The h Bar

3:33 AM

@NovaliumCompany Useful if your first name is Paul.

Jake Rose

3:47 AM

@NovaliumCompany please stop the nonsense talk please I’m begging you

Sir Cumference

4:21 AM

@JakeRose Ah come on it's a joke

A bit of nonsense is healthy

5:32 AM

@JakeRose yes.

Secret

5:57 AM

Not just bullies, injustice as an abstract entity also

They knew well that complacency is their ally, and hence they will reign

They are also above the law, thus in order to punish injustice and persecute it, we need to be witty and push them back into the very laws they try to escape from

Rich companies, spy agency, corrupt governments, bullies, environment destruction, cultural degeneration, moral degradation, poverty etc.

they are all but one and the same thing

This year is 2020, the Final Year to fix everything

8:56 AM

@Secret please stop it.

Novalium Company

9:35 AM

wow only 2 people online

A: Sources on Screens and the Gibbons-Hawking term

10:49 AM

Is it possible to hide a question I asked for a while? I ask since I have given it as an assignment to a couple of students and I don't want a part of the answer online.

1

I don't think the GHY term can be obtained this way, at least not directly. The expression $A$ does not contain the trace of the second fundamental form, but rather the jump of the trace of the second fundamental form. If $\kappa_{\mu\nu}$ is defined as $[\partial_\kappa g_{\mu\nu}]=\epsilon n_...

This is the one I want to hide

11:03 AM

@NaveenBalaji No, if a question has received an answer you cannot delete it

(and deletion/undeletion is the only "hiding" mechanism there is)

oh, alright

John Rennie

@NaveenBalaji I guess you could ask the guy who answered to delete their answer ...

Oh ok, thanks!

In any case, I feel deleting a question/answer because you want to hide it from some specific students is not really in the spirit of our site - what about the not-your-students who might be interested in this question and then cannot find it because you wanted to make it slightly harder for some students to cheat?

11:40 AM

Would it be more in the spirit of the site to tell the students where the question is and to encourage them to give an answer to it here?

-or, perhaps, improve on the question

Thanks a lot for the answer. Could you please delete your answer for a while since I am presently taking a course in which an assignment demands this as a partial answer. Please take it off only for a while (about a month and a half), later you can put it back on. Thanks again! — Naveen Balaji 34 mins ago

too late :(

12:08 PM

@skullpatrol Do you know driving?

@Knight yup

@skullpatrol When did you learn it?

@skullpatrol I’m learning it now

Practice makes perfect.

@skullpatrol Did you ever hurt anyone? Lol I mean during your learning period

Nope

It is scary in the beginning.

12:16 PM

How long you took to learn “apply the brakes slowly!”

? Lol

that takes "a feeling" for how the brakes work

the same goes for the gas peddle

Wow! Although I’m good with clutch but when it comes to brakes and when many other drivers city takes blind turns so all I do is to transfer my whole power to brakes

@skullpatrol does gas peddle means the same thing as accelerator ?

Yes

Okay

Learning to use a clutch is harder

12:21 PM

Yeah but I’m good at it, whenever we have to drive in a very narrow place we should drive our car in half clutch? Am I right?

That is called "riding" the clutch, and yes when you need to stop fast you do it that way.

Hi everyone!

Got it

@skullpatrol Do you drive the steering with one hand or both hands?

Both

21 hours ago, by ACuriousMind

> Don't advertise your recent questions. If you just posted something on the main site, give it some time, and don't tell people to go there and look at it. Particularly by pinging people. That's rude. Those who can answer are already watching the queue on the main site!

12:25 PM

Ah okok sorry

Deleted

@ACuriousMind But that's not a homework

he doesn't like "advertising"

@skullpatrol How to know that how wide your car is? I often mistake in this and therefore I get dents and scratches (on my car and on others too)

@Shootforthemoon Whether it is actual homework doesn't matter for our homework policy. It is exactly the kind of calculation request that would show up in a homework exercise.

That takes practice @Knight

Just leave yourself room

HAhahaha okay

12:30 PM

@ACuriousMind I mean, that would explain why we use two different expressions in two different contexts to indicate the same thing. I asked that for understand. Isn't it physics?

A proof is mathematics behind physics

@Shootforthemoon ACM meant that people will see there and you don’t need to post it here

Yes, but he also closed the question as off-topic

@Shootforthemoon Please read the meta posts linked in the closing notice. We don't close homework-like questions because they are "not physics", we close them because a) they are rarely helpful to any users except those having to do the exact same exercise and b) we would be drowned by these questions if we allowed them uncritically.

@Shootforthemoon I know that feels very bad.

Yes, but please see that my question is not an exercise. It is intended to be a theoretical demonstration of what's behind our instruments. I asked it only for a theoretical purpose, and that's why I feel it can be useful also to others.

12:34 PM

@skullpatrol I’m not any good in driving two-wheelers motor cycle.

Can you ride a normal bicycle?

hahahahaha yeah of course

But only light ones not those sophisticated ones

Same idea, no?

But motorcycles are quite heavy and you need to be powerful to make balance in it

Just the idea of an accelerator needs to be mastered

12:38 PM

The front brake is just another form of death

I don’t know why it is there

Yeah, you need to be gentle.

I hurt my shin last week only because I applied that front brake

Gently apply the brakes at first.

Come on, @AC you also put the tag homework XD

Same for a car @Knight

12:41 PM

@skullpatrol the front one or the rear one?

Both

Braking is a skill

30 mins ago, by skullpatrol

Practice makes perfect.

Handling skidding comes much, much later.

You can lose control very quickly.

1:02 PM

@skull patrol hi.

hi pal

@YuvrajSingh...

why the "..." in your username

It is not my real name.

Photo is in my profile is of swami vivekananda

Today is national youth day

Now yuvraj is my favorite cricketer.

So my user name based on that.

None of that explains the ellipsis.

I see.

1:17 PM

Earlier it was just yuvraj singh.

No he retires so.(.....)

Right.

@skull patrol where are you from?

@ACuriousMind sir it becomes hectic that everyone post their question here.

@skull patrol no issue.

The World Cup of cricket final was the closest ever played in over 200 years @YuvrajSingh...

@skull patrol yuvraj singh hit six sixes.

Yeah, extraordinary

1:26 PM

To Stuart broad.

cool

15 Year Old YAASHWIN SARAWANAN Is A HUMAN CALCULATOR! | Asia's Got Talent 2019 on AXN Asia

I was watching this video, is there any trick these guy doing

►

@ACuriousMind

@skullpatrol

1:43 PM

@YuvrajSingh... Dot and Sticks

Ekadhiken Purveen Sutra Vedic Mathematics.

Do you have some link where I can read this @AbhasKumarSinha

@skullpatrol You are german and you know cricket!!?

Cricket is international

Multiply Numbers By Drawing Lines

@YuvrajSingh... Graphical Form:

►

...why would he be German?

1:45 PM

this: - wikihow.com/Multiply-Using-the-Line-Method

why not :P

@skullpatrol really? Does germany plays that?

@AbhasKumarSinha German?

@YuvrajSingh... I saw you on TV when you stormed 6 sixes against Stwart Broad.

@YuvrajSingh... Asfar I know, Germany doesn't plays cricket (doesn't has a team)

@AbhasKumarSinha I was going to hit 12.then I thought leave that poor guy.

After getting 12 sixes, he may try for suicide.

1:48 PM

@YuvrajSingh... I can understand, he angered you.

the shame

@AbhasKumarSinha yes, he saying something in a slow voice.

@YuvrajSingh... After that, he never came in fields against you.

@AbhasKumarSinha kauf hain Mera!

@YuvrajSingh... Brown Socks

@YuvrajSingh... Khaufff!

1:49 PM

English, please.

@YuvrajSingh... You said blank paper

@AbhasKumarSinha no!

@ACuriousMind I was just kicked for writing german.

@skullpatrol Bro, let's talk in General Chat room, we are safe there.

@AbhasKumarSinha You were kicked for doing exactly what I just asked you not to do - write non-English. That the content of your message was "No, we won't do that" wasn't particularly helpful, either.

@ACuriousMind Oh, you can read german... hehheheh okay

1:55 PM

did you look at any of the Human Language link @ACuriousMind?

@skullpatrol Yes, but if I understood correctly I'd have had to pay to watch any of it, right?

@ACuriousMind sorry sir, it all started with me.

@ACuriousMind For how much duration you kicked me?

I think they give a few for free to begin with @ACuriousMind

Just as a hook :P

@AbhasKumarSinha Room owners cannot set the duration of kicks, the first kick is always 1 minute, then 5 minutes, then 30 minutes. It resets after some time.

1:58 PM

@ACuriousMind If I recall correctly, it was for 15 seconds...

15 sec is next to nothing pal

@skullpatrol Didn't look that way to me, I only saw options to buy the whole course or to get their 'Plus' subscription

@skullpatrol Yes pal

@ACuriousMind Do you know Quantum Entanglement?

Sure

@ACuriousMind Qbits?

2:02 PM

askaway pal

@AbhasKumarSinha I did quantum field theory and string theory. You can safely assume I'm familiar with all basic concepts in quantum mechanics.

@skullpatrol Pal the problem is that ama trying building a Quantum Processor....

you will never find out if you don't ask

How to prove entanglement of particles.

I'll write a simpler proof for antimatter particles too.

2. Anomalies in QCD and similar non-Abelian gauge theories

@ACuriousMind right, I think they give it for free on Audible books if you are a member

I forgot you don't listen to audiobooks :P

2:10 PM

@ACuriousMind ....?

@AbhasKumarSinha Yes?

@ACuriousMind Tell me.

Tell you what? You haven't really asked any well-defined question.

6 mins ago, by Abhas Kumar Sinha

How to prove entanglement of particles.

What do you mean by that? What have you given? Do you know the definition of an entangled state?

2:12 PM

@ACuriousMind A state function for 2 particles that can't be separated.

@skullpatrol Pal can you help me?

@AbhasKumarSinha Exactly, so if your function is not separable, then the particles are entangled, otherwise not. What's the question?

@ACuriousMind if your function is separable, then the particles are entangled

Are you sure?

No, I forgot a 'not' :P

@ACuriousMind Example of such function.

sorry

2:16 PM

@skullpatrol no problem pal, we are friends.

First you want a proof of something, now you want an example. Maybe you should first work out what you actually want to know.

@ACuriousMind Can you answer my question? That's even bigger problem -_-

@ACuriousMind Simple mathematical logic - If example exist, it's true, no need to prove.

That's...not how logic works.

@ACuriousMind I doubt if you even understand my question or not.

@ACuriousMind example man example only.

@skullpatrol Can you give me an example?

@AbhasKumarSinha I think that is true for a "counter example," no?

2:21 PM

You can get an example of an inseparable state from any four distinct states $\lvert a_1\rangle, \lvert a_2 \rangle$ and $\lvert b_1 \rangle, \lvert b_2\rangle$ of the two particles ($a$ are states of the first particle, $b$ of the second) by writing $\lvert a_1 \rangle \lvert b_1 \rangle + \lvert a_2 \rangle \lvert b_2 \rangle$

@skullpatrol If you want to statement $A$, then for $x \in S$ if $A(x) = 1$ then $x$ is an example and existance of a single example proves that statement $A$ is true.

@dmckee @ACuriousMind Why do most people (physicists?) associate events happening with "seeing" them happen: "If we cannot see it, it didn't happen or happens in the future". Just because light from beyond the visible universe cannot reach us doesn't mean it lies in our future. Am I missing something?

@ACuriousMind So they are entangled?

@YuvrajSingh... In relativity, "future" is a relative notion, too.

@AbhasKumarSinha Yes.

I got a answer from my friend what he said is.

2:23 PM

@ACuriousMind How to calculate the momentum from the combined state function? Also, if I use usual operators then, I get momentum of whole system combined.

that equating "seeing" with "being" would be a mistake here. I think the OP implicitly seems to have made that mistake. I don't think physicists generally make that mistake, although you may see it in popularizations or in writing by people who lack specialized expertise

@YuvrajSingh... Just because light from beyond the visible universe cannot reach us doesn't mean it lies in our future What are you trying to ask, can you give an example.

People do say "seeing is believing" @YuvrajSingh...

but, "seeing" is a sense impression

@AbhasKumarSinha I don't quite understand why you assume that there's 'momentum' if we're talking about qbits. If we're not talking about qbits, just apply the momentum operator - you'll have to be a bit more precise what you don't understand.

I said, what I meant? @AbhasKumarSinha

2:26 PM

@ACuriousMind My idea is to re-design Logic Gates using entangled photons, to get even faster alternatives to usual logic gates, then I'll make an adder circult, Divider, ALU Circuit from it to phinally get a processor, a quantum processor

"your idea"? Using entangled qbits for logic gates instead of classical bits is what quantum computing is all about!

@ACuriousMind See $i \hbar \nabla$ works for a statefunction. A statefunction is representation of system. If a system is a single particle, then momentum is of single particle. If the statefunction is of 2 particles, then momentum is also combined. So, how to get individual momentum.

@ACuriousMind No, don't steal my idea, it's not good.

@ACuriousMind one abhas finish I have some questions, so if you left with some time please ping me.

@AbhasKumarSinha Sorry, I don't think this conversation will lead anywhere useful. Good luck with your "idea".

@ACuriousMind Okay, but answer my previous message.

2:31 PM

@AbhasKumarSinha Your function for two particles is a function of two positions. If you only take $\nabla$ w.r.t. to one of them, you only get the momentum w.r.t. to one particle.

@YuvrajSingh... Just ask your questions, how often do we have to say this? If I want to answer them I'll come back to them.

@ACuriousMind How to get wrt one of them? They are combined na? They can't be separated! :(

You can differentiate a function $f(x_1,x_2)$ only w.r.t. to its first variable, it doesn't matter whether it's separable or not.

@ACuriousMind But, it's an approximation na? (using infinite series to get the individual functions)

I don't see any series involved here

@ACuriousMind Oh, okay, sorry, I misunderstood, Okay

2:34 PM

@ACuriousMind For example, it can not be said simultaneously that the horizon is an appearance due to the difference of the reference frames (and in fact, as on the sea, it retreats when one approaches it), but that it is also an objective reality which produces physical effects (locally, it can only be traversed in one direction, it produces Hawking radiation, etc.).

@ACuriousMind Second question : Can you prove that local derivative of a Ricci Tensor is equal to the local derivative of 1/2 metric tensor times Ricci Curvature Scalar?

I'm desparate for proof for it.^

@AbhasKumarSinha What does that have to do with any of the other questions?

Are you just asking me random questions?

@ACuriousMind no.

I understood That entanglement thing.

Now, that one^

@YuvrajSingh... Physics has no intrinsic concept of "objective reality"

@ACuriousMind I've some bery great idea, once it completes you'll see, it'd be best.

2:38 PM

It just has models that make predictions.

@skullpatrol Can you answer that?

I have one more example, What you want to say on this

Another example, if the distant observer or universe can only see Hawking radiation once the BH and its horizon really disappeared from the universe, it would be necessary to be able to express this disappearance according to a universal time, which does not exist not in GR. Ditto for the formation of the horizon. The fact that there is no universal time in GR to describe the history of the universe and history in the universe is not the solution but the problem behind all these questions

@ACuriousMind

@ACuriousMind I'll be back tomorrow. I've exams tomorrow, going back to study.

Loong

3:10 PM

grr, stupid captcha, doesn't let me post my answer

heh, it worked when I tried with Internet Explorer, although it says "Sorry, we no longer support Internet Explorer"

Q: Integral over 4 eigenstates of the harmonic oscillator

4:40 PM

1

Let $\psi_n$ be the $n$-th eigenstate to the quantum harmonic oscillator, it is well known that $$\int_{\mathbb R} \psi_n(x) \psi_m(x) \ dx = \delta_{n,m}.$$ I wonder, can we also compute $$\int_{\mathbb R} \psi_{k}(x)\psi_{l}(x) \psi_m(x)\psi_n(x) \ dx?$$ Certainly Mathematica cannot do it...

Ugh

I feel like this should have definitely been closed

Semiclassical

@AaronStevens I'm more confused why it's a physics question vs. an MSE question, given that it's ultimately about computing a definite integral

5:07 PM

@Semiclassical Yeah there are many reasons why I think it should be closed

5:27 PM

I'm very surprised that two high-rep users thought this question that gives no indication of prior research and no indication of physical relevance worth answering.

@ACuriousMind The +500 bounty might have acted as a pair of subconscious blinders.

@AaronStevens The timeline shows that the question never entered review, i.e. no one ever cast a close vote on it.

wait a moment

look at the revision history

OP edited their prior question to something completely different, then immediately bountied it!

Oh snap

Pretty sneaky sis.

Is there some sort of moderator tool to remove bounties when that happens?

Yes

But we can only refund it

Which would make it even better for OP - they got their answer and don't even need to pay the bounty

Oh dang that is a tricky situation.

5:34 PM

Well that's frustrating haha

Were they even question banned, or did they just randomly decide to completely change an old question?

@JMac There may be something even fishier here, but I don't want to talk about it just yet.

@ACuriousMind Understandable. At least they left that nice clue for you.

@ACuriousMind Did they use Reddit karma to fund the bounty? :P

On a completely unrelated note, anyone else here listen to the band Rush?

5:42 PM

Never heard of them

Their drummer (Neil Peart) died this week :( Often called one of the best drummers in the world. He apparently had brain cancer for 3 years and just didn't tell people because he wasn't very public.

Well...wanting not to draw major media attention to one's illness is an understandable move, I think

@ACuriousMind I have some urgent things to do and will be offline for a while. I see you’ve taken action already. We can discuss this at some later time maybe?

Yeah for sure. Just surprised me quite a bit. Especially since when he retired like 5 years ago it was only because he couldn't play at 100% for 3 hour sets every night in his 60's.\

@ZeroTheHero No worries. I just didn't want to delete the existing answers without any warning.

5:58 PM

Yeah I fixed that.

I pinged him by error.

I gotta go now. I’ll find some way to reach you later.

Secret

so a random thought: Is there any theory that proposed spacetime dimensions where the value of that dimension is itself a tensor?

Intuitively I would expect that should be common in background independent theories, but I am not sure

@Secret Non-scalar-valued dimensions do not have any meaning in standard geometry.

Secret

ok

6:51 PM

@ACuriousMind back now...

@AaronStevens I kinda actually disagree with you there. Admittedly it's a borderline case in my mind but this kind of Gaussian integral is prevalent in physics and the expertise to solve it and interest in this would be much greater in physics.

Now there was a follow up comment where the OP asked for a specific case and I thought this additional comment really was too much, i.e. "please do the work for me"

I was completely floored to see the extent to which this question was edited from the original...

I'm comfortable with things the way they are now...

and quite honestly I think more physics context - perhaps linked to the many-particle nature of the problem - would have been helpful.

but there are some math-oriented problems which have a better home in physics and maths, and I thought this was one of them.

@JMac very sad.

especially considerin' the other terrible things that happened in this life.

'couldn't catch a brea.

*break.

7:11 PM

@ZeroTheHero Yeah for sure. It's pretty amazing that he bounced back and kept going so strong after those really rough years.

Yeah... Geddy and Alex were doing all the promo stuff to "shelter" Neil from having to answer personal questions.

anyways... very sad.

That band produced some magical tracks... "La villa Strangiato"...

Haha I have Rush in Rio playing in the background right now and La Villa just started

personally prefer the "Exit Stage Left" version...

That's the one that actually includes the intro solo, isn't it? I think that's probably my favourite version too

you into drumming in a big way?

7:23 PM

Not really no. I'm personally not very music oriented

or musically inclined might be a better word

when I was a grad student I shared a flat with a guy doing an undergraduate degree in musical composition.

it kinda open my ears ... so to speak.

He would bring all kinds of non-commercial stuff... like only the brass sections of Stravinsky...

or only the string section of something else...

pretty amazing to hear these sections by themselves without the big orchestration around it.

gives a totally different appreciation of music.

Yeah that's something you wouldn't hear very often in isolation unless you were actually performing it yourself I would guess

yes the way these parts are arranged was what mattered to him as a composer.

Oh my, the rush in rio version of La Villa has a 4 minute part added in where they let Alex on the mic

8:33 PM

@ZeroTheHero I agree that important integrals appear in physics. My problem isn't with the subject, but with the question itself. The question is essentially just "how do I do this integral?" It's an off-topic question for this site, even if its subject is relevant to physics.

@ACuriousMind I had requested the person who answered my question to take it down temporarily. I want him to re-post it once the course I am teaching is done. Is there a way to hide the question?

@AaronStevens well... I would have let it pass but honestly it's not that big of a deal AFAI'm concerned.

I actually happen to think these problems are kinda cool to investigate from an oscillator perspective - ref my answer . Admittedly I had a student look at a similar problem a couple of years ago so I'm terribly partial.

Totally puzzled as to why this question was basically completely changed. Not sure of the advantage of doing this to be honest.

dmckee

11:07 PM

@JMac I’ve seen them in concert four times, and have all the studio albums. I don’t actually have the Rio concert album.

@dmckee Oh nice. I was lucky enough to see them live once. They definitely put on a good show.

dmckee

Peart was always shy of either media or fan attention.

It was definitely fitting that people didn't know about his cancer and word of his death wasn't even shared for 3 days.

dmckee

Yeah.

I did go home and put their whole discography on shuffle.