The h Bar

user84215

13:00

@ACuriousMind You think that I am sly?

Secret

13:21

today, I saw a student with a T shrit printed:

$$\frac{E}{c^2}\sqrt{-1}\frac{PV}{nR}$$

Now suppose we simplify this using the known rules of energy momentum equation and ideal gas equation we get:

$pi T$

Does there exists a physical quantity involvinig momentum and temperature multiplied together?

Slereah

(it's mit)

I assume it's supposed to be an MIT T-shirt

Secret

Ah I see

Semiclassical

i sorta wish people talked in terms of particle density more than volume and particle number

e.g. writing the ideal gas law as $p=\frac{N}{V}k T$

Slereah

Volume is easier to measure

Semiclassical

i guess that's true.

Slereah

13:26

And since particle number is a constant there's usually no need to track it

Semiclassical

and, tbf, if you want to do everything in terms of densities, you have to do some work to get the thermodynamics

0celo7

@Semiclassical maybe we should measure temperature in terms of vibrations too

Secret

well, we physical chemists does that somewhat (cf vibration spectra and vibration temperature)

Semiclassical

namely, use $dG=d(\mu N)=-S dT +Vdp+\mu dN$ to get the relation $N d\mu = -S dT+Vdp$

Slereah

Hey @0celo7

0celo7

13:28

"today we have a high air temperature of 55GHz"

Slereah

Anything you want in that book?

press.uchicago.edu/ucp/books/book/chicago/T/bo27962774.html

Semiclassical

and therefore $dp=\frac{N}{V}d\mu+\frac{S}{V}\,dT$

Slereah

I ordered it

Secret

(memory correlations again leading to weird google searches)

16

Q: Is there a relativity-compatible thermodynamics?

I am just wondering that laws in thermodynamics are not Lorentz invariant, it only involves the $T^{00}$ component. Tolman gave a formalism in his book. For example, the first law is replaced by the conservation of energy-momentum tensor. But what will be the physical meaning of entropy, heat and...

cds.cern.ch/record/347536/files/9803007.pdf

0celo7

@Slereah Is there no legal copy available?

Semiclassical

13:29

My gut feeling is that there shouldn't be an real impediments to doing thermodynamics in a relativistic setting

Slereah

I'm afraid not

Not even a digital version at all

0celo7

@Slereah Are you gonna scan the whole thing?

Slereah

at least none I could find

Semiclassical

though i guess the issue is really how one defines the ensembles in such a seteting

Slereah

No I am not

But if there's a specific article in it you want

that is fine

Secret

13:29

Well relativistic statistical mechanics is well established, so I guess we can do that somewhat

Semiclassical

yeah

Slereah

I also ordered the two papers on magnetic wormholes from that weird astrophysics journal

Secret

though I have no idea how they will define entropy since energy conservation is nonexistent in GR

Semiclassical

plus there is such a thing as thermal QFT

Slereah

By "ordered" I mean that I sent them money so an intern can xerox them and send them to me by mail

Since apparently that's how they run things

Semiclassical

13:30

@Secret I guess it's a matter of SR stat mech---which shouldn't be hard---and GR stat mech

i can buy that the latter more problematic than the former

0celo7

@Slereah that Geroch paper is famous but I don't need it

Penrose's paper should be good

Secret

Since global energy is not well defined in GR, I will suspect global entropy will be problematic

Slereah

yeah that's why I ordered it

It's apparently only available there

0celo7

let's see if the library has it

Semiclassical

something something black hole thermodynamics? :P

Slereah

13:32

Also there's a paper by Martin Schwarzschild

Secret

which caused me to wonder, how do we know the big bang is of low entropy

Slereah

Son of Karl Schwarzschild

0celo7

they do have it

so no need to scan

Semiclassical

ugh, the arrow of time gives me a headache

Slereah

Once I get a new flat I should buy a bigger bookshelf

Secret

13:33

It will be interesting but weird if the entropy of the whole universe is dictated by the total surface area of all black holes it contains

Slereah

So that a single shelf can hold all the GR book

0celo7

@Semiclassical time in GR is a scalar field whose gradient needs to be future-directed. It's a bit confusing the first time you see it

Slereah

I am officially out of space

Semiclassical

sure

I mean the arrow of time in stat mech

Slereah

don't trust statistical mechanics

Secret

13:34

probability yada yada yada

Slereah

Everything in it is STATISTICAL

0celo7

@Slereah I got first two vols of reed and simon

CooperCape

Boo!

Semiclassical

[insert old line about lies-damned lies-and-statistics]

0celo7

I put them with the physics books which might be a sin

Slereah

13:34

Doesn't it have physics in it?

Like they construct QFT stuff

0celo7

they do free fields yeah

Slereah

I tend to put math books in the physics section if they're more physics related

0celo7

I have O'Neill in the physics section

Slereah

Like that book on Ricci calculus or that book on Hilbert spaces

Semiclassical

my office shelf has a copy of Watson's Analysis book, Saunders MacLane's book on category theory for physicists, and Arnold's Classical Mechanics book

0celo7

13:36

the third one is a physics book

Semiclassical

but I also have a lot of random crap

0celo7

beats me how it became a GTM

Semiclassical

It's a physics book that asks the reader to learn homology theory

Slereah

Speaking of which, they still haven't shipped MTW

0celo7

They ask you to learn what homology is

Slereah

13:37

Dang it

0celo7

Actual homology theory is very different

Slereah

I hate having stuff in the mail

Dealing with the post office is such a hassle

although at least right now I don't have to work

So I can receive packages directly

0celo7

@Slereah get amazon prime!

Slereah

Amazon prime only works for Amazon products

Not for third party vendors

0celo7

why did you not get MTW through amazon?

was it cheaper someplace else?

Slereah

13:38

I think I did get it through Amazon

But the problem with that one isn't the delivery

They just haven't shipped it right now

I'm guessing it wasn't in stock, that's the usual excuse

0celo7

@Semiclassical I have to main shelves right above my desk that have the books I use a lot

and then other shelves with random crap

Slereah

Apparently Martin Schwarzschild got the Karl Schwarzschild medal

NEPOTISM

0celo7

the only outlier on my main shelves is the single algebra book

Semiclassical

@0celo7 my point is that there's enough math in Arnold that it's a clear outlier among physics books

Whether or not it should be an outlier is another question entirely.

Slereah

It has the solution of a mass on a spring

pretty physicky

Semiclassical

13:45

it discusses time evolution of a system using Hamiltonian flow and the symplectic 2-form

pretty mathy

Slereah

Hamiltonians are physics!

Semiclassical

Sure they are. But how many physicists would know how to describe it in terms of symplectic manifolds?

Slereah

The good ones

Semiclassical

I think he may introduce differential forms and symplectic structure on manifolds before he talks about Hamiltonians

Slereah

My laser has been shipped

Hurray

I've got so much stuff waiting right now

Bunch of electronics, laser, MTW, that GR book, those weird papers

John Rennie

14:13

Goodness, the things archaeologists get up to

HsMjstyMstdn

Hmm

Practice Midterm says "Extra Credit: Perform the sickle dance of the Austrian honeybee. You will be graded by how well your classmates understand you."

🤔🤔🤔🤔🤔

Sid

@JohnRennie That's a pretty cool research

0celo7

@Semiclassical yeah it's in this weird place where it's very mathy for physicists but not careful enough for mathematicians

(like Witten papers)

John Rennie

@Sid So, genital herpes was apparently first contracted by homo erectus. Insert joke here :-)

0celo7

@JohnRennie you have a sick mind

John Rennie

14:24

@0celo7 Hey, it wasn't me spending taxpayers money researching this stuff!!

0celo7

hmm

I can't argue with that, although you're not off the hook

HsMjstyMstdn

Aren't you guys going to star John's bawdy message as is oft the case

HAHAHA

John Rennie

@HsMjstyMstdn I can see the second suspension in two days approaching :-)

HsMjstyMstdn

Inescapably

Slereah

I should probably buy some laser goggles

For safety

vk.com/video51098255_170416641?list=80ed392903ba8ddf1e

example of goggle use

Anonymous

14:30

@Slereah You should :) What are you planning to do with the laser, though? (Other than blowing up the white house)

Slereah

Interferometry

Anonymous

Ah. Sounds interesting

Slereah

u sound very interested indeed

Anonymous

Because I am :P

Sid

@Blue I like the idea of blowing up the white house

Slereah

14:32

I got some beamsplitters as well

But since they're expensive, they're tiny ass beamsplitters

I'd better be careful with 'em

Anonymous

I'd like to try out the single photon experiment sometime in the future (young's double slit experiment)

Slereah

I'll send u a photon by mail

Anonymous

No matter how much I learn about it, I still can't believe it somehow

Anonymous

:P

Anonymous

@Slereah Heh. Thanks :'P

Semiclassical

14:35

@0celo7 yep

Slereah

How easy is it to generate single photons anyway

Anonymous

Some French guy did it first, I heard

Slereah

"One should never look into the beam of any laser - especially if it is collimated. Use an indirect means of determining proper operation such as projecting the beam onto a white paper or laser power meter. "

Semiclassical

More in the tradition of Euler than of Gauss, perhaps

Slereah

Laser's not working, let me take a look inside!

Anonymous

14:37

Alain Aspect

Alain Aspect (French: [aspɛ]; born 15 June 1947) is a French physicist noted for his experimental work on quantum entanglement. == Education == Aspect is a graduate of the École Normale Supérieure de Cachan (ENS Cachan). He passed the 'agrégation' in physics in 1969 and received his master's degree from Université d'Orsay. He then did his national service, teaching for three years in Cameroon. In the early 1980s, while working on his PhD thesis from the lesser academic rank of lecturer, he performed the elusive "Bell test experiments" that showed that Albert Einstein, Boris Podolsky and Nathan...

Anonymous

Hah. Found him!

Semiclassical

Though I’m not sure Gauss is really the right figure to compare with. Weierstrass, maybe?

Anonymous

@Semiclassical What are you talking about? =P

Slereah

apparently the one photon experiment requires a bunch of filters

I'm not sure what they are

PBS and NPBS filters

Sid

My prof of Physics sucks while delivering punchlines(which are intended to be jokes)

Semiclassical

14:39

Re: Arnold in relation to math physics

Slereah

Also ND filters, which are just attenuators

Is that how you do it, just block most photons?

Semiclassical

With Euler being unconcerned with rigor and more interested in all the crazy stuff he could cook up

Anonymous

ND filters reduce intensity, so probably yes

0celo7

@Semiclassical Euler was too early for rigor, no?

Semiclassical

Yeah

Slereah

14:41

Well I guess it's not too hard then

So the hard part is having a detector that can detect single photons

Anonymous

@Slereah Is that hard? A photon striking a certain "screen" can be detected I guess

Slereah

I don't know

Semiclassical

The comparison of Euler and Gauss is that Gauss didn’t like to publish until he had a comprehensive view on the subject

Slereah

I don't know the typical response of light detectors

also if it detects single photons you need to isolate it pretty well

Semiclassical

Whereas Euler was more adventurous in terms of what he was willing to put out there

Anonymous

14:43

@Slereah That's true

Anonymous

But probably detecting it at the screen is the only way as of now

Anonymous

0

A: The double slit experiment - methods used to observe single photons prior to striking the target

In the famous double-slit experiment using photons, you have a couple of configurations: Configuration A - 2 slits and 1 screen: After sending 1 photon at a time at the double slit, the photon hits the screen seemingly at random, but over time an interference pattern builds up. But each photon ...

Semiclassical

I vote for doing a version of the GHZ experiment

Slereah

the light detectors I ordered are simple photoresistances

Anonymous

Ow. :P Same here. Even I have a couple of photoresistances which have terrible accuracy

Semiclassical

14:45

No statistics needed! (Not really, but it’s much closer to a one-and-done test for quantum nonlocality)

Anonymous

Sometimes it takes over 10 secs to detect torch light

Slereah

yeah so probably not ideal for detecting single photons

Anonymous

Lol

Sir Cumference

@JohnRennie Let's be real here, to be a scientist you must be able to say risqué-sounding things with a straight face. Then deal with people smirking everytime you mention them

John Rennie

@SirCumference that's a significant part of the fun in doing science :-)

Sir Cumference

14:47

Literally every time I mention "pp fusion", "the Big Bang" or "Uranus", I get those jokes

@JohnRennie Yup

0celo7

you need to talk to less stupid people

Slereah

Stupid people are hard to avoid

0celo7

@Slereah Just avoid everyone unless you know for sure they aren't stupid

Sir Cumference

@0celo7 Literally, several kids in my math class were so proud when they figured out that searching "hairy balls" in wikipedia redirects you to the hairy ball theorem

Slereah

Alas I need to go to things for job purpose

Sir Cumference

14:49

You can't avoid the jokes

0celo7

@SirCumference Uh, never take gen ed math classes

Sir Cumference

@0celo7 You don't need to for kids to point out dumb things :P

0celo7

@SirCumference what?

Slereah

So where can one buy some of Erdös' patented math amphetamines

I've got a lot of math to do

Anonymous

Wait for Balarka. He must be knowing

Slereah

14:56

Single-photon avalanche diode

A single-photon avalanche diode (SPAD) is a solid-state photodetector in which a photon-generated carrier (via the internal photoelectric effect) can trigger a short-duration but relatively large avalanche current. This avalanche is created through a mechanism called impact ionization, whereby carriers (electrons and/or holes) are accelerated to high kinetic energies though a large potential gradient (voltage). If the kinetic energy of a carrier is sufficient (as a function of the ionization energy of the bulk material) further carriers are liberated from the atomic lattice. The number of carriers...

Ah, I remember those from class

0celo7

@Slereah it's called covfefe

Slereah

Garry Gum

►

The largest number and cDonalds Theorem - Look Around You

►

Slereah

15:54

So what is today's EVENT

Alex K Chen

@Slereah How to properly rickroll newbs to hbar

Slereah

Sorry this isn't 2007

David Z

Do we have anything particular to discuss in the chat session (other than gravitational waves)?

Alex K Chen

Hmm... then how south korea is making a mini-sun to lynch Trump, perhaps :D ?

Oh back to serious topics, KIP THORNE got a nobel. We should disucuss about that !

Anonymous

That's old news

Slereah

15:58

Did he get it for rereleasing MTW

2

David Z

@Blue Yeah but still fair game for discussion

John Rennie

It's the fiftieth anniversary of the electroweak theory today!

0celo7

@Slereah holy shit it was all planned

Slereah

Time to bake an electroweak cake

David Z

Time to get started anyway

0celo7

16:01

@JohnRennie boo

David Z

Welcome to our biweekly chat session everyone!

John Rennie

It's true. Weinberg's paper was submitted on 17th October 1967.

lılostafa

@AlexKChen Yeah we need to first see if we have any fresh fish here today

David Z

Not much on the agenda today, we'll just do our usual 5 minutes introductory stuff and then we have some physics news to discuss

Is anyone here new to chat sessions, new to chat, or new to the site?

Or, any general site-related questions to ask?

Slereah

here's a weird physics news : arxiv.org/pdf/1707.07439.pdf

Well, not new since it's a few months old I suppose

David Z

16:05

(Sure let's jump right into physics since there doesn't seem to be any intro stuff :-P)

@Slereah I'd link to the abstract

Slereah

arxiv.org/abs/1707.07439

John Rennie

There is video from a flyby of the Juno satellite on YouTube here (no, it's not a Rick roll!)

David Z

That's kind of cool

Anonymous

Rick Roll Detector :D

John Rennie

And if anyone is still looking for the LIGO neutron star merger paper it's now available

The web site was groaning under the strain yesterday.

Slereah

16:12

Oh boy

David Z

@JohnRennie can't say I'm surprised

0celo7

190 references?

David Z

Let me sneak in a mention of the Nobel Prize rewarding the discovery of gravitational waves by LIGO too... it's been a good couple weeks for them

Slereah

Oh man it's one of Those papers

With 4 pages of authors

John Rennie

The paper doesn't actually tell you that much. Presumably there are other papers describing the astronomical observations. Does anyone have links?

@DavidZ it makes you wonder if the Nobel committee knew about this latest detection.

Slereah

16:15

I mean, even without that it was still a pretty good result

David Z

I suppose it's possible that someone on the committee is also in one of the collaborations, but I would think that'd be a conflict of interest they'd try to avoid

And anyway, it did seem like the obvious choice even when (almost) nobody knew about the latest detection

Slereah

the real question is

John Rennie

I note that Virgo failed to detect the neutron star merger, but actually the detection failure helped pin down the merger location. So in this case a null result was an important one.

2

Slereah

Is the result real or is it an Illuminati plot

David Z

@JohnRennie oh that's weird

Due to the transverse orientation of the waves, I guess?

John Rennie

16:21

@DavidZ it's described in the paper. The orientation of the event was such that the Virgo arms were in virtually the perfect position to miss the event :-)

vzn

a question that occurred to me re neutron star merger (breakthru news...). could a neutron star merger theoretically ever result in a black hole?

lılostafa

I found this NASA's animation of the event interesting, which depicts various emissions (GW, gamma, X, UV, visible, IR) of the merger.

John Rennie

@vzn yes it could. It is currently unknown whether the remnant left by the merger is a black hole or just a bigger neutron star.

vzn

@JohnRennie any idea why it failed? was it due to lack of sensitivity or something else? (also note that the 1st 3way gravitational wave event incl Virgo was announced recently...)

John Rennie

@vzn partly lack of sensitivity, but most just bad luck that it happened to have the wrong orientation for the direction from which the waves were coming.

vzn

16:29

@JohnRennie is there theory on what "typically" causes black holes? is it occasionally "large star collapse" vs "mergers"?

Slereah

it is just related to density

So either of those can work

John Rennie

@vzn we don't know enough about the black hole distribution to know what the dominant mechanisms are.

0celo7

@JohnRennie will you read "The Formation of Black Holes in General Relativity" by Christodoulou with me?

@Slereah too

John Rennie

Wow, the whole book is on the Arxiv

vzn

@Slereah worth noting this is a breakthru result partly because light astronomy was able to correlate with gravitational astronomy for 1st time as was hoped on 1st detection of g-waves. reading 1 article, the g-wave community alerted the light observation community & the latter scrambled to detect the event. wondering how long it lasted? its interesting the light event long outlasted the g-waves. & sort of a reversal in the "lightning vs thunder" analogy (latter vaguely analogous to g-waves...)

0celo7

16:35

@JohnRennie it's the first book on rigorous dynamic formation of black holes

Alex K Chen

Is the chat session over ?

0celo7

@JohnRennie so does it look good?

Alex K Chen

Oh then take a look at this question .... ROTFL !

David Z

@JohnRennie just found this: blogs.cornell.edu/arxiv/2017/10/16/gw170817

@AlexKChen Officially no, it lasts for an hour (out of which 20 minutes are left). But we don't have specific topics being discussed today.

John Rennie

@DavidZ Aha thanks :-)

Semiclassical

16:42

@0celo7 rigorous being the key word there

0celo7

@Semiclassical look at it!

it's so rigorous it hurts

Semiclassical

it puts the rigor in rigor mortis

0celo7

I think it would take a year to properly read

Semiclassical

wow, you think you could get through it by then? :P

Terry Bollinger

Hi all. Fascinating conversation, especially John Rennie's points/refs on gravity waves.

0celo7

16:43

@Semiclassical If I had a year and minimal responsibilities? Yeah I think a year is fair

Semiclassical

kk

0celo7

With classes and crap, who knows

@Semiclassical The trick with these massive rigorous GR texts is to know when an argument is being repeated, then you just skim that section

Semiclassical

for me it'd take a minute to go through...in the sense that it would take me a minute to decide there's no way I want to try reading it, and move on

Which I guess is more like reflection than transmission

0celo7

The proof is supposed to be very complete so there's repetition

Semiclassical

right

0celo7

16:46

@Semiclassical and some of it is a repetition of his 1991 book on the nonlinear stability of Minkowski spacetime

he is not a n00b at writing god-awful books like that

John Rennie

@TerryBollinger the detection of a neutron star merger is a really big deal because (a) there are a lot of neutron stars out there and (b) we can see the bang they make when they collide :-)

0celo7

he either has a gift for forseeing how a 500 page calculation gives the answer, an army of grad students, or probably both

John Rennie

@TerryBollinger and while we've believed that GRBs were a neutron star merger for a while, we now have direct evidence for it.

Terry Bollinger

@JohnRennie very cool...! (Quite a blog that...)

Slereah

Do we have any info on the neutron stars themselves from it?

Like composition and such

IIRC the core of neutron stars is still pretty mysterious

0celo7

16:49

@Jim

we summon thee

John Rennie

@Slereah I don't think we're likely to get detailed info about the neutron stars from this sort of observation.

Slereah

Too bad

John Rennie

Look how much the event changed the luminosity of the host galaxy! You wouldn't want to get too close :-)

Terry Bollinger

@JohnRennie ouch for any civilizations there...

Sir Cumference

@JohnRennie It's unbelievable how a collision between two stellar objects (mere remnants, especially) can outshine billions of stars...

Slereah

16:54

'twas a big boom

John Rennie

1

Q: Can a Kilonova sterilize a galaxy

I recall recently reading that a supernova explosion would produce enough radiation to sterilize or severely damage Earth-like worlds within a radius of a dozen or so light-years. Kilonovas/Macronova of the type recently observed in a galaxy 120 million light years away, as the name suggest, ca...