The h Bar - 2015-09-12 (page 4 of 4)

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5:00 PM

You'd have to change his identification to make the title wrong.

@ACuriousMind this mouse...I want to bear its children

where is @Huy

@0celo7 Uhhhh...what?

I love my mouse!

Oh, your gaming mouse arrived?

yeah

it looks like a damn spaceship, but I like it

5:01 PM

@ACuriousMind Well it's not factually incorrect, I just like complaining.

Ah. So you're a troll ;P

ACM has figured out SJWs

user image

quite an upgrade

looks really cool

I have copy + paste and forward and back in webpages on the mouse buttons!!!

@ACuriousMind Nawh. It affects Fuzzy's oppression status and therefore the modifier to his offendedness attack.

5:07 PM

@0celo7 You use HIM as a mousepad? :D

@dmckee I see. It seems I've missed some rule revisions for modifiers.

@ACuriousMind I'm an engineer, I like my paperweights to have multiple purposes

oh GTA is so much better now

I can activate the special abilities on the mouse now

oh this is too cool

0

Q: Quantum Flavordynamics and messenger particles

My question is about messenger particles and how they relate to the concept of flavordynamics. I know that messenger particles travel between other particles to "communicate the force" like a photon traveling between charged particles to communicate the electromagnetic force. But how do messenger...

particle-physics

@NeuroFuzzy lol

> Keep in mind that I'm only 14 so technical Jargon and equations probably won't make sense to me.

We need the most complicated answer ever

@ACuriousMind You have clearly not been exposed to enough gender studies

My mandatory course on "Identity in a global city" (or something like that) made sure to RAM that into me.

>Doesn't the weak force work within the neutron and not outside?"
Is he/she confused the strong force with the weak force?

and if my memory serves, neutrons can also participate in beta decay and exchange W and Z bosons?

5:19 PM

@Danu oh, that's not really what I meant. My thoughts were like this: if it were a discussion on the main site, then yes, absolutely, it should be moved to chat. But on meta we tend to be more lenient about comment discussions. Between that, and the fact that Michael didn't really know how to use chat (he said), I wasn't as sure whether moving would be the right thing as I would be if it were on the main site.

It's not that I thought moving the comments was the wrong choice. I was just kind of ambivalent, and just hesitant to do it without careful consideration first.

@DavidZ Okay.

In any case, could you take a look at maybe restoring the first few comments?

$\text{>Keep in mind that I'm only 14 so technical Jargon and equations probably won't make sense to me}$

We need something akin to my diagrams on matrix multipication to do that, but I seriosuly doubt this will be easy given the maths in weak force is very messy involving a lot of group theory and lie algebra, and talking about visualising that, well at least I am not up to that task yet

and it will be more difficult if he/she is actually asking about the strong force, which is so messy that perturbation theory cannot be applied easily (I think...?)

(PS I don't know how to make quotes without accidentally quoting the next line on chat)

> what?

it's easy

@0celo7 Alas diracpaul quit the site. Otherwise we could have had 3D glasses diagrams.

@dmckee Wait, what? I'd love that! Damnit! Dirac, don't abandon us!

5:29 PM

why did he leave?

@danu yes, that's the problem I ran into, the quote line going through all my lines at once when I am just putting a ">" on the first line

I guess it's a matter of skipping to the next message

I think your messages are a bit long anyways, most of the time ;)

I have trouble finding good terms to simplify my messages, that's why I rely on latex and drawing diagrams a lot

I can say the same thing in a much shorter length probably because body language helps me to simplify the message

@ACuriousMind 12,000 DPI is crazy

@Secret you're a strange fellow indeed

My chemsitry supoervisor had identified one stragne thing about me, such as how I read sentence compared to most people

5:34 PM

@Danu Here's one: physics.stackexchange.com/a/194688/520

I know there is a better one out their.

For most people given a sentence that describe a diagram as follows:

.Panal a blahblahblah, Panal b blahblahblah, Panal c blahblahblah

The read "panal a" and then they look at panal a of the diagram, after returning, they then start from the last fullstop to read to panal b, etc.

@0celo7 He didn't tell us, but I guess frustration with the site rules.

for me, I can start right where I last left off, and not from the last fullstop

[Discography] Emancipator [3 albums]

@0celo7 That's why my supervisor said my sentences are lengthy

because it is a nonstop sequence of commas

5:36 PM

@dmckee !! I think I have some 3D glasses

So in improving my research proposal, I have took account of that and started putting fullstops every now and then

Another couple: physics.stackexchange.com/a/200611/520 physics.stackexchange.com/a/197239/520

And physics.stackexchange.com/a/198171/520

and so on. They are impressive diagrams, but like the level of math he often used overkill for the purposes they are put to.

One more: physics.stackexchange.com/a/192583/520

@dmckee Very neat

@dmckee Back in high school, I used to always get in trouble for being too loud/bored/annoying during the classes. I often had to stay after school until 5 PM, sitting in the classroom with nothing to do. My chemistry teacher used to spend those hours, spent in dead silence with just us two in the room, but putting on his 3D glasses and watching models of molecules on the internet. Maybe an early fan of (the late) diracpaul...

@FenderLesPaul you're a bum

you've ruined all hope that I had for you

wtf?

5:50 PM

he knows what he did

Well, I don't.

Really sorry dude I blazed a bit and put on some electric moon and totally went into a trance

and lost track of time

by the time I woke up it was like 9am

Lolwat

wat

How was the football game though? Did that happen already?

You guys hang out IRL?

5:53 PM

oh no usually on Skype

we're too far away to hang out IRL

I think he's mad at me :(

@0celo7 I love you.

2

@FenderLesPaul I'm leaving at 4:30

Oh ok

@FenderLesPaul yeah like a wifebeater loves his wife :'(

2

@0celo7 youtube.com/watch?v=fm0T7_SGee4

sniff

Maybe you guys should keep these things to your Skype conversation? :P

2

I'm not sure of how much interest it is to the others here

6:04 PM

1

Q: Retarded Quantum Harmonic Oscillator

Suppose there is a harmonic oscillator and at some time acts on him a force. The external force $F (t)$ being zero before $t = 0$ and after $t = T$ . The oscillator was in its ground state for all time $t < 0$ until the force starts acting on it. Compute the dispersion ∆E of the energy at times $t >

quantum-mechanics harmonic-oscillator uncertainty-principle

the title of this post is offensive and politically incorrect

should be "differently abled" QHO

I'm terrible at differential geometry.

(step 1: acceptance)

@Danu about as much as for your love life

battlelog.battlefield.com/bf4/servers/show/pc/…

@FenderLesPaul that's your kind of server

6:29 PM

here I am @0celo7

@0celo7 I did ask, before starting to talk about that, if anyone was interested in hearing me out (the answer was yes).

So I don't think you're right.

Anyways, it seems we just can't get along today so let's just leave it at that.

@0celo7 lmfao

@Danu we get along!

6:44 PM

I think @0celo7 be mad

@Danu indeed

I would agree

is that what football does to people?

@FenderLesPaul only in 'Murica ;)

(jk, everywhere, except what we call footbal is your soccer)

Hehe

7:13 PM

@DavidZ I'm going to be going to a bunch of "frequent" questions to scan all the comments for useless material, so expect a bunch of flags ;)

@Huy the mouse is a lot bigger than I expected

I can't use the same grip as I did with my cheap dell

@Danu no

Good

@DavidZ Please give me some feedback: What do you think about flagging back-and-forth chains of comments such as here: physics.stackexchange.com/questions/2110/…

I think they're obsolete, but maybe you don't think they should be flagged; please let me know what your opinion is.

7:40 PM

Anything that old is absolutely fair game for flagging IMO

Months is more than enough time for any useful material to be incorporated into a post

@DavidZ awesome

You will be buried in flags ;)

Why do I like doing this so much? :P

Hah @DavidZ you're deleting faster than I can flag ;)

It's easy :P

Damnit, trying to flag only to see "this comment has been deleted" once more!

Ah, that page is so clean now :)

For flagging I'd say prioritize the discussions - where the comments are long, and/or occur in large numbers. Obviously we can't actually delete all old comments.

@DavidZ YOU JUST WAIT :D

But yes, I agree.

8:18 PM

All you need is someone with comment OCD to do it for you

9:18 PM

Oh internet, you're so great:

F. Galetto, "Riemann Hypothesis proved" (2014)

[abstract:] "We show a proof of the so-called Riemann Hypothesis. We prove the RH using the theory of 'inner product spaces' $I$ and $l^2$ Hilbert spaces, where is defined the 'functional' $(a,b)$, named scalar [or inner] product of the vectors $a$ and $b$. The proof is so simple that we suspect that there could be an error that we are unable to find."

user image

woo!

@NeuroFuzzy Hairy ball theorem?

@Danu Huh? No, parallel transport.

@NeuroFuzzy It reminded me of a vector field that has a zero on top haha

10:03 PM

And there's the kick-off @0celo7

10:23 PM

@Danu I agree.

10:59 PM

@Danu

I need you to do something for me.

Express some interesting information about physics.

Anything.

@DanielSank Anything?

Is this a trick question?

Something interesting that we understand because of physics, you mean?

Take your pick from GR stuff!

Alternatively I find it interesting how we can get away with QFT without bothering too much about fundamentals: Cross-sections all the way!

Also I am a bit confused atm, and you can probably help me: The trajectory of a vector field that starts at a point where the vector field is nonzero can never end up in a point where it is zero (try to trace it backwards to see why); but what is up with the charges in electromagnetism then? Is it just that the vector fields are not defined on the charges, or something like that?

@DanielSank Now what was this about?

@Danu $\frac{1}{r}$ doesn't look as if it is defined at $r=0$ to me :P

@ACuriousMind Yeah okay, so it's all just boundary conditions 'n' stuff

So the field generated by a point charge isn't defined at the position of the charge. Is this somehow surprising?

When things get confusing, believe in the boundary conditions

@ACuriousMind It started with me being confused about this statement about trajectories staying within the support of the vector field

I thought, somehow, that the physics stuff seemed like a counterexample

Then I came up with the tracing backwards argument

Then I realized the physics thing being a problem probably didn't make much sense, but wanted some confirmation

You know, how when you just get into uni they make you draw these vector fields with sinks and sources?

They seem like zeros of the vector field or something

...they're not, I guess

also wtf Daniel just disappeared again

I really want to know why he wanted me to give him some example

11:30 PM

More dumb questions about vector fields:

In my notes we have the rotational vector field on $\mathbb{R}^2\cong\mathbb C$ "given by $X(z)=iz\in\mathbb C\cong T_z\mathbb C$"

I don't really feel super comfortable translating this to the usual vector notation

I want to say $X=i\partial_z$

But shouldn't I somehow first split off $|z|$? I have the feeling I should be identifying $z/|z|$ with $\partial_z$ instead, maybe

..so $X=i|z|\partial_z$?

wb Daniel

and home

@Danu I need you to convey information to me through the internet.

@DanielSank I tried!

I need you to change my brain from not knowing a thing to knowing a thing.

Meeehhhhh, you pointed out some curiosities.

Dude, what are you on about

11:35 PM

Just teach me something.

What are you looking for

Ok here, what's the deal with black holes? Do they suck things in and never let them out or not?

@DanielSank Unsettled question what exactly comes out in terms of Hawking radiation

...but something comes out

And it's due to purely QFT in curved spacetime effects

basically, it comes from the notion of particle being ill-defined in general spacetimes

@Danu Like I always say, asynchronous communication protocol.

@Danu Woah, weird.

Any experimental evidence?

@DanielSank But after making such a direct request it's a bit weird, but okay

@DanielSank No, but it's an inevitable consequence of QFT in curved spacetimes

11:37 PM

@Danu Oh, interesting.

Thank you.

Now about your vector thing...

Basically, we're stuck with the non-vacuum "perspective" on a black hole so we see "particles" popping out with a thermal spectrum

You don't even need to deal with particles

note the quotation marks

Just do the solution of any field

@Danu When you talk about vector trajectories, do you just mean the integral curves?

11:38 PM

Around black holes, the vacuum splits

@DanielSank Yeah

It turns into an inward flow of negative energy and an outward flow of positive energy

^I don't like that interpretation

@Danu The trajectory can have a limit at a point where the field is zero, yes?

It's not an interpretation

It's what the equation gives you

11:39 PM

^negative energy is

It's not.

It's a common feature of QFT.

Cool story, but that's not true.

It's reducible to the interpretation of a single sign in an exponent

If you check the stress energy tensor of those solutions it violates the NEC at some point

It's purely interpretation

@Slereah Yeah it is. You can look at equations one way and see energy flow, but from another perspective you can rewrite without any mention of energy.

It's just like the difference between particle and wave pictures.

11:40 PM

@DanielSank A limit being what?

NEC violation is independant of any interpretation

You agree that it can never leave the support of $X$, yes?

It's also frame independant

Although it does depend of how you define the vacuum in your theory

Though IIRC all vacuum definitions engender NEC violations

@Danu Meaning that if I integrate the vector field and parametrize it then I have to put the parameter to $\infty$ to get to the null point.

This would be easier with an example field.

@DanielSank Sure

Not so interesting

I care about finite times

11:42 PM

In this set of lecture notes, the author writes that$$cP^0=\gamma mc^2=\frac{mc^2}{\sqrt{1-v^2/c^2}}=mc^2+\frac{1}{2}mv^2+\cdots\tag{1.41}$$Is this a Taylor series, and if so, why do we care besides taking the limit for low velocities?

@Slereah Who guarantees me that the NEC is even relevant at all?

@HDE226868 Yes

@Danu : Relevant to what?

and nothing except low limit

@Danu Well, are you certain we can't get to a null point in finite time?

Probably need some smoothness condition for that to be true.

The NEC is just an expression of the relation between energy and momentum

11:44 PM

@Slereah Why should I attach any value to its violation (not to mention an interpretation)

@Danu Thanks.

@DanielSank Trace it backwards

It can never leave

Because the NEC is very relevant to a wide variety of GR theorems?

Including black hole ones?

once it gets there

@Danu Right I get that.

It's hard to do that mentally if I allow nonsmooth fields.

11:45 PM

@Slereah Not convinced yet, but okay that's something, maybe

@DanielSank Doesn't matter; I care only about the smooth case

I mean what other interpretation do you have for hawking radiation

@Danu Ok, I tried to get that out of you before :-)

The whole virtual particle pair is kind of a pop science thing

My second question doesn't even make sense in the non-smooth case; vector fields fail to be derivations.

@Danu Fine whatever.

So what's the question?

11:46 PM

@Slereah Correlation functions.

@DanielSank Second one; How do I translate that sentence

15 mins ago, by Danu

In my notes we have the rotational vector field on $\mathbb{R}^2\cong\mathbb C$ "given by $X(z)=iz\in\mathbb C\cong T_z\mathbb C$"

@Danu : You get the stress energy tensor from correlation functions :p

Express $X$ in explicit "derivation" form

They're the ones giving you the energy flow

(I already know the correct expression in "real coordinates", if you want help)

$iz = i ( x + iy) = ix - y$.

11:48 PM

@DanielSank lol yeah... so

So, if you're taking the real part as the $\hat{x}$ component etc. then you get

No, I want $X=\text{something}\partial_z$

what is "something"

a vector field $-y \hat{x} + x\hat{y}$.

@DanielSank right

no, your correction is wrong

second correction is right

:D

@Danu :D

11:49 PM

but can you do that?

@Danu What does $X$ mean

in terms of $\partial_z$?

?

the vector field

Oh

What does $\partial_z$ mean?

11:50 PM

What I assume to be the single complex basis vector on $T_z\mathbb C$

(I think you're trying to recover the idea of Polya vectors)

lmao

oh god no

@Danu No really.

sigh... okay...

@Danu What is $T_z C$?

11:51 PM

Why is it harder to express the v.f. in terms of $\partial_z$ than $\partial_x$ and $\partial_y$

@DanielSank Tangent space to $\mathbb C$ at $z$

Tangent complex plane at z?

$\cong \mathbb C $ of course

hence $X(z)$ being given in terms of an element of $\mathbb C$ in the first place

but I want to translate it to the standard notation of elements of the tangent space

so... any progress? :P

@Danu I'm just confused. This is not related to previous question, right?

No

Well, it is, but only in the sense that it appears in my lecture notes :)

@Danu Ok, well, I have to figure out what the tangent space to $C$ looks like.

11:55 PM

@Danu so what are you talking about? Wouldn't a tangent field be like $X=x_z \frac{\partial}{\partial z}+x_{\bar{z}} \frac{\partial}{\partial \bar{z}}$?

I'm sure you're way ahead of me, just curious :)

@NeuroFuzzy Is it?

If so then we're done

Ok have fun.

What is $x_z$?

a complex number

I have no idea, I've never read anything about complex manifolds before

I'm just guessing

I see no reason why not!

yeah but in this particular case, what is $X_z$ and what is $X_{\bar z}$

both $i$?

11:58 PM

Hmmm??? So for my post I meant $x_z$ and $x_{\bar z}$ as arbitrary complex fields. If I saw $X_z$ I would guess it would be the basis vector $\frac{\partial}{\partial z}$.

You didn't look at my question, did you?

I have a vector field that's given by $X(z)=iz\in\mathbb C\cong T_z\mathbb C$

Now, this is in $\mathbb C$-notation

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