The h Bar

user228700

09:01

^ Yes, it really would. My exam isn't until April, but I've to write practice exams so I need to finish the syllabus by the end of December.

user228700

@JohnRennie Thing is, Sir, this past summer was tremendously painful for me, because of consistently failing to pass the exams that then lead to other personal problems. I've gots to do better next year. So the rushing.

John Rennie

I guess the thing to do is just stick with the syllabus for now. I just hope it doesn't put you off physics for life :-)

user228700

It certainly won't :-) I've learned more in these past months than I have in the past two years, that's for sure. Well, at least I've had more fun doing it.

Mew

she wants to be a physicist of rcourse she won't be put off

user228700

:-) Idk what I want to be but "physicist" doesn't look so bad. It has never looked bad...

Mew

09:10

what about doctor?

user228700

Nope. Didn't take Biology in High School.

Mew

cool that would be a bad job

user228700

:-P I'ma do physical chem. for awhile, before switching back to Electrostatics.

Mew

yeah k imma go play a game

user228700

Have fun :-)

user228700

09:22

@JohnRennie: Approximately how much time dyou reckon it will take to tell me about:

user228700

yesterday, by John Rennie

The spectre of Gibbs free energy floats into view ... :-)

user228700

It's been nagging me ever since and I'm studying about the elevation of boiling point due to the presence of a solute, which makes it worse.

user228700

Dyou reckon it'll take an hour at least? If so, I might as well just skip it...

John Rennie

The trouble is that I can't tell you just about Gibbs free energy. I'd also have to explain enthalpy and entropy and we'd end up discussing pretty much all of thermodynamics.

However I can talk in general terms about how to understand processes in terms of the Gibbs free energy.

user228700

That's OK. Dyou think it'll take long? Just to explain about the boiling point.

user228700

09:26

(Given that now u have a rough idea about how looong it takes me to wrap my head around new concepts)

John Rennie

Well the basic principle is that a process occurs spontaneously if the change in Gibbs free energy is negative.

That is the total Gibbs free energy of the products is lower than the total Gibbs free energy of the initial system.

user228700

Yes, of course...

John Rennie

It isn't that different to the basic principle that everything settles into the lowest energy state.

user228700

Okay...

user228700

Let's stick only to boiling point. U said:

user228700

09:28

yesterday, by John Rennie

Don't worry about the vapour pressure. That's related to why there is a boiling point (and it's to do with the free energy). The boiling point is defined as the division between the liquid and vapour ona phase diagram.

John Rennie

The thing about Gibbs free energy is that it includes entropy as well as energy. So you need to think about the entropy changes involved in any process.

user228700

OK...

John Rennie

@Kaumudi OK.Do you want to talk about boiling of a pure liquid, or why a solute increases the boiling point - or both?

user228700

We could talk about the latter-that way, we'd sort of end up covering both, no?

user228700

I will tell u how I understand the concept: when solute molecules are dissolved in the solvent, the surface now contains some of these too. Hence, not all the solvent molecules are able to vaporize as before. Therefore, the vapour pressure of the solvent decreases.

John Rennie

09:32

Suppose you're considering boiling of a liquid, then the initial free energy is the free energy (per mole) of the liquid and the final free energy is the free energy (per mole) of the vapour.

user228700

Since the vapour pressure has decreased, and the boiling point is defined as that temp. at which the vapour pressure becomes equal to the "external pressure", more heat must now be added to the system to achieve this equality. Hence, the boiling point increases.

user228700

Is my understanding at least "OK"?

John Rennie

We need to put energy in to vapourise a liquid, the latent heat of evaporation, so in the equation $$\Delta G = \Delta H - T\Delta S$$ the enthalpy $\Delta H$ is positive.

user228700

Right.

John Rennie

But that tends to make $\Delta G$ positive, which opposes vapourisation. That means vapourisation only happens because the entropy change $\Delta S$ is large. A large $\Delta S$ means $-T\Delta S$ is large and negative and it outweighs the positive $\Delta H$.

user228700

09:35

Don't u mean "large and positive"?

John Rennie

Now suppose we add some salt to the water.

user228700

Since the term is being subtracted...

John Rennie

@Kaumudi oops yes.

user228700

@JohnRennie OK...

John Rennie

Anyhow, adding salt to the water doesn't change the vapour because the vapour is still just water vapour. So when we look for the reason the BP rises it must be a change in the water. Yes?

user228700

09:39

Uhh, I can't agree with u right away, but do go on...

John Rennie

@Kaumudi we should probably check why you're not sure about this before proceeding ...

user228700

No, I'm pretty sure that I'll understand what u mean when I understand why the change in water is causing this change in BP. I don't exactly understand what u mean by that. If u proceed, I think I will. I'll shout if I don't :-)

John Rennie

OK. Remember that the free energy change is $\Delta G = \Delta H - T\Delta S$.

The $\Delta H$ is basically just the energy we need to put in i.e. the latent heat of vapourisation.

user228700

@JohnRennie That equation has been imprinted onto my brain, I will never forget it! :-)

user228700

@JohnRennie Yes...

John Rennie

09:43

And in fact the latent heat of vapourisation (as measured by experiment) of salt solutions is almost independent of the salt concentration.

Mew

@JohnRennie can you derive the equation pls

user228700

@JohnRennie That fact is an "Eff you" to the explanation that my textbook uses, is it not?

John Rennie

I guess the reason for this is because for a few percent of salt most water molecules are still surrounded mostly by other water molecules, so the energy needed to pull a water molecule out of the bulk doesn't change much.

So if $\Delta H$ doesn't change much that means the boiling point elevation must be due to a decrease in $\Delta S$.

user228700

Wow. Okay...

John Rennie

If $\Delta S$ decreases then that means $T\Delta S$ decreases, so we have to increase $T$ to keep the product $T\Delta S$ constant.

And increasing $T$ is of course exactly what we mean by the boiling point going up.

So far so good?

user228700

09:48

@JohnRennie Hang on. I don't understand why $\Delta S$ has to decrease...

user228700

Gimme a minute to think it through, please.

John Rennie

@Kaumudi I'm arguing that if $\Delta S$ decreases then $T$ must increase to keep $\Delta G$ negative.

user228700

Yes, but why does $\Delta S$ decrease?

John Rennie

So the converse is that if we see the boiling increase (which we do), and $\Delta H doesn't change, that implies $\Delta S$ is decreasing.

user228700

Yep, OK.

user228700

09:50

(I thought there was some other physical reason...is there?)

John Rennie

$\Delta S = S_{gas} - S_{liquid}$. Yes?

In other words the entropy of the final state minus the entropy of the initial state.

user228700

Yep.

John Rennie

And the entropy of the vapour doesn't change (much) because whether we have salt in the liquid or not the vapour is just water vapour. So that means the change must be due to an increase in $S_{liquid}$.

The entropy of the water must go up when you add salt to it.

user228700

Oh, right.

user228700

Because the salt molecules take up some space that was previously available to them?

John Rennie

09:54

So we need to understand why the entropy of water goes up when we add salt to it.

Entropy has a precise definition that unfortunately is hard to understand, but a common handwaving definition is to say that it's a measure of disorder.

user228700

Is my reasoning correct?

John Rennie

@Kaumudi not really, or at least that isn't the way I would describe it.

user228700

:-( OK...

John Rennie

Pure water is relatively ordered because everywhere you look is just water.

user228700

^ That doesn't make a lot of sense to me .___.

Mew

09:57

na water is very entropic

John Rennie

But when you add salt to it you now have a mixture of molecules, so if you look at any random point in the liquid there could be water there of there could be salt there.

So in a vague arm waving way salt solution is more disordered than pure water. So its entropy is higher.

user228700

^ That is the most arm-wavy explanation that u have given me.

Mew

I agree salt+water is more disordered than water

there are more possible states in the salt+water system than in the water system alone

and entropy is proportional to the number of possible microstates

John Rennie

@Kaumudi because defining the entropy of a liquid, and a liquid solution is mind manglingly complicated. Arm waving is the best I can do.

user228700

Hmm, OK.

user228700

09:59

So that's why the boiling point increases.

user228700

God, it appears exactly as if high school is setting up students for quite a lot of hair-pulling and head-desking once they get to college.

user228700

My textbook explained this by saying that $\Delta H$ increases.

user228700

John Rennie

Sorry for the timeout - phone call ...

user228700

That's OK :-) Alright, what about this boiling point itself, then?

John Rennie

10:05

@Kaumudi Where does that say $\Delta H$ increases?

user228700

Oops, hang on:

user228700

I guess they haven't exactly spoke about the increased $\Delta H$, after all. They've spoken about the surface area...

John Rennie

There are always two ways to approach things like this this. One way is the microscopic approach i.e. you think about what happens to individual molecules.

And the other is the macroscopic approach i.e. you think about bulk properties like entropy and enthalpy and you don't worry too much about exactly what happens on the micro scale.

user228700

Right .___.

John Rennie

10:16

What I've done here is talk about the macroscopic approach. So I've said the entropy increases and I've waved my arms around when you asked why the entropy increases.

Your book is trying to justify things with a microscopic approach.

But to honest the book's microscopic approach is pretty arm waving as well :-)

user228700

:-) Yes. Alright, dyou have the time to explain about boiling point, real quick?

John Rennie

Yes OK.

The entropy of an ideal gas depends on the pressure in a scarily complicated way

But all we need to know is that as the pressure goes down the entropy goes up.

So as we decrease the pressure of the gas the free energy also decreases.

user228700

WHICH PRESSURE?!

John Rennie

If it's a pure gas then it's just the regular pressure. If it's in a mixture, e.g. water vapour in air, then it's the partial pressure.

Clear?

user228700

@JohnRennie I'd figured the opposite, actually, but OK...

user228700

10:22

@JohnRennie How are we doing the decreasing, exactly?

John Rennie

@Kaumudi well, consider this. If we leave a gas to itself its pressure will decrease. That is, if we put a lump of gas in a vacuum the pressure goes down and the gas expands.

That means the free energy change for the expansion must be negative.

Mew

IF you apply so much pressure to a gas that it turns into a solid, it has become more ordered and entropy has decreased

John Rennie

And that means the free energy must fall as the gas expands and its pressure goes down.

user228700

@JohnRennie I see...

John Rennie

So the free energy of a very dilute gas is lower than the free energy of a higher pressure gas.

user228700

10:24

@JohnRennie Uhh, one second...

user228700

@JohnRennie Alright...

John Rennie

Suppose we start with liquid water at 0C. To form water vapour we need to put a lot of heat in and that makes for a large and positive $\Delta G$.

So water can only vapourise if there is a very large and positive entropy change.

And the water vapour can only have a very large entropy if it's very dilute i.e. if its partial pressure is very low.

And the partial pressure of the water vapour is just the vapour pressure of the liquid water. So we conclude that the vapour pressure is going to be low at 0C.

user228700

::scratches head violently::

John Rennie

Consider the change water -> water vapour

For this change we have $\Delta G = \Delta H - T\Delta S$

user228700

OK, no, Sir, let's let it be. I think my head might just burst any time now.

John Rennie

10:30

OK :-)

As I said, it is a bit of a distraction.

user228700

Thank you :-) _/\ _

user228700

@JohnRennie I wonder what counts as "distraction" to u...(?)

John Rennie

Is the emoticon a namaste?

user228700

Yes! Well, in this case, it signifies "dhanyavaad" =Thanks.

John Rennie

@Kaumudi my exams are far, far behind me. These days I'm free to pursue any distractions I want. And jolly good fun it is too :-)

user228700

10:33

@JohnRennie Quit bragging :'-(

John Rennie

You too will one day be in the same position. Of course the downside is that you too will be middle aged by then! Life's like that :-)

user228700

:-)

user228700

Alright, gots to go eat s'thing. Dang it, we're out of oranges!!! >.<

DanielSank

11:14

@JohnRennie what's wrong with middle age?

31 is nice: I'm trained professionally, financially independent...

I can spend money on chocolate as I see fit!

3

John Rennie

@DanielSank Nothing. I am thoroughly enjoying a disreputable middle age. However experience suggests that the ladies are less keen on being middle aged.

DanielSank

Ah

John Rennie

@DanielSank Incidentally, Bernardo asked if I could set up a play server for his experiments with rust, and I've done this. Do you want the details? NB it's a Server 2008 installation. I feel uneasy hosting a Linux server because i don't know it well enough to be sure it's secure.

DanielSank

@JohnRennie yes please. If you want to email, you can find my contact info through my profile.

I don't promise not to pwn you though...

John Rennie

@DanielSank e-mail on the way. If the FBI come calling remember I know where you work :-)

DanielSank

11:25

@JohnRennie :|

Rust is weird. Have you tried it at all?

John Rennie

I compiled a HelloWorld sample to check the Rust compiler had installed correctly. Apart from that I haven't looked at it. It looks superficially very like C++.

DanielSank

How can 2008 software be secure?

@JohnRennie hmm, no classes though!

John Rennie

I feel like I've used a dozen languages over the years and apart from the outliers (LISP) they are all much the same. The key thing for using a language is the availablity of libraries.

DanielSank

Yes, libraries are why Python is so useful.

John Rennie

C++ has the huge advantage of a massive code base, and C# has the huge MS supported class library. Any new language has to compete with this.

@DanielSank yes, Python, has made the jump to critical library mass.

DanielSank

11:30

@JohnRennie Rust is definitely not competing with C++.

Rust is competing with C.

user228700

Can anybody help me w/ some organic chemistry?

John Rennie

Why would anyone try and compete with C? Who uses C for anything but legacy work these days?

user228700

in The Periodic Table, 6 mins ago, by Kaumudi

DanielSank

@JohnRennie !!???!

Git is written in C!

Operating systems are written in C.

user228700

^ Which of these two structures is more stable?

user228700

11:33

in The Periodic Table, 6 mins ago, by Kaumudi

I vote (b), because it looks like both structures have the same number of $\alpha$ hydrogen atoms and trans is more stable than cis, correct..?

John Rennie

@DanielSank if you were writing a new OS now, why would you choose C over C++?

@Kaumudi Do the two isomerise? I can't see an obvious mechanism.

Or do you mean which has the lower heat of formation?

@DanielSank I didn'tknow git was written in C. That seems a strange decision. I can't see what possible advantage you get from using C rather than C++.

user228700

@JohnRennie No, I don't think so. I'm supposed to predict their relative stabilities in terms of effects such are resonance and hyperconjugation.

John Rennie

@Kaumudi I don't know what that means. What is the actual question in your book?

user228700

John Rennie

Don't know. Sorry :-(

user228700

11:39

OK :-( I'll wait to see if anybody responds at The Periodic Table.

user228700

I posted a question on CSE almost a week ago and I've received literally no answers yet >.<

user228700

1

Q: Is the inductive effect always measured relative to hydrogen?

Wikipedia has defined the Inductive effect thus: "In Chemistry and Physics, the inductive effect is an experimentally observable effect of the transmission of charge through a chain of atoms in a molecule, resulting in a permanent dipole in a bond." Recently, I learned from a teacher that t...

user228700

Can anybody help me to choose the correct option as to why I'm starting a bounty?

user228700

It looks like most of them apply in my case :-/

user228700

What is a "Canonical answer"?! :-|

DanielSank

11:44

@JohnRennie Linus tornados CV me r THIS

user228700

There. Started a bounty.

John Rennie

@DanielSank Torvald's views on C vs C++. Well, he's a better programmer than me. But I can't help feeling this is all down to design skills rather than language features.

@BernardMeurer you have mail (on Facebook)

Sir Cumference

Goddammit I have a huge test today and I couldn't sleep

user228700

@SirCumference: :-( All the best for ur test, man.

Sir Cumference

@Kaumudi thanks

John Rennie

11:49

Yes, good luck!

Sir Cumference

I'll just need coffee I guess

Solenodon Paradoxus

@JohnRennie C++ has a huge disadvantage of being unsafe. Its extremely easy to shoot yourself in the foot with C++.

John Rennie

@SolenodonParadoxus yes, but that's just as true of C.

Solenodon Paradoxus

@JohnRennie managed languages such as C# and Java have a huge advantage when it comes to safety

John Rennie

@SolenodonParadoxus yes, but the question is why Linus Torvalds should choose C over C++ for writing git and the Linux kernel.

Sir Cumference

11:53

@MAFIA36790 RIP obe

Solenodon Paradoxus

@JohnRennie ah I see

Sir Cumference

The stackexchange SUCKS and John Rennie is an ASShole

►

2

Wtf

user228700

@SirCumference That's kinda...creepy.

user116211

@SirCumference ;_;

John Rennie

@SirCumference That's going to haunt me for the rest of my life :-)

4

Sir Cumference

11:55

@Kaumudi Almost as creepy as the vid above

user116211

Well, @sirC, we have fortunately added him in Skype; let's hope he comes in Skype.

user228700

Does anybody know why an $sp^2$ carbon in a 3 membered ring is unstable due to "ring strain"?

Sir Cumference

@JohnRennie Don't worry, we don't think you're an ASShole

user228700

Okay, the better question would be "Wtf is ring strain"?

John Rennie

@Kaumudi the sp2 bond angle is 120° while the bond angle in a three membered ring is 60°

user116211

11:57

Know about ring torsion?

user228700

@JohnRennie Ohh, right .__.

user228700

@JohnRennie Yeah, you're more like a God to me :-P

user116211

Did something actually happen with obe @SirC?

user116211

I didn't get his behaviour lately.

Sir Cumference

@MAFIA36790 No clue

Let's hope he'll come back when @0celo7 is back

user116211

12:00

@SirCumference hmm

Solenodon Paradoxus

Pretty harmless. Come on. Harmless. HARMLESS!!!

2

Secret

After more than 3 hours of trying to make sense of this question by another user, I have tied myself into knots. I am going to just go back to algebra because this is going nowhere

4

Q: How do you prove this very different method for evaluating $\sum_{k=1}^nk^p$

I found the following formula in my previous question. This differs from my previous question in that I want an alternative proof of the below recursive formula for calculating $\displaystyle\sum_{k=1}^nk^p$. Suppose I had a function recursively defined as $$f(x,p)=a_px+p\int_0^xf(t,p-1)...

real-analysis definite-integrals summation recurrence-relations alternative-proof

Recurrence relations are interesting, but the lack of ways to visualise the general case means it is very hard to probe for symmetries

John Rennie

@SolenodonParadoxus ???

Secret

not to mention I knew almost nothing on how integrals behave as an abstract linear operator

Solenodon Paradoxus

In the video that Sir Cumference posted

A guy tries to explain how his question is harmless

Made my day

Sir Cumference

12:02

@SolenodonParadoxus That video is kind of scary

John Rennie

@SirCumference Let's just say I'm quite pleased there is a large ocean between me and him :-)

2

Sir Cumference

He said evolution is physics

Secret

This is what I get when I substitute away all the integrals in the recurrence relation:

$$f_p-x\partial_xf_p+x^2\partial^2_xf_p=x^2p(\partial_xf_{p-1}+f_{p-1})$$

one sign short of being cauchy euler for the LHS!

Sir Cumference

@SolenodonParadoxus @JohnRennie He made a sequel

double slit and Arago spot

►

Solenodon Paradoxus

- The photon is described by QED
- That's what I'm saying - the photon is described by bullshit

Copenhagen made-up crap XDDD

I can't stop laughing

Seriously considering that it might not go away ever

In some individuals the feeling of self-importance knows no boundaries

It appears that the thought that he might not know all of it never crossed his mind

John Rennie

12:13

The belief that scientists deliberately make things complicated to conceal the truth from the masses is more widespread than you might think.

Bernard Meurer

@JohnRennie You're a god

John Rennie

Have you attempted to log in? Does it work?

Bernard Meurer

@JohnRennie I did, and I sent you a message on facebook saying I couldn't. I can ping the server, but I can't RDP into it nor can I telnet it

John Rennie

The only ports open are port 3319 for RDP and 6666-6669 for your chat app.

When you attempted to RDP did you specify port 3319?

Bernard Meurer

@JohnRennie I did

John Rennie

12:24

@BernardMeurer that IP address is wrong.

Bernard Meurer

OMG4

IT WORKS

It's fast!

Sir Cumference

@SolenodonParadoxus Why is he shirtless?

Am I the only one wondering that?

Dude is like a stereotypical caveman, complete with the accusation that physics is magic

John Rennie

C:\Users\Administrator>query user
USERNAME SESSIONNAME ID STATE IDLE TIME LOGON TIME
bernardo rdp-tcp#0 3 Active . 30/11/2016 12:25
administrator rdp-tcp#1 5 Active . 30/11/2016 12:25

Bernard Meurer

It even has Powershell!

@JohnRennie You're a literal god

John Rennie

@BernardMeurer Only 2GB memory - that will be the limiting factor. That's the trouble with VMs. It's easy to get CPUs fast enough to handle lots of VMs, but buying enough memory is expensive.

Bernard Meurer

12:28

@JohnRennie Last server we were using had 1GB :P

John Rennie

Anyhow feel free to play. I've left a folder on the desktop with various info in it.

Bernard Meurer

As long as you don't try and compile GCC it works

heather

hello everyone

John Rennie

To be fair 1GB goes farther on Linux than on Windows.

@heather do you want access to Bernardo and Daniel's play development server?

Ramanujan

@heather hello (^ム^)

heather

12:29

@JohnRennie, that would be cool, but I think the chances of me breaking something are a bit high =) what are they doing on it?

John Rennie

> what are they doing on it?

Playing :-)

heather

=D that's awesome

John Rennie

So breaking it isn't an issue. Anyway i have a backup

heather

okay. if they don't mind, then sure!

John Rennie

How do I get the user credentials to you without showing them in plain text here? E-mail? Facebook?

heather

12:32

probably email, but its not in my SE profile

user228700

> Cyclonic storm ‘Nada’ heads towards TN coast, heavy rains expected in Chennai from Dec 1

user228700

Oh, crap.

Sir Cumference

@JohnRennie By the way, just wondering

heather

@Kaumudi, hello =)

Sir Cumference

Why didn't you run for mod earlier?

user228700

12:33

Hey :-)

John Rennie

@heather E-mail me at [email protected] and I'll mail you back with the details.

heather

@JohnRennie, okay =)

Bernard Meurer

@JohnRennie It's not a problem until we break out of ring -1 and escalate our privileges and control your brain

Sir Cumference

@JohnRennie Ratsauce?

John Rennie

@BernardMeurer I have placed a potato restriction zone round the server :-)

2

Bernard Meurer

12:34

Goddammit, my powers are useless now

Sir Cumference

Goddammit, that excruciating pain when you stub your toe so hard it bleeds

heather

a potato restriction zone, lol

John Rennie

Monty Python, Season 3, Episode 4 - 2

►

1:30 in

heather

@JohnRennie, email: sent

Bernard Meurer

Okay folks, I gotta head to class, I'll be back to play later tonight, catch y'all later

heather go check the github repo, it now has arbitrary precision

(The Collatz computer)

Qmechanic

12:37

@SirCumference : FYI, the video refers to Phys.SE question #196812 (visible by 10k+ users only).

John Rennie

@heather you have mail

Sir Cumference

@Qmechanic Can't read it :/

heather

@JohnRennie, thank you =D

Sir Cumference

@Qmechanic I know only 10k rep people can read it

Ain't one of those people

Screenshot?

John Rennie

@heather you'll need an RDP client. I'm pretty certain there will be one available for the Chromebook. Bernardo and Daniel can help if you run into problems.

heather

12:42

@BernardMeurer, okay

@JohnRennie, oh, so it isn't something I install on the linux side of my system but on the chrome side?

John Rennie

@heather ah, I had forgotten your Chromebook dual boots linux. On linux I think the app is called rdesktop. See rdesktop.org

Swapnil Das

Hello, minds!

Solenodon Paradoxus

@SirCumference I know right

John Rennie

@heather I have absolutely no idea what incantation of apt-get installs rdesktop, though Bernardo will know.

heather

i could use that, or i could use this which is for the chrome side...which would be better?

@JohnRennie, okay. =)

John Rennie

12:46

An RDP Chrome app will work fine, but it's $9.99 and rdesktop is free :-)

Solenodon Paradoxus

@SirCumference anyway it looks like he's on drugs

John Rennie

@heather Why not try the seven day free evaluation of the Chrome app and see how you like it?

Solenodon Paradoxus

@SwapnilDas Hi

heather

oh, its 9.99, i hadn't noticed that...

Swapnil Das

Some questions on theoretical physics education, if someone cares to answer:

Does condensed matter theory take lesser time for PhD than GR?

Time is here average time.

And can both fields be related to one another, possibly?

John Rennie

12:50

@SwapnilDas no-one does PhDs in GR these days. It's too mature a subject. You might use GR in a PhD on cosmology or string theory or whatever but GR wouldn't be the main subject.

Swapnil Das

Doesn't GR have unsolved problems? @JohnRennie

John Rennie

On the other hand condensed matter is a booming subject and a PhD in it will make you highly employable.

Solenodon Paradoxus

@JohnRennie a fellow of mine did PhD in numerical relativity

Swapnil Das

@SolenodonParadoxus if it doesn't hurt you, could you tell me what's that?

John Rennie

@SolenodonParadoxus I can't comment. I just get the impression that post-docs in GR are few and far between.

Swapnil Das

12:52

And yes, any relation in the two fields?

Solenodon Paradoxus

@SwapnilDas it won't, but I don't think I can put it better then wiki

Numerical relativity

Numerical relativity is one of the branches of general relativity that uses numerical methods and algorithms to solve and analyze problems. To this end, supercomputers are often employed to study black holes, gravitational waves, neutron stars and many other phenomena governed by Einstein's Theory of General Relativity. A currently active field of research in numerical relativity is the simulation of relativistic binaries and their associated gravitational waves. Other branches are also active. == Overview == A primary goal of numerical relativity is to study spacetimes whose exact form is not...

Swapnil Das

Haha, was seeing that.

Solenodon Paradoxus

However, I agree with @JohnRennie that PhD in condensed matter will make you highly employable

Swapnil Das

Employed in?

If it would be industry , then a big no.

John Rennie

@SwapnilDas Both academia and industry.

Solenodon Paradoxus

12:55

@SwapnilDas take a look at this paper
https://arxiv.org/abs/1206.4276

Its the best example that I know of how condensed matter and high-energy physics (including gravity) are connected

John Rennie

Actually industry doesn't really care what PhD you have as long as it isn't completely unrrelated. As far as most companies are concerned the PhD just means you're bright and hard working, which is obviously good for them.

Swapnil Das

@JohnRennie I saw some papers. It is more of materials than fundamental physics :(

John Rennie

But when you're looking for post-docs you'll find far more openings in condensed matter than GR.

@SwapnilDas no, no, no :-)

Try reading Witten's papers on symmetry breaking and superconductivity and tell me it's all just materials :-)

Swapnil Das

Witten in CM!

John Rennie

6

Q: Seiberg-Witten theory and Superconductivity

There seems to have some (deep) relation between Seiberg-Witten theory and superconductivity. e.g. this Witten paper. Q: Could someone introduce the relations between the twos both physically in terms of intuition? and mathematically in terms of formalism? How exactly is the relation?

quantum-field-theory string-theory research-level superconductivity seiberg-witten-theory

Swapnil Das

12:59

@SolenodonParadoxus thanks for the paper. Is there a special name for their junction?

Solenodon Paradoxus

@SwapnilDas luckily for us, it is pretty legal to change the research subject :)

Swapnil Das

Oh!

Solenodon Paradoxus

My advice will be - don't worry that you'll "get stuck" with condensed matter.

But the choice is ultimately yours and nobody should have to make it for you :)

Swapnil Das

I even don't like it that much.

Solenodon Paradoxus

Well you have your answer, then)

Swapnil Das

13:01

I like gravitational physics :)

Solenodon Paradoxus

Yes, but it's been stagnant for quite an amount of time

Swapnil Das

That's sad.

Solenodon Paradoxus

I'm willing to bet that the situation will change in 15 years though :)

Swapnil Das

@JohnRennie silly question. Do condensed matter theorist have to study organic chemistry?

@SolenodonParadoxus Golden words. I'll be 30 then ;)

Solenodon Paradoxus

You're 15 years old and you are choosing a PhD topic? :D

Swapnil Das

13:03

Nah :P I just get hooked with physics.

On my own right, I'll be 16 on Monday :)

@SolenodonParadoxus is Ads/CFT a research topic?

Solenodon Paradoxus

@SwapnilDas it is obviously

Swapnil Das

Yay!

Physics is so beautiful.

Sir Cumference

Is there a formula relating the refractive index and the speed of sound of a medium?

Swapnil Das

I don't think speed of sound and optical density of a medium are related. Moreover speed of sound in a given medium is a specified speed(at a given temperature) and not relative like RI.

Andras Deak

@DanielSank I'd argue that one should write new projects in python 3 (except a few very rare cases), and should even consider porting existing ones. For the same reason you said: so that we don't end up with "most code being python 2" when they pull the plug;)

The python wall of superpowers (née wall of shame) shows that the vast majority of packages are available in python 3, and some scientific projects are pledging to abandon python 2 :)

also, hi

Bernard Meurer