The h Bar

3:32 AM

@AaronStevens "Update on November 14, 2019: Following the publication of this article, the neurostatistician Manjari Narayan noted on Twitter that the identity found by Parke, Zhang and Denton also appeared in an unpublished 2014 manuscript by Piet Van Mieghem. In a comment on his blog, Tao confirmed that it does seem to be the same identity." What a rollercoaster

arxiv.org/abs/1401.4580

A: Centripetal and Centrifugal acceleration/force

4:14 AM

How is PM 2 RING.

Aaron Stevens

4:24 AM

@JMac yeah really. I was sent this article because Denton got his PhD at Vanderbilt where I am currently at.

Still crazy to have an interaction with Tao

-1

Centripetal force is required to keep the object moving in a circle by constantly pulling it towards the center. The centrifugal force just arises due to the object's tendency to continue motion in a straight line. It isn't a force applied to any body. Its direction is opposite to that of centr...

Keeps pinging me to remove the downvote that isn't mine

user8718165

@AaronStevens sorry for the pestering...I thought you were the one. And moreover...I'm happy to correct errors. We're here for learning.

@AaronStevens I think if there's a downvote, there's room for improvement and I'd be very glad to know where I could improve. Anyways, not being arrogant ;)

So I misinterpreted it as your vote hence I was asking if I could improve and get rid of that down-vote. I'm happy at 0.

Q: On the method described by Purcell for finding the magnetic field by measuring the force on a test particle

4:40 AM

@AaronStevens pm 2 RING changed his name

user8718165

@AaronStevens We had been discussing about improving the answer so I was having the false impression.

Sir Cumference

5:16 AM

argh why does flash need to be retired

there are plenty of nostalgic flash games

Emilio Pisanty

10:17 AM

4

The following text is a method for finding the magnetic field as described in Purcell's Electricity and Magnetism (page $151$, the top part). Measure the force on the particle when its velocity is $\bf{v}$; repeat with $\bf{v}$ in some other direction. Now find a $\bf{B}$ that will make $\tex...

magnetic-fields vectors vector-fields

Seriously?

that got on HNQ?

🤷🏻‍♂️

I really don't get this shit sometimes

Kyle Kanos

12:10 PM

@EmilioPisanty yeah, the algo seems a lot messed up for us on physics

PolarBear

1:23 PM

Can someone please help me point out the things I should learn to be able to solve this?

I'm unable to solve this even after doing my lecture slides and I've an exam tomorrow and I'm utterly confused

PolarBear

1:34 PM

Could someone please help or refer to some website/video please? I don't know what to search for.

I would be really really grateful.

1:49 PM

@Slereah @bolbteppa check the instructor registrar.princeton.edu/course-offerings/…

2:11 PM

@RyanUnger It's the guy!

2:29 PM

Recommending his own book for his class

How self centered

it would be if there were no other recommendations

I once read Dirac only used his book and when asked questions he said go read the book

heh

why even go to the class

2:49 PM

> Harish-Chandra (1987) remembers dropping out of his lectures when he found that they were the same as his book. When asked to clarify something during a lecture, he repeated it exactly since it was already expressed the best way.

Dirac was a robot all along

@RyanUnger that's incredible, totally wasted on you :p

Does @RyanUnger still hate string theory

How about AdS/CFT which is GR'ey

It's still a quantum field theory

3:01 PM

he's a pure mathematician now

Is he

Why is he doing GR lectures

GPA boosting :P

Aren't the mamericans supposed to studies the humanities too

What are his humanities courses

ask'em

I just did I suppose

3:04 PM

He just doesn't know what AdS/CFT is all about and is prematurely stifling himself

is it about love

It would tap into that GR thing of his and not be a waste

@Slereah they say he was more of a perfectionist

3:18 PM

@bolbteppa $$ \psi = a e^{i \frac{S}{\hbar}}$$ true na?

where S is the action...

$\approx$

@bolbteppa ah, but doesn't that mean the probability which is defined as $\psi \psi^{*}$ is independent of both S and $\hbar$...?

The equality is just approximate

@bolbteppa okay, but that approximate equality implies probability is independent of S and hbar?

It gets more and more accurate in the classical limit in which $\hbar$ goes to zero forcing $S$ to be extremised giving classical mechanics back

3:26 PM

@bolbteppa weird...! That's what I was asking, for any function, $$f(x) \stackrel{def}{=} a e^{i y}$$, has it's square of modulus independent of $y$ and is equal to $$ |f(x)|^2 = a $$... So, whatever limits we put on $y$ is meaningless... Isn't it?

because $$f(x) = a (\cos y + i \sin y)$$ whose square of modulus is 1 as $\sin^2 y + \cos^2 y = 1$

It's explained in Landau's QM section 6

@bolbteppa I'm asking because I was reading that part.

page 20

@Slereah humanities in grad school?

I dunno

I don't know how the universities work there

Princeton math has no course requirements

3:29 PM

Practical

Not gonna study poetry then?

@Slereah @RyanUnger we should post proper full derivations of every equation from arxiv.org/pdf/0712.0689.pdf here

@bolbteppa I’ll be sure to heckle

Or underwater basket weaving

I don’t care about AdS-CFT

Should we

3:31 PM

$\psi \neq a e^{iS/\hbar}$ though, it's equal to that + ...

@bolbteppa hm......

Are @skillpatrol @skullpetrol and @skullpatrol same person?

@skullpatrol ah okay...

The only point of analysing $\psi \approx a e^{iS/\hbar}$ is that $\psi$ should reduce to that more and more in the classical limit, and so we can use this to derive things like the Schrodinger equation or the momentum operator, this is made more formal in the quasi-classical chapter

@bolbteppa How? I don't see if $\hbar \rightarrow 0$, this reduces to classical equations. Because in case of classical equations, the probablity function should be equal to 1 or $a$ in this case, which doesn't happens to be.

@AbhasKumarSinha it's the whatchamacall it

Stationary wave method

ofcourse I assume $\psi$ is normalized to understand the intitution easily...

@Slereah wut?

3:37 PM

If $\hbar \to 0$ then $e^{iS/0}$ is nonsense, only way it can make sense is if $S = 0$ also (or $\infty$)

@bolbteppa So that $e^{i S/0}$ is a classical mechanics equation?

No it is nonsense

@bolbteppa so you mean that nonsense is equation in classical forms?

$1/0$ is nonsense, it's the same idea

@bolbteppa so how can we get classical mechanics equations from it which makes sense...

3:40 PM

The only way it can make sense is if e.g. $S = 0$ as well so that we get $0/0$

But this forces $S$ to be minimised

Which is classical mechanics

@bolbteppa ah okay... That makes sense...

S isn't 0 when minimized >:|

@Slereah who said that?

Me

24 secs ago, by Slereah

S isn't 0 when minimized >:|

cf here

lol

3:42 PM

@Slereah "* I don't have a measurement problem, I can stop whenever I want *" - @Slereah

@bolbteppa Thanks sir :)

@RyanUnger you will be laughed at when they find out, there, that you don't care about AdS/CFT

Also I'm not sure 0/0 is something to aim for to "make more sense" :p

0/0 = 0*(1/0)

not wrong

0*a = 0

3:50 PM

Does it mean that $$\lim_{x \to 0} \frac{x}{x} = 0$$

@yuvrajsingh No, I did not change my name!

@PM2Ring hello :)

@AbhasKumarSinha Hello.

@PM2Ring How's everything there, heard a lot of wildfires and stuff.

Hi. So I saw the fire is almost taken the whole Sydney.

@PM2Ring

Are you fine.

4:02 PM

that's why I asked. I think that there is still official emergency there.

for a week

Why there are tree account of the same name, are you same. Or different users.

@yuvrajsingh different names, look carefully

Sorry my mistake.

@PM2Ring Can you suggest me a good on thermal statistics.

@AbhasKumarSinha do you have any idea.

@yuvrajsingh sorry no idea for thermal statistics and thermodynamics...

OK.

4:08 PM

@AbhasKumarSinha I'm fine. The area I live in is too urbanised for wildfires (BTW, in Australia, we call them bushfires). But I did smell the smoke for a few days: eucalyptus tree smoke has a fairly distinctive odour.

3

@PM2Ring ah, good to hear that you are safe :)

@PM2Ring hi.

@PM2Ring I was active on twitter hashtags asking random people how was the condition there. Most of them were unaffected...

@yuvrajsingh Sydney does have a lot of trees, and large nature reserves that can be affected by fire, but it also has a lot of very urban areas. Those areas do have trees, but they generally aren't in dense clusters.

That, s good.

@PM2Ring

4:16 PM

Here's a photo from Wikipedia of one of the main roads in my area. The road is split, with a corridor of trees in the middle.

@PM2Ring People don't die from bushfires due to actual fire. They actually die because of smokes. See Brazil fire, where 90% of the people were affected due to affected air. Only small tribes have direct effect from fires, otherwise, it's not a big problem.

@PM2Ring do you have any suggestions.

@yuvrajsingh No, I don't.

Smoke inhalation

Smoke inhalation is the primary cause of death for victims of fires. The inhalation or exposure to hot gaseous products of combustion can cause serious respiratory complications.Some 50–80% of fire deaths are the result of smoke inhalation injuries, including burns to the respiratory system. The hot smoke injures or kills by a combination of thermal damage, poisoning and pulmonary irritation and swelling, caused by carbon monoxide, cyanide and other combustion products. == Signs and symptoms == Symptoms range from coughing and vomiting to nausea, sleepiness and confusion. Burns to the nose, mouth...

Can we see you house in the image.

4:22 PM

@yuvrajsingh hehehehe... Cool idea..

@AbhasKumarSinha True, but Sydney is very large, and I live quite near the coast, so the smoke from bushfires gets dispersed by the time it gets to my area.

@PM2Ring that's good :) (A house near coast <3)

@yuvrajsingh No, but that area isn't far from my place, and I often walk (or catch a bus) along that section of road

Do you have sea near your house, if yes, do you have a pic.

Few people die from bushfires in Australia, but plenty of people lose their houses and valuable items.

4:28 PM

@PM2Ring that's sad...

@yuvrajsingh Well, the beach is a couple of kilometres away. Before I moved back to Sydney 2 years ago, I lived near the coast. I could see the ocean, and a couple of islands, from my balcony.

@PM2Ring wooooooooooooooow

@AbhasKumarSinha It's a complicated situation. People like to live in "leafy" areas surrounded by trees, so the expensive areas have more trees. But the trees get overgrown, and a bit too close to the houses...

@PM2Ring btw, it's summer there?

@PM2Ring trees are not a problem, they don't catch fire when green...

For tens of thousands of years, the Australian Aboriginal people managed the forests by regular burning to prevent a build-up of fuel. That put a certain kind of evolutionary pressure on the forests. Many Australian plants actually need fire for the seeds to germinate.

4:36 PM

@PM2Ring true, it should be done...

@AbhasKumarSinha Summer is starting. We've had a few warm days. But 2 weeks ago it was still getting chilly enough some nights for me to turn on the heater.

@PM2Ring same here :)

weather here - satellite.imd.gov.in/imgr/animation3d/sanew_3d.htm

What precaution you people are taking. @PM2Ring

@AbhasKumarSinha It does get done, but sometimes it doesn't get done at the proper frequency, so fuel can build up to dangerous levels.

@PM2Ring hmm....

4:46 PM

Some people living next to areas that need regular burning don't like it when there's a fire nearby, and complain if there are too many "burn-offs". But they complain even more if the burn-offs don't get done and their nice neighborhood bushland turns into a raging bushfire that destroys their house.

@bolbteppa lmao why would I care about physicists laughing at me

@PM2Ring well, in India Aboriginal people live in isolation, away from human settlements and the government has some areas reserved for them so that they can enjoy their own rights to live like that. So, on one complains here

@AbhasKumarSinha Australia is a rather dry country. Australian forests are full of eucalypts, which regularly shed bark. So it doesn't take long for fuel to accumulate. And once a bushfire is blazing, even green trees will burn, especially the smaller ones. They're full of flammable eucalyptus oil, and it doesn't take a lot of heat to dry the smaller branches enough to make them burn.

@PM2Ring oh okay

@PM2Ring this is the block where I live

@PM2Ring have seen Delhi pollution level AQI EVEN reach to 937

4:56 PM

@yuvrajsingh AQI 340 in UK - 1000 people died same month, AQI 1300 in Delhi - no deaths

Nobody cares about the value of $0/0$ in this case

6:21 PM

Hello, is there anyone here with an understanding of electric circuits?

@Typo What level of understanding are we talking here?

high school and above

since I'm in high school

Sure, I understand them at that level, what are you looking to ask about?

I want to understand how neutral wires and grounding works in mains electricity

I don't understand how/why the neutral wire doesn't have current through flowing it (or if it does, why it isn't shocking you)

I've looked at some answers on the site about it but most of them talk about phases and such which are way beyond my scope. I still went out of my way to learn about it but I can't seem to connect the dots here

normally with an AC source, the two ends of the wire should act identically but in mains, the live and and neutral wires are different because of neutral wire being grounded

what does the grounding change?

@Typo I'm not super well versed in electrical wiring specifics, but the neutral wire should be at the ground potential. You should also be at the ground potential. Current flows from high potential to low potential, with greater current the greater the difference. If you and the wire are approximately the same potential, minimal current flows between you and the wire; which is what would harm you.

If you touched the hot wire, part of you would be ground voltage, and another part would be the mains voltage. This would cause a large current due to the large difference; which can harm you. The same would happen if you shorted a neutral to a hot wire.

6:34 PM

I see but what is happening to flow of electricity in the neutral end?

why exactly is the neutral wire at low potential?

@Typo It has current; it just would rather keep traveling through the wire than through your body, unless your body was at a lower potential. There's some resistance involved with going between a copper wire to your body, I'm pretty sure its much greater than the resistance of just going through the wire, so the current mostly chooses the wire.

@Typo Because it's grounded at the panel, and electrical codes are designed so that it should remain at ground potential. Sometimes that actually fails, and you can get shocks from the cases of objects; for example.

what does it mean to be grounded? I assumed it just meant part of the wire goes through the ground, how does that change the original potential of the AC source?

@Typo Grounded means "at the same potential as the ground". So if you have the neutral potential at the same potential as your ground, it should be the same potential as the people standing on the ground, because we are essentially at the same potential as the ground since we're directly connected to it most of the time.

In inflation, since income and prices go up, that shouldn't mean that people are "getting poorer" (since they get more money and therefore can buy the same amount of stuff), but money devalues?

(if not, current would also be flowing between us and the ground)

6:44 PM

That would be funny

I think something may have clicked. I just need a bit more clarification

@NovaliumCompany Money devalues, but the value of all their stuff goes up approximately the same amount as inflation. They wouldn't be getting wealthier, even though they make more money; but they wouldn't be any poorer, because as you mention they can buy the same amount of stuff.

Cool, so why is too much inflation bad? People think they have more money and before prices have gone up buy a lot of stuff, and later they can buy less stuff cuz they've spent their money while thinking they were rich and not have small amount of money and the prices are high? But why are prices high if there is less demand at that point? Is this were deflation happens?

The grounding is accomplished by splitting the neutral side of the circuit into and connecting 1 part of it to the ground and another becomes the neutral wire?

into two*

@Typo I don't know the specifics, but I don't think you really split the neutral in two. In a circuit, the neutral is just connected to the ground at the panel, so that it should be at the same voltage as ground. There can also be ground circuits though as far as I know; which are typically used to make sure that the casings of high voltage equipment doesn't go above ground potential and shock you when you touch it. I'm not an electrician or electrical engineer though, so I may be a bit

off

Even still, would the principle still be the same?

6:55 PM

@Typo Possibly, but again that's getting too far out of my knowledge. I'd basically be guessing

Alright, thank you so much

Most my confusions are cleared

I still have a final question

All this explains why the neutral wire itself is neutral.
Say a live wire is connected to an appliance, as in the connection comes in from one end of the appliance and exits out the other and is connected to the neutral wire. Would touching the connection where it exits the appliance be harmful?

@Typo There's current running through it, but for the current to travel through you instead of the wire is a path of greater resistance typically, if the neutral has no breaks. electronics.stackexchange.com/questions/76726/… Really good explanation here that words it much better than I can from a real electrical engineer.

It shouldn't be harmful, but it definitely can be harmful.

alright thank you for all the help

Q: theory of everything is bullshit

7:16 PM

physics.stackexchange.com/a/514016/127931 Does anyone understand what this answer is saying... It was at +6 but to me it doesn't seem to answer the question remotely.

Rishi

Hi , is anyone there

Aaron Stevens

8:03 PM

@JMac Yeah seems like one of those answers that is talking physics but not really getting to the point of the question.

Loong

8:29 PM

-7

The missing link that's giving us all depression by: KY-LA-20 I am so frustrated by what I have realized today that I have to say something about this before I start to go insane wondering if the catholic church was literally controlling Stephen Hawking all along or if he just didn't care about ...

tag-removed

hello things.

@Loong Classic "I think I've figured it out" word-salad post.

@JMac Can I ask u some questions about inflation?

@NovaliumCompany You can, but I would advise against it if you want accurate answers (assuming you're talking about cosmic inflation, and not like balloons or something).

Economic inflation.

8:39 PM

@NovaliumCompany Oh right, we talked about that. You can ask but, similar to cosmic inflation, I don't know a whole lot about it.

So government prints too much money --> income rises --> demand rises --> prices rise --> you can buy less stuff --> money devalued. Or simply, income rises --> scarcity is reduced --> value lowers. That's inflation in a nutshell right?

@NovaliumCompany I'm really not sure of the order of cause and effect or anything.

Aside rant, again on this question, how does this get +3 in 10 minutes? physics.stackexchange.com/a/514086/127931

Alright, no problems. I'mma talk with my father, he should know.

Good night atoms.

ACuriousMind

@JMac Suspicious voting behaviour is a fine occasion for a custom mod flag (but in this case I'll look into it without one anyway).

@ACuriousMind I literally just starting digging a bit more and was about to flag it. Thanks though.

Definitely some weird patterns there as far as I see.

ACuriousMind

8:51 PM

@JMac No worries. Thanks for being attentive!