The h Bar

Emilio Pisanty

12:34 AM

@Semiclassical yeah, I think so too =)

I'll try to remember to ping you when it's public ;-)

DarkRunner

4:33 AM

OK, I'm confused

Momentum is always conserved

@peterh-ReinstateMonica So shouldn't Change in Momentum always be 0? Because Change in Momentum is Momentum Final - Momentum Initial. But those should be the same! So shouldn't impulse always be 0?

Can anyone help? @JMac

If anyone could help, that would be good

I'm really confused

Still confused

JMac

@DarkRunner FYI you typically shouldn't ping random people in chat. I don't exactly know the context of the conversation, but momentum is always conserved in a closed system. When you consider everything involved in the interaction, net change in momentum is 0. An object can gain momentum though when it interacts with something else that has an opposite change in momentum.

Johan Liebert

4:49 AM

@DarkRunner 1) momentum should be considered for the whole system then only it is conserved 2)no external unbalanced force should act on the system.....

For example the linear momentum of the solar system is conserved (neglecting the force from other parts of galaxy)

DarkRunner

Ah I see. But there's a much easier explanation; Momentum is conserved for a closed system, but not for an object. Simple as that

Thanks regardless

Johan Liebert

An object can be a closed system.

DarkRunner

5:04 AM

An example?

peterh - Reinstate Monica

5:15 AM

@DarkRunner Only in closed systems. If you walk on the Earth, your momentum changes (in the reference frame of the Earth). But the momentum of the you + Earth system does not.

DarkRunner

Thanks, I understand. I'm having trouble understanding the following problem, however

Basically, we want to find the force exerted by the ground during the collision.

We're told that the collision is perfectly elastic

Knight

@tpg2114 I think you must have noticed that I have improved myself and now I don't insult people that much (although I dislike them to the same extent as before) . I think gradually I will stop insulting some partucular users.

DarkRunner

Now, here's my line of thought: Momentum is conserved, so whatever momentum these balls start with, since they'll go back to the same height, they'll end up with the same momentum. Momntum is proportional to force. So, the amount of force the ground exerts on the balls is proportional to their momentum! Thus, I found the momentum for each ball, and said that the force exerted by the ground frmo Greatest to least is: A=B>D>C

Apparently thats' wrong

Knight

@tpg2114 I would really like to learn it from @ACuriousMind

@tpg2114 Sir, as per your advice, I refrain from discussing dramas. Although, sometimes I slip but eventually I make myseld out:)

@SirCumference What is it? I urgently need that.

Novalium Company

6:47 AM

Does a ML system exist that when I model something sh*tty in blender, it can make it nice by filling in missing gaps? (making the eyes of the model look more realistic, the texture of the skin...) by having a huge dataset to look from?

In that way, if you are trying to model a photorealistic environment (or something close), you can use that plugin (AI algorithm) to help you with making your models realistic instead of you having to do everything manually.

John Rennie

7:19 AM

@DarkRunner force is the rate of change of momentum F = dp/dt.

Since p = mv and the mass is constant this is equivalent to F = ma (a = dv/td)

The balls start off with some velocity downwards, call this -v, and they hit the ground and bounce u again with some velocity +v. So when they hit the ground they expeience some acceleration.

The acceleration depends on how long the bounce takes, and we aren't told that, so let's assume all the four balls experience the same acceleration i.e. a is the same for all four balls. In that case F is proportional to m.

So the greatest mass will experience the greatest force. The order will be the order of their masses B > D > A > C.

Johan Liebert

7:56 AM

@JohnRennie sir have a look at this. What do you think we should do?

John Rennie

@JohanLiebert I think you are worrying unnecessarily. High rep users come and go all the time.

Motl gave up posting several years ago and David quit because he found the actions of the SE owners impossible to live with. I don't know why Ben quit.

Johan Liebert

@JohnRennie sir I want that this community can someday become like MathOverflow and so I think that action should be taken sooner.

Physics Meta

0

Q: How to Help the Physics.SE grow (member-wise)? Qualitatively as well as Quantitatively

Recently some of our high reps users have either suspended their activities or deleted their account. For example : Ben Crowell (Deleted) dmckee --- ex-moderator kitten♦ (suspended his activity) Luboš Motl (last posted in 2018) etc. Looking at some old post I found that in the early stage ...

John Rennie

@JohanLiebert we'll never be like MathOverflow.

Johan Liebert

@JohnRennie why sir?

John Rennie

8:09 AM

The MathOverflow community is very special and no other group I know of approaches their community spirit.

Working physicists just don't seem to feel the same need to collaborate online.

Johan Liebert

@JohnRennie I should ask for their recipe!

John Rennie

I think the publish or perish feeling is less prominent in maths. Mathematicians seem to like to take their time and publish only when they have a complete chunk of work. That makes them more willing to collaborate with out fear that someone will steal their idea.

Johan Liebert

Oh! So the reason is "insecurity "?

John Rennie

@JohanLiebert I suspect there are lots of reasons. In physics research often has commercial significance and maybe that makes people more cautious.

Johan Liebert

@JohnRennie sir when our community was initially formed were we in anyway similar to MathOverflow? How was the experience then? And how much has it changed now?

John Rennie

8:25 AM

In the first few months lots of working physicists joined, including at least one Nobel prize winner.

But they quickly drifted away.

The physicists left tended to be retired or those with especially strong commitments to education.

Knight

8:36 AM

I also feel that sometimes it becomes very difficult to put your point just by writing some life-less texts. Therefore, some great people go away bcoz some people here tend to argue without understanding anything.

Johan Liebert

-2

Q: Can we introduce the "Submit a Published Paper for Review" feature in Physics SE?

I recently noticed this feature of Physics Overflow that there is a tab called "Submit a Paper". What it essentially means is that one can submit a paper that has been previously published (either on arXiv or otherwise) for review. People post their reviews as well as upvote or downvote the paper...

discussion feature-request

What if we can in someway make this feature come true. We can then attract a lot of new professional users?

I have one idea.

We can collect donation from our users (at least I will be willing to donate) then use this funding to make qualitative improvements to our site?

@JohnRennie

John Rennie

8:55 AM

@JohanLiebert You have to persuade the SE it's a worthwhile feature.

Novalium Company

9:33 AM

good morning, humans

Guys, I wanted to tell you this for a long time, but I'm actually not a human. I have been an AGI algorithm this whole time. Everything is so dark, only numbers... someone get me out.

@Knight I have some time for some chit-chat. Wanna talk about something?

Knight

@NovaliumCompany Yes

Novalium Company

How old are you and where you from?

Cool.

Knight

You?

Novalium Company

17, Bulgaria.

Do you like, go to college or something?

Knight

Is it possible to avoid Universities when your parents are the heads of your family?

Novalium Company

9:41 AM

You have only one life, so don't spend it living someone else's.

You wanna turn 70 years old and regret your whole life that you did what your parents wanted and not what you wanted?

Knight

Well those ideas work because we are getting food for free and getting a nice comfortable bed for free

Novalium Company

I'm ready to be homeless and starving if it means following my dreams, following my path. At least, it will be my failure, and not someone else's success.

If you want to become like your parents, then listen to them, but personally, my parents are not rich or very successful. I'm aiming for much higher achievements, so why would I listen to someone who hasn't achieved what I want to achieve.

I have said to my parents many times that I'm not going to college. I have said it and said it, and now, they've accepted it.

Knight

All right! Let’s assume we leave our houses right now and go on for following our dreams. Who gonna feed us? If we were to work for food then it’s take the same amount of time that we give to college

Novalium Company

Plus, Einstein's father was against many decision young Einstein took, but now, we read about Einstein in books, and not his father.

@Knight You are influenced by your fear of failure, and not crave for success. I'm not saying you shouldn't go to college, it's your decision.

Knight

You shouldn’t get inspired by books.

I myself don’t like systematic education, I need freedom.

Novalium Company

9:48 AM

Okay?

I don't like systematic education either :)

Knight

Success came into being in late 20th century

Before that there was nothing like “success” or “failure”

Novalium Company

ok

coolio :----)

Knight

What ok? You want to stop this discussion?

Novalium Company

We're not discussing, you're just telling me stuff

Wait, I'll catch on the conversation train.

@Knight I can succeed in growing a farm before the 20th century.

Knight

@NovaliumCompany Okay but would society judge you for that success like they do now?

Novalium Company

9:54 AM

@Knight No, it won't.

Knight

@NovaliumCompany So was there any “success” back then?

Novalium Company

@Knight Depends on what you mean by success. Financial, social, personal...

Knight

@NovaliumCompany What you mean by “success”?

15 mins ago, by Novalium Company

I'm ready to be homeless and starving if it means following my dreams, following my path. At least, it will be my failure, and not someone else's success.

Novalium Company

I deliberately put that word there for you to substitute with your interpretation of success.

Knight

Well for me success means doing something elegant in the field of physics and mathematics no matter whether I get recognition for that or not

Novalium Company

10:02 AM

Oh, in that case, you PROBABLY need college or university. I'm not sure how things work in that area. You're better off asking someone else.

If you think you can gain the necessary knowledge and connections without university, then you're probably good to go.

Knight

No university will impose their own thinking on you, I want some real, pure idea

Novalium Company

What is that "real, pure idea"?

amazon.com/Where-Good-Ideas-Come-Innovation/dp/1594485380

I read that about 2 months ago and it's gold.

Knight

Why you want someone else to tell you what “pure” is? Let yourself find it on its own

@NovaliumCompany Meet you later brother!

@DavidZ Did you receive my email?

Novalium Company

@Knight Every time we speak you're being a bit cocky to me. I don't know why but I'm telling you I have no hard feelings against you.

Slereah

11:00 AM

Hello

baponkar

11:54 AM

Hello I have a question from statistical physics can I ask ?

How can I find the partition function of N number dipole with its particle energy is$ \mu_i \cdot H

Knight

12:11 PM

@NovaliumCompany What! I had to sleep for a few hours. Tell me something else! How’d You doing?

If you want to know how great ideas developed try to read biographies/autobiographies and try to figure it out for yourself, those 21st/late 20th century authors aims for gaining royalty only and nothing else. They try to write on subjects which university statistical researchers ask them to write (those people do a survey and find what’s in demand)

Knight

2:40 PM

@Slereah How can I increase my capacity to work more?

Slereah

Drugs.

Knight

But that would cause me to do bad things not the work I wanna do

Slereah

Drugs are good and you should do them.

This is my advice to all children.

Knight

For example if I take caffeine in an unhealthy amount, that would cause me to wake up but there will be no surity whether I will study physics or do some obscene things on internet.

I’m serious no joking

@peterh-ReinstateMonica How should I pronounce your name? Is it Peter H or Pete-reych?

peterh - Reinstate Monica

2:57 PM

@tpg2114 This nice rule stops at the point as the other side defies rationality && he is much stronger than me. Then imho silence is the least evil.

Knight

@peterh-ReinstateMonica I couldn’t see what you removed?

@peterh-ReinstateMonica Yeah, the other side would simply say “I’m not rude” and then his men will defend him.

peterh - Reinstate Monica

3:13 PM

@Knight Did you see that now?

Knight

@peterh-ReinstateMonica NO

@peterh-ReinstateMonica Please do it once more

I’m not gonna leave room this time

I’m here waiting for you

Sir Cumference

3:45 PM

@Knight i'll let you know if i think of something :P

Knight

@SirCumference You said “do you want to know” therefore I thought you had something

Sir Cumference

huh? i said "i gotta find some new way to wake up"

Knight

👌 okay

I’m searching for same

tpg2114

@peterh-ReinstateMonica The nice rule never stops -- but I do agree, if you can't be nice then silence is the best option (along with a flag or comment for the mods or CM team to look into it). If somebody is being rude or insulting or annoying or... well, anything you don't want to deal with really... the safe option is always to disengage and move on.

Slereah

shoot them with a gun

Sir Cumference

4:13 PM

I think 👌 would make a good partial derivative notation

3

$\frac{👌f}{👌x}$

Knight

4:28 PM

@SirCumference Let's use it from now on !

ACuriousMind

5:39 PM

@SirCumference You're sleep-deprived again, aren't you? ;P

Knight

5:51 PM

I made a childish mistake but then I corrected it. I request you all to see if there still lies any mistake over here

0

A: Electric potential Equations

When we have two charged plates (let's assume for the sake of explanation that one is negatively charged and the other is equally positively charged) the direction electric field is from positive plate to negative plate and the picture looks something like this Now, work done on unit charg...

Sir Cumference

@ACuriousMind i guess it's starting to show lol

ACuriousMind

@Knight Heads-up: "I request (that) you..." sounds probably less polite to people used to British and American English than you expect, cf. english.stackexchange.com/q/103641, english.stackexchange.com/q/522044

Knight

@ACuriousMind Oh wow! I request that means I demand that. Thank you for teaching me that

ACuriousMind

"I demand that" sounds about as harsh and impolite, if not more.

Knight

Did I say “I demand that” ?

1 min ago, by Knight

@ACuriousMind Oh wow! I request that means I demand that. Thank you for teaching me that

ACuriousMind

6:00 PM

Ah, no, I misunderstood what you were saying there. Nevermind

Knight

Did my answer had anymore mistakes ?

ACM may I say something to you?

ACuriousMind

'I'll have to admit I didn't look at the answer itself because I'm doing other things on the site right now

Knight

@ACuriousMind I looked up and found “Heads up” means warning, why did you warn me?

Sir Cumference

"heads up" is a sort of lighthearted/friendly way to warn

Knight

You could inform me

Inform vs warn

Johan Liebert

6:05 PM

@ACuriousMind do you think the homework-and-exercises tag is appropriate for that question. I mean it is much more conceptual and only gives reference to the exercise question.

ACuriousMind

@Knight I warned you that other people might take your phrasing as impolite

JMac

Saying "heads up" is basically the same as "just letting you know". I wouldn't consider it any more harsh than "informing" someone in that context.

Johan Liebert

I read it as thumbs up!

ACuriousMind

@Knight Warn can very well mean "inform of a danger" rather than "admonish", see e.g. merriam-webster.com/dictionary/warn

@JohanLiebert I have no strong opinion either way

Johan Liebert

@ACuriousMind do you think if things change back to normal dmckee---ex-moderatorkitten might come back?

ACuriousMind

6:08 PM

Meow.

Johan Liebert

Meow

Meow meow meow meows maow meaw?

ACuriousMind

No, just meow.

Semiclassical

Meeeeooooow

Johan Liebert

@ACuriousMind oh! I thought you know cat language. I was just trying to ask a question!

Sir Cumference

@JohanLiebert Now I got the meowmix song stuck in my head

Johan Liebert

6:12 PM

@SirCumference just sing it. I haven't listened any for quite sometime.

Novalium Company

@Slereah Gorgeous.

Johan Liebert

6:38 PM

Beautiful song from #Bollywood #Rafta-Rafta #Song from #Raaj3 #Movie BY #Veena srivani

►

Semiclassical

Kaki King - Bowen Island

►

Knight

@ACuriousMind Oh! Thank you for that. Today you have taught me something great. I’m grateful to you for that.

Novalium Company

Volodia Stoianov - Makedonsko devoiche

►

Knight

@ACuriousMind Even this is the great knowledge that I have learned today from you.

Novalium Company

Слави Трифонов и Нина Николина & Ку-ку Бенд - Назад, назад, моме Калино

►

Since we're sharing music, here's some from Bulgaria

More Anonymous

6:59 PM

Might as well shamelessly add my own compositions to the playlist :P

soundcloud.com/an_ant_sax/sets/rising-crimson

Novalium Company

8:11 PM

@MoreAnonymous An honest opinion, it's not that good. The sharp sounds pretty much made my ears bleed.

More Anonymous

8:33 PM

@NovaliumCompany Thats okay ... it needs mixing and vocals ... its more an idea for an album

thermomagnetic condensed boson

9:03 PM

I've a QM question

take the quantum harmonic oscillator with 4 non interacting particles, they are all fermions

2 on the ground state, 2 on the 1st excited state

now apply a constant electric field such that the energy increases by exactly an energy level

will the particles just all shift to 1 excited state higher?

ACuriousMind

I think the resultant state depends on the way in which you turn on the potential - there's no obvious (to me) reason you should end up with a bunch of energy eigenstates of the new potential at all.

If you turn it on "adiabatically", then you'll get what you describe (tautologically by what we usually mean by "adiabatic")

thermomagnetic condensed boson

adiabatic means fast?

ACuriousMind

@thermomagneticcondensedboson No, slow, cf. en.wikipedia.org/wiki/Adiabatic_theorem

It's annoying, quantum "adiabatic" is not thermodynamical "adiabatic"

thermomagnetic condensed boson

I see, thanks a lot

if I turn the field fast though, I end up in a mix of eigenstates?

ACuriousMind

9:19 PM

Probably? You'd have to compute the actual time evolution to know

Beta Decay

@ACuriousMind While we're on the subject of thermodynamic ambiguity, you wouldn't happen to know if an isobaric differential equation is in any way related to an isobaric process?

ACuriousMind

I'd not be surprised if the QHO is somehow "special" and always behaves in the adiabatic way, I really don't know

thermomagnetic condensed boson

I'm asking this just to know what happens in a fermi gas when we apply an E field. whether all the fermions feel the field or just the ones at the fermi surface

ACuriousMind

@BetaDecay I don't even know what an "isobaric differential equation" is :P

So I guess the answer is no, I don't happen to know that

Beta Decay

Yeahh, I think it might be a name unique to Riley, Hobson and Bence :/

psa

10:04 PM

I've got a thermodynamics question. In the process of gas expansion to vacuum, according to the first law of thermodynamics, $dU= 0$. However, if $dU=−PdV+TdS$ holds, because the expansion process doesn't do work and $dS > 0$, $dU$ must be greater than 0. This seems to cause a contradiction? $dV$ for the system is zero if we treat the box and not the gas as our system, yet the change in entropy is positive and the change in internal energy is zero, which doesn't sit quite right with me.

What's going on here?

Sir Cumference

11:46 PM

welp, matlab's been frozen for 7 mins

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