The h Bar

Emilio Pisanty

2:00 PM

@ACuriousMind you reckon this user will go on to earn 50rep and start commenting on stuff?

ACuriousMind

@EmilioPisanty No.

Emilio Pisanty

that's a weird use of "once", then =P

ACuriousMind

I take the "fake it till you make it" approach to optimism :P

Emilio Pisanty

and yeah, I was on the fence on protecting that one, but it's probably worth doing, yes

btw @ACuriousMind (and other Europeans) this may be of interest

ACuriousMind

@EmilioPisanty I am usually only careful about protecting questions that don't have any proper answers yet, in all other cases I usually protect once they've received non-answers from new users.

Emilio Pisanty

2:03 PM

@ACuriousMind yeah, but there's a balance w.r.t. the age of the question

e.g. something that's six years old, has five good answers, and then gets one non-answer, probably isn't worth protecting unless something else comes along

John Rennie

@EmilioPisanty Hmm, it's a good question. Presumably the neutron is tunneling through a barrier in order to decay?

Emilio Pisanty

@JohnRennie yeah, OP got a really good phrasing of the core ???ness of the thing

John Rennie

@EmilioPisanty Do we know what the barrier is?

Emilio Pisanty

@JohnRennie I'm not sure there's a great formulation in terms of actual barriers

but it'd make a great question for main

hint hint nudge nudge wink wink

John Rennie

Is it a Fermi Golden Rule type calculation then?

ACuriousMind

2:09 PM

What, exactly, is the "interesting" question you two are seeing?

Emilio Pisanty

@ACuriousMind the one you just protected?

ACuriousMind

How would that make a "great question for main" when it's already there?

John Rennie

@ACuriousMind If I were to place a bounty on the question would be be OK for me to edit an appendix into the question to explain exactly what an answer would have to do to qualify for the bounty?

ACuriousMind

@JohnRennie Only if you can't fit that into the bounty notice - don't forget you can type a freeform additional explanation in addition to the canned bounty reason!

user685252

how much of a bounty are you willing to offer?

(given your requirements are fulfilled)

Emilio Pisanty

2:22 PM

@ACuriousMind ah, no. As in, is free neutron decay modelable as a tunnelling phenomenon, and if so, how

John Rennie

@user685252 I'm going to research the question myself. There might be a simple answer out there in Googlespace. If I can't find an answer then I think a formidable bounty would be in order.

Emilio Pisanty

@JohnRennie you want to tag on tunnelling on the existing thread?

John Rennie

I'm undecided whether to bounty the existing question, possibly edited to clarify what the bounty is for, or to post a new one.

ACuriousMind

@EmilioPisanty Ah. I'd say it's much more akin to an excited atom decaying to its ground state than any sort of tunneling. What's supposed to tunnel here - there is no electron "within" the neutron that could tunnel out, like there is a helium nucleus inside the larger nucleus in the case of $\alpha$-decay, where we usually speak of tunneling?

John Rennie

I think the accepted answer is rubbish. It just sidesteps the question.

Emilio Pisanty

2:24 PM

@JohnRennie that depends on what you want to know, but if it involves tunnelling, I'd say ask a new one

John Rennie

@ACuriousMind yes, but that happens in picoseconds not 14 minutes.

Emilio Pisanty

@JohnRennie so?

user685252

@JohnRennie let's see what "googlespace" has to offer :-)

ACuriousMind

@JohnRennie So? Difference in scale, not in principle. Some decays are fast, some decays are slow

Emilio Pisanty

a picosecond is a long time

plus there's probably plenty of much slower alpha decays

John Rennie

2:25 PM

@EmilioPisanty yes, but they do have a barrier to tunnel through

The nucleus has to pass through an excited state to rearrange enough to get the alpha particle out.

Secret

Are all well ordered sets necessary totally disconnected?
in particular, is $\omega_1$ totally disconnected. I tried to make an interval $(0,\alpha)\cup (\alpha,\infty)$ for some $\alpha \in \omega_1$ but that will mean I will always miss $\alpha$?

ACuriousMind

@JohnRennie There are also $\gamma$-emitters with relatively large half lives - e.g. Cobalt-60 at 5.27 years - and there's no tunneling there, either.

Emilio Pisanty

@JohnRennie "pass through an excited state" is not how tunnelling works

John Rennie

Hmm, true

Emilio Pisanty

Isotopes of bismuth

Bismuth (83Bi) has no stable isotopes, but does have one very long-lived isotope; thus, the standard atomic weight can be given as 208.98040(1). Although bismuth-209 is now known to be unstable, it has classically been considered to be a "stable" isotope because it has a half-life of over 1.9×1019 years, which is more than a billion (1000 million) times the age of the universe. Besides 209Bi, the most stable bismuth radioisotopes are 210mBi with a half-life of 3.04 million years, 208Bi with a half-life of 368,000 years and 207Bi, with a half-life of 32.9 years, none of which occur in nature. All...

John Rennie

2:28 PM

It's just that if there's no barrier I'd naively expect the decay time to be on the order of the period of the EM wave released - or a few multiples thereof.

ACuriousMind

@JohnRennie Well, but where's the "barrier" for the long-lived $\gamma$-emitters?

John Rennie

@ACuriousMind If I knew that I wouldn't have to ask the question!

Emilio Pisanty

@JohnRennie it's not that there is no barrier, it's that there's no Hilbert space subspace that you could even assign to a barrier

And also, there is no relationship between the frequency and the decay width of the EM emission from an electronically excited atom

ACuriousMind

@JohnRennie I think there's just no way you can apply the concept of "barrier" here - in $\alpha$-decay it's clear: You can identify the $\alpha$ particle as a subset of the nucleus, compute a potential for it and see the barrier in that potential. But in $\gamma$-decay or neutron decay the thing that is emitted does not exist as a subset of the decaying object.

John Rennie

Actually, now I think about it, the lifetime of the state associated with the 21cm hydrogen line is long. I forget how long but millions of years I think.

Emilio Pisanty

2:31 PM

the width is independent of the energy and the lifetime can be many orders of magnitude (nine in many typical cases, fifteen in reasonably accessible ones) longer than the period

ACuriousMind

So there's nothing you could compute a potential for, hence no way to identify a barrier.

Emilio Pisanty

@JohnRennie or, more pragmatically, the hydrogen 1s-2p transition has a lifetime in nanoseconds

and even better, there are octupole transitions in the optical range with natural linewidths measured in millihertz

John Rennie

@EmilioPisanty you calculae that using Fermi's Golden Rule don't you? So the transition rate there is a fairly obvious result of how the dipole operator affects the two states involved.

Emilio Pisanty

@JohnRennie doesn't need to be a dipole transition, but otherwise, yes

John Rennie

And the 21cm decay is slow because it turns out to be a forbidden transition.

Emilio Pisanty

2:35 PM

@JohnRennie is it actually?

yeah, it's a spin flip, innit

so an M1 transition?

John Rennie

@EmilioPisanty I'd have to Google the details, but I think it is forbidden for an oscillating electric dipole.

It's actually the magnetic field associated with the EM wave that allows the transition.

Emilio Pisanty

@JohnRennie yup, that's what M1 means ;-)

John Rennie

I'd still like to know the details of why the $d \rightarrow u + e + \bar{\nu}$ decay is so slow in a neutron ...

Emilio Pisanty

@JohnRennie what does "slow" mean?

John Rennie

15 minutes

Emilio Pisanty

2:39 PM

@JohnRennie seems pretty quick to me

a bit long for a quickie, but still a quickie

ACuriousMind

I remind you again of the 5 year $\gamma$-decays...

0celoñe7

@JohnRennie do you know why the proton decay is so slow?

John Rennie

@ACuriousMind well that's a complicated many body process. The neutron decay seems simpler in principle.

0celoñe7

@EmilioPisanty What?

John Rennie

If I had any hope of understanding why the timescale is so long it seems it would be more likely with neutron decay.

ACuriousMind

2:42 PM

@JohnRennie But it involves the weak force, of which you have no useful classical picture available.

Emilio Pisanty

@0celoñe7 mistake

user685252

(removed)

John Rennie

@0celoñe7 if you blieve in GUT decay processes then it's because the X any Y bosons are so heavy.

0celoñe7

@EmilioPisanty Have you read/heard of cambridge.org/us/academic/subjects/physics/… ?

ACuriousMind

That is, the neutron decay inherently treads on non-Abelian QFT grounds if you want to really understand it

Emilio Pisanty

2:43 PM

@0celoñe7 nope

ACuriousMind

And since we don't understand actually understand the Hilbert spaces of interacting QFTs, the best you can currently hope for is really the half life/decay probability, imo

John Rennie

@ACuriousMind well, the way Fermi's Golden Rule works is non-classical but it's still possible to understand the processes involved without having to go through the details of the calculation.

0celoñe7

amazon.com/Inequalities-Elliott-H-Lieb/dp/3540430210/…

what a riveting title

user685252

propagating inequality in the world :P

ACuriousMind

@JohnRennie I think your best best of "understanding" neutron decay is actually Fermi's theory of beta decay

0celoñe7

2:49 PM

get rekt acm

@ACuriousMind I assume you never used any mesh editing mods for Skyrim?

user685252

google.ca/…

ACuriousMind

@0celoñe7 Nope

user685252

since when did they put Gifs in the urban dictionary?

John Rennie

@ACuriousMind thanks, yes, the Wikipedia article does look as if it will be within my grasp if I work at it.

Secret

3:26 PM

hehe, this is why I love the cross pollination of physics with maths:

New MSE question

Physics Meta

0

Q: Let's apply the lighter to this tag

applied-physics seems like a bit of a catch-all tag like general-physics (which is now removed from all questions and soon to be blacklisted). Thoughts on burnination and blacklisting? Note that There's no tag wiki or tag excerpt, making it confusing what it was even intended to be used for i...

ACuriousMind

@Secret That has got nothing to do with physics, it's literally a pure topology question. Since every connected metric space is uncountable, examples in the bottom left will be rather pathological. E.g. you can't have a finite (non-trivial) Hausdorff space that's connected. Here are examples of countable connected Hausdorff spaces.

Secret

Yeah sorry, I should made it explicit that I am referring to that this question exists purely because of today's discussion in this chat

dmckee

3:51 PM

@JohnRennie We actually catch quite a few who make accounts but then write "I'm # years old" in their profile or in a comment explaining why people should be nicer to them.

John Rennie

@dmckee I blame the schools for failing to teach pupils that duplicity and evasiveness are essential requirements for a career in academia :-)

2

(that is mostly a joke, but not entirely!)

user685252

here here

dmckee

Well, a certain amount of graceful duplicity keeps the social wheels turning smoothly in any context.

The issue is just one of know how much and when.

0celoñe7

@JohnRennie What does it mean when something is a "script"

Like I wrote a code that takes in some numbers and gives a time

Is that script?

ACuriousMind

Why does it matter?

dmckee

3:57 PM

Come to think of it, knowing when to overlook the duplicity you've detected in others is also part of keeping the social wheels turning smoothly.

John Rennie

@0celoñe7 The term script tends to refer to any simple interpreted program. Typically shell scripts or snippets of VBScript that do OS related stuff would be regarded as scripts.

ACuriousMind

I.e. why does it matter whether your piece of code is a "script" as opposed to just code. Is there a committee for the detections of scripts that will come after you if you fail to declare it as a script?

0celoñe7

@ACuriousMind I am writing a thing explaining why they are giving me thousands of dollars for my research

John Rennie

@0celoñe7 what was your code written in?

0celoñe7

I'd like to be accurate

@JohnRennie matlab

Anonymous

3:58 PM

As far as I know script languages use interpreters rather than compilers

John Rennie

225

Q: Scripting Language vs Programming Language

Can anyone explain the difference between Scripting Language and Programming Language please? Also can you state some examples for each. I have Googled a lot but I always find the best answers from Stack Overflow.

scripting

dmckee

@Blue Many of them actually use compilers these days, they just compile (quickly! and often to an internal representation) and then execute every time you run them.

Most python implementations do that. And gawk, but not some other awk implementations.

Anonymous

@dmckee Oh. That's something new :)

user685252

if you're going for thousands of dollars, use the largest words possible

John Rennie

@0celoñe7 I think whether a Matlab program is called a script or a program is a matter of convention among the Matlab community. I think strictly speaking it would be a script. But check on the Matlab forum (assuming such a thing exists).

dmckee

4:01 PM

@Blue Oh, but it gets more muddles. You see, tcc will compiler and run c programs and can be used on the command line like tcc helloworld.c.

Does that make c a scripting language?

Anonymous

Maybe a hybrid :P

dmckee

Part of the problem here is that the language is arguable the spec and not an implementation. There are quite a few language that have both interpreted and compiled implementations.

So the question then might be "Was the designer planning on using a compiler or an interpreter when she laid out how this language would work?"

But that rapidly gets us into subjective territory.

As a result my preferred whay to think about the problem is by usage patterns.

Programming languages are regularly used to build complex programs that take design and considerable time to write.

Abcd

@Kaumudi.H yes, why?

dmckee

Scripting language are mostly used to bang out short code for task automation and similar purposes.

In my view python is a 'programing language', and matlab is too because its use in industry involves quite elaborate constructs.

Not that I would willing write anything substantial in matlab—it's a tarpit—but people do all the time.

user685252

The "Art of Programming" comes into play...

...nobody talks about the the art of scripting.

dmckee

4:09 PM

Uhm ... spent much time with serious sysadmins?

user685252

no

John Rennie

@Abcd I suspect @Kaumudi.H was expressing sympathy. She and many others hereabouts have already been along that long and painful path.

dmckee

They have a huge culture of admiring really good script work.

But that world's intersection with the programming world is surprisingly peripheral.

John Rennie

@dmckee It helps that shell scripts are utterly incomprehensible to anyone who isn't a shell scripting guru :-)

dmckee

They know each other and speak much the same language and don't interact much most of the time. Weird.

@JohnRennie I like to think that I know a bit about shell scripting, and those guys still use incantations that I can't even begin to parse.

user685252

4:12 PM

sounds like a tight nit group

John Rennie

The syntax is just so utterly alien to those of us used to more conventional programming languages.

0celoñe7

Dammit

Did I trigger a CS discussion?

user685252

yup

John Rennie

@user685252 That's a tight knit group. A tight nit group is what you get when you don't wash often enough. Quite appropriate for computer nerds some might say ... :-)

No, I would never do such a thing!

user685252

:-)

John Rennie

4:15 PM

nits are lice eggs.

Abcd

@JohnRennie Oh, is it? Did she qualify? I know it's painful :(

John Rennie

@Abcd the intricacies of the Indian education system are lost on me, but she did a load of exams this yer and she is going to M. E. C. in Kochi, Kerala.

2

Abcd

@JohnRennie That's good.

@JohnRennie I didn't get what you mean by "The intricacies....lost on me"

Anonymous

@Abcd Unless you are only aiming for the results, enjoy this time. You will learn a lot of new things and improve your problems solving abilities. No need to be scared about the competition.

John Rennie

@Abcd it's an English idiom. It means the situation is so complicated that I don't understand the details of how it works.

Abcd

4:24 PM

@Blue I want both - those abilities as well as a good rank :(

@JohnRennie Okay.

Anonymous

@Abcd Honestly speaking, the rank isn't in your hands. There's always a luck factor involved.

Anonymous

Your focus should be on learning things well.

Abcd

I don't think hard-work will go to waste

@Blue Yes, that's why I always question the solutions but most people around me simply accept them

Anonymous

@Abcd Questioning whatever you don't understand clearly is a good habit. Don't let that go.

Abcd

yes

0celoñe7

4:31 PM

@Abcd On the flip side, if you do it too much you will get stuck on inconsequential things.

John Rennie

@Abcd there is a JEE room specfically for JEE related stuff such as the sort of problems you've been working through.

Problem Solving Strategies

General chat for high school physics. For MathJax see [here](m...

0celoñe7

@Abcd On the flip^2 side, if you're still in high school I think it's reasonable to understand everything clearly.

Abcd

@0celoñe7 I know :(.

@0celoñe7 flip^2 side?

vzn

@JohnRennie awesome news, was just scanning the web site, need to talk to her sometime (timezones seem make it tricky). wondering did she mention a major yet?

Abcd

@JohnRennie Do people answer there?

0celoñe7

4:33 PM

@Abcd Flip twice, obviously.

Emilio Pisanty

@0celoñe7 that reminds me

Anonymous

@vzn She is taking CS

John Rennie

@Abcd yes, the room is quite active.

ACuriousMind

@0celoñe7 Obviously $\text{flip}^2 = \text{flip}\circ\text{flip} = \mathrm{id}$.

0celoñe7

@JohnRennie Can I take credit for that?

ACuriousMind

4:34 PM

So it's just "on the side"

0celoñe7

@ACuriousMind You're assuming the flips are about the same axis.

vzn

@Blue haha ok wild stuff... what about you any plans? youre in india?

Emilio Pisanty

Non-euclidean virtual reality

►

that and 4D toys are the reasons to invest in VR, I should think

ACuriousMind

@0celoñe7 Sure. Otherwise you'd have to write "On the $\text{flip}_x \circ\text{flip}_y$ side"

0celoñe7

@ACuriousMind Abuse of notation.

Anonymous

4:36 PM

@vzn I'm taking up Electronics engineering :)

Anonymous

Yes

vzn

@Blue great, what city?

0celoñe7

@Blue why the :)

Anonymous

@vzn Kolkata

vzn

@0celoñe7 lol/ sigh, try to be nice once in awhile

Anonymous

4:38 PM

@0celoñe7 Don't know...I didn't think before typing it :D

ACuriousMind

@EmilioPisanty Running that program on psychedelics is either the best or the worst idea ever, I think.

Emilio Pisanty

@ACuriousMind yeah, I agree

ACuriousMind

@EmilioPisanty What sort of...toys?

Emilio Pisanty

4D Toys: a box of four-dimensional toys, and how objects bounce and roll in 4D

►

0celoñe7

@vzn you need to lay off

EE is not what he wants to do, he is being pressured by his family

DanielSank

4:40 PM

Hi, everybody.

0celoñe7

@DanielSank Hi

Anonymous

@0celoñe7 It's not like I hate EE. Just that I would have preferred Physics. :P

vzn

@0celoñe7 its a rather subtle concept at times that probably has long historical roots/ etymology, basically "scripts" seemed to show up 1st in unix (maybe earlier?). they are interpreted "shell" languages that mainly call other programs in unix. then they got increasingly elaborate such that they could do a lot of logic to do stuff without calling other rudimentary programs eg "expr"... it would be cool if someone wrote up some of this history somewhere...

ACuriousMind

@EmilioPisanty Good lord, flatland in 3d

Emilio Pisanty

@ACuriousMind yeah, it looks really good

0celoñe7

4:42 PM

I had a nightmare last night

vzn

@0celoñe7 lay off asking others to be nice? geez man. anyway not aware of his family bkg...

Emilio Pisanty

probably about the best you can do to visualize 4D with a monkey brain

vzn

@0celoñe7 let me guess, banned from chat? :P

0celoñe7

I was back at high school and had to explain >3 dimensions to people

@vzn I enjoy being banned

DanielSank

@Blue There are some interesting overlaps between EE and physics.

vzn

4:43 PM

@0celoñe7 part of the problem it would seem... o_O

DanielSank

If you understand feedback amplifiers you can easily understand some parts of QFT.

0celoñe7

@ACuriousMind @JohnRennie Why did you clear the board?

John Rennie

That was me.

DanielSank

@JohnRennie Thanks, Dad.

ACuriousMind

@EmilioPisanty It looks cool and fun, I wonder how fast the novelty factor wears off though

John Rennie

4:45 PM

I'm not going to tell people not to discuss banning and being banned because, well, you're all old enough. But I have no wish to encourage it either.

ACuriousMind

As in, is there actually anything these simulations give you after the initial "whoa" effects?

Emilio Pisanty

@ACuriousMind well, ideally, a bit before you get your hands on the devkit and you start visualizing nontrivial surfaces in your work

vzn

@Blue seems Kaumudi is in a similar situation. push on in life & life pushes back. compromise (verging on sacrifice...) is often the name of the game...

Emilio Pisanty

a significant fraction of my PhD was understanding the topology of a 2D surface embedded in 4D space

absolute nightmare, that was

ACuriousMind

@EmilioPisanty Ah, for that I can see the appeal. Sadly, four dimensions are usually too few for me ;)

0celoñe7

4:47 PM

Whoever stars this will go bald in 1 year.

4

vzn

@0celoñe7 stop getting uppity, the star police will decide that for you.

Emilio Pisanty

@0celoñe7 why not just come out and say "hey guys, pls star my comment"

0celoñe7

@EmilioPisanty Because I'm more clever than that.

Anonymous

@DanielSank I know. My parents told me that I can choose any one out of Computer Science, Electronics, Electrical or Mechanical. I choose Electronics because it had maximum overlap with Physics esp. Semiconductors, Electromagnetic theory, QM etc. The other necessary parts like Relativity and Thermodynamics -I will try to take up extra courses to cover those up. I was initially a bit sad for not being able to take Physics, but now on pondering a bit I realize that it wasn't that bad a choice.

ACuriousMind

Is it "more clever" or "cleverer"?

Emilio Pisanty

4:49 PM

@ACuriousMind What I would really like to understand is how rotations work in >3D

0celoñe7

@ACuriousMind idk

I'm not clever enough to know

user685252

latter

cleverest

ACuriousMind

@EmilioPisanty Oh, that's easy: You rotate about/in planes. The thing with having an "axis" is an artifact of 3 dimensions.

vzn

@Blue think all thats sensible/ practical/ pragmatic & not bad choices. sometimes it comes down to $ and who has it/ shares it/ earns it... ran across an extremely cool EE prj that is breakthrough physics... would like to do something similar...

DanielSank

@Blue An physicist with excellent electronics skills can be the best experimentalist.

0celoñe7

4:50 PM

@ACuriousMind I was going to say that but surely he knows that.

DanielSank

I would encourage you to keep up with physics and electronics as this is a very powerful combination.

Emilio Pisanty

@ACuriousMind yes, precisely, but what does that mean?

0celoñe7

He must be talking about something deeper.

Emilio Pisanty

@0celoñe7 I always do

ACuriousMind

@EmilioPisanty Oh, you're one of these people

Emilio Pisanty

4:51 PM

@ACuriousMind what, you don't have a moment like that at least once a year?

0celoñe7

A year?

Damn, once a week is more like it.

Anonymous

@DanielSank Yes. I will surely try to do so by taking up extra classes/courses in physics.

Emilio Pisanty

if so, you should come back in for examination, you're probably due for revocation of your physics license

@0celoñe7 well, it depends on how often you think about spin

0celoñe7

@EmilioPisanty Not spin, just random things.

vzn

@ACuriousMind if youd just drink the ~~purple coolaid~~ fluid dynamics, itd all become clear :P

0celoñe7

4:52 PM

Last week it was ion beam current

That broke my mind

ACuriousMind

@EmilioPisanty Yeah, I do have a moment like that regularly: When I ask myself what "What does <mathematical abstraction> actually mean?" actually means.

John Rennie

What's weird about ion beam current?

Emilio Pisanty

@0celoñe7 I read that comic as being very specifically about spin

0celoñe7

@JohnRennie The beam is 3x3mm and you need to irradiate a 6x6mm target. Doing that efficiently and correctly is a complete nightmare.

John Rennie

@0celoñe7 Ak, OK, fair enough

vzn

4:54 PM

@DanielSank which reminds me of that recent Nature article on the waveguides... did you like it? :) ps whats new

0celoñe7

@EmilioPisanty I thought it was about anything regarding "mysterious black box" stuff

Emilio Pisanty

@ACuriousMind No, but seriously: could you just off-the-cuff point to the rotation planes that will provide symmetrical behaviour of a hypercube?

0celoñe7

@EmilioPisanty Like the change of variables formula for integrals

NO ONE knows how that thing really works

dmckee

@0celoñe7 These are the kinds of things that experimental student deal with that never make a splash outside their dissertation (i.e. never make a splash at all), but which translate well to the 'real' world.

Emilio Pisanty

e.g. if you take a 3D cube and project it in the [111] dimension then the projections will be triangles or hexagons

but projections along [110] will leave two-fold symmetric rectangles

how does that work for a hypercube?

ACuriousMind

4:57 PM

I don't really have any intuitive idea about how a hypercube even looks like

John Rennie

I must resist trying to visualise this as the effort can prove fatal at my age

0celoñe7

@JohnRennie You didn't seem that old

Emilio Pisanty