The h Bar - 2020-01-19

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12:21 AM

@ACuriousMind true. But it has some issues with the answer they want in the example sheet sadly.

If I have a particle in a box, and I add a perturbation to the hamiltonian of the form $eEz$, then can I use time independent perturbation theory? Then just take on the time dependence later on?

12:42 AM

15 hours ago, by skullpatrol

the moustache joined to the side burns has a 70s look to it

Sideburns, sideboards, or side whiskers are facial hair grown on the sides of the face, extending from the hairline to run parallel to or beyond the ears. The term sideburns is a 19th-century corruption of the original burnsides, named after American Civil War general Ambrose Burnside, a man known for his unusual facial hairstyle that connected thick sideburns by way of a moustache, but left the chin clean-shaven. == Variations == Sideburns can be worn and grown in combination with other styles of facial hair, such as the moustache or goatee, but once they extend from ear to ear via the chin they...

1:06 AM

user image

1:18 AM

8

Q: Does momentum conservation imply energy conservation?

I was trying to figure out the situation in which energy is conserved and momentum is not and it was quite easy to find out one case which is of a stone tied to a string moving in a uniform circular motion. Then I thought to consider the reverse situation in which momentum is conserved but energ...

newtonian-mechanics energy momentum conservation-laws symmetry

Please I need perspective of this community regarding my recent question. I had this false intuition that momentum conservation imply energy conservation but a part inside me told that might not the case. I thought that since they arise from different symmetries then it might be the case that they are independent, but I also thought that since space and time are related then what can I conclude. ....

You tagged your question newtonian-mechanics. In Newtonian mechanics, time and space are not related at all.

And beyond Newtonian mechanics, i.e. in relativity, time and space are not separate concepts, so neither are energy and momentum.

So what I did was to form a question which asked for falsification of any of the thoughts that I had which were incorrect. And I got an answer. Even though it completely answered my question by giving a particular example against the case and hence falsifying (Isn't that the real science?).

But I have found that a user pointed out that there are other good answers so why did I accept a two liner? So I would like to know what are your perspective on this question? (like is it poorly written or something else?)

1:33 AM

@JohanLiebert 1. You should always accept the answer you found most helpful. Accepts are like votes, no one can tell you how to use them. 2. I think the question suffers from this bit: "To me it seems that as soon as we chose a system in which momentum is conserved then it automatically is implied that in such system energy is conserved too.", but you never explain to us why it seems to you that way.

So you get a zoo of answers that all point out in one way or another (if they are correct) that momentum conversation does not imply energy conservation. But we can't really tell if they told you what you wanted to know, because you never revealed to us how you came to this idea in the first place.

@ACuriousMind but I think that modifying the question now would not be correct to add that information?

Indeed, you should not edit a question in a way that invalidates existing answers.

Stop and think about when and where you first developed your misconception

@skullpatrol I think that goes back to when I was in class 9th. I even tried to prove that momentum conservation imply energy conservation! But later failed and said to myself that I don't have proper tools to do so but I might be able to that in near future (like when I go to UG)!

Ok, now go and dig up those notes and re-examine your thinking.

1:43 AM

@JohanLiebert FWIW, the first thing I thought when I read your Q is "OP doesn't define what the system is, so it's easy to come up with ones where momentum is conserved but energy isn't." Which is why you got so many answers talking about heat transfer from a body to places outside of the "system"

@skullpatrol ...in what world do you live where people keep notes from 9th grade?

he's in 12th now

@skullpatrol In what world do you live where people took notes in 9th grade :P

lol

@ACuriousMind @skullpatrol actually I have a vivid memory of what I did back then (but as you know without proper knowledge I wasn't able to use proper reasoning)!

1:46 AM

ok, at least look at the textbook that gave you that incorrect idea...

Correct me if I'm wrong but currently I have this view regarding the question : " A question acts as a substrate to host the answers and hence it is isn't like what the OP accepts is the true answer to the question rather others too are correct and hence accept tick given by OP should not act as a determining factor."

That's a lot of words and I'm not sure what it's trying to say... but what ACM said is correct: select the one that helped you the most.

That may not be the one that helps me the most when I stumble on your question

But that's okay. It's just signifying that it helped you the most

And when I get to the question, I vote for the ones that helped me

@tpg2114t @ACuriousMind yes you are correct. Thanks for clarifying it. Now I don't feel guilty about it.

We see that a lot on questions where somebody posts a "plain english" way to answer a question, and somebody else posts the "PhD-level obscure math" way to answer it. Both are equally correct, but the OP may not understand the math one, or maybe they needed the math details but didn't specify. So they pick one

But other people, later, who have the same question may think the other is "better"

Ultimately though -- don't feel guilty about using the tools they way they are supposed to be used. It's only fake internet points, after all

if a two-liner clears up your misconception, then you have nothing to feel guilty about @JohanLiebert

2:09 AM

@ACuriousMind why doesn't the protected notice appear to me when I look at my question?

@JohanLiebert Since they redesigned the notices, there's no explicit "protected" notice anymore, just the "highly active question" banner at the top.

@ACuriousMind when I looked at the edit history I found that the question has been protected but the highly active question notice appears in incognito tab or a different browser in which I have not logged in. Why is this the case?

No idea

But I guess it's not really relevant to you that the question is protected if it's your own?

144

Q: What is a “protected” or "highly active" question?

Questions can be protected (i.e. marked "highly active"). What does it mean for a question to be protected? Why are some questions protected? Who can protect and unprotect questions? Who can answer a protected question? How are protected questions displayed? When should I protect or unprotect a...

support faq terminology protected-questions

@ACuriousMind how are protected question displayed? There it answers the question.

2:34 AM

@JohanLiebert If you look at this question: physics.stackexchange.com/questions/525262/… you'll see what it looks like for a protected question when you aren't OP

If it doesn't show the post notice to you on your question that is protected, it's probably because it doesn't impact you -- it's intended for people who want to answer the question, not for the people who ask it (I suppose... I don't know what you're seeing exactly)

4 hours later…

6:51 AM

I want you all to tell me something. Does my inability to solve a problem implies that I'm not in Physics or Maths?

Consider this scenario: I began studying Integral Calculus, followed a well accepted book ,say Stewart Calculus, I solved all the problems that were in the book and became good in integration (according to me). But one day, someone gave me a problem on evaluating an indefinite integral, I tired diligently and enthusiastically but ended with a failure.

Now, does this imply that I need to study even more? Or is it all right, all I need is to accept it as a failure and learn how to solve that problem and move on? Or should I declare myself a stupid as even after studying a well accepted book I made a joker of myself by being unable to solve that given problem from someone?

Please tell me the truth, the whole truth with logic being explicit in your reply.

7:55 AM

@tpg2114 actually given my current status (wrt to my reputation) I would not be able to see that banner unless I have 15k+ reputation.(👇).

5

A: Remove or make "Highly active question" post notice less visible / annoying

The Highly Active Question banner is now only shown to users who either do not have enough rep to answer (10 earned rep), or who have enough rep to unprotect (15K earned rep). Users who are in between these two privilege levels (and thus are able to answer, but can't do anything about the prote...

@descheleschilder

@descheleschilder the reason that I accepted that answer was because it provided a counter example of the statement I made that "momentum conservation implies energy conservation". Now I think in the field of science it is sufficient to provide a counter example to prove something wrong and hence even if it is a two liner it does help.

1 hour later…

9:20 AM

@Knight it just means integration is hard

9:38 AM

Hi @Mithrandir24601

@Knight have a look at this integral!

$5 Integral Vs. $500 Integral

@JohnRennie lol my mathjax is rendering on the title

@SirCumference me too :-)

Novalium Company

10:08 AM

@JohnRennie bit sad cuz I don't understand anything in the vid :P

@NovaliumCompany that's OK, neither do I :-)

10:53 AM

@Mithrandir24601 If you are available, I just have a quick QM computing query...

Mithrandir24601

@JohnDoe ask away, but the usual no guarantee of a quick or even right answer applies as per usual

@Mithrandir24601 Thanks. Are you familiar with graph states?

Mithrandir24601

@JohnDoe I know of them but they're not something I've particularly studied

@Mithrandir24601 Okay is not really about them but the queried paper is about graph states. I will type the question now...

@Mithrandir24601 In [this paper](https://arxiv.org/abs/1908.05047) on page 3, equation (22) given some observable $S_M$ on $n$-qubits. We are given the expectation values
$$\langle S_m \rangle = 1-(\theta^2/2)\mathcal{Q}(G) + \mathcal{O}(\theta^3)~~\text{and}~~\langle S_M^2\rangle = 1$$ where $\mathcal{O}$ is Big-O notation.
They then evaluate error propagation formula $\Delta \theta^2$, hence we need to show $$\Delta \theta^2 = \frac{\Delta S^2_M}{|\partial_{\theta}\langle S_M \rangle|^2} = \frac{\theta^2 \mathcal{Q}(G) + \mathcal{O}(\theta^3)}{\theta^2\mathcal{Q}(G)^2 + \mathcal{O}(\theta…

@Mithrandir24601 The query is about evaluating the derivative of a expectation value which contains a Big-O notation term.

@Mithrandir24601 I can show that the expectation value $\langle S_M \rangle$ is differentiable at $\theta = 0$...But I think to get the correct expression I need the derivative for all $\theta$.

Mithrandir24601

11:27 AM

@JohnDoe Nah, you're still taking things to $\mathcal O(\theta^3)$ and the $\partial_{\theta}\langle S_M \rangle$ is squared

so $\partial_\theta\mathcal O(\theta^2) + \mathcal O(\theta^3) = \mathcal O(\theta) + \mathcal O(\theta^2)$

Which is then squared, so the terms in $\mathcal O(\theta^3)$ are as ignored as they've ever been

Having said that, I don't think they way they've written it is particularly helpful, as you have no way of knowing whether this is a small number, a big number, or 1...

@Mithrandir24601 How do you get this "$\partial_\theta\mathcal O(\theta^2) + \mathcal O(\theta^3) = \mathcal O(\theta) + \mathcal O(\theta^2)$"? for the derivative do we not need $\partial_\theta\mathcal O(\theta^3)$ instead of $\partial_\theta\mathcal O(\theta^2)$?

Mithrandir24601

@JohnDoe No, because $\lvert\partial_\theta \theta^2 f/2 + \mathcal O(\theta^3)\rvert^2 = \lvert\theta f + \mathcal O(\theta^2)\rvert^2 = \theta^2 f^2 + \mathcal O(\theta^3)$

@Mithrandir24601 Getting confusing...What is $f$?

Mithrandir24601

@JohnDoe $\mathcal Q(G)$

Ah, what a nice salad of symbols for breakfast.

Mithrandir24601

11:38 AM

@ACuriousMind Perfect alongside my oolong tea :)

More like $\mathcal{O}\mathcal{O}$long, right?

Mithrandir24601

@ACuriousMind Ooooh, I dunno... $\mathcal O(oooooooooooooooo)$?

Or is that too cryptic for a Sunday morning? :P

I've been awake for about 15 minutes and the coffee is still brewing, so...yes? :P

Mithrandir24601

@ACuriousMind 15 minutes to brew coffee?

Or are you telling me that it's not the first thing you put on?

...it's not the first thing if certain bodily functions take precedence :P

11:44 AM

@Mithrandir24601 Oh okay that makes sense. Where did you get this "$\partial_\theta\mathcal O(\theta^2) + \mathcal O(\theta^3) = \mathcal O(\theta) + \mathcal O(\theta^2)$" result?

Mithrandir24601

@ACuriousMind Ummm... Forget I asked?

:P

Don't ask the question if you can't handle the answer :D

Mithrandir24601

@ACuriousMind Haha! "Don't ask about asking, just ask. But you have to be able to handle the answer"

@JohnDoe As in, $\partial_\theta\left(\mathcal O(\theta^2) + \mathcal O(\theta^3)\right) = \partial_\theta\mathcal O(\theta^2) + \partial_\theta\mathcal O(\theta^3) = \mathcal O(\theta) + \mathcal O(\theta^2)$

I'm not using notation properly because we're in chat and it's a bit of a mess

@ACuriousMind Some questions on the main sites look like "fire and forget"; i.e. ask and never come back to check the comments or answers.

2

@Loong Some people order drunk on Amazon, then forget they ordered. Less thrifty drunks might ask SE questions instead? :P

11:52 AM

@Mithrandir24601 Oh okay, I wasn't reading the expression correctly without the brackets. This makes sense thanks a lot.

Mithrandir24601

@JohnDoe No problem :)

Ugh. I need one of those "Did you call first?" doormats.

Novalium Company

12:10 PM

How to market a wearable device so that the users do not feel socially awkward going out with it?

12:50 PM

@NovaliumCompany Clever marketing, which can get very expensive, and isn't guaranteed to work. Eg, product placement in a smash hit movie.

1:02 PM

Just put a symbol of a half-eaten fruit on it

Yuvraj Singh...

1:22 PM

@PM2Ring hi sir! How are you?

I have some GR questions if you have some time?

@YuvrajSingh... I am upset with you. As I've told you before, you cannot copy other people's work without attribution. Your answer here is copied from this comment:

I would like to endorse Raskolnikov's important comment, too. Energy is not something one starts with while constructing a theory; energy is a "cherry on pie" that one can find out to be conserved. It is given by a fixed formula that can be found and when this formula is evaluated at any time, the number is always the same. It didn't have to exist at all. However, energy is really special because the information about the formula for the energy is equivalent to the information about the way how the system evolves in time - so it's a bit more fundamental than Raskolnikov suggests. — Luboš Motl Jan 16 '11 at 18:01

Yuvraj Singh...

Sorry, actually as the comments address the answer of that question quite well so I use them.

@PM2Ring

I deleted them.

And question consist of two of the question which was asked earlier.

Sorry If I disappoint you. Again.

I would write my own answer.

Do you still angry with me? @PM2Ring

@YuvrajSingh... It's ok to use other people's work. But it's not ok to do it without proper attribution. It's bad manners, dishonest, and a violation of copyright law and the terms of the CC-by-SA licence that covers the material published on Stack Exchange sites.

@YuvrajSingh... I'm not angry, but I am upset that you did this again after I caught you doing it last time.

@YuvrajSingh... Just ask your question. I might be able to help, I might not. As has been explained many times, you shouldn't target specific people in chat with your questions, unless it's part of an ongoing discussion, or you know that the specific person is likely to be very interested in discussing the topic. Targeting an individual with your questions makes you look like a help vampire...

Yuvraj Singh...

1:41 PM

@PM2Ring I do sir! I will take this advice with me forever.

Yes sorry sir I said to ACM for that.

And he explained me when to ping someone.

And from that time, I never ping anybody I just question and that, s it.

Now if you haven, t caught me then too, I was going to delete the answer.

Because I felt that, s not right. Thank you sir for guiding me, forgive me as kid.

I promise you that I will never ever use any body comment or answer without attribution.

Does anyone know why we only migrate to Math.SE and meta.Physics.SE? Actually I wanted a question to be migrated to other site (and have raised a custom moderator flag) but later I found that in the off-topic flag there was an option for migration to these sites but not others. Why?

@JohanLiebert they tend to be the most relevant

just saves hassle

@JakeRose so should I just delete the post here and repost it on the target site?

Yuvraj Singh...

@JohanLiebert ask the moderator they will surely transfer that post to another site.

It’s not a bad idea, I’ve done it myself before.

Yuvraj Singh...

1:48 PM

If they find it.

its usually the quickest and easiest

@YuvrajSingh... Ok, I forgive you. But please don't use the excuse that you're just a kid. Young people are welcome here, but they're expected to do their best to behave in a mature fashion.

I heard somebody had a GR question?

let me procrastinate my own GR work with it

Yuvraj Singh...

@PM2Ring Thank you, sir, hope you forgive me from heart because I do not want that you remain angry with me.

@JakeRose I was going to ask but before that this happen!

@JakeRose so should I just retract the flag now or wait and see what happens next?

1:51 PM

@JohanLiebert See physics.meta.stackexchange.com/a/10232/50583 and its linked posts

@YuvrajSingh... if you have a question just ask

Yuvraj Singh...

Is there exist a point or points within the universe in which time is least contracted due to relativistic effects?

@JohanLiebert The problem with migration is that if you make it too easy then low quality questions posted on one site will get dumped on another site where it's more on-topic but still low quality. That's especially a problem if the destination site is less busy than the original site, since they have less people who can deal with the influx of unwanted questions. And it's not a great experience for the OP either if they get negative feedback on both the sites.

@YuvrajSingh... Let me add two things: 1. If you see a question that is the same as earlier ones, flag it as a duplicate instead of answering it. 2. You should not mainly be concerned with PM2Ring's "anger" at you here. Repeated plagiarism - i.e. quoting material without mentioning where you quoted it from - will get you suspended on the site.

@YuvrajSingh... what do you mena

Yuvraj Singh...

2:00 PM

@ACuriousMind I do sir.

I will not repeat such action.

In future, I take your thing a permanent note.

@JakeRose leave it! I do not want to discuss it now.

@YuvrajSingh... Asking a question and then telling people to leave it instead of clarifying is rather rude. Please be respectful of the time others are willing to spend on you.

Yuvraj Singh...

@ACuriousMind sir some urgent work come up, so I have to leave that in between, leaving doesn, t Mean that I behave rude, it just that I want postpone the discussion, hope now sir you agree with comment and you will not treat the comment as rude.

@JakeRose thanks, and I will clarify what it mean, but it take some time to finish that work hope you understand, and once again thank you for showing interest in my question.

@ACuriousMind For you 😇😇

2

Q: Conceptual block on energy transfer

I recently posted a question about energy transfer in oblique elastic collisions between equal mass balls, asking how much energy the slower ball can transfer to the faster ball. The correct answer that the slower ball can transfer all of its energy to the faster ball was posted, and I liked the ...

newtonian-mechanics thermodynamics education

@J. Murray - I agree with your assessment. It's more about teaching physics and avoiding leading people down wrong paths than about the physics itself. — looksquirrel101 10 hours ago

user444094

2:16 PM

Just curious, how does an up quark and an anti down quark destroy each other when they are different particles?

This question is clearly off topic. But is it off topic due "details of clarity" or "balantly off topic"?

@PeterBarendt They don't - they form e.g. pions

Abhas Kumar Sinha

yo yo yo

@JohanLiebert Don't sweat close reasons. You don't need to pick the "perfect" one, just pick one that fits.

Then leave a comment if you feel you need to explain it, as I just did there.

Abhas Kumar Sinha

@ACuriousMind Moderators should not say that.

2:26 PM

@AbhasKumarSinha Who said loose motions is exclusively used in India?

@AbhasKumarSinha Why not? A question can be off-topic for multiple reasons. It's not necessary to figure out which of these reasons is the most "important" one to know it is still off-topic.

Abhas Kumar Sinha

@ACuriousMind You don't need to pick the "perfect" one

@AbhasKumarSinha I really do not want to argue with you anymore.

@AbhasKumarSinha Yes, that's what I said. Please express your problem with my statement in a coherent sentence so that I can understand where you're coming from.

Abhas Kumar Sinha

leave it, Today I had one of the best days, dun wanna spoil that.

user image

hehehehe

2:30 PM

@AbhasKumarSinha You started this conversation by telling me what I should not say! Please just don't say anything to me if you aren't willing to explain yourself.

Abhas Kumar Sinha

@ACuriousMind I wanted to tell, but I realized that I'd be wasting my time.

@AbhasKumarSinha My friend, do you realise that Bjoern Jueliger is double of your age (no joke is intended) and you should respect him

→ 4 messages moved to Trash

@Knight Please don't use my real name unless it's relevant to the conversation. It's not a secret, but on the internet, I'm ACM.

And no, you shouldn't respect me just because I'm older! That's one of the most terrible reasons to respect someone.

4

Doesn’t age imply more experience which in turn is real knowledge?

@Knight You don't think people can have experiences which leads them further from real knowledge?

2:36 PM

I've met clueless septagenerians and wise teens. On average, age may make you wiser, but the standard deviation is rather high :P

No. If you are in this chat room and you’re older than me then it implies with all possible induction that you will be having more experience and hence knowledge than me @JMac

I believe JMac's point was that people can have experiences that make them worse. Humans do not continuously improve over their lifetime!

Abhas Kumar Sinha

Yep

Well I would love to know examples of that.

Abhas Kumar Sinha

@ACuriousMind +1 star for it.

2:38 PM

@Knight That seems like such a weird assumption to me. My physics knowledge has actually declined in the past ~6 years because I've been out of school and this is basically the only way I keep my physics knowledge relevant at all.

Abhas Kumar Sinha

@Knight Joker

Ama back.

@Knight Flat Earthers are the obvious example that came to my mind. Most of them didn't believe the Earth was flat until they "educated" themselves with too many youtube videos.

@AbhasKumarSinha Do you have gastritis?

Abhas Kumar Sinha

@Knight I'm fit with my 8 packs.

@AbhasKumarSinha You have more than 1 eight-pack? That must be uncomfortable.

Abhas Kumar Sinha

2:41 PM

@JMac hehehehe. No single set of 8 packs :P

:)

I'm very active now-a-days in Tiger Clan Kung Fu.

I’m not in mood of laughing @AbhasKumarSinha

Abhas Kumar Sinha

@Knight ..? You need to see my videos as proof? I've tournament on 26th

I'll be back, talking to my friend now.

3:01 PM

@JohnRennie Sir I have seen that video but I’m unable to decode what you wanted for me to learn from this.

How to send the message that I wrote earlier? I know people send transcripts but I don’t know how to do that

Abhas Kumar Sinha

Use Integrals like smart, (Guess it using reduction forms) then differentiate it,

that's genious.

Xenioux

I use Taylor expansion for integrals, that's even faster and can integrate most integrals which can't be easily integrated in elementry forms.

I'm EXTERA-ORDIINARYYYYYYYY.

That’s not the matter brother

Abhas Kumar Sinha

@Knight Then what? Tell me, i'll do integrations.

Need proof why area undercurve is antiderivative of the curved function?

That's too ezi

Knight Knight
6:51 AM
I want you all to tell me something. Does my inability to solve a problem implies that I'm not in Physics or Maths?
Consider this scenario: I began studying Integral Calculus, followed a well accepted book ,say Stewart Calculus, I solved all the problems that were in the book and became good in integration (according to me). But one day, someone gave me a problem on evaluating an indefinite integral, I tired diligently and enthusiastically but ended with a failure.
Now, does this imply that I need to study even more? Or is it all right, all I need is to accept it as a …

Abhas Kumar Sinha

@Knight How you become a joker by not able to solve integrals?

No one in this universe can solve every integrals completely, even JEE Advanced Toppers.

Considering yourself foolish by not able to solve one, is still a foolish.

3:13 PM

Preliminary nitpick: It's to make a joke (out) of oneself, not a "joker". Also, I don't know what "I'm not in Physics or Maths" is supposed to mean. But anyway, you shouldn't expect to always be able to solve all problems. One can be good at something without being able to do everything in that field instantly. You're not a failure just because you're not perfect.

Abhas Kumar Sinha

Well said again.

ACM I forgot ‘good’ in “I’m not in Physics or Mathematics”.

Abhas Kumar Sinha

@Knight Same meaning.

(for the context)

“You’re not a failure just because you’re not perfect “ all right I agree with that. But surely I’m not perfect if I cannot solve everything right?

Abhas Kumar Sinha

:53278509 Who's the perfect guy, you wanna be?

3:19 PM

I don’t want to be a perfect guy, all I want is to exterminate the lunatic in my head. It requires reason for exterminating him

Yuvraj Singh...

@AbhasKumarSinha percentile?

@Knight Yes, that's the definition of "not perfect". Perfection is almost always an unattainable goal

Abhas Kumar Sinha

@YuvrajSingh... 92 bhai

Yuvraj Singh...

@AbhasKumarSinha why?

Abhas Kumar Sinha

@ACuriousMind I'm perfect in being imperfect, prove me wrong! XD

@YuvrajSingh... Boards, no time for JEE Mains. :( I can do better only if I leave school.

I'm not in a dummy school.

Yuvraj Singh...

3:21 PM

@AbhasKumarSinha so leave the school XD

Abhas Kumar Sinha

:53278529 My secret Dream XD

Yuvraj Singh...

@AbhasKumarSinha dream come true you need to do hardwork . I meant for school XD @AbhasKumarSinha

@ACuriousMind Was Feynman perfect?

Abhas Kumar Sinha

@YuvrajSingh... *Conditions apply- Without school

@Knight Of course not

Abhas Kumar Sinha

3:23 PM

@Knight no, read, You are surely Joking Feynman

You'll see that he made mistakes.

@ACuriousMind Who was perfect?

Euler

?

Abhas Kumar Sinha

@Knight I told you

No one

Abhas Kumar Sinha

@Knight no.

So what made them great.

?

Yuvraj Singh...

3:24 PM

@AbhasKumarSinha they are pappu.

Abhas Kumar Sinha

@Knight Euler did extensive amount of Mathematics, which no mathematician ever did.

@YuvrajSingh... yes.

@Knight Euler's proof for zeta prime regulation (see it, how genious that he was!)

@AbhasKumarSinha So, how he was genuis? You see he solved the misconceptions at that time.

Abhas Kumar Sinha

@Knight Yep, solving misconceptions make you genious.

So why Terence Tao is so celebrated? Why top universities students are so celebrated? All they have done is to solve the problems that were assigned to them

"Genius" is often as much about being at the right place at the right time as it is about any sort of intrinsic qualities

Abhas Kumar Sinha

3:29 PM

@Knight Terence Tao solved IMO paper 100% when he was merely 13 years old

@Knight That's not how it works. After you're done with studying, you don't get problems "assigned"

The challenge is to find - for yourself - open problems that you can actually solve.

Abhas Kumar Sinha

@ACuriousMind no, the challenge is to ask the right questions - Feynman! XD

Tao has solved problems many others could not, but most mathematicians don't celebrate him because that's a demonstration of how smart he his. They celebrate him because he's increased the sum total of their knowledge considerably.

@ACuriousMind Why others couldn’t solve it? Is it just because of the way the nature is?

With all the politics and qualification requirements and whatnot going on in academia, it's easy to forget that science is about acquiring knowledge for us all, not about bolstering your CV.

Abhas Kumar Sinha

3:34 PM

@ACuriousMind No, I disagree, you need something for your CV

@Knight Biologists and psychologists have wondered about that for decade, but a model of such intellectual abilities - and especially their causes - that most would agree on is nowhere in sight

Abhas Kumar Sinha

@ACuriousMind Politics in adacemia? Cool who will win?

@AbhasKumarSinha Sure, you need something for your CV because the world expects it. But it should be a means to an end, not an end in itself.

Abhas Kumar Sinha

@ACuriousMind awkei.

@ACuriousMind So why other mathematicians couldn’t solve what Tao solved? Is it that they didn’t want to solve? For me Timothy Gowers have much more knowledge than Tao.

3:36 PM

...I just told you that I don't think we have an established model that can actually explain such differences in ability.

Abhas Kumar Sinha

@Knight Tao thought the prime factorization proof in a different way (If I were or any other mathematician, we'd have jumped to calculus directly!)

It's some mixture of innate ability, training, motivation and dumb luck. But I wouldn't trust anyone saying they can tell you the proportions in that mixture.

Abhas Kumar Sinha

@ACuriousMind dumb luck

Yes I agree

@ACuriousMind Do you ever wish to solve some open problems in physics or mathematics?

Novalium Company

@ACuriousMind I liked that one

3:48 PM

@AbhasKumarSinha You may come back tomorrow, provided you can abstain from advocating Nazi ideology then.

Have you kicked him out?

21 messages deleted

@Knight He has been suspended from chat for a day. Further infractions will incur longer suspensions.

Novalium Company

Aw lord

What the hell is going on here

Yes sir

@ACuriousMind what wrong did I say there that you deleted it?

3:51 PM

He cannot leave any things without context there.

@NovaliumCompany chat.stackexchange.com/transcript/message/53264321#53264321

He is indeed sort-of homeless. Metaphorically as well as literally

How literally?

Novalium Company

@ACuriousMind cool

I need to change mine someday

@ACuriousMind I would like to say that your action was wrong. I must say that it might be the case that neo-Nazism is still active in Germany but that isn't the case for India. Why would any Indian support Nazism? I don't have a clue. Can you please explain your action?

4:08 PM

@JohanLiebert Suggesting that Mein Kampf contains "answers" to the questions Knight asked is an outright endorsement of Hitler's views. This is not Nice and I will not tolerate it in this chatroom.

4:20 PM

@Knight The point I was making is that integrals can be insanely hard to do. Even though you can do some, or even most, integrals you'll still find integrals that totally defeat you.

"Differentiation is mechanics, integration is art"

Quantum-meatball

Hello everyone! I recently answered a question relating to Newton's third law and a user suggested an edit in it through the comments. I could not fully understand what the user was trying to say and I wanted to clarify some things. I thought pinging the user again and again through the comments would take up time.
I was hoping that maybe you guys could help.
The link to the thread is given below:
https://physics.stackexchange.com/questions/525524/how-can-action-and-reaction-forces-be-equal/525535#525535

@Quantum-meatball I don't think Bill is suggesting an edit. He's saying that your answer is wrong - "That is, the acceleration of your hand is smaller than the acceleration of the object." is simply false: While the hand and the object are in contact, their accelerations are necessarily the same (if the hand was slower, it would lose contact!)

Quantum-meatball

Ohhh okay.. now I get it. But if I assumed that the hand and the object do not stay in contact after applying force, then?

4:36 PM

Then I don't think you're answering the question anymore (I think OP means "pushing" in the sense of continuously pushing an object along), but honestly it's not quite clear to me what the question is to begin with.

Quantum-meatball

I also think that the question was not really clear and some users also pointed out clarifications in the beginning. I assumed that the question that he really wanted to be answered was that 'how can a reaction force exist if the object on which the force is being applied on be so small?' and I tried to clarify that in the last paragraph of my answer.

4:54 PM

@JohnRennie oh! Now I have got you

Quantum-meatball

Thank you for the help! @ACuriousMind

user444094

5:09 PM

Okay @ACuriousMind but then why are pions unstable and release the signature gamma rays of an antiparticle particle anhilation?

user444094

I thought this was a physics chat, sigh...

@PeterBarendt Note that only the neutral pion decays into gammas, the charged ones do not. And the neutral pion can decay into gammas because it has no conserved quantities that would prohibit it from doing so

And the neutral pion is, in fact, a quantum superposition of an up + anti-up and a down + anti-down pair and not a up + anti-down pair

So regardless which of the two superposed states you look at, it's annihilation of particle and anti-particle of the same species, either up or down.

1 hour later…

Constantine Black

6:34 PM

Hi to all.

Does anyone has any idea if there is a reason not to consider the presence of positrons in an ultra-relativistic fermion gas ( ultra relativistic gives the energy of the particle as ε=cp ) .

Is there any reason not to have electron-positron pairs in the T--> 0 limit ? In my thinking, the temperature here is not the factor that decides whether to have positrons or not

No, I think this is it: in the zero temperature limit we cannot have appearance of positrons.

Only in highest temperatures.

quickdraw.withgoogle.com/data

Constantine Black

6:51 PM

Could it be that in the zero temperature limit the pauli exclusion principle forbids an electron into lowering it's energy giving a pair or electron-positron?

it seems unreasonable to me for anyone to assert Tao is not "celebrated" eg by other mathematicians or the larger community. he is probably the most celebrated living mathematician in certain senses. hes likely the "highest-winning" by a basic metric... breakthroughprize.org/Laureates/3/L58

Constantine Black

or due to charge conservation, one can only have production of pairs, so in the end, if all states are occupied in the zero temperature limit, no pairs can be created, and also, there are no thermal fluctuations to produce them .

@ConstantineBlack How is a free fermion supposed to do pair production?

Constantine Black

no it cant

So where are the positrons coming from?

I may not have understood your question :P

Constantine Black

6:56 PM

can't t there be pair production and annihilation from the vacuum?

Is this wrong?

The vacuum does not produce real particles.

Constantine Black

so, from the point of view of statistical mechanics, one should not be concerned with such a case in an ultra relativistic fermion gas?

I don't think so, no

Constantine Black

I was thinking that it would somehow affect the particle statistics

mmm

can I show you some notes online? Through a link I mean

Sure

Constantine Black

7:01 PM

On page 64, paragraph 5.2.9

https://www.tkm.kit.edu/downloads/ss2014_theof/Theory_F_2014.pdf

What would he mean then, by considering the positron particles?

I find the presentation there very unclear :P

Constantine Black

Really?

It's being troubling for some time now

I am not sure if I have to consider such an effect on the particle statistics

What seems off to you, if I may ask?

E.g. I have no clue what "Since positrons are just 1−not observable electrons at negative energy" is supposed to mean

Constantine Black

hahaha

yeah

Mean either

that sentence is a bit problematic, for sure

*me neither

And they compute $N_e$ and $N_p$ and then suddenly talk about "particle excess" $N = N_+ - N_-$. Why are there five different $N$s and what is "particle excess"?

I'm willing to believe that there is some effect here - statistical physics is not my forte by far - but this source doesn't exactly fill me with confidence, either

Constantine Black

7:11 PM

I interpret that as that one cannot track the positrons or the electrons, but that their difference is

But what, then, is the "number of observable electrons" if we can't actually observe the electrons?

Constantine Black

yes, yes. On the other hand, the author seems to be serious... tkm.kit.edu/mitarbeiter_1127.php

Sure, he probably knows what he's talking about. He just doesn't do a very good job at explaining it

Constantine Black

Which, as always, doesn't help :)

Anyway, thanks. I am not sure what to do one this. Perhaps I will check the exercise without considering any positrons or whatever, and see if I can add a sensible comment in the end

I'm also confused why one would expect such highly-relativistic gases to produce only fermions and anti-fermions of their own species

Constantine Black

7:16 PM

and not other particles, right?

muons or whatever, that's what I meant

If this gas has conditions under which pair production can happen, it should also be losing a lot of energy by radiation (i.e. photon creation), and could also produce other fermions (muons, quarks).

Constantine Black

Would that play a role in cosmology, you think? Because if so, then the professor who is lecturing the class would have mentioned something, since he is a cosmologist

It seems he says that

production and annihilation happen together

I don't know, really

I think it matters in cosmology in so far that you should be seeing characteristic radiation from the annihilation reactions of the particle-anti-particle pairs.

Constantine Black

Could he be considering high temperatures and somehow have these effects?

Well, the individual fermions here need to have enough energy for the pair production reactions, so yes, they must be at high energies/temperatures

Constantine Black

7:22 PM

Could they have this energy on their own, since this is ultra-relativistic regime, but still the temperature be low?

Does that even make any sense?

I'm not sure!

As I said, my statistical mechanics is rather weak

Constantine Black

wouldn't that be then a "mainstream" thing in physics expositions? I mean if an accelerator was to have somekind of these fluctuations on particles?

Yeah, ok. I am just discussing this. As I said, this has me completely off.

I think I will proceed without positrons and see if I can make any sense of it.

Thanks for the thoughts

Novalium Company

8:05 PM

Ya laik ma new pic guyz?

Novalium Company

8:33 PM

Does anyone know if sensory substitution actually works? Neosensory are doing some stuff but they seem too good to be true.

9:20 PM

@ConstantineBlack I would recommend david tongs notes which are available on his website. My current course is based on them.

10:00 PM

Anybody get how to do this?

user image

I'm sure it should be easy

But I'm having huge issues

Constantine Black

10:22 PM

@JakeRose Thanks, I have these notes. The question was about those specific notes I posted earlier and on what logic they make sense. Thank though.

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