The h Bar

1:25 AM

AdS has $\mathbb R^n$ as a cover yes

pZombie

2:00 AM

Is inertial mass an emerging property?

2:10 AM

@ACuriousMind what on Earth is this sentence supposed to mean?

amazon.com/methods-general-relativity-obshchey-otnositelnosti/…

Oh no

It's in Russian

@ACuriousMind "Es möge $\vartheta(x,y,z)=\vartheta(\tau)$ eine in $T$ und auf dem Rande $S$ von $T$, kürzer in dem Bereiche $T+S$, erklärte beschränkte, integrierbarge Funktion bezeichnen"

I can decipher most of that except for the shorter part and the erklärte part

@Slereah probably full of crank math anyway

Q: First descriptions of ultrastatic spacetimes?

It's Petrov!

Of the Petrov classification

Not some crank

0

What's the first appearance of ultrastatic spacetimes (that is, spacetimes with a metric of the form $ds^2 = -dt^2 + h$, with $h$ a Riemannian metric)? The oldest reference I can find on the topic is Fulling's 1977 paper "Alternative vacuum states in static space-times with horizons", but from th...

plz halp

@Slereah is that stronger than static?

Yes

2:24 AM

why

The timelike Killing vector is constant

constant in what sense?

you can always adapt coordinates to a Killing field and make it constant

Constant norm

It has some nice properties

For ultrastatic spacetimes, null rays basically follow optical paths

you can just extremize the distance using Fermat's theorem

Loong

6:31 AM

Fog at −4 °C; I should stay at home today.

We have a storm on the way. There are currently flood warnings in force!

Captain Bohemian

it's 22 C here now; I feel it's the coolest day after summer. I really hate the desolate atmophere. I wish it's like summer every day here.

Emilio Pisanty

7:02 AM

@JohnRennie is that ophelia? Or had that already passed?

7:26 AM

@EmilioPisanty Storm Brian

David Z

7:53 AM

Here it rained yesterday for the first time in about a month

I tested that beamsplitter and it works pretty well

I need to make a support for it though

Mithrandir24601

@EmilioPisanty Pfft - Ophelia was the nicest day I've ever seen in any October

9:28 AM

@JohnRennie it was a partial success I guess

How was it?

And how did you cook it? In a skillet?

Yeah. I forgot to use butter. It dawned on me when it was too late.

It was ok. Not as good as standard Schnitzel

Butter isn't essential, but it makes the schnitzel richer.

Hmm, should we uppercase German nouns when using them in English ...

It looks more like fried chicken than Schnitzel. I have to look up an actual recipe. There must be a trick for making the coating

I put them in flour, then egg, then flour again

I think that's all my Mum does.

9:31 AM

gyazo.com/53d5cdbb9db0efca0a581e3db08ab8a1

Just dip the beaten out chicken in egg yolk then into a disk of flour.

Oh I used the whole egg

Maybe it's the whole egg. Now I think about it I'm not sure.

@0celo7 that looks about right, but I would have cooked them more to get a browner finish.

@JohnRennie it wasn't getting any browner!

I made two rounds and the second ones just started burning but were still white. It was strange.

Oh well. Maybe try using butter next time? Or just not bother and stick to what you know you like :-)

9:38 AM

@JohnRennie I'll reheat the leftovers in butter

I have to go to VA in a few minutes to prove I'm still alive. Fucking bureaucracy

On a Saturday?

@JohnRennie I can't very well go on a day trip out of state during school

VA = Virginia?

Yeah

Voter registration? Or some such thing? Why would Virginia care that you're at college out of state?

9:44 AM

I stupidly let my driver's license expire which is legally equivalent to dying

Ah :-)

That's why I'm up at an ungodly hour

Gotta get there early

DEFCON 19: Steal Everything, Kill Everyone, Cause Total Financial Ruin! (w speaker)

10:01 AM

Security conferences are pretty great

►

@JohnRennie What value of $R$ should I take in Arrhenius equation?

@Abcd 8.31 isn't it?

@JohnRennie Yes, I used that but then I got the right answer $\times 1000$.

That's the correct value for $R$ so the error must be somewhere else.

Let me share the question (PS: It's very easy.)

$\ln k_1 = \ln A - \dfrac{Ea_1}{RT}$

$\ln k_2 = \ln A - \dfrac{Ea_2}{RT}$

We want to find $Ea_1 - Ea_2$

$\therefore \ln\dfrac{k_2}{k_1}\times RT = Ea_1 - Ea_2$

Which yields $9,491$ instead of $9.491$

$k_2 = 2 \times 10^{-2} $ and $k_1 = 5 \times 10^{-4}$, $R = 8.3$

Is there any error @JohnRennie?

I don't think so...

$T = 310 K$

10:16 AM

Why did someone star my timelike killing vector

It is not very memorable

@Abcd I get 35.5kJ/mol

@JohnRennie It's correct (because you will have t subtract from 45 after that). But how is my method wrong?

to*

You say Which yields $9,491$ instead of $9.491$, but $9491$ is correct isn't it?

I suspect you're mixing up kilojoules with joules

@JohnRennie how can 9491 kJ be correct?

$9491$ joules is correct

10:22 AM

@JohnRennie Yes obviously... But doesn't my method yield the answer in $kJ$

12 mins ago, by Abcd

$\therefore \ln\dfrac{k_2}{k_1}\times RT = Ea_1 - Ea_2$

Doesn't this give answer in kJ?

because we take $R$in $kJ$

we took $T$in $K$

R is 8.31 joules per mol

OH! It's wiki's fault @JohnRennie they say it's in kJ/mol

Gas constant

The gas constant (also known as the molar, universal, or ideal gas constant, denoted by the symbol R or R) is a physical constant that is featured in many fundamental equations in the physical sciences, such as the ideal gas law and the Nernst equation. It is equivalent to the Boltzmann constant, but expressed in units of energy (i.e. the pressure-volume product) per temperature increment per mole (rather than energy per temperature increment per particle). The constant is also a combination of the constants from Boyle's law, Charles's law, Avogadro's law, and Gay-Lussac's law. Physically, the...

See the table on the right.

Yes there is an error in the tble on the right, but the above from the main text is clear.

10:27 AM

Yes, I was checking from the table directly. (PS: I didn't notice that they had given same values for J and kJ)

Anyway, thanks for the help.

Emilio Pisanty

10:53 AM

@Abcd I don't see the discrepancy

1 J/mol = 1 kJ/kmol

Cc @JohnRennie

@EmilioPisanty oh yes :-) I hadn't noticed the kmol :-)

Student404Mus

Hi all

Giving units as kilojoules per kilomole seems a remarkably silly thing to do.

Student404Mus

My question about Christoffel symbols

Shoot

Student404Mus

11:06 AM

Taking an example of cylinder with constant "ro" or r then we calculate the gradients of basis vectors which are only e_z and e_theta and we find: d_theta e_theta= -ro e_ro why?

So the coefficients vanish for a cylinder

12:03 PM

Time to see if the government recognizes me as a human

@BernardoMeurer at the DMV in Virginia

Good news: I am still an American human.

Anonymous

@0celo7 Alive?