and not be able to explain it. Still, I'd consider it as an excuse to blame the lecturer even in that case, if I don't pass

@Mr.Feynman Why is "not good at conveying stuff" a trait in a lecturer that frees them of responsibility for the result, but not "not good at understanding badly conveyed stuff" a similar trait in a student?

Mhhh, I would say that it is in the student's interest to learn the material (to gain knowledge, to be sure), so I don't consider this to be symmetrycal

if you don't want to teach people, don't become a teacher

Guys, to know if a system is moving, I just need to observe that $\mu_s \leq \tan(\alpha)$? Another way would be to observe that $mg\sin(\alpha)>f_s$?

@ACuriousMind To be sure, it is not something I would ever do, nor do I like this. My point is that - and I still had to spell this bit - in many cases it turns out that it's just an excuse for students to be lazy

Maybe this is about the view I have of universities. I surely enjoy and admire good lecturers and I guarantee I'm not a fan of bad ones. Nonetheless, I tend to consider the exam as something separate from the classes. During the exam you want to prove that you have an understanding of the subject, not of their course if you know what I mean

Guys, nothing, in the end I always get from mg etc to tan, sorry for the inconvenience!

@Mr.Feynman "lazy" is the explanation for why a pass rate of 100% is unrealistic, not for a rate of 10% being acceptable

@Mr.Feynman yeah, no - the exam is specific to the course, and of course it can contain things not explicitly taught in the lectures, but it's on the lecturer to communicate their expectations of what is necessary to pass the exam clearly in advance

@ACuriousMind Alright, perhaps it was rash on my behalf to extend this to everywhere but I don't consider 10% as a scary percentage at all, as things stand here

if these expectations require some hard work by the students outside just passively absorbing the lectures, that's fine - but as long as this work is reasonable within the rest of their course load, even difficult courses should show pass rates above 10%

What I say is influenced by my personal experience and view, though. That's how I feel about uni

@ACuriousMind In my uni, a full professor can't solely do research, but must also teach a(multiple) course(s), and a good percentage of them don't care about being good teachers and consider this a pain in the ass, as long as they can get to do their research. Yeah, you must compile some questions at the end of every course in order to make it better, but most of the professors could not care less :P

but it's a small percentage of them, thankfully

I do understand both of your standpoints

I've been playing with the gyroid, "an infinitely connected triply periodic minimal surface discovered by NASA scientist Alan Schoen in 1970". The true gyroid is parameterised by elliptic integrals (of the first kind), but there's a close approximation in terms of circular functions: $\cos(x)\sin(y) + \cos(y)\sin(z) + \cos(z)\sin(x) = 0$. Here's the approximation:

sagecell.sagemath.org/…

Here's the true gyroid, which I adapted from code by Parcly Taxel, who's active on Mathematics.SE gitlab.com/parclytaxel/Malibu/-/blob/master/malibu/minimal/…

sagecell.sagemath.org/…

Here's a more colourful version. It can use any matplotlib colormap. It takes a bit longer to render. Reduce plot_points to speed it up, or increase it to enhance the quality.

sagecell.sagemath.org/…

The Sage window can be a bit narrow on a phone. Here's a Bookmarklet that lets you change the width. javascript:(()=>{let%20w=prompt('Width?','150%');if(w)jQuery('.sagecell').css('width',w);})()

10% seems insanely low

Looking back at undergraduate, it seemed like nearly all of my lecturers cared about delivering a good course

Looking back, I wish I stayed on for CMP instead of falling for the String Theory hype

I'm interested on asking if LIPC (laser induced plasma channel) can make laser weapons relatively safe to bystanders, but I'm unsure if this fits in the physics or worldbuilding stackexchange.