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12:13 AM
Heyo, wondering if anyone can recommend a book on introductory lagrangian mechanics that is friendly to someone who probably can't do something too rigorous

I know calculus 2 and am learning calculus 3
just for fun, so don't have to consider the suitability of the textbook for class-use

Thanks~

2 hours later…
1:57 AM
@KenWang John Taylor might be good
I'd say probably good for self-learning too

2:30 AM
@NovaliumCompany Ha ha you guys still play gta

3:31 AM
@Akash.B I think GTA is popular again, or was a month or so ago

Wow! @RyanUnger impressive Final Thesis. Congrats on getting into Princeton.
5

3:52 AM
Any mods here, please see this :
1

I recently came across this in a textbook (NCERT class 12 , chapter: wave optics , pg:367 , example 10.4(d)) of mine while studying the Young's double slit experiment. It says a condition for the formation of interference pattern is $$\frac{s}{S} < \frac{\lambda}{d}$$ Where $s$ is the size of ...

The accepted answer is clearly wrong. The OP's textbook referes to 's' as "size of source" and then gives a relation involving it. But the accepted answer conveniently assumes 's' to be "fringe-width" and proves the relation. One of the unaccepted answers is the correct one. I have flagged the answer for mod attention. This answer wastes time, because I naturally looked at it first ( it being an accepted answer) only to realise it proved something entirely different and trivial.
Can anything be done here?

4:39 AM
0

This question was considered a duplicate because of a previous question titled "Height of Water 'Splashing'". However, the previous question only considers the height of the splash, whereas answers to the later question may consider a lot of different effects on the body of water, such as height ...

1 hour later…
6:04 AM
Can someone tell me why I cannot find the scattering cross section of single vertex feynman diagram online? I tried to figure out the cross section but I know my answer is wrong. Here is what I did:
0

I was trying to figure out the cross section $\frac{d\sigma}{d\Omega}$ for spinless $e^{-}\gamma\rightarrow e^{-}$ scattering. First I wrote the terms associated with each component. Vertex: $$ie(P_A+P_B)^{\mu}$$ External Boson: $1$ Photon: $\epsilon_{\mu}$ Multiplying these will give the inv...

1 hour later…
7:25 AM
having fun . . . . 12:24 AM over here. Internal fun solving string theory classics . . . like a boss
Have me bois hacking in the back. Should be a fun couple of hours

7:46 AM
Actually the string thing is not working out tonight. Heading to bed

that was quick

0

As I am now studying on the history of discovery of electricity so I am searching on each scientists on Google but I am not getting a good answers on some scientists.So I want to ask you to provide a good app for studying on the history of scientists?

0

I am working on correlation in quantum systems. Consider for an arbitrary finite dimensional bipartite system $A$ with elements $A_{1}$ and $A_{2}$ and a bipartite system $B$ with elements $B_{1}$ and $B_{2}$ under the assumption which fulfilled continuity. My question is that would it be possib...

4 hours later…
12:02 PM
@EmilioPisanty Sup. I finished Part I of Q is for Quantum. I'm a little confused why a black ball turns into a misty of white and minus black, and not into white and black? Is it like a little trick so the second PETE box can cancel out the contrary states? Also I really like that the book avoids words like quantum, superposition, etc.

@NovaliumCompany make sure you have an idea what ‘superposition’ means. It’s actually s really important thing to get your head wrapped wround

12:22 PM
Anyone here Aussie and eying on the election?

you're having an election during the World Cup of rugby year?

@SDFG Moderators are not judges of correctness. If you see a wrong answer, downvote it (if you can) and/or leave a comment pointing out why it is wrong.
3

1:05 PM
Please correct me if I'm wrong in saying that they may not be "judges of correctness," but they are "executioners of policies."

@skillpatrol I haven't killed a single policy :P

(you mean "executors", not "executioners")

@skullpatrol thanks
so what has happened with the JEE crowd

@ACuriousMind oh.
Where is the undo button?

1:09 PM
Just glue the head back on, no one will notice

If I can find it …

that's what the bucket is for!

Ah!

@RyanUnger you scared them away into separate rooms.
Mostly, John's problem solving room :-)

@vzn not something, a lot of thing in Godot. I was there as a 3d environment designer artist

1:20 PM
@ACuriousMind Well, I don't have enough rep, so I can't comment/downvote. I could only flag the answer and I did that.

@ACuriousMind slacker.

@skillpatrol When hotmail, in the 90s, told me "nitsua" was already taken as a username this was their suggested alternative.

I see.

1:36 PM
isnt that how most ppl get numbers in their names

1:48 PM
@JakeRose Oh yep, I know about superposition :) (or at least I think I know)

2:02 PM
why is it that the emissivity of a material is not mentioned in any solid state/condensed matter textbooks? not even the classics like Aschcroft Mermin
so in the end, we're left with 0 knowledge on how to compute from first principles, epsilon
i don't even know whether the radiation is due to the electrons, or ions of the lattice, or both, etc

@thermomagneticcondensedboson I'd wager because it is a surface property rather than a bulk property.
The condensed matter structure of the body is wholly irrelevant for its emissivity, but e.g. whether it's polished or not is.

yeah but these books do mention the boundaries and the surfaces
and surface currents and what not
they're not focused solely on the bulk properties
black body radiation is a topic that looks, to me at least, completely forgotten from all the textbooks I've checked out (around 8)

Googling search terms like "ab initio emissivity" seems to indicate that it requires rather involved simulations.

im not so sure, I had checked out a paper which gives it in terms of an integral
that was related to the electronic density
but clearly, this cannot be applicable to non metallic materials
i mean even a piece of wood where the electrons are all tightly binded to the atoms do emit like T^4 and so the formula from DFT I found doesn't apply there
it should be another formula
precisely the kind of stuff I would expect to find in any serious solid state textbook, but which is totally depreciated

@thermomagneticcondensedboson And computations of electronic densities for real materials in fact do require simulation, as far as I know!

2:11 PM
right. if you want to evaluate the integral, yes you have to solve it numerically
but for physics sake, please at least show me that integral! (im talking to the book authors)
they do not even cover the topic at all

@ACuriousMind you should find an alternative approach to Perelman's third paper
Yau would give you some award

anyway im digging back to the textbooks. ive got some equations to solve

When does @EmilioPisanty usually come online?

I don't think he has a fixed schedule, especially not on weekends
Why?

@NovaliumCompany look at his profile: chat.stackexchange.com/users/38598/emilio-pisanty

2:27 PM
Is this correct? "The closer you get hovering (as opposed to falling) to a black hole, the further away you see the black hole from you. You would need an impossible rope of an infinite length to reach the event horizon from a hovering ship". From physics.stackexchange.com/questions/480767/…

@ACuriousMind I need him about something in Q is for Quantum :p

@NovaliumCompany you could try also asking the rest of us ;)

The reason we can't extract zero point energy is that the core definition of zero point energy relies on it not being extractable? I wanted a more satisfying definition.
@ACuriousMind I will try, but it's specific to tge book, but I'll ask anyways, sec.

You can't make a system go to a lower state than its zero point, so you can't do work with ZPE. Similarly, to run a hydroelectric generator you not only need water, you need a height difference so you can make the water run downhill. — PM 2Ring 3 hours ago

So in Q is for Quantum there's a box called PETE that has 50% chance of changing the color of a black or white ball. When two PETE boxes are connected, an input white ball will always come out white and the same with a black ball.

2:35 PM
@NovaliumCompany You may find it helpful to learn a little about torsors.

@NovaliumCompany I remember that (I read the first chapter or so), what about it?

@ACuriousMind There is also a NOT box that changes the color of the ball. In the book it's described that each ball has a misty (possible outcomes I suppose). For example a white ball coming into a PETE box will have output misty of WB (it can come out as white or black). But the misty of a black ball is W-B or -WB. (the black ball comes out with a minus). I understand that with the minus the math works out, but what is that minus and why?

@NovaliumCompany Why does it have to "be" anything?
It is, at first, just a marker that the state of the black ball after PETE is different from the state of the white ball, you could choose any way you like to denote that.
Then we realize that we can do useful things by writing the states as W+B and W-B, The minus is in our description, not in the world.

2:58 PM
@AbhasKumarSinha intriguing/ impressive! would like to hear more! :) am very interested in using physics simulation systems for fluid dynamics vs particle dynamics experiments, alas very few in the world are thinking along the same lines right now, even as the technology improves substantially...

@NovaliumCompany When we observe a misty ball, is there a 50:50 chance that it's black or white?

3:18 PM
@PM2Ring When we put a black or white ball, it has 50 percent of staying the same color and 50 percent of switching.
@ACuriousMind Why doesn't a white ball misty come out as -WB, but the black comes out as W-B? Physics is racist?

@vzn for physics/simulation, you may use Blender, that is very accurate. If you want to experiment lens and optics, the you may use Mistibushi Renderer, those are made for accurate scientific purposes.

@NovaliumCompany The inner workings of the PETE box are purposefully left unspecified.

*mitsuba renderer specifically
@vzn Here's my artstation: artstation.com/abhassinha

@ACuriousMind That isn't very satisfying but I guess I'll "accept" it for now.

@ACuriousMind is there a canonical SE thread for mathematicians learning string theory

3:34 PM
@RyanUnger physics.stackexchange.com/q/27700/50583 is about QFT for mathematicians, which overlaps in the sense that you can't really do string theory without first doing QFT. I think the canonical recommendation is indeed Deligne et al's *Quantum Fields and Strings: A Course For Mathematicians *, but I haven't read it myself

@NovaliumCompany not following this closely but think/ picture QM optics devices related to polarization. this is a neat book that uses similar rhetorical devices. by David Z Albert. amazon.com/Quantum-Mechanics-Experience-David-Albert/dp/…

@vzn Thanks.

@vzn the whole point of "Q is for quantum"'s PETE analogy is not to tie this to any particular physical implementation.

The standard example would be Stern-Gerlach apparati, but to understand the essence of QM you really only need the input/output description of the PETE box, not what happens inside it.

3:39 PM
@AbhasKumarSinha when you say you were there, did you work at some kind of Godot facilities/ headquarters? where? dont see something relevant on google yet on "mitsubishi renderer" do you have a link for that?

@ACuriousMind I know about that set but it's 20 years old now
surely there's something more modern (incorporating mirror symmetry ideally)
I was at Yau's bday conference and there was so much mirror symmetry

@RyanUnger I don't think it's really outdated though, the basics of string theory haven't changed.

completely incomprehensible talks tho

chat.stackexchange.com/transcript/message/50339235#50339235 So you mean to say that there's no way this can be handled? I can't do anything other than bring this to the mods' attention given my low rep. @ACuriousMind

@ACuriousMind thats exactly how DZA presents it. understand the idea of "not tying it to any particular physical implementation" but that kind of gets stretched thin because the point is that there are "devices from our reality" that match the description and theyre all part of the mystery/ complexity/ inscrutability of QM. actually its QM experts that dont fully grasp the idea because (on deep research) it seems possible classical components exist that fulfill the descriptions...

3:40 PM
@ACuriousMind OK I don't know about string theory but the foundations of GR have actually changed a lot in the last 20 years

Why do we say space is cold when the temperature skyrockets in the thermosphere and above?

*30

@SDFG Yes, I'm saying if you can neither comment nor downvote there's nothing to be done. Moderators do not delete answers simply for being wrong.

@RyanUnger have they

for mathematicians, yes
where did you come from
do you have a GR detection script

3:42 PM
@ACuriousMind All right. Thanks, though!

@RyanUnger If you say 'GR' three times in front of a mirror, Slereah will appear and talk to you about wormholes
8

Oh no
I mean I guess that there has been plenty of theorems proven and such
But foundational stuff?

yeah, things about regularity of horizons, for example
formation of black holes
low regularity existence theory

@RyanUnger I have a feeling we might have different ideas of what the "foundations" are :P

yeah those are more like
derived things

3:44 PM
GR is just a manifold with an equation
if that's what you mean by foundations, then sure

I don't think much has changed wrt the axiomatic basis of GR
since like the 70's

but there are some errors in HE/Wald that were corrected 20 years ago, for example

Hawking died before he could answer for his crimes

When I say "the basics of string theory haven't changed", I basically mean the story of string theory up to (but excluding) compactifications, branes and what not. It is the latter that has rapidly evolved, not the former.

I don't rly know a whole bunch about string theory, rly
Well

3:45 PM
isn't compactiifcations where the action is

I probably know more about string theory than 99% of people

But still fairly low on the "knowing a lot about string theory" scale

but he's an intimidating guy

Is it
his phenotype

3:46 PM
He's a large man

IRL it looks larger

lol iirc isnt there some cartoon evil genius somewhere with the same shape :P

If you ask the wrong question he may consume your brain to add it to his cranium

@RyanUnger Yes, it's where the actual model building happens. But there's a lot of things to work out independently of that
And that is what I mean by "the basics".
Yes, with mirror symmetry and all that jazz, there's been a lot of things happening in string theory, but I think that's still comparatively "fresh" research where the best you'll find are some survey papers

3:49 PM
I get these urges to learn string theory
But why should I, really

you fool
look at Motl and his hubris

These urges are a natural part of being a young physicist ;)

I'm not a physicist...
@Slereah you should read this paper arxiv.org/abs/math/0109053

perhaps
Though right now I am mostly cleaning the kitchen
it is quite a mess

this looks cool too

3:51 PM
it was once famously said combinatorics is the slums of topology but maybe thats a projection and its just slums of topology... :P

I'm mostly just procrastinating right now

I can tell
from you being here and all

@RyanUnger Wait, you just graduated, didn't you? What are you procrastinating?

@ACuriousMind I have two papers where most of the work is done, need to write

He's got that mindset where the goal in life is to increase the GDP

3:55 PM
and I'm writing notes on the Poincare conjecture but I have to slog through some un-fun harmonic maps shit

Anytime he's not at the river panning for gold nuggets is lost

I don't regret not staying in a field where not working on a Saturday can be considered "procrastinating" :P

Hell I'd love to go back in it
I do a whole lot of reading physics at work
When I shouldn't
Still getting paid for it but with more guilt :V

Are you still making websites for a living?

I'm doing data science stuff now
which is like

A very generous term for it

did we lose Amazon one-boxing

It's mostly just "find out how to get those two libraries to work together"
very little algorithm to do

@ACuriousMind I also have three other ppl that want me to work on GR projects

@Slereah what kind of data do you work with

3:58 PM
@vzn Fairly boring stuff
Server use

two have to do with AdS-CFT, which I have no clue about really

that kind of stuff
hard drive use
etc

@Slereah can u make my computer faster

@Slereah how many jobs are not really boring? ps real data scientists luv data in all forms :) :P

@RyanUnger put it in a Malament-Hogarth spacetime
@vzn I'm very much a fake data scientist

3:59 PM
@Slereah do you want some low hanging GR fruit

People seem to think I enjoy programming but rly I don't

@Slereah lol know the feeling o_O

@RyanUnger shoot

show path connectedness of maximal black hole initial data sets

Most of my university days were me trying real hard to avoid doing programming stuff
Which was probably a bad idea because there were probably more thesis money for that stuff

4:00 PM
I'm fairly sure the tools are all there, one just has to come to grips with them

@Slereah been waiting my whole life for a MBI like benefit, maybe it will finally arrive at my retirement age :(

Yeah there's a lot of that in science I think
Just
take two fields
Combine them
Bam, easy theorems

@ACuriousMind did we lose Amazon one-boxing

Physics is so wide that it's hard to combine everything with everything

@Slereah similar story for me, except it was avoiding java, and then finally bit the bullet over a decade ago...
@Slereah it doesnt help that physicists prefer compartmentalization almost by training... :(

4:02 PM
Like right now I'd like to try showing that gluing spacetimes has unique geodesic solutions mb?
In the sense of Filippov
I'm not sure if it's true
It's probably true in reasonable cases
and there doesn't seem to be a whole lot on the topic but enough that proving it shouldn't be too hard
It's one of those Physicist Thing where people just assume that things are probably fine
Despite the dire warning of every GR book about having a $C^2$ metric

@RyanUnger what do you mean "black hole initial data sets"? are you talking simulations?

initial data in the sense of Choquet-Bruhat

@Slereah wut

@RyanUnger just saw neat new survey on that by Swingle. AdS-CFT crowd now talking about "entanglement spacetime fabric"... want a ref? o_O =D

4:07 PM
no that sounds like woo

@RyanUnger Yes, about a year ago and they don't seem to have gotten around to fixing it meta.stackexchange.com/q/308166/263383

I assume it's ER=EPR stuff
Which
sounds interesting
But I don't know enough about AdS/CFT to really look into it

@RyanUnger lol any sufficiently advanced theory is indistinguishable from woo™ :P

And also from what I hear it's on bit flimsy grounds?
i dunno

most physics these days sounds completely nuts

4:08 PM
Well you know
A lot of it is basically just math
What was that quote

not correct math

About theoretical physicists being not good enough at physics for experimental physics

physics is at a crossroads. an interregnum (re great quote on that) o_O

and not good enough at math to do math

rekt

4:10 PM
it was quite a wrecking quote

now picturing miley cyrus video :P

@Slereah Is he like super smart or something? Why is his head so big? Maybe his brain is big?

lol

It's Ed Witten so yes
I wonder if he's aware of the memes about him
mb you can ask him @RyanUnger

my brother wants to ask him if string theory is BS when he visits me

4:15 PM
Well, is it

there's no evidence
and as we all know
Einstein and the evidence are the two things one needs

exactly, its just to get inbred grants. just ask hossenfelder. :P

who?

@RyanUnger we had some epic discussions on her while you were gone. she has a new book out. you might find it amusing esp with your own sense of humor. :)

I wasn't aware I had one

4:22 PM
@RyanUnger trying to think of an adjective for it... nihilistic? :P ps have you seen this? think youll like it, thought of you when found it... Kurzgesagt optimistic nihilism youtube.com/watch?v=MBRqu0YOH14

4:38 PM
So anyway
If I'm so smart
Why do I still use my fingers to find out what month is what number
I don't really have a good intuition of what number a month is past March usually

I wish someday I can be as smart as you guys

@Slereah do you have to write dates with month number? That's kind of ingrained in my mind which one is which. I still have to think about whether a month has 30 or 31 days though

Also why do we say space is cold when the temperature skyrockets in the thermosphere and above?
Is it bcs less air is present at higher altitudes?

I use the old algorithm to find out if a month has 30 or 31 days
The knuckle mnemonic is a mnemonic device for remembering the number of days in the months of the Julian and Gregorian calendars. == Method == === One handed === One form of the mnemonic is done by counting on the knuckles of one's hand to remember the numbers of days of the months. Count knuckles as 31 days, depressions between knuckles as 30 (or 28/29) days. Start with the little finger knuckle as January, and count one finger or depression at a time towards the index finger knuckle (July), saying the months while doing so. Then return to the little finger knuckle (now August) and continue for...

@NovaliumCompany are you a student?

4:44 PM
It's that old PhD comic all over again

Ah yeah that's the one that I do

@vzn high school student, but I dont like school at all. I'm very good at teaching myself though.

@NovaliumCompany defn know that feeling :) what year? do you want to go to college? any particular subj?

@vzn I dont want to go to uni nor college. I prefer to dive into the depths of life early. I'm 16 (2 more years and I graduate). I'm interested in business, physics, neuroscience, philosophy, biology, engineering and other stuff and technologies. I just have constant hunger to widen my view on the world.
@Slereah It's like the brain has a limited capacity on math skills it can store.

4:49 PM
@NovaliumCompany STEM! theres so many good resources now for that for anyone sufficiently motivated, its defn the info age... :)

you definitely need to go to college
a good one at that
you need to interact with people infinitely smarter than you

I agree, and I will. I doubt smart people exist only in colleges.

Also it's gonna force you to actually learn things

socializing is a big "peripheral" part of university...

Otherwise you risk only learning about fun topics
and miss out on some fundamental stuff

4:51 PM
"I dont want to go to uni nor college. "
"
I agree, and I will."
??

I agree and I will on that I need to iteract with smart pipl.

"biting the bullet"...? again know the feeling...

I agree and I will on that I need to interact with smart pipl.

the smartest people are definitely at universities

@RyanUnger I really need to find a new job.

4:54 PM
What are you up to these days
still doing reactor stuff?

@NovaliumCompany btw think either way is acceptable, relate to the feeling of low enthusiasm to submitting to "the higher establishment," but for many, universities are indeed "diving into the depths of life"

I think you should go if you want to learn, but I'd also argue that waiting a couple years could be a sensible option. I know a number of people who went to college because they were told that it was what they should do and ended up wasting a bunch of time/money
It does give you more of a sense of who actually knows what they're talking about and who doesn't though. While there's a lot of information available these days, it isn't all good information and it can be a very difficult thing to judge without some background knowledge

the university system is getting a little-to-lot out of control in various ways, its becoming a little too corporate etc...

well universities should mostly be shut down anyway

Hello people, does anyone have a suggestion for some good lecture notes on what surface codes are and how are they used for quantum error correction? I just want to have an overview as I might have the possibility of doing a master thesis on the subject. I looked around a bit and it sounds cool but "it sounds cool" doesn't sound like a good enough motivation for devoting 6 months of my life to it

4:57 PM
@RyanUnger Yes, decommissioning one right now.

Well, we'll see. I'm not considering uni nor college at the moment, but if I ever feel the need to go, I will. But I think I'll try the no uni path first.

oof, my old friends in NE said those classes were awful

don't know about the job itself

@RyanUnger NE? what classes?

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