The h Bar

123

02:16

Hello Everyone...

user430580

hello

qwerty

02:50

@Slereah actually love this lol

Nick Alexeev

03:05

Is mid- and far-IR spectroscopy ever done in water? I looked at the absorption spectrum of liquid water, and it absorbs a lot in those bands. I imagine that water would absorb a lot more than an analyte dissolved in it.

naturallyInconsistent

04:43

@user430580 mandatory. But dry ice is not exotic. You can easily buy it.

@Sanjana then you might want to look into geometric algebra. Which is different from algebraic geometry.

@Arjun Goldstein is clearly doing proto-quantum. There must be corrections due to inter-particle collisions, but that turns out to be negligible for a tremendous range of accessible experimental parameters, and so we generally begin with neglecting such corrections. It is just like with how blackbody radiation must be corrected at superbly high densities, but we havent begun to experimentally find these corrections.

@qwerty You are always allowed to assert that you only know the path from a certain premise to a certain conclusion and have yet to map out the territory. Deviations could be cliff's edge. That's how most profs teach QFT. Just because someone isn't sure of everything is not a show-stopper for teaching.

but yeah, note the ppl who are so confidently incorrect and unapologetic about it.

Ryder Rude

07:29

hi

@naturallyInconsistent please don't suggest fringe topics randomly, when they have nothing to do with the question

Mr. Feynman

07:59

🤔

qwerty

08:50

@Slereah may I ask how much time do you spend on your blog? for example that free particle blog post

Arjun

09:04

@naturallyInconsistent what are "accessible experimental parameters" ? Are they properties of the system that we can experimentally measure?

Slereah

@qwerty If you read them you will notice that probably not that much

I stop mid-sentence a lot

I need to finish them

qwerty

@Slereah I did notice that... but still, it looks like a good chunk of effort

Slereah

Someone has to figure out what a free particle does

qwerty

@Slereah and write it down comprehensively all in one place neatly and with no inconsistencies, obviously

Slereah

I believe in dumb examples

Too many books don't want to use their fancy theories on a dumb example

qwerty

09:18

I approve

Slereah

Sometimes you have to work out the BV-BRST complex of a rock

Slereah

09:55

I should probably make a tree structure to describe the different possibilities

Because there's a lot you can mix with

Lucky Chouhan

@qwerty what we see in blog is polished presentation of a topic. Don't think that Slereah writes his whole blog in one stream of consciousness.

Hi @Slereah do your friends and family members call you "Sam"? 🤔🤔

qwerty

@LuckyChouhan huh? it still makes sense to ask how much time someone devotes to something...

also while it is impressive it's not exactly polished as slereah himself pointed out.

Lucky Chouhan

@qwerty what I think is, whenever someone writes a good blog post it really means that [s]he wanted to write that blog. It doesn't mean they have dedicated time for writing blog every day. They write whenever they feel like writing it.

@qwerty I understand,

qwerty

I never suggested any of what you're saying

Lucky Chouhan

@qwerty I'm sorry,

Are you thinking to start your own blog?

qwerty

10:04

no, it's not my preferred format.

Lucky Chouhan

@qwerty then what is your preferred format?

Have you got github account?

Slereah

@LuckyChouhan No we're not Americans

qwerty

i write pdfs

no I do not have a GitHub I'm sharing at the moment

Lucky Chouhan

@Slereah then may I know where you are from :')

Slereah

France

Lucky Chouhan

10:08

@Slereah Then you're Jean Sam

Slereah

As with most French stereotypes they are a bit old

Nobody is called Jean these days

This isn't the 60's

Lucky Chouhan

Oh, I didn't know that. Then what do French people use in the place of Mr, Mrs, Ma'am and sir?

ACuriousMind

@Slereah Your unfinished articles look much like how I experience technical writing - I excitedly put all the section and subsection titles up and imagine how nicely structured the final result will be, and then get discouraged at writing down the actual content :P

Slereah

@ACuriousMind That's ADHD for you

I should finish like one article someday

The closest to being finished is probably samuel-lereah.com/articles/CS/making-plasma-effects

But like a fool I added a section about GPU methods to it when I don't know how to do it yet

Ryder Rude

Susskind says that a string can be approximated by a N particles joined together by springs, and we can talk about the wavefunction evolution of this

when strings join, it is because two particles get close and a
new spring forms

Lucky Chouhan

10:22

Hi @Slereah I remember a word, Monsieur ;)

Slereah

I'm not one for formality

qwerty

haha you people have structured articles because you see the big picture. my sections don't come in until mid way through the whole process at least when ive finally managed to chart the territory as NI put it

Ryder Rude

then can we derive the sum over topologies thing from this approach

qwerty

and I'm learning as I go

Ryder Rude

also, the use of compactification is exactly reminiscent of Kaluza Klein... cuz they say that gravity in higher dimensions becomes EM+gravity in lower dimeneions

Slereah

10:26

You know what happens in France to the people with the titles

communism intensifies

►

ACuriousMind

...did you make a youtube channel just to upload that?

Slereah

No but I did upload it

Originally saw it on twitter and I don't think it's available on youtube :p

Ryder Rude

is it possible to obtain spin-2 and spin-1 particles by quantising 0+1 worldline field theory

or is this one of the reasons why we need 1+1

qwerty

@Slereah uploaded 6 mins ago lmao

ACuriousMind

@Slereah but now it is!

Slereah

10:33

I should probably give it a thumbnail

qwerty

I thought you made it in 6 minutes

now that would have been impressive

Slereah

Intro seems to be from this movie :

Louis XVI guillotiné

►

qwerty

viva la revolution

Ryder Rude

10:48

> In string theory, conformal symmetry on the worldsheet is a local Weyl symmetry. There is also a potential gravitational anomaly in two dimensions and this anomaly must therefore cancel if the theory is to be consistent.

but this symmetry is not of the original string theory, but of the wick rotated one. why must this anomaly cancel

i think conformal symmetry is just a calculation tool after wick rotation? Is it physically relevant too?

Slereah

It is also present in the Lorentz version of 2D manifolds

Ryder Rude

but that has a minus sign?

Slereah

So what

Ryder Rude

wow. So it is conformally invariant anyway

yes, the definition of conformal Invariance doesn't require Euclidean metric

Slereah

All 2D spacetimes are conformally flat locally, since the Weyl tensor vanishes

Ryder Rude

10:52

this is y string theory is so cool. they can convert Feynman diagrams to spheres because of this

im trying to list all the good features of string theory, things that are not ad-hoc

Susskind says that we can talk about the wavefunction of the string as a collection of N particles joined together by springs. and when string ends come together, a new sring forms and the strings can join

can this derive the sum over topologies

leave this aside for a moment. another good feature is that the quantisation of the 1+1 CFT gives u a bunch of particles. Standard model does not have this feature

i think the sum over topologies is kinda ad-hoc. but the particles thing is cool

and finally, there is the feature that compactification produces gauge theories, while gauge theories are ad-hoc in the standard model

but this is a feature of compactification in general, not specific to string theory

naturallyInconsistent

11:40

@RyderRude you have absolutely no position from which to say this.

@Arjun of course. Pressure, density, for example. When you send a beam of particles onto a target, you get to tune a lot of parameters for both the beam and the target. Apparently, for the properties of these corrections that you are interested in, what we are doing is almost always in the low-density limit, i.e. corrections are negligible.

@Slereah finally, something fast enough that there is no need to 2x it

nickbros123

@Slereah damn this is good. I wish you made this in C++

for the longest time I wanted to first make an image renderer in cpp and then possibly a ray tracer. but never found the time to do it

Slereah

The code is all there, you can implement it yourself

naturallyInconsistent

11:58

@nickbros123 those javascript bits are not very difficult to port to other languages

Slereah

You pretty much just have to figure out how to change single pixels

nickbros123

must just be a double for loop with rgb values i guess

maybe one has to use PPM file format tho

naturallyInconsistent

@Slereah actually, your code seems to still need other stuff outside of it? Like, even if we put in the big code chunk at section 4, we would get something that has an image array, but no way to put it on the screen as of yet.

@nickbros123 no; look at section 4, where it actually populates the image array. It is only a double loop of x and y, and for each pixel it fills in all three colours at once.

Arjun

@naturallyInconsistent I see thanks!

nickbros123

12:16

@naturallyInconsistent I suppose the output of the code comes out as binary pixel information, like I have seen some people use P3 or P6 for writing into a PPm file. after that i suppose they use a ppm image viewer or something? I am not sure of this

naturallyInconsistent

@nickbros123 with the way that Slereah wanted to use it, i.e. as a wave to be displayed directly onto the screen, I'm thinking that he is not thinking of saving it out to a file. If you want to, though, of course you can just make a gif of that.

nickbros123

yeah that makes sense, given that its real time and all that. I cant even begin to think how he implemented this

Silly Goose

12:39

is the publication of a purported proof of the geometric langlands conjecture going to have any substantial impact on physics?

Ryder Rude

was the Veneziano amplitude guess correct or was it just close

ACuriousMind

@SillyGoose why would it have any impact?

Ryder Rude

it seems it was just a guess

Silly Goose

i thought there was some relation between mirror symmetry and geometric langlands

Slereah

@naturallyInconsistent samuel-lereah.com/js/plasma.js

naturallyInconsistent

12:47

oh nice thanks

Slereah

Langland stuff is used in physics iirc

For dualities

naturallyInconsistent

I kinda see why javascript is the default now; you simply implemented it for the web

Silly Goose

The n-lab has documented some references where geometric langlands is invoked in this context (I think)

ACuriousMind

@SillyGoose it's S-duality due to Kapustin-Witten, but 99% of physicists will not know what that is, so sure, some string theorists will be happy about this

I would not classify that as "substantial impact on physics" :P

Slereah

Well you never know

Maybe it will be the root of a revolution in physics!

qwerty

12:58

how has nLab been a thing since 2008 and I've never heard about it until twice in the same day today

ACuriousMind

impressive - it comes up all the time in my searches for physics topics, and not because I'd be using their category lingo

Slereah

yeah they are easy to end up on if you look for physics stuff

Sep 16, 2013 at 13:03, by Urs Schreiber

Maybe the following information helps: Part of the motivation behind the nLab site is that there are many important developments in mathematical physics these days which are rooted in recent progress in homotopy theory but for which practicing physicists will have a hard time tracking down the relevant entry points or of which practicing physicist will have a hard time even becoming aware of (as maybe this dicussion here shows).

Apparently he used to be among us

qwerty

>.> they must have only just added it to the universe in the latest update and backdated it :P

ACuriousMind

well, maybe you're just not searching a lot for QFT and string theory topics :P

Ryder Rude

is particle statistics put in by hand in string theory or enforced by some theorem

qwerty

13:05

> Higher differential geometry is the incarnation of differential geometry in higher geometry.

Ryder Rude

i mean identical particle statistics

qwerty

they just went and thought, hey, all these maths topics arent advanced enough, we gotta elevate them (to be said in the tone of voice of a 2010s celebrity tv chef)

ACuriousMind

@Slereah he still occasionally answers questions on the site, you just need to ask about geometric string theory stuff like this question of mine

Ryder Rude

Homotopy type theory

In mathematical logic and computer science, homotopy type theory (HoTT) refers to various lines of development of intuitionistic type theory, based on the interpretation of types as objects to which the intuition of (abstract) homotopy theory applies. This includes, among other lines of work, the construction of homotopical and higher-categorical models for such type theories; the use of type theory as a logic (or internal language) for abstract homotopy theory and higher category theory; the development of mathematics within a type-theoretic foundation (including both previously existing mathematics...

nlab thinks this idea will bring some revolution

the revolution is doubted by other mathematicians rn

ACuriousMind

@qwerty they're aware this view isn't shared by everyone - it's discussed at nPOV

qwerty

13:11

haha yeah, I've not heard of a lot of this so I'm just poking fun at the name...

Sep 16, 2013 at 13:04, by Urs Schreiber

Notice that the nLab is widely cited on Matheoverflow (the mathematics SE discussion group with, if I may say this, a good bit higher average quality than the current Physics.SE site, notably Mathoverflow has lots of active bigshot mathematicians participating); it is referred to as a standard cite to turn to before asking questions (see here: http://web.archive.org/web/20130606040144/http://mathoverflow.net/howtoask#homew‌ork).

:( no bigshot physicists

Silly Goose

i think some partook (not sure if actively now) in PhysSE

e.g. peter shor

Ryder Rude

are Dbranes supposed to be part of our universe or the dual theory?

Ryder Rude

14:28

what r some big co incidences in string theory which increase its plausibility

Slereah

15:28

Some nerd proposed some edits to my question to replace $d$ with $\mathrm{d}$

ACuriousMind

as it should be

Slereah

Slanty d's all the way

naturallyInconsistent

miao miao simply defines \extd for exterior derivative

and then reuse it for CoOL

Silly Goose

how does one work on physics research without having to ever write a grant :P

Relativisticcucumber

@SillyGoose not by whining in hbar

Slereah

15:40

@SillyGoose be independently wealthy

That's what most physicists did until the 19th century

Most physicists used to be nobility

Relativisticcucumber

in e&m if we have a case where the half space $z<0$ is a conductor where the plane $z = 0$ is a zero potential surface, is this any different than having a finite width conducting body? by "is this any different" i mean if i solve the first case using method of images, can i say the solutions for potential and field are the same in the second case?

Slereah

Check out Count of Laplace

naturallyInconsistent

@Relativisticcucumber should be the same

Relativisticcucumber

@naturallyInconsistent yippee thats what i thought

naturallyInconsistent

@Slereah Louis de Broglie was a prince

@Relativisticcucumber careful, yall dont want to be complained by 4 or 5 JAQ bros

Relativisticcucumber

15:44

@naturallyInconsistent what does this mean

naturallyInconsistent

the acronym?

Relativisticcucumber

the whole thing

naturallyInconsistent

err... i dont know if I should be explaining the whole thing...

Relativisticcucumber

now i must know

naturallyInconsistent

lol

id rather talk about the nice time miao miao just had

Relativisticcucumber

15:56

0.0

Ryder Rude

17:44

do u believe in utilising time efficiently or not respecting time

and what do u do in practice

Bml

17:59

@Slereah I'm the nerd :-)

Slereah

You'll never straighten my d's

Bml

@Slereah OK, do I have any hope for the $\left(\right)$ in some of your equations? Your round brackets don't cover all the terms...

Slereah

That is fine

though I'm not sure which ones you mean

Bml

@Slereah I modified my "edit suggestion" on your question. Let me know :-)

Slereah

Oh you mean the lack of \left \right

Bml

18:06

@Slereah Yes.

Amit

21:43

@Slereah what is $\dot{t}$ in your question? What prevents it from being identically $1$?

Slereah

It is a function of tau

Amit

so it's $\gamma$?

Slereah

$t(\tau)$

Gamma?

Amit

well if you're not constrained to SR or GR you may not wanna do that identification

$ dt/d\tau = \gamma $

Slereah

No this is not that

Amit

21:47

it's not $dt/d\tau$?

Slereah

Tau is a parameter of the curve in spacetime, t is the time coordinate

Amit

is $\dot{t} = dt/d\tau$?

Slereah

It's non relativistic and also not proper time, it's an arbitrary parameter

Yes

Amit

ok

Relativisticcucumber

23:47

if i have a thin conducting plane of thickness w, with the right hand surface at z = 0, and the left hand surface at z = −w, I have concluded that the electric field to the left must be zero. however, i dont see how this is possible conceptually. why does the left side not "feel" the field from the charge on the right side?

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