The h Bar

Slereah

14:04

Let's use unicode characters for physics

I want a snowman function

☃(x)

Jimself

too hard to draw on the blackboard for us less artistic physicists

3 circles? Maybe you can draw that, Michaelangelo

Slereah

what about this symbol : upload.wikimedia.org/wikipedia/commons/4/41/Bi%C3%A1ng.svg

0celo7

@ACuriousMind on page 69, why must Wt satisfy the properties it does?

Wait I'm retarded

It's a Lorentz transformation smh

Jimself

@Slereah yes, that would be fine

0celo7

I can't even draw a pretty psi

Slereah

14:09

the worst symbol I had to learn was lower case xi

Took me a while to draw it correctly

0celo7

I can do that

ACuriousMind

xi is not that difficult, if you're taught it correctly and not "draw some squiggly line, no one can tell anyway"

0celo7

Can anyone here draw psi well

If yes please post a picture and then a tutorial

gonenc

@0celo7 wait for a sec

Slereah

My psi's okay

some symbols I disagree with

Like

nu

nu is too close to v, do not use it!

gonenc

14:12

@Slereah I just make nu more wiggly than v :D

ACuriousMind

@0celo7: What about this^?

0celo7

@ACuriousMind no

Kyle Kanos

I can draw psi pretty well, see: $\psi$

0celo7

It's OK but not great

Kyle Kanos

Also, holy crap:

21

Q: Grant fraud, should I bust my PhD advisor?

For obvious reasons I will try to maintain some anonymity here. So I defended my thesis. Which was funded through a government grant. In order to obtain this type of grant, a professor needs to cooperate with several other research organizations and privately-owned industries. Then it is requir...

ACuriousMind

14:13

@all: The nu properly has a small hook at it's left side - elongating that hook is what evolved the nu into the Latin n, I think

gonenc

Slereah

4

gonenc

@0celo7 ^looks a bit too big but it's the best I can do with this laptop cam :)

Kyle Kanos

My psi's tend to look like a U with a vertical line through the middle; Psi tends to look the same but with horizontal bars on the vertical line.

I suppose I don't really care for calligraphy

Slereah

One of my goal was to one day use a heart as a math symbol

Then a few years ago I found a math paper with that!

gonenc

14:17

@Slereah took notice of it :D

@Slereah shoot too late I guess...

ACuriousMind

@Slereah Lol, not even your gimmicky paper ideas are original :P

Slereah

Shit is hard man

ACuriousMind

@gonenc Too short on the right, imo

0celo7

^^

Slereah

I wanted to see if exact solutions of the quadratic KG violated energy conditions

But then I found a paper saying that no potential of KG can violate them!

ACuriousMind

14:19

@0celo7 What's missing/wrong?

Slereah

shakes fist

gonenc

@ACuriousMind I usually like it that way, it fits better with my slant handwriting :)

0celo7

@ACuriousMind it looks exactly like mine

And I don't like mine

Slereah

My current idea is to maybe check out what the energy conditions look like for thermal states of interacting fields

Because interacting fields tend to have the most horrendous violations

ACuriousMind

@0celo7 Haha...I maintain it is the correct shape. though ;)

gonenc

14:21

@0celo7 I think you guys over do it. yours really look like the latex one but latex one is drawn with a proper calligraphy pen (at least some point in time) and it doesn't have the same effect with a usual pen :D

FenderLesPaul

Hello darkness my old friend

ACuriousMind

14:33

@gonenc: How did the thing with your visum go, by the way?

gonenc

@ACuriousMind I was at the embassy today. I'll get my visa in ca. a week

the guys in heidelberg refused (not literally but by not returning my emails) to send it by email

but luckily and astonishingly the post came in 14 days :D

after the day I had my zulassung in my hands they send only the first page of it by email #insert angry face#

but I'm good to go :)

ACuriousMind

Ah, well, that's the main thing :)

gonenc

@ACuriousMind I don't get it why heidelberg people are so old-fashioned. münchen doesn't do this crap they don't even bother to send the original and do it by email only

whatever at least I had it in time :D

It'd be awkward to go to the embassy without the acceptance letter

ACuriousMind

@gonenc Well, the university's motto is "Future. Since 1386.". I guess we haven't changed our conception of "modern communication" since then, either :D

gonenc

@ACuriousMind you hit the jackpot :D

I gotta find a place to stay now... studentenwerk hasn't said anything yet :/

and the fact that only 15% has a wohnheim creeps me out to be fair

ACuriousMind

14:41

@gonenc Well, not everyone wants to live in a wohnheim. Many people seek flats with friends they found here after a few semesters

gonenc

@ACuriousMind true but I gotta meet someone first and I think wohnheim is the best place to do that

at least in my dormitory in highschool I made pretty good friends

ACuriousMind

But yeah, the places are limited

@gonenc True that

gonenc

@ACuriousMind and I don't know about this WG thing too much either

I mean what if you don't like the people that you are WG-ing

^that was such a bad denglisch :D

ACuriousMind

@gonenc Then...you're fucked :D

That's why most WGs don't rent out a room before meeting you at least once

gonenc

@ACuriousMind but what about all the WG websites?

and if I have to go to germany to meet the people then I might as well seek my own place, I guess

Jimself

14:45

a friend of mine published a paper recently about a modified gravity theory that reproduces observations and accelerated expansion without the need for a cosmological constant

arxiv.org/pdf/1503.05560v3.pdf

gonenc

but WG-friendship would also be like a wohnheim-friendship imo

Slereah

bigravity

Jimself

yes, that's where gravity is calculated from 2 separate rank-2 tensors rather than just the metric

gonenc

@ACuriousMind fuck I thought "Future since 1386" was a joke... I didn't think it was real :D

Jimself

they use $g$ and $\bar f$

ACuriousMind

14:47

@gonenc They usually invite you to meet them first, I think

@gonenc lol

gonenc

@ACuriousMind the motto is like nonsense

Slereah

what does f correspond to?

gonenc

we are looking forward from backwards kinda thing :D

Jimself

@Slereah the modification to gravity

ACuriousMind

@gonenc It's meant to mean "We've been progressive since always", I think

Slereah

14:49

But like, what is the product of two vectors

Jimself

I think it's impressive work because they have taken dark energy out of the picture and still reproduced the necessary observations

gonenc

@ACuriousMind is it Ruprecht-Karls-Universität Heidelberg or just Uni Heidelberg??

Jimself

@Slereah what?

ACuriousMind

@gonenc Most people will say the latter, but formally it's the former

Slereah

Well the metric gives an inner product for tensors

But what does the second metric do

is it just a second definition of an inner product?

Jimself

14:51

they interpreted it as being the metric for a dark gravitational sector spacetime

whatever that means

gonenc

@ACuriousMind who is that guy if it is a guy's name (Ruprecht Karl)?

ACuriousMind

@gonenc He was the lord of this region back when the university was founded, I think

@Jimself "Come to the dark side. We have another metric." is one of the lamer slogans I've heard.

gonenc

@ACuriousMind huhu a rich guys university you say :D

Jimself

@ACuriousMind Man, the dark side has everything

@Slereah the metric does more than give an inner product for tensors. It describes the geometric foliation of spacetime and how it normally couples to mass/gravity. I think $f$ allows them to add mass to the graviton too

come to the dark side, we have massive gravitons

Slereah

also do they have new predictions from it?

Jimself

14:56

haven't gotten that far

but if not, it still removes the fine-tuning aspect of a cosmological constant

Kyle Kanos

Volcano Eruption in Papua New Guinea

►

Possibly old & seen before, but pretty awesome

gonenc

@KyleKanos holy shit I've never seen it before

0celo7

@ACuriousMind I do this thing where I try to translate rap I'm listening to into German and make it fit into the original structure...it never works

It sounds so silly in German

FenderLesPaul

15:12

rap just sounds silly period

ACuriousMind

@0celo7 Almost all translated lyrics regardless of genre sound silly in German, imo

FenderLesPaul

@0celo7 I kid!

0celo7

@FenderLesPaul I love gangster rap because it's so hilariously stupid

FenderLesPaul

haha

0celo7

When an album has censored words in every other title, you know it's gonna be awesome

Having something like Money, Clothes, Hoes in the background while doing homework is the best.

FenderLesPaul

15:19

I actually like listening to ambient music when doing work

like LoTR soundtrack

or Oblivion soundtrack

or Nick Drake

0celo7

Blunt Blowin is great index manipulation music.

FenderLesPaul

that sounds interesting...

gonenc

@FenderLesPaul good point

FenderLesPaul

:)

Why do smiley emoticons always look creepy

0celo7

@ACuriousMind :)

Dunno...

gonenc

15:22

@FenderLesPaul they didn't until now :D

ACuriousMind

They don't look creepy at all to me :)

FenderLesPaul

:D

:3

ACuriousMind

@FenderLesPaul Okay, that one does look creepy

gonenc

@ACuriousMind that one shouldn't be used anyhow :D

FenderLesPaul

@ACuriousMind :(

:D

obe

15:23

:>

gonenc

@FenderLesPaul what is that anyway?

@obe -_-

FenderLesPaul

@gonenc I'm not sure actually

I think it's meant to show flustering

or blushing

gonenc

@FenderLesPaul isn't blushing :$ ?

FenderLesPaul

@gonenc oh, could be I have no idea

obe

@gonenc Huh?

FenderLesPaul

15:25

my emoticon knowledge is lacking unfortunately

gonenc

@obe nah I meant :3

@obe how far are you with carroll?

obe

@gonenc Still same old.

I'm trying to learn QM fast!!!

gonenc

@obe me too I am too busy watching modern family :D

obe

You already won.

Ch 5 ends relativity for the part that matters at least.

The rest is extra.

gonenc

@obe I think so too. At least I try to make myself believe that it is so :D

obe

15:29

Did you understand all of it and do the exercises/proofs?

Physics Meta

0

Q: Has any physicist answered a question citing his own work on PhysicsSE?

Imagine if when reading a question about a theory or paper by Michio Kaku, you scrolled down to see an answer "When I wrote this theory, [...]". I always thought it'd be neat to see something like that here - has it happened? More specifically, has any question, citing a specific theory or wor...

discussion

gonenc

@obe not all exercises but I understand almost all of it.

obe

Start answering general relativity tagged questions already then...

gonenc

Killing vector and diff forms stuff is a bit shady though

@obe if there were any unanswered for my level

I am reluctant to answer something that I am new :)

obe

The next race is on who can get 50 general relativity tagged questions answered.

Ends 1 year from now, though it shouldn't take that long.

gonenc

15:34

@obe I bet that I'll forget about this bet :D

obe

Now for the other one... what should I do for you?

FenderLesPaul

Ew why are you using Carroll?

obe

Because we're beginners.

or gonenc is an intermediate now.

FenderLesPaul

So...?

obe

what other book is there?

FenderLesPaul

15:39

There are infinitely better begginer books on GR lol

Hartle or Schutz

obe

like...?

those are low level though.

FenderLesPaul

No the aren't

they*

they explain the physics really well

they don't go into the formalism but that isn't important

Carroll basically explains no physics

obe

can you go h or s -----> wald?

FenderLesPaul

and doesn't do the math justice

so what's the point?

Sure that's what I did

I did Schutz then Wald

gonenc

for the reference about make myself believe: 54.33 min

Shing

15:41

what wrong with my answer? Not only people rebuke things I did not say, but also it is required to be deleted. I have spend quite a hard effort typing it, especially my english is lousy, it took quite some of my time to proof reading. If I made serious mistakes, please let me know.

-2

Q: Why is the speed of light limited to (only) 299.792.458 m/s?

The speed of light (in a vacuum) is limited to 299.792.458 m/s. This sounds very fast, and it is on a global scale. But if you look at the Universe on a larger scale than it sounds quite slow, For instance it takes light from one and of the Milky way 100.000 years to get to the other end. So some...

special-relativity speed-of-light physical-constants

gonenc

@FenderLesPaul I really think Carroll was a good read. After having watched the theoretical min

Carroll felt really good

FenderLesPaul

I can assure you it's a waste of your time

0celo7

My favorite song begins with I started selling dope back in 1986

obe

Danu and 0celo7 recommended Carroll.

FenderLesPaul

I have no idea why

the exercises are way too easy

and the text doesn't discuss anything substantial at all

gonenc

15:43

@FenderLesPaul they don't feel that way when you first learn GR

FenderLesPaul

@gonenc no I disagree

obe

@0celo7 @Danu What are your thoughts on what he says?

FenderLesPaul

there are some exercises in Hartle that I can still say are hard

but Carroll's exercises are all just basic computations

you won't really know any deep concepts after reading that book

obe

That's the point, trivial exercises are the best way to learn the concepts.

gonenc

@FenderLesPaul that just means that Hartle is too hard to begin learning GR with

user54412

15:44

@ACuriousMind Am I the only one who distinguishes nu from v according to the concavity of the left stroke?

FenderLesPaul

@gonenc no it just means Hartle is a good book

Kleppner and Kolenkow has harder than average exercises but it's still one of the best introductory mechanics books available

gonenc

@ChrisWhite most certainly not count me too

FenderLesPaul

hard is good

gonenc

@FenderLesPaul too hard aint too good though

FenderLesPaul

You should have a really good understanding of the conceptual aspects of GR

user54412

15:45

@obe As do I. I still hold it as the the book to learn GR from, and I say this as someone getting a PhD in the subject.

FenderLesPaul

before trying to learn the more formal aspects

gonenc

@FenderLesPaul I don't know about you but formalism helps me understand better I don't like books that are too wordy

obe

same^^

FenderLesPaul

I didn't say anything about being wordy

Jimself

@Shing it lacks grammatical coherency, it doesn't say much beyond "that's not a question we ask", it has partially incorrect statements, it seems to have included speculation. In general, it isn't an overwhelmingly great answer. Check spelling and grammar first. A mediocre answer won't get downvoted, but a mediocre answer with poor grammar and spelling will get downvoted significantly

gonenc

15:47

btw I've just looked at schutz and my first imperssion is that he uses too less maths

disclaimer: I haven't read the book and don't know how awesome it is if it really is awesome

FenderLesPaul

I mean it's up to you in the end but all I can say is the most important part of learning a subject is having really good exercises

and Carroll has no good exercises

they're waaaay too easy

obe

I don't like doing exercises.

FenderLesPaul

@obe then why are you learning physics?

John Rennie

@gonenc However Schutz is excellent for amateur relativists like me to get a handle on the ideas involved.

FenderLesPaul

lol

You can't learn physics without doing exercises

that's ridiculous I'm sorry

gonenc

15:49

@FenderLesPaul some of the exercises are too computational I admit that and I don't do them but I mean some of them are good too

obe

True though, I'd rather think about the concepts or do the derivations myself to understand it.

I don't like exercises though.

ACuriousMind

@ChrisWhite Nah, that's how it is in print, but I rarely see people writing that concavity in handwriting

gonenc

@JohnRennie that may be true, as I've said I haven't read it so it'd be inappropriate for me to judge it

FenderLesPaul

@gonenc at the end of the day it's whatever you feel you like best, you're the one learning

but to me exercises are very important

gonenc

@ACuriousMind really? how do you distinguish $\nu$ from $n$

FenderLesPaul

15:50

which is why I prefer Hartle and Schutz

obe

read carroll ---> exercises in hartle.

FenderLesPaul

If I had tried to use Carroll when I took the GR sequence here

I would've undoubtedly failed the class

ACuriousMind

@gonenc The hook on the right of the $\nu$ does not touch the baseline

user54412

@ACuriousMind Computer Modern, annoyingly, puts the same concavity on both.

gonenc

@FenderLesPaul I'll probably read them but imo it feels better to know the formalism first but I guess it is a preference like anything else

FenderLesPaul

15:51

@obe I don't think I could do a good amount of the exercises in Hartle after reading just Carroll

Shing

@Jimself if "things are faster than light" then I get imaginary number for the Lorentz transformation, since an imaginary number for time or position doesn't make physics sense, is that not counted as a prediction?

FenderLesPaul

@gonenc indeed it's a preference thing

gonenc

@ACuriousMind that should've been a $v$ and you know it :D

FenderLesPaul

again, whatever makes you happy

Jimself

@Shing no, that was programmed into relativity because it was a prior observation. It was not a "prediction"

obe

15:52

@FenderLesPaul This is making me feel really weird.

I didn't finish carroll yet so I can switch now.

FenderLesPaul

@obe I'm not saying to switch

I'm just saying you should also check out the other books

obe

Though I don't feel like it's the right choice.

user54412

@gonenc FWIW, I read Schutz on my own the summer before I took GR (which used Carroll, MTW, and Wald). I think it's good for that purpose -- a warmup book.

ACuriousMind

@gonenc We sorta used Schutz for our GR course. I hated it precisely because it is not very mathematical, and does not enable you to do actual GR

FenderLesPaul

What's this "event" thing that just popped up o.o

ACuriousMind

15:54

@FenderLesPaul Chat session!

obe

@FenderLesPaul I'm also looking at wald's book and poisson lecture notes.

Shing

Is general relativity by Talyor and Wheeler good?

FenderLesPaul

@ACuriousMind ah

@obe Poisson's notes are great, I really like them!

His book, which are based off the notes, is totally worth getting

obe

I saw him before.

John Rennie

@ACuriousMind I've heard bitter criticism of Schutz on the grounds that he does nothing rigorously and uses all sorts of special case arguments to calculate things.

gonenc

15:55

@ACuriousMind like a true physicist :D :P

FenderLesPaul

@obe Oh right you're in Canada

John Rennie

I can see the point of this argument, but I still found it an accessible way into GR starting from little or no knowledge of differential geometry.

FenderLesPaul

@obe he's kind of a celebrity in our GR group haha

gonenc

@ChrisWhite that I'd believe :)

FenderLesPaul

@JohnRennie that and he spends time on the down to Earth physics

which is always nice

ACuriousMind

15:57

@JohnRennie Yeah, it depends very much on the purpose you read it for.

John Rennie

@FenderLesPaul Down to Earth physics? I don't remember anything I'd describe that way in his book.

0celo7

@FenderLesPaul for you maybe

FenderLesPaul

@0celo7 fight me

@JohnRennie compared to Wald anyways :p

0celo7

@FenderLesPaul AFAIK you're a skinny Indian kid, I can take you

user54412

@JohnRennie Some of those arguments are actually rigorous though (just unsatisfying to the types coming from QFT who have an algebra fetish). For example, he liberally derives manifestly covariant formulas in nice coordinates, and then we know the formula for arbitrary coordinates.

FenderLesPaul

15:59

honestly anything is down to Earth for me if it involves actual numbers

@0celo7 that's probably true :(

I can't fight

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