The h Bar

enumaris

00:00

that's a long answer for what seems to be an easy question lol

Anonymous

It's rare to find such creative questions on Math SE these days

Anonymous

@enumaris Yeah, and there are also a lot of assumptions made

Anonymous

But it's an interesting read

bolbteppa

02:11

Page 19 fse.studenttheses.ub.rug.nl/10496/1/… seems to answer the issue with $\nabla_{\alpha}$ above, basically writing it out as I did but the intuition on $\Gamma^3$ is what I was hoping for

enumaris

05:36

So many recruiters...

can't...manage them all...

Seems like most of them come from 1 or 2 firms...and the glassdoor reviews say some shady stuff is going on...

BCLC

09:16

How are rings defined in the GRE Subject Test in Physics please? Unlike 'rectangles', rings don't seem to have a standard definition. In Algebra by Michael Artin, rings are

commutative under multiplication
associative under multiplication
unital
In the GRE subject test in mathematics, I guess rings are defined as same as in Algebra by Michael Artin except

not necessarily commutative under multiplication
not necessarily unital.
I have emailed several email addresses to ETS but have gotten no word on the matter. I hope that rings in GRE Subject Test in Physics will have the same definition.

Qmechanic

0

Q: How are rings defined in the GRE Subject Test in Physics?

Unlike 'rectangles', rings don't seem to have a standard definition. In Algebra by Michael Artin, rings are commutative under multiplication associative under multiplication unital In the GRE subject test in mathematics, I guess rings are defined as same as in Algebra by Michael Artin except ...

Anonymous

09:37

@BCLC I doubt there was ever a question about rings in the history of GRE physics.

Anonymous

About the unital thing, see:

Anonymous

9

A: Why does the smallest ring have two elements at least?

I think you're correct a ring can have only one element, this ring is called the 'trivial ring' or 'zero ring'. If both identity elements are identical (i.e. 1 = 0) we have that $$\forall r \in R, r = 1*r = 0 * r = 0$$ This implies that $R = \{ 0 \}$.

Anonymous

@BCLC In most standard definitions I've seen, rings are not necessarily unital

Anonymous

Ah:

Anonymous

Rng (algebra)

In mathematics, and more specifically in abstract algebra, a rng (or pseudo-ring or non-unital ring) is an algebraic structure satisfying the same properties as a ring, without assuming the existence of a multiplicative identity. The term "rng" (pronounced rung) is meant to suggest that it is a "ring" without "i", i.e. without the requirement for an "identity element". There is no consensus in the community as to whether the existence of a multiplicative identity must be one of the ring axioms (see the history section of the article on rings). The term "rng" was coined to alleviate this ambiguity...

Anonymous

09:50

> The term "rng" (pronounced rung) is meant to suggest that it is a "ring" without "i", i.e. without the requirement for an "identity element".

Anonymous

> There is no consensus in the community as to whether the existence of a multiplicative identity must be one of the ring axioms (see the history section of the article on rings).

John Rennie

They got the name by removing the "i" from "ring" on the grounds "i" is the identity? They urgently need to get out more.

Anonymous

LOL

John Rennie

This was a surprisingly entertaining calculation to do

These order of magnitude calculations on unlikely subjects are always good fun.

Anonymous

@BCLC And as for commutativity, I've never seen anyone say that rings must be commutative under multiplication. See Noncommutative ring

Anonymous

09:55

Under multiplication they're simply defined to be monoids

BCLC

@Blue Oh thanks. I figured physics' maths was really high even for undergrad. What maths do physics undergrads have anyway? (I'm referring to the physics undergrads who may take the GRE in Physics. So, if the GRE in Physics is geared towards theoretical physics more than applied physics, then I guess we may assume I'm referring to BS Physics undergrads instead of BS Applied Physics major in engineering, material science or computer systems or something.)

Anonymous

> What maths do physics undergrads have anyway?

BCLC

@Blue Okay, definitely calculus 1,2,3, linear algebra and probability (and statistics, if that's maths). What's next? I guess elementary (real) analysis, ordinary and partial DE and complex analysis. Um, real analysis and abstract algebra?

Anonymous

That depends on the university and the place. But you can rest assured that GRE never asks questions from abstract algebra in their physics test

Anonymous

And from the papers I've seen, the physics papers should be mostly a cakewalk if you are a physics major

BCLC

09:58

@Blue Well not a pure maths question, but some physics thingy that somehow involves abstract algebra. So what are the maths in the physics gre anyhoo?

Anonymous

@BCLC Very few physics majors take real analysis. Probably only the mathematical physics students. Calculus and linear algebra are common, yeah

Anonymous

And Differential equations too

Anonymous

But complex analysis....not so much

Anonymous

Check the syllabus here: ets.org/gre/subject/about/content/physics

Anonymous

If you're going to attempt the physics test, better prepare for the physics part rather than the out-of-syllabus math :P

Anonymous

10:05

> Those taking the test should be familiar with certain mathematical methods and their applications in physics. Such mathematical methods include single and multivariate calculus, coordinate systems (rectangular, cylindrical and spherical), vector algebra and vector differential operators, Fourier series, partial differential equations, boundary value problems, matrices and determinants, and functions of complex variables.

BCLC

LOL THANKS. Also 'But complex analysis....not so much' vs 'functions of complex variables' ?

Anonymous

@BCLC Well, a complex variables course is normally an intro to complex analysis. You deal with complex variables stuff in QM, so physics majors usually have a basic knowledge of that

Anonymous

But that's usually nowhere near the depth to which math majors study complex analysis. For example you don't need contour integration, residue theorem and all that stuff in undergrad physics

Anonymous

BTW looking at your profile I suspect that you're a math major. Are you changing your stream to physics? :)

BCLC

@Blue No. I wish I were good at physics. I'm like Polya: 'I am not good enough for physics and I am too good for philosophy. Mathematics is in between.' I was just wondering about the GRE subject in physics' definition for rings if any because I'm taking the gre subject in maths on sat. LOL

Anonymous

10:23

@BCLC I see :) And OK, it's pretty rare to hear a mathematician say: "'I am not good enough for physics" XD

Anonymous

> Ach, die Physik! Die ist ja für die Physiker viel zu schwer!

BCLC

@Blue You're kidding right? My understanding is that most maths majors/mathematicians were bad at physics! (Or 'didn't like' physics, for a less fixed mindset term. The rest of this comment is extremely on fixed mindset than growth mindset) For engineering majors, I believe their maths skills are next to maths majors and physics majors. (cont)

@Blue (cont) I've always assumed physics majors were doing just as much maths as maths majors or at least applied maths majors. My engineering friend told me that physics is unthinkable without maths.

Anonymous

@BCLC on the contrary, my understanding was that math majors don't study physics because it's too easy for them ;) Jokes aside, it's really more about what you're interested in and what you spend time on. Math majors spend more time on math and hence they're better at it. Physics majors spend more time on physics, and so on. And of course, it's logically impossible that "physics majors were doing just as much maths as maths majors". Everyone has the same number of hours per day.

Anonymous

Both mathematicians and physicists are a smart bunch and they could learn the other subject at any depth they want, if they wished to, and if they could devote sufficient time.

Swapnil Das

11:07

@Blue Any other countrymen will be badly defeated if Indians started giving GRE :P

Anonymous

@SwapnilDas Eh, don't underestimate the Chinese and the Russians

Anonymous

And the Koreans (although they might struggle with the English part)

Anonymous

BTW tons of Indians already appear for GRE every year

Swapnil Das

Tons only?

@Blue And will you?

Anonymous

@SwapnilDas I'll only appear for the main GRE (English + Quantitative) probably. The CS GRE doesn't exist anymore

Swapnil Das

11:10

@Blue What is the next level if you qualify?

Anonymous

@SwapnilDas Nothing. You get the scores and apply to the universities

Anonymous

But then, I'm not quite sure if I want to apply to the US

Anonymous

Let's see

Swapnil Das

And do universites take students on the basis of scores?

Anonymous

@SwapnilDas No. There's a minimum cut-off but they check your background too

Anonymous

11:12

The GRE is just a high pass filter

Swapnil Das

What if you have scored a perfect score?

Anonymous

@SwapnilDas They don't give a damn

Anonymous

Above 320 anything is good

Swapnil Das

Any Indian can score perfect in Phyisics GRE, no?

Anonymous

Eh

Anonymous

11:14

No, a perfect score is rare

Swapnil Das

Rly?

Secret

White–Juday warp-field interferometer

The White–Juday warp-field interferometer is an experiment designed to detect a microscopic instance of a warping of spacetime. If such a warp is detected, it is hoped that more research into creating an Alcubierre warp bubble will be inspired. A research team led by Harold "Sonny" White in collaboration with Dr. Richard Juday at the NASA Johnson Space Center and Dakota State University are conducting experiments, but results so far have been inconclusive. == Motivation for the experiment == The NASA research team led by Harold White and their university partners currently aim to experimentally...

Anonymous

@SwapnilDas There's always a chance you'll make some silly error. Or you forgot some topic

Secret

5 years later, almost no news

Swapnil Das

@Blue hmm, true.

Secret

11:17

RF resonant cavity thruster

A radio frequency (RF) resonant cavity thruster, also known as an EmDrive, is a hypothesized type of propellant-free thruster that was proposed in 2001 by Roger Shawyer. The proposed theory behind this drive is inconsistent with known laws of physics, including conservation of momentum and conservation of energy.Several prototypes of this concept have been constructed and tested, including by the Advanced Propulsion Physics Laboratory at NASA. Initially, a few tests of prototype drives were reported to produce a small apparent thrust, but subsequent testing has failed to reliably reproduce these...

and this one is dead (probably)

Meanwhile, GR and Slereah reign supreme

and.. I cannot spell

Anonymous

@SwapnilDas Very few places ask for the Physics GRE scores btw. Subject tests are almost becoming obsolete these days

Anonymous

I've only seen Caltech (and a couple more which I can't recall) ask for them. Other places most ask for the main test results only

Anonymous

Anyway, the competition for good PhD positions in physics is very high. You shouldn't assume that a near perfect score in GRE would be enough :P

Emilio Pisanty

hmmmm. any mods around? I'm a tiny mite confused as to why my flag here was declined.

(I do mean the 'tiny', btw.)

the review basically confirmed the flag

was there an explicit mod intervention?

Madhuchhanda Mandal

12:21

Please help me understand why Fig 3.6 is a reasonable approximation of Fig 3.5(c)

Slereah

Define "reasonable approximation"

I mean you could compute error bounds on the PDE solution but I doubt that's what you want

Madhuchhanda Mandal

In Fig 3.6 Region One (I) is designated as Free space (with constant potential, zero field force) where as in Fig. 3.5(c) same region has nearly infinite potential (large electrostatic force due to proximity to the atom)

I understand why Region II can be approximated like that in 3.6 but my problem is in approximating Region I as Free space due to the Reason mentioned in the above message

Slereah

I'm guessing the true answer is "It was easier to compute and it seems to work"

49

A: Why can't we produce gravitational waves in the lab?

In 1973, Grishchuk and Sazhin proposed in their paper, "Emission of gravitational waves by an electromagnetic cavity", a method by which to generate gravitational waves for experiments, using the argument that while the generation would be very weak, it would also not suffer from the decay in $r^...

One vote left and I win the gold badge for a +50 answer!

Nobody recognizeable

12:38

I wish i could upvote it twice!

Slereah

I found that paper while looking for informations about graviton production by photons

user1414

enjoy your gold badge, pal

Nobody recognizeable

@Slereah congratulations.

Slereah

user1414

lol

Nobody recognizeable

12:51

Lol

Slereah

Oh wait, got nothing

Does that badge not exist anymore?

"Answer score of 100 or more"

Dammit

I need 49 more votes!

user1414

-_-

Slereah

oh well

Nobody recognizeable

stackoverflow.com/help/badges

Slereah

thanks anyway

user1414

12:53

np

Secret

Listening to this:

TV Anime Steins;Gate 0 OST - Anger

►

and this is the first thing that came to mind

I wonder if the place known as oblivion is really that dystopian high tech

(yeah I suck at drawing metals)

> The best way to explore this place is to listen to Steins Gate 0: Anger. The bass in the background encodes the deep royal purple color of the metallic walls and floor (or the formless fog) and the muffled piano encodes the desolation and oblivion, forgotten nature. Very ominous, desolate and hopeless where a dictatorial technology or power controls everything in the place

It is in general not recommend to physically visit this place. Like all oblivion, it has the ability to cause whatever exposed to its environment to be forgotten, literally and figuratively

I am immune to this because I have been forgotten for a total of 43 times in the past already

And my mission is simple:

To ensure everything else in the world become one with oblivion

This should be ensured once Trump is re-elected in 2020 and the economy crashes again also in the same year

user1414

powerful track

bolbteppa

14:40

"Wigner considers a free particle whose four-momentum is known. Then, are there other degrees of freedom for this particle? The Lorentz group has six degrees of freedom (three boosts and three rotations). If we fix the four-momentum, we are freezing three degrees of freedom (three, not four because the energy is determined by Einstein's energy-momentum relation). What happens to the remaining three degrees of freedom.

If a particle has its nonzero mass, like the proton or the earth, there is a Lorentz frame in which this particle is at rest. In this case, this particle has three rotational…

Poincare group has 10 parameters

4 are like a constant shift, momentum is determined by 3, spin in the rest frame by 3, two casimirs represent the constants the squares of two 4-vectors (depending on those 3 parameters) are equal to

hmm

danielunderwood

Doesn't specifying the 4-momentum take away the boosts?

bolbteppa

Boosts depend on velocity, i.e. momentum, right, so yeah fixing the 4-momentum fixes the boosts

Emilio Pisanty

15:40

@JohnRennie ah, c'mon, John, where's your old-English-guy humour?

what do you call a fish with no eyes?

a fsh

(of course)

but what do you call a deer with no eyes?

John Rennie

@EmilioPisanty :-)

@EmilioPisanty No eye deer

What do you call a deer with no eyes and no legs?

Emilio Pisanty

@JohnRennie good. I imagine you know the deer with no eyes and no legs, then

damn, jinx

anyways

John Rennie

I fell out of my cradle laughing at that one :-)

Emilio Pisanty

@JohnRennie the fact that you posted this disqualifies you from poking "rng"

... terrible as it is, of course.....

John Rennie

But they do need to get out more

Emilio Pisanty

15:44

@JohnRennie yeah, that's also true.

Anyways, what do you call an automated system that won't let you submit your paper unless it's below some semi-arbitrary length limit calculated from your LaTeX submission, and claims to leave things like acknowledgements out of that calculation but in practice puts in those sections anyway?

John Rennie

@EmilioPisanty anything you like - it isn't listening and doesn't care!

Emilio Pisanty

@JohnRennie heh

I was going to go with "APS, of course", but that also works

John Rennie

@EmilioPisanty American Perverse Software

enumaris

16:01

meep

2

enumaris

16:16

Anyone know of a good resource for solved probability theory questions? Nothing too insanely difficult...just something to get used to doing those types of problems.

I seem to only be able to find either totally trivial questions (flip 3 coins, what's the probability for 3 heads?) or very difficult questions that might take hours to solve or involve funky subtleties...

danielunderwood

There's probably something like "problems in probability" or similar books, but I don't know how helpful that would be to you unless you have a library or could find a pdf

enumaris

yeah I mean like online resources :P

the digital textbook Blue sent yesterday had the right level of questions imo, but each chapter only has like 3

danielunderwood

If you google "problem book in probability theory" you may or may not find a pdf of a problem book

I don't know if it's the level you're looking for or not though

ACuriousMind

@ShaVuklia When you quantize the electromagnetic field, you get creation operators for particles (photons) of definite energy and these are the quantization of the Fourier modes (= states of definite frequency). That's the handwavy connection between frequency and energy. More technically, you can show that a coherent state of many photons of the same energy $E$ corresponds in the classical limit (i.e. the limit of many particles and small $\hbar$) to an electromagnetic wave of frequency $E/h$.

enumaris

16:36

@danielunderwood yeah my quick googling attempts so far have yielded the 2 extrema

danielunderwood

@ACuriousMind so having photons be discrete packages of energy isn't taken as an assumption like I had thought?

ACuriousMind

@danielunderwood For Planck it was certainly an assumption, a leap of faith.

Today, we can tell the story of quantization a bit more coherently, but of course there are other assumptions that go into it

Anonymous

@enumaris brilliant.org/courses/probability

Anonymous

That's a very good source for problems ^ :)

danielunderwood

@enumaris The one that I was suggesting that you may or may not find was Meshalkin. It looked slightly complicated, but I don't have a great knowledge of probability either

ACuriousMind

16:40

And there are different starting points. Weinberg's explanation of QFT still very much starts from assumptions about particles, while other formulations start from assumptions about a quantization process and a map from classical to quantum field theory

Anonymous

You can select the topic and level and practise problems. In case you aren't being able to solve, you can click to get the solutions by other people

enumaris

@Blue @danielunderwood thanks :D

Anonymous

Level 5 is the hardest...takes hours usually. I recommend starting at level 3 first

Anonymous

@enumaris Np

Anonymous

Feel free to discuss the interesting problems with us!

enumaris

16:42

Where are the levels?

Anonymous

They've apparently changed the UI a bit. I used to use it long ago. Just a min, checking

enumaris

a lot of the quizzes are locked, is that cus I haven't "taken the course" or is that cus I have to upgrade to premium?

Anonymous

@enumaris Ah, I see. They've made the courses paid but the problems are still mostly free. Go here: brilliant.org/discrete-mathematics/?subtopic=probability-2

Anonymous

Curious Fish

hello

Anonymous

16:48

Let's click on CP for example

Anonymous

You need to select the Level from the left bar, bottom

Anonymous

enumaris

hold on

I can't view images here lol

Anonymous

This is a level 5 problem. So you need to try it out first

Anonymous

16:50

And in case you get stuck, click on Discuss Solutions

Anonymous

You'll find that some people who have solved it earlier have left solutions

Anonymous

@enumaris Okaies :P

enumaris

ok, looks like it's a good resource, I'll look into it :D

Anonymous

And after you run out of Level 4 and Level 5 problems, just to the Search Bar on the site's home page. Type "Probability" and click "Problems" -> "Hard"

Anonymous

You'll find many more popular problems posted by the community

enumaris

17:05

nice

I actually have some work to do tho, so I'll get to it later today lol

Emilio Pisanty

in TeX, LaTeX and Friends, Oct 22 at 11:37, by samcarter

HAPPY CAPS LOCK DAY TO ALL OF YOU (https://www.daysoftheyear.com/days/caps-lock-day/) sorry for shouting :)

lolz

curiosity

17:29

Im reading about bound states in a 1-D potential well and i dont understand these seemingly easy deductions:

"The bound state wave function far away from the well necessarily behaves like $e^{\kappa x}$ for negative (positive) x. As we traverse the well, the wave function has to change its slope by $2\kappa$ over a range R. This costs kinetic energy $\sim \hbar^2 2\kappa/(mR)$ that has to be provided by the potential energy −V . We deduce that $\kappa \sim mRV/2\hbar^2$"

what does it mean to say that this change of slope "costs" kinetic energy and how can we deduce the form of $\kappa$ ?

i guess we have to use $\frac{d^2}{dx^2}\psi=\frac{2m}{\hbar^2}(V-E)\psi$ and say that $\Delta(slope)=R \frac{d^2}{dx^2}\psi =2\kappa$ and assume that $\psi$ is constant and equal to one along the well (or something like that) but i dont see how that would be justified.

the point of this is to show that in 1D, even for very low potential strengths, bound states can always form if the R is large enough. in that case the length scale of the bound state would be much larger then the lenght of the potential.

vzn

← is there a caps unlock day? maybe 1 day ppl wont hassle me in chat/ SE/ reddit/ blog/ cyberspace etc about eecummings style :P en.wikipedia.org/wiki/E._E._Cummings

enumaris

18:00

"Your first solution is free!
Upgrade to Brilliant Premium to get unlimited solutions to all 20,000 Brilliant problems."

ouch

Anonymous

@enumaris Eeeeh. They seemed to have changed the policies

enumaris

money grabbing!

Anonymous

It used to be all free back then

enumaris

I'll ask you guys if I find one I can't solve then

Anonymous

I'm sorry :/

enumaris

18:01

more work for you! :P

Anonymous

@enumaris Sure. Or on Math SE :)

enumaris

no need to apologize lol, it's still a good resource :D

danielunderwood

Your first solution from me is free as well

enumaris

is it guaranteed to be correct?

Anonymous

They're offering me Brilliant Premium at a discounted rate of 52$ for one year (for being active there 2 years ago :P)

Anonymous

18:05

Not bad

enumaris

whoop, concept quizzes are locked to premium it seems

Anonymous

Try the Challenge Quizzes

Anonymous

Those are free

Anonymous

With full solutions

enumaris

alrighty

Anonymous

18:13

The community wiki's also have lots of solved problems and exercises with free solutions

Anonymous

brilliant.org/discrete-mathematics/?subtopic=probability-2

Anonymous

Scroll down a bit and click on any topic

Anonymous

This is the Monty Hall CW: brilliant.org/wiki/monty-hall-problem/…

enumaris

brilliant.org/practice/discrete-probability-level-1-challenges/… why am I not getting this one...am I brain dead...

why isn't the answer 1-1/2*9/20*2/5=91/100...

dam I'm dumb

it's 1/2*9/19*8/18 durrr

-.-

I seem to do this quite often lol

Anonymous

It happens, move on :)

Anonymous

18:39

Oh, it's possible to sort all the community problems from here: brilliant.org/community/home/problems/popular/hard/…

Anonymous

There seem to be 1000s of problems :D

Anonymous

19:07

-1

A: Effects of inner painting in the temperature of room

bla nbuhugyugigyfuygfyuguyfguyhgyufyugufuygfyugfuygufuyfyufggfyufuyfhkgyuhgnbjgyiyvtvtyyuytfgghghfyuyguyyyyyyyyyyyyyyyyy

Anonymous

I wonder why people waste 1 rep on downvoting this stuff :P

Anonymous

Just flag!

ACuriousMind

@Blue You get the rep back when the post is deleted

Anonymous

@ACuriousMind Oh, that's nice!

ACuriousMind

Also, spam and r/a flag cast an automatic downvote from Community

danielunderwood

19:10

So for that particular post, what would be the appropriate flag? I did not an answer, but I'm not sure if it should have been something else

Anonymous

Wow. I didn't know that. Even a spam flag from a low rep user will convert into a downvote from the Community?

Anonymous

Or there's a rep threshold?

ACuriousMind

@danielunderwood It's completely fine to cast a "rude or abusive" flag on gibberish

danielunderwood

Ahh yeah I suppose it would be abusive in some sense. I always thought of it as being abusive towards a particular user

user2236

does r/a stand for rude/abusive?

ACuriousMind

19:11

@danielunderwood That's its main purpose, yes

Semiclassical

I'd say it's "abusive to the system"

ACuriousMind

@user2236 yes

Semiclassical

I think other flags would probably be appropriate as well, but r/a isn't wrong

user2236

yeah, just call it "spam"

Anonymous

20

A: Community downvotes posts that were just fixed

The system will now revoke the automatic downvote if, after the flag is marked Helpful, the post later gets an upvote. Remember, the automatic downvote essentially exists because folks use this flag in cases where they should be downvoting. As such, it serves an important role... But should sti...

ACuriousMind

19:17

@user2236 That's the one flag you shouldn't cast on it because on SE we reserve that flag for promotional spam, as is evident in the explanatory text of the spam flag.

user2236

Thanks for the info

Anonymous

Hmmm, yeah, I am usually confused by whether to mark as spam or VLQ

Anonymous

Makes sense now

user2236

too much pedantry, imho

Anonymous

87

A: Why is Community♦ downvoting questions/answers?

When you flag a post as offensive or as spam, an automatic down-vote is cast. That down-vote is attributed to the Community User. See What are the “spam” and “rude or abusive” (offensive) flags, and how do they work?. Each flag carries an implicit downvote for calculating the post's score (it...

Anonymous

19:21

Finally a comprehensive answer explaining it :D

Anonymous

@MartijnPieters seems like a loophole a sadist could exploit. How about flagging and downvoting than just a downvote? :-S — Sufian Feb 16 '15 at 13:07

Anonymous

That was my question too ^

Anonymous

@Sufian: see how far that behaviour gets you before receiving moderator attention.. — Martijn Pieters ♦ Feb 16 '15 at 13:11

ACuriousMind

@user2236 It's not pedantry - spam flags help feed several automatic anti-spam measures intended to block commercial spammers, which should not be triggered just by people posting low-quality content.

Anonymous

19:23

Sorry for this one, lol ^ :P

Anonymous

(Excuse: Instructions were not clear enough on flag page)

ACuriousMind

lol, there was one flag of every type on that post, each one by a different user

enumaris

lol, looks like I need to practice a lot of probabilities questions...

getting a ton of these wrong

mostly by dumb mistakes but still...-.-

Avnish Kabaj

I have a good question on probability

danielunderwood

@Blue I almost did VLQ, but it kind of looks like it's for things that attempt to answer but do so poorly?

Anonymous

19:34

@danielunderwood I guess "Not an answer" would have been the most suitable one

Avnish Kabaj

danielunderwood

Yeah that's what I gathered. It seems fairly difficult to choose in some cases

Anonymous

Although my first reaction was to mark it as spam without bothering about the definition they gave, as I only trust Urban Dictionary for the correct definitions ;)

Anonymous

@AvnishKabaj Did you drop ink on it?

user 2646

19:49

pedantry is like porn: you know it when you see it

Anonymous

I wouldn't know

user 2646

whelp, the urban dictionary gave the idea

Anonymous

Can't help...stiff neck

user 2646

You wouldn't know porn if you saw it?

Anonymous

@user2646 Kept the statement intentionally vague

user 2646

20:02

:P

user 2646

20:14

(I apologize if I made you feel uncomfortable)

ACuriousMind

2 messages deleted

Anonymous

@user2646 Nah, it's okay. Kids are not lurking

Anonymous

Or maybe...

ACuriousMind

@gateprep If you cannot even be bothered to rotate an image so it can be easily viewed or to post anything more concrete than "pls help", you don't need to bother posting here at all.

user 2646

You can't stop kids from hunting for it...

gateprep

20:21

@ACuriousMind I am sorry but I haven't received any help from you except kicking me out of the group a couple of times and giving me advices..I don't remeber a time when u have helped me in solving a problem.

user 2646

Did you ask politely?

@gateprep try that^ please :-)

gateprep

@user2646 I had no intention to do that..He has been extremely sarcastic and impolite with me over the last 4-5 months..

danielunderwood

Listen to the advice he gives you and people will be more likely to help

user 2646

so put him on ignore @gateprep

ACuriousMind

@gateprep You're the one that is being impolite in that you again barged in here with a demand for help, no elaboration whatsoever on what your problem is, and are now getting upset that I again tell you that is unacceptable here.

gateprep

20:28

@user2646 I would like to put ACuriousMind on ignore Pls tell me how to do that

Anonymous

@user2646 I don't think that'll help much. Most people here resonate with ACM's take on this

ACuriousMind

@user2646 Bad advice. If you ignore a room owner or moderator you're not going to see any warnings they might be trying to give you before taking action.

Anonymous

Firstly, this isn't the right place for the type of questions gateprep asks. There's a separate problem solving room for this. And secondly, we tend to avoid helping those who simply ask for homework help without showing any effort. It's necessary to boil down questions into small chunks and point out exactly the place where you're getting stuck.

user 2646

chat.stackexchange.com/faq#mute

Anonymous

Also, you need to patiently wait instead of making demands from others. People have lives and not everyone is interested in solving physics homework. Most of us come here to relax from work and/or talk about interesting issues

gateprep

20:32

@ACuriousMind I do not think I have any intention of barging into the room uselessly.Neither do I intend to get into any tussle with the moderator.I have spoken with moderators of other chatrooms who have been extremely down to the earth persons. ACM has suspended me for seven days and I was unable to get into other chatroom as well...I wish next time people would choose a moderator not as strict as him..

user 2646

Calm down pal.

Take a break from the computer.

gateprep

@Blue has advised something worthwhile...

As much as I understand this group is for quantum mechanics so not worthwhile to post JEE questions here.However I saw that it is the General chat for Physics SE and hence"barged" here.

user 2646

Backup Room – The h Bar

A backup room for when The h Bar is busy. (chat.stackexchange....

Semiclassical

in other news: I'm sitting in on the main physics colloquium this week, which is titled "Number theory and spacetime" (Steven Gubser)

user 2646

Niiiice

ACuriousMind

20:39

@Semiclassical So, the first half of the talk will be about number theory, the second about spacetime, and they will have no relation whatsoever to each other? ;P

Semiclassical

lol

abstract: physics.umn.edu/events/calendar/spa.all/thisweek/index/…

ACuriousMind

"But quantum theory hints at the existence of a smallest possible length, the Planck length"

::twitches::

Semiclassical

hah

i am not optimistic about this talk

user 2646

Wow! Impressive bio.

Semiclassical

from the second main slide: ""AdS/CFT plus an idea from number theory makes a particularly simple discretized spacetime natural"

(as one of two objectives for the talk)

user 2646

20:45

Should be a packed house, no?

enumaris

Gosh, it's been so long since I've done combinatorics I've forgotten how "n choose k" boils down to n!/(n-k)!k!

fail

danielunderwood

Well you take n things and choose k things out of them, duh

Anonymous

Learning stars and bars is a good way to remember these formulae

enumaris

I'll just use it lol

the question boiled down to (36 choose 16)/(35 choose 15)

fun beans

Semiclassical

what i remember being annoying is doing asymptotics on binomial coefficients

danielunderwood

20:50

I worked out some combinatorics stuff a few weeks ago. It took me way longer than it should have and I've already forgotten how I did it

Semiclassical

typically b/c you need to include more terms than just the leading ones in stirling's approximation

vzn

A p-adic version of AdS/CFT / Gubser arxiv.org/abs/1705.00373 Signs of the time: Melonic theories over diverse number systems arxiv.org/abs/1707.01087

ACuriousMind

Nov 10 '15 at 16:22, by ACuriousMind

@yuggib You will regret those words when we have the p-adic Theory Of Everything

Semiclassical

lol

enumaris

these level 3 problems are already pretty tricky

vzn

21:09

"discretized spacetime" ≈ digital physics o_O en.wikipedia.org/wiki/Digital_physics vzn1.wordpress.com/2017/03/31/…

enumaris

discrete analysis

it's so hot right now

user280247

When an atom is irradiated with any wavelength, does it react as a ship does when in the sea?

user280247

(not in a stationary state)

vzn

@enumaris are you serious? how/ where?

user280247

I now it is not true when solving Sch Eq in stationary state but what when it is not...

enumaris

21:14

@vzn I was just commenting on your comment

vzn

@enumaris the field is controversial among physicists to say the least... "twitch" o_O

enumaris

hehe

vzn

AdS/ CFT is defn hot though...!

enumaris

I really need to get better at combinatorics lol

Anonymous

@WrichikBasu Yo

Anonymous

21:21

Long time no see

Anonymous

Lol, were you stalking on me and JR? :P

enumaris

21:41

It seems almost all of these probability questions are combinatoric ones...

Anonymous

What type are you looking for?

Semiclassical

A hard-looking probability question I saw last week goes like this: suppose you’ve got a tree graph, ie a graph with exactly one path between any two nodes

enumaris

@Blue nah, these are ok

I'm just making an observation

Anonymous

@enumaris Sure, sure. I remembered a few more resources which I had in mind earlier. If you need some other type of questions you can ask. I used to love solving probability questions :)

enumaris

Pretty sure I'm gonna fail that test tho

lol

these problems are hard for me

Semiclassical

21:49

You then go through the nodes and choose (with probability p) whether to keep the node or delete it, along with its edges

Anonymous

@enumaris Is it possible to take the test a month later or something?

enumaris

nope, within 1 week is the deadline

Anonymous

Eeeh

Anonymous

Nevertheless, all the best!

Semiclassical

in doing so, you’ll almost inevitably end up the tree graph splitting into a bunch of disconnected trees ie a forest

How should you choose p if you want to end up with as many trees as possible?

enumaris

21:51

o.o

is it a binary tree or does that not matter

Semiclassical

Not binary as far as I know

enumaris

I'm also not visualizing how you get disconnected trees in this process..by "delete the edges" what do you mean

cus all I'm seeing is deleting like an entire subtree

Semiclassical

just the edges connected to the node being deleted

enumaris

oh

so the subtrees stay alive...got it

no clue how to go about that one lol

Semiclassical

Right

Anonymous

21:53

Nice problem

Semiclassical

Yeah. Lemme link the source

fivethirtyeight.com/features/…

It’s the main Riddle problem

I didn’t include the context they gave but that’s superfluous

Anonymous

p will obviously not be a constant value I guess

Anonymous

So we need some algorithm to choose the p

Anonymous

For a certain tree

Semiclassical

Yeah

Anonymous

21:59

One key point I think is that for trees: edges + connected components = vertices

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