The h Bar

Dvij Mankad

00:27

Hi. I am getting a little confused about some basic things. When we say that our theory has a certain translational symmetry (say, of translations by some "a") then we only demand our wavefunction to be the same after translations of "a" up to a phase. But when we impose periodic boundary conditions on our theory, say of a period "L", then we demand our wavefunction to be exactly the same (not just up to a phase) after shifts of L. Why do we do this?

In particular, why do we make this distinction?

I can see the validity of this distinction based on the requirement of a single-valued wave-function. But how does an ant living on a circle know if it is living in a space which has a translational symmetry of 2*piR or it has periodic boundary conditions with a period of 2*piR?

Kyle Kanos

00:54

Just getting back into running & the Fitbit didn't even track it 😫

Liquid

01:31

Why can't I post a image:/ here

John Rennie

04:42

@DvijMankad if a wavefunction overlaps itself then it will interfere with itself and this places constraints on the phase. That's why with typical periodic conditions like a particle on a circle we require that the phase be the same at the boundary.

dmckee

@KyleKanos I hate it when that happens.

I've been robbed of wrist-mounted-robot-overload points!

Robbed, I tell you!

kyle campbell

05:19

@JohnRennie Just to reply to what you said earlier about the pendulum - I realize it's kind of an elementary thing to go through, but I'm still curious as to how (numerically or analytically, but most likely the former with an elliptic integral) we could approximate a pendulum wave (coupled and uncoupled). PM actually gave some pretty nice tips for this, especially the useful algorithms involved.

I feel like I'm going to need to do a bit more work to add the damping coefficient into account though.

John Rennie

@kylecampbell in the small angle approximation? Or taking into account the anharmonicity?

kyle campbell

@JohnRennie We don't need small angle approximation if we're using the elliptic integral, it apparently has less than 1% error even at an initial angle of 163 degrees. But mostly taking into account the anharmonicity.

Really, I just want to figure out how long it will take for a pendulum to stop (in a realistic, lab-like setting).

I did a bit of finite difference approx. methods for a nonlinear pendulum at some point, but yeah I'm just curious.

John Rennie

I have no idea how to do the damped pendulum with elliptic functions

kyle campbell

@JohnRennie I don't either.

Do you have any other suggestions?

I really don't care the method, if you give me something I can approximate that's just as useful as an analytic solution.

enumaris

fun timesssssss

prolly gonna be a restless night...fun timesssss... somebody shoot me -.-

kyle campbell

05:37

why? do you have finals?

enumaris

finals are long behind me bruh

I'm too old fo dat

kyle campbell

what are you so busy with tonight?

enumaris

not busy lol

restless is diff

crap internet is slow

crap internet company overcharged me and hasn't fixed my bill

Getting my wisdom teeth pulled on the weekend

no good things this week I think

just shoot me lol

John Rennie

06:05

@enumaris ouch :-(

enumaris

also got rejected today so there's that I guess

fun times

PM 2Ring

08:23

How odd. physics.stackexchange.com/questions/473272/… Maybe it was accidentally created by a bot. Or a prankster with access to their account. Or maybe they're rage-quiting after the massive downvotes on their recent question. I hope they aren't cracking up.

Akash. B

@PM2Ring what sort of language?

kyle campbell

"Hiding questions because of your Ignored Tags preferences for tags:

black-holes cosmology hamiltonian operators …"

lol

PM 2Ring

@kylecampbell Here are some Dancing Pendulums I did several years ago, hosted on a friend's blog. The are just fake pendulums, executing pure SHM, but they make nice patterns. :) You can do this with real pendulums, if you keep the angle smallish, although the damping obscures the alignment effects a bit. Sadly, the forums mentioned on that blog page no longer exist.

kyle campbell

Very nice

PM 2Ring

@Akash.B Sorry, what do you mean?

Akash. B

08:35

@PM2Ring what the headline of the question say?

it is full of letters without a clear meaning

PM 2Ring

@kylecampbell Thanks! I haven't written in Javascript for a few years, I mostly do Python these days. But I'm glad that script still runs, it's even ok on my phone.

kyle campbell

Yeah I'm keeping that. It's nice to watch.

PM 2Ring

@Akash.B It just looks random to me. And the body of the question looks like a crude Markov chain, as used by spambots. In fact, I assumed it was a spam precursor, until I noticed the user has several hundred rep points.

Akash. B

@PM2Ring oh

PM 2Ring

@kylecampbell Oh, good. :) It can be rather hypnotic. I actually raytraced the raw ball image, using POV-Ray.

PM 2Ring

08:54

@dmckee Yesterday, on SO, I del-voted a recent HNQ. It still needs a few more votes, but once it goes, several people will lose quite a few points. They ought to know better than to answer a basic dupe... but I won't be surprised if there are a few revenge downvotes. I also found a dupe target for another HNQ, but someone else took responsibility for hammering it (& thus kicking it off the HNQ list), and it doesn't need deleting.

I've delvoted lots of stuff, but I most admit I feel a little nervous at being party to wiping out around 170 votes.

I just used this in an Astronomy.SE answer. From the USGS, here's my favourite image to show there's not a lot of water on the Earth:

The larger blue ball is the salt water, the smaller one is the fresh water. You may need to zoom in to see the fresh water...

@JohnRennie This OP just edited, but I guess it's still pretty confused. And confusing. physics.stackexchange.com/questions/472308/…

John Rennie

09:15

@PM2Ring I'll look again, but it still seems like an incomprehensible mess to me.

PM 2Ring

09:41

@JohnRennie Questions like that scare me. If I read it too closely, I might end up with less knowledge than when I started. ;) I was just giving you a heads-up because at least the OP tried to improve their closed question (& probably doesn't realise that close-voters don't get alerted to edits).

Qmechanic

10:37

I would appreciate it if someone could explain-to-OP/mediate/step-in/vote-to-reopen/vote-to-close here.

John Rennie

@Qmechanic since they are keen on the work fuck I would just let them fuck off

Kyle Kanos

10:59

@dmckee I think the issue is that I used an app on the thing that want made by Fitbit & it didn't use the GPS or trigger a workout (which is weird since my heart rate was through the roof)

David Z

11:17

@Qmechanic I'm on that

well, to some extent

JMac

Can someone protect this question? physics.stackexchange.com/questions/473061/…

David Z

We could, but it's only gotten one answer from a low-rep user so far and it doesn't seem especially likely to get more. Personally I'd defer protecting it until we see at least one more problematic answer which protection would have prevented.

JMac

Idk, maybe I'm just irked because the second highest voted answer doesn't do a single thing to answer the question, and the other answers seem to rehash what tfb explained in much more vague terms

David Z

Yeah, but protection doesn't help with that. All but one answer were posted by high-rep users.

Kyle Kanos

12:14

@JMac protection only prevents users with <10 rep from answering. There could be something said about protecting any/all HNQ, but this one doesn't seem to have drawn that much negative responses.

PM 2Ring

Speaking of protection, Dvij Mankad recently proposed an extra level of protection for pending dupes. It hasn't got much feedback, so far.

Emilio Pisanty

12:44

@PM2Ring interesting case. That definitely looks like it received a massive pile of abusive or spam flags after it was closed. @Qmechanic, is that the right conclusion?

PM 2Ring

13:12

@EmilioPisanty Spam / abusive flags wouldn't surprise me. I did actually spam flag it, but retracted 30 seconds later, when I noticed the user's rep, and recalled a slightly odd interaction with them a few days ago. Plus I figured that a flag was pointless, since a mod was obviously already aware of the post, but I was a bit puzzled that it wasn't deleted.

And I guess it's not Markov text, just a text dump of the front page.

Semiclassical

huh

i called travelocity customer support to get helped on something, and i'm still waiting

and, of course, there's hold music. so far, nothing too strange

Qmechanic

@EmilioPisanty : Yeah, I don't recall seeing any spam flags when I closed it.

Semiclassical

...but then "never gonna give you up" came on

the travelocity customer support literally rick-rolled me

Kyle Kanos

@Semiclassical I wonder if that's an intentional song that plays just to mess with people

Semiclassical

I gotta wonder.

John Rennie

13:25

The falling body is falling into the black hole because the speed of light is reducing. It falls faster and faster, until at some point it's falling at the local speed of light. Then it erupts into a gamma ray burst.

Sigh. And we can expect the same soon.

Kyle Kanos

GRBs are due to something falling into a black hole!?

Semiclassical

@JohnRennie ow

oh no

noooo

John Rennie

@Semiclassical :-)

PM 2Ring

@JohnRennie I was just reading that too. But I've given up on responding to him. It's like mud-wrestling a pig. You can't win, you get covered in dirt, and the pig enjoys it.

Kyle Kanos

Well, if the trend of his low quality answers continues, would his suspension resume? And for longer?

Semiclassical

13:29

I wouldn't have thought it's low-quality answers which would get someone banned, at least not in chat

John Rennie

@KyleKanos that's up to the moderators ...

Kyle Kanos

@Semiclassical I imagine it's basically something along the lines of it's assumed they're just trolls and/or spammer

Semiclassical

yeah, there's a fine line between "consistently wrong" and "spams low-quality answers"

PM 2Ring

13:43

Guys like the "I've derived the fine structure constant from ~~numerology~~ first principles" guy that I linked yesterday aren't really a problem. It doesn't take much expertise to recognise that he's pushing a crackpot theory, and the occasional comment is enough to make that clear to newbies without that expertise.

But JD is pretty subtle, and is an expert at smoothly transitioning from mainstream material to his pet theory, so he manages to accrue upvotes.

Semiclassical

I'm not sure "subtle" is the right word for it, but he writes in a way that presents the appearance of credibility

PM 2Ring

Well, he doesn't make it blatantly obvious that he's on a mission to push his pet theory to anyone who'll listen. But anyway, I better shut up about this. ACM said we shouldn't discuss people who aren't here to defend themselves.

So to totally change the topic, I tried to get into Bohmian mechanics when I was younger, but I only read his Wholeness and the Implicate Order, which is more of a philosophy book than a physics book. One of my grandads was a Bohm, so I might be distantly related. :)

Semiclassical

that was my first exposure to Bohm as well

Kyle Kanos

I had some friends at grad school that studied Bohmian mechanics

Semiclassical

at the time I didn't have enough physics under my belt to grapple with the physics part of it, so I stuck to the philosophy part of it

which was interesting enough

Kyle Kanos

13:52

As their doctoral research, I mean

Semiclassical

nice

later on I did get interested in pilot wave theory itself, though I tend to avoid Bohm's own route to it

I'm more fond of how Bell proceeded

PM 2Ring

I've always had a soft spot for Cramer's Transactional Interpretation. It's a shame that he hasn't been able to develop it into a viable interpretation, and has been accused of distorting facts to fit his theory.

Emilio Pisanty

@JohnRennie sigh

I guess the only thing to do is to downvote incorrect content, and to consistently raise flags when there is a pattern of low-quality contributions stating as much

PM 2Ring

@Semiclassical I found Bohm really easy to read, almost like reading something written by a distant uncle. Or maybe that was just wishful thinking. ;)

Emilio Pisanty

@Semiclassical which number did you dial? The one here or the one directly on travelocity.com?

Semiclassical

14:02

the former, I guess?

@PM2Ring there are certain parts of it which are pretty easy to get into, yeah

the only section I remember having to wrestle with was the part on the rheomode

Emilio Pisanty

@Semiclassical did it work?

Semiclassical

insofar as the line connected, yes

but the line mentioned that you ocould contact them via the messenger on their facebook page

so i tried that and got a response

Kyle Kanos

14:20

People still use Facebook?

5

Semiclassical

apparently, yes

i had to guess what my password was, lol

enumaris