The h Bar

i think the distinction with cmt and something like string theory is not so much 'theoretical vs. not theoretical' as 'fundamental vs. not fundamental'

it's a broad gloss, but string theory is aimed at understanding the fundamental interactions of the universe

@Icemybread Why do you want to draw a sharp border instead of having it just be a gradient without clear-cut distinctions?

cmt isn't

that doesn't make condensed matter any less theoretical, though

I meant fundamental physics

fundamental physics is less useful than pure math, patriotically speaking

7:28 PM

@BalarkaSen That's still what it says as far as physicists are concerned ;)

@ACuriousMind you have to make the distinction somewhere, the cut doesn't have to be fully linear.

i'd agree on that, though I think it's a bit subtle: one doesn't get the atom bomb without people working on theoretical physics

@Icemybread No, I refuse to draw the border. What now?

Slereah

Electricity used to be fundamental physics

@ACuriousMind I don't know. I guess I'm forced to agree with you :p

7:29 PM

@ACuriousMind lol

@ACuriousMind who is your current dp supposed to be?

however, the places where fundamental physics is working now are really not liable to lead to breakthrough technologies as far as I can tell

@Semiclassical I'm not saying my analysis is foolproof, but it's a good rule of thumb

6 hours ago, by ACuriousMind

@PrathyushPoduval Kaelyn the Dove, Priestess of Ilmater, from NWN2: Mask of the Betrayer. A video RPG character like all my pictures.

oh, sure

7:30 PM

Fundamental math in the last 70 years has led to more applications than fundamental physics

Er, not fundamental math

Fundamental math is garbage like logic

I mean pure math

is category theory fundamental math?

Maybe, but I bet crazy number theorists use cats and that stuff is good for GDP

that's not to say that breakthroughs can't come through the pursuit of fundamental physics. but I would expect them to be more of the form of "What technology do we need to invent to study this part of physics" and less "What technology becomes possible by learning about this physics"

@Semiclassical sorry didn't see your message. I agree with what you said, that's a better way of putting it.

it is a little funny, though, that basic research means a different thing than fundamental research.

i don't think i'd ever count CMT as fundamental research, but I do think it falls pretty well under the rubric of basic research

...of course, I say that, and then WP's definition of basic research undermines that entirely: en.wikipedia.org/wiki/Basic_research

7:34 PM

we need a string bomb already

something that can just evaporate places

lol

yeah, places like ~~"the entire earth"~~ the entire solar system

spaghetti bomb

@Semiclassical what about the ads/cmt stuff or emergent stuff

A certain place north of a certain southern place

@0ßelö7 wow

7:35 PM

ehhh. ads/cmt has gotten a lot of hype, but I think the number of people who actually work on it is fairly small

@0ßelö7 such geography

much geopolitical

there is someone doing a talk about it next week

phillip phillips from illinois

i'm gonna sit in just for exposure

sure

@BalarkaSen It's either Canada or North Korea. Not sure I want to get more specific.

Slereah

@Icemybread What is ads/cmt

Conformal meal theory?

7:36 PM

lol

@Slereah dunno but i'm gonna find out

ads/ condensed matter theory

lol

AdS/CFT is the proposed correspondence between anti de Sitter space theories and conformal field theories

He said CMT above

yes. i know. i was getting there.

@MetaEd what's up

7:38 PM

my current understanding of ads/cmt is that metals are actually black holes so stay away from large metal objects

AdS/CMT refers to attempts to apply that correspondence to condensed matter theory systems

be safe than sorry

@0ßelö7 speak of bombs and UNO comes in

@BalarkaSen Did I get flagged?

for a critical take on AdS/CMT, see Phil Anderson's letter to Physics Today ~~here~~

7:39 PM

404

MetaEd

@0ßelö7 I came to find that out myself.

oh ya isn't that guy really critical of ads/cmt

i read something somewhere sometime

well, this is annoying

WP's citation entry for Phil Anderson's letter: "Anderson, Philip. "Strange connections to strange metals". Physics Today. Retrieved 14 August 2013.[permanent dead link]"

-_-

@Semiclassical was that a roast of ads/cmt?

okay, here's a not dead link: physicstoday.scitation.org/doi/10.1063/PT.3.1929

7:43 PM

strange metals? Like what

like sodium

have you ever seen what he does when he contacts water?

what a weirdo

...

In condensed matter physics, one of the big paradigms is 'Fermi liquid theory.' if you want to describe a normal metal at low temperatures, you usually can use that

but you do see breakdowns of that, and such non-Fermi liquid behavior has led to people referring to such systems as 'strange metals'

@ACuriousMind don't use pretty girls as your dp... it's WEIRD

cuprate superconductors are a big example

@Semiclassical oh that's the subject of the talk next week

something something hidden dimensions in cuprates and EM

7:48 PM

yeah, that's what i'd expect from an AdS/CMT talk

Anonymous

What's the proper way to frame a follow up email to a professor in order to address a typo in my previous email? (My phone's autocorrect changed "theoretical condensed matter" to "theory of condensed matter" and I didn't notice :P) Should I just re-send that email after correcting the typo?

@Blue that is basically the same

like your prof will know what you meant based on the context

Anonymous

@Icemybread Actually the department's name is "Theoretical Condensed Matter"

@Blue doesn't matter lol

Anonymous

I should just rest and hope for the best. Lol

Anonymous

7:51 PM

I hate you Autocorrect

Anonymous

I should turn it off immediately

if I said "I want to work in the department of Theory of Condensed Matter" versus "I want to work in the department of Theoretical Condensed Matter"

it would not decrease my chances of getting in there.

but I think e-mailing them again to fix such a trivial error would decrease your chances.

Anonymous

@Icemybread Ya, that's what I thought. :P

Anonymous

Lemme leave it as it is

@Blue if you want to do CMT you're in luck because this year like 5 new awesome CMT books are being released/have been released.

Anonymous

7:54 PM

Ya, lately I've become interested in applications of QM in CMT. It's a part of my course though.

like shankar's qft and cm, nastase's cmt and string theory, and a bunch of other books on qft approach to cmt.

applications of QM?

I thought cmt was basically based on qm for the most part

did you mean QFT?

Anonymous

@Icemybread Yes, that too. But I haven't done much QFT (if at all)

Anonymous

I've just started with basic solid-state this semester

Anonymous

(This is my freshman year)

if you know qm and em I would recommend reading "qft for the gifted amateur" it's a really good and easy book even high school students can read while also covering a lot of important qft stuff found in advanced books.

people talked about it in the chat before

7:57 PM

@Blue I agree with that too

Aug 11 '15 at 16:37, by FenderLesPaul

@JohnRennie I don't think I know of an easier book that still does the subject justice

Anonymous

@Icemybread Oh, thanks. I'll surely have a look. I'm trying to complete QM properly from MIT OCW currently.

oh ya they updated their qm 1 recently right?

Anonymous

@Icemybread I'm using the 2013 version by Allan Adams. There's a more recent one but I didn't have a look. Allan Adams teaches really well with lots of enthusiasm. I love that.

i'd recommend watching zwiebach's too

8:02 PM

@BalarkaSen This guy is known for bad writing. Theorem 1.1 doesn't make any sense.

Anonymous

I'll check for sure

i'd watch them too if i didn't hate lectures but it's basically worse for me to learn from lectures than books

@0ßelö7 I have heard that name somewhere...

@BalarkaSen from this book bookstore.ams.org/gsm-111

I like to keep all of my Riemannian geometry books on my main shelf but that book is on my secondary shelf. I had a bad experience working through it over the summer.

In many cases I found it easier to check the references and read the original papers.

@BalarkaSen The problem is that he says dimension blah blah, or locally conformally flat. But he doesn't say in which metric. But then the conclusion says "for every metric"

8:42 PM

How to add link in messages? (the title appears in blue and when u click it u are redirected to the linked site)

Anonymous

Like [<message>]()<----and link within ()

$\mathrm{[what\ you\ want\ it\ to\ be\ named](link)}$

[<message>]()

don't put it in $$

Anonymous

@Abcd Don't put $$

8:45 PM

When Bohr model is completely wrong why do we use it to explain K capture?

@Blue ^

Anonymous

@Abcd That wiki page doesn't really go into the intricacies of K-capture

Anonymous

They are mostly stating what the K-capture phenomenon is without going into the whys

Pretty sure Bohr is close enough for basic explanations of most things anyway... As long as you don't go too high up shells 'cause 4s comes before 3d (iirc?) etc...

Anonymous

Also, I don't see where they mentioned they are using Bohr model

I hate Bohr's model.

Anonymous

8:51 PM

Although Bohr's model is good enough for basic chemistry explanations

@Blue See the diagram.

What's wrong with Bohr's?

Bohr's model has been disproven and it's completely wrong due to many reasons.

Anonymous

@Abcd As a representation it's good enough. It's impossible to show all orbitals and stuff in a small diagram like that. It's better to visualize a bit rather than not visualizing at all (according to me).

Q: What is wrong with the Bohr model?

1

What is wrong about the Bohr model? Many books say it is wrong but doesn't say why and I don't know why.

8:53 PM

Useful for basic explanations, however... Though still annoying when it's taught alongside concepts to do with orbitals.

Some of my classmates still visualise an atom as Bohr's model while studying chemsistry. :"(

It should be banned :p

We should be taught the correct model from junior classes.

I found it helpful whilst thinking about basic shell jumping concepts (Not going into maths or anything detailed ofc.)

Anonymous

There's nothing wrong with using Bohr's model to explain basic concepts. Similar to how we approximate cows as spheres in physics. ;)

@CooperCape shell jumping?

I missed out the word electron and was being distracted

and said a stupid lol

@Blue Nothing worse than A-level (American high-school?) mechanics where it says 'Susie is on a plank. Model her as a point particle'

never understood why a point particle couldn't be on a plank.

Anonymous

8:56 PM

@CooperCape Actually if real-life engineers didn't use approximations then their lives would be hell

isss true

Still its assumption city

Anonymous

The level of rigor you need depends on the field you are in

Bohr's model isn't even close to an approximation. It's horrible.

(I dislike mechanics maths and stuff etc. severely soooo)

oh, 1 more question: Is nucleus with it's protons and neutrons a wave too? just like an electron?

Anonymous

8:58 PM

@Abcd If you are that rigorous you should become a mathematician, really :)

neutron* yes

Anonymous

@Abcd Yes. Everything is

Interesting.

hi

Is there any connection between electrical conduction and flint stones having sparks when rammed?

Why doesn't nucleus collide with electron then (while waving)?

Anonymous

9:00 PM

@Abcd You'll learn in Quantum Mechanics later on

Okay ....

gfy! wish i was studying physics

do you think it's ok if I ask this question on the site? or will they block me from asking anymore?

"
Is there any connection between electrical conduction and flint stones having sparks when rammed? "

Anonymous

In short: yes

Anonymous

But you should ask on the main site for details

Anonymous

I am out of time

Anonymous

9:07 PM

But do show your efforts while asking the question on the main site

@parvin It has the potential to be a good question, but you should show what research you've done - a cursory search on the internet for something like "why do stones produce sparks" should explain at least partially what you want to know.

So first look what you can find elsewhere with a simple search, then ask something more specific about that here

I see. you are right. thank you

DanielSank

@parvin That's a pretty vague question.

When you ask questions anywhere, think about the person who could answer your question. Make sure you respect that person's time in several ways:

1. Ask clearly so that the other person doesn't have to spend effort trying to figure out what your words mean.
2. Ask something as specific as possible. Give the other person the least amount of work as possible. If you say "how does physics work", then other person has to spend time figuring out what you already know.
3. Do your own research ahead of time so that you're prepared to understand the answer.

9:28 PM

@parvin If you've already asked so many bad questions that you're at risk of getting blocked because of one more... I would suggest not taking a chance on a question you're not sure about. I'd say it's better to ask some definite good questions first.

Cows

Decided to really understand special relativity this weekend

I think it is time to soak it in. It turns out to be very important

@BalarkaSen help

wut

@BalarkaSen You know how you can characterize the op norm of an operator $T:X\to Y$ by either $\sup ||Tx||_Y$ over the unit sphere of $X$ or as the inf of constants $c$ such that $||Tx||_Y\le c||x||_X$?

@DavidZ i see ! thanks

9:43 PM

@0ßelö7 Yep

@BalarkaSen Well instead I have $1\le (T+1/j)||\nabla u||_2+A_2(1/j)||u||_2$, and $T$ is the "smallest constant" for which this is true. I'm having trouble formulating this in a useful way.

DanielSank

@Cows When I was a student, I did that once a year in December.

I still don't understand special relativity.

@ACuriousMind I don't understand the part about the energy gap; why is an $E_g$ necessary and what is its significance in the definition? If this is an adiabatic process, the system necessarily remains in the initial state.

DanielSank

@lılostafa That's like saying "Why do you need metal to build a car? If it's car then it's a car."

You need an energy gap in order for an adiabatic process to be possible at all.

Does it mean a gap has to exist in order to define and distinguish the ground state?

9:54 PM

@BalarkaSen I think I should solve that so I have $stuff\le T$ and take a sup on the lhs

10:12 PM

does any body know about lightning and reasons why it happens?

i've done a few research
some say it's the electrical discharge (?) between the air and the clouds

some say it's because when it gets too cold the water vapors change to ice and then the ice particles clash and it creates static electricity in them so two pols would be created in the could and that would cause a lightning

which of them are true?

find it out. both can happen.

now another question

WHY IS THE EARTH NEUTRAL?

10:29 PM

@parvin Why wouldn't it be?

so much anger

It seems to be a pretty charged issue, yeah...

@ACuriousMind Ugh.

Yes, that pun was meant to be painful :)

@ACuriousMind Why are you Elsa?

I liked that movie as much as the next guy, but cmon

10:38 PM

10 hours ago, by ACuriousMind

@PrathyushPoduval Kaelyn the Dove, Priestess of Ilmater, from NWN2: Mask of the Betrayer. A video RPG character like all my pictures.

@ACuriousMind But it's your first female avatar.

Did you self-identify as female when choosing your new picture?

@lılostafa Not at all, I've been e.g. Ciri and Triss from the Witcher or Kreia from KOTOR before

Triss has unnaturally large boobs btw

Anonymous

it's always bothered me

Anonymous

10:42 PM

Here, to find $<E_i>$ why do they use $\sum E_i P(E)$ and not $\sum E_i P(E_i)$ ?

@ACuriousMind ah..so you're not sure about that self-identification thing

Anonymous

Why are they finding expectation value of $E_i$ using probability of the system having total energy $E$ ? @ACuriousMind Any ideas?

LOL

@lılostafa Given that I'm a goth vampire AI with a side gig as Alicia Keys, not really, yeah

AI programming failed and ACM is completely genderfluid

I love it

10:44 PM

i dont like the new avatar

it's elsa from frozen

@ACuriousMind do you like spiderman?

it sucks

frozen of course sucks

@0ßelö7 Not really

have you even watched it?

Yeah, I have

10:45 PM

I was talking to the kid

no but i can tell it sucks because it's a walt disney animation

aha

@ACuriousMind It was a reference to a meme. I guess you didn't catch that?

walt disney animations are the normiest

@0ßelö7 It flew right over my head indeed

@ACuriousMind r/outoftheloop

10:47 PM

maybe you should check it every now and then

this guy is my favorite animation character of all time

from my all time favorite animation

of all time

@BalarkaSen It's nothing new...people have always disliked them:

Mar 13 at 22:42, by AccidentalFourierTransform

I dont like your new avatar

Apr 4 at 16:35, by AccidentalFourierTransform

I don't like your new avatar

May 23 at 14:38, by AccidentalFourierTransform

I dont like you new avatar picture.

Jul 13 at 10:41, by AccidentalFourierTransform

I dont like your new avatar

looooooooool

Sep 5 at 13:44, by AccidentalFourierTransform

I dont like your new avatar

(I'll be kicked if I continue)

10:54 PM

multi-lel kekking

Q: What is $\bar{E_i}$ here ? (Equipartition of energy)

5d underwater lol

Anonymous

0

This is an extract from my textbook (Physics for Degree Students B.Sc Second Year By C L Arora) Here, to find $\bar{E_i}$ why do they use $\sum E_i P(E)$ and not $\sum E_i P(E_i)$ ? Why are they finding expectation value of $E_i$ using probability of the system having total energy $E$ ? I'm n...

thermodynamics statistical-mechanics

Anonymous

I'm not sure if this should be on Math SE or Physics SE

why would it be math?

Anonymous

@0ßelö7 Probability and stuff

Anonymous

11:01 PM

Anyhow, lemme go with physics. If it doesn't get response I'll delete and ask on Math SE

@Blue it should be neither until you type out the text rather than putting it in an image!

But given that the question arises in a physical context, it should be on topic here.

You can definitely include that link, but I don't think it gets you out of having to type out a quote. You need to make sure the question makes sense to people who aren't able to click the link.

wow you did post a picture

way to go

heather

you deleted it...

you're a random JEE kid now

Bear in mind I'm not saying you have to transcribe the entire picture's worth of text - you can pick and choose however much or little is necessary for your question.

Anonymous

11:06 PM

@DavidZ Alright. Got it. I included the picture to add to the context. But okay, I'll type out only the necessary portion

Q: What is $\bar{E_i}$ here ? (Equipartition of energy)

Thanks.

It's definitely good to provide context, so you had the right idea in a way, but any textual content (including math) should be typed, not posted as a picture.

Anonymous

11:23 PM

0

This is an extract from my textbook Physics for Degree Students B.Sc Second Year By C L Arora. [Image Source] "For every independent quadratic term appearing in the energy expression of the system, the average energy corresponding to temperature $T$ of the system is $\frac{1}{2}kT$" ...

thermodynamics statistical-mechanics

Anonymous

Okay, typed it out!

better

Anonymous

Duh, I'm waiting for intelligent bots to come up who can convert image to text.

Anonymous

It's 2017 and still we can't do that. What a shame. :P

11:41 PM

@Blue Don't need intelligence for that, just OCR.

Anonymous

@ACuriousMind That doesn't work well for math formulae/equations

Anonymous

There are many softwares like that on the net

Anonymous

For just text it is fine