The h Bar

ZeroTheHero

03:25

@CaptainBohemian The rule of thumb is: if it’s that easy it’s already been done. It is not easy to discover and publish new results in ANY field.

PM 2Ring

04:50

@GodotMisogi The behaviour of default mutable arguments in Python isn't weird, IMHO. It's quite logical that they're evaluated when the function definition is executed. OTOH, I agree that if you do use a mutable default arg you should comment it so that readers won't automatically assume that it's a bug. I don't use them often, but I don't avoid them either. They're great for memoization caches: in my tests they're faster than all of the alternatives.

Ultradark

How does one learn to ask the right questions?

PM 2Ring

I missed the discussion about strong vs weak typing. Python has strong typing, not weak. I guess you can say it has dynamic typing, but even that's a little misleading because Other languages have "variables". Python has "names".

For a deeper discussion, from a slightly different viewpoint see Facts and myths about Python names and values by SO veteran Ned Batchelder.

TL; DR: The type of any Python object is a property of the object itself, and is not (easily) changeable. A Python variable is just a nametag, it has no associated type (although Python now has type hints); a Python object can have one or more nametags, or none (eg it may be a member of a collection).

@Ultradark Good question. ;) Are you asking specifically about Stack Exchange Physics, or are you being more general?

Ultradark

05:14

Both I guess I've asked a lot of questions but I feel like I could ask better ones

user351417

@PM2Ring Is it worth trying to learn about the nature of Python (like the deeper details of what it means to be strogly/weakly typed or object-oriented and the implications of such classifications)? Like I guess I'm pretty proficient with using flow tools, data types, classes and so on, but I know almost nothing about how other languages differ beyond the requirement of brackets and slightly different syntax... How much do you gain by understanding that stuff?

PM 2Ring

05:33

@Ultradark There's an art to asking good questions, but it's not easy to explain. I suggest you browse good questions to try & get a feel for what they've done right. Good questions aren't necessarily the ones with high scores, since an ok question can get boosted by the HNQ. But if the question has a decent score, and the OP has a good rep, and asked the question when they'd been a member for a while, so they know how SE works, then the question's probably good. ;)

@Ultradark Draft your question, then try to read it from the perspective of someone who doesn't know your thought processes. Keep it as short as possible while providing all necessary context. Focus on asking about the general physical principles & concepts. If you need to introduce a specific scenario to illustrate your point try to keep it general so that it doesn't end up looking like a homework exercise.

Secret

I tend to ask good questions in real life (good enough that the impression is often the reason why briefly met people remembers me) but my questions tend to be bad in the internet due to the lack of gesture and other cues to articulate it

PM 2Ring

@Chair I think that kind of knowledge can be helpful, but you don't have to go too deeply into it, unless you're doing a CS degree, or want to design your own language.

But knowing that Python variables are nametags and not boxes is pretty useful, especially for experienced programmers coming from "variable is a box" languages, since their preconceptions of how variables work can be misleading when applied to Python, and can lead to bewilderment when Python doesn't behave how they expect it to, and frustration when they try to get Python to do some stuff that they're used to doing in those other languages.

Ultradark

05:56

@Secret can you tell me if this is a bijection

user351417

Thanks! I've never heard of the 'variable is a box' concept; I'll check it out.

Ultradark

Is there a bijection between these two parts

Secret

06:41

What is the function equation

there is no way to work out bijection by staring at a diagram

Sir Cumference

@Ultradark It's not clear what that diagram is.

Ultradark

@Secret can't you take a line and intersect both parts

showing that the sizes are equal

Sir Cumference

Is that a graph first off?

Ultradark

its an algebro-geometric representation

PM 2Ring

"try to read it from the perspective of someone who doesn't know your thought processes. Keep it as short as possible while providing all necessary context."

Sir Cumference

06:47

Oh wait you're just talking about those two sets right?

I'm pretty sure there is a bijection between any uncountable subset of $R^2$

Might be wrong

Ultradark

sir cumference here's how I think of it

if you let a line $y=mx$ intersect that

then there is a correspondence for every point between the two

Secret

Ok I think I am seeing what you are getting at. However a bijection only exists if the ends of the lower curves are both open since you do not have infinity to biject to e.g. (0.8,0) or (0,0.8)

Sir Cumference

Wait I'm probably very tired but $R^2$ is equinumerous with $R$. Assuming the continuum hypothesis is correct, wouldn't that mean that any uncountable subset of $R$ must be equinumerous with any other?

Secret

07:03

That is true, but for curves to have a continuous bijection with each other, the topology is also important. There is no continuous injection between an open interval and a half interval for example

Sir Cumference

Huh, interesting

Though we'd still have a bijection, just not continuous, right?

Secret

yup

Sir Cumference

Welp there you go @Ultradark. Just solve the continuum hypothesis and you'll get your answer

Ultradark

yeah the endpoints

Sir Cumference

Assuming you're only working off information from that diagram

Ultradark

07:04

are undefined

what's the continuum hypothesis

Sir Cumference

Continuum hypothesis

In mathematics, the continuum hypothesis (abbreviated CH) is a hypothesis about the possible sizes of infinite sets. It states: There is no set whose cardinality is strictly between that of the integers and the real numbers. The continuum hypothesis was advanced by Georg Cantor in 1878, and establishing its truth or falsehood is the first of Hilbert's 23 problems presented in 1900. Τhe answer to this problem is independent of ZFC set theory (that is, Zermelo–Fraenkel set theory with the axiom of choice included), so that either the continuum hypothesis or its negation can be added as an axiom...

Ultradark

oh yeah I've heard of that

Sir Cumference

I'm kidding about solving it of course. It's an open problem (iirc inaccessible to proofs)

Ultradark

iirc?

Sir Cumference

"if i recall correctly"

Yep, it's unprovable with standard set theory

You're gonna have to give more information about those sets to determine if there's a bijection

Ultradark

07:08

I'd rather prove something else

that sounds too hard

this is turning into a math chat lol

PM 2Ring

07:32

@Ultradark Something like that. I'll assume both of those sets are closed. Draw a line L that passes through the left endpoints of the two sets, and a line R that passes through the right endpoints. Find Q, the point where L & R intersect. Now every line through Q with slope between the slopes of R and L (inclusive) passes through a unique point in both sets, and every point in each set corresponds to one such line.

Ultradark

Yes!

I'm glad there's a correspondence

Anonymous

@ZeroTheHero I see, that maybe true. My advisors were pretty lenient about authorship stuff (I mean, I even got to add two Stack Overflow users as first authors on my papers :P) and not once mentioned that wanted to be a co-author just for guiding me, so my experience was probably different.

Anonymous

49

Q: Listing a Stack Overflow user as co-author for having provided substantial programming support

I received a lot of help from an active Stack Overflow user in my undergrad summer research project, which was based on statistical physics. Now, I'm writing a paper on it under my professor's supervision. The professor knows about the help I received and asked me to mention it in the "acknowledg...

authorship

bolbteppa

07:53

PM 2Ring

For sufficiently small values of |x|, and sufficiently sloppy definitions of equality.

Anonymous

@CaptainBohemian I wouldn't say you can produce papers easily in computational physics. It's still a lot of hard work. However, it is true that in certain areas you don't need 5-10 years of background knowledge.

PM 2Ring

On a more serious note, it's sometimes useful to have a slightly more useful expression than $\sin x \approx x$. About 10 years ago I stumbled on $\sin x \approx x(12-x^2)/(12+x^2)$

bolbteppa

08:10

Seems legit:
$$x\frac{12 - x^2}{12 + x^2} = x \frac{12 + x^2 - 2x^2}{12+x^2} = x[1 - \frac{2}{12} x^2 \frac{1}{1 - (- x^2/12)}] = x[1 - \frac{1}{3!} x^2 (1 - \frac{x^2}{12} + \dots )] = x - \frac{x^3}{3!} + \dots \approx \sin x $$

Avnish Kabaj

@bolbteppa didn't gettit

Help

bolbteppa

This explains it

PM 2Ring

08:33

@bolbteppa I discovered it by a combination of series manipulation and numerical trial & error.

Slereah

10:15

Just use the continuum hypothesis

I'm so sick of that debate

We don't argue that much about the axiom of choice and it's much worse

ACuriousMind

@Slereah 4 pages of hits for "axioms of choice" vs. 1 page for "continuum hypothesis" in this chat says you're wrong ;)

John Rennie

Apparently arguments about the axiom of choice and the continuum hypothesis cannot be proven to be different or the same.

Slereah

10:32

Also it's like really

It doesn't matter that much

The type of theorems relying on the continuum hypothesis are so abstract that saying that they're right or wrong is close to meaningless

Just assume the CH or its negation and see where it leads

Slereah

10:47

I think I only ever saw one paper that actually invoked the CH

and even then it wasn't that salient to the point it was making

Avnish Kabaj

11:01

@bolbteppa oh

Thanks

Slereah

11:18

I should make an article on my site about spacetime gluing

There's a lack of good ressources on that

Takes a lot of papers to get a good picture of it

Slereah

11:29

Also i'd like to know if there's some decent thing on gluing manifolds wrt their bundles

ACuriousMind

@Slereah What do you mean?

Slereah

@ACuriousMind Well like something to show properly what happens to bundle sections when you glue manifolds together

I mean I know what happens, but something to show it properly

ie the metric is continuous if there's an isometry on the boundary, all that

ACuriousMind

@Slereah Depends on what bundles you mean. For the "natural" bundles like the tangent bundle, the gluing straightforwardly extends to them since they are locally products and it's obvious how to glue $M\times V$ and $N\times V$ when you glue $M$ and $N$

Slereah

is there any standard book for all that?

It's pretty hard to find much on the topic of gluing

Almost all the physics on the topic is done with physics math

And i can think of maybe like 5 books that cover gluing a little

Avnish Kabaj

11:54

The pollution season's over

ACuriousMind

"pollution season"?

Slereah

yes all cars have been destroyed

pZombie

12:09

is it possible to shoot photons with a certain energy through a tiny hole in a box with mirrors inside that almost perfectly reflect those photons and thereby trap the photons inside there for quite some time while more are being sent in?

Slereah

I mean i guess it depends what you mean by "quite some time", yes

pZombie

@Slereah well, i am interested in a setup where if you were to shoot a laser beam with a specific frequency through the box's tiny hole containing the mirrors which are capable of reflecting this frequency almost perfectly, according to our current state of technology. Then if you were to open the box at some point, at a given location, you would end up with a more intense beam than the laser beam shooting inside

if such a thing would be possible in principle

replace laser with any other kind of light source if that would enable to achieve success

Slereah

Errr

do you know how a laser works

pZombie

forget about lasers if that is your objection. It is beyond the point. See above

the question is if i can pump my box full of photons such that when i open it, i would get a more intense emission than the light source i used to pump the photons into the box

Slereah

12:26

My point is more that it's similar to how a laser works

I mean not quite, but still

pZombie

i found some related article

"Scientists have devised several ways to trap light and save it. The “easy” way is to get two perfect mirrors and face them precisely at each other. Then you can “bounce” a beam of light back and forth between them as many as 500,000 times. “With the best mirrors, if you arrange them at some distance you can store light for a fraction of a millisecond or so,” says MIT physics professor Vladan Vuletic. "

Secret

@ACuriousMind probably JEE stuff

John Rennie

@pZombie your problem is that all light trajectories are reversible, so if you can shoot light into your box then light can get out of the box.

You'd have to use a pulsed light source and some form of switching to turn your mirror off as the pulse entered the box and turn it on again once the light was in the box. If you get the geometry right you could do this repeatedly to gradually fill up the box with light.

Offhand I don't know how this would actually be done.

Slereah

12:43

@JohnRennie Get maxwell's demon to shut the door

pZombie

what would happen if i filled a box with photons and i had the ability to push one side of the wall like a piston to compress the photons? Would i end up with a black hole?

Secret

I wonder, can we produce a powerful capacitor by trapping light this way...

pZombie

@JohnRennie I am having trouble understanding how when a trajectory is reversible, it would necessarily mean that a beam i shoot inside would have to also exit at some point from the same hole it came in

ACuriousMind

@pZombie Yes, but only if you are powerful enough to overcome the pressure that you build up while doing so. It is no easier to compress a photon gas into a black hole than it is to compress any other gas.

(from the lack of manufactured black holes so far you might deduce that this is very difficult indeed)

pZombie

12:59

@JohnRennie Ignoring quantum behavior and assuming a photons just follows a straight line, it would of course be trivial that a photon shot into the exact opposite direction, at any position the photon shot into the box is at currently would then of course result in that opposite shot photon exiting the hole but why would the photon shot inside the box eventually have to exit as well the same way it came in?

I mean, is there like a mathematical prove for an idealized spherical elastic object which is shot inside an idealized box and through an idealized pipe just fitting exactly that object such that the result is always the spherical object having to exit the same way it came in but in reverse?

or can one shoot the object through the pipe, by adjusting the pipe's angle such that the sphere would never end up exiting the pipe in the exact angle required to do so?

pZombie

13:20

The trivial case of course would be to shoot the object through the pipe pointing straight towards the other side's wall. It would just bounce back and exit the same way it came in. But how do you prove that for any angle of the pipe, the object would eventually exit the pipe in the exact same angle it came in, but in reverse?

Avnish Kabaj

@ACuriousMind Delhi haze

Spm 150+

That's gone

Springs here

ACuriousMind

13:40

@AvnishKabaj Assume I have no idea what you're talking about :P Are you saying that every winter Delhi is covered in smog?

GodotMisogi

@ACuriousMind Delhi is always covered in smog

ACuriousMind

But what does "pollution season is over" mean then?

GodotMisogi

They blame it on pollution from neighbouring states

ACuriousMind

Does it mean the smog is slightly less thick than otherwise? :P

Captain Bohemian

@ZeroTheHero but in some fields, doing something new is really easy--just changing a small factor (material in experiments) in others' results--though that new result wouldn't make significant contribution.

and there may a great number of factors to change. Some have not been done, not beceause they are not easy but because nobody is interested in doing them.

@Blue I don't have experience in computation physics. I just observe others in computational physics can produce publishable results far easier and thus faster (because there isn't that much prerequisites to learn) than people in highly analytical fields.

ZeroTheHero

14:17

@CaptainBohemian I don't think this is generally true in the sense that such trivial contributions are at most very rarely published, at least in physics.

Publishing in reasonable journals is sufficiently competitive to weed out such clearly incremental results. Of course, it may well be that what you think to be incremental is not seen in this light by others, but beyond such differences of opinion the top-tier physics journals rarely publish nominally incremental papers.

Captain Bohemian

@ZeroTheHero I don't know if in experiment-related fields, changing a material is a big contribution. I just have heard changing a material in others' result,like from Br into Cl in others' research result can produce research result for thesis or paper. But I know in theoretical high energy physics, result deriving from such a change, like changing Minkowski to Anti-deSitter, changing calculating energy-momentum into angular mmentum in teleparal gravity theory, is often nontrivial and publishable.

ZeroTheHero

14:33

@CaptainBohemian it may not be experimentally trivial to change Br to Cl...

The exception to this is a new field, where there could still be lots of low-hanging fruits remaining...

Captain Bohemian

15:20

today I made horrible dream--a student making some mistake in school will be sentenced to guillotine.

that student is like my junior classmate.

vzn

15:38

Oct 22 '18 at 16:40, by Blue

[Insert 99 problems meme...]

’The night I went toe-to-toe with the biggest popstar on the planet over using sex to sell music': Ariana Grande tries to convert PIERS MORGAN to ‘proper’ feminism and it all ends... in a hug dailymail.co.uk/news/article-6737807/…

Keep these mind

15:50

Anybody have any idea how long it takes to upgrade to Ubuntu 18.10 from 18.04? I'm looking at "> Installing the upgrades" for over an hour or so.

ZeroTheHero

@CaptainBohemian What we do not tell our incoming graduate students is that we have human sacrifice every other Friday before beer.

ACuriousMind

At least there's beer

@Keepthesemind I think a couple of hours is normal

Keep these mind

@ACuriousMind Thanks. I'll wait then.

ACuriousMind

But it of course depends on a lot of factors like your connection's speed and how much you have installed that needs to be upgraded

Keep these mind

@ACuriousMind It's at "> Installing the upgrades", so connection shouldn't be an issue. And 18.04 was brand new (ie, clean).

ACuriousMind

16:06

Then the limiting factor is probably disk speed, but I'm really just guessing here :P

GodotMisogi

@CaptainBohemian Are dreams discovered or invented?

Keep these mind

@ACuriousMind Hmm. SSD.

Captain Bohemian

17:02

@GodotMisogi what do you mean? I think dreams are created by brain by some unknown way which can't be controlled by self's will.

I have never never made this kind of horrible dream before. But these several days the dreams I made often contain somewhat horrible scenarios.

vzn

@CaptainBohemian you seem to be under pressure/ stress lately and its basic psychology this can manifest in dreams... note however that many students find the academic experience stressful... btw meet secret... o_O

Emilio Pisanty

Sven2009

6

particle-physics quantum-field-theory

there are people born on 2009 who hold masters degrees in mathematical physics?

OK, no that's obviously wrong

but there are now people with 2001 in their email addresses who are studying physics in university and where the 2001 does not mean the year they signed up to yahoo mail

Captain Bohemian

@vzn what is counted as academic experience? I almost always make dreams as long as I sleep, and a great porportion of my dreams include scenarios occurring in school campus.

vzn

@CaptainBohemian "academic experience" → going to school ... have had school dreams too they seem to be a common theme... there are a lot of reasons, school mixes up a lot of stuff eg social dynamics, performance pressure, learning, teaching, etc, its a nearly universal human experience aka jungian archetypes etc

Captain Bohemian

but not all of my dreams regarding school is about academic. Like I often dream of outing held by school.

vzn

17:15

@CaptainBohemian maybe a lot of your life has been influenced by school. maybe it plays an outsize role.

Captain Bohemian

I don't know how to call that, just some kind of traveling to a long distance held by school('s social clubs).

vzn

do you mean your school is a long way from your home? yes dislocation is another aspect of school for many esp university etc

Captain Bohemian

@vzn no, I mean the traveling activities held by school. Before university, all of our schools usually held the activity of taking students to travel to somewhere. In university, the school administration wouldn't hold this kind of activities, but if you join a social club, they will hold this kind of activity. And during graduate school, if you go to academic conferences, you get the chance to travel because conferences are often held in a place from school, even abroad.

in a place far from school

vzn

17:31

@CaptainBohemian ok. reminds me of this. The Chinese word for "crisis" (simplified Chinese: 危机; traditional Chinese: 危機; pinyin: wēijī) is frequently invoked in Western motivational speaking as being composed of two Chinese characters respectively signifying "danger" and "opportunity". en.wikipedia.org/wiki/Chinese_word_for_%22crisis%22

ACuriousMind

@EmilioPisanty Yes. Can't staunch the flow of time

Emilio Pisanty

18:16

@ACuriousMind that's not gonna stop me from trying, though

Ajay Mishra

Hey, any body here of electronics/transistors ?

Jake Rose

18:55

Is there an easier way of evaluating commutator relationships between $p^2$ and $x^2$?

Captain Bohemian

19:10

@vzn I can't understand what (in school traveling) remind you of crisis. This is usual the happiest time for students.

I think academic experience is only highly stressful before university. I hate schools before university, but I love university.

ACuriousMind

@JakeRose An easier way than what?

vzn

19:43

@CaptainBohemian conferences/ travel/ clubs are opportunities. in life opportunity and risk are often mixed together. re stress, youve written quite a bit about various stresses youre coping with in chat. your dream about a guillotine for academic mistakes seems to relate to stress.

in Language Overflow, Jan 15 at 16:30, by Captain Bohemian

if Zen really means 禪, I feel it boring. When I was in university, some clubs invited me to 禪, I turned them down.

Student404Mus

20:39

"suppose that Alice and Bob share a Bell state
$| \Phi ^ { + } \rangle =2 ^ { - 1 / 2 } ( | 00 \rangle + | 11 \rangle ) = 2 ^ { - 1 / 2 } ( | + + \rangle + | - - \rangle )$ . If Alice measures the Pauli Z observable on her system, then Bob can guess the outcome of her measurement with
certainty. Also, if Alice were instead to measure the Pauli X observable on her
system, then Bob would also be able to guess the outcome of her measurement
with certainty, in spite of the fact that Z and X are incompatible observables."

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