The h Bar - 2019-03-15

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dmckee

00:56

@Secret Okay. That's cool. And cold, too, I suppose since we're talking about single ion traps.

user351417

Your ball analogy is flawed. It isn't reversed, it rebounds and could (would almost always) do so in a different direction. For instance, if you threw it forwards and down at 90 degrees, when it hit the ground would it rebound to you or continue forward? If you weren't including gravity and hit it at exactly 90 degrees it would rebound, but you did include gravity because you said 'arc'. — Bill K 18 mins ago

user351417

::sighs:: clearly someone jumped to the conclusion 'this is wrong' a bit enthusiastically.

gansub

@DavidZ Both the questions you helped migrate to ESSE have been answered - earthscience.stackexchange.com/questions/16434/… and earthscience.stackexchange.com/questions/16431/…

dm__

01:33

relevant; the opening words to Sakurai's time-reversal section

"This is a difficult topic for the novice, partly because the term time reversal is a misnomer; it reminds us of science fiction. What we do in this section can be more appropriately characterized by the term reversal of motion. Indeed, that is the phrase used by E. Wigner, who formulated time reversal in a very fundamental way (1932)." - J. J. Sakurai

1 hour later…

vzn

02:42

No, scientists didn’t just “reverse time” with a quantum computer — "Amazing headlines about time machines are a long way off the mark, sadly." / MIT techreview

vzn

02:59

the new experiment seems to favor the time symmetric interpretation of QM, stated by wikipedia to be a minority view. recent experiments also refer to the subclass of two-state vector formalism. some of this is championed by Aharanov. en.wikipedia.org/wiki/Two-state_vector_formalism en.wikipedia.org/wiki/… A time-symmetric formulation of quantum mechanics / Aharanov et al

Time-symmetric formulation of quantum theory provides new understanding of causality and free choice / physorg

vzn

03:16

> "Our work shows that if we believe that time symmetry must be a property of the fundamental laws of physics, we have to consider the possibility for phenomena beyond those conceivable in standard quantum theory. Whether such phenomena exist and where we could search for them is a big open question", explains Oreshkov.

2 hours later…

user212860

05:29

@Semiclassical Do you know of anyway to obtain that singlet state experimentally

dm__

05:46

I finally know how to use the projection theorem. today is a good day.

CaptainQuestion

06:37

In an elastic collision why does the coefficient of restitution (e) have to be one? It is easy to prove for a two body point mass system but when dealing with rigid bodies I've always used the result as it is.

John Rennie

07:09

@CaptainQuestion the coefficient of restitution is proportional to the sqrt of the ratio of kinetic energy. In an elastic collision KE is conserved to the coefficient of restitution has to be one.

CaptainQuestion

07:28

@JohnRennie I meant in the sense $$e = \frac{\text{Velocity of separation}}{\text{Velocity of approach}}$$

undefined

good morning

John Rennie

@CaptainQuestion right, but that's equivalent to energy being conserved.

CaptainQuestion

07:45

@JohnRennie Why?

John Rennie

@CaptainQuestion KE is proportional to v^2

CaptainQuestion

@JohnRennie Velocity of approach is $V_1 - V_2$ it's the ratio of relative velocities

John Rennie

@CaptainQuestion work in the centre of mass frame.

Slereah

08:24

morning

undefined

08:47

morning slereah

user351417

> 2ih(bar)ekmlxlxm

user351417

physics.stackexchange.com/q/466579 is fantastic

user351417

I can barely tell what's supposed to be subscripted in that expression.

Emilio Pisanty

11:44

@ACuriousMind daymn, that internet really does love itself some time-reversing

can I get a second Epic badge now?

@Chair $2i\hbar \epsilon_{kml} x_l x_m$

user351417

12:02

@EmilioPisanty regarding this:

user351417

@rob The appropriateness of such close votes needs to be revisited. I think the new mechanism makes those needs obsolete, and that policy needs to be revisited. I will edit when I have time. — Emilio Pisanty 3 hours ago

user351417

That's kind of what I was trying to say in the answer, but I guess I said it very badly; I understand how disastrously weird the idea sounds. I think I even sound like I'm recommending an automated system, though I'm not, since that would need to be posted on Meta SE.

user351417

I'll fix the answer up sometime, whenever I find the time to do that.

user351417

My point was that now we don't need to actually hammer questions to get them off the HNQ, but if mods see something which looks borderline enough for genuine VtCs to be cast, then it could be removed from the HNQ.

Emilio Pisanty

12:33

@Chair why do we need such a system?

why can't we just rely on flags that lay out the arguments in more depth?

user351417

We could, but isn't it nice to see if there's some level of agreement between close voters too?

Emilio Pisanty

@Chair I don't see why the two need to be tied together. There is now plenty of room to manoeuver on the remove-from-HNQ side, we should use it.

@Qmechanic btw, if this coincides with the return from suspension of candidates on previous elections, that'll certainly get interesting.

(probably not in a good way, though.)

user351417

12:49

That person won't be able to run though...

user351417

(I'm guessing it's that person)

Emilio Pisanty

@Chair they'll still be able to troll, though

Avnish Kabaj

Who's that person

PranshuKhandal

@Qmechanic Sir, will you please explain why is it off-topic? What can I do? It seems a nice question to me. My question is physics.stackexchange.com/q/466599/221932

Avnish Kabaj

The bullet thing happens irl

As for the rod it's too vague

user351417

13:04

We avoid talking about that person because we don't talk about people when they can't reply here :P

user351417

But people used to say their content was non-mainstream, if you catch the drift.

Avnish Kabaj

John Duffield

Or maimon

Wait maimons gone for eternity

user351417

13:20

@PranshuKhandal There's a comment there which describes exactly why the user voted to close it as off-topic...

user351417

Is that a reposted question? I'm sure that I've seen it before.

daysofsnow

13:38

In this excellent answer physics.stackexchange.com/a/258135/99418 by @David Bar Moshe, there is a derivation of the non-Abelian Berry curvature from the holonomy/Wilson loop. However, it seems there was a term A_x^2 + A_y^2 dropped in the very last line of the derivation. Anyone know the justification for this?

(I unfortunately cannot comment on the answer; lack of reputation)

Avnish Kabaj

13:59

@daysofsnow You need one more upvote

daysofsnow

14:31

Ah, thank you - I appreciate that.

Nearly there then :)

Physics Meta

0

Q: About an "on hold" question

My question [1] has been put on hold as unclear. I can't understand why. I think I gave sufficient definition of my question and of its purpose. Some further explanation of why it appears unclear would be most welcome, as otherwise I don't see any way of improving it. Maybe it depends on my be...

discussion close-reasons

undefined

@daysofsnow looks like you're there now :)

Physics Meta

14:54

-1

Q: Is this a bad question? Or a poor fit for this site?

I wrote this question yesterday, and it got a downvote. I'm not unhappy about it, but I feel that I don't understand why. Is my question not relevant for this site? I have almost no formal education in physics. I have a number of questions that are probably very basic and ignorant. I want to ...

discussion down-votes

daysofsnow

@undefined That's wonderful! Thank you!

undefined

:)

user351417

15:36

@PhysicsMeta 17k network rep user, but goes to meta after receiving one downvote.

Captain Bohemian

yesterday I waked from a somewhat horrible dream. I went to visit my friend but he was not in, so I stayed in the top floor of the building he lives in to wait him. I got tired so I fell asleep, then a woman came to encroach on me. I waked up finding being supressed by her, feeling panic considering I met a villain. Then she liberated me and smiled. I asked her if she was going to hurt me and where my friend went, and she replied:"He goes to a conference and won't come back in several days."

vzn

↑ its clearly about FOMO lol! :P

PM 2Ring

15:54

@Chair Ah. I didn't bother to check their network rep. Oh well. I'm still happy with my answer to their question.

user351417

@PM2Ring Yeah, that answer pretty much hits the nail on the head.

user351417

That was a really bad joke, but I'm still laughing.

PM 2Ring

@Chair Thanks. Actually, the more I think about it, the more I like the (non-meta) question. ;) And see my comment.

user351417

@PM2Ring Meh I think it's engineering.

user351417

Though I love those magnetic stuff because if I didn't have those, I'd need to shake the devices I anatomize upside down to pull out the screws.

PM 2Ring

16:05

After several decades of playing with magnets, I like to feel that I've got a good understanding of how they behave. But they still fascinate me. ;) And I can't rule out that there's magnetic stuff that I don't know about that could surprise me.

Only in the last decade did I learn what happens when 2 strong spherical magnets (eg, a pair of Nanodots) collide at a medium slow speed on a smooth flat surface.

PM 2Ring

16:19

If you don't know about this, and you don't have a pair of magnetic balls to do the experiment yourself, see youtu.be/BnpHstXjTBs

Anonymous

@user151841 from my usage of screwdrivers, I'd say that it helps me position it, and saves me the trouble of shaking the screw out by flipping the whatever-it-is upside down to get the screw out. That's engineering, not physics. — Chair 9 mins ago

Anonymous

Well, that comes down precisely to how you define engineering. :)

Anonymous

I can completely understand why a new user would be confused after going through the meta post.

Anonymous

Anyway, as common sense doesn't scale well, we could try making the meta-faq on engineering questions a bit more explicit.

Anonymous

I'd argue that that particular question falls in the "questions inspired by engineering considerations" category.

PM 2Ring

16:29

@Blue I'd agree with that argument.

Physics Meta

0

Q: The on-topic page in the help center does not mention engineering

It recently came up in a meta post that OP had checked out the on-topic page in the help center, and could not see anything about engineering. That does seem to be the case, and although the tour mentions engineering, I do think it is something important enough to merit a place in the on-topic pa...

Anonymous

A handy rule of thumb for me is: does this question ask something like "how to use X" or "how to design X"? That's engineering (and belongs to Engineering). "How exactly does this setup X work?" (when the design already exists)...that's physics and belongs to Physics.

enumaris

how does Blue work?

to the engineering page!

Rico

What was the core idea for representing ether in space,I know it was to assume a medium for light waves. Is there any something more specific answere

PM 2Ring

@Rico The Wikipedia article has a good rundown of the history. en.wikipedia.org/wiki/Luminiferous_aether

enumaris

16:41

pretty much just medium for EM waves

PM 2Ring

@enumaris Sort of, but historically it's more complicated, because tradionally the connection between light, electricity & magnetism wasn't understood. And let's not forget about gravity.

enumaris

to the history of science-mobile!

vzn

16:59

@PM2Ring its still not fully understood :o o_O

Rico

I believe ether was thing which turned enstien to smart genius(I mean proving non existenting of ether , I'm I Right . I had bow working on this article so thought of to collect some random opinions from you guys . Would guys little mind please.. . when he was 21 I had written letter to his mom saying "it would be better if didn't born " finally ether made him to build the foundation for modern physics

:) plz place he after 21

@enumaris Let's talk about money , are we get paid for researching after phd

enumaris

are we?

what do you mean?

Rico

@PM2Ring "A major breakthrough was the theory of relativity, which could explain why the experiment failed to see aether" found it on your given link ,what does it mean

Sorry whatever . Me

PM 2Ring

@Rico I'm not sure that I understand what you're trying to say. The other day you were talking about your school options. I suggest you put extra effort into working on your English.

That will make it easier for you to discuss physics with people using English, and it will make it easier for you to learn physics from textbooks and articles written in English. Otherwise, there is a big chance that you will misunderstand stuff due to language issues, rather than lack of ability in physics itself.

@Rico Special Relativity explains the constancy of the speed of light, and Fitzgerald contraction, as being due to the geometry of spacetime itself, without needing an aether.

Rico

17:20

Hanmm ok

John Rennie

@Rico I worked as a colloid scientist after my PhD and I was paid very well :-)

I was working for a large multinational called Unilever. They have a large market in India I believe.

JMac

how big is the research and development in a company like that, it must be pretty extensive

John Rennie

@JMac they have a large development department, but they don't do that much fundamental research. I left (after 12 years) because I was finding it all a bit boring.

ACuriousMind

Only so many ways to make better soap, eh? ;)

John Rennie

Unilever sell loads of stuff, not just soap.

JMac

17:25

@JohnRennie So a lot of testing and improvements instead of really trying to push for anything new?

John Rennie

205

A: Why does ice cream get harder when colder?

A couple of decades ago I was peripherally involved with some research on the properties of ice cream being done by the company Walls in the UK. The work was on relating the consistency of the ice cream to the microstructure, so it was quite closely related to your question. Anyhow, ice cream ha...

@JMac Unilever sells basic consumer products not high tech. There's really not much fundamental research needed. It's not like working at Google :-)

But, it was fun for a decade or so and it was very well paid! :-)

JMac

@JohnRennie Did you analyze all types of their stuff in depth like you got to see for the ice cream?

I'm sure that would have been interesting at least for a bit until you saw too much similar stuff

John Rennie

I worked on microstructure of all sorts of stuff. Toothpaste, antiperspirants, shampoo and some industrial chemicals. I've got a patent of stabilising silica slurries using depletion flocculation.

And a patent for stabilising antiperspirant sprays

It was all good fun while it lasted. There's some good science in there!

PM 2Ring

@JohnRennie What a rude OP! Two dozen questions, and only 1 Accept. :(

JMac

@JohnRennie Well, basically all of this goes over my head, but that's interesting. The amount of research that goes into things like keeping anti-antiperspirant stable when stored (assuming I didn't also misunderstand that) is fascinating. Something a lot of people don't think about very often

PM 2Ring

17:41

I've heard of people using liquid nitrogen to make ice cream, since the rapid cooling encourages small crystals, so the ice cream is extra smooth. But I've never tried it myself.

John Rennie

The main think I liked about the job was learning so much about everyday things. As you say, you don't stop to think have antiperspirant or washing powder etc work because they're just everyday things. It's fascinating to learn how they actually work.

@PM2Ring you make smooth ice cream by churning it vigorously while it's cooling. You don't need liquid nitrogen.

JMac

@JohnRennie Yeah, that's what I liked about studying engineering too. When things work, they work, and most things you use you don't even think about how. It's nice to at least take a peek behind the curtain for a couple things people take for granted

John Rennie

Anyhow, I'm off to finish the fifth, and last, Witcher novel. I've been reading the entire five book series this week.

Rico

@PM2Ring cut that word . I Know how one feel whenever I try to jump up to random topics after every single line I text in . The reason I am here to have kinda reality check , now it's even more stranger . I think reality check is pretty much what we want when we are growing . So don't be a victim thinking about my strange behavior that I am putting next to you ... Have great day PM 2 ring 8-)

@JohnRennie Witcher novel ? Is that about gerlth (main character in Witcher video game franchise) . Now I am reading" Rich Dad poor Dad "from Robert

About to complete

Emilio Pisanty

dammit, Ben, you're in my spot

well-earned honorary mention to @JohnRennie

also points for trying to @DanielSank

@PM2Ring "bring back the accept ratio!", huh?

(context)

@JohnRennie the point there isn't to make ice cream, it's to make ice cream in a ridiculously cool way

you definitely need liquid nitrogen for that

PM 2Ring

17:56

@JohnRennie Agreed. The churning is the main thing, the liquid nitrogen mostly just makes it faster, so the icecream sets before large crystals have a chance to form. But the churning is the main thing keeping the crystals small. And I assume it also makes the crystals rounder & less jagged.

@EmilioPisanty That too. :D

user351417

If any mods are about, I just flagged a random post on the main site with regards to something going on in chat.

user351417

Interesting. When I put markdown (like bold** marks) in a custom flag message, my flagging history shows bold text.

PM 2Ring

@EmilioPisanty Oh, people aren't obliged to accept an answer if they don't feel satisfied by any of the answers. But when the top answer has 200+ votes, and no Accept, it does look a little odd, which is why I investigated that OP's profile. If he had an Accept ratio of 50% it wouldn't bother me. Under 10% does.

I remember one guy on SO with 40 or 50 question & around 5 accepts, and 2 of those were on crappy self-answers that were inferior to higher scoring answers to those questions.

Rico

@Chair last night hardcore puberty hit Right. Sorry bro I'm not an Indian nor one who wants to go for IB , I was just having fun . Had a 6 days all around the mission . So last night I was in India , got some trouble shoot so wanted to bring back my mood ,

user351417

I understood pretty much none of that...

3

PM 2Ring

18:11

I don"t pester people for Accepts, but I don't mind informing newbies (via a Meta link) about the Accept process (especially if they've never accepted an answer), and humbly requesting that they consider accepting, both on my own posts and on those of others.

Avnish Kabaj

18:22

@Chair lol

This is gold

And there's no context to this

He got a random ping

DanielSank

@EmilioPisanty Yeah well... I got the feeling folks don't like self-answered post, so I stopped doing them.

Avnish Kabaj

@DanielSank You can use a sock to ask the question it is allowed

Anonymous

Good Q&As are assets to the site. Doesn't matter whether they're self-answered or not.

Anonymous

Can I answer my own question?

PM 2Ring

That's dumb. Self-answered Q&As are explicitly encouraged. OTOH, they can attract downvotes. If the Q&A is merely a thinly disguised rant, it probably deserves that treatment. Or if the OP is incompetent &/or misinformed.

Anonymous

18:36

One of the problems with community-run websites is that there are 100 different people with 100 different opinions (opinions which are not policies). So it's understandable if you've been discouraged by some. Do note the site policy.

PM 2Ring

A borderline case is when the Q&A is only of marginal interest, and should instead be a blog post (I've often seen comments to that effect on SO).

From time to time in the SO Python room it's decided that we need a decent canonical Q&A as a better dupe target for a common question. Usually, the OP has an open discussion in the room while they're working on the question, and quickly responds to feedback after posting. So the quality of both the question & answer are pretty high.

But a couple of "automatic" downvotes are invariable, even if the question has a disclaimer (in the body, or a comment) that this is a canonical aimed at common dupes.

Generally, it's no big deal, and both the Q&A gather a good score. But it can be a little disheartening when the Q&A is fresh.

Anonymous

19:09

Unrelated: I finally received a Physics t-shirt today morning. I wish they shipped real Mexican hats too! :)

Anonymous

The SO grey t-shirt looks cooler though. I love the design.

Anonymous

The occasional Meta SE giveaways are certainly fun. :D

DanielSank

19:42

@AvnishKabaj Oh man, I wonder if you've been around long enough to know how funny that comment is.

@PM2Ring Why would that be marginal?

Many questions here are only interesting to a small fraction of users.

cf all the unanswered questions...

@Blue HOW!?

thermomagnetic condensed boson

how can I search for the messages I posted in this chat room? I tried the search approach on teh top right, without any success

DanielSank

That's the way to do it.

thermomagnetic condensed boson

ah indeed, thank you.

DanielSank

chat.stackexchange.com/search?room=71

thermomagnetic condensed boson

I had left blank the input, only put my name, didnt return anything

DanielSank

19:47

You can choose the search text and you can set the user who posted the message.

thermomagnetic condensed boson

I thought it would return every messages

yeah I used that feature

Anonymous

@DanielSank SE was clearing their old swag stock, and they had some Physics t-shirts left.

Anonymous

So I specifically requested for a Physics t-shirt and a SO t-shirt.

Anonymous

(Basically, it was a part of this).

DanielSank

@Blue Bah! I missed it.

Anonymous

19:57

@DanielSank Run for mod; you'll get it. :P

Anonymous

Along with a nice hat! :)

Anonymous

They're also revamping their swag collection. So the April mods would probably get even better swag.

PM 2Ring

@DanielSank I suppose it's more likely to happen on SO than here. Foe example, the OP has a problem that in the early days of SO would've been closed as Too Localized. They figure out a solution & post a self-answered question, but because of the nature of the problem future readers are unlikely to find it, and it's not easy to see how the techniques used in the answer can be applied in other scenarios.

A similar thing happens when the OP has trouble interfacing with an obscure API. They solve the puzzle, but the solution just uses very standard techniques. The hard part wasn't in writing the code, it was in figuring out the docs & behaviour of the API that virtually nobody else is using anyway.

Physics Meta

20:23

0

Q: Are industry related questions acceptable?

I was looking at this question on Physics SE which looks very much like a "trying to find an easy solution by someone else and take the credit at work" kind of thing. I personally think that this kind of question should not be allowed on the site but I looked at the "Tour" and "About" pages of S...

discussion scope

DanielSank

20:41

@Blue Isn't it too late to run for mod?

Anonymous

2 days ago, by Qmechanic

@AvnishKabaj : This is just in: An election of 2 new moderators is scheduled to start some time in April to replace Manishearth and because of increase in traffic.

Anonymous

You could run for the April election! :)

PM 2Ring

I just flagged this as NAA physics.stackexchange.com/a/466689/123208 Maybe I should've flagged it as a possible spam precursor...

Anonymous

Well, the spam flag is for commercial spam only...

Anonymous

NAA should suffice.

Anonymous

20:49

And ugh. Unregistered account again.

Anonymous

I've been complaining about unregistered accounts on SE, for ages.

DanielSank

@Blue orite

Anonymous

@DanielSank And I'd say you have a pretty good chance, with a candidate score of 31.

Anonymous

Emilio is 40/40 tho (JR too). :P

PM 2Ring

@Blue Understood. But a post that just looks like a frivolous NAA can be edited into commercial spam after a few hours. That's what I mean by spam precursor.

Anonymous

21:04

It would also be nice to have someone who's active in chat, as otherwise all the Physics mods are (more or less) busy these days.

2

Anonymous

@PM2Ring Oh, I see. That too.

PM 2Ring

IME on SO, chat regulars tend to have a lot less time available to chat after they get elected as mods.

Anonymous

SO is a different beast. :P

Anonymous

2k flags in the queue!

PM 2Ring

With beast being the operative word. ;)

rob

21:09

@Blue Heck, I'm not 40/40 now, 2.5 years into moderating. I don't remember where I was during that election.

PM 2Ring

That silly NAA has already disappeared. Nice work, mods.

rob

@PM2Ring I flagged that as "abusive." There's some guidance somewhere on Meta.SE that "abusive" applies to gibberish posts, like afsdvnmw8ioew89v, because it's a waste of time for readers to decide whether there's any meaning in it. I thought the same logic applied to that "answer" about peanuts.

Anonymous

@rob Well, you're missing the Marshal and Copy Editor badges. Those are not too hard to get. You probably didn't receive the former as mods hardly need to raise flags. ;)

Anonymous

You could also abuse your privileges and validate 500 flags raised by yourself. :P

Anonymous

(Not a recommendation...)

PM 2Ring

21:18

@rob Ah, of course. I've read that somewhere on SE or SO meta, now that you mention it.

Anonymous

BTW it's hard to say what your score was during the election. I wonder if I can create a query for it (I doubt as SEDE doesn't store historical data). Or perhaps it's on the WayBack Machine.

Anonymous

@rob Yeah, so it is on the WM. 35 back then.

rob

@Blue Oh, I'm right on the cusp in both cases, then.

HDE 226868

21:43

Has anyone taken a look at any of the Astro2020 white papers yet?

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