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10:00 AM
@Kaumudi.H Why? Have they become rare now ?
 
user228700
Yes, sort of.
 
@Kaumudi.H we still get those in the UK, though usually the ice cream they sell is a bit on the cheap side and isn't as nice as the better of the ice creams I buy from the supermarket.
 
@JohnRennie Yesterday you said: "@LuBu Because understanding Gibbs free energy will tell you why the boiling point exists."
Did you mean that the thing that is explained with the GBE then, is why the
values of vapor pressure are what they are at different
temperatures?
 
@JohnRennie In the sense that there is a lot of geometry in mathematics built off of QFT, probably.
 
@Danu I'm afraid that was just an attempt at a poor joke
I don't see the connection ...
 
10:14 AM
...lol
I'm still going to say something more about it
 
One insight that I really liked is the following idea: In doing a path integral, we are integrating over some infinite-dimensional function space ("configuration space") and in mathematics the principle of understanding a manifold by examining the space of functions on it goes back to at least Morse theory, and probably before that. Thus, one may hope that the integral over this function space is an invariant of the manifold. And indeed it is, and a remarkable one at that:
The Seiberg-Witten invariants for example, which in physics are path integrals for some $N=2$ SUSY theory, turn out to be* invariants that can distinguish different smooth structures on the same topological manifold (!!)
In general this idea of doing some functional stuff on infinite-dimensional function spaces associated to a manifold has turned out to be extremely fruitful since the 80's.
 
user228700
@JohnRennie Ah, I see. The icecream that they sell is actually the very same ones we get at the supermarket so no problemo! :-)
 
user228700
@JohnRennie See, this is why I didn't get the joke :-P
 
In mathematics, a connection on a fiber bundle is a device that defines a notion of parallel transport on the bundle; that is, a way to "connect" or identify fibers over nearby points. If the fiber bundle is a vector bundle, then the notion of parallel transport must be linear. Such a connection is equivalently specified by a covariant derivative, which is an operator that can differentiate sections of that bundle along tangent directions in the base manifold. Connections in this sense generalize, to arbitrary vector bundles, the concept of a linear connection on the tangent bundle of a smooth...
 
user228700
10:19 AM
@JohnRennie There are fibers in Math? .__.
 
@Kaumudi.H Bundles of them!
 
@Kaumudi.H You're just trying to visualize it in 3D. Stop doing that and the triangles become obviously different.
 
In mathematics, and particularly topology, a fiber bundle (or, in British English, fibre bundle) is a space that is locally a product space, but globally may have a different topological structure. Specifically, the similarity between a space E and a product space B × F is defined using a continuous surjective map π : E → B {\displaystyle \pi \colon E\to B} that in small regions of E behaves just like a projection from corresponding regions of B × F to B. The map π, called the projection or submersion of the bundle, ...
 
user228700
@JohnRennie Ah, another joke :-P
 
And then there are moduli spaces of those ;D
 
10:20 AM
We should note here that fibre bundle is the correct spelling :-)
 
8
Q: Reference request: moduli spaces of vector bundles

Mohammad F. TehraniI am trying to study the moduli spaces of holomorphic vector bundles quickly, and I'm primarily interested in understanding: Why and where the stability condition is used. How are the moduli spaces constructed. What are the examples, especially in the case of vector bundles on curves. I was l...

@JohnRennie Get outta here
US > UK spelling
6
 
user228700
@Danu India sides with the UK and so do many nations that were once under the British Raj, so I'm afraid UK>US.
 
@JohnRennie Yesterday you said: "@LuBu Because understanding
Gibbs free energy will tell you why the boiling point exists."
What did you mean by "WHY"?
Did you mean that the thing that is explained with the GFE,
is why the values of vapor pressure are what they are at
different temperatures?
 
user228700
@JohnR: Thoughts on naps. Go.
 
10:23 AM
3 p.m. in your part of the world? A good time for a nap. Dream of physics :-)
Oi, who just starred Danu's comment? Philistines!!
4
 
@Danu Hypernationalistic sentiments ? :P
 
Or just hyper :P
 
user228700
@JohnRennie Er, 4 PM, actually, but I will dream...of rats wearing hats, speaking to me an unearthly language, trying to explain their proposal for a new coordinate system (No kidding, I dreamt of this once)
 
IIRC Danu is Dutch. I don't think we've offended the Dutch for several centuries ...
 
German too.
 
10:26 AM
@LuBu re Gibbs free energy
 
@JohnRennie re?
 
The variation of the vapour pressure with temperature cannot be understood without considering the Gibbs free energy and how it varies with temperature for the liquid and gas phases.
 
wrt @LuBu
 
@JohnRennie Oh, ok.
 
Once you understand how the Gibbs free energy explains the liquid gas equlibrium it all becomes surprisingly simple.
Incidentally the letter F refers to the Helmholtz free energy
 
10:31 AM
@JohnRennie I probably can get by with this basic knowledge for some time.
 
@anonymous Ehh?
@Pissedofflayman I'm not German.
 
I should be the one asking "Ehh" ? :D
 
I'm not from the US, as pointed out by John.
 
What does US > UK spelling even mean ? :P
Both are correct spellings
 
I also kinda see path integrals that way, however, trying to visualise the space where integrals and other continuous functional live in is more difficult than some manifolds. One reason I am interested in the symmetry of the integrand is it provide me ways to find my way around such space
 
10:42 AM
@anonymous you're taking this far too seriously :-)
 
@JohnRennie I will brush off Danu's comment as an attempted joke in that case :D
 
It was an attempted joke.Danu and I have known each other for long enough to be able to freely insult each other :-)
 
@Pissedofflayman Are you a user I already know who changed names, or are you new here?
 
@JohnRennie I came up with another weird question though.
If we have some sort of ventilation to prevent the partial
pressure of the water vapour from accumulating, and heat it
to the boiling point.
Does that mean that our water will not be boiling, by definition?
Wouldn't there still be gas bubbles forming within the liquid.
And this would give us some vaporization rate, but by the
definition of boiling, we would not be boiling?
 
@LuBu Depends on how you define boiling I suppose.
 
10:53 AM
@anonymous That's what i'm thinking.
 
@LuBu consider a bubble in the boiling water.
 
@JohnRennie Yeah?
 
That bubble contains just steam, no air since it grew in the water, at a pressure of 1atm
 
@JohnRennie Yes.
 
So at the edges of the bubble you have water in equilbrium with steam at a partial pressure of 1 atm
 
10:57 AM
Isn't the pressure within the water over 1 atm.
 
If you direct a powerful fan on the surface of the water to blow the steam away then I suppose you could argue that at the surface we have just evaporation not boiling, but this seems a slightly dubious argument.
 
But there are gas bubbles forming and vaporizising.
 
@LuBu the pressure will be slightly greater than 1 atm because pressure increases with depth in water, but if you're dealing with a pan on a stove then the pressure increase will be negligable.
I need to take a break for a while ...
 
@JohnRennie Can you hear this out.
@JohnRennie So by definition then we would not be boiling?
@JohnRennie Given that the pressure within the water would be higher.
@JohnRennie Oh yeah, nvm.
 
11:16 AM
@LuBu yes...
 
11:27 AM
@anonymous What?
 
@LuBu "So by definition then we would not be boiling?" Yes.
 
@anonymous But we would be boiling within the water.
 
12:14 PM
hello all
 
Morning :-)
Are you seriously considering learning some GR?
 
user228700
@heather Ello :-)
 
@JohnRennie just some of the basics, why?
(for now, until i get a better hold on the math.)
 
@heather because I think you can learn lots of interesting GR stuff without it getting too hairy.
GR kind of divides in two.
 
heh
 
12:17 PM
On the one hand you have the hard core stuff that deals with the gory details, but on the other hand if you're prepared to just accept some metric (like a black hole) there's lots of fairly easy stuff to tell you what happens with that metric.
 
Found a 1914 pop science article on relativity
Oh what fun
 
@heather e.g it's really easy to calculate time dilation from a metric ...
 
huh, cool.
 
@Slereah link?
 
i'm probably getting into too much of the hairy stuff.
 
12:20 PM
So my point is that if you want to have some fun playing with GR then I think you'll find it quite easy.
 
Then if you decide at college to start taking it seriously you'll have a background understanding that will help a lot.
 
i'm watching a 2 hour (!) video on the Einstein field equations, and it's going fairly well. i think once i go over the math again for some more intuition i'll get it.
and if i reread my notes on partial derivatives.
my one complaint though is that i have heard no really good explanation of tensors.
 
Starting with Einstein's equation is pretty hardcore!
 
i probably got in over my head, yeah =P
 
12:23 PM
@Slereah ah, special relativity.
Light clocks ...
 
Well, 1914
GR wasn't out yet
 
but the video doesn't expect anything more than calc, so.
 
If I never read about another light clock that will be too soon.
@heather have you got a link to the video?
 
Thanks :-)
 
12:29 PM
np
 
12:42 PM
@Kaumudi.H any interesting problems solved recently? Did you figure out that proof?
 
user228700
I think it depends in ur definition of "interesting" but if u read the transcript, u may find something :-)
 
user228700
Also, yes, I did--it was very trivial, actually.
 
@Kaumudi.H that's good that you solved it, though.
@Kaumudi.H JR's "masterpiece" drawing =)
 
user228700
@heather Yes :-) He loves to create masterpieces!
 
he does a very good job =)
i mean, that sphere...geesh.
 
user228700
12:54 PM
Oh, tell me about it! :-o
 
i'm for finding a picture of a sphere that looks like that on the google at that point.
 
0
Q: can an immovable object produce an irrersistable force

dragonif all mass in the universe was in one place it would be an immovable object. there would be no force outside of the object. since all that mass is in one place it would have a large gravitational force. there would also be no mass outside of the object to resist the gravitational force that the...

a twist on the clasic philosophy question
 
1:15 PM
@heather Huh, you're looking at the field equations? That's pretty impressive.
 
@LuBu "But we would be boiling within the water." What does that even mean ?
For boiling temperature should stay constant while the liquid is "boiling".
The entire mass will boil and only after that can temperature change.
But in case you artificially reduce the external pressure I don't think boiling point will ever be reached like that.
@heather I'm liking your dedication :) To learn tensors by yourself I think this pdf is a good one. Have a look! web2.ph.utexas.edu/~jcfeng/notes/Tensors_Poor_Man.pdf
(Assuming you know basic linear algebra and vector calculus)
 
1:55 PM
@Danu Well, in general, that hope is just wrong :P Only very special theories yield invariants in their path integrals.
 
@anonymous John: "If you direct a powerful fan on the surface of the water to blow the steam away then I suppose you could argue that at the surface we have just evaporation not boiling, but this seems a slightly dubious argument."
 
2:29 PM
Hi chat
 
I'm afraid the chat is not self-aware and cannot yet respond on its own.
> Allow me to preface this question by stating that I am not a Big Bang denier.
Nothing makes me more suspicious than a question that goes out of its way to assure me that it is not, in fact, crackpottery. :P
 
@ACuriousMind Well, that's where physicists did a great job :)
 
I hate people who do 85% downvotes and 15% upvotes,yeah that you
 
@Danu Read: Witten :D
 
Seiberg is here now, giving talks
 
2:34 PM
@Danu here=Munich?
 
Yeah
 
What's he talking about?
 
Two uniform solid spheres of equal radii R,but mass M is projected from the surface of mass M directly towards the centre of the second sphere.
 
duality in 2+1
 
Uh,how to ask iam stuck in middle of solution
 
2:36 PM
@Danu Well, most of physics seems to be about duality these days ;) What kind of duality; E-M?
 
I honestly don't know. Probably. It's related to cmt apparently
 
How to find mechanical energy at surface of M?
 
@Danu And hearing cmt you did not inquire further? ;P
 
actually, the technical talk for the strings group starts at 4:15
 
2:41 PM
Hi,i need some help in physics,can I ask here?
 
@Fuckoffsittian Yes, just ask your question. If someone wants to answer/help you, they will.
 
I think there + should come but I may be wrong,can someone say where iam going wrong?
 
@Danu wasn't that talk yesterday? Or was that the non-technical talk?
 
@SirCumference hi ,sup?
 
@Ramanujan Nothing much
 
2:54 PM
@anonymous hey, I need some help in gravity topic
 
I am reading it
@Ramanujan Gravitational potential energy is taken to be negative w.r.t sphere as a negative amount of work is done to bring an object closer to the sphere (without causing the body to accelerate)
 
So body is moving from left to right,so gravitational potential energy by right side sphere should be positive ?(because it is moving in that direction)
 
@Ramanujan Gravitational potential is ALWAYS negative (in classical physics)
 
@anonymous if body is dropped on earth,still negative?
 
@Ramanujan No matter where the body is, Earth will provide it a negative gravitational potential.
12
Q: Why is gravitational potential energy negative, and what does that mean?

BlueRaja - Danny PflughoeftI usually think of gravitational potential energy as representing just what it sounds like: the energy that we could potentially gain, using gravity. However, the equation for it (derived by integrating Newton's law of gravitational force)... $PE_1 = -\frac{GMm}{r}$ ..has me thrown for a loop...

Potential energy and Kinetic energy are just book-keeping tools and vary w.r.t reference frame @Ramanujan
@Ramanujan Also, it does not depend on in which direction the body is moving. You need to think of them as isolated two-bodies to get the gravitational potential
 
3:18 PM
@Daniel that was indeed the nontechnical talk
 
Ok,@anonymous thanks
 
4:01 PM
Gotta love when the answer to a question is "Feynman was wrong. He sometimes is."
-1
Q: Feynman Lectures. Lecture 43

Username160611000000Feynman Lectures. Lecture 43. Lecture Summary [http://www.feynmanlectures.caltech.edu/I_43.html] $\text{The current of particles / area sec.} = - \frac{1}{3}lv\frac{dn_a}{dx} = - \mu kT\frac{dn_a}{dx} = - D\frac{d}{dx}(\frac{n_a}{n_0}).$ Can you show how did he get $\frac{n_a}{n_0}$ ? In ...

"We all sometimes write stupid crap on a blackboard and our students don't correct us. It's because we raise them in a society where misunderstanding is somehow viewed with negative moral valence, you were 'wrong' and therefore 'you should be punished.'"
 
4:20 PM
@CRDrost where's that quote from?
 
4:58 PM
@Fuckoffsittian nice username :P
 
5:10 PM
@ACuriousMind You around?
 
Somewhat
 
and asked if there's a way to give him chat rights
 
@BernardoMeurer Of course; the way to do that is for him to earn 20 reputation :P
 
@BernardoMeurer he'll need to get 20 rep.
Two upvotes? Shouldn't be hard.
 
I told him just that
Apparently he's lazy
Also, I might be getting a job as a research assistant @JohnRennie :)
 
5:13 PM
I believe mods can join a user to a chat room even when they don't have the rep.
@BernardoMeurer Cool :-) Doing something fun?
What happened with that job as a unix sysadmin? I guess you didn't get it.
 
There is a way to grant low-rep users write access to specific rooms but that's only to be done for moderation purposes or other exceptional circumstances
 
@JohnRennie Hopefully, it's a small group working on heterogeneous core architectures, focusing on ARM and things like that. That also do some work on using FPGA's as special purpose coprocessors
For things like HEVC decoding
 
That sounds really good.
Though I guess it depends on what they give you to do.
 
I didn't go forward with the sysadmin one once my prof said he was considering hiring me for his research
 
obe is an "exceptional circumstance"
 
5:16 PM
Since afaik I want to do research it made more sense to me
 
Yes, I would have done exactly the same. That sort of experiece will look really good on your CV, as well as being great fun!
Are you still wondering about changing universities, or are things looking better?
I guess that research assistant job makes a difference?
 
@ACuriousMind It's not a quote per se, I am kind of just saying "this is what the answer is". It's a quote from me, basically. :D
 
@Pissedofflayman No, users who voluntarily deleted their accounts and then open a new one are not treated differently from other new users.
 
Nice quote @CRDrost
 
@BernardoMeurer: tell obe to get his sh*t together and post an answer and I'll upvote it (as long as it's not totally stupid).
It only takes two of us to get him back into the room and I'd guess there will be plenty of people glad to see him back.
 
5:20 PM
@JohnRennie Makes some difference, but not much, I still have the same issues with the methods of the school
 
@CRDrost I see :D I thought it was a quote because you surrounded it with quotation marks, but anyway, I large agree
 
and those are not going away
@JohnRennie Just sent him that
 
When would you switch? At the end of the first year?
 
@ACuriousMind I was speaking metaphorically :P
 
Eh, it's complicated. I plan on applying to some canadian universities now, mid-year, but I'm kind of broke so fees are a pain
 
5:22 PM
Hence the quotation marks.
 
Then I'll do a larger application at the middle of the year, i.e. after a full year of school
 
@BernardoMeurer Any particular reason why Canadian universities?
 
Why not just dig in your heels wherever you are now?
It doesn't get any easier.
 
@ACuriousMind Canadian dollar is cheap, cost/quality ratio is very good, it's in north america
 
@BernardoMeurer okay, okay, what?
 
5:25 PM
Closer to the Ivy League?
 
@ACuriousMind It's easier to go to the US from Canada than from Portugal. Most of my friends, you and John excused, are in the US :P
@Pissedofflayman It's not about it being "easier"
 
You are allowed to make new friends ...
 
@JohnRennie There's a reason that motif was the last one
It's more of a note than a motif
 
@BernardoMeurer I see
 
5:29 PM
@BernardoMeurer I'm just saying You're gonna have to dig in your heels sooner or later.
 
@Pissedofflayman What on earth does "dig your heels in" even mean?
 
Take a stand.
Stand your ground when the going gets tough.
 
Is wanting to move not a stand?
 
What do you think?
 
The going isn't getting tough, I'll pass all my classes, the problem is I'm not learning as much as I hoped, and my course structure isn't as flexible as I want, for the most part my professors seem to not like their jobs too much , and the classes are "stupidly difficult", with the stupid being literal there, e.g. my Chem course
 
5:34 PM
First year is like that.
 
Yeah, well, it doesn't seem to improve talking to the older people it's just like this
 
@Pissedofflayman Still don't know what you want to say with that
 
nvm then
 
You are not, by any chance, a fan of the raiders? :P
 
5:37 PM
Lol
 
@Pissedofflayman You, I was reminded of this:
Feb 15 '16 at 16:46, by ACuriousMind
@skullpetrol Why do you always sound like a self-help book? :P
 
@BernardoMeurer Is attendance at your university compulsory (I mean is there any minimum attendance criteria ) ?
 
Only for Lab classes
You don't have to go to any theory if you don't want to
 
@BernardoMeurer If everyday attendance is not compulsory then you can just stay back and use online courses parallel to your course. On online courses you will find many good professors.
Everything is available online nowadays.
 
@anonymous That's not what I pay university for though
I'd just be wasting my money
 
5:44 PM
True.
 
@BernardoMeurer That's the second best option if you can't transfer to another uni.
Otherwise you need to change your university I guess. I'm not sure if that is possible.
 
The whole point is that I am trying to transfer
 
At present you are wasting both your money and your time by going there :)
 
tbh though moving all my stuff is going to be a fucking odyssey
 
@BernardoMeurer Wish you all the best then !
Where are you planning to go?
 
5:47 PM
@anonymous Fair enough, I didn't attend my Chem classes after a while, just used IEEE videos and khan and so on
Ended up passing the class
never want to see it again]
@anonymous I'll try some canadian unis now
 
So have less stuff then? :D
Or is there a charge where you live for throwing things in the dumpster?
 
I've always learnt a lot lot more by bunking classes and staying back to study myself. Good Professors are rare to find!
 
Rare indeed.
 
 
3 hours later…
9:10 PM
@DanielSank About the Fourier transform of white Gaussian noise, I saw your nice answer here: http://dsp.stackexchange.com/questions/24170/. I had a question if you had the time.

What can be said about the power of the transformed noise? I mean, if we know the power of the white Gaussian noise (WGN) and then Fourier-transform it, can we say anything about the power of the resulting WGN?
Or maybe this is worth a separate question?
 
9:32 PM
@Mostafa actually I'm not sure what you're asking.
You want to know the relation between Fourier transform and spectral density, perhaps?
 
9:52 PM
@DanielSank Yeah, exactly. Which is constant (white noise) for the input noise. I want to know the spectral density of the F-transformed noise.
 

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