The h Bar

0celo7

13:00

Do they

What does diff geo mean to them

Slereah

Well somewhat similar to Hawking Ellis, really

But back then I was not quite yet up to that

0celo7

No, Hawking Ellis is not real diff geo

Slereah

Nihal Jalaluddin P

12 2

0celo7

Diff geo is the study of principal bundles.

Slereah

Is that guy old enough to be on SE

HE discusses bundles a bit

Tho not as much as a gauge gravity book

0celo7

13:03

I think Sharpe's book is about as close as you can get to REAL diff geo

Slereah

I've read gauge gravity stuff, it is not a very pleasant read

They're the kind that start with LET X BE A SOLDER FORM ON A PRINCIPAL BUNDLE BLA BLA BLA

0celo7

I wonder if thermodynamics is a principal bundle

Slereah

Don't think so

Not quite sure what it is

I remember the state space being a contact manifold but not much beyond

0celo7

Oh fuck it's snowing

Slereah

arxiv.org/pdf/1111.5056v1.pdf

let's see

"The equilibrium manifold is defined by using a harmonic map which includes the specification of the fundamental equation of the thermodynamic system."

Just the abstract is driving me to madness

"Consider G as a non-degenerate metric on T ."

Oh no

Thermodynamic metric

I can't wait to see the temperature-pressure tensor

I just did a search, the word "temperature" does not figure at all in the text

I suspect this is too hard for me

Oh wait, they do reference it

just as T

the horror

skull petrol

13:16

"That last LinkedIn request set a new record for the most energetic physical event ever observed. Maybe we should respond." "Nah."

the horror

Slereah

The metric of the ideal gas law

"Do gravitational waves corresponds to aether wind?"

Make it stop

skull petrol

It has just begun.

Slereah

Usually when there's a big announcement there's about 2 months of stupid questions

I wonder if we could do an analysis of this

look up all the questions on FTL neutrinos, EM drive, etc

See the time distribution

skull petrol

Good idea.

Slereah

although the stupid ones are deleted

So hard to check

skull petrol

13:25

Yup

Slereah

Oh god a thermodynamic curvature

Secret

https://www.google.com.au/search?q=thermodynamic+curvature&oq=thermodynamic+curvature&aqs=chrome..69i57&sourceid=chrome&es_sm=93&ie=UTF-8

Try google and you will be amazed at the sheer number of them

Slereah

"We see that the scalar curvature diverges at the critical points determined by the algebraic equation P V 3 −aV + 2ab = 0. This is exactly the equation that determines the location of first order phase transitions of the van der Waals gas [5]. Consequently, a first order phase transition can be interpreted geometrically as a curvature singularity."

Thermodynamic singularity D:

"This is in accordance with our intuitive interpretation of thermodynamic curvature."

I don't have one, what do I do???

Apparently thermodynamic curvature is linked to the notion of interaction in the system

So ideal gas has curvature 0

It is the thermodynamical minkowski

0celo7

@Slereah link me this shit

I smell another thesis topic

Slereah

13:42

arxiv.org/pdf/1111.5056v1.pdf

0celo7

I wonder if this has any GDP applications

Slereah

Doubt it

The usual thermodynamic methods are perfectly servicable

Secret

actually where does the notion of thermodynamic gravity came from. I knew that there are a small group of researchers working on this all over the world?

Slereah

Do you mean like black hole thermodynamics

Secret

like why is gravity believed to be tied to entropy for these guys?

0celo7

13:45

They're probably insane.

Secret

Entropic gravity

Entropic gravity is a theory in modern physics that describes gravity as an entropic force—not a fundamental interaction mediated by a quantum field theory and a gauge particle (like photons for the electromagnetic force, and gluons for the strong nuclear force), but a probabilistic consequence of physical systems' tendency to increase their entropy. The proposal has been intensely contested in the physics community but it has also sparked a new line of research into thermodynamic properties of gravity. == OriginEdit == The probabilistic description of gravity has a history that goes back at least...

Slereah

Oh that one

It stems from a pretty old idea, IIRC

Gravity just being a consequence of motion rather than a force by itself

0celo7

There is no motion in spacetime, @Slereah

Ben Crowell said so!

Secret

hmm...ok...

Slereah

Quantum gravity theories are a dime a dozen

Secret

13:49

Wow, is this the same lubos that roams around the PSE?

Slereah

Yes.

Secret

Have not read the paper in detail yet, but my gut feeling suggest they are kinda trying to massage thermodynamics in terms of geometry, like how gravity is explained as spacetime curvature in GR

Not sure if their apporach is sensible, but I guess as long they have the correct manifold, anyting can be described in terms of geometry, right?

Slereah

Pretty much

Might be useful to generate theorems

0celo7

Or calculate heat flow in something GDP worthy

Is there a journal of engineering physics?

Today is Lincoln's B day, thanks iPhone.

So my roommate didn't come home last night

Secret

Ouch, my generalisation gone overdrive and end up asking a question that is equivalent to asking how to achieve omniscience

I didn't expect I tread so far out into the muddy waters...

Slereah

14:05

@0celo7 Tons, probably

Secret

For more insane stuff, last night I dreamt about gravity aliens. Basically lifeform like spacetime warping, thus the way spacetime is warped is their 'body'

Guess my brain got overdrive by the LIGO announcement under the hood...

Slereah

Geon creatures

Secret

---
https://www.youtube.com/watch?v=72LWr7BU8Ao

Why oh why fluid mechanics has so many parallels with gravity?

I mean look at 0:37 for example, isn't that reminds you of a wormhole in the rubber fabric analogy?

John Duffield

@Secret : I wouldn't spend any time on entropic gravity if I were you. General relativity is one of the best-tested theories we've got. I recommend you read the Einstein digital papers instead. It's actually quite easy to understand what a gravitational field is, and why things fall down. And that understanding will tell you it's absolutely nothing to do with entropy.

Slereah

Both are nonlinear fields

that's about it

Not a whole lot more in common

Secret

14:16

@JohnDuffield Well I never said I spend time on entropic gravity. the youtube clip just reminds me of the various analogous systems in solid states that can simulate string theory stuff

@Slereah I see

Slereah

They don't have any more in common than with EM

Secret

@JohnDuffield Btw guess what Gravity waves now detected. That's Einstein's prediction

@Slereah I see, I guess that justhappen to be mathematically simailr because they are nonlinear then

Slereah

Not even that, in this case.

nothing particular about vortexes specific to fluids

Secret

ok. Still kinda interesting by itself though. Never thought about a tunnel will form beneath the whirlpools

Slereah

also not much to do with wormholes, either

John Duffield

14:19

@Secret : see You Are Made of SpaceTime by Sundance Bilson-Thompson, New Scientist August 2006.

Secret

@Slereah ok

@ Slereah (This statement is intentionally cryptic. You will understand it in time) I love when misaligned things loop closed because nature decided to give just the very thing they believed to be

@JohnDuffield Well that does not really fit the gravity alien stuff I dreamt because we, human beings are opaque to EM radiation

John Duffield

@Secret : we aren't opaque to X-rays.

We are made of electrons. (And other things too, but start with electrons). Electrons can be made out of photons, in pair production. And photons have an E=hf wave nature. A photon is not some billiard ball thing, it's a wave in space. And they don't call it the wave nature of matter for nothing.

Secret

@JohnDuffield Yes, but we are opqaue (and actually radiate) pretty much everythign else) (take IR as an example), but a gravity lifeform is hypothetically somethign composed entirely of spacetime curvature that cannot be detected via their photon emission at all

Secret

15:34

https://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion
How does spontaneous parametric down conversion ensure the photon polarisation from the two cones of trajectories must be correlated and how the phase must be matched. What conservation law allow these to be possible?

Secret

15:47

user116211

@ACuriousMind: Can you tell me why a trajectory never intersects with itself during time-evolution?

user116211

> A trajectory in the phase space corresponds to the time evolution of the microstate. This
trajectory never intersects with itself since the solution of the system of equations of
motion is unique given certain initial conditions (self-avoiding random walk).

ACuriousMind

@user36790 The text already tells you - because the solutions to the equations of motion are unique

user116211

@ACuriousMind Oh! The microstates never repeat themselves during the time-evolution?

ACuriousMind

@user36790 It doesn't say that. A closed curve is not a self-intersection.

vzn

15:58

@Secret thx for link on entropic gravity, hadnt seen it. gravity/ relativistic effects have a lot of similarities/ analogies to density in thermodynamics. it appears to relate to a "density of spacetime" so to speak. & if you think thats wild, look into solitons...

0celo7

@ACuriousMind Is Picardy Lindelhofer a global theorem

ACuriousMind

@0celo7 no

0celo7

@ACuriousMind Ok, that's what I thought

What are the conditions for it to be a global theorem

Slereah

Good old Picard Lindyhop theorem

0celo7

16:13

@Slereah did you ever figure out the homotopy proof

Secret

@vzn the probelm is entropic gravity has a lot of experiment constraining it strongly thus it might be dead end.

But anyway one must know the basics before trying to tackle the advanced, I should sharpen my GR first and then investigate it later if time

Secret

@Secret .

A report on trying to better understand quantum interference
--WARNING POTENTIAL NONSENSE--
(See linked pics by the reply for context of the report)
Ok, it appears that 3 weeks back then I was unawarely really thinking about some variation of the delayed choice experiment when inspired by the feymann lecture and the notion of paths

This is the reason I was interested in how fast the hamiltonian detect the experimental setup became practically a different one (because mathematically speaking the states for each setup lies in different hilbert spaces) because of raising and lowering the det…

0celo7

How the hell can a closed curve cross a surface and odd number of times???

vzn

@Secret from wikipedia on entropic gravity, no small feat, the basis for its study:

> In 1995 Jacobson demonstrated that the Einstein field equations describing relativistic gravitation can be derived by combining general thermodynamic considerations with the equivalence principle.[1]

0celo7

*an

@ACuriousMind So if $X$ is compact, then $\pi_Y:X\times Y\to Y$ is proper. Suppose $Y$ is compact, then $\pi^{-1}_Y(Y)=X\times Y$ is compact because $\pi_Y$ is proper?

By induction, if $\{X_i\}_{i\in I}$ are compact, then $\times_{i\in I}X_i$ is compact?

Slereah

16:27

@0celo7 I did not

I should write an email to Ellis

Tho I don't have a good track record of getting answers from famous scientists

0celo7

@Slereah You want me to ask my adviser, he's taught out of HE before

He might know

@ACuriousMind Oh, $I$ has to be a finite set.

Secret

Corrections (missing line between "Therefore it become interesting..." and "as we have observed in experiment") Combining both parts together, then we have the paths evolving determinstically as according to the hamiltonian (hence satisfy the schrodinger equation) with the randomness in which path the particle decided to choose
(because we never detected half of a particle, we only either have detction or no detection, even though repeated number of particles hitting the detector eventualyl build up a probability distribution

Slereah

@0celo7 Would be nice

0celo7

HE is one of the books he has on his "next to desk" shelf, actually.

Slereah

globaljournals.org/GJSFR_Volume13/…

Secret

16:32

@Secret and thus sometime in the future, in order to complete this analysis, I will need to figure out what are the missing bits I have not fully understood yet

ACuriousMind

@0celo7 Yes, what is the question?

0celo7

@ACuriousMind What

Is my reasoning for the compactness of $X\times Y$ correct?

My second question is if the case for a general finite product is simple induction.

ACuriousMind

@0celo7 Ah. Yes.

Secret

@Slereah I am guessing that using a similar argument that thse hydrodynamic system act like the quanutm ones might be because both systems are quite linear?

0celo7

Oh boy, Theorem 9.4 is going to be rough.

@ACuriousMind Ugh, I already don't understand (1)-->(2)

For there to be a contradiction, one must show that the $U_x$ form an open cover, this is not clear to me.

@ACuriousMind So are we saying that we can find such a $U_x$ for all $x\in X$?

Because no $x\in X$ is a limit of $(x_n)$ (or a subsequence thereof)?

ACuriousMind

16:43

@0celo7 I have no idea which "we" or which "Theorem 9.4" you are talking about

0celo7

@ACuriousMind Bredon, Theorem 9.4 on page 25.

Hmm, is this an alternative proof of Bolzano-Weierstrass? By Heine-Borel, a bounded sequence is contained in a compact set.

ACuriousMind

@0celo7 Yes

@0celo7 Yes, this is a generalized version of Bolzano-Weierstraß

0celo7

You and your fancy s

Secret

Still have not wrap my head around this guy in the context of hilbert spaces...

0celo7

@ACuriousMind Why does the nonexistence of an $\epsilon$-ball covering allow us to pick the $(x_n)$ so that $d(x_i,x_j)>\epsilon$ for $j<i$?

(this is part two of the proof)

ACuriousMind

16:54

@0celo7 Because if you couldn't pick them like that, that would imply existence of the $\epsilon$-ball covering.

0celo7

@ACuriousMind I know that, why?

@ACuriousMind It's intuitively clear to me, I don't know how to make it precise.

0celo7

17:12

@ACuriousMind Basically, given any sequence $(x_n)$ that fails that condition, one constructs an $\epsilon$-ball covering by centering a ball at each $x_n$ until we get a covering?

@ACuriousMind I don't know how to show that this will be finite, though.

msh210

Just came across this...

5

Q: What theoretical predictions took the longest to be experimentally confirmed?

Looking forward to Einstein's general relativity centennial in 2015, I was thinking about how cool it would be if LIGO detects gravitational waves in 1916 (centennial of Einstein's "weak field" paper) or more likely 1918 (centennial of his quadrupole formula paper). What are other examples in ph...

history big-list

ACuriousMind

@0celo7 If you can't pick $x_i,x_j$ with $d(x_i,x_j)<\epsilon$, then the space is already covered by a single epsilon ball.

If you can only pick finitely many like that, then the space is covered by finitely many balls (one around each of the points you picked and one further that contains all the rest.

0celo7

17:30

@ACuriousMind Oh, danke

0celo7

17:43

Why do people say "derive" for "differentiate"?

I cannot believe that a calculus prof would make that mistake.

Someone had to teach them that horrible word -- who?

ACuriousMind

@0celo7 Native speaker?

0celo7

@ACuriousMind Yes, person in my physics lecture.

msh210

@0celo7 It's a fairly natural back-formation from "derivative".

0celo7

@msh210 But surely they've heard "differentiate"!

And "differentiable function"

msh210

@0celo7 Sure.

Slereah

17:47

French uses "dériver"

0celo7

The French lost the war, no one cares what they do.

Slereah

When was the last time the US won a war

0celo7

We've never lost one.

FenderLesPaul

@GPhys UChicago might come out today

Slereah

You haven't had a war on US soil since 1812

FenderLesPaul

17:52

and looks like Cornell sent out a shit ton of rejections today

0celo7

@Slereah Civil war

Slereah

Oh jee, poor you

0celo7

We also had a war or two with Mexico

Slereah

Fighting against YOURSELVES

It's a wonder you won

0celo7

@Slereah No, fighting against the north.

Slereah

17:54

Well don't want to put a damper but you kinda lost at fighting the North

0celo7

Nope

GPhys

18:07

@FenderLesPaul Waiting on U Penn big time and Columbia of course - I hope Columbia doesn't send out rejections late

Also seeing if Brown/UCLA/Boston sends out more today

FenderLesPaul

Seems like Columbia sends out late

GPhys

Yeah QQ

FenderLesPaul

I'm just waiting on UChicago and Princeton at this point

Berkeley doesn't seem like they're sending out anytime soon

@GPhys As an aside, have you contacted any PoI yet at universities?

GPhys

@FenderLesPaul I can't find information on this - is that kosher if I've been accepted? Especially if I mentioned the person in my statement of purpose?

I want to contact someone at NYU but I'm waiting for the 'official' acceptance to come

Slereah

Hm

FenderLesPaul

18:15

@GPhys no idea if it's kosher or not I've been wondering the same thing

Slereah

What was that paper with the generalized theorem on CTCs and homotopy that I found

GPhys

There's also places like Stony Brook where I'm overwhelmed by the number of professors in hep-ex

FenderLesPaul

I just wanted to ask two people at UCSB if I can meet them on visit day because I'm interested in working with them

0celo7

@Slereah I know I proved it using the Frobenius theorem

FenderLesPaul

Visit day is April 7th so I didn't want to wait that long

GPhys

18:16

@FenderLesPaul At Stony Brook in the open house email they ask you to list name(s) of any professors you want to have them schedule meetings with you during the visit

0celo7

do you still know what exactly happened there?

GPhys

That's for the open house, though

FenderLesPaul

@GPhys oh let me see if there's something like that for me

Slereah

@0celo7 Yeah that's the original Godel proof

0celo7

@Slereah link?

FenderLesPaul

18:17

Nope

GPhys

@FenderLesPaul basically Stony Brook has an RSVP they want you to fill out

Slereah

@0celo7 The original Godel paper

GPhys

UC Irvine had basically the same thing

FenderLesPaul

@GPhys btw do you know if stony has sent out all their acceptances?

Slereah

You can lift your fat American arse and google it

FenderLesPaul

18:17

my friend was wondering

0celo7

@Slereah not fat and not American

link?

I don't know what it's called

Slereah

Well then you can google it easily

0celo7

What am I googling?

GPhys

@FenderLesPaul they sent out some yesterday it looks like, but there's definitely hope still

Slereah

Just look at the wiki page for the Godel metric

Jeez

0celo7

18:19

@Slereah please just give me the link lmgtfy.com

Slereah

Do I need to spoon feed it to you like a giant physics baby

GPhys

I somehow got into Stony Brook during their first round of acceptances

ACuriousMind

@Slereah *engineer baby

0celo7

@Slereah yes please

GPhys

Anyway heading out

FenderLesPaul

18:20

@GPhys cool beans

0celo7

@ACuriousMind good, good

@Danu Does GP prove that a non-compact manifold always admits a smooth, regular vector field?

Slereah

18:37

please, stop these gravitational waves questions

I can't stands no mores

ManishEarth

19:12

11

Q: Chemistry — Top User Swag!

We want to congratulate and thank everyone that helped this site and community grow healthily into what they are today! If you can find your name among the top 72 users in the first two pages here, we have a surprise for you! Hoping to get a reaction with that joke... (｡ˇ艸ˇ) We want to se...

discussion featured

best swag ever

It's a mug! It's a beaker! It's superma--oh, no, it's just a mug.

Slereah

I have a mug shaped like a klein bottle

Well like a 3D immersion of a Klein bottle

ACuriousMind

@ManishEarth So, when do we get our physics swag?

ManishEarth

@ACuriousMind three years ago

0celo7

Woot finally getting paid

ACuriousMind

@ManishEarth Guess I'll go build a time machine then...

0celo7

19:15

@ChrisWhite I have to report my income, just filled out my first W4

David Z

Just noticed this:

6

A: What do I need to know about tagging?

How to find out if a tag is good to have/make I present to you, the MAR Tag Test™ (abbreviated as MATT), a short test with three possible responses to each question, designed as a crude way of diagnosing the health of a (imaginary) tag. Imagine X, a tag$\,\ldots$ 1: Ignore spam. Some people ...

which I think would come in quite handy sometimes

user54412

@0celo7 Cushy then

user54412

sometimes schools withhold more than they have to from students' minimal incomes (to be on the safe side of the IRS), forcing people to file just to get their money back

user54412

I know mine let me opt out of giving the government an interest-free loan, but most students didn't know they could

user54412

@FenderLesPaul The more organized and/or smaller departments will try to get you talking to everyone you're interested in working with (unless that person is terrible in real life). But for many departments it helps to be a bit proactive.

user54412

19:27

There's hopefully an internal wiki schedule somewhere, and if you email your point of contact asking to be able to meet with certain people, they can ensure those meetings are scheduled.

FenderLesPaul

@ChrisWhite Sweet thanks

I'll do that now

would it be ok to email two people that you're interested in? Or would that be in bad taste?

user54412

Well, I would actually email whoever the "director of graduate admissions" or whatever sent you the admission -- they're the ones organizing the visit. Just say "I'd like to meet with A and B and C while there. Can this be arranged?"

user54412

This way you avoid scheduling meetings that conflict with whatever else they have planned for you when you visit.

user54412

But if it comes to it you can always email the people you're interested in directly, in which case by all means email both of them.

0celo7

@ChrisWhite $11 an hour

FenderLesPaul

19:34

@ChrisWhite awesome thanks

user54412

@0celo7 more than me then

0celo7

I'll be working 10-15 a week, 20 over the summer and again more in the fall

hours

@ChrisWhite you also work a hell of a lot more than I will

user54412

still not as cushy as library duty

user54412

get paid to sit around and do your homework

0celo7

If I can get on a paper...

Hell, math tutoring only pays $8.50 an hour

And it's probably 10,000 times more frustrating

@ChrisWhite How much do you get paid?

Grad students here make $35 an hour IIRC

@ChrisWhite the limit for having to report is $4000, I will easily pass that

user54412

19:46

uh, we're salaried, not hourly

user54412

I could also make 35 if I just worked less

0celo7

@ChrisWhite well what's the salary?

user54412

when I started grad school, every position in science/engineering was base 22-30k

user54412

I'll let you figure out which end Princeton leaned toward

0celo7

20:01

@ChrisWhite 30k since they charge tuition in firstborn children.

user54412

they charge us tuition too

user54412

>40k to be a grad student

0celo7

oO

user54412

basically, it's a tax on prof's grant money, so grad students here cost as much as postdocs

0celo7

My department waives tuition if you research.

user54412

20:03

but that's just because the administration hates grad students

0celo7

@ChrisWhite Why do they hate grad students?

user54412

undergrads are too precious -- it would be a shame if all these (probably rapey pedophile) grad students got too much attention

0celo7

@ChrisWhite Wait, are you taking a net loss on grad school, financially?

user54412

no, my adviser had to shell out 70k on my behalf

0celo7

What the fuck?

user54412

20:06

plus taxes and healthcare and whatnot

0celo7

Are you even worth that much?

(only half joking)

user54412

good question

0celo7

Do Princeton profs get insane grants?

user54412

cynically, I've seen some pretty incompetent postdocs, so I'm pretty sure I'm worth at least as much as them

user54412

@0celo7 yes

user54412

20:07

at least my department is rich that way

user54412

also, being a princeton astrophysics prof is kind of an ultimate career goal

user54412

at this point, they're interested in community-building and influencing things on large scales

user54412

so they are willing to take on short-term losses that are redeemed less tangibly when their proteges go on to do great things of their own

0celo7

Is your adviser tenured?

user54412

yes

0celo7

20:11

How many profs are in the astro dept at Princeton?

Tenure/tenure track

user54412

~20

user54412

maybe a few less if you discount the permanent researchers who aren't technically professors

0celo7

That's bigger than my department, which is supposedly the largest in the country (in our field).

@ChrisWhite Does Princeton fuck over all grad students in all departments?

user54412

yes

0celo7

That's a shame.

user54412

20:15

in more ways than one to be honest

0celo7

Princeton is supposedly a really good place for fusion.

user54412

still, what really matters in grad school is the department, not the university

0celo7

@ChrisWhite Yes, but if the university fucks you then the department doesn't matter as much.

user54412

@0celo7 well there's only like 5 places in the country, right? ;)

0celo7

@ChrisWhite Pretty much...Michigan, Tennessee, Princeton, Wisconsin?

Maybe one of the PA schools, too.

user54412

20:17

I guess not MIT anymore

0celo7

Beats me, none of our fusion guys are from MIT.

psfc.mit.edu

Ok, MIT.

user54412

I think their funding was completely cut

0celo7

Oh?

My school gets that sweet DOE money from Oak Ridge.

DoE?

ManishEarth

17 mins ago, by Chris White

they charge us tuition too

wtf

0celo7

You know what I'm talking about.

user54412

20:21

I guess NIF/LLNL are too far from any university to share

0celo7

I can't remember all those lab acronyms!

Qmechanic

20:38

@user36790 : Not dead; just without internet for a while :)

dmckee

@0celo7 I see both on a regular basis.

@ManishEarth Damn. The swag has gotten better since the last time I got some.

@Slereah That's not quite the right complaint. You meant "Please stop these unbelievable ignorant and shitty gravitational wave questions".

Though you can be forgiven for thinking they don't come in any other kind.

We have this problem following every public announcement of a Cool Physics Event (tm).

ManishEarth

So on Hacker News there was a bunch of random discussion about gravitational waves and gravitons

one guy was bewildered that gravitons can have mass

"how can the thing that carries gravity be affected by gravity"

I'm all like "we've passed that stage of absurdity in physics half a century ago"

skull petrol

:O you are a hacker?

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