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1:23 AM
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:

$(\eta_{\mu \nu} a^{\mu} a^{\nu})^{1/2} = \gamma ^{3} a$
2 hours later…
3:20 AM
@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.
I think Physics SE is awesome, and maybe I'll return after a while.
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.
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
But this meta post kind of made me feel sure that quitting was the right choice.
3:36 AM
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.
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.
3:47 AM
(cc @PM2Ring @JMac @KyleKanos and everyone else in that discussion)
4:54 AM
@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.
2 hours later…
6:55 AM
@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.
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.
7:20 AM
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?
7:34 AM
Greetings, hu-mans
8:06 AM
@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
@EmilioPisanty blarg
Though maybe you're not quite deep in enough that you need to break out the Ito calculus guns
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
@Slereah greetings, sle-reah
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
i think that one uses it
p. 17 on
3 hours later…
11:28 AM
@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.
Anyways, see ya!
@RyanUnger welcome back (later today)
@Slereah where's the Ito'ness
p. 20
Ah, integrating over fractal paths
11:52 AM
@JohnRennie you there?
@JohnRennie is always with us in spirit
12:08 PM
^ I second that emotion
12:36 PM
This user has been automatically suspended for posting inappropriate content and cannot chat for 6 hours 24 minutes.
countdown to the GR group reassemble
1:18 PM
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"
1:37 PM
Q: How I learned to stop worrying and start asking questions

Emilio PisantyAs 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
1:57 PM
@Jim that'd be a dentist I'd like to visit, were I to go to one
@Akash.B hi. I had left by the time you posted, but I'm around now for an hour or two.
@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
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.
@Rishi That's reasonable enough. Have a good summer, and good luck in college!
@Secret more of an unknown known, I would say
ah sorry I might have swapped it around, I sometimes mixed up the hybrid types of the 4 unknown classifications
2:06 PM
@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
yup. Blindspots also belong there, which is why it is often used as a management tool for managers to discovery their strengths
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
@JohnRennie I see some defects in bohrs model of atom
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
@Akash.B well, yes, the Bohr model was an early attempt to describe atoms and it is only partially successful.
2:20 PM
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?
@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.
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...
Oh I see
@JohnRennie I have another question
It was discussed here
@Akash.B yes?
2:25 PM
@JohnRennie well it was about digging a hole through the centre of the earth
Isn't it possible?
If you can survive the heat & pressure, sure
Define "possible"
I wouldn't recommend trying
Metals requires some time to heat up so is it possible to escape within that time limit?
@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! :-)
And I'm not sure how you'd go about storing the molten core
2:26 PM
Just eject it into spaaace
although everything around would just fall towards the center
One possibility, I suppose. Might be tricky
I mean
if you have some time
@JohnRennie I edited my statement
you can simply wait until the earth's core cools down
should only take a few billion years
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
2:28 PM
@curio don't worry about it, he won't remember you.
I suppose you could try grabbing an asteroid/meteor and crash it thru Earth, that'd makea hole, right?
the speaker was invited by my supervisor and im worrying that it makes him look bad
@KyleKanos probably more than a hole
@Slereah I am talking about escaping from the core before our vehicles gets heated
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
2:29 PM
Or turn yourself into neutrinos, then you can just go through Earth
@curio he meets thousands of students and forgets them immediately afterwards. He won't remember you!
3 mins ago, by Akash. B
Metals requires some time to heat up so is it possible to escape within that time limit?
@curio do you normally give your full name when meeting someone? Because I almost never do...
@JohnRennie what's your opinion?
About the above statement?
i havn't met too many people in such a setting before
2:31 PM
@curio setting is irrelevant to my question
@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.
well, when im talking to people of my age i just say my first name
@JohnRennie but you've seen "The Core", right
but when I`m talking to my supervisior i say Mr. X and he calls my Mr. Y
What would you use to keep the tunnel from collapsing?
2:33 PM
@curio so then comfort yourself. If you can do it with some people, you can do it with all people.
@PM2Ring Russians had invented a way
@KyleKanos but not with people who are "above me" in the academic sense, right?
@PM2Ring wooden supports
@curio no, you can do it with anyone
@KyleKanos :D
2:36 PM
but i think my supervisor, who was standing right next to us, was a little disturbed when i did that
Did you ask him if he was actually disturbed by that? Or at you just assuming?
Because, as far as I know, it's a complete non-issue
@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.
thats really good to hear
do you think i should say something to my supervisor?
2:40 PM
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
@curio no. Forget it happened.
@PM2Ring I meant that they had a more convenient way to prevent tunnel from collapsing
Your supervisor will say something to you if he's really concerned.
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.
ok. thanks guys.
2:45 PM
@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
what type of relationshit do you mean? the Mr. X?
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
im in germany btw
@curio yes
@curio then I don't think this is an issue. I'd leave it alone unless your supervisor brings it up.
alright. this is relieving.
im worried because my supervisor invited the speaker. and he is an important person i think.
2:52 PM
@curio seriously. It's nowhere near important.
yea im probably just paranoid about it
3:28 PM
@EmilioPisanty Thanks = )
5:16 PM
physics.stackexchange.com/questions/480367/… @KyleKanos Should I not answer questions like this?
5:29 PM
@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
2 hours later…
7:01 PM
@RyanUnger welcome back
Don't play coy @RyanUnger
You're not too good to be here
what's been happening
the opposite
@RyanUnger nothing. Chat has been frozen for the last year...
7:10 PM
Hey you're back
@KyleKanos good! now it can resume
Yeah tbh
need to relearn this
Apr 2 at 5:00, by Bernardo Meurer
@SirCumference after they banned @0celo7 the soul of this chat was gone
@RyanUnger Possibly.
7:11 PM
@SirCumference the best part about being gone for a year is that I don't remember where you are
@RyanUnger lol sounds good
so were there mod elections
Oh speaking of which you're a grad student now?
I got an email
@SirCumference starting in the fall
@RyanUnger Yeah. There was drama with said elections too
7:12 PM
oh, do tell
I remember someone with 700 rep applying
I stopped following after that
@SirCumference you're gonna be a senior?
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
Haha, what were you suspended for?
And that really upset a fair number of people
@KyleKanos was there really? I mean, compared to the pretty fractious show we had on the previous go-round
@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
7:16 PM
I remember being told one cannot be mean to hypothetical people
The hilarious thing is that I was making fun of the hypothetical person's reading abilities & everyone was misreading the comment. Talk about irony...
Let's see how long I survive this time
@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.
@ACuriousMind Hi
I wouldn't mind seeing the comments
@RyanUnger Hey, welcome back
7:20 PM
Thanks. I actually had a good break from here
How's life been to you?
Really good
You still at SAP?
Yup, got promoted to non-junior developer and have settled in rather nicely
@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
@RyanUnger Still doing geometry?
7:22 PM
Yes. Going to Princeton in the fall to work with Fernando Marques
@KyleKanos link?
@RyanUnger that's like 2+ weeks ago, no idea.
@ACuriousMind I need you to explain the famous picture of Spec Z[x]
@RyanUnger For your PhD? I never quite got my head around how the American system proceeds
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
"Copies of Spec Z", I think?
The "intuitive" view of algebraic geometry never made much sense to me
7:27 PM
@RyanUnger Oye, yeah
@RyanUnger For math or physics?
@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
Oh, no
I'll take a look
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
Stupid question
7:36 PM
Was the removed question directed to me, bc I totally missed it
@KyleKanos Very well: i.stack.imgur.com/9zDL5.png. All comments not by you are from the same other user.
I appreciate the moderatorial drama to make me feel at home
@skullpatrol no idea. Not given any indication
@ACuriousMind "Because maximal ideals do not contain any other prime ideals" Really?
take a non-maximal prime ideal and use Zorn, no?
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)
7:39 PM
(pardon the removal ;)
dare I ask who the other person is
@KyleKanos the edit rant on the post is something else though
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
@KyleKanos haha!
@KyleKanos incidentally, the worst part of that exchange is clearly the 'poor impression' comment
@RyanUnger congrats
7:43 PM
Hi @bolbteppa thanks
\o @NovaliumCompany
How can anyone get a poor impression of @KyleKanos
You must be doing something wrong
@skullpatrol sup
You being the hypothetical person!
@bolbteppa I'm not easily offended, so it didn't bother me. Looking back, probably not the kindest thing that person could have said
7:44 PM
@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.
@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
@ACuriousMind I'd assumed it was auto deleted, but wasn't sure...good to know the reason though
Wait, we're literally not allowed to say bad words any more?
@ACuriousMind reading
@RyanUnger if it's flagged, apparently that is the case
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
7:48 PM
@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...
@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.
@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
any DFT guru in here?
density f unctional theory, not discrete fourier transform
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.
@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.
7:53 PM
well I'm registered but was literally unable to attend
I'll try to make it from now on
@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
@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 :)
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
@ACuriousMind Well do they mean that maximal ideals aren't contained in prime ideals?
Because of the inclusion reversing thing
that would make sense
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 ;)
7:57 PM
my algebra 2 professor would be proud
I want to get ready for this
there's also this one which sounds like a meme registrar.princeton.edu/course-offerings/…
@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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