The h Bar

4:00 PM

I'm not sure how the site decides who to ping. Maybe you've visited the Physics chat once too often and it now knows where you live :-)

Down Christopher

@JohnRennie I think I came here once to test a bug that turned out not to be a bug

ACuriousMind

Welcome to the chat session everyone! If you are new to the site, new to chat, or have other questions about our site, now is the ideal time to ask.

Down Christopher

$Doe$ thi$ $crew $LaTaX$?

John Rennie

@DownChristopher Oh no! You're now a marked man! :-)

Slereah

@EmilioPisanty lame

ACuriousMind

4:01 PM

We don't have much of an agenda today, so if you don't have something you wish to bring up, I guess we'll just chatter along as usual

vzn

@ACuriousMind somebody said something about an agenda earlier? is there one today?

Slereah

Today's agenda is cake recipes

Share your best cakes

John Rennie

@vzn no-one has raised any outstanding issues

Down Christopher

@JohnRennie I guess so

Anyways bye!

ACuriousMind

If you have interesting physics news that developed in the recent past you'd like to discuss, now's also a good time to get more than the usual regulars' input for discussing them

David Z

4:02 PM

howdy

Emilio Pisanty

In that case, maybe it's a good idea for folks to go over their posts and make sure that there's no non-imgur http images?

ACuriousMind

@EmilioPisanty Ah, yes, that's a good point

Emilio Pisanty

This is a good query

vzn

yesterday, by vzn

The quest to crystallize time — Bizarre forms of matter called time crystals were supposed to be physically impossible. Now they’re not. / nature

AnimatedPhysics

jlab.org/conferences/3Dmodeling/index.html conference this week. Are there really lots of quark/anti-quark mesons in a proton or are they created the the energy of crashing protons together.

0celo7

4:05 PM

@ACuriousMind Ahhhh. I forgot the definition of closure. The closure of the unit ball of $X$ is a closed set that contains the open unit ball of $X''$ (the esimate gives that much, just choose $\epsilon$ small enough!). So that has to contain the closed unit ball in $X''$ by definition of closure. However, the closure of the ball in $X$ $\subset$ closed unit ball in $X''$ since it's an isometric embedding. So they must be equal.

Slereah

So anyway

Secret

As starred previously, this is quantum cognition (a field in cognitive science). They are currently using the quantum inspired mathematical framework to understand how jokes are interpreted

Slereah

marmiton.org/recettes/…

This is my favorite cake recipe

it is fairly simple and good

vzn

LHC: Five new particles hold clues to sub-atomic glue / bbcnews

ACuriousMind

@EmilioPisanty I get no results on physics, is there something to adjust in that query?

Emilio Pisanty

4:06 PM

@ACuriousMind I'm looking into it

Its behaviour has changed since I last used it

John Rennie

@AnimatedPhysics particles are a surprisingly elusive concept in quantum field theory. It can be very hard to point to anything specific and say look there's a particle.

ACuriousMind

@0celo7 Why are you telling me that? :P

0celo7

@ACuriousMind Because you like functional analysis

John Rennie

@AnimatedPhysics So askign how many particles there are ina proton is a surprisingly ill defined question.

Secret

New approach to measurement problem. I do not really understand it

Slereah

4:07 PM

that's because there's no such thing as a particle in QFT

that's why it's called a field theory

0celo7

What I need to check is that the closed unit ball is actually closed in the wk* topology.

But since the norm topology is stronger, that might be immediate.

Or is it weaker?

Slereah

Although I think you can find that roughly the sum of quarks and antiquarks average to 3 quarks

vzn

@ACuriousMind whats up with non-imgur links? missed that

Emilio Pisanty

OK, here goes

ACuriousMind

@vzn SE is switching to forcing https for linked images. Imgur links are updated automatically, the rest needs to be adjusted manually because they can't automatically repair arbitrary image links

Emilio Pisanty

4:09 PM

Can folks go to this query and make sure that their posts don't contain non-https images? They will stop displaying correctly.

Ideally all images should be on stack.imgur to avoid link rot

Secret

Entanglement area law in superfluid 4He

vzn

@ACuriousMind strange/ seems weird, wonder why, did they announce this somewhere?

AnimatedPhysics

At the conference they had a very nice history of the proton. In the 70's we had 3 quarks and some gluons, now we have 3 quarks and an indetermined (variable, unknown?) number of gluons and mesons.

ACuriousMind

@vzn This post is still featured and contains the roadmap. The thing about forcing https images is linked in one of the steps.

Slereah

Oh you have way more than 3 quarks

It's just that you have $\sum q - \sum \bar q = 3$

0celo7

4:12 PM

@Slereah what?

the number of quarks and antiquarks should be the same, no?

Secret

There's a limitation in how accurate we can measure clocks in spacetime trajectories

Slereah

In a proton?

No

0celo7

oh

ACuriousMind

@AnimatedPhysics I never really understood why people are so adamant about there being "sea quarks" or "sea gluons". They arise from the same faulty interpretation of Feynman diagrams as the silly idea of particle-antiparticle pairs "popping from the vacuum".

AnimatedPhysics

@slereah I think the number of quarks in a proton is fixed at 3.

ACuriousMind

4:13 PM

What is a fact is that hadrons are messy QCD bound states that are rather difficult to understand in terms of their bound constituents

Slereah

@ACuriousMind Well you know, it's easier to compute if you think of it this way :p

0celo7

the definition of proton is three quarks, no?

Slereah

@AnimatedPhysics Nah, you get plenty of quark antiquark pairs

0celo7

uud

@Slereah those are virtual though

Slereah

They are all virtual, @0celo7

John Rennie

4:14 PM

@EmilioPisanty 580 images!!! That will keep me busy for a while ...

AnimatedPhysics

Absolutely @slereah, they are called mesons

Slereah

They all get destroyed and created all the time

The 3 is just an average number

ACuriousMind

@JohnRennie @EmilioPisanty The query also returns imgur links, which don't need to be fixed

For me, it returns all 10 of my posts that contain any images at all

And all of those are imgur links

So I can't even say whether it returns non-imgur links at all

@Slereah ::twitches::

Slereah

Well what do you want me to say instead, "It's all some kind of soliton on a hilbert space we can't divine"?

I mean rigor is nice but in QCD it doesn't lead you far

AnimatedPhysics

user129412

4:17 PM

Silly question that I'm somehow not sure about.. In the absence of a magnetic field and such, do the different states (-1, 0, 1) of a spin-1 particle have a different energy? For spin 1/2 you have that -1/2 and 1/2 have the same energy when not split by a magnetic field; I'm assuming this should also hold for spin-1 right

Slereah

I guess you could talk about lattice QCD but I don't know anything about it

ACuriousMind

@Slereah It's not about rigor, it's about this silly myth that virtual particles are "particles" at all.

user228700

BTW, @JohnR: The site decides to ping when one has explicitly "joined the event". I, for one, didn't get pinged because I didn't RSVP.

Slereah

@ACuriousMind well what is a particle

David Z

@ACuriousMind technically, perhaps, but it's a very useful way of thinking about proton structure in high-energy phenomenology at least

Slereah

4:18 PM

@user129412 Free particles don't have any spin interaction, yes

ACuriousMind

They only exist in a perturbative formulation - you can't even say what the hell a virtual particle is supposed to be in a non-perturbative formulation where you don't have Feynman diagrams

Slereah

All spin orientations have the same energy

@ACuriousMind well yeah

ACuriousMind

If the "existence" of a physical object depends on you using a particular approximation method, it's not a meaningful physical object to begin with

AnimatedPhysics

@Slereah Picture from the conference, 3 quarks, a bunch of gluons and a bunch of mesons (quark/ant-quark pairs)

John Rennie

@Kaumudi.H and yet the chap who was wondering why he got pinged had not explicitly joined the event ...

ACuriousMind

4:20 PM

@DavidZ I think it's fine when experts use such phrasings as long as they're clear about the actual meaning, but I really think it's rather misleading to present this interpretation to laymen without a host of qualifiers

Slereah

Eh in the end the layman doesn't need to understand it nor has the mean to

(here is me being an elitist)

John Rennie

@EmilioPisanty the query gives me a big list of imges with no indication as to whether they are on imgur or not.

David Z

@ACuriousMind Yeah, that's fair

user228700

@JohnRennie Huh. I see...

Slereah

what would be the rigorous description

I guess the conserved isospin charge of the proton bound state?

0celo7

4:22 PM

@yuggib Are you here?

John Rennie

@Kaumudi.H Over the years we've had other people say they've been pinged apparently for no reason. I wouldn't be surprised to learn the SE software is a bit buggy in this respect.

0celo7

@yuggib Yosida Corollary 3, p. 114 doesn't make much sense to me without a proof. My proof seems to be pretty convoluted.

Bernardo Meurer

0

Q: Implementing Miller-Rabin in C

I'm trying to implement the Miller-Rabin primality test in C99, but I'm coming across some problems getting it to work. I crafted a small test-set to verify whether or not the implementation works, here's how I'm checking for primes int main() { int foo[11] = {0, 1, 2, 3, 4, 7, 28, 73, 125,...

ACuriousMind

@JohnRennie I think the algorithm randomly decides to ping people who've been here at some point in the last few days and are currently in another chat

MartianCactus

hello specail event

Bernardo Meurer

4:23 PM

If anyone knows C or Miller-Rabin :P

vzn

@ACuriousMind it would be nice to see an entire paper/ study/ survey on the concept of "virtual particles" by leading authority/ expert... there have been some major debates in here/ on site wrt topic (some wrt a "gadfly"/ "black sheep" member)... has caused a lot of thought/ consternation maybe even among experts...

David Z

@vzn There are probably several out there already. Certainly it's addressed in most QFT books, at least.

John Rennie

@BernardoMeurer OK remind me which #include the rand function is in

0celo7

@yuggib I'm not sure why the weak* closure of the ball of $X$ should be contained in the ball of $(X_s')_s'$. Conway says it's obvious. The topology is not first countable so I'm not sure if I can use sequences

Slereah

is it obvious

David Z

4:29 PM

Oh, random note since I'm here: I'm in the midst of a very busy few weeks IRL, so I'll be scarce on the site for a little while

just in case anyone notices and wonders about it

0celo7

@yuggib But I do think that closure = set + limits regardless of the countability. So I need to show that a weak* limit of elements of ball $X$ remains in ball $X''$?

But that's probably easy using the simple convergence definition of the weak* topology + the definition of the embedding $X\hookrightarrow X''$

A sequence in ball $X$ gives rise to a sequence of operators on $X'$ with norms $\le 1$. It doesn't make sense that these could converge outside of the unit ball in $X''$ in any topology.

But maybe I need to check that. I don't know.

Slereah

I guess the proof of the boundedness of the causal diamond in Minkowski space would just be like

Emilio Pisanty

@JohnRennie yeah, I've seen it, working on it

vzn

@BernardoMeurer Computer Science / chat.stackexchange.com/rooms/2710/computer-science

Slereah

Show that everything is within the bounds of an area delimited by the coordinates of $p$, $q$, the past cone of $q$ at $p$ and the future cone of $p$ at $q$

Emilio Pisanty

4:43 PM

@ACuriousMind It's curious that they haven't rewritten all the stack.imgur links here

Slereah

So just take the min and max of all those and it should be a cube large enough to encompass everything

ACuriousMind

@EmilioPisanty I noticed that, but the http ones seem to still work fine

It's odd

Maybe we're the last site to get any update, now :P

Slereah

Like the $t$ coordinate is $t \in [\phi(p)_t, \phi(q)_t]$

while the $\vec x$ will be bounded by the limits of the lightcone on the Cauchy surface of $p$ and $q$

yuggib

@0celo7 you should use the bipolar theorem

the bipolar of a set is the closure (in the weak*-topology) of the convex hull of the original set

and you can easily see that in Banach spaces the polar of a ball centred in zero is the ball with inverse radius

(as you can imagine, you can find the definition of a polar, and the bipolar theorem in Bourbaki's TVS)

0celo7

@yuggib I'm sure there are other ways of doing it, but I'd like to understand the comment in Conway and what Yosida is doing

Why is it clear that the closure of the X ball is contained in the X" ball?

Closure in the weak* topology

yuggib

4:55 PM

you are taking the continuous dual of $X$ with respect to which topology? The Banach norm topology (supposing it is Banach) ?

0celo7

I think Conway talks about polars

yuggib

And then, you take the dual of the dual with respect to which topology?

0celo7

@yuggib $X$ is a Banach space, take $X'$ with the strong/norm topology

Then take $X''$ and let $b(X'')$ be the closed unit ball with the strong topology

But we give $X''$ the weak* topology when viewed as the dual of $X'$ (which still has the strong topology)

Then, embed the ball $b(X)$ into $X''$, and take its closure wrt. the weak* topology

The claim is that this closure = $b(X'')$

So, is $b(X'')$ closed in the weak* topology?

yuggib

yes

0celo7

I don't even need that, I just need $\overline{b(X)}\subset b(X'')$.

Conway says it's clear, but I don't see it...

yuggib

5:04 PM

do you agree that $e(b(X))\subset b(X'')$? (where $e:X\to X''$ is the embedding)

0celo7

That's clear since the embedding $X\to X''$ is isometric if we give $X''$ the strong topology.

yuggib

then you just need to convince yourself that the ball is weak*-closed

0celo7

The ball $b(X'')$?

yuggib

yes

0celo7

Will I need some version of Hahn-Banach?

yuggib

5:06 PM

Hint: by Banach-Alaoglu, the ball is compact

0celo7

I don't have Banach-Alaoglu

yuggib

?

0celo7

It's proved on page 137 of Yosida, I'm on 114

Hmm, when does Conway prove it

Ah, Conway does have it available.

So I think the Yosida proof should be different

I'm going to think more about this

yuggib

probably there is also a direct proof of its closedness, but it is essentially mimicking the proof of banach-alaoglu

0celo7

@yuggib And a compact subset of a hausdorff space is closed, I know

@yuggib Do you know the book by Brezis?

Emilio Pisanty

5:18 PM

OK, @ACuriousMind @JohnRennie It seems that there isn't really a good way to find those images

2

A: Help us fix broken images!

I've written the following snippet so you can return and filter the Crowdcrafting tasks by site. It currently returns up to 100 tasks (the maximum the API allows). It looks like a lot of sites have fewer affected posts than that, there's no instant way to get further posts for the ones that do t...

that's probably the best way

but that looks tricky to modify to return posts for a single user

yuggib

@0celo7 which one?

0celo7

@yuggib Functional analysis, sobolev, PDE

John

Would anyone be able to help with a buoyancy question?

A balloon has an initial volume of 0.5m^3 containing air at atmospheric pressure. 2.5x10^2kg weights are attached to the balloon, the system is placed in water and floats. Assume the skin of the balloon has negligible mass and elasticity.

yuggib

@0celo7 I have it in pdf, but I did not read it

John

The balloon is then pushed further under water until it remains in equilibrium. Find the depth under water which it must be pushed

0celo7

5:29 PM

@yuggib I need to rewrite the proof on page 69

I think that's what Yosida has in mind

Slereah

heheheh

$69$

yuggib

@0celo7 it seems pretty easy

0celo7

@yuggib did you look at page 114 of Yosida? His lemma has $||x||\le ||x''||+\epsilon$, so if $x''$ is on the boundary of $b(X'')$ then you get $||x||\le 1+\epsilon$ which is worthless

and it's $x=x(\epsilon)$ :/

yuggib

@0celo7 no I did not look...

however in the end the important thing is that you can find a proof (even if it is not the same as in Yosida)

0celo7

Sure

bolbteppa

5:40 PM

@yuggib have you read TVS?

yuggib

@bolbteppa yes

bolbteppa

That is incredible

yuggib

why?

it is a very neat book

and I use it in my work

Slereah

What is TVS

yuggib

Espaces Vectoriels Topologiques

bolbteppa

5:42 PM

I want to know it

yuggib

@bolbteppa know what?

the book?

bolbteppa

Yeah

Bornological space

In mathematics, particularly in functional analysis, a bornological space is a type of space which, in some sense, possesses the minimum amount of structure needed to address questions of boundedness of sets and functions, in the same way that a topological space possesses the minimum amount of structure needed to address questions of continuity. Bornological spaces were first studied by Mackey. The name was coined by Bourbaki. == Bornological sets == A bornology on a set X is a collection B of subsets of X such that B covers X, i.e. X = ⋃ B ...

0celo7

Is TVS only chapters 1-5 or are there more?

Sir Cumference

One of my friends is struggling in high school physics

Anyone recommend her a good book?

Slereah

Maybe she is meant for STEAM

Sir Cumference

5:47 PM

:36186375 She says her teacher doesn't know physics

Slereah

yuggib

@0celo7 only 1-5

Sir Cumference

So...anyone have a good textbook?

yuggib

@bolbteppa yeah that is interesting stuff

Slereah

@SirCumference Feynman

Good for basic physics

Sir Cumference

5:49 PM

@Slereah High school

0celo7

Weinberg

@SirCumference

@yuggib Springer Link has TVS then

Sir Cumference

You guys...

0celo7

Not sure if I really need it

Slereah

Feynman's physics lessons has plenty of high school level stuff

Sir Cumference

@Slereah I remain highly skeptical

Slereah

5:50 PM

Then I don't know

vzn

@Slereah ? did you mean not meant for STEAM?

Sir Cumference

@Slereah Well, what book did you use in high school?

Slereah

@vzn The joke is that @0celo7 said STEM

yuggib

@0celo7 I know ;-) I have it in french however

Slereah

The difference being art

send her to the humanities

vzn

5:51 PM

@SirCumference it will not help unless its a better textbook than the one she has, does she have trouble understanding her textbook? which one is it?

Slereah

@SirCumference I just used whatever book was used for the class

They weren't particularly good or bad

0celo7

serious question, how is someone who is failing high school supposed to succeed in life?

vzn

@Slereah lol ok that occurred to me

Slereah

Also I don't recall their titles

Sir Cumference

@vzn She doesn't have a textbook

0celo7

5:52 PM

nothing against your friend @SirCumference

vzn

@SirCumference lol then theres her problem right there :P

Sir Cumference

@vzn Yes, you have any recommendations?

Slereah

Well, with the economy the way it is

Most people will fail, anyway

vzn

@SirCumference any std high school physics textbook there are many

John Rennie

Simple maths question for the panel: suppose I want to calculate $a^d mod n$, but I only have 32 bit integers so I can't let any intermediate number get larger that $2^31$. What's the easiest way to step through the calculation making sure the numbers don't get too large?

Sir Cumference

5:52 PM

@0celo7 She says she likes learning about the universe and she likes math, but her teacher is awful

So she's looking for a textbook

vzn

not sure how anyone can take a physics class without a textbook, incl high school level...

Sir Cumference

@vzn std? o_O

0celo7

sexually transmitted textbook

2

Slereah

@JohnRennie Are $a$ and $d$ integers

vzn

awww geez, ~~peanut gallery~~ ppl triggered by chat abbrevs, yeah luv it, whats new around here

John Rennie

5:54 PM

Yes, it's all integer arithmetic

Sir Cumference

I always abbreviate "standard deviation" as "STD" in my notes, if the professor talks ridiculously fast

Just habit

ACuriousMind

@JohnRennie Why would you have intermediate numbers that are larger than the starting number?

vzn

@SirCumference are you in HS yourself? do you have a book?

Sir Cumference

@vzn College

No idea what book I had

Slereah

Is there an equality like $(a \times b) \mod n = (a \mod n \times b) \mod n$

0celo7

5:55 PM

@Slereah ??

Slereah

I dunno

vzn

← struggling to remember a high school physics book name

Slereah

Trying to think of ways

John Rennie

@ACuriousMind for example 14^9. If I just feed this into Excel it's bigger than a 32 bit integer

Slereah

(a + b) mod n = [(a mod n) + (b mod n)] mod n.

ACuriousMind

5:56 PM

@JohnRennie Oh, you want to give the tuple $(a,d)$ and not $a^d$ itself as input?

Slereah

ab mod n = [(a mod n)(b mod n)] mod n.

Those are properties yeah

John Rennie

Can I multiple 14 by 14 8 times and keep reducing intermediate values to keep them small

Slereah

So I guess for $a^d$, just do $a*a$ d times, but do mods in between?

Sir Cumference

@vzn She says a good website would be nice too

Slereah

that way you don't risk overflows

vzn

5:56 PM

@SirCum Halliday & Resnick is popular in colleges, not sure if it is HS level, think it might be

ACuriousMind

Well, then you just use that taking modulo n is a group homomotphism, so you just take $(a\mod n)^d \mod n$

Slereah

yeah

pretty much

Although if you do that directly you also risk an overflow

ACuriousMind

If you fear that $(a\mod n)^d$ might be too large still, then apply mod after each multiplication by $a\mod n$.

Slereah

I mean 2^50 mod n would overflow

Sir Cumference

The thing about high school physics is that a mediocre teacher can confuse everyone

She's dealing with that

John Rennie

5:58 PM

@ACuriousMind $a$ is always less than $n$

Slereah

Even better then

Just do $((a * a) \mod n * a) \mod n * a ...$

ACuriousMind

^yeah, that

Sir Cumference

By the way, anyone want to hear an amazingly stupid joke?

Transcript for