The h Bar

M.N.Raia

01:23

Hello everyone!

I really need a step-by-step derivarion of the norm of 4-acceleration. I know how to write down the definition and I understand why. But I simply don't get the relation:

$(\eta_{\mu \nu} a^{\mu} a^{\nu})^{1/2} = \gamma ^{3} a$

user351417

03:20

@EmilioPisanty I'm a bit busy right now; I have tests, so I can't look at the whole conversation. But no, I didn't rage-quit, and I've been toying with the idea for about a week.

user351417

I think Physics SE is awesome, and maybe I'll return after a while.

user351417

But I did consider the impact this would have on other peoples' rep, since I used to vote a lot, and I was very sure that I'd qualify for vote-preservation. I might contact the CMs. I know that after my 24 hour timer elapsed, my account was still alive and I had a message saying that a developer would be required to review my account's deletion.

user351417

I'll probably keep this account lying around: it's linked to my chem account, so if I choose to restart after a while, I might get an association bonus on physics : P

user351417

But this meta post kind of made me feel sure that quitting was the right choice.

user351417

03:36

My, this is disastrous. If I'd known that I wouldn't get a vote-preserving deletion, I'd have just quietly abandoned my account : ( I'm so sorry, this looks like a whole lot of people lost rep.

user351417

Maybe it would have been a better idea for me to announce it in chat, considering the strange way OP of this question appears to have been deleted.

user351417

03:47

(cc @PM2Ring @JMac @KyleKanos and everyone else in that discussion)

John Rennie

04:54

@M.N.Raia you have to work out the coordinate transformation between the accelerated and unaccelerated observer. This is a somewhat messy calculation that you'll find done in any standard text on relativity. For example in Misner, Thorne and Wheeler it's done in chapter 6.

Once you have the equations relating the two frames more messy calculation allows you to calculate how the acceleration transforms. You'll finally end up with $a = a'/\gamma^3$ where $a'$ is the proper acceleration in the accelerated frame and $a$ the acceleration in the inertial frame.

The various equations, though not the working, are in Phil Gibbs' relativistic rocket article.

Emilio Pisanty

06:55

@Rishi I can't speak for anyone else, but on my side the lost rep is not a concern.

But account deletion does have significant consequences beyond just the rep, both on main and on meta, particularly in what it does to the historical record - it becomes much harder to piece together the fact that it's the same person behind different posts.

We've seen users who cycle through account deletion and re-creation multiple times, and it gets extremely annoying.

But

If you had your reasons, you had your reasons.

If all you need is some enforced time away from an SE account, though, you should consider asking the mods for a voluntary suspension of the account.

DanielSank

07:20

Yo, @EmilioPisanty

Suppose I have a differential equation $\dot x(t) = f(x; p)$ where $p$ is a set of constant parameters.

That's easy to solve.

Now suppose $p$ itself changes in a probabilistic way as a function of time. How do we treat that case?

Slereah

07:34

Greetings, hu-mans

Emilio Pisanty

08:06

@DanielSank with a whole lot of ingenuity and hard work, I should imagine, and a complete revamp of the mathematical framework

It sounds like a job for stochastic calculus

DanielSank

@EmilioPisanty blarg

Emilio Pisanty

Though maybe you're not quite deep in enough that you need to break out the Ito calculus guns

Slereah

pew pew

I had to break out the Ito calculus guns once

But I used

The physicist way

It was quite possibly the worst possible thing I've done, rigor-wise

u see, from the uncertainty relation, you have $$dx dp ~ approx \hbar$$

So that $$dx m \frac{dx}{dt} \approx \hbar$$

Or $$dx^2 \approx \frac{\hbar}{m} dt$$

Which means that in the Riemann sum, u have to keep terms of the size $dx^2$

This is 100% something that serious physicist have written down and put in very serious articles on path integration

And it actually gives the same results as Ito integrals

Emilio Pisanty

@Slereah greetings, sle-reah

Slereah

It gets even worse when you do it on a curved background

I don't remember what article used that

Let's see if I can find it again

iphc.cnrs.fr/IMG/pdf/pint.pdf

i think that one uses it

p. 17 on

user351417

11:28

@EmilioPisanty Hehe no I'm sure I'm not fickle enough to do that. I'll see if I have the time and interest to re-join after a few months of college, and that starts in September. I was planning to write some answers on Physics SE over my summer break, but I decided it'd be more intelligent to spend that time taking courses and learning stuff instead: a few of the stuff I've written weren't great.

user351417

Anyways, see ya!

bolbteppa

@RyanUnger welcome back (later today)

@Slereah where's the Ito'ness

Slereah

p. 20

bolbteppa

Ah, integrating over fractal paths

Akash. B

11:52

@JohnRennie you there?

Slereah

@JohnRennie is always with us in spirit

Jim

12:08

^ I second that emotion

Secret

12:36

This user has been automatically suspended for posting inappropriate content and cannot chat for 6 hours 24 minutes.

countdown to the GR group reassemble

Jim

13:18

I went to a new dentist the other day and they made a joke that made me never want to go to any other dentist but them. They said "Both dentistry and physics have a lot in common. You see, in dentistry, like in physics, calculus is hard"

Secret

13:37

26

Q: How I learned to stop worrying and start asking questions

As has been noted in the past, particularly in Question self-destruction: why don't experts ask more questions? and in Does reputation correlate with the question-to-answer ratio?, and also here, this site has the peculiarity that, in overwhelming proportion, our 'expert' users, by multiple measu...

Actually I found I tend to do the opposite, but I guess it's because I am still young in the academic ladder, being a PhD

Actually, I think I can wrote a whole essay to analyse this post, there are a lot of interesting things. Problem is it does not look like a Q and A

The part about academic folklore interested me as part of my broader personal research of the nature of the unknown

Kyle Kanos

13:57

@Jim that'd be a dentist I'd like to visit, were I to go to one

John Rennie

@Akash.B hi. I had left by the time you posted, but I'm around now for an hour or two.

Emilio Pisanty

@Secret that sounds weird to me

the way I intended the term has much more to do with the nature of the known than the nature of the unknown

so to speak

Secret

well, it is kind of a known unknown: You knew that many people in the circle said some practice or claim, but it is often hard to pin down where that claim and practice is based on.

Emilio Pisanty

@Rishi That's reasonable enough. Have a good summer, and good luck in college!

@Secret more of an unknown known, I would say

Secret

ah sorry I might have swapped it around, I sometimes mixed up the hybrid types of the 4 unknown classifications

Emilio Pisanty

14:06

@Secret well, that classification always leaves one box empty, right?

I reckon that folklore goes in that box

we know it, but we don't know that we know it

or perhaps more precisely, we know it, but we don't know how we know it

Secret

yup. Blindspots also belong there, which is why it is often used as a management tool for managers to discovery their strengths

Emilio Pisanty

For the specific example linked there, it's particularly interesting - I now understand the claim and its scope of validity, and I am now in a position where I need to convince a senior researcher that the claim is essentially true for all the cases that we care about

I can't go "Look, It's True", 'cause it isn't

Akash. B

@JohnRennie I see some defects in bohrs model of atom

Secret

It is always satisfying when one can explain where a folklore, or more generally, some kind of common sense within a given circle came from and ground it to reality

John Rennie

@Akash.B well, yes, the Bohr model was an early attempt to describe atoms and it is only partially successful.

Akash. B

14:20

Anyway recent educational videos shows that the protons are attached togethere inside the nucleus but how is this possible? The protons have like charges, right?so it should repel right?

@JohnRennie

John Rennie

@Akash.B the protons are held together by the strong nuclear force. This is stronger than the electrostatic force so it holds the protons together even thought their charges repel.

Nuclear force

The nuclear force (or nucleon–nucleon interaction or residual strong force) is a force that acts between the protons and neutrons of atoms. Neutrons and protons, both nucleons, are affected by the nuclear force almost identically. Since protons have charge +1 e, they experience an electric force that tends to push them apart, but at short range the attractive nuclear force is strong enough to overcome the electromagnetic force. The nuclear force binds nucleons into atomic nuclei. The nuclear force is powerfully attractive between nucleons at distances of about 1 femtometre (fm, or 1.0 × 10−15...

Akash. B

Oh I see

@JohnRennie I have another question

Slereah

Akash. B

It was discussed here

John Rennie

@Akash.B yes?

Akash. B

14:25

@JohnRennie well it was about digging a hole through the centre of the earth

Isn't it possible?

Kyle Kanos

If you can survive the heat & pressure, sure

Slereah

Define "possible"

I wouldn't recommend trying

Akash. B

Metals requires some time to heat up so is it possible to escape within that time limit?

John Rennie

@Akash.B The centre of the Earth contains liquid iron at several thousand degrees. You can't dig a tunnel through liquid iron, and even if you could, the heat would roast you! :-)

Kyle Kanos

And I'm not sure how you'd go about storing the molten core

Slereah

14:26

Just eject it into spaaace

although everything around would just fall towards the center

Kyle Kanos

One possibility, I suppose. Might be tricky

Slereah

I mean

if you have some time

Akash. B

@JohnRennie I edited my statement

Slereah

you can simply wait until the earth's core cools down

should only take a few billion years

curio

hello. how rude is it to just tell your first name when you are introduced to the speaker (who is a professor) of a seminar talk ?

because i accidentally did just that

John Rennie

14:28

@curio don't worry about it, he won't remember you.

Kyle Kanos

I suppose you could try grabbing an asteroid/meteor and crash it thru Earth, that'd makea hole, right?

curio

the speaker was invited by my supervisor and im worrying that it makes him look bad

Slereah

@KyleKanos probably more than a hole

Akash. B

@Slereah I am talking about escaping from the core before our vehicles gets heated

Slereah

I don't know if your lab has ever given you the Safety Talk, but I would say any experiment that could destroy the planet is ill-advised

Kyle Kanos

14:29

Or turn yourself into neutrinos, then you can just go through Earth

John Rennie

@curio he meets thousands of students and forgets them immediately afterwards. He won't remember you!

Akash. B

3 mins ago, by Akash. B

Metals requires some time to heat up so is it possible to escape within that time limit?

Kyle Kanos

@curio do you normally give your full name when meeting someone? Because I almost never do...

Akash. B

@JohnRennie what's your opinion?

About the above statement?

curio

i havn't met too many people in such a setting before

Kyle Kanos

14:31

@curio setting is irrelevant to my question

John Rennie

@Akash.B it's a non-starter. We don't have any technology that could tunnel under the conditions even a few tens of kilometers below the surface let alone right through the centre of the Earth.

I think the deepest hole ever drilled was less than 20km deep.

curio

well, when im talking to people of my age i just say my first name

Kyle Kanos

@JohnRennie but you've seen "The Core", right

curio

but when I`m talking to my supervisior i say Mr. X and he calls my Mr. Y

PM 2Ring

What would you use to keep the tunnel from collapsing?

Kyle Kanos

14:33

@curio so then comfort yourself. If you can do it with some people, you can do it with all people.

Slereah

Magic

Akash. B

@PM2Ring Russians had invented a way

curio

@KyleKanos but not with people who are "above me" in the academic sense, right?

Kyle Kanos

@PM2Ring wooden supports

@curio no, you can do it with anyone

PM 2Ring

@KyleKanos :D

curio

14:36

but i think my supervisor, who was standing right next to us, was a little disturbed when i did that

Kyle Kanos

Did you ask him if he was actually disturbed by that? Or at you just assuming?

curio

assuming

Kyle Kanos

Because, as far as I know, it's a complete non-issue

PM 2Ring

@Akash.B I seriously doubt that. It's hard enough to tunnel a few km into the crust. Tunnelling through the mantle would be extremely difficult, and through the liquid core would be insane.

curio

thats really good to hear

do you think i should say something to my supervisor?

Kyle Kanos

14:40

That's up to you, really. If you are curious enough to know whether they were disturbed it not, sure. But it's not really a big deal

John Rennie

@curio no. Forget it happened.

Akash. B

@PM2Ring I meant that they had a more convenient way to prevent tunnel from collapsing

John Rennie

Your supervisor will say something to you if he's really concerned.

PM 2Ring

The inner core is hotter than the melting point of iron, but it's solid due to the enormous pressure. Good luck trying to tunnel through that, even if you had some amazingly strong tungsten alloy to line the tunnel.

curio

ok. thanks guys.

Emilio Pisanty

14:45

@curio The precise details can depend on the cultural setting - it's impossible to give a complete answer with the amount of context you've given.

For all the places I've seen in Europe and the US, this would be a complete non-issue

@curio but then again it's very rare that supervisors and students would have this type of relationships in either Europe or the US

curio

what type of relationshit do you mean? the Mr. X?

Emilio Pisanty

There's nothing wrong with asking your supervisor if it was a faux pas for that particular situation in the specific context of your institution

curio

im in germany btw

Emilio Pisanty

@curio yes

@curio then I don't think this is an issue. I'd leave it alone unless your supervisor brings it up.

curio

alright. this is relieving.

im worried because my supervisor invited the speaker. and he is an important person i think.

Emilio Pisanty

14:52

@curio seriously. It's nowhere near important.

curio

yea im probably just paranoid about it

user351417

15:28

@EmilioPisanty Thanks = )

kyle campbell

17:16

physics.stackexchange.com/questions/480367/… @KyleKanos Should I not answer questions like this?

Kyle Kanos

17:29

@kylecampbell I'd say probably not. Such questions are considered off-topic; answering them occasionally leads to downvotes but surely gives other people the idea that they can post such questions here

Loong

19:01

@RyanUnger welcome back

8

Slereah

Don't play coy @RyanUnger

You're not too good to be here

Ryan Unger

yo

what's been happening

skullpatrol

chillin'

you?

Ryan Unger

the opposite

Kyle Kanos

@RyanUnger nothing. Chat has been frozen for the last year...

Sir Cumference

19:10

Hey you're back

Ryan Unger

@KyleKanos good! now it can resume

@SirCumference

Sir Cumference

Yeah tbh

Ryan Unger

need to relearn this

Sir Cumference

Apr 2 at 5:00, by Bernardo Meurer

@SirCumference after they banned @0celo7 the soul of this chat was gone

Kyle Kanos

@RyanUnger Possibly.

Ryan Unger

19:11

@SirCumference the best part about being gone for a year is that I don't remember where you are

Sir Cumference

@RyanUnger lol sounds good

Ryan Unger

so were there mod elections

Sir Cumference

Oh speaking of which you're a grad student now?

Ryan Unger

I got an email

@SirCumference starting in the fall

Kyle Kanos

@RyanUnger Yeah. There was drama with said elections too

Ryan Unger

19:12

oh, do tell

I remember someone with 700 rep applying

I stopped following after that

@SirCumference you're gonna be a senior?

Kyle Kanos

Well no one was nominating themselves, so I tipped my hat in. But since I was hilariously suspended like 2 weeks prior, SE CM took me out of the running after like 30 hours

Ryan Unger

Haha, what were you suspended for?

Kyle Kanos

And that really upset a fair number of people

Emilio Pisanty

@KyleKanos was there really? I mean, compared to the pretty fractious show we had on the previous go-round

Kyle Kanos

@RyanUnger someone complained about one of my posts saying that a hypothetical person might misread it. So I mocked the hypothetical person, to which everyone thought I was mocking the complainer. So I got suspended for not being nice

Ryan Unger

19:16

I remember being told one cannot be mean to hypothetical people

Kyle Kanos

The hilarious thing is that I was making fun of the hypothetical person's reading abilities & everyone was misreading the comment. Talk about irony...

Ryan Unger

Let's see how long I survive this time

3

ACuriousMind

@KyleKanos Do you want me to post the comments in question so that people can judge for themselves? At least one CM definitely agreed with the assessment that the line between "hypothetical person" and "other user" was rather slim in this case. I'm also fine with letting the matter rest, but it is not really fair to let other users only go on your interpretation of the matter if we insist on repeatedly discussing it.

Ryan Unger

@ACuriousMind Hi

I wouldn't mind seeing the comments

ACuriousMind

@RyanUnger Hey, welcome back

Ryan Unger

19:20

Thanks. I actually had a good break from here

ACuriousMind

How's life been to you?

Ryan Unger

Really good

You still at SAP?

ACuriousMind

Yup, got promoted to non-junior developer and have settled in rather nicely

Kyle Kanos

@ACuriousMind pretty sure I posted the exchange in the mod vote aftermath (or at least a paraphrase of it), but go ahead if you want

ACuriousMind

@RyanUnger Still doing geometry?

Ryan Unger

19:22

Yes. Going to Princeton in the fall to work with Fernando Marques

@KyleKanos link?

Kyle Kanos

@RyanUnger that's like 2+ weeks ago, no idea.

Ryan Unger

@ACuriousMind I need you to explain the famous picture of Spec Z[x]

ACuriousMind

@RyanUnger For your PhD? I never quite got my head around how the American system proceeds

Ryan Unger

Yeah

Like I get that there's a fibration Spec Z[x] -> Spec Z and that gives the vertical lines

but what are the horizontal ones

ACuriousMind

"Copies of Spec Z", I think?

The "intuitive" view of algebraic geometry never made much sense to me

Sir Cumference

19:27

@RyanUnger Oye, yeah

@RyanUnger For math or physics?

Ryan Unger

Math

@ACuriousMind I figured I'd read AM this summer and do all the exercises

They have an exercise to draw Spec for a bunch of rings

It's driving me crazy because I don't have a precise idea of what they mean

ACuriousMind

I assume you've read neverendingbooks.org/mumfords-treasure-map?

Ryan Unger

Oh, no

I'll take a look

Kyle Kanos

Apr 29 at 17:46, by Kyle Kanos

@JMac Someone said that someone might misread my post, so I said that if that hypothetical person reads my post (which explains how to read it) and comes to the wrong conclusion, then their reading comprehension is cruddy (except the vernacular used there)

Though reading back to that, there was also a remark after the "cruddy" part in which I said no one should listen to them

Ryan Unger

Stupid question

Kyle Kanos

19:36

Was the removed question directed to me, bc I totally missed it

ACuriousMind

@KyleKanos Very well: i.sstatic.net/9zDL5.png. All comments not by you are from the same other user.

Ryan Unger

I appreciate the moderatorial drama to make me feel at home

Kyle Kanos

@skullpatrol no idea. Not given any indication

Ryan Unger

@ACuriousMind "Because maximal ideals do not contain any other prime ideals" Really?

take a non-maximal prime ideal and use Zorn, no?

Kyle Kanos

For reference: the reason the "comprehension is shit" remark appears twice is because the first was apparently flagged & deleted (without intervention?) while I thought it was a dropped message (an issue that still persists)

skullpatrol

19:39

(pardon the removal ;)

Ryan Unger

dare I ask who the other person is

SDFG

@KyleKanos the edit rant on the post is something else though

Kyle Kanos

And I stand by my insistence that I didn't ever insult the other user; all remarks are pointed towards the person who is misreading the post (i.e., the fictional person)

@RyanUnger I ain't gonna say it, but if they want to come forward, that's on them

@SDFG certainly felt good though

SDFG

@KyleKanos haha!

bolbteppa

@KyleKanos incidentally, the worst part of that exchange is clearly the 'poor impression' comment

@RyanUnger congrats

Ryan Unger

19:43

Hi @bolbteppa thanks

skullpatrol

\o @NovaliumCompany

Ryan Unger

How can anyone get a poor impression of @KyleKanos

You must be doing something wrong

Novalium Company

@skullpatrol sup

Ryan Unger

You being the hypothetical person!

Kyle Kanos

@bolbteppa I'm not easily offended, so it didn't bother me. Looking back, probably not the kindest thing that person could have said

ACuriousMind

19:44

@RyanUnger Yeah, that line is nonsense. Maybe this is a better explanation for the maximal ideals as points: "These are depicted as the ’points’ in the drawing and the curves are drawn such that they pass through all maximal ideals containing their principal prime ideal"

@KyleKanos If we're at it: The first instance was auto-deleted because r/a flags on comments containing words such as "shit" just do that, there was no intervention at that point because no human handled it.

JMac

@KyleKanos The issue as I see it is that you're really opening the doors for anyone who happened to misunderstand it to be directly insulted by your comments. The commenter was saying "I think this could be misunderstood" and your reply was basically "Well anyone that misunderstands it has shit comprehension". Although it's possible no one will misunderstand it, it's potentially insulting to anyone who would, which violates the be nice policy

Kyle Kanos

@ACuriousMind I'd assumed it was auto deleted, but wasn't sure...good to know the reason though

Ryan Unger

Wait, we're literally not allowed to say bad words any more?

Automatically?

@ACuriousMind reading

Kyle Kanos

@RyanUnger if it's flagged, apparently that is the case

JMac

Presumably they are working off the idea that comments are transient, mixed in with the fact that rarely if ever is swearing required to get a point across. If the comment is useful, it's probably just as useful without swearing, and wouldn't be subject to auto-removal

Kyle Kanos

19:48

@JMac well the post the thread is on explains how to interpret the post. So yeah, if you are misreading it then it's probably a fact...

ACuriousMind

@RyanUnger This has been that way for comments on the main site for years. Chat and flags on answers or questions do not have this insta-deletion feature.

JMac

@KyleKanos Still though... if someone posts complete nonsense here it also violates the be nice policy to say "You're an idiot". It doesn't matter if you're right, it's still pretty obviously not-nice

thermomagnetic condensed boson

any DFT guru in here?

density f unctional theory, not discrete fourier transform

SDFG

Just to leave this out here : Recently the event "Physics chat session" was scheduled here, and there weren't half as many people here, then. 156 had registered.

ACuriousMind

@thermomagneticcondensedboson I don't think any of the regulars is specifically a condensed matter, let alone a DFT, specialist, Emilio or Daniel are likely your best bet.

Ryan Unger

19:53

well I'm registered but was literally unable to attend

I'll try to make it from now on

ACuriousMind

@SDFG Many of those registrations are from users who haven't visited chat in years. The event stems from the beginning of the site and we don't really do anything special for it nowadays

If someone has good ideas for something we could do with them, don't hesitate to air them

SDFG

@ACuriousMind Ah, I see. Well, I'm relatively new here, so I was a bit excited to see how it would go..Pardon me if my earlier comment came off in a wrong tone, though :)

bolbteppa

The only 'prime ideals as points' thing I remember is say an ideal $I$ in $C[a,b]$ of functions vanishing at some point $c \in [a,b]$, no larger ideal $J$ exists strictly in $C[a,b]$ containing $I$ so the point $c$ determines the ideal and so you call it a point

Ryan Unger

@ACuriousMind Well do they mean that maximal ideals aren't contained in prime ideals?

Because of the inclusion reversing thing

that would make sense

ACuriousMind

Yes, that's probably what they meant to write, now that you say it

See, you already understand the drawing better than I think I ever did ;)

Ryan Unger

19:57

my algebra 2 professor would be proud

@ACuriousMind registrar.princeton.edu/course-offerings/…

I want to get ready for this

there's also this one which sounds like a meme registrar.princeton.edu/course-offerings/…

ACuriousMind

@RyanUnger Mine probably wouldn't talk to me because he also lost two post docs and a master student to SAP :D

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