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heather
heather
1:23 AM
the 20 reviews in the queue go so fast...
and there's always so many left in the queue. (it's lower right now, but still.)
 
Cows
Cows
1:34 AM
Off to Long Beach for some epic fun
Listening to the rolling Stones . . . Hehe not driving . She likes the rolling stones
 
 
2 hours later…
dmckee
dmckee
3:10 AM
Even in special relativity if you close the system to all transfers for energy or momentum as well as matter the mass of the system remains constant (using the modern nomenclature where "mass" means invariant mass), simply because the four-momentum remains constant.
 
danielunderwood
danielunderwood
3:21 AM
Come to think of it, does pure SR even allow mass converting to/from energy? There isn't really a classical mechanism that can do that is there?
Although I guess it could if you said a box of stuff has a mass, but a hot box of the same stuff has some larger mass
 
Cows
Cows
3:41 AM
Just got done eating at buppa Gump. Got partially ambushed by a few peeps. Got tricked into making new friends and meeting friends of friends hehehe . Almost had a 💓 attack lol
Heading to see 🔥 works now.
🎆 🎆 woohoo!!!
 
Secret
Secret
Hehehrhrhrhrhehrhryrhehehehehehegehehehehrhehehehejrhrhfhrhehrhejehrjrjrryeyyeut‌​hehtytufggejrhfmeqrjatbqshwvwwbehhehehehrbrjrhehhsgwgehehhrhdhrhehebfhehrhehjrheh‌​rfiedoediwdiediediedifidduddoexiedordiediefurdirdjrdgi
 
user400188
user400188
I'm left very confused
 
Secret
Secret
Confused on what?
 
danielunderwood
danielunderwood
Woah cern has their own tld home.cern
 
Secret
Secret
Any doscovery is going to come from the neutrinos sector
what's the present status of the sterile neutrino?
MiniBooNE
MiniBooNE is an experiment at Fermilab designed to observe neutrino oscillations (BooNE is an acronym for the Booster Neutrino Experiment). A neutrino beam consisting primarily of muon neutrinos is directed at a detector filled with 800 tons of mineral oil (ultrarefined methylene compounds) and lined with 1,280 photomultiplier tubes. An excess of electron neutrino events in the detector would support the neutrino oscillation interpretation of the LSND (Liquid Scintillator Neutrino Detector) result. MiniBooNE started collecting data in 2002 and was still running in 2017. == History and motivation... ==
 
dmckee
dmckee
4:00 AM
@Secret Not ruled out.
I understand that MiniBooNE's latest paper still shows the excess.
So there is room to be optimistic.
Especially if the WIMP dark matter searches keep coming up null.
@danielunderwood And any radiative process in which a bound system becomes more bound is taking mass and making light.
All the mass is still there if you count the bound thing and the light together, but there is less if you count them separately.
 
danielunderwood
danielunderwood
Ahh yeah that's true as well. I think I had matter in the place of mass in my head for some reason
 
 
7 hours later…
Noah P
Noah P
11:06 AM
Hi guys, does anyone know how to reference Pauli's 1930 letter?
6
Q: "Dear radioactive ladies and gentlemen" - Letter by Wolfgang Pauli

mate64In 1930, Wolfgang Pauli wrote a letter to Lise Meitner for a convention in Tübingen, considering the problem of beta decay. Does anybody know, where to find the original letter online ?

specific-reference nuclear-physics radiation history neutrinos
The one mentioned here to be exact :)
 
rob
rob
11:51 AM
@NoahP "Pauli, private correspondence, 1930; downloaded from (URL) on (date)." Or "quoted in (book)". Your favorite style guide has examples for secondary sources like this.
 
 
1 hour later…
More Anonymous
More Anonymous
1:19 PM
any help?
0
Q: Backreaction of FRW metric on QFT in curved spacetime?

More AnonymousI was recently wondering the following: QFT in curved space time tell us that the Friedman Walker metric yields particles (1). At what order/scale will one be able to notice the back reaction of this particle creation on the einstien's field equation which need to be satisfied (I was thinking of...

cosmology qft-in-curved-spacetime
 
Slereah
Slereah
@MoreAnonymous For a start the change may only be in the vacuum energy
FRW metric will violate energy conservation but it may simply be due to the change of volume
as the vacuum energy term is proportional to volume
 
Semiclassical
Semiclassical
QFT: vacuum energy proportional to volume
Real life: vacuum energy proportional to surface area of carpet
[insert holography joke here]
 
Slereah
Slereah
badababada, badababada, badababada BA
 
Semiclassical
Semiclassical
(the hidden holography joke is that what i wrote is only the boundary theory of the joke)
(the actual humor is deep in the bulk)
 
Slereah
Slereah
1:34 PM
Though really
You can compute it directly @MoreAnonymous
There's an explicit expression for FRW propagators
it's in Birrel Davies
 
apt45
apt45
1:53 PM
Any help?
0
Q: Are scalar fields defined up to harmonic functions?

apt45Disclaimer: this question may be very stupid. It looks like I am missing some fundamental point. Let's consider a massive scalar $\pi$ $$ \mathcal{L}_\pi = -\frac{1}{2}(\partial \pi)^2 -\frac{m^2}{2}\pi^2 + g \mathcal{L}_{int}(\pi) $$ where $g$ is a coupling and $\mathcal{L}_{int}$ includes ...

quantum-field-theory field-theory classical-field-theory
 
Emilio Pisanty
Emilio Pisanty
2:11 PM
@DanielSank speaking of music, have I showed you this one?
 
 
1 hour later…
vzn
vzn
3:20 PM
in theory salon, Feb 18 '17 at 16:15, by vzn
saw this last nite on appletv, awesome flick, recommend it CERN documentary / Geyrhalter
@Secret lol argh sigh just bought issue online for $5 for that article alone & it looks only ~250 words. but maybe it was worth it just for this quote of top nobel-prize winning string theorist aligned with fluid paradigm™ (thx again for tip)... gotta look into this further :)
> So here's a clue: drop the marbles and think of reality as a pond. "The fundamental thing is the water," says Wilczek, "and the particles are disturbances in that water." Whatever those particles are.
 
bolbteppa
bolbteppa
Sometimes a silly convention like $-1/4$ in an equation hints at insanely deep crazy theory
 
Semiclassical
Semiclassical
3:36 PM
hi chat
@bolbteppa for an elementary example, the $+1/2$ in $E_n=\hbar \omega(n+1/2)$ for a quantum harmonic oscillator
As a signifier of how the classical minimum $E=0$ isn't allowed
 
bolbteppa
bolbteppa
Yeah, the stupid $-1/4$ in the radial hydrogen Schrodinger people usually insert by hand for no apparent reason is another
 
Semiclassical
Semiclassical
yeah
There's a way you can justify that---something like "if you substitute $z=e^x$ first, then it's not 1/4"
I know there's a name for that
L-something transformation
hmm, this is what I was thinking of
Langer correction
The Langer correction is a correction when the WKB approximation method is applied to three-dimensional problems with spherical symmetry. When applying WKB approximation method to the radial Schrödinger equation − ℏ 2 2 m d 2 R ( ...
But i'm not seeing the characterization I was appealing to
 
bolbteppa
bolbteppa
That looks pretty nuts, Regge stuff coming up too yikes
 
Semiclassical
Semiclassical
ah, yeah, see this page: books.google.com/…
 
bolbteppa
bolbteppa
Will look into that when I get my Regge on
 
Semiclassical
Semiclassical
3:42 PM
i know nothing of that, lol
but yeah, the key point is apparently: "Following Langer, we substitute $r=e^x$..."
so that instead of having a problem over $[0,\infty)$ it's over $(-\infty,\infty)$
and therefore the quantization rule is the usual one
(the 'therefore' should probably be in scare quotes given how much I'm sweeping under the rug there, lol)
Stuff like this is why I tend to restrict my WKB attentions to strictly 1D problems though
WKB for multiple variables is confusing
 
bolbteppa
bolbteppa
Third equation there
Literally no book says why they want to end up with $1/4$, some books don't even end up with it, but many do for no apparent reason
 
Semiclassical
Semiclassical
right
hmm, now i'm curious what $\rho=e^x$ will do in that case...time to actually follow the details for once
 
bolbteppa
bolbteppa
Yeah I periodically come back to the details of this :p
 
Semiclassical
Semiclassical
nice thing is that $\partial_x = (\partial_x \rho)(\partial_\rho) =\rho \partial_\rho$
 
bolbteppa
bolbteppa
I think I got the point, basically the $\frac{l(l+1)}{r^2}$ term tells you immediately this equation may be related to the confluent hypergeometric equation in Whittaker form, and the 'canonical form' of such an equation has that stupid $-1/4$ very naturally
 
Semiclassical
Semiclassical
3:50 PM
so if you multiply through by $\rho^2$ and note that $\rho\partial_\rho(\rho \partial_\rho)=\rho^2 \partial_\rho^2+\rho\partial_\rho$
 
bolbteppa
bolbteppa
Whittaker function
In mathematics, a Whittaker function is a special solution of Whittaker's equation, a modified form of the confluent hypergeometric equation introduced by Whittaker (1904) to make the formulas involving the solutions more symmetric. More generally, Jacquet (1966, 1967) introduced Whittaker functions of reductive groups over local fields, where the functions studied by Whittaker are essentially the case where the local field is the real numbers and the group is SL2(R). Whittaker's equation is d ...
 
Semiclassical
Semiclassical
you end up with $(\partial_x^2 R-\partial_x R)+2 \partial_x R-\ell (\ell+1)R+(\lambda-e^x/4)e^x R=0$
...huh
That's less helpful than I'd hoped
 
bolbteppa
bolbteppa
It's scary how people plug in random substitutions into these equations
e.g. Bessel equations
 
Semiclassical
Semiclassical
ikr
 
bolbteppa
bolbteppa
I think they are not so random and there's a reason behind all of them
 
Semiclassical
Semiclassical
3:53 PM
i mean, with bessel the usual substitutions are things like $x=au^p$ iirc
 
Emilio Pisanty
Emilio Pisanty
@bolbteppa ugh
 
bolbteppa
bolbteppa
e.g. the $(1-z)/2$ in the Legendre equation is just about sending singularities $-1,1,\infty$ to $0,1,\infty$ which the hypergeometric equation has
 
Emilio Pisanty
Emilio Pisanty
who invited Whittaker functions to hbar?
 
Semiclassical
Semiclassical
lol
 
bolbteppa
bolbteppa
The hydrogen atom forced the issue :(
 
Semiclassical
Semiclassical
3:54 PM
I actually looked at the old Whittaker and Watson text on Bessel functions
it was...not fun
 
Emilio Pisanty
Emilio Pisanty
@bolbteppa did it really force the issue?
 
Semiclassical
Semiclassical
 
Emilio Pisanty
Emilio Pisanty
@Semiclassical oh, yeah, that's a scary place
I've had to go there a couple of times
 
bolbteppa
bolbteppa
I now think it's possible to just look at the harmonic oscillator Schrodinger equation and just immediately know it's just the parabolic cylinder equation and know it's functions without writing anything down, trying to get there
 
Emilio Pisanty
Emilio Pisanty
the scars
I still have them
 
Semiclassical
Semiclassical
3:55 PM
I actually do have a copy of Watson's Real Analysis now
which is kinda neat
 
bolbteppa
bolbteppa
Had such a breakthrough with this stuff the past few days
 
Semiclassical
Semiclassical
@bolbteppa with regards to semiclassical quantization vis a vis the hydrogen atom, you might find this interesting: arxiv.org/abs/1404.5333
quantization in polar coordinates vs. quantization in parabolic coordinates
 
bolbteppa
bolbteppa
Cool, Landau has a section on solving hydrogen in parabolic coordinates I keep meaning to go through
 
apt45
apt45
@ACuriousMind is this question so stupid? physics.stackexchange.com/questions/415244/…
 
Semiclassical
Semiclassical
neat. the solution in parabolic coordinates was apparently known historically
so they're probably drawing from that tradition as well
 
bolbteppa
bolbteppa
4:01 PM
Interestingly, I think the reason the LRL vector arises in the Coulomb problem is literally because the problem is separable in both spherical and parabolic coordinates
 
Semiclassical
Semiclassical
yeah
one thing I found interesting is that the trajectories in cylindrical coordinates are rotations (i.e. $r(\theta+2\pi)=r(\theta)$) whereas the trajectories in parabolic coordinates are librations
 
bolbteppa
bolbteppa
I don't understand the like to the whole SO(4) stuff yet, but that might be the deeper deeper explanation
 
Semiclassical
Semiclassical
I know at least one math guy who would argue that the SO(4) business isn't the right way to look at it (see arxiv.org/abs/1309.2694 for details) but I've steered clear of worrying about it for the most part
 
bolbteppa
bolbteppa
"The solution of the problem of motion in a Coulomb field in terms of parabolic coordinates is useful in investigating a number of problems where a certain direction in space is distinctive; for example, for an atom in an external electric field" hmm
 
Semiclassical
Semiclassical
(the distinction between libration/rotation I'm using is this one: books.google.com/…)
 
enumaris
enumaris
4:15 PM
hmmmm
 
ACuriousMind
ACuriousMind
4:42 PM
@apt45 No, but it is a bit confused ;) I'll try to write an answer
 
apt45
apt45
5:09 PM
@ACuriousMind Thank you :) What's wrong with treating $f(x)$ as a constrained dynamical field, by multiplying the partition function by $\int Df(x) e^{i\int d^d x \lambda(x) \square f(x)}$? This term does not affect the dynamics of the system and does not affect physical quantities.
 
ACuriousMind
ACuriousMind
@apt45 It's not "wrong" per se, but I simply see no reason for the new system to be equivalent to the old one.
Your "gauge fixing" approach is the right idea - it eliminates the spurious degrees of freedom that you introduced.
 
apt45
apt45
@ACuriousMind If you add this constraint and then you perform the field redefinition, solve the equation of motion of $\pi$ for the lagrangian multiplier $\lambda(x)$, you see that all the dependence on $f(x)$ drop out, and you still end up with a massive scalar.
@ACuriousMind Ok, this is what I wanted to know. My point of view is that all the information has to come from the lagrangian. I should not need external input like the suggestion "f(x) is not dynamical" to study the system. And this gauge fixing approach seems to be essential for this. doesn't?
 
ACuriousMind
ACuriousMind
@apt45 "$f(x)$ is not dynamical" is not an input external to the Lagrangian!
The Lagrangian is a function of spacetime and a functional of certain fields. It has to be part of its proper definition which fields in it it is a functional of, and which are fixed.
 
apt45
apt45
@ACuriousMind Yes, I agree. I am just not able to explain myself in a better way :)
@ACuriousMind Thanks
 
Emilio Pisanty
Emilio Pisanty
5:35 PM
aw shit
did I just help propel a terrible question to HNQdom?
 
heather
heather
@EmilioPisanty ?
 
Emilio Pisanty
Emilio Pisanty
@heather this one but please don't vote there or the system will think it's as hot as a hot potato
 
heather
heather
@EmilioPisanty wait, downvoting gets something on HNQ!?
 
Emilio Pisanty
Emilio Pisanty
@heather well, you can downvote
 
heather
heather
but you didn't upvote, so...
oh, by answering
 
Emilio Pisanty
Emilio Pisanty
5:40 PM
yeah, one of three answers in the span of four minutes
that's a recipe for disaster =/
 
danielunderwood
danielunderwood
Hey at least it wasn't "please do my homework" with pictures of the textbook
 
enumaris
enumaris
Someone should troll SE by typing out a clear and concise question in the appearance of a textbook question...and then posting a picture of that question as their question...
mmmm
 
danielunderwood
danielunderwood
5:59 PM
Oh man that would be great. I have wondered if it would be effective to have basic homework questions be only self-answerable or something
 
heather
heather
i get so annoyed at the homework policy when i think about it, so i avoid thinking about it.
i don't mind not allowing homework, i do mind the inconsistency and confusing-ness of its implementation.
 
danielunderwood
danielunderwood
I honestly don't even know what the homework policy is. I've just noticed that the homework-type questions are often people expecting us to do their homework and the good homework question seems rare
 
heather
heather
yeah, i'm also kinda of the opinion that tag should be burned with fire, but y'know.
i've actually seen some good-ish homework questions that i feel like actually put in some effort. but people just see a quote from a textbook and vtc. it's really annoying, because sometimes those questions actually follow the homework policy.
 
Anonymous
@heather That one is real...I've seen that
 
Anonymous
Meanwhile some terribly posed easily google-able questions showing no effort get through
 
heather
heather
6:07 PM
yup.
the homework policy doesn't really do what it's supposed to do, is terribly confusing for new and experienced users alike, blocks good questions from the site, makes the site look more negative, and also makes many users bang their heads in meta discussions that go nowhere.
Feb 15 '17 at 17:00, by John Rennie
@DanielSank I gave up debating the homework policy in favour of hammering nails into my kneecaps because it was less painful and more productive.
 
Anonymous
True, I'm not taking part in any meta discussion about hw policy again, until they introduce a "pay and get hw done" section on SE :P
 
heather
heather
lol, that ain't happening
 
danielunderwood
danielunderwood
Yeah I've seen the good questions too, they just get drowned in a sea of bad ones. Sounds like an interesting thing to see if you could programmatically separate them. Or I guess low-rep questions could go into an approval queue or something...but I suppose those ideas are somewhere in the meta discussions
They already have that, it's called chegg lol
 
Anonymous
Chegg is good, yeah
 
danielunderwood
danielunderwood
Or if you happen to do computer stuff, red hat's q&a site :(
 
Anonymous
6:11 PM
At least for undergraduate math and physics
 
Anonymous
Not much useful for a bit more advanced questions though
 
heather
heather
but that's the thing! most people let "advanced" questions that technically should be closed as per the homework policy slide.
 
danielunderwood
danielunderwood
Well I think the more advanced questions usually get away from people asking just to give them the answer, doesn't it?
 
heather
heather
and i don't really mind that at all, but it just shows how bad the policy is.
 
Semiclassical
Semiclassical
now part of me wants to see a parody website called 'chugg' where all the answers are fine but written by someone completely drunk
I suppose the stack exchange equivalent would be "shot exchange"
 
danielunderwood
danielunderwood
6:14 PM
lol I did one of my first quantum homeworks while drunk...it didn't turn out well
 
Semiclassical
Semiclassical
"drunk physics" videos
 
danielunderwood
danielunderwood
Well drunk history is my favorite resource for historical facts
 
Semiclassical
Semiclassical
lol
 
danielunderwood
danielunderwood
I'd pay good money for a youtube series of drunk physics explanations
 
Loong
Loong
Sounds like waiting for beam time in Dubna.
 
Avnish Kabaj
Avnish Kabaj
6:41 PM
> when forces are in equilibrium net torque about a point remains the same
I've made cases and this is true
But I can't seem to prove it
It's not a law is it?
I do have an exam please help
Please
 
danielunderwood
danielunderwood
If forces are in equilibrium, $\mathbf{F}_\rm{net} = 0$ and since the torque is $\mathbf{\Gamma} = \mathbf{r} \times \mathbf{F}$, $\mathbf{\Gamma}_\rm{net} = \mathbf{r} \times \mathbf{F}_\rm{net} = 0$.
Really that answer should probably have been "What is the definition of torque and what does it mean for forces to be in equilibrium?"
 
Avnish Kabaj
Avnish Kabaj
Is this legit?
 
enumaris
enumaris
can't view image ehhh
 
Avnish Kabaj
Avnish Kabaj
Huh
That's weird
I don't think you live in iran
 
danielunderwood
danielunderwood
lol
 
dmckee
dmckee
7:22 PM
@Blue Caveat emptor: I've had students turn in solution they found on Chegg that used concepts, symbols, and techniques we never covered in class.
Obviously when confronted they couldn't explain the answer.
Worse they shared their work with some of their fellows who couldn't even copy it down correctly.
They mistook a $v_c$ for a $\sqrt{c}$ which generated a pretty obvious failure of the result expression to make any sense at all.
Mind you the work provided by the guy on Chegg was elegant, clever, and correct; but they still got goose eggs on the assignment.
 
Semiclassical
Semiclassical
ugh
 
danielunderwood
danielunderwood
One of our professors made everyone scared of looking at solution manuals. She just instantly reported anyone suspected of doing that for academic integrity. She got a fair number of people the first couple of semesters, but I don't know of anyone by the time I was in her courses
 
dmckee
dmckee
Our academic integrity policy formally allowed me to fail them for the class, but practice on the ground was to try to make the penalty just stiff enough to discourage repetition while encouraging them to continue to take courses (and thus to pay the school...).
 
danielunderwood
danielunderwood
I don't really know what happened to those people that were reported, but she certainly would fail anyone that didn't understand what they should. It was kind of annoying as a student, but now it's the way I wish all of my courses would have been
 
enumaris
enumaris
you get a 0, you get a 0, everyone gets a 0!!
I got so much hate on my end of quarter report for failing a bunch of my students lol
not for plagiarism or w/e though...just for crappy work
Mostly I was just told to be super harsh in grading and then the curve will be adjusted later
 
Anonymous
7:37 PM
@dmckee Well, they obviously deserved the eggs :P
 
enumaris
enumaris
I wonder how early I can go home and still get away with it...
 
Avnish Kabaj
Avnish Kabaj
@Blue
UPIMAR18
This is correct?
 
Anonymous
I mean if you're cheating, at least you got to be smart enough to not get caught ;)
 
Anonymous
@AvnishKabaj What's this?
 
Avnish Kabaj
Avnish Kabaj
57 mins ago, by Avnish Kabaj
> when forces are in equilibrium net torque about a point remains the same
 
enumaris
enumaris
7:38 PM
sometimes one does wonder if someone is so ingenious at cheating...why not just put a little bit of effort to actually learn something lol.
 
Anonymous
@enumaris Adrenaline boost
 
enumaris
enumaris
going skydiving or something might be better
 
danielunderwood
danielunderwood
@enumaris I spent a ridiculous amount of time in my freshman courses trying to come up with creative solutions to avoid doing all the trig...I would have saved a bit of time just by doing it the normal way
 
enumaris
enumaris
lol
 
Anonymous
@AvnishKabaj If it's for a rigid body, then $\sum_i F_i=0$, yes?
 
enumaris
enumaris
7:40 PM
did u learn the trig?
 
Anonymous
Now, what exactly do they mean by "remains the same"?
 
bolbteppa
bolbteppa
Those stupid $1/\sqrt{ax^2+bx+c}$ integrals, e.g. mechanics, the amount of pain I went through trying to avoid the normal way
 
danielunderwood
danielunderwood
Yeah I think most of the time I ended up having to do it the trig way anyway
 
Semiclassical
Semiclassical
lol
the joy of elliptic integrals
 
Avnish Kabaj
Avnish Kabaj
@Blue yes
 
Semiclassical
Semiclassical
7:41 PM
actually, I guess by themselves it'd just be inverse trig
 
bolbteppa
bolbteppa
It just makes perfect sense to use trig substitutions, now...
 
Semiclassical
Semiclassical
What I found fun was when the relevant trig substitution had some physical meaning
 
Anonymous
@AvnishKabaj The question is ambiguous. It is not clear what their initial and final states are? Remains the same, with respect to what?
 
enumaris
enumaris
like in the MSW effect and the effective mixing angle in media?
 
Semiclassical
Semiclassical
eh, I had in mind the more elementary example of the electric field of a charged rod :)
the difference between "integrating with respect to the position of the rod" and "integrating with respect to the angle with the rod" is just a trig sub
 
enumaris
enumaris
7:45 PM
oh
 
Anonymous
@AvnishKabaj If net force on a body is 0, it does not mean the net torque on it will be 0.
 
Anonymous
So that statement looks false to me. But then again, the question is ambiguous
 
enumaris
enumaris
$\Sigma \vec{F}_i = 0\nrightarrow \Sigma \vec{r}_i\times\vec{F}_i=0$
ayyyyyy, flexing my latex muscles
 
Semiclassical
Semiclassical
@enumaris your muscles are made of rubber? wtf
 
enumaris
enumaris
Latex
 
Anonymous
7:49 PM
1 hour ago, by danielunderwood
If forces are in equilibrium, $\mathbf{F}_\rm{net} = 0$ and since the torque is $\mathbf{\Gamma} = \mathbf{r} \times \mathbf{F}$, $\mathbf{\Gamma}_\rm{net} = \mathbf{r} \times \mathbf{F}_\rm{net} = 0$.
 
enumaris
enumaris
no...
that's not right
 
Anonymous
Yes, the second statement doesn't follow from the first
 
Semiclassical
Semiclassical
For one, there's no reason to expect that the forces all act at the same point
 
enumaris
enumaris
You can't just pull the summation over to the $F_i$ by itself
 
Anonymous
@danielunderwood $\mathbf{r}$ isn't a constant. The forces can act at different points
 
Semiclassical
Semiclassical
7:51 PM
Hence there's no reason to expect that $\mathbf{\Gamma}_i = \mathbf{r}\times \mathbf{F}_i$
 
Avnish Kabaj
Avnish Kabaj
@Blue thaaaaaanks
 
Semiclassical
Semiclassical
And if they do all act at the same point, then the torque about the axis through that point is zero since there's no lever arm
 
Anonymous
Right
 
danielunderwood
danielunderwood
Yeah you guys are right. Oops
 
Anonymous
@AvnishKabaj Was that circuit problem resolved btw? I couldn't find any reason why that symmetric circuit method should have worked for your asymmetric one
 
Anonymous
7:57 PM
@enumaris Skydiving ain't cheap :P
 
enumaris
enumaris
hmm
 
bolbteppa
bolbteppa
I wish I learned what a f***ing Whittaker function really was before I picked up a QM book, literally the last thing one should do when given an ode in physics is actually solve it by plugging things in
Even the 'simplifying' substitutions make sense
 
Avnish Kabaj
Avnish Kabaj
@Blue oh yes
I got an answer
 
Anonymous
Oh, cool. Someone found a reason?
 
Avnish Kabaj
Avnish Kabaj
8
Q: Why does the superposition principle for calculating equivalent resistance work for asymmetrical objects?

Avnish KabajThe method has been discussed in this question: Effective resistance across 2 adjacent vertices of a dodecahedron with each edge $r$ I used this method for an asymmetrical object to calculate its equivalent resistance. The method shouldn't have worked as the branches connecting the o...

electric-circuits electrical-resistance
@Blue it was a fluke :P
 
Anonymous
8:04 PM
Thank you. The question was integer type, after rounding off your answer it's coming as 3A. — Avnish Kabaj Jun 26 at 5:59
 
Anonymous
Oh, lol. What's up with this new rounding off thing for integer-type questions
 
Avnish Kabaj
Avnish Kabaj
Fiitjee aits does weird stuff
 
Anonymous
Yeah, makes sense now ;)
 
Anonymous
fiitjee aits is terrible, lol
 
enumaris
enumaris
fun beans
3
 
Anonymous
8:10 PM
Saw the stars and starred it for no reason at all :P
 
heather
heather
pythagoras was scared of beans
he and his followers thought dead souls were trapped in them.
 
Anonymous
2 days ago, by Blue
@ACuriousMind Sounds like a variation of "cool beans" ;)
 
Anonymous
Pythagoras was a crazy guy
 
Anonymous
Lots of other stories about him too
 
Anonymous
 
Anonymous
8:13 PM
" For a while, the Pythagoreans treated as an official secret the discovery that the square root of two is irrational, and, according to legend, Hippasus was murdered for divulging it."
 
bolbteppa
bolbteppa
Hippasus
Hippasus of Metapontum (; Greek: Ἵππασος ὁ Μεταποντῖνος, Híppasos; fl. 5th century BC), was a Pythagorean philosopher. Little is known about his life or his beliefs, but he is sometimes credited with the discovery of the existence of irrational numbers. The discovery of irrational numbers is said to have been shocking to the Pythagoreans, and Hippasus is supposed to have drowned at sea, apparently as a punishment from the gods for divulging this. However, the few ancient sources which describe this story either do not mention Hippasus by name (e.g. Pappus) or alternatively tell that Hippasus drowned...
 
enumaris
enumaris
lol wut
 
Avnish Kabaj
Avnish Kabaj
I really want Russia to win tomorrow
 
enumaris
enumaris
8:52 PM
who they playin?
 
bolbteppa
bolbteppa
Brazil and France craziness tomorrow
 
enumaris
enumaris
hmmm
 
David Hammen
David Hammen
Russia plays against Croatia on Saturday. Start time is about 45 hours from now.
 
enumaris
enumaris
i see
 
 
1 hour later…
enumaris
enumaris
10:12 PM
It is not known whether π + e (or π − e) is irrational.
woah...
 
danielunderwood
danielunderwood
10:29 PM
I'll put $1 on them both being irrational
 
enumaris
enumaris
probably they have to both be in the same class right...
I mean, can it be that a+b is rational while a-b is irrational?
 
danielunderwood
danielunderwood
That's surely the case if a and b are rational, but I don't have a clue about real math with irrationals
My view of irrational numbers is $\pi^2 = 10$ :D
 
enumaris
enumaris
seems like maybe they can actually be different
difficult
Greek mathematicians termed this ratio of incommensurable magnitudes alogos, or inexpressible. Hippasus, however, was not lauded for his efforts: according to one legend, he made his discovery while out at sea, and was subsequently thrown overboard by his fellow Pythagoreans “…for having produced an element in the universe which denied the…doctrine that all phenomena in the universe can be reduced to whole numbers and their ratios.”[9]
lol wat...talk about killing the messenger
 
rob
rob
11:17 PM
Man, the existence of the Pythagoreans is really strange.
 
danielunderwood
danielunderwood
Pythagoreans didn't have any time for new knowledge
 
rob
rob
A secret cult where people think about numbers and murder their colleagues who discover unpleasant truths about the numbers.
 
Semiclassical
Semiclassical
tbf, a lot of what we 'know' about the Pythagoreans is probably apocrypha
 
rob
rob
... but whose discoveries still merit discussion after two thousand years.
 
danielunderwood
danielunderwood
They were quite special people
That quote does make me wonder if it's possible to come up with some space where all geometric quantities are rational numbers
 
Semiclassical
Semiclassical
11:20 PM
"Pappus merely says that the knowledge of irrational numbers originated in the Pythagorean school, and that the member who first divulged the secret perished by drowning.

Iamblichus gives a series of inconsistent reports. In one story he explains how a Pythagorean was merely expelled for divulging the nature of the irrational; but he then cites the legend of the Pythagorean who drowned at sea for making known the construction of the regular dodecahedron in the sphere. In another account he tells how it was Hippasus who drowned at sea for betraying the construction of the dodecahedron and t…
from the wiki page on Hippasus
 
danielunderwood
danielunderwood
Shouldn't a regular dodecahedron in a sphere be an easy thing?
Really any regular polyhedron
 
vzn
vzn
discovery of irrational #s: early example of paradigm shift... in math... + human psychology wrt science/ discovery/ "inconvenient truth"/ cognitive bias/ groupthink/ scapegoating etc...
 
Semiclassical
Semiclassical
it does seem a bit curious
bottom line for me is that we really don't have any primary sources when it comes to the Pythagoreans
looooots more discussion of that here: plato.stanford.edu/entries/pythagoras/#PytQue
 
rob
rob
My mental picture of the Pythagoreans is like the Heaven's Gate cultists, but if instead of doing web development they were inventing the Beowulf cluster. And everyone twenty years later who uses a GPU card or cloud instance or any other massively parallel system would call it an "Applewhite system" and frowns politely when asked who that is.
I'm aware that's not a terribly accurate picture, but it amuses me anyway.
 
Semiclassical
Semiclassical
11:36 PM
my main conclusion, looking at that Stanford entry, is that doing good history is hard when all you've got are secondary and tertiary sources
that is a really complicated article and not easily summed up in any slogan
 

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