The h Bar

DIRAC1930

00:30

How do we know that we can decompose a representation into irreducible representations by symmetrizing and anti-symmeterizing accordingly?

So it seems like we are just projecting out invariant subspaces however how do we know that there are no more invariant subspaces left

naturallyInconsistent

@Pizza tell us what you did and what are your reasonings

Obliv

04:18

is it true that a field in physics isn't the same meaning of field in math?

naturallyInconsistent

@Obliv obviously true.

Obliv

To what limit? Surely when we speak of vector fields we're talking about the same fields in math as in physics?

This part of these lecture slides bother me: "The concept of a field in physics has nothing to do with what is called a field in mathematics. A field in physics is simply a quantity that depends on space and time. That’s it. That’s all that a field means."

Surely they're related..

I guess I'm too newbie to know the extents of fields in mathematics though.

I thought that maybe he wrote that to keep people from getting in over their heads and to keep people focused on some simple ideas from the start

so I didn't take it 100% seriously but since you said obviously true @naturallyInconsistent I wanna know why

Because math is inherently not physics?

naturallyInconsistent

Field (mathematics)

In mathematics, a field is a set on which addition, subtraction, multiplication, and division are defined and behave as the corresponding operations on rational and real numbers. A field is thus a fundamental algebraic structure which is widely used in algebra, number theory, and many other areas of mathematics. The best known fields are the field of rational numbers, the field of real numbers and the field of complex numbers. Many other fields, such as fields of rational functions, algebraic function fields, algebraic number fields, and p-adic fields are commonly used and studied in mathematics...

@Obliv Under Peano axioms, we can modify the axioms so that 0=1. That is a perfectly valid mathematical system. It is just that it is useless. Maths is very necessary for physics, but it is not physics.

Silly Goose

05:20

@Obliv in physics language: field. in mathematics language: a section of a bundle.

in physics language: the real numbers. in mathematics language: a particular example of a field.

naturallyInconsistent

S C H W E G

Silly Goose

schweg !

^ "section of a bundle" Lol

when the first page of a book is like either of these perhaps it's a book that shall be read later :-)

ACuriousMind

06:28

@Obliv you're overthinking this, they just mean it's not the algebraic notion of field (like the real or complex numbers are); apparently they forgot that geometers use "field" in much the same way physicists do

123

07:05

Hello Everyone...

In inelastic collision between two objects can we determine individual objects contribution elasticity?

Let say if object 1 is perfectly elastic and object 2 is perfectly inelastic. Does collision experiment can tell which object deform.

Sir Crackpot

@ACuriousMind you're an impostor

The real ACM would never be awake so early

@lucabtz also @fqq (EDIT: Oh, fqq started that conversation)

By the way, there is an English edition of Fasano Marmi

I had to use it because my Boringhieri edition apparently had some blank pages

l4teLearner

07:28

a lot of formula references are scrumbled and there are some obvious typos here and there but it seems a good book to me

Sir Crackpot

It's a nice book and it has a lot of content

Chapter 10 is my favorite (canonical transformations) but that belongs to an ancient past

l4teLearner

for me it still is a remote future :)

Sir Crackpot

08:17

Time will heal any incomprehension, young lad

Adiabatically

Ryder Rude

09:19

Andy Clark - What is Panpsychism?

►

what do u think are the holes in this scientist's understanding of consciousness?

Sir Crackpot

09:39

@Relativisticcucumber HONKRACK

naturallyInconsistent

09:51

S Q U A C K

lucabtz

10:42

@SirCrackpot i didnt know before yesterday though

@SirCrackpot symplectomorphisms vs canonical transformation: which term is better?

ACuriousMind

10:55

@SirCrackpot that's because of the internet troubles I have to commute to the office! -.-

lucabtz

@ACuriousMind you work from home otherwise?

thought id add some ACM emphasis to it

Samyak Marathe

hi

I need some help regarding (PINN-Physics Informed Neural Network) to make an AI that solves a non linear differential equation. Someone with enough knowledge about this please DM.

ACuriousMind

@lucabtz usually I work ~3-4 days a week from home, yes

@SamyakMarathe you don't need AI to solve differential equations

there's well-established numerical methods for a large range of equations; an "AI" will not beat them

lucabtz

@ACuriousMind oh but its a trend now

even if its bad af people will try to do it with AI

anyhow i have a question about complex functions. say i have the function $(1-z)^a$ i have seen a paper say this is equal to $$e^{\pm i \pi a}(z-1)^a$$ depending on the choice of the branch

now i forgot the question though

Samyak Marathe

@ACuriousMind I know. But this is my class project. I need to use ML in physics. I need some help. If someone who can atleast solve non linear differential equations, could also help.

lucabtz

11:07

@SamyakMarathe i can solve them analitically but i will keep how to to myself /s

Samyak Marathe

@lucabtz can u help me. I have made the AI, I used the FDM to solve it. Unfortunately both the solutions are different. I need help

lucabtz

@SamyakMarathe no no i was just kidding, i know nothing about these PINNs

it is the first time i hear this acronym tbh

Samyak Marathe

u don't have to. Can u atleast solve it for me analitically

using whatever numerical method suitable

the equation is called allen cahn equation. I am at UG level and this project has this equation which is unknown to me

lucabtz

@SamyakMarathe it was a joke based on the fact that the analitical solution of those equation is at best hard at worst impossible

Samyak Marathe

ohh yess, because it's non linear. But can u do it using any numerical methods, say FDM

if u know how to solve non linear equation, even with python, that would help

Sir Crackpot

11:11

@lucabtz "symplectomorphism" is a flex

So that's my answer

Samyak Marathe

CAN ANYONE SOLVE NON LINEAR DIFFERENTIAL EQUATION USING PYTHON!!!???

I NEED HELP TT

Sir Crackpot

@ACuriousMind I haven't seen that emoji in a decade and yet it conveys your displeasure

Samyak Marathe

I wish it does, I am in serious trouble

Sir Crackpot

@SamyakMarathe Please, do not yell. Some of the users here have sensitive ears.

Samyak Marathe

I hate this AI I made, and Idk if it works or not

@SirCrackpot shatapppp

ACuriousMind

11:22

@lucabtz I know, I spend a lot of time dissuading people from trying to plug ML into unsuitable use cases :P

@SirCrackpot My old person trait is that I think ASCII emoticons are superior to all the new-fangled emojis

naturallyInconsistent

@ACuriousMind for a while miao miao didn't know if you meant HTML, XML, MathML, kind of ML, or OCaml kind of ML...

Sir Crackpot

11:39

@ACuriousMind We've entered a new era where the new emoji are considered cringe by most

Also, you can write old-fashioned emoticons on paper

naturallyInconsistent

@SirCrackpot technically, you can draw anything you want on paper...

123

What is load and effort?

I searched on Google but didn't find clear answer.

Sir Crackpot

@naturallyInconsistent not if you suck

naturallyInconsistent

11:54

No, if you suck, you can still draw stuff, it is just that they might be... interpretative

Sir Crackpot

12:22

What's the point of an emoji conveying wrong emotions, though?

Because I'm that bad

Relativisticcucumber

12:50

@SirCrackpot HONKBAH

ditto returns

naturallyInconsistent

13:36

H O N K B A H

lucabtz

14:00

@ACuriousMind yeah, people think neural networks are some sort of magic box and you can get anything from them

Slereah

14:11

also quantum computing

Such was also the case for a variety of things through history

ie. electricity, magnetism, radioactivity, nuclear power, etc

If you look at early 20th century pop science boy did people love electricity

Chemistry was also fairly magical

lucabtz

14:36

@Slereah yeah also

or the combination of the two: quantum machine learning

how do i get mathematica to expand Log[(t^(1/2 + [Lambda]0) e[0])/(1 + 2 [Lambda]0)]

Slereah

14:54

But then I'm not gonna complain about people funding QM

lucabtz

@Slereah yeah i mean quantum computing is interesting, also quantum machine learning

but its just weird that people try to use it in ways that make no sense sometimes

Slereah

You just have to remember that most people in charge of the important parts of society do not know anything

lucabtz

advertising the ODE/IM correspondence

Slereah

As you may remember in this Feynman anecdote :

> The Army told me everything, all the weapons they had, and all the gadgets, everything and they asked me all kinds of questions. Then they had cocktail parties, meeting generals and so on; informal things. A general would tell me that what they need is a tank that uses sand for fuel, because it would be great if you could just scoop up the sand and turn it into power, because they could keep on going.
The problem is refueling the damn things when they go too far, and so on and so on. They apparently thought that science could do anything. There probably is a way of solving this tank probl…

DIRAC1930

16:13

@Slereah I think the attitude towards science has completely changed now though

The inventions coming from science now are mainly just a slightly more refined iteration of something that already existed. The inventions from science especially in the first half of the last century were completely revolutionary

e.g. aeroplanes, radio

Just think how crazy radio is

Slereah

Things certainly have changed although I wouldn't say we don't innovate now

DIRAC1930

My point is that the innovations now are not entirely new things. They are just incremental improvements to an already existing invention

Slereah

You could argue that about most things

DIRAC1930

I would say the radio and powered flight is something completely new

even television

Slereah

I don't think it matters much as far as their impact goes

Radio is just wireless telegraph

DIRAC1930

16:21

Powered amplification

Slereah

Which is just the electric version of the optical telegraph

DIRAC1930

@Slereah Yes but imagine how crazy it would have been when it first came out. You would think that anything is possible with science

Slereah

Yeah but the same is true of modern tech, as we can see

AI is certainly feeling like that to a lot of people

DIRAC1930

Yes but we don't notice the effects because it's an incremental improvement of an already existing product

Slereah

Only time will tell

Ryder Rude

16:26

gps is completely revolutionary but it's also pretty old now

Slereah

Also you have to remember that you only think that from your perspective living in the future

Things didn't change that fast for most people

Ryder Rude

i cant think of a "completely new" invention in recent times

Slereah

Faster than in earlier eras certainly, but it took decades for radio to spread

Plenty of people didn't have fridges up until the 60's

Ryder Rude

VR is a potentially revolutionary thing from recent times

DIRAC1930

The biggest hyped thing I can think of is chatgpt

I swear it barely does anythign that couldn't be done before

I'm more impressed by google translate translating pictures

Ryder Rude

16:30

gpt certainly isnt a slight improvement from what we had earlier

VR and AI are the "science magic" stuff from recent times

Slereah

VR has been a gimmick for like 40 years

DIRAC1930

Tbf I am impressed by how it can write code

Ryder Rude

@Slereah yeah, but it will take over in a few decades

it has been shit so far

Slereah

Chatgpt can mostly adapt copy pasted code from the internet

Which makes it as competent as many people employed as programmers, but still

Ryder Rude

i cant think of big innovations in travel beyond airplanes. maybe in the far future, u cud hav portal travel. but thats all fiction for now

DIRAC1930

16:32

The biggest thing I take for granted without realising how amazing it is is YouTube

Slereah

The thing is that I don't think a technology being original is that important

Plenty of technologies are very old but were pretty useless for a long time

Incremental improvement is important

DIRAC1930

I agree but you can see why people in the first half of the last century thought that science could do anything like make fuel out of sand in your example

Slereah

Yeah but you're focused on specific examples

I have seen the magazines, people were also impressed by the incrementals

The development of medicine and chemistry was a huge deal

Ryder Rude

the extent to which all fields got revolutionised in the last century is hard to match up to

DIRAC1930

It's like, going to the moon in the 60s is a big deal but it's not that big of a stretch to see that it's just the technology of already existing missiles on steroids. It's not like radio where something you can't see is travelling through the air carrying what appears to be your voice. Nothing like that had ever existed

Ryder Rude

16:38

i agree. wireless is the most magical thing to come out of science

it's the sort of thing fantasy stories wrote about

flying is also up there

the new equivalent of wireless would have to be something like portals. the bar is too high

i would say VR is really close to magic if it gets perfected, but people wont notice it as magic as VR got perfected over decades

wireless is more a binary thing. u hav wires, and then u hav wireless. so people noticed it as magic

DIRAC1930

Maybe some new technology will come out far beyond the atomic scale

Shashaank

Hello!

Ryder Rude

vaccines are exceptional too

last century progress is hard to match up to

u had incremental progress in science and meds till 1800s and in 1900s it all blew up

Shashaank

The gas mixture of N1 moles of one gas and N2 of another has additional microstates compared to (N1+N2) moles of one gas, the additional microstates are given by (N1+N2)Na!/(NaN1)!(NaN2)! ?

How is the number of microstates computed, I am new to statistical mechanics?

Ryder Rude

if u go far back in history, societies that are 500 years apart may not have tons of changes. but society is changing extremely fast now

Silly Goose

17:01

@Relativisticcucumber ditto returns !

someone is giving a talk at my school today about the category theoretic formalism of classical mechanics :D. what a coincidence (though, geographically not really...) since slereah (I think) recently posted Baez's post about this

Slereah

It is the cool modern thing to do for theorists

Never trust people who would have you believe that physics is dead :p

Silly Goose

hehe i wish to know more about treating physical systems as categories

Ryder Rude

a theory as a category

Silly Goose

oh right yes a physical theory as a category

Ryder Rude

i wasnt correcting u. im just somewhat interested too

i think of a theory as axioms

oh but it can just be axioms for a category

Slereah

17:17

you can try here

math.ucr.edu/home/baez/topos_physics

Ryder Rude

do u think this has benefits

Slereah

> A youth who had begun to read geometry with Euclid, when he had learnt the first proposition, inquired, "What do I get by learning these things?" So Euclid called a slave and said "Give him threepence, since he must make a gain out of what he learns."

This is my answer

Obliv

17:41

Anyone wanna give me a tough but doable electrostatics problem

DIRAC1930

@Obliv Probably not electrostatics but can work out how to do the lifetime of positronium calculation

Obliv

Okay, where would I learn how to do that lol @Dirac1930

DIRAC1930

It's in L&L 4

I think you just need coloumb interaction

So it is kind of electrostatics

lol

It is under "The relativistic equation for bound states"

On 2nd thoughts I wouldnt bother lol

Obliv

well I'm taking an electrostatics exam in like an hr so after that I'll look into it for fun lol

DIRAC1930

GL with the exam

I used to love electrostatics and electrodynamics

Might look into it again some time

Obliv

17:48

QFT really got u lost huh :P

DIRAC1930

Yes lol

Obliv

what's your background? Maybe trying a diff resource besides L&L might help

I recall thinking about trying L&L years ago but then realizing it's way beyond my level

I was like, I'll just casually read bourbaki & LL

nickbros123

18:01

@Obliv given the case of a thick conductor with a cavity, within which a charge $\rho$ resides, suppose that the internal surface develops a surface charge density $\sigma_{\text{inside}}$, and the outer surface develops a surface charge $\sigma_{\text{outside}}$. prove that the fields due to $\sigma_{\text{inside}}$ and $\rho$ cancel out at all points outside the conductor, and also prove that the field due to $\sigma_{\text{outside}}$ cancels at all points within the conductor.

"hint; use the uniqueness, Luke"

Sir Cumference

18:30

You know, sometimes I'm just glad the world agrees on a common unit of time

If there's one thing that ought to be consistent, it's probably that

Slereah

18:46

Boy have you ever read about time standards

It's a huge mess

Sir Cumference

OK, sure. But imagine if some continents used the second as their unit and others used 0.6 seconds

it'd be a nightmare to adjust to

Slereah

Me I am French

I proudly adhere to metric time

10 hours a day, 100 minutes of 100 seconds per hour

Sir Cumference

well so do most people who work in physics lol

I have no intuition for the imperial system, so it's always confusing for me

even though I live in the US

Slereah

I mean metric time never caught on unfortunately

Sir Cumference

oh, thought you said "metric units"

Slereah

18:52

apparently they made a few clocks in metric time back then

Sir Crackpot

19:31

Ok people, I decided that I'll be ad interim ACM

l4teLearner

20:03

folks. what are your thougts about the "Kerr vs Penrose" thing? I am particularly curious if Penrose has ever commented last Kerr article...

Obliv

20:38

@Slereah is it feasible to work in physics without a phd? I'm okay being a pipette monkey equivalent for physics if there's room for growth?

btw i mean in research

@nickbros123 Need more info. Thick conductor is to mean a volume or some sort of shell? If it's the latter, $\sigma$ is the surface charge density for a given shell but if it's the former then $\sigma_{inside}$ might be the cavity's border and $\sigma_{outside}$ would be the conductor's surface

Sir Crackpot

@Obliv Dyson did not have a PhD!

Obliv

I appreciate you believing in me @SirCrackpot but I am not freeman dyson

Sir Cumference

well I guess it depends on what kind of physics

if you're doing mathematical physics then you really just need a pen and paper

if you're working on experiments then that's a different story

Obliv

@SirCumference what were your options pre-phd like did you consider going straight into the industry?

Sir Cumference

20:53

I just applied to PhD programs

granted i'm 50/50 at this point on whether I'm going to go beyond the master's

Obliv

may I ask where you went to school? my school has a professional option geared towards phds but it would have taken an extra year of schooling which would be out of pocket for me so I didn't do it

but I wanna work at a cool place like cern but I don't think I could do anything more than custodian work with a bachelors

Sir Cumference

I'd rather not say, but in my case the PhD is paid for

or rather, I get paid to do TAs and RAs

Obliv

my friend in bio works at a biopharm research place and he only has a bachelors (had to write a paper to complete his masters) i would like to do something equivalent for physics

he doesn't do the theoretical stuff obviously but still gets paid well (ya i know it's pharm, so funding is no issue I think)

@SirCumference No problem, I was only curious as to whether your school had multiple options for physics bachelors

and whether you did something that was specific to phd candidates

Sir Cumference

by school, do you mean undergrad university?

Obliv

yeah

Sir Cumference

20:57

not as far as I'm aware

they did have stuff like 5 year Master's programs in the math department

Obliv

What do you think gave you the best shot at getting into a Phd program?

Sir Cumference

it mostly comes down to research and recommendation letters

I didn't have to take the physics GRE since it was waived during the pandemic, so I'm not sure how much it matters nowadays

Obliv

lol that's interesting

Sir Cumference

most schools ask for 3 recommendation letters, so I'd say you should ideally have at least two be from professors you did research with

Obliv

Idk, from what I hear about phds, they underpay and overwork so I wonder if it's even worth it. I guess it's necessary for some areas though

Sir Cumference

21:03

some people do love it

IIRC @JohnRennie said it was some of the best years of his life

personally I'm not really a fan, hence why I'm thinking of leaving

Obliv

what do you wanna do instead?

Sir Cumference

being underpaid and overworked are the main factors for me, plus not really knowing whether I enjoy research

programming is the only other thing I'm pretty good at, so probably something utilizing that

still thinking over my options

Obliv

what does the work include for you? I know you're in astronomy but I have no idea what you're doing :P

Sir Cumference

most of my research has been analysis of data from surveys of galaxies

which largely boils down to creating a billion plots and explaining what I see

Obliv

would you wanna do something tangentially related to astro research like something more applied maybe (I guess working at a space agency)

Sir Cumference

21:08

I'm not 100% sure yet

Obliv

I get the sense you really like astronomy though so I imagine you'd wanna stay in the field but move away from academia

Sir Cumference

at this point I still haven't figured out whether research isn't my thing or my projects have just been kinda boring so far

Obliv

I see

Sir Cumference

learning physics is something I could always do as a hobby in any case

DIRAC1930

@SirCumference What areas have your projects been on and what are your main interests?

Sir Cumference

21:13

@DIRAC1930 It's mostly been data analysis for extragalactic astronomy

ideally I'd probably like to do some cool mathematical physics

but that's a pain in the ass to work in

it's just hard to get funding for those kinds of things

Obliv

you don't really need funding for that.. you just need to not have to worry about living expenses :P

Sir Cumference

well to be more specific, it's a very competitive field with not a lot of job security or pay

DIRAC1930

Are you interested in condensed matter theory?

Sir Cumference

and given how I've always cared more about learning than research, I could probably just get a different job and study physics as a hobby

@DIRAC1930 nope, cosmology mostly

DIRAC1930

So you are more interested in GR than QM?

Sir Cumference

21:16

I'd say so

Obliv

i feel like that's an especially competitive area for theoretical physics research but that's just my gut feeling

Sir Cumference

the job conditions for being a physicist are just not great, which sucks

especially when you focus more on theory

Obliv

@SirCumference I hear people say that but it blows my mind since physicists lead the way in innovation i think

in some cases at least

Sir Cumference

well the more you can convince the public that the research will be useful to their everyday life, the better off you are

DIRAC1930

At the end of the day, I think you should apply for the projects you are interested in and if you get offered a place, you can make a descision then

Sir Cumference

21:19

it's hard to do that with GR, string theory, etc

@DIRAC1930 tbh I'm not really sure if I like research to begin with

it's a much slower process than learning new things

user 85795

How so?

Obliv

'new' to you but perhaps not new. good research fundamentally provides 'new' information no?

Sir Cumference

@user85795 papers can take years to get published

you need to dot all your i's and be very careful not to miss anything or make mistakes

user 85795

right

DIRAC1930

Ok, I knew I liked doing research so it wasn't really a choice for me and as soon as I got to do my first research project, I loved it

Sir Cumference

21:21

it's not really the same as just opening a textbook and learning something new each day

@Obliv in the grand scheme the paper should generally be something new, but getting that published takes a lot of small steps

it's hard to remind myself this is a cool, exciting new thing when the procedure is writing mountains of code each day

it just gets tedious tbh

Obliv

yeah.. it's super gradual

Sir Cumference

pretty much

and when the job conditions kinda suck, it makes me wonder if I actually want to do that as a career

DIRAC1930

But now it's different and I prefer going through lectures

Obliv

do you teach @Dirac1930

DIRAC1930

Nope

And thank god for that lol

Sir Cumference

21:26

@DIRAC1930 amen

DIRAC1930

Wouldn't want to ruin peoples lives by showing them QFT lol

Obliv

not for everybody i guess lol

Sir Cumference

i mean I like teaching but it would break my back to do that on top of all my other work (classes, research, etc)

Obliv

if u could estimate your progres in QFT as a percentage, how far do you think you are @Dirac

Sir Cumference

it's already brutal grading 50 labs per week on top of everything else i gotta do

DIRAC1930

21:27

And then doubly ruining their lives by wrongly showing them QFT lol

Obliv

dang that's a lot of grading..

DIRAC1930

@Obliv Well I don't really understand it very well at all

But it's a lot better than how well I used to understand it

Obliv

i'm afraid to take a peek at L&L

DIRAC1930

L&L are honestly perfect

Obliv

does it just go through mechanics to QM non-rel then add rel and then QFT->QED->more QFT

DIRAC1930

21:33

Mechanics, Classical Field Theory, Non-Rel QM, QED, Stat Mech, Some other ones, and then L&L 9 is QFT in cond matter

There is an electrodynamics book perfect for you

lol

I think it is L&L 8

"Electrodynamics of Continuous Media"

There is a joint 1st and 2nd volume called A Shorter Course in Theoretical Physics which I prefer since it has less information

However L&L 3 and L&L 4 are my main texts that I like (alongside L&L 9 sometimes)

Sir Crackpot

21:52

@Obliv not yet

@DIRAC1930 volume 9 is the second part of volume 5

DIRAC1930

23:08

@SirCrackpot L&L 9 is essentially the ideas of L&L 4 transfered to condensed matter theory

The full title is "Statistical Physics, Part 2: Theory of the Condensed State. Vol. 9"

lucabtz

23:20

@DIRAC1930 lol the "probably" makes it even more fun

"hey somebody can recomend me a good movie?" "probably not a movie but the little prince is a great book"

DIRAC1930

It has the coulomb potential in it so I dunno if it's classed as electrostatics lol

quantum electrostatics

And then since the bound state is an eigenstate of $\hat{H}$, its a stationary state so it's 'quantum electro-stationary-states statics' which is almost electrostatiscs

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