The h Bar

5:02 PM

yeah that integrate-the-point-particle-action thing looks a bit shady, but maybe it's an even better way to understand how to get to strings

vzn

@nbro so you have some interest in QM and have some contrarian questions eh? and any idea at the moment, how much energy do you want to put into that?

bolbteppa

nbro don't take the bait :p

Anonymous

^

nbro

?

bolbteppa

'contrarian questions'

nbro

5:04 PM

I usually don't read the whole sentence if the meaning of that sentence composed of only the first words doesn't interest me much

Anonymous

Except that the answer is right...

Anonymous

Single-photon source

Single-photon sources are light sources that emit light as single particles or photons. They are distinct from coherent light sources (lasers) and thermal light sources (such as incandescent light bulbs and mercury-vapor lamps). The Heisenberg uncertainty principle dictates that a state with an exact number of photons of a single frequency cannot be created. However, Fock states (or number states) can be studied for a system where the electric field amplitude is distributed over a narrow bandwidth. In this context, a single-photon source gives rise to an effectively one-photon number state. Photons...

nbro

If you hate egocentric people/entities and you like this approach, then you may avoid reading all sentences starting with "I"

lol

Anonymous

@nbro I'll take that advice seriously

nbro

:D

vzn

5:11 PM

@Blue copenhagen interpretation rejects that QM has any "deeper theory".

Anonymous

@vzn Not sure what you understand by "deeper theory" and what I meant by it, match

vzn

@Blue not sure you know what copenhagen interpretation is :P

Slereah

Oh I have the best definition of the Copenhagen interpretation

Which doesn't involve any bullshit that could be misinterpreted

Abcd

Hey @Tanuj! I did it, are you there?

Slereah

"the Copenhagen view, which states that, when a complete commuting set of observables is measured, then the interpretation of dial readings is as a classical probability model, given by the Gelfand-Kolmogorov construction of sample space and measure"

Try to get a crank to misinterpret that

Cows

5:15 PM

Today will be quite involved. I will be working out soon, then have to decide between coding some "cool" actually awesome AI or writting a basic entanglement entropy computation tool. Personally i want to do the AI stuff because it is awesome and harder. Will know for sure when i am in front of my computer. But first got to get my workout in then make and eat breakfast.

bolbteppa

That's how Landau does QM in his book basically, that's within the bounds of reason of interspersing big words

@vzn what's contrarian about that perspective on Copehnhagen

Slereah

Landau's QM book is weird

It's very nicely done but also very old school

No Hilbert spaces at all

vzn

@bolbteppa (?) it was nbro that was writing "contrarian" stuff (or questions) about QM. but ofc hes an admitted n00b... ps re "bait" think it was more n00b bait by him than anywhere else :P

bolbteppa

Yeah you don't need to waste time defining Hilbert spaces, you just invent them as you go along

haha

Basically from the hand of Bohr

Abcd

@Tanuj I have posted my solution in PSS.

@Blue I got the answer by simply approximating the motion to be linear simple harmonic motion.

There were such problems in HCV.

Slereah

5:20 PM

My thesis advisor was a russian dude

So that's why I got Landau for QM

ACuriousMind

@EmilioPisanty I indeed have generally no qualms about such blasphemy in public ;)

Slereah

He was big into Landau

Anonymous

@vzn Okay, explain it to me, in your way

Emilio Pisanty

@ACuriousMind you shall burn at the stake, sir

vzn

@Blue explain what? lol dunno, you guys seem to be a bit )( nervous or something :P

Emilio Pisanty

5:21 PM

I foresee it

btw @ACuriousMind is there any info you can share on this question? is it a bunch of roomba deletions or is there something else going on?

nbro

The only person who I can right now perceive as nervous is you, @vzn.

5

Emilio Pisanty

can you share the rough number of answers involved?

Anonymous

@vzn I don't understand what you mean by "copenhagen interpretation rejects that QM has any "deeper theory""

Anonymous

Please, explain it to me.

vzn

← lol always a little paranoid around here :P

Abcd

5:22 PM

@Blue Is that fine and legal?

Anonymous

@Abcd Yes, sure. SHM is always locally linear

Anonymous

That's the definition of SHM :P

vzn

@Blue copenhagen interpretation was not so definite, not easy to define, it was given by bohr in rejection of einsteins basic idea that theres a "deeper theory" to QM... it takes on different hues... idea that theres a "deeper theory of QM" now considered somewhat )( fringe by mainstream physicists...

nbro

I am out of here. Have a nice continuation of your 24 hours.

ACuriousMind

@EmilioPisanty I'll look into it when I'm at my desktop and can access all the mod tools

Emilio Pisanty

5:24 PM

@ACuriousMind a'ight

it's a curious case, that one

@vzn [citation needed]

Anonymous

@vzn Yes, sure. But that is not what I meant by "deeper theory". Einstein was expecting things like hidden variable theory which was proved false

vzn

@Blue the difference between "deeper theory" and "hidden variables" is merely semantics. essentially 2 names for the same thing. but some credit for using semi accepted terminology there. (einsteins own famous phase was "spooky action at a distance" etc)

ACuriousMind

But in general I can say your answer is right - if you've provided a lot of answers to questions which get deleted, the method of fixing one's answers doesn't work.

Anonymous

@vzn Yes, the difference is in semantics. I wanted to convey something else than "hidden variable theory" when I said "deeper theory".

Anonymous

This is getting too boring now, though

vzn

5:29 PM

@Blue am listening if you want to define "deeper theory" but physicists basically reject both as the same thing. ps bohm spent decades defining "deeper theory" etc. (to little mainstream acceptance) ... as for boring, talk about whatever you think is not boring.

Emilio Pisanty

@vzn that's a notably restrictive view of what "deeper theories" might be ─ so, particularly surprising coming from you.

Anonymous

That ^

Emilio Pisanty

There's no reason at all why a theory that reduces to QM needs to be a HVT.

superdeterminism, say, falls out of the HVT class, if I understand it correctly.

ACuriousMind

What is "merely semantics" even supposed to mean? Semantics are about the meaning of things, so this is saying "the difference is merely in meaning" - ???

vzn

@ACuriousMind (sigh) youve (not) heard the expr before?

HsMjstyMstdn

5:32 PM

@ACuriousMind Usually what people mean when they say "you're just arguing semantics" is actually "you're just arguing about our particular conversational pragmatics"

At least, from a Linguistics viewpoint.

Though I would be remiss not to include that the moment you try to scrutinise when exactly two people are arguing "semantics" versus "pragmatics", you're kinda hoping that the act of digging deeper will get you out of a hole

ACuriousMind

Maybe I heard that before but I never thought about the expression. Interesting, there's a Merriam-Webster areticle on it

HsMjstyMstdn

Iow, not so much a difference in meaning, per se, but rather a discrepancy between what the meaning is to one person compared to the other in the context of the conversation being held.

ACuriousMind

Maybe I heard that before but I never thought about the expression. Interesting, there's a Merriam-Webster article on it

vzn

lol leave it to SE, perfect for this audience :P

36

Q: Is the phrase "it's just a matter of semantics" meaningless?

I hear this phrase from time to time, and I really don't know what it means. Two people are debating, and one says "the difference between your position and mine is just a matter of semantics." This would seem to me to be quite an important difference. That is, if one person means one thing, ...

semantics

HsMjstyMstdn

@ACuriousMind There's a whole field in linguistics on it hahaha

ACuriousMind

5:37 PM

@HsMjstyMstdn What? "It" in my sentence refers to the expression "arguing semantics", not semantics as such

HsMjstyMstdn

@ACuriousMind Yes, there is a field (or at the very least, a sub-field) on arguing about semantics and whether or not it's the same as pragmatics and whether or not it holds no importance

vzn

@ACuriousMind nice ref wrt etymology. ps thx for clarification of semantics of pluton vs hades... :)

Slereah

amazon.com/Lost-Causes-beyond-Physics-Streater/dp/3540365818

ouch

cheapest at $50

HsMjstyMstdn

@Slereah Digital at $12

but we all want books

Slereah

I already have the digital :p

HsMjstyMstdn

5:42 PM

but you want the book ?

Slereah

Yes

vzn

@Slereah (cool!) string theory :P

Slereah

For my fancy library

@vzn It's more QM-related

Emilio Pisanty

@Slereah pretty cheap, no?

Slereah

Quantum logic, Bohm interpretation, non-hermitian observables

That kind of stuff

Emilio Pisanty

5:43 PM

I mean, I keep wanting the full five-volume set of Prudnikov's Integrals and Series, but it ain't gonna happen anytime soon

HsMjstyMstdn

@Slereah Buk is luf, buk is laif

Slereah

you may not have heard of many of the topics involved, because they are lost causes :p

HsMjstyMstdn

@Slereah are they truly lost, then ??

bolbteppa

I looked in that 5 volume set, lots of obscure stuff alright

vzn

@Slereah Ch 6 p 73 EPR and the dangers of Cannabis (?!? lol! maybe something for BaSe there) :P

HsMjstyMstdn

5:44 PM

Jk, it's just semantics at that point

Slereah

@vzn It is a clever title :p

the cannabis part is used as an example of the dangers of misusing statistics

Emilio Pisanty

@bolbteppa it can be a real lifesaver, though

Slereah

A lot of the book is dedicated to the notion of probability in QM

Which a lot of QM books don't really do

Emilio Pisanty

plus, it's got the best indexing / ordering in the genre

HsMjstyMstdn

@Slereah They don't ?

Slereah

5:46 PM

@HsMjstyMstdn not in a lot of details, no

HsMjstyMstdn

I mean, I'd not be surprised at "a lot of the book" but it seems a notion worth a solid treatment

sad

Slereah

that's why there's so much problems with understanding QM interpretations

most books basically just go $\langle \psi, \psi \rangle$ is the probability okay done

vzn

"QED"

HsMjstyMstdn

I remember Sean Carroll saying that it's also the fault of physicists, that we either don't explain it concisely enough or that we don't come out of the woodwork to shoot down "quantum woo"

John Rennie

@HsMjstyMstdn shooting down "quantum woo" is like playing whack-a-mole

vzn

5:50 PM

but dont forget, women LIKE to be WOOed (one told me herself!) :P

HsMjstyMstdn

@JohnRennie hahahaha true true

ACuriousMind

@JohnRennie Just less fun because there are no prizes :P

HsMjstyMstdn

@vzn inb4 scathing remark on QM being easier to understand than women

John Rennie

@ACuriousMind and ultimately an unholy combination of more boring and less productive

ACuriousMind

Keep your sexist remarks to yourself everyone, please. Thank you.

vzn

5:52 PM

strange, dictionary doesnt seem to have the denigrating defn used by physicists dictionary.com/browse/woo?s=t

HsMjstyMstdn

@vzn rationalwiki.org/wiki/Quantum_woo

vzn

@HsMjstyMstdn apparently "QM woo" is woo :P

Anonymous

"If a sentence has the word "quantum" in it, and if it is coming out of a non-physicist's mouth, you can almost be certain that there's a huge quantum of BS being dumped on your head."

bolbteppa

Diff M gauge group as a lost cause?

Anonymous

I like the pun in "huge quantum"

Slereah

5:54 PM

@bolbteppa sorry, turns out it's not actually a gauge group!

HsMjstyMstdn

I like the challenging Chopra to solve Schrodinger equation first hahaha

bolbteppa

Quote by Peierls on ch. 3: 'The Copenhagen interpretation is quantum mechanics'

Anonymous

I was curious about something: Given a distribution we can find all the cumulants, but given all the cumulants is it possible to exactly get back the distribution ? Didn't really find any definitive answer on the net except some on Stack Overflow which were talking about approximating the distribution given some number cumulants.

Slereah

@Blue hamburger

vzn

@bolbteppa WOOHOO

Anonymous

5:58 PM

@Slereah Is that a theorem?

Slereah

en.m.wikipedia.org/wiki/Hamburger_moment_problem

Anonymous

Ah, looks interesting. Reading

Slereah

And delicious

Anonymous

Heh

bolbteppa

Apparently the moment problem is a continuous version of solving systems of equations and also motivates Hahn-Banach

This in a continuous setting

dmckee

6:01 PM

@JohnRennie Shooting down relativistic woo is similarly Sisyphean.

Rick

Is dark energy/dark matter real? Like how are we sure it is and luminiferous aether isn't if we can't observe both of them?

HsMjstyMstdn

@Rick Here's a good place to start: en.wikipedia.org/wiki/Dark_matter

dmckee

@Rick "Dark mattter" and "Dark energy" are labels for the causes of two (quite different) sets of observations not currently explained in detail.

John Rennie

@dmckee after a bit you have to concede that woo is like Mills and Boone novels. We may decry them but they give some people pleasure, and the harm they do is probably limited to those who are beyond redemption anyway :-)

2

HsMjstyMstdn

@Rick and re: luminiferous aether en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment

dmckee

6:03 PM

Each has one (or more) leading contending theory that have a lot more details than that, and these theories might be falsified, but the fact that there is something going on is rather beyond doubt.

Note, also, that the only two things that dark matter and dark energy have in common are

(A) They are not yet fully explained.

(B) They have the word "dark" in the names we give them.

John Rennie

@Rick the observations that led physicists to suggest dark energy and dark matter are real i.e. there is certainly something unknown out there not described by existing theories. Exactly what that something is no-one knows for sure.

dmckee

@JohnRennie :chuckles:: Touché.

Abcd

One of my messages in PSS got automatically removed . #Magic?

Rick

ok

John Rennie

@Abcd I don't think chat messages get automatically deleted. Either a moderator deleted it or it got flagged.

Abcd

6:12 PM

@JohnRennie there was nothing wrong with that. Tanuj replied "thanks" to that message

And even Tanuj's message got automatically deleted. (the one I had replied to)

John Rennie

It looks like the moderator ArtOfCode deleted it. Why he did that I have no idea.

Abcd

@ArtOfCode Why did you delete it?

John Rennie

@Abcd that one?

Abcd

@JohnRennie yes

John Rennie

Perhaps he though SHM was some deviant practice.

Anonymous

6:15 PM

Maybe it was just a mis-click. Happens while on mobile devices

Abcd

@JohnRennie lollll

rofl

Rick

lol

John Rennie

vzn

(AoC recently vaporized a large swathe of chat msgs discussing mod actions after a flag...)

John Rennie

This is getting weirder. A second moderator has deleted a totally innocuous message.

Anonymous

6:18 PM

I like the suspense :P

Abcd

@JohnRennie Maybe tanuj flagged them?

Oh, but he can't flag his own message.

John Rennie

Even if they had been flagged that doesn't mean a moderator would have to deleted them. Oh well - one of those things.

Now I'm going to collect together my leather and whips and go indulge in some SHM.

I can just feel a suspension looming :-)

Anonymous

I just checked out urban dictionary...

Abcd

@Blue what does it say

Rick

shaking my head?

oh thats smh

ArtOfCode

6:20 PM

@Abcd someone asked for it to be deleted as part of a discussion they'd rather not have public

Anonymous

urbandictionary.com/define.php?term=SHM

Anonymous

Nothing! XD

Abcd

Somebody hit me!

ArtOfCode

no rules broken or even bent as far as I'm concerned, feel free to repost it if you want

Slereah

@ACuriousMind Is there the equality $$(A \# B) \times \mathbb R \cong (A \times \mathbb R) \# (B \times \mathbb R)$$

Abcd

6:21 PM

Shaking head maliciously

John Rennie

@ArtOfCode hmm, maybe you'd better delete the two edit histories I posted above then.

Slereah

I'm mostly sure it's true from the distributive property of the cartesian product with unions, but since there's the quotient involved too, I'm not a hundred percent sure

ArtOfCode

@JohnRennie eh, I'll delete 'em if we get asked to

Abcd

@ArtOfCode who asked you to do that?

ArtOfCode

@Abcd I'm not at liberty to say who created a flag

John Rennie

6:23 PM

@ArtOfCode thanks. I confess I'm mystified why the request for deletion was made. They seem to me to be perfectly routine comments about aspects of physics.

ArtOfCode

@JohnRennie yeah, seemed a little odd, but I figure I'd rather delete it on the off-chance it was part of a sensitive discussion and let the people involved figure it out if it's still required

Slereah

Wait I just realized that it's not true

It's not even true for $A = B = S^2$

nvm

Back to the drawing board

Sid

Urban Dictionary rocks, btw. :P

Cows

OK ML it is

all day

ACuriousMind

@EmilioPisanty It's indeed just a bunch of roomba deletions, nothing extraordinary going on

Emilio Pisanty

6:53 PM

@ACuriousMind well, they still deserve a chance to turn a new leaf, I reckon

just the one chance, though

ACuriousMind

Perhaps, but as you say there's nothing we mods can do about automatic bans

Emilio Pisanty

@ACuriousMind indeed

but yeah, the fact that it's a bunch of roomba deletions makes me feel pretty nil sympathy here

Ben Niehoff

roomba deletions?

Emilio Pisanty

@BenNiehoff automated deletions enacted by the Community user

345

Q: How does deleting work? What can cause a post to be deleted, and what does that actually mean? What are the criteria for deletion?

What circumstances can cause a question or answer to be deleted, and what does that actually mean? How can a post be deleted? When can't I delete my own post? Can I see a list of my deleted posts? How can I undelete one of my posts? What does deletion mean for a post? How do votes to delete wo...

support faq delete deleted-questions deleted-answers

meta.stackexchange.com/help/roomba

Ben Niehoff

oh

so what was the topic of conversation before it shifted into complaining about deletions?

Emilio Pisanty

7:05 PM

@BenNiehoff we're not complaining

we're contemplating this case

Ben Niehoff

discussing then

Emilio Pisanty

0

Q: Answer ban correction

I am banned from writing answers, and all the answers I wrote, the question has been already been deleted by someone. Actually they were homework questions and I answered them, so it is not acceptable that I get banned right? What can I do?

support answers

Ben Niehoff

wow, I'm glad I'm not any sort of moderator here

bleh

Anonymous

@BenNiehoff Hi, seeing you after long

Ben Niehoff

hey

Cows

7:08 PM

some cross-validation

Anonymous

Last time I remember you were here, was when you had trouble finding an inverse matrix :P

Ben Niehoff

oh, I solved that a long time ago

in hindsight, the answer was obvious

Anonymous

@BenNiehoff Really?

Ben Niehoff

that was a joke

Anonymous

I forget. What area of physics do you work in?

Ben Niehoff

7:10 PM

I do string theory

ah, so here's an example of the type of matrix I was trying to invert:

Anonymous

@BenNiehoff Ah, cool, cool

Ben Niehoff

you are probably aware that the n-sphere S^n is a quotient of groups SO(n+1)/SO(n)

and the Lie algebra of SO(n) is [L_{AB}, L_{CD}] = \delta_{BC} L_{AD} + other terms determined by symmetry

where A, B, C, D range from 1 to n, and L_{AB} = - L_{BA}

you are probably also aware that every Lie group has a bi-invariant metric given by minus the Killing form

Curio

Does a body moving with constant velocity have kinetic energy?

Anonymous

Umm, I don't know lie algebra. Beginner in abstract algebra :P

Ben Niehoff

there's a neat trick where you can use this to write the metric on the n-sphere

but it gives you the inverse metric

it's g^{mn} = k^{AB,CD} L_{AB}^m L_{CD}^n

where k^{AB,CD} is the bi-invariant metric in SO(n+1)

so, the task is to invert g^{mn} to get the line element

but the point is, the matrix on the right-hand-side is too big

if we're talking about a 5-sphere, for example, the L_{AB} are in SO(6), and there are 15 of them

and you could write these L_{AB} in terms of coordinates in R^6, but then you'd have a 6x6 matrix instead of 5x5

Physics Meta

7:20 PM

0

Q: Should we keep a list of wrong top/accepted answers?

Sometimes a wrong answer is the accepted answer, sometimes a wrong answer is the most voted answer, sometimes a wrong answer is both at once. Should we make a list of those? The purpose would be that newcomers (and any member who hasn't already voted in those questions) would make up their minds ...

discussion feature-request

Ben Niehoff

never mind, I guess

GPhys

7:33 PM

Just got out of seminar by Nima Arkani-Hamed

Something about scattering amplitudes and positive geometries in string theory?

vzn

@Slereah fyi someone else (JD) pursuing same ideas reddit.com/r/Physics/comments/80tvjr/…

Slereah

I hope JD isn't John Duffield

Oh no

vzn

@Slereah he has 2 phds + some masters etc

Slereah

Duffield isn't banned anymore

2

Everybody panick

Anonymous

He's been around

Anonymous

7:41 PM

Seen 6 hours ago

Slereah

Aaaaaaaaaaaaaaaaaaaah

vzn

DONT PANIC en.wikipedia.org/wiki/The_Hitchhiker%27s_Guide_to_the_Galaxy

Anonymous

Buckle up ;)

CooperCape

9:03 PM

"The list $1,z,...,z^m$ is linearly independent in $\mathcal{P}(\mathbb F)$ for each nonnegative integer $m$." Surely this isn't true for say $z=1$ and $m=1$ though cause like $1(1)+(-1)(1)^1=0$?

Physics Meta

9:24 PM

0

Q: Tag for free energy

I recently proposed the tag free-energy, and wrote a usage guidance for it; however, it has been almost immediately set as a synonym of energy. I am wondering, however, whether we should have a separate tag for free-energy. I feel that the tag energy is really too vague, and as a matter of fact ...

discussion tags tag-synonyms

skullpatrol

9:36 PM

Welcome back @BenNiehoff :-)

GPhys

9:59 PM

went to this

bolbteppa

@GPhys so, ..., what is the amplitu-hydraheaded-hedron?

GPhys

I had no idea what was happening

something about scattering amplitudes and string theory and carving out the phase space

bolbteppa

and twistors

GPhys

Nima was very excited about it though

no_choice99

which fundamental force is involved in the Casimir effect ? the electroweak one?

Mithrandir24601

10:10 PM

@GPhys The best bit of this is that it's entitled as a High Energy Physics seminar

GPhys

@Mithrandir24601 that part is not particularly meaningful, the HEP group just schedules somebody to give a talk every week under "HEP seminar"

Mithrandir24601

@Blue As a non-expert in QKD, albeit one with a large interest (i.e. it was a potential PhD :P), I feel the need to point out that the paragraph "Although such a source [attenuated laser] can be used for certain applications, it has a second-order intensity correlation function equal to one (no antibunching). For many applications however, antibunching is required, for instance in quantum cryptography." seems to be wrong, as e.g. the Coherent One Way (COW) protocol uses exactly that

(although rigorously proving the security of various protocols isn't exactly a simple procedure, to be fair)

Sir Cumference

Welp, DiffGeo is offered in fall whereas Topology is offered in spring. Guess I'm taking DiffGeo first then...

vzn

10:29 PM

aaronson on the amplituhedron o_O scottaaronson.com/blog/?p=1537

lol found another review, woit, 2014, maybe same talk? :P math.columbia.edu/~woit/wordpress/?p=6607

GPhys

Yeah but this is string theory so won't woit say the same thing as usual ?

Something like a mathematical constructivist reviewing a non constructive logic article

Not to say it's invalid, but just that I feel like I already know what he will say

loocsieulb

10:49 PM

@SirCumference you could take topo now

it doesnt have many prereqs really for an introductory course just try your best

Sir Cumference

@loocsieulb It's too late to take it this semester, so I'll have to wait until junior or senior year

Lozansky

How do I integrate $\int_0^{R} J_0(\alpha_{0k}r/R) r dr$, where $J_0$ is the Bessel function of first kind and $\alpha_{0k}$ are its zeros for $k=1,2,...$?

bolbteppa

10

Q: How do you integrate a Bessel function? I don't want to memorize answers or use a computer, is this possible?

I am attempting to integrate a Bessel function of the first kind multiplied by a linear term: $\int xJ_n(x)\mathrm dx$ The textbooks I have open in front of me are not useful (Boas, Arfken, various Schaum's) for this problem. I would like to do this by hand. Is it possible? I have had no luck...

integration special-functions

Lozansky

11:32 PM

@bolbteppa Thanks

vzn

11:42 PM

for the mathematicians in here... ahead of the pack! surprised to see this, 9/2016... mentions madelung fluid...

in theory salon, 19 hours ago, by vzn

Semiclassical Quantum Dynamics and Bohmian Trajectories / Sparber, notices AMS

Transcript for