The h Bar

0celo7

14:01

@HariPrasad what

ACuriousMind

@2718281828459045360235 Have you looked at the example proposals?

0celo7

@HariPrasad How much Riemannian geometry do you know?

2718281828459045360235

@ACuriousMind yes, i have

0celo7

Do you know some global results, like Hopf-Rinow, Sphere theorem, etc.?

yuggib

@2718281828459045360235 I would focus on an original idea on the detector

ACuriousMind

14:02

Those are well-thought out ideas that seem to have support by experienced coaches. I don't think you'll be able to compete with some idea with which we come up here, you'll need someone competent who will aid you through the whole process

yuggib

do you live nearby some universities?

maybe you should look for some experimental physicist there for an advice

Hari Prasad

@0celo7 quarter-pinched sphere theorem?

0celo7

@HariPrasad stuff like that

Hari Prasad

@0celo7 Why is Reimann Geometry so important?

2718281828459045360235

@yuggib I don't....

0celo7

14:06

@HariPrasad Ricci flow is all about using Riemannian geometry to study topology...

Hari Prasad

@0celo7 is that the only thing that does so?(i mean using Riemannian geometry to study topology) or is there anything else which can help me to workout the poincare conjecture?

2718281828459045360235

@yuggib I got some books and other stuff to understand particle physics better

@yuggib But other than that, I don't have anything else

@yuggib that's why i've come here

yuggib

@2718281828459045360235 yeah, but I agree with @ACuriousMind that the example proposals are done under the guidance of someone really expert in experimental methods, and willing to use significant time to help

the chat people here now (and usually) are for a starter not experimentalists

and however in my opinion you cannot be guided to reach what I saw in the proposals via some comment on the web

you need to interact more directly with some expert

Hari Prasad

@0celo7 are you a professor ? or do you do these things on the daily basis other than just casual work ?

John Doe

Problem 2.24 on page 77 of Griffiths second edition "introduction to quantum mechanics" states: Let $\theta(x)$ be a step function: $$\theta(x) := \begin{cases}
1,~~~~~\text{if }~~ x > 0
\\ 0,~~~~\text{ if } x < 0
\end{cases}$$
Show that $\frac{\partial \theta}{\partial x} = \delta(x)$.

This can be shown using integration by parts:
We get $$\int_{-\infty}^{\infty}f(x)\frac{\partial \theta}{\partial x} dx = f(x)\theta(x)|^{\infty}_{-\infty}-\int^{\infty}_{-\infty}\theta(x)\frac{df}{dx}= f(\infty)-f(\infty)+f(0) = f(0)$$ This implies that $\frac{d \theta}{dx} = \delta(x)$.

yuggib

14:17

@JohnDoe that's just bad physics notation

the proof is very easy, using properly the tool called distribution theory

John Doe

@yuggib Okay just wanted to confirm that it is just a notational preference.

@yuggib Have you worked through Griffith's book?

yuggib

@JohnDoe no

I would not have tolerated such poor math ;-P

Hari Prasad

;-P

John Doe

Okay thanks

user54412

14:57

@0celo7 calling you out

John Duffield

@0celo7 : ask the question. Because there's space and motion. I can hold my hands up a foot apart and show you the gap, the space, between them. And I can waggle my hands and show you motion. Which is what clocks clock up. But you can't show me time.

dmckee

::snaps fingers::

::waits::

::snaps fingers::

Jiminion

Hey, what do you all think of the "Let's change science so we can justify the multiverse" thing? Doesn't that seem a little strange?

John Duffield

@ACuriousMind : physics is right, and your pet theory is totally wrong. Only you think your pet theory is physics when it isn't.

ACuriousMind

@Jiminion Most people I know find the idea of the multiverse either risible, ill-defined, or irrelevant, sometimes all three at once.

3

John Duffield

15:03

@Slereah : I don't get beaten down because I refer to Einstein etc, whilst you believe in woo from Kip "time travel" Thorne.

@ACuriousMind @OMG, I agree with ACM.

dmckee

In other words John doesn't believe there can ever again be any progress in relativity because only the Sainted Albert has the holy insight.

He gives himself away with vast regularity.

Jiminion

@ACuriousMind How close does multiverse beliefs relate to string theory?

0celo7

@dmckee Wow, stinging critique

@ChrisWhite proof?

@yuggib lol

@HariPrasad Ricci flow is on my list of interests

I don't know anything about it, really

I just know that you need to know a lot of geometry, PDE and topology

ACuriousMind

@Jiminion There are models (not necessarily stringy ones) in which there are different branes, one of which corresponds to our universe. Some people would like to endow the other branes with similar meaning, but neither the extra-dimensional models as such nor the claim that the other branes constitute actual "universes" is currently within reach of experimental testing, as far as I know

Slereah

Then again what in string theory is within that reach

ACuriousMind

15:10

@Slereah Didn't claim anything is. However, The models with low-energy supersymmetry arguably are, but they seem to be just false.

Slereah

What's the beefed up LHC energy range btw

Let's see

13 TeV

Not too bad

Not sure we'll get to see any new shit, tho

That isn't MORE HADRONS

John Duffield

@dmckee : no I don't think that. Instead you think think MTW is some bible, and you dismiss hard scientific evidence in favour of Roger parallel antiverse Penrose and Kip time travel Thorne. There is no time flowing inside a clock. Instead there's cogs moving, or a vibrating crystal that's moving instead. When the clock goes slower it's because that motion goes slower. And when it's a light clock, the clock goes slower when light goes slower.

Slereah

I am so sick of hadrons

The LHC is a neverending hadron buffet with hadron sauce

yuggib

15:27

This repeated discussion is so boring that, compared to it, a 20h footage of sloths climbing trees makes me crave for ten times more.

ACuriousMind

Sloths are awesome

Danu

Baby Sloths Get Potty Trained | Too Cute

►

Sloths are da bomb

Slereah

Hari Prasad

what? sloths and physics?

Slereah

I used to be on a general relativity chat

We mostly posted photos of birds

Hari Prasad

15:30

@Slereah he he birds are non relativistic though!

Slereah

Well technically everything is relativistic

Very small boost, though

What is the Lorentz factor of an unladden swallow

user116211

@Slereah that's so cute; more cute than my pup ;/

0celo7

@Slereah what

Slereah

Oh that's right

yuggib

well, I managed to change the subject, and make the repeater drop out of the chat

Slereah

15:32

@0celo7 has never seen any movies

user116211

@Slereah: How could you tolerate the debates with JD?

yuggib

a pretty good job B-)

Slereah

I put JD on ignore months ago

I'm not insane

Hari Prasad

@Slereah maybe this will help you unladden swallow

yuggib

@Slereah says who?

Slereah

15:33

Napoleon

ACuriousMind

@0celo7 It's a Monty Python reference.

Slereah

he told me himself

yuggib

@Slereah then it must be true

user116211

Avenged Sevenfold - Almost Easy [Official Music Video]

►

Hari Prasad

now what Music?

0celo7

15:36

@ACuriousMind huh?

@ACuriousMind I'm confident my proof is correct.

It wonderfully explains why Lorenz ruins things.

Because you get a minus from the inner product of N with itself.

@ACuriousMind @ChrisWhite Thanks for the help last night.

Hari Prasad

its really interesting that i wrote about gravitational waves and the BICEP2 anomaly a few months ago on by blog here: p h i s y k s and after a few months there comes LIGO with gravitational wave detection. PS: i said that "So we don’t have a proof yet to confirm the existence of gravitational waves but that doesn’t stop scientists from working hard to prove its existence and it may occur soon."

David Z

15:52

random thing that they're doing on Worldbuilding that seems interesting:

14

Q: Worldbuilding Scope - Risk Factors

TL;DR: This question is the foundation stone of an attempt to more thoroughly define the scope of Worldbuilding by defining "Risk Factors" that make something Out Of Scope. The discussion of individual risk factors has started can can be found: Risk Factor definition: Too Individual/Character ...

FenderLesPaul

16:22

hai

Hari Prasad

hai! anyone there?

0celo7

16:45

Done.

6

A: Stokes theorem in Lorentzian manifolds

This is version two of my proof. The OP discovered a sign error in my first attempt that revealed my argument to be circular. The correct proof is below. Not surprisingly, this has to do with the signature of the spacetime metric not being positive definite. Furthermore, this issue is very subtl...

@all Do I lose the rep I gained from a deleted answer even if I undelete it?

ACuriousMind

@DavidZ @dmckee: There's a user that mostly just copy-pastes Wikipedia articles without clearly marking the quotes. I can't raise a specific mod flag on one of the answers because I already raised low quality flags, and I think I'll trigger the serial voting script if I go on looking through their answers. Could you look into that?

0celo7

@ACuriousMind link?

ACuriousMind

drvrm

198 6

quantum-mechanics newtonian-mechanics homework-and-exercises x-rays electromagnetic-radiation energy quantum-spin

David Z

@ACuriousMind Yeah, I don't know that there's much we can do except warning the user, but we'll look into it.

I was going to (try to) look the profile up from your flag history but that works too I guess

0celo7

wow!

@ACuriousMind My algebra prof's kid is running around the halls of the math department...

Doesn't have have school?

David Z

16:55

@0celo7 hm? basically, as long as the answer is undeleted, you have the rep, and as long as the answer is deleted, you don't have it. I think.

ACuriousMind

@DavidZ I already told them in the past that that's unacceptable, but they just claimed that they misunderstood the "cite" feature and would really have liked to give proper attribution. After I explained that's not how "cite" works, they deleted their answer instead of fixing it, and they seem to just keep posting copy-pasted answers.

0celo7

@DavidZ I didn't get the 70 points refunded when I hit undelete

David Z

@ACuriousMind I do remember noticing that comment exchange. We'll do something about it.

@0celo7 well, I'm not sure, so you could check on Meta Stack Exchange for official guidance.

Slereah

"MI6 Wernher von Braun was technical adviser to Walt Disney studios as they landed Mickey Mouse and Donald Duck on the moon.

Mickey Mouse and Donald Duck had to travel faster than a speeding bullet to land on the moon. It is a mircle that Donald Duck didn't lose all his feathers! "

ACuriousMind

@0celo7 The answer is probably caching. I'd only worry if they aren't back by tomorrow.

0celo7

16:59

@DavidZ Ah, it just took a while. My rep shot up by 70 points just now.

@ACuriousMind yep

@ACuriousMind So, am I crazy or did that proof require way more machinery than the average GR book contains

ACuriousMind

@0celo7 Both ;)

David Z

@0celo7 Ah, OK. I thought you were talking about something that happened a while ago. Anything can take a few minutes to update, sometimes up to a day if it involves some infrequent script.

0celo7

@ACuriousMind According to Wald it's "easy to show"

ACuriousMind

@0celo7 Well, he didn't say at which level of rigor! I'd not be surprised if there's some quick-and-dirty physicists' derivation of that.

David Z

@ACuriousMind since you identified parts of some of that user's answers which are copied from other sources, can you edit the posts to quote them? Only if you have time, of course. I can also do it, but then I'd have to repeat some of the work you did comparing the answers to the sources.

At the moment I've been awake for about 36 hours and I really don't want to do that kind of detailed reading :-P

ACuriousMind

17:06

@DavidZ It's mostly the entire answer, with some paragraphs/sentences left out, but I can do that, yes

David Z

This doesn't replace whatever sort of mod action we might decide on, of course.

0celo7

@ACuriousMind Yeah, maybe.

David Z

@ACuriousMind cool, thanks

0celo7

@FenderLesPaul If you go to visit him you should ask

FenderLesPaul

@0celo7 visit who and ask what?

David Z

17:06

I really have to sleep but I promise we will do whatever needs to be done

(soon)

0celo7

@FenderLesPaul ask Wald how to prove the "easy" thing that took me two pages

ACuriousMind

@DavidZ No worries, I don't think it's that urgent. Sleep well!

0celo7

Night, @DavidZ

@ACuriousMind Mine host Mr. Morton only made a small cameo on my lit midterm

But I managed to work him into the essay ;)

::reads Wald again::

I still am not proving what he says :/

FenderLesPaul

@0celo7 oh ok

will do

I'm seeing him next week on Monday

0celo7

@FenderLesPaul I'm 100% confident that my proof is correct

See the above link

But his "hint" on how to prove it does not make sense

@JohnDuffield I would appreciate an explanation of your downvote

crap Libgen is down

1

Q: Higher-Dimensional Metrics in (Hyper)-Spherical Coordinates

I want to compute the components of the Riemann curvature tensor (for a case similar to the Schwarzschild solution) in 4 + 1 dimensions, but I want to use a higher-dimensional analogue of spherical coordinates. I first want to investigate a metric for the Euclidean case, i.e. "flat" space-time wi...

homework general-relativity curvature metric-tensor

@HDE226868 Did you ever figure this out?

I think I have an algorithm for doing just that written in some personal notes somewhere.

ACuriousMind

17:45

Geez, this user plagiarized even more answers than I first thought

Danu

Link?

ACuriousMind

physics.stackexchange.com/users/109006/drvrm?tab=answers

Look at the more recent ones, I haven't got to the older ones yet

Danu

I'll check it out once I get home

Slereah

So anyway

In the Polyakov action

Does the induced metric mean anything

Is it ever a dynamic quantity

Or is it always just a mathematical trick

ACuriousMind

The induced metric is physical, it is the actual metric on the worldsheet. The dynamical metric $h$ in the Polyakov action is only the induced metric when the equations of motion are fulfilled

The dynamical metric $h$, however, consists purely out of gauge degrees of freedom, its components do not really have meaning afaik

Slereah

17:53

Okay

Because Polchinsky says like "We only use that metric to go from Nambu to Polyakov"

0celo7

*ski

I thought this question was gonna be about number 2

1

Q: Three-log problem

Three uniform round rigid cylindrical logs of the same size and weight are placed on a horizontal plane. The two at the bottom are touching each other, the third one is placed on the top as shown in the picture. The coefficient of friction between any two logs is $\mu_1$, the coefficient of fric...

homework-and-exercises newtonian-mechanics friction equilibrium

I can't say I've ever made three logs.

Slereah

Maybe you need more fibers

fiber bundles

0celo7

Heh

Slereah

Guys

What if

BOTH STRING THEORY AND LQG ARE TRUE

D:

Strings in a spin network

Dun dun duuun

Also I don't know what I'm saying

0celo7

@Slereah so no different than normal

Slereah

17:59

I'm wondering what that would be like

Closed strings are always graviton-like

What would happen if you put them in a dynamic spacetime

0celo7

I've never seen a string theory thing explain how closed strings curve spacetime

Sure you have the beta function vanishing

But that's bullshit

Slereah

How much string theory have you seen tho

0celo7

@ACuriousMind how does it work

Slereah

Also they do not curve spacetime

ACuriousMind

How does what work?

Slereah

18:00

The point of string theory is a fixed background

String theory is basically a fancy Fierz-Pauli

0celo7

how does string theory explain the expanding universe then

Slereah

The metric isn't changing in string theory

The change is whatever closed strings do

0celo7

That's bullshit

Ok but how do the closed strings make stuff change

That's my question

Slereah

Well I don't know string theory

But I guess the same thing as covariant quantum gravity

0celo7

I didn't ask you

Slereah

18:03

Photons and other particles interact with the gravitational field

In a way equivalent to curved spacetime

0celo7

Right and you can show that in string theory.

But how does it work at the level of strings

Slereah

Hopefully yes, but who knows

Isn't string theory like hopelessly unsolvable

dmckee

@ACuriousMind I certainly don't approve of answer like physics.stackexchange.com/a/241063/520

(and especially the first revision) which is simply misleading, but I don't know that we have a policy on them.

My personal opinion is that they should be deleted and a comment liking wikipedia substituted.

Simply because we want rep to represent some kind of positive contribution, rather than the ability to copy material from a widely available reference.

Danu

@yuggib So, after all is said and done

It turns out the model Connes has is classical

(but possibly naturally extends to incorporate quantum corrections [citation needed])

big woop

ACuriousMind

@dmckee Yeah, there is almost no own contribution to those answers, except that the user actually takes care to remove most references to content "above" or "below" and sometimes randomly omits sentences or words. I'm not sure if they do not understand the concept of plagiarism or if they are fully aware this is intellectually dishonest.

dmckee

18:15

Care to post a meta question about it? With a consensus we might be able to do more than merely downvoting them.

ACuriousMind

I'm currently working on marking all quotations in the answers, I'll post the meta question after I'm done with that

dmckee

Thanks.

For both.

@Slereah One in it's own frame of reference. You meat to ask about the Lorentz factor with respect to the air of a unladen swallow.

ACuriousMind

13

Q: Plagiarism checks?

Without mentioning any names, I observe the following. Some answers given on the main site by certain individuals are consistently long and not really relevant to the question, instead giving inappropriate amount of minute and highly technical details related to keywords in the questions - withou...

discussion

@dmckee; We have the above question already, DavidZ says "flag for moderator attention" there.

Also, the user has started to delete some of the posts now

yuggib

@Danu to be honest, of that I had no doubt...as his QFT model is classical I am pretty sure :-P

anyways...big woop indeed

I like better when he uses physics for number theory questions

like when the primes are the spectrum of an operator related to second quantization, or the Riemann hypothesis via a quantum-like trace formula

you can ask about those if he does another lecture ;-)

however I have been told he's not the nicest of guys

so maybe it's better not to ask too much :-D

0celo7

18:32

@dmckee Pedant alert

@ACuriousMind bully!

dmckee

Just trying to parallel the source material as closely as possible. Pedantically.

@ACuriousMind So I think the question of how much acknowledged copying is acceptable isn't really covered in that question.

Which is of course separate from the user's particular brand of unacknowledgment followed by defending the material as "cited".

ACuriousMind

Hm, that's right, I'll ask that specifically

0celo7

imgur.com/a/8eNeX

What's up with that square root

Physics Meta

18:53

0

Q: What is our position on answers that consist almost entirely of copied content?

We know that plagiarism is bad, and unacknowledged citations will be dealt with. However, what about answers that properly acknowledge their sources, but consist of nothing but quotes? I believe such answers do not consititute sufficient effort to be actually counted as answers, and should be ...

discussion answers policy

0celo7

19:19

@ACuriousMind Is Wald wrong?

I've proved that you have to reverse the normal vector, but for a different reason.

Danu

19:44

I'm willing to bet that your proof is flawed, if it leads you to contradict Wald ;)

0celo7

@Danu Please find the error then

Danu

No, I've said many times that I don't like how you keep on pushing everybody to solve your problems for/with you all the time.

0celo7

@Danu Well the answer has 8 upvotes so if there's an error it's subtle

@Danu are you serious

is my proof wrong because it contradicts Wald?

What if I fold you Wald contradicts Lee

I get the same result as Wald does, but I think he is wrong about something

Danu

@0celo7 Then I think you're probably right.

0celo7

:)

HDE 226868

21:10

@0celo7 Uh, I think so? I'm not sure.

0celo7

21:34

@ACuriousMind Have you ever heard of "generic tensor" being used as a technical term?

Slereah

My god why does my bounty question only have crazy answers

0celo7

link

Slereah

8

Q: Do any quantum gravity theories deal with closed timelike curves?

As far as I'm aware, there are no quantum gravity theories that deal directly with closed timelike curves. Some of them (like canonical QG, CDT and LQG) forbid them outright, others merely seem to not discuss the topic. I've found quite a variety of QFT behaviour in classical spacetimes with clos...

general-relativity quantum-gravity closed-timelike-curve

I'm losing my internet points downvoting those clowns

0celo7

lol

> The clue to get this right was the mass-less Froude-number 1=v2/ar1=v2/ar
And the Mass-less Euler Turbomachine YY, m2/s2

> Just a Civil Engineer.

Wow he gives engineers a bad name

ACuriousMind

@Slereah quantum gravity and time travel is a risky combination ;P

Slereah

21:48

Well yes but so many papers are like

"MAYBE THE QUANTUM GRAVITY WILL HELP GET AROUND THE CHRONOLOGY PROTECTION"

You'd think they'd have something around

It is their messiah but nobody is that hurried to go find it

I mean I can see why that's a hope

But I can't really think of any current formalisms dealing directly with it

How hopeful is it, even

I guess you could transition from a causal metric to an acausal one without geodesic CTCs

0celo7

22:04

@ACuriousMind generic tensor :(

Slereah

But I'm not even sure those aren't divergent as well

"The timelike curve is not closed as you expect it to be. And this paper doesn't deal it with the words you expect."

We should have debates between that guy and Duffield

0celo7

I like the third one best

Slereah

How fancy

ACuriousMind

@0celo7 I don't see what about the two words is unclear to you

0celo7

@ACuriousMind what does it mean

ACuriousMind

22:10

A generic X is an X without special properties, some X you might pick at random

0celo7

@ACuriousMind no shit

I was asking if there's some technical thing that's called generic

Slereah

$\forall x$, $x$ does some shit

2

ACuriousMind

@0celo7 X may well be a technical thing.

Slereah

"Just a Civil Engineer. -Like ie. Da Vinci"

Oh my god

that man is bananas

0celo7

@ACuriousMind :/

@ACuriousMind What's with some math books not using Einstein notation when working in coordinates

is it seen as "poor form" by some mathematicians?

ACuriousMind

22:16

Yes, some don't like it

@Slereah Is that the some-shit-theorem one needs for the some-shit-inequality?

0celo7

@ACuriousMind why

ACuriousMind

@0celo7 because

user54412

@ACuriousMind clearly all forall's are inequalitites $\forall... \sphericalangle... \triangleleft... <$

0celo7

@ACuriousMind but why

ACuriousMind

@ChrisWhite ...what?

user54412

22:27

@ACuriousMind exactly what I asked myself while writing that

Slereah

Lots of shit going on in math

0celo7

Granddad smoking weed

►

Danu

Dat quality though

0celo7

@Danu I couldn't do any better

HDE 226868

@ChrisWhite This paper you pointed me to is fantastic and really helpful, although some pages and equations are illegible because of 1) official stamp thingies and 2) terrible photocopying. Do you know if there's a non-photocopied version of it?

0celo7

22:41

@HDE226868 what is that

HDE 226868

@0celo7 Proof that nuclear weapons probably won't cause runaway nitrogen fusion in the atmosphere, thereby possibly causing fusion in ocean water and basically blowing up the planet.

Emphasis on "probably".

0celo7

wth

Danu

@HDE226868 Don't think there is a better version.

HDE 226868

@Danu Awwwww. . .

user54412

@HDE226868 I think the whole point of classified documents is that they don't have lots of other versions floating around :p

0celo7

22:45

> unclassified

HDE 226868

@ChrisWhite Well, yeah, but with the amount of times I've seen the work cited elsewhere, I would have thought that the text could be found somewhere.

The calculations are referred to in pretty much every detailed biography of Bethe I've seen.

user54412

@Danu could re-typeset it... for HSM glory!

user54412

I guess you could always file a freedom of information petition?

HDE 226868

@ChrisWhite Heh, that would be amusing. "I'm requesting a copy of the text of this seminal paper so I can disprove some shmuck on the Internet."

user54412

> The only disquieting feature is that the "safety factor" [...] descends to a value of only 1.6.

user54412

22:53

I can't imagine writing that sentence when discussing the possibility that the secret project I'm working on might detonate the planet.

0celo7

@HDE226868 mb we can exhume Einstein and shut up a certain other schmuck

HDE 226868

@0celo7 Sounds like a good senior thesis project for you, if you can relate it to math or whatever you're studying.

0celo7

23:54

@HDE226868 On the Wrongness of A Certain Physics Stack Exchange User

Transcript for