The h Bar

How much angular momentum each planet had when it finished forming.

And impacts after it formed

(I think)

user280247

Yes but it was too long...@EmilioPisanty

Formation and evolution of the Solar System

12:02 AM

@santimirandarp did you try looking on Wikipedia?

Axial tilt

In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, or, equivalently, the angle between its equatorial plane and orbital plane. It differs from orbital inclination. At an obliquity of 0 degrees, the two axes point in the same direction; i.e., the rotational axis is perpendicular to the orbital plane. Earth's obliquity oscillates between 22.1 and 24.5 degrees on a 41,000-year cycle; Earth's mean obliquity is currently 23°26′12.7″ (or 23.43685°) and decreasing. Over the course of an orbital period, the obliquity usually does not...

The formation and evolution of the Solar System began 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed. This model, known as the nebular hypothesis was first developed in the 18th century by Emanuel Swedenborg, Immanuel Kant, and Pierre-Simon Laplace. Its subsequent development has interwoven a variety of scientific disciplines including astronomy...

@santimirandarp If you want a short answer, ask a concise question.

"I don't understand the Earth's axial tilt" simply isn't going to get you short and concise answers. It's way too broad and formless.

user280247

Well, I supposed axial tilts could be explained by sun's magnetic field, or gravity...

@santimirandarp To be clear, they're not "caused" by any present feature of the solar system.

Has wikipedia always had green locks beside open articles or is that new?

user280247

Yes, it's clear...

user280247

maybe a change of browser? @danielunderwood

12:08 AM

they came to be what they are now because of collisions in the early solar system, as well as complex tidal interactions between planets and moons over timescales in the tens to thousands of millions of years.

any other answer is just you fooling yourself.

@danielunderwood what?

I don't see any.

I just see this.

user280247

besides the url @EmilioPisanty

@danielunderwood ah. No, that's not wikipedia, that's your browser.

user280247

Well that's what i've said ... @EmilioPisanty

@danielunderwood OS / browser / browser version?

user280247

mozilla firefox...

user280247

12:12 AM

maybe the proper question should be why different planets have different tilts @EmilioPisanty

user280247

Anyway, the answer is clear XD

4 mins ago, by Emilio Pisanty

they came to be what they are now because of collisions in the early solar system, as well as complex tidal interactions between planets and moons over timescales in the tens to thousands of millions of years.

@EmilioPisanty damnit I clicked on a link from AFT to that yesterday

Ubuntu/Firefox 62

user280247

Should I repeat also 'anyway, the answer is clear'? @EmilioPisanty

12:15 AM

@danielunderwood ah

Interesting

Also what that article is...tensor-vector-scalar gravity looks someone got a bit field-happy to me

the obvious answer is "no, that can't have always been there because Wikipedia is older than the OA open-lock logo"

but as to when it was introduced... no idea.

New question: Are the green locks on wikipedia new?

lol

Help talk:Citation Style 1/Archive 27

== id-access support == Per #Which identifiers, we should support |bibcode-access=free |doi-access=free |hdl-access=free |jstor-access=free |ol-access=free |osti-access=freeTo make them display green open access locks at the end of their identifier. We should also update {{bibcode}} {{doi}} {{hdl}} {{JSTOR}} {{OL}} {{OSTI}}to also support the same |foobar-access=yes and have the green open access locks. And then we should update {{arxiv}} {{biorxiv}} {{CiteSeerX}} {{IETF-RFC}} {{PMC}} {{SSRN}}to always display the green free access locks. Headbomb {talk / contribs / physics / books} 14:50, 23...

looks to be some two years old to me

Ahh guess I'm just bad at noticing things that should be obvious

5:11 AM

This might be of interest given how much we all love the HNQ list:

Revisiting the "Hot Network Questions" feature: what are our shared goals for having it?

8

Q: Breaking the HNQ feedback loop on bad questions

@JohnRennie Yes, we should participate in that discussion. I see some Physics folks there already.

user351417

5:56 AM

@rob Emilio Pisanty has tonnes of stuff about HNQs; his comments are all over that page. I actually really love his post about the feedback look with HNQs, but unfortunately SE employees don't appear to have responded to that.

user351417

40

The Hot Network Questions sidebar is a bit of a contentious issue, because it tends to promote questions that are often perceived as 'cheap', of relatively low quality, or on the fringes of topicality for the site that hosts them. One reason for this is that they're subject to a feedback loop: t...

@Chair Well, now that a semi-famous Twitter personality is involved, maybe they'll move.

user351417

@rob That person on twitter was semi-famous?

@Chair I actually don't know enough about Twitter to answer that question.

I have a problem in real life which my mother calls "deep voice syndrome."

user351417

I was really-really put off by that twitter post though: it looked an awful lot like cherry-picking. I mean, someone found a string of consecutive unusually strange HNQs, and decided to connect that up to SE being unwelcoming.

5:59 AM

It's where I don't quite know what I'm talking about, but I speculate in delcarative sentences with a deep voice.

People listening to me say, "Oooh, authoritative."

And misconceptions are born.

I forget that having a diamond gives me some deep-voice-syndrome issues on SE as well.

user351417

@rob I scratch my chin thoughtfully and stare into space, hoping that I look like I'm thinking.

user351417

It usually works

user351417

Except it looks kinda lame because I'm among the least bearded people in my class.

Anyway, I was reading one of those HNQ discussions today, and wondering how much of the issue would be solved if the association bonus didn't let people vote up, like the association bonus doesn't let people answer protected questions.

The latter restriction was put in place in response to HNQ trouble, as far as I can tell --- I remember being able to answer protected questions with just the association bonus and thinking it was probably not a great privilege.

user351417

I'm surprised that there's very little on the mother meta post and the IPS meta post about how this connects to that April Wensel (or something) and the welcoming issue. That's the point that the twitter post was trying to raise, but everyone's coming out of the woodwork to just talk about inappropriate stuff in general

user351417

6:04 AM

Like the twitter stuff seems to focus on the content being there on SE in the first place, but everyone's focusing on how we advertise it as HNQs.

A: Is Stack Overflow really racist/sexist?

I dunno about that. I think there's a difference between having dirty laundry in your house and having dirty laundry on your front yard.

user351417

6:19 AM

@rob Yeah, but which one are we being criticized for?

user351417

109

I have no more stats than you do. I do know what I've validated as comment flags recently though, and I planned on going through some of those recent flags. I, unfortunately, found the history of what I've handled was lacking in the length of time it's easily accessible. So, I have a much smaller...

user351417

Andy's answer suggests that a lot of the rude content is in comments, which are not very visible and easily removable. I think that's the stuff that the welcoming posts are criticizing.

@Chair The problem is that they ignored years of meta discussions about HNQ's, but a developer changed the code within 40 minutes after an outsider Twitter post.

user351417

@Loong Hmmm. That means we're fighting about too many things at once. (1) Random outsider says something and a developer removes a site from the HNQ list without talking to the site's mods/community (2) We don't like the questions which end up as HNQs because they're argumentative (3) The same as point 2, except because they're unwelcoming, (4) Some of us don't like HNQs at all and think they should be removed altogether (5) There's lots of apparently discriminatory content in general.

user351417

If only we could have had these things discussed separately.

6:31 AM

and in addition to (1) now this new meta post as a cover-up

For what it's worth I generally like the HNQ list, and if I have a few minutes of idle time I'll often spend it surfing through the list. It's mildly annoying when a silly physics question makes the list, but only because I feel proud of the PSE and want people to be impressed by it.

I often enjoy HNQ's. However, I am mainly annoyed by quick low-quality answers to HNQ's that get much more upvotes than any good answer to a normal question.

I don't think there's an easy fix for that, though someone suggested removing the association bonus so that new members can't upvote.

@JohnRennie what do you mean by micro gravity?

@Akash.B microgravity normally just means very low gravity. That is, the gravitational acceleration isn't exactly zero but it's so small that it can usually be ignored.

@Akash.B There's a nice NASA article on it here

6:48 AM

I frequently enjoy HNQ when I'm using the site in my spare time. But if I am trying to solve a technical problem I find them super-distracting.

Maybe that's my ADHD working against me.

But I think the Physics questions that end up on HNQ have a very distinctive character to them, and that character is less interesting than the questions that bring me back here as a physicist.

Right now there is a HNQ from physics about arguing with a Flat Earther.

user351417

@rob And we recently had one which invited arguments about how global warming is a hoax.

user351417

(well, that answer was deleted, but the question still wasn't a great one IMO)

hey I found out something new

we cannot draw straight lines

A while back I wrote two answers the same day. One was about precision beta decay experiments and touched on some work I've done professionally. The other said, "If you have a puddle with corners, it'll round out as it dries."

Guess which went HNQ and got 150 votes? The dumb one.

That's what I mean.

user351417

6:59 AM

HNQ effect gave an unregistered user 150 votes for a picture of an ant walking on mercury with no physics at all :(

@Chair Wasn't that in answer to the question "can ants walk on mercury"?

I have no problem with those upvotes

The OP went to the trouble of doing the experiment. Full marks to them for that.

(no ants were harmed in this experiment)

I've used a picture of an ant as well :-)

user351417

8:10 AM

@JohnRennie @rob yeah that's the one. I don't really like that because I don't see the point of doing an experiment if you aren't going to try to explain results in the end. If all one learns from the episode is that ants can walk on liquid mercury, I don't think that's very productive.

@Chair but you'd concede that it is an important contribution to the discussion?

user351417

@JohnRennie Yes, it's an extremely important contribution, and it supports the other answers well, but it isn't a good answer (though it is an answer). But it isn't the sort of thing which should make a question an HNQ and it shouldn't have received more votes than the other answers. SE says "the best answer rises to the top", and that's not what happened there.

Anonymous

8:44 AM

@Loong Unlike what we might wish at times, the world doesn't work on the principles of absolute and objective fairness, and it's probably not worth our time worrying about it. People like to vote on creative/fun answers even if it doesn't completely address the question.

9:18 AM

@Chair yes

@enumaris @danielunderwood Any more GR questions?

I am board at work

user351417

@Slereah I haven't spent much time on SO (I use it occasionally for programming when google search results take me there, and I also end up there through Charcoal HQ every now and then, but I don't hang around there the way I do on Physics SE), but I haven't seen anything bad at all. I've seen plenty of offensive stuff (particularly from the chats) being called out on meta SO; it really doesn't seem so severe to me. I'm sure I've never seen anything hateful sticking around on Physics SE.

Oh that was a joke

user351417

Oops hehehe

I am only prejudiced towards Duffield

9:37 AM

@Slereah I strongly doubt that

did you have those opinions before seeing any of his content?

I am postjudiced

user351417

@EmilioPisanty Is it really nice to say that? He isn't here and he wouldn't be able to say anything in his defense even if he was.

He knows what he did

@Chair Is it really nice of him to continuously litter the site with pseudoscience every time his account is allowed to post?

3 hours ago, by Akash. B

hey I found out something new

user351417

9:43 AM

I will agree with him when he says that some of the downvotes he received were probably mob stuff. For example he has -24 or so for something about majorana spinors. I find it hard to believe that there are so many people who know enough to see what's wrong in that and have read that post (I don't know why it's that bad).

Seriously. JD has found a weakness in the SE Q&A engine and exploited it to great effect to take advantage of the hard work of many many people who built a quality platform with a high reputation and search-engine ranking, to position his pseudoscience in places of high ranking that should be completely barred to that kind of harmful content.

4

@Chair Then you do not understand that question and that answer well enough.

@Chair about the ant on mercury thing. Sure he didn't provide an explanation. But he didn't pretend to, either.

It's not hard to realize his answers are nonsense

The physics of an ant walking on mercury can be pretty complex as you know

and hard to get right without making mistakes

user351417

@EmilioPisanty I know that I don't understand that question, and I didn't vote on it. But I really can't believe that there are so many people who do understand that field to the extent that they know exactly what's wrong there.

9:45 AM

why not

Majorana spinors aren't really obscure

@Chair Because you don't understand the question of the answer. I find that score perfectly plausible.

also ants on mercury sounds like something best done via experiment

It isn't "wrong", it's "not even wrong"

Get me ants!

the question asks an exclusively mathematical query about mathematical structures within theoretical physics

the answer is a rant about the applicability of that branch of theoretical physics to experiment

user351417

9:47 AM

@EmilioPisanty Maybe I'm misjudging the complexity of the subject (never studied it myself). At what stage are people taught about it? (early/late undergrad, graduate...)

@Slereah agreed

regardless of whether the rant contains valuable content or not (it doesn't), it's a terrible answer to the question as posed.

Majorana spinors are graduate stuff

@Chair Anybody with a completed physics undergrad degree with any sort of theoretical bent will be able to understand how much of a not-an-answer that post is.

Yeah really

if you know basic things about quantum theory

it would basically like if you read "because of magic"

9:49 AM

@Slereah heck, you don't even need to know much about quantum theory

does anyone have a link to that answer?

you just need to understand the relationship between mathematical physics and experiment.

user351417

@EmilioPisanty Oh okee, I stand corrected.

@AlNejati physics.stackexchange.com/search?q=user%3A76162+majorana

ty

9:49 AM

@Chair please don't link directly.

user351417

@EmilioPisanty Why not? Also, how can I not link directly? Looks like the image and stuff didn't show up for you, so presumably that's what classifies as "not direct".

@Chair as in, please don't link directly to JD content.

it gets enough advertisement as is.

user351417

@EmilioPisanty Oh owie. Still kind of lacking in explanation but less so. How do you post links which aren't 'direct'?

user351417

Anyways, I deleted that one because I could

I'm not 100% fluent in the topic but it seemed like he is mostly just giving his opinion, which is blatantly not OK

9:53 AM

@Chair where possible. see e.g. the example above. It's not a Strict Imperative, though.

and he didn't even address the question

just some random quotes from various sources

user351417

@EmilioPisanty Slick ;)

it may not be worth -23 but it's definitely worth -3

user351417

How did you manage to put that together so quickly?

user351417

(@EmilioPisanty)

9:54 AM

@Chair that's how I found the question when you mentioned it

user351417

Like I had that post open in a different tab so I only needed to go there and copy the URL, but you still posted it first.

user351417

Oh ok... you already had it open too

user351417

@EmilioPisanty I guess you're busy partying about the impending demise of HNQs? ;)

"question by JD about Majorana fermions", eh? well, Users > type Duffield > go to his profile > click on the search bar and it will have the user ID already populated > type "Majorana" > search > as expected there is only one result

@Chair ain't no party yet

I hope it gets fixed

but there's no guarantee that SE will learn the error of their ways

user351417

@EmilioPisanty Well, your Chirped Pulse Amplification posts kind of deserved the full wrath of the HNQ effect.

user351417

9:57 AM

@EmilioPisanty I think a lot of the answers on the newest featured meta post seem to suggest that people like HNQs.; people don't want them to go

@Chair beware of sampling effects.

the population of people posting on that thread ≠ the population of people reading that thread ≠ the population of people who see the sidebar

user351417

@EmilioPisanty But where does voting sit? it's approximately the same as the people who're reading it, right?

user351417

for example, I've been watching the developments since IPS mentioned something in their chat, but I have made zero comments but a lot of votes

@Chair to a large extent, the voting sits with the Fastest Gun in the West

user351417

@EmilioPisanty That explains a lot. I get the feeling that meta.stackexchange.com/a/316939 is not as high up as it once was.

user351417

10:01 AM

But other than yours, almost all suggest reform rather than removal.

@Chair I'm not sure how you're reading my answer as suggesting removal rather than reform.

user351417

I equate HNQ=Clickbait

user351417

If a question isn't clickbait, it probably won't be HNQed

user351417

That's the way people write.

user351417

If you don't want to factor in the popularity of a question once it ends up in the HNQ list, it's not really avoiding the clickbait any more.

10:06 AM

@Chair imma check out of this preaching-to-the-choir conversation for now. The real world calls.

user351417

See ya!

Secret

nature.com/articles/s41586-018-0599-8

> This result implies that a broad class of conjectured particles, if they exist and time-reversal symmetry is maximally violated, have masses that greatly exceed what can be measured directly at the Large Hadron Collider.

More negative results from the particle physics sector. Looks like we are slowly narrowing down the possibilities

nature.com/articles/s41578-018-0036-5

Review paper at undergraduate level on well semimetals and other topological matter

11:43 AM

@HDE226868 If I may - I have to say that justkelly's point about mansplaining is pretty much on target.

The content of the post is irrelevant

The title of the post is content that IPS is (was) pushing onto other (technical) sites' pages

"the author is also autistic" isn't on the title. Therefore it isn't in the content that IPS is pushing elsewhere.

ditto with whatever justification IPS thinks is OK with the sexist titles on the other threads.

or call it "male tropes" if "sexist" is too hard to swallow.

Lozansky

1:44 PM

Imagine a spherical shell of radius $R$, carrying a uniform surface charge $\sigma$, set spinning at $\mathbf{\omega} = \omega \hat{z}$. Now I'm interested in the magnetic dipole moment of the sphere and there are two ways that I see to approach this:

1) Write down the current density $\mathbf{K}(\mathbf{r})$ and compute $\mathbf{m} = \dfrac{1}{2} \int (\mathbf{r} \times \mathbf{K} )\text{ da}$. With $\mathbf{K} = \sigma \mathbf{v} = \sigma (\omega \times \mathbf{r}) = \sigma \omega R\hat{\phi}$ and $\mathbf{r} = R \hat{r}$ so $\mathbf{r} \times \mathbf{K} = \sigma \omega R^2 \hat{z}$ toge…

I know the second one is correct, but I don't see where the first approach breaks down

1:59 PM

Phi hat-cross-r hat should be theta hat

Secret

I wish I can help, but whenever I see vector cross products in integrals, my head get tied into knots

I have terrible intuition on magnetic systems

You only care about the z-hat component, but you’ll pick up a sin(theta) factor from that

I don’t think that finishes it tho

@Lozansky $\mathbf{K} = \sigma \mathbf{v} = \sigma (\omega \times \mathbf{r}) = \sigma \omega R\hat{\phi}$ looks dodgy to me

Yeah, that as well

it's also missing a geometrical $\sin(\theta)$ factor

2:08 PM

right. $\hat{z}\times \hat{r}\propto \hat{\phi}$ but not $=\hat{\phi}$

The issue is that $\hat{z}$ is an orthogonal basis vector in cylindrical coordinates, whereas $\hat{r}$ is in spherical coordinates

(there is also a tension in this problem: It's only the $\hat{z}$ component that survives---suggesting either cylindrical or Cartesian coordinates---but the integration seems most naturally done in spherical coordinates)

Ah, got it. $\mathbf r\times\mathbf K \propto \hat z$ is also wrong. That's the only component that contributes to the integral, but the exact result is $\mathbf r\times\mathbf K \propto \hat \theta$. Once you project on $\hat z$ you get another factor of $\sin(\theta)$.

That changes the integral from $\pi\int_0^\pi \sin(\theta)\mathrm d\theta=2\pi$ to $\pi\int_0^\pi \sin^3(\theta)\mathrm d\theta=\frac43\pi$.

and you're done.

Yeah, that's what I meant earlier (though I should have said "r-hat cross phi-hat = theta-hat")

@Semiclassical yep, you said it first. I thought it was still worth putting it all together, though.

ya

anyways, @Lozansky doesn't seem to be responding, so we can just stop arguing about their homework now =P

2:14 PM

lol

@Semiclassical boy did I get a scare earlier this week

oh?

compare the topics treated in this vs this

on exactly the same arXiv mailing

ooo, nonperturbative physics

@Semiclassical that's the name of the game, yes

2:17 PM

i mean, nonperturbative can mean a lot of things

@Semiclassical sure

specifically, high-order harmonic generation

one of the main applications of the semiclassical WKB approximation is to compute tunneling rates, and that's nonperturbative

nice

@Semiclassical indeed, though WKB tunnelling is static, which makes it a bit flat sometimes

yeah.

HHG kicks off with a tunnelling step, but it's a non-adiabatic tunnelling because the barrier is generally shifting on timescales comparable to or slightly longer than the tunnelling rate

2:19 PM

neat

closest thing I know about in that realm is the Landau-Zener problem

which is still pretty much adiabatic

that's getting closer, though

Lozansky

I am here now :P

lol

Lozansky

Ah yes

Now I see

i mean, the fact that both calculations involved da in the same way meant that the discrepancy had to be coming from K-cross-r

A: Is quantum tunneling related to imaginary time?

2:22 PM

@Semiclassical see e.g. this old answer of mine for flavour

10

Yes, the two are intimately related. One way, as in QMechanic's answer, is via Wick rotations, but in general there is a lot more freedom once you allow integration contours to go over into the complex plane. In my area, strong field physics, the use of complex time to understand tunnelling probl...

which makes it easier to zero in

though there's no HHG there

nice

one silly thing I've found myself interested in is how tunneling works in the pilot-wave account. (Not that I expect to get any grand insight from it.)

For instance, suppose you've got a quartic oscillator (set up as a double-well potential) and you prepare the initial state to be approximately in the ground state of one of the wells

@Semiclassical yeah, that's an interesting testbed

surely it's been done before, though?

or maybe it has but it doesn't work so the pilot-wavers decided not to publish it?

oh, it definitely works. I'm just not sure it leads to anything interesting

2:26 PM

@Semiclassical how does the particle cross the barrier, though?

or is the particle's EOM so far removed from the hamiltonian that it doesn't even see the particle?

Well, the first thing to do is ask how the wavefunction involves

Eh, talking about an EOM in the pilot-wave story is a bit dicey since the momentum and position aren't independent variables

to the extent that there's an EOM, it's a first-order equation not a second-order one

But, lemme table that for a moment

The wavefunction will evolve simply enough: You start off with a Gaussian probability density over the first well, with no probability density in the second well. (these are approximations, of course)

@Semiclassical eh

though I guess, if you're reinventing mechanics...

At any later time, though, the wavefunction will be a superposition of the two ground states (one for each well)

So $\psi(x,t)=A(t)\phi(x-a)+B(t)\phi(x+a)$ where $x=\pm a$ are the well positions

@Semiclassical yes

more precisely, you'll have $\psi(x,t)\approx e^{i \Delta t}[\phi(x-a)+\phi(x+a)]+e^{-i \Delta t}[\phi(x-a)-\phi(x+a)]$

(the true ground and excited state of the double well will be the symmetric and antisymmetric combinations of the two wavefunctions, with energies $E_{\pm}\approx E_0\pm \Delta$ and where $E_0$ is the energy of the single-well ground state)

oh, and hbar=1

so that's $\psi(x,t)=\cos(\Delta t)\phi(x-a)+\sin(\Delta t)\phi(x+a)$. There's probably a phase factor in front of the second term

also, i'm being careless about overall multiplicative values in my wavefunction

2:38 PM

@EmilioPisanty I'm gonna try and maybe start a discussion on IPS about better title-writing, no matter what the outcome of the HNQ discussion on Meta SE is. We've touched on it a bit, but there are still some areas of concern, obviously, and specific problems I want to fix.

Anyways. It's not hard to see what that'll do to your probability density as a function of time: You'll approximately have a sum of two Gaussians pdfs, one centered at each well, with the respective weights for the two pdfs oscillating in time

@HDE226868 to be frank, my reaction to IPS getting banished from HNQ is an unequivocal "good riddance"

IPS?

y'all might have some quality content beyond what makes the list?

it doesn't matter, though

What matters is what makes the list, and that is uniformly awful content.

So at time $t=0$ you'll only have a Gaussian centered at $x=a$, while at $t=\pi/2\Delta$ you'll instead have a Gaussian centered at $x=-a$. At $t=\pi/4\Delta$, you'll basically have two Gaussians with equal weight.

2:41 PM

@EmilioPisanty No offense taken here. While I'm not happy with the precise chain of events here, getting off the HNQ something we've been talking about behind the scenes - and in public, a bit - for about . . . 8 months now? Obviously, that only solves a tiny piece of the problem, but it deals with an issue pretty quickly.

@Semiclassical "Inter-Personal Skills". Because apparently the SE format can produce helpful content for that.

ah

@HDE226868 I agree that the precise chain of events leaves much to be desired.

but then again I've been asking for HNQ reform for years

@EmilioPisanty Well, I'm going to be hopeful about where we go from here.

@EmilioPisanty Yeah, I've seen some of your old Meta answers to that effect. Your new one yesterday was (I thought) very good.

I wish it didn't need an HNQcalypse to bring it to a head like this, but given that SE was set in a track of not listening ever-at-all-not-even-for-a-second just made it inevitable

@HDE226868 thanks =)

2:43 PM

"it's not a problem until it is"

@Semiclassical it was a problem

Well . . . I'm glad there's enough support for HNQ reform in a number of directions.

they just point-blank refused to see it until it slapped them in the face

i guess i should have said "until it's too big to pretend it isn't"

Previously by OP on the topic: Can the many worlds interpretation use the Born rule for decoherence? (on hold), If the Many-Worlds Interpretation cannot derive the Born rule does it need mind body dualism to make sense of probabilities? (closed, then deleted by OP), How does the Many Worlds Interpretation define probability? (closed). — Emilio Pisanty 12 mins ago

::sigh::

2:53 PM

mm

ArtOfCode

let's not start the good ole' h bar superfluous flagging again please

user367139

3:10 PM

How do I delete my account?

@EmilioPisanty i'm realizing i'm forgetting how i thought about some of this stuff, so i'm going to table it for now

Q: How can I delete my account?

231

How can I delete my Stack Exchange account(s)? Also, What happens to my content? Can I request it be deleted as well? What if I'm suspended, rate-limited, or banned from posting questions or answers? What will happen to my votes? Will other users be impacted? Why wasn't my account deleted immed...

support faq user-accounts deleted-accounts

3:27 PM

Is a ray essentially a vector where we don't care about the magnitude?

Vinícius Peixoto

In what context do you ask, though?

Well I originally wanted to know in the case of a state being described as a ray in Hilbert space, but I have heard people say similar things with other vector spaces

I have a feeling that the answer may be to learn more algebra

That seems like a good enough gloss tbh

The more precise way to say it is that a ray is a set of vectors with different magnitude but identical direction

(I forget if you'd always consider $v$ and $-v$ to be in the same ray. In the context of Hilbert space you definitely would.)

So when one says that when talking about QM, they're basically just saying $a \lvert \alpha \rangle$ and $b \lvert \alpha \rangle$ for $a,b \in \mathbb{C}$ correspond to the same state?

right. both of them would give the same expectation values

(so long as you write expectation values as $\langle A\rangle = \frac{\langle \alpha|A|\alpha\rangle}{\langle \alpha|\alpha\rangle}$)

3:43 PM

i.e. normalise it :-)

well, it also gets rid of phase factors

so even within the normalized states you'd still have $|\alpha\rangle$ and $i|\alpha\rangle$ giving the same statistics

But if you consider it as equivalent over all complex C, not just phase factors, then such a ray is closed under addition, i.e. $a|\alpha\rangle+b|\alpha \rangle$ is in the same ray as $|\alpha\rangle$

Of course, this does mean it's not meaningful to talk about addition of vectors from different rays

@danielunderwood in that context, a ray is the set $\{a|\psi⟩ : a\in\mathbb C\setminus\{0\}\}$, for a given nonzero $|\psi⟩$.

every linear combination of vectors from two different rays will in general lie in an another ray

3:59 PM

Ahh good. All the material that I've seen just mentions a state as a ray without ever saying what a ray is. I just wanted to make sure I wasn't missing anything big in the meaning of ray

@danielunderwood well, there's several big things that go under the definition of ray

but in this instance you're OK

I mean he is a quantum state of some sort

wow that's cold

question I answered with 6 upvotes got deleted

lose 60 rep

feelsbadman

@enumaris link?

that normally shouldn't happen

physics.stackexchange.com/questions/432612/…

now I need 140 more rep for 3k lol

4:02 PM

huh. That's odd

lol you have made the rep gods unhappy

Normally normal-user deletion votes won't delete content with upvotes

They deleted the question

so I guess my answer was collateral damage

@enumaris I'm still surprised that it went through.

Anonymous

The question had 5 downvotes

4:03 PM

But my answer had 6 upvotes

so net it was 1 upvote

Anonymous

So maybe it's possible to be deleted even if it has highly voted answers?

:P

Frankly, I don't think it was deletion-worthy

Anonymous

>

I understand that all matter increases in size when approaching speed c

I also understand that all electrons are exactly the same.

Anonymous

:P I don't see any relation between the two statements

Anonymous

4:05 PM

No wonder it got so many downvotes

@Blue how come you can see it?

wayback machine?

Anonymous

google webcache

Well, if the former were true, then how could electrons moving near the speed of c be exactly the same?

Anonymous

@EmilioPisanty webcache.googleusercontent.com/…

It seems like a normal misunderstanding to me

1. assume electrons get more massive when they move faster (common misconception)

2. electrons aren't identical since the faster moving ones are more massive

4:07 PM

and then equate 'mass increases' with 'matter increases in size'

Just clear up the misconception in 1. and the user is good to go, dunno why it's deleted

tbh

Well, the second is also flawed in my book: Does "all electrons are exactly the same" entail that they all have the same total energy? The same velocity?

that they have the same rest mass yes

the misconception is really equating "relativistic mass" with some inherent mass of the object

Anonymous

@enumaris Yep, your answer was on-point (a good answer to a low-effort question). My condolences

Anonymous

Lemme secretly go and upvote some of your stuff XD (Don't tell the mods)

4:09 PM

lol

I think u just did bruh

I have just made kitchari rice (John style) for lunch and oh my goodness it was absolutely delicious.

Anonymous

I have to space out the upvotes or else the system will detect patterns and revert it tomorrow morning :P

@Blue …

Anonymous

@JohnRennie kitchari rice with? Plain kitchari doesn't taste too good :D

@Blue I added extra veg. I agree that just rice and lentils is rather bland.

Anonymous

4:13 PM

@JohnRennie Yumm, that looks more like pilau :)

@Blue basically yes, a pilau with lentils

user351417

@Blue What on earth is with your spelling of indian dishes?

user351417

Who spells pulau with an 'i'?

Anonymous

Pilaf

Pilaf or pilau is a dish, originating from the Indian subcontinent, in which rice is cooked in a seasoned broth. In some cases, the rice may attain its brown or golden color by first being sauteed lightly in oil before the addition of broth. Cooked onion, garlic cloves, sliced carrot, other vegetables, as well as a mix of spices, may be added. Depending on the local cuisine, it may additionally contain meat, fish, vegetables, pasta (orzo), or dried fruit. It is also sometimes called rice pilaf. Believed to have originated in ancient India and spread from there to ancient Iran, pilaf and similar...

tfw when you try to recreate a calculation you've already done in mathematica, but now it stalls out rather that proceeds. "why isn't this working like it was before"

4:14 PM

@Chair I've seen it spelled loads of different ways.

@JohnRennie do you have lunch at 5PM?

user351417

Khichdi

Khichdi (pronounced [ˈkʰɪtʃɽi]), or khichri, is a dish from the Indian subcontinent made from rice and lentils (dal), but other variations include bajra and mung dal kichri. In Indian culture, it is considered one of the first solid foods that babies eat. Hindus, who avoid eating grains during fasting, eat Sabudana Khichadi made from sago. Kichri is a salty porridge. Dalia is another similar sweet porridge made from the crushed wheat or barley mixed with sugar and milk. Khichdi was the inspiration for the Anglo-Indian dish kedgeree. == Etymology and spelling == The term Khichdi (Khicṛī) (Urdu...

Q: Should this question have been deleted?

0

This question recently came up in chat, because a user lost reputation when their upvoted answer went overboard as collateral damage when its question was deleted: Don't get me wrong, I think this is a dreadful question, but I don't think this should have been deleted. It's a bad question ...

discussion specific-question deleted-questions

there you go

Ayyy thanks :D

Anonymous

@Chair Yeah, I was just following JR's spelling there ;)

user351417

4:16 PM

@EmilioPisanty meta.stackexchange.com/questions/312038/… :(

Anonymous

Normally I spell it as khichdi

@danielunderwood I normally eat lunch quite late, but today I got tangled up fixing a failed Internet connection and got delayed by a couple of hours. I wouldn't normally eat this late.

tales from IT

@Chair I've also seen that spelled lots of different ways in the UK. I guess there isn't a unique mapping from the Hindi script to the English alphabet.

My local Indian restaurant spells it kitchuri. I was advised by a Keralan friend to spell it kitchari.

Anonymous

There's a LOT of variation in the pronunciation of those dishes even in India. So take it easy :)

user351417

4:18 PM

@JohnRennie Oh well. I guess kichadi is the closest to the way I say it

> In Indian culture, it is considered one of the first solid foods that babies eat.

Damn, that's put me in my place :-)

@Chair I provided a factual description of the activities of a person who is out to troll this site. Don't feed the troll.

user351417

@JohnRennie I think the name corresponds to "mess".

user351417

Yeah, all of us like it even though it's baby food though.

user351417

@EmilioPisanty Anyways, just thought I'd bring it up because it was kind of an accusation and he was treating it as an opportunity to push his theories. No point in talking any more about it.

Q: Should this question have been deleted?

4:21 PM

@Chair ditto on that last part.

ACuriousMind

@EmilioPisanty Since you've now posted a meta thread, do you mind if I dismiss your mod flag on that post?

Physics Meta

4:48 PM

4

This question recently came up in chat, because a user lost reputation when their upvoted answer went overboard as collateral damage when its question was deleted: Don't get me wrong, I think this is a dreadful question, but I don't think this should have been deleted. It's a bad question ...

discussion specific-question deleted-questions