The h Bar - 2016-09-09 (page 4 of 4)

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4:00 PM

@0celo7 bummer :-(

JohnRennie, I have that black hole quesiton for you

> We knew that black holes have entropy proportional to the area of the event horizon. But since the no hair theorem is generally regarded as true (thus a black can be characterise by its angular momentum, charge and (forgot)), what are those microstates that store all that entropy of a black hole actually is?

@Secret No-one knows how the entropy is encoded onto a black hole. There are ideas based on AdS/CFT that I don't understand and there is a recent paper by Hawking et al suggesting it's supertranslation modes, which I also don't understand.

@JohnRennie I got a charger for a smaller Mac from the library, currently trying to bootstrap a small charge from it.

ok thanks, I will get a read then

I've got a programming exam at 3:30 that I need my laptop for.

4:06 PM

@0celo7 $80 for a replacement charger seems very steep ...

user218912

@0celo7 what book does your qm course use?

@3075 Sakurai, Cohen-Tannoudji, Goldstein for background.

user218912

what year is it again?

Second

user218912

second year using sakurai???

user218912

4:13 PM

whaaat

Well, I'm second year

user218912

I asked what year the course is

The students are mostly new grad students

user218912

I know you're second year.

user218912

exactly

4:14 PM

It's required for them, and we're all bored as shit

user218912

lol

user218912

obv

@BalarkaSen : polite cough... Maths is not a science. Hence when you do a maths degree in Cambridge, you get a BA. Ergo mathematics is an art.

The course is meant as a second course in QM but the prof is teaching it like a first.

Quite annoying

There are a bunch of people who obviously haven't had QM through

They're ruining it for everyone else

user218912

@JohnDuffield it's a B.Sc in most other universities.

4:21 PM

@0celo7 BTW you remember that stuff I was babbling about Reissner Nordstrom black holes? Well the point of zero four acceleration turns out to be where the horizons merge for an extremal RN black hole.

How have I not blocked JD? I'm such a patient person

@JohnRennie Hm.

I'd have to look at a book to recall what that means

What book would I have to look at

Which actually makes a lot of sense. It isn't really anything very surprising.

But it was kind of fun to play with.

user116211

@3075 It's B.A. here.

user116211

I never thought there was BSc. in Maths.

user218912

it's b.sc here.

4:24 PM

Cambridge awards BAs for science as well as maths.

user218912

I'm gonna be dumb and take qft again this year.

user116211

@3075 oh, okay.

Or at least it did in 1983 because I got one :-)

I think the way the degree works there has changed in the intervening 33 (gulp) years.

It's now a four year course because the youth of today are too crap to do it in three years like their ancestors did :-)

@3075 Why?

I bet you can't do my QM homeow

PHONE

user218912

wanna bet

4:27 PM

WHY ARE YOU BREAKING

@0celo7 Ho meow? Rappers name for a female cat?

user218912

xD

user116211

> In practice, this is essentially equivalent to a Bachelor of Science or Bachelor of Arts degree with a speciality in mathematics. Relatively few institutions award Bachelor of Mathematics degrees, and the distinction between those that do and those that award B.Sc or B.A. degrees for mathematics is usually bureaucratic, rather than curriculum related.

user116211

> However, schools that offer Bachelor of Mathematics degrees argue for a separate degree, maintaining that the study of mathematics is vastly different from other fields.

user218912

waterloo offers a b.math.

user116211

4:29 PM

@3075 ah! I never heard of that, actually.

@JohnRennie Turns out respectable women don't like to be called that.

Even when it's meant affectionately

@0celo7 Who knew? :-)

I do, now.

Ok I have give a skim of that paper, while I have at least 90% of the stuff I don't really understood, it seems supertranslation modes are modes that arises due to there are multiple degenerate vacua at the black hole's horizon due to some kind of charge conservation laws

Basically, some symmetry breaking stuff result in the blackhole to have more degrees of freedom that scales with area

and they are all degenerate with the vacuum

@Secret: I think you should bear in mind that the idea has not attracted widespread support, even with Hawking and Strominger's names attached!

4:33 PM

Hawking is a crackpot.

Well considering I just said I have 90% of the stuff I don't understood, I am not sure whether I am convinced it meake sense to me, let alone whether I thought I know or not it make snes to me

Anyway, following that thought pattern above, it leads me to this PSE question

17

Q: Is the Ground State in QM Always Unique? Why?

I've seen a few references that say that in quantum mechanics of finite degrees of freedom, there is always a unique (i.e. nondegenerate) ground state, or in other words, that there is only one state (up to phase) of the Hamiltonian with the minimum eigenvalue. My questions: Q1) Is it true? Q2...

quantum-mechanics hamiltonian

this is because my possibel naive thought that the vacuum is a groudn state

4:51 PM

In mathjax can you put a little dot above, the way some use as notation for dx/dt?

@SpaceOtter use \dot

Thank you

user116211

@SpaceOtter Just a quick note,

user116211

1518

Q: MathJax basic tutorial and quick reference

To see how any formula was written in any question or answer, including this one, right-click on the expression it and choose "Show Math As > TeX Commands". (When you do this, the '$' will not display. Make sure you add these. See the next point.) For inline formulas, enclose the formula in $......

discussion faq mathjax reference

I've since found the Mathjax tutorial on Maths meta if that's what youre going to say

Oh right...

user116211

4:54 PM

@SpaceOtter oops ;P

But thanks

@JohnRennie Does using a smaller charger to charge my large laptop damage the battery

@0celo7 No.

@JohnDuffield That's fair.

I do not disagree.

In fact I like to think that's the major difference between mathematics and physics, the former is an art and the latter is a science. I didn't want to spell it out because that's a personal, not really a particularly logical belief.

@0celo7 Assuming your Macbook (or whatever it is) recognises the charger it will automatically make any adjustments necessary to charge the battery safely. Using a small charger just means that the laptop may take longer to charge.

5:05 PM

@JohnRennie Ok. It's not even taking that long (because I'm not using it)

It's at 88%

More than enough until I can run to the Apple Store later.

@0celo7 OH MY GOD when it reaches 89% it will EXPLODE VIOLENTLY!!

CLEAR THE AREA!

HOLY SHI

And that's the last we heard from 0celo7 ...

rip

Something tells me chat will be significantly quieter without him

5:07 PM

And peaceful.

@0celo7: if you can heat cerium and conc HF to 1700C in an oxygen atmosphere with a bit of plutonium added for extra flavour and survive, then I doubt you have much to fear from a laptop charger.

It's all good, guys.

I threw it into the HF storage area, which is explosion resistant.

:-))))))))))

@BalarkaSen No such luck for you.

Couldn't you just unplug it? That would prevent it from reaching 89%. (0.0)

5:11 PM

I...didn't think of that. Crap.

XD

Now it's covered in HF. Not good.

HF is explosion resistant?

As in Hydrogen Fluoride?

user116211

Jun 10 at 16:16, by 0celo7

I'm clearly the reason this chat exists

5:11 PM

HAHAHA!

@SpaceOtter No Heegaard-Floer.

hydrofluoric acid

@BalarkaSen No, but we keep it in a bomb proof safe.

@BalarkaSen I never know when to take mathematicians seriously...

Mathematicians do not know how to joke.

They don't even know how to fun.

They claim the foundations of math have to be reworked for it.

This is how I feel @BalarkaSen

Later folks

5:17 PM

@BalarkaSen wow that actually exists. I bet you could choose any two words, including made up ones, and hyphenate them and there would be a theorem matching that name.

The Einstein-Trump theorem?

How about Xenophillius-Zodiac?

The Bumpack-Flatus theorem.

Quasilinear-Xenomorph?

Bumfuck-nowhere theorem

No

5:20 PM

@0celo7 John's hand twitches towards the delete link ...

@JohnRennie You won't.

I wish I could imitate SLJ

I would double dare you

@0celo7 I might if I hadn't also used the word bum two posts earlier. I didn't use the f bomb though ...

On that tasteful note I'm going to retire for the evening. see you all at 5 a.m. tomorrow.

5:49 PM

@yuggib Topology prof used AoC, what do?

I do not understand Jech.

I cannot accept the AoC.

6:08 PM

@0celo7 read the book "the axiom of choice" by Herrlich

And everybody in mathematics uses the axiom of choice in one form or another

(Maybe not full choice, but very few use only finite choice)

6:26 PM

@yuggib Why should I read the book...My very soul disagrees with AoC

7:01 PM

Gravitation is $500 for the book (!?)

not very surprising, by now it is relatively ancient book

@0celo7 nah

Nobody disagrees with choice

Per se

7:24 PM

it is possible not to like some of its consequences

7:36 PM

apparently MTW is out of print

:(

8:03 PM

@yuggib I do.

@GPhys It's not a good book.

Way too much physics. Not rigorous.

A GR book without geodesic balls is for girls!

user218912

9:02 PM

but what if you're a physicist

9:12 PM

@3075 Why would you want to do that?

user218912

because physics is fun :D

@3075 You poor soul.

10:08 PM

Hi, everybody.

Hi :-)

10:33 PM

Avertisement:

3

Q: How does one compute the state of a quantum system following imperfect measurement?

Suppose I have a quantum system $S$ ("system") with Hamiltonian $H_S$ and initial density matrix $\rho_S(0)$. I allow $S$ to interact with another system $P$ ("probe"), which has Hamiltonian $H_P$ and initial state $\rho_P(0)$, via an interaction Hamiltonian $H_I$. Then I measure $P$ in the basis...

quantum-mechanics quantum-information measurement measurement-problem density-operator

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The h Bar

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