The h Bar

hahahaha

@0celo7 Flag it or not?

@0celo7 Now look at the answer to it

Finally I got a chance to use that link

homepage.ntlworld.com/jonathan.deboynepollard/FGA/…

@BernardMeurer awesome answer.

@HariPrasad :p

6:11 PM

@0celo7 @BernardMeurer He says he was told to change 0.14 PSI into m/s

lol

6:33 PM

$k$ is a function of the comoving density, which is constant. That's why $k$ is constant.

@JohnRennie Please elaborate on that.

@0celo7 The correct response is "Might you elaborate on that?" :P

@ACuriousMind Proof?

Curious fact: Our top five referrers are StackOverflow (with 61.2%), facebook (11.6%), news360.com (9.9%), reddit (6.1%) and askubuntu (2.7%).

2

@0celo7 see the derivation. k tells you where you are relative to the critical density.

6:41 PM

@0celo7 Obvious.

What the hell is news360.com?

I'm more puzzled why SO would link to us so often

@JohnRennie still behind FLRW metric?

@JohnRennie So it's only constant if it solves the EFE?

The EFE tells us k depends on the density

comoving density that is

6:42 PM

I hadn't even considered the EFE.

and the density is constant in comoving coordinates

I was looking at this purely geometrically, not analytically.

@ACuriousMind I blame the HNQ bar

@EmilioPisanty Ah, that makes sense.

@ACuriousMind You'd hope for analytics that at least account for that

6:44 PM

@JohnRennie not near any GR books, what equation are you looking at specifically?

but no, not really, says the SE team

it also classes duckduckgo as a referral instead of a search engine, though that is just simply google analytics being a bit of a moron

@0celo7 I'm at my brother's house at the moment (sorting his broadband) so I don't have my books to hand. I worked it out during the four hour drive to my brothers.

You have the Robertson-Walker equation memorized?

Or whatever it's called

Well yes, it's pretty simple. Just the Minkowski metric in polar coords, all multiplied by a(t) and with a factor of 1/(1+kr^2).

No the equation you get when you plug that into the Einstein equations

If you can calculate the Einstein tensor in your head...I'm pretty damn impressed

So there's $3(\dot a/a)^2=8\pi\rho-3k/a^2$

That it?

6:50 PM

@0celo7 I can prove mathematically that gauge theories with spontaneous symmetry are renormalizable "in my mind" :P

Good for you?

I can't solve a quadratic equation in my head

@HariPrasad I am highly sceptical of that :P

@0celo7 No, I can't remember that :-) I only thought of it in the car, so I'll need to sort the details when I get home. Or do some frenzied Googling.

@ACuriousMind I remember that proof (or something similar) taking Weinberg many pages.

What does "frenzied" mean?

6:53 PM

frenzied: with your ass on fire

Well google says: "wildly excited or uncontrolled".

I like Bernie's description better.

@ACuriousMind Yah i too. But google's answer seems creepy.

@ACuriousMind Who?

@0celo7 Not going to explain this to you again.

Q: Is it possible to integrate a function over a null hypersurface?

6:58 PM

:(

2

For $f$ a compactly supported function on a spacetime $(\mathcal{M},g)$, one may define its integral over $\mathcal{M}$ by $$f\longmapsto \int_\mathcal{M}\star f,$$ where $\star$ is the Hodge star of $\mathcal{M}$. Since $\star$ is unique, this map is canonical. Suppose that $\Sigma$ is a null h...

general-relativity mathematical-physics differential-geometry

@ACuriousMind Uh, what now?

You wanna write the answer?

Does anyone here have a solution to EPR Paradox? I'am done with it now.

@0celo7 What?

@ACuriousMind Valter comment answered it.

Why would I write the answer to that?

Because I don't want to steal his answer.

And he probably won't write one.

6:59 PM

lol, and it's fine for me to steal it, or what?

Yes.

Besides, when it's a comment, it is perfectly fine to take the comment and turn it into an answer, though it is good form to first ask the commenter to turn it into an answer themselves.

@ACuriousMind done.

@ACuriousMind I'm considering to make a dictionary "Honest descriptions of casual words"

@ACuriousMind would you close "is a hypersurface consisting of null geodesics a null hypersurface" as off-topic?

7:02 PM

OK a serious question now. Why quantum cloning is impossible. Is it because it violates conservation of probability? or is it something else?

@0celo7 I think that would be completely on-topc at math.SE, and here I would not act either way on it (i.e. neither vote to leave open nor vote to close).

@ACuriousMind How can I ping Valter? He'd know the answer

@0celo7 You can't.

@ACuriousMind sigh...

@ACuriousMind ooooh, working on a proof. If I forget, remind me I want to show that any null hypersurface might be the union of a bunch of achronal surfaces

I am not your personal assistant.

7:18 PM

@ACuriousMind maybe not!

vzn

@0celo7 wondering. are you taking GR class(es)? not reqd for your (nuclear engr) major are they?

7:40 PM

@vzn No, no

7:52 PM

@0celo7 Know web programming?

@HariPrasad no

it is false that $\Delta x \Delta v = h/4pi$...right?

in heisenberg uncertainity principle

rd.springer.com/book/10.1007/978-3-319-19000-6

> Black-Hole Bombs

what does it have to do with black holes?

@manshu 1. Don't use $v$. Velocity is not a quantum-mechanical operator, the proper thing to use is momentum $p$. 2. Yes, it's $\geq$, not $=$.

7:57 PM

@ACuriousMind i only asked bcz my practice sheet had marked it as correct...thanks for clarification.. :)

> Algebraic K-theory of Crystallographic Groups

@ACuriousMind Will this help me with neutron scattering experiments in crystals?

@0celo7 How the heck am I supposed to know?

@ACuriousMind We've been over this

You're the smart one

@0celo7 And you won't ever get smart if you keep relying on me.

4

If I have you I don't need to be smart

8:03 PM

Your skill in compressing entitlement into a few simple words is amazing.

@ACuriousMind My skills are amazing, yes.

how to use a sword then?

@manshu I can teach you

what is the first lesson Mr. Miyagi?

Who?

8:09 PM

Hey-o

oh hey

@Danu Hey.

hey

@ChrisWhite Massive gravity... as in what? Perturbative expansion around $\eta$ with a massive field?

@Danu Would you happen to know the proof that the boundary of the light cone is a null hypersurface? (Yes, I've googled it, no it's not anywhere obvious.)

8:19 PM

Hey guys I'm seeing another discussion with JD again @DanielSank @ACuriousMind; can't we all just try to get over it and stop this?

@0celo7 I'm pretty sure there is a way of defining hull hypersurfaces that makes this a trivial consequence.

I'm not very interested in being pedantic about it

@Danu I am currently ignoring him.

@ACuriousMind Thanks---I really think it's best if we all try to just resist temptation

@BernardMeurer You too ^^^^

hey i am unable to post any answer on Physics SE

Do you guys know how to select multiple items in a file that are not consecutive?

@DanielSank Ah---I see I should've read a bit further.

@0celo7 Lmao. Use Ctrl

8:22 PM

How come I'm not being told to stop?

@ACuriousMind Me too what?

@Danu Why are you laughing?

@0celo7 use Ctrl and then click with mouse on that file

@0celo7 Because it's simple

@BernardMeurer That was Danu, not me

8:22 PM

@Danu Oh cool, thanks.

Never heard of that before.

@BernardMeurer The upward arrows guide you to the relevant message

@ACuriousMind i am unable to post any answer on Physics SE

@ACuriousMind Btw I've almost got bingo ;)

@Danu I was considering posting a random "Bingo!" yesterday but then I decided it would not be constructive :P

@sharafzaman That's too bad. How are you unable?

I.e. what happens when you try to post one?

@ACuriousMind I'm actually keeping track :)

8:25 PM

@ACuriousMind this message pops up "We are no longer accepting answers from this account" :(

That means you posted too many bad answers before. Sorry to tell you.

@sharafzaman Yeah, that means you've posted too much crap so you were blocked.

lol!! but i have posted only 2 question on Physics SE

You never posted an answer?

it looks like you don't have any negative votes

8:27 PM

yes!!!

@0celo7 You're discounting deleted answers.

@sharafzaman Looking at your account, you have at least two answers, too. And I suspect there are more that are deleted.

@Danu True

And honestly, the two answers that are not are also kind of bad.

So I'm not exactly inclined to do anything to help you get around this.

dmckee

@sharafzaman I can confirm ACuriousMind's conjecture. There are four deleted answers with a net -3 score.

8:28 PM

oh!!! yaaa i remember yesterday i deleted two answers because they were impossible for me to explain
haahahaha

does it mean i can never post answer here

dmckee

The answer ban is fairly aggressive with new accounts, but I think it will time out eventually. However, in the mean time you could working on improving the answer that you still up.

Right... So these answers were bad. You should aim to only post good answers :P

@dmckee care to respond in the other chat?

dmckee

A few up-votes goes a long way to getting you out of the a-ban (or the q-ban).

@0celo7 Also see the above---stop biting please.

oh!! i c!

can i post answers on other sites

8:31 PM

@Danu I'm latino, resisting the temptation is not exactly my specialty :p

Jokes aside you're right and I won't respond any longer

@ACuriousMind It's exactly this---in both cases one needs to do the proper "Stueckelberg accounting" of degrees of freedom.

Unless he comes with that "It's all jelly" thing again

No, just get over it.

@Danu @ChrisWhite, see linked message

The Stueckelberg formalism is really great for understanding massive/massless gauge field issues

8:37 PM

@Danu that was a joke inside a joke

too bad I'm bad at jokes

@yuggib You, too, should stop taking the bait.

@ACuriousMind is there any way to see question which i have marked a star

@sharafzaman Geez, I'm not your personal SE guide

Everyone stop asking me random questions!

6

@ACuriousMind What's your fav fruit?

@BernardMeurer Okay, lol

8:38 PM

@ACuriousMind but you are much familiar with this site

@ACuriousMind Is Austria a real place?

@ACuriousMind I still wonder why you keep being patient with ocelot ;)

lol

@sharafzaman Yes, and I didn't get this familiar by asking someone. I just looked around, figuring things out. On my own. It's not that hard.

@Danu Because @ACuriousMind Reads Schop and is part Buddha

8:41 PM

@BernardMeurer Your fanboy comments are also getting boring

Meh, reading the transcript really ruined my mood.

Please, everybody cut the god damn arguing with JD out.

@ACuriousMind i am enjoying on your research of SE, like everyone are enjoying albert enestien's research

@Danu Nice way of being a dick :)

I'll be off, have a good one

@sharafzaman I have no idea what that means.

@Danu Wow

@ACuriousMind lol

hmm!!! just have a conclusion you are Albert Einestien of this site!!

8:46 PM

@BernardMeurer He's just mean

lol

@0celo7 grumpy*

^ACM

@Danu Are you always grumpy?

@sharafzaman That's ridiculous.

Q: Will relative velocity of light exceed $c$?

-1

Suppose I'm standing a few light minutes away from a light emitting object, as soon as the light is turned on, I project myself towards the object with some speed. Will the relative velocity of my speed and $c$ add up to give a velocity higher than speed of light?

speed-of-light

@0celo7 If you ponder the three stars on my "you won't ever get smart" comment, it appears he is not the only one wondering that.

8:49 PM

because of this stupid question i can't answer any question

@ACuriousMind huh?

@ACuriousMind And I never even saw that message ;)

i think someone should change room title from h Bar to discussion with ACuriousMind!!! lol

2

DanielSank

@Danu Yup. That ignore button is pretty easy to click.

?

9:05 PM

@dmckee He'd be my QM prof: researchgate.net/profile/Cristian_Batista