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04:01
@SirCumference answering the question
Tidal forces would tear us apart
not if it's big enough
Dude, its size is proportional to its mass
Look at the schwarzschild radius formula
haha you're telling me that
HAHA
I bet you don't understand the derivation of it :D
Actually, reading on it as we speak XD
Since it requires no calculus
But yeah, big black hole = massive black hole = strong gravity
= we dead
04:03
@SirCumference lol
Solving systems of DEs requires no calculus
It's pretty straightforward
I got a textbook next to me
which one
@SirCumference no
"no" what?
curvature is inversely proportional to radius squared
radius squared grows faster than the schwarzschild radius
so as the black hole gets larger the curvature near the horizon gets smaller
so once it gets large enough and you can spend lots of time near the horizon
you'll be fine
04:07
For what part
Most of it
if you want some quick curvature estimates take the square root of the Kretschman scalar
plug in the Schwarzschild radius
you'll find the curvature at the horizon goes to zero as $M$ goes to infinity
yes, it goes to 0 like $\sim M^{-2}$
Why couldn't you just use the schwarzschlid radius formula alone?
that tells you nothing about the curvature
Why would you need to know the curvature?
04:10
What do you think tidal forces are
Basically when the gravitational pull of one side of an object is way stronger than the pull on the other side
Magic words, what does that mean in math
What do you mean "what does that mean in math"?
@SirCumference what are tidal forces in GR
I haven't gone into GR yet
The textbook I'm using is an intro to GR book...
04:13
what book
Exploring Black Holes: Introduction to General Relativity
basically tidal forces are a curvature gradients that cause geodesics to spread/despread
why don't you get a real GR book
I've never heard of that one
04:14
Zee, Carroll, Wald, Hawking, Straumann, Weinberg
there's plenty
I own all but one of those
What's one that would be good for someone with just Newtonian physics and some-calculus knowledge?
you shouldn't be studying GR
I want to
you should have a firm grasp of vector calculus
linear algebra
analysis and topology
last two are for higher books
Goddammit I'm givin up
04:16
if you're a badass you could read Sachs and Wu or BEE right off the bat
This is gonna take months or years
@SirCumference that's why physicists go to school for months or years
And when in God's name did you start looking into things like analysis and topology?
senior year of high school
still working on those two
Linear algebra and vector calc?
04:18
junior
Mmm...maybe I can still do this
I just gotta learn a lot
are you not a senior
I am
But I wouldn't be late if I learned it a year after you
but you haven't mastered calc 1/2
why would you think about going to higher dimensions
Well actually, our calc teacher came back
So he's teaching AP Calc AB + BC
Quit ruining my dreams...
04:22
@SirCumference what?
so tell me how to derive the Schwarzschild radius
Goddammit I'm reading it...
It tells me the basics of it in chapter 3 and goes to the rest in chapter 11
I'll probably want to read everything in between to get an understanding of it
I'm debating how much I want to troll you right now.
Screw it...
what
You're gonna give me a headache
04:24
uhhh
@SirCumference do you want me to tell you how
Go ahead
Not sure if I'll understand it yet
But I'm also thinking that you're gonna screw with me...
"I'm debating how much I want to troll you right now." I don't know who to trust anymore
dude first I have to remember what the hell the Schwarzschild radius formula is
$2GM/c^2$?
hmm
trying to remember, bear with me
haven't done this since I was your age
Ya make me feel young
04:30
alright, so we know that the gravitational potential energy at the distance $R$ is $-GMm/R$
by a standard argument we set this equal to the kinetic energy of the thing trying to escape, $mv^2/2$
then we get $v_{escape}=\sqrt{2GM/R}$
you might have seen that in your physics class
now suppose we want the escape velocity to be greater than the speed of light
so we get $c<\sqrt{2GM/R}$
Yeah
What are you trying to find?
04:33
so if $R<2GM/c^2$ light cannot escape
done
Oh there we go...
OH
SENSE
::waits to be called out::
ok, I guess people accept that argument
@SirCumference this derivation is due to Laplace ca. 17something
maybe 18earlysomething
if you can spot the critical error you get a cookie
Okay, you're interested in black holes yet you don't care about astronomy?
(protip: this derivation was completely wrong)
@SirCumference I'm interested in them from a math standpoint
Astronomy is loaded with ways that they form
"(protip: this derivation was completely wrong)" Wait what?
04:37
:)
I said I'd troll you
I never troll without telling you
But it makes sense...
Wtf
it's the coincidence of coincidences
the problem is of course that $-GMm/r$ is wrong for something that moves at the speed of light
because such a thing IS
???
MASSLESS
$m=0$
04:39
wow
Wasting my time thinking I've learned something
Hawking actually has the original paper in his monograph
Forgetting that nothing with mass can get to lightspeed
@SirCumference you did learn something
Yeah, what?
04:40
@SirCumference well, that and the fact that $-GMm/r$ and $mv^2/2$ are wrong
I literally used only wrong equations and you believed me :)
@SirCumference you learned that Newtonian mechanics ain't shit
fml I'm done falling into your traps
the real way is to solve the Einstein equations for a $\mathrm{SO}(3)$ symmetric mass distribution
Newtonian mechanics ain't shit
It just isn't as accurate as it should be
It uses hundreds of year old equations
A lot changes in hundreds of years
04:42
then compare the solution with the expected long-range geometry you get from Newton
I get your point
what's my point
But with Newtonian physics, you don't learn the cool stuff
Like what mass actually is
Or how space and time are related
I can do Newtonian mechanics with far more math than you've ever seen...
Or what happens if you travel at relativistic speeds
04:43
@SirCumference that's philosophical
Sorta...
@SirCumference that concept does not exist there
@SirCumference they're not in Newtonian mechanics
I know
That's my point
it's not that it can't answer those questions
2
Q: Why particles in Quantum Mechanics are indistinguishable?

user1620696Currently reading about tensor products in Quantum Mechanics and composite systems I've read that in Quantum Mechanics particles are indistinguishable while in Classical Mechanics that's not the case. This leads to the requirement that the wave function be symmetric or antisymmetric and thus, to ...

04:43
it doesn't care to
It's missing the cool stuff
The stuff that would actually interest students
@SirCumference Newtonian mechanics can get cool
The only mystery in quantum is not the double slit, but why particles are indistinguishable
Of course, but it's not always mind-blowing the same way a lot of GR concepts are
Newtonian mechanics is phase flow on the cotangent bundle of space
if that doesn't sound cool you're got issues
04:44
I am not got issues
Newtonian physics is cool in its own right, but it misses the cool things that happen at relativistic speeds
Or the concept of spacetime
Newtonian mechanics has spacetime
Eh...I've never seen it explain how space and time are related
can GR?
Probably?
dunno, I've yet to see someone explain why there's space and time and why the two are different
04:47
If kids knew about time dilation, it'd blow their minds
@SirCumference if kids knew about symplectic geometry it'd blow their minds
Then we gotta reform the geometry classes
yes
go get Arnold's book
get Lee's book
read them
then teach a course on it
if you think you're ready for hard core GR, get Straumann
Most physics classes refuse to teach anything discovered within the last 150 years
Ya know how much changes in 150 years? It'd be like not learning about WWI and WWII in History, or DNA in biology
Newtonian mechanics:
04:52
Where'd ya get that from?
a German physics book
In English?
they all write in English
cf. e.g. @ACuriousMind
Who writes in German then?
the Germans who can't speak English, obviously
04:56
@0celo7 Trying to find your book, but I just find this
That would be German
I know
It's very clear to me
Rudolph & Schmidt
Differential Geometry and Mathematical Physics
Where does it go into Newtonian physics?
chapter 9 and on
05:00
I gotta pay $70 to read it...
lol
this book is way harder than any GR book
maybe on par with Choquet-Bruhat
Some papers can be so complex they're ugly
Is that even real
it seems very poorly written
Yep
Hohmann sent it to me
I've seen it before
it's a meme
05:07
Wait really?
maybe 3 people can actually understand it/care
I'm going, bye.
Hundreds of pages...
'Night
 
3 hours later…
08:25
I prefer the telephone operator joke :p
 
2 hours later…
09:57
2
Q: What experiments prove the greenhouse effect?

VoyskaWhat experiments prove that heat can be "trapped" by a layer of material with suitable optical properties, such as carbon dioxide? I've read a little on Wikipedia but I've got only some names, not the experiments.

I'd appreciate thoughts on whether any cleanup of the answers is warranted
(note comments on the question)
lawl
The global warming denier is quoting the daily mail
10:12
@DavidZ 1. I don't think that was a drastic edit. 2. I think Kurtovic is correct; the answers all talk about whether global warming happens or not, while the question asked specifically about evidence for the greenhouse effect. Ron's answer doesn't address this, Alan Rominger's does, Martin Beckett's does not, John Rennie's does not. Being literal, I'd delete every answer but Alan's.
It was a risky question
Might as well ask about the physics of abortion
10:48
@ACuriousMind well, let's be clear: what exactly do you mean by the greenhouse effect?
@DavidZ Exactly what you've written in the edit - that layers of gases can trap heat, i.e. lead to a higher temperature of the body they enclose than it would have without them.
Do you mean that some might construe "greenhouse effect" to refer to the specific claim that that is what our atmosphere does, and that that is the relevant mechanism for global warming?
Also Luest got #rekt in that review
@ACuriousMind yeah, that's what I assumed Kurtovic's original comment was about
And apparently Klinkhamer is a total dick
@Slereah Someone was very angry when writing that :P
About Susskind: "extraordinary physicist, always happy to discuss. not very interested in explicit calculations though"
hahaha
Nice to see Plehn is actually rated as friendly as he is
"He is good in writing his name on the papers"
Polarized!
So, who will contribute? ;D
11:13
::crickets::
Hey @ACuriousMind where do I learn about sheaves?
I have this book on mirror symmetry but it's way too imprecise
"sheaves are like bundles but you just put some module hurr durr"
Is it possible to get the basic idea in ~10 pages?
lol
basic idea + nlab
what is more basic than categories? :-þ
Plehn is cool. But surely his qualities are overestimated by that webpage - he has more general expertise in math and physics than Susskind
@Danu Also, what do you expect to be basic about something that originated with Cartan, Serre, and Grothendieck?
11:29
@yuggib I'm sure you know what I mean. Basic as in approachable for someone comfortable with vector bundles, but not categories.
Oh sorry, he's only Susskind's equal in physics
I do note that Susskind not caring much about math is a thing
@Danu In algebraic geometry textbooks ;)
@ACuriousMind So one step down from there
In Forster's book on Riemann surfaces there is an intro, I might try that out.
Anyhow, the system is flawed. I could eg write a script to give someone I (dis)like high (low) slighlty randomised scores at random times of about every few weeks
11:34
They also appear in algebraic topology where one is mainly interested in their cohomology, but I think those treatments mostly assume the reader already knows about sheaves as such
@innisfree Definitely
That's assuming people aren't already doing things like that or writing there own reviews
(though there is the "I am not a robot" thing)
@ACuriousMind I think this is what Forster cares about and he does introduce them, so maybe he doesn't assume much.
@Danu Looking at it, yes, he doesn't assume anything
Awesome-o.
I'm off to Connes' lectures now! Cya guys
11:38
He goes very quickly to the cases he wants to apply them to, though
@danu oh so there is. Well anyway even if it's not automated, there submission system is easy to exploit to skew the ratings
@Danu lectures on what?
more precisely, lectures for mathematicians or physicists?
11:56
What is it with all those users going against established physics or promoting their own pet theory lately? I have the feeling I'm seeing "Physics is wrong and my personal theory is totally right" almost every day now.
Lately?
Pretty sure it has been going on since physics was a thing
@yuggib for physicists, and very vague.
But it's about non-comm geometry, of course
@Slereah Sure, but I have the impression the frequency of that has increased recently
He claims to have a working model for QG
Maybe it just increases with activity of SE
But rate remains the same
11:59
I think there is a slight increase. That's because I believe most new users are now of a lower level

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