The h Bar

12:05 AM

Howdy

12:19 AM

Any of y'all ever think about the fact that Boltzmann's constant isn't really a constant of nature?

It's really just a fudge factor to make up for the fact that we had a temperature scale before we understood statistical mechanics.

And maybe it's needed in practice because there's no good way to calibrate energy against temperature over a wide range.

Kinda interesting in any case.

knzhou

12:31 AM

Yeah. Another way of saying why it's needed: $Nk_B$ needs to be a 'reasonable' number so we can use human-scale units to work with gases. So $k_B$ must be tiny because $N$ is big, i.e. we are much bigger than atoms.

Sir Cumference

12:46 AM

Er...can I ask an astronomy question here?

No one on the Astronomy SE goes on the chat

0celo7

Ping @HDE226868 and @ChrisWhite

Sir Cumference

Er, ya think? Would it annoy em?

0celo7

Probably.

@StanShunpike Old schoooooool youtube.com/watch?v=PRXnAzeWeaA

Sir Cumference

Then...er...I'll just keep it to myself

HDE 226868

@0celo7 I have nothing better to do at the moment, although Chris White's the best choice.

@SirCumference Ask away.

0celo7

12:52 AM

@HDE226868 Daww, I like annoying you

Sir Cumference

A'right :D
So in variable star designations, the wikipedia page states to abandon the latin alphabet after 334 combinations of letters: https://en.wikipedia.org/wiki/Variable_star_designation

HDE 226868

Yes.

Not too elegant.

Sir Cumference

So after writing Z..(333 times)..Z, would I then go onto numbers?

0celo7

Why not name stars like

Charlie

Bob

etc.?

Sir Cumference

That's not really convenient

HDE 226868

12:54 AM

@SirCumference You wouldn't ever get there. You only have two letter names, max.

0celo7

Give them names like Spanish royalty

Sir Cumference

Since these stars are named after they are discovered. Most stars are named after the brightest to dimmest in the constellation/association

Except variable stars

HDE 226868

@0celo7 "Eta Philip II" isn't too catchy.

Sir Cumference

@HDE226868 Gotcha, thanks

0celo7

Charlie Bob Fernando Rodriguez Carlos Louis Witten Heinz Ketchup

@HDE226868 and SC 11239.0-121348 is??

Sir Cumference

12:56 AM

Wait, is that a real star?

K good, it's not

0celo7

how do you know

HDE 226868

@0celo7 At least the jumbles tell you something about the star, most of the time.

Sir Cumference

Well @0celo7 there's an obnoxious designation system, but it sorta makes sense

Just counterintuitive

HDE 226868

PSR $\cdots$ immediately brings to mind pulsars.

Sir Cumference

Then there's comet designation

Ugh

0celo7

12:57 AM

I need to read that one pulsar proof

In Straumann

Can't be bothered to learn PNP tho

Not an astro nerd

Sir Cumference

And sometimes stars like NML Cygni are just named after the people who discover them (Neugebauer, Martz, and Leighton)

HDE 226868

Exoplanets are nice. Although putting letters in order of discovery, not distance from the parent star, is annoying when all the planets in a system are finally discovered. Before then, it's a hassle to rename bodies.

Sir Cumference

Exactly

No wonder why some variable stars still have greek letters

Imagine trying to fix it instead of leaving those stars as they are

HDE 226868

Brown dwarfs are terrible.

Sir Cumference

Haven't looked into those

Why's that?

0celo7

12:59 AM

@StanShunpike ooooo I think I'm gonna be on an old school kick for a while

this stuff is awesome

HDE 226868

@SirCumference No unique brown-dwarf-only naming structure whatsoever. That I know of.

Sir Cumference

Seriously?

HDE 226868

Yep. Especially because some objects aren't confirmed brown dwarfs, just generic sub-stellar objects.

0celo7

The Masochist - LDMF (2005) (Scantraxx)

►

HDE 226868

Awesome way to CYA if it isn't what you think it is, but painful otherwise.

0celo7

1:00 AM

@StanShunpike Not sure what that is exactly but it's good

Sir Cumference

"Various catalog designations have been used to name brown dwarfs; names ending in 'b' are in orbit around a primary star." ~Wikipedia

user54412

@HDE226868 Some would call them stars. It's not like we have a separate system for M stars ;)

Sir Cumference

So it's not consistent

user54412

Of course, others would call them planets

0celo7

M stars?

Sir Cumference

1:01 AM

I dislike the name brown dwarf. I've never even heard of one being brown

HDE 226868

@ChrisWhite (cough cough) Fusion failure (ish) (cough cough)

Sir Cumference

It's pretty misleading

user54412

@HDE226868 Fusionist.

Sir Cumference

Say, HDE

Ya mind answering another question?

user54412

Let's not judge here.

HDE 226868

1:02 AM

They do fuse, I'll grant them that, but still. . .

0celo7

Fucking astro nerds

user54412

Also, should there be a distinction between PP stars and CNO stars?

HDE 226868

@SirCumference I'm open.

Sir Cumference

@0celo7 Goddammit dude, astronomy is awesome

HDE 226868

@ChrisWhite Touche.

Sir Cumference

1:02 AM

It's the study of the Universe

0celo7

It's an application of GR and some other things

user54412

@0celo7 Yes, all the supermodels are.

0celo7

That's about it

Sir Cumference

@HDE226868 What's the difference between the apparent and absolute horizon of a black hole

no_choice99

what is physics then

Sir Cumference

1:03 AM

GR isn't all

0celo7

@ChrisWhite you forgot the not there

HDE 226868

@SirCumference Ask Chris White.

Sir Cumference

@no_choice99 The same study at a smaller scale

no_choice99

i thought the study of the universe was called physics

0celo7

Also they're getting great postdoc positions ;P

Sir Cumference

1:03 AM

Sigh...

Astronomy is how physics makes huge stuff happen

Like pair production supernovae

no_choice99

and neutron stars?

Sir Cumference

Yep, electron capture

user54412

Apparent horizon: everything is required to move inward at the moment. Absolute horizon: once inside, nothing will help you get out again.

HDE 226868

@ChrisWhite By the way, King's papers are fascinating. I had already seen the first installment, but the others are pretty awesome.

Sir Cumference

@Chris White Er...I don't think I understood that part about the apparent horizon

no_choice99

1:04 AM

is FenderLesPaul here?

Sir Cumference

Absolute horizon = event horizon, no?

user54412

^ yes

Sir Cumference

So then the apparent horizon is...?

0celo7

@no_choice99 What do you need him for

user54412

the event horizon depends on the whole of spacetime

no_choice99

1:05 AM

0celo isn't him the guy who knows about GR?

and the sagnac effect

user54412

let's say you think you fell into a black hole, because spacetime is dragging you and everything else inescapably inward

0celo7

I know some GR. So does @ChrisWhite

no_choice99

oh

Sir Cumference

Yep, mostly the space is dragging me in, but yeah

no_choice99

is the ergosphere of a black hole finite in extension in space?

user54412

1:06 AM

but then later on something happens and mass rearranges and pixies make wormholes or whatever

Sir Cumference

So by "fall in", you mean I reached the event horizon?

Wait what?

user54412

and then you find a way out, and you can escape to infinity

Sir Cumference

.-.

user54412

then you never were inside an event horizon, by definition

0celo7

@no_choice99 Yeah, why wouldn't it be? It is an ellipsoid or something.

user54412

1:07 AM

but you could say you were inside an apparent horizon

Sir Cumference

I don't...what...?

no_choice99

so the ergosphere ends "abruptedly" ?

Sir Cumference

Of course not, @no_choice99

no_choice99

it's like a weird part of space that rotates or something like that

with well definte contour

hmm no?

Sir Cumference

Really?

user54412

1:08 AM

@no_choice99 the edge of the ergosphere is where a photon can just barely hold its position by moving against frame dragging

Sir Cumference

Huh, gotta look into that

no_choice99

@FenderLesPaul please help me :D

Sir Cumference

Ain't that the photon sphere?

I'm pretty rusty with black holes

no_choice99

Chris , right outside that ergosphere the photon behaves like "usual" ?

Sir Cumference

So I still have no exact idea what the apparent horizon is...

no_choice99

1:09 AM

i.e. locally it's minkowski's metric

user54412

no, there's always frame dragging

Sir Cumference

Since ya started bringing in wormholes and pixies...

no_choice99

oh I didn't know that

user54412

it's just overcomeable outside the ergosphere

0celo7

Locally it's the Minkowski metric everywhere

no_choice99

1:10 AM

that frame dragging stuff has infinite distance ?

0celo7

(on the manifold)

user54412

yes

no_choice99

are we slighly getting dragged by many black holes?

0celo7

yes

Sir Cumference

Of course

0celo7

1:10 AM

also by the Earth

no_choice99

oh loll this is hilarious

0celo7

maybe that explains my sudden light headedness

no_choice99

ah it doesn't take a black hole for frame dragging?

0celo7

no, any rotating thing

no_choice99

ok thanks

0celo7

1:11 AM

Gravity Probe B measured the Earth's frame dragging

or something like that

user54412

or tried to at least

Sir Cumference

So...Chris?

0celo7

@ChrisWhite Stupid question, why can't $R$ and $R^2$ be homeomorphic

no_choice99

so the ergosphere is when that dragging becomes so strong that a photon can't move forward with respect to an observer outside of that ergosphere or something like that?

0celo7

@no_choice99 Yeah

no_choice99

1:13 AM

ok thx guys

0celo7

Or is that the stationary limit surface

Or are they the same

no_choice99

black holes seem funny, they should teach that in high school or something

Sir Cumference

Er...stupid question, but then how is it different from the photon sphere?

They do, no_choice

Or at least how they form

So...

@0celo7 You good at particle physics?

0celo7

No

Sir Cumference

K

You good with what then?

0celo7

1:16 AM

nothing

Sir Cumference

._.

But you just went on about GR

0celo7

so

Sir Cumference

Okay never mind, I guess

Wait, ya study black holes?

0celo7

no

Sir Cumference

Then how'd ya know about the ergosphere?

Which isn't exactly a sphere...it's a spheroid

In fact, atmosphere should be atmospheroid, etc.

0celo7

1:19 AM

Ah, you remove a point from $R^2$.

Then there is no homeomorphism between $R^2-\{0\}$ and $R^+\cup R^-$

Sir Cumference

Uh...is this statistics $R^2$ or...?

0celo7

I'm too lazy to write $\mathbb{R}$

Sir Cumference

Er, what's that referring to?

Excuse my ignorance

0celo7

real numbers

Sir Cumference

Yes, what branch of math/physics?

0celo7

1:21 AM

Topology

Sir Cumference

Oh

Maybe I should look into that

It require calc?

0celo7

No

no_choice99

requires mathematical analysis?

0celo7

That's not a well-defined question

no_choice99

edited

0celo7

1:24 AM

I know what you mean

Topology is very broad

Analysis is very broad

no_choice99

i think i'd rather study QFT or sometihng like that instead of topology right now

Shiyloh Fisher

hi

no_choice99

sup

0celo7

QFT needs topology and analysis to be done "rigorously"

no_choice99

hmm really?

0celo7

1:25 AM

Yes

no_choice99

i was expecting some textbooks would be self contained

and still be good enough

Sir Cumference

Okay, so what'll I need to learn first to go into topology?

no_choice99

is there anything from laudau and lifshitz about it?

Sir Cumference

Any sort of geometry past high school?

0celo7

Depends how much topology you want to do

@no_choice99 Haven't read those books

But probably not

Gauge theory uses a lot of topology/geometry

Sir Cumference

1:27 AM

A'right, how about enough that I can tie it into astronomy?

And GR?

0celo7

@HDE226868 How does one tie topology into astronomy

@SirCumference GR uses a lot of topology

Sir Cumference

I imagine there's some way...?

Then there we go

So what'll I need to learn first?

0celo7

Some basic set theory

Sir Cumference

Okay

I like the word "basic"

0celo7

Just get a book like Munkres or Bredon

Sir Cumference

1:29 AM

And to learn that I need anything?

0celo7

experience with analysis

Sir Cumference

And for that...?

HDE 226868

@0celo7 GR. Modeling anything under really extreme gravity.

Sir Cumference

Any prerequisites?

0celo7

@HDE226868 tell me more

what is this "GR"

Sir Cumference

1:31 AM

General Relativity

DanielSank

Hey @ChrisWhite, how do you write $\delta(x^2 + y^2 - r^2)$ as something over which I can integrate out the $y$?

0celo7

@DanielSank Give it up that can't be answered

@SirCumference what is that

DanielSank

Or, do you know any mathy astro folks who understand all kinds of technical details about probability?

Sir Cumference

Einstein's General Theory of Relativity

DanielSank

@0celo7 That's hard to believe.

0celo7

1:33 AM

@SirCumference sounds interesting

what's it about

Sir Cumference

So I should just dive into mathematical analysis?

0celo7

yes

Sir Cumference

No need for calc or anything else?

0celo7

wait no

explain GR pls

Sir Cumference

.-.

General relativity

General relativity (GR, also known as the general theory of relativity or GTR) is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics. General relativity generalizes special relativity and Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations...

0celo7

1:34 AM

too techincal :/

Sir Cumference

Simple Wikipedia:

General relativity

General relativity is a theory of space and time. The theory was published by Albert Einstein in 1915. The central idea of general relativity is that space and time are two aspects of spacetime. Spacetime is curved when there is gravity, matter, energy, and momentum. The links between these forces are shown in the Einstein field equations. A central idea in general relativity is the "principle of equivalence." An example is that two people, one in an elevator sitting on the surface of the earth, and the other in an elevator in outer space accelerating at 9.8 meter/sec^2, will each observe the same...

0celo7

Wiki articles are written for PhD people

no_choice99

post doc people u mean

or life long researchers

0celo7

Prof. Emeritus people

@SirCumference so you don't know what GR is about?

Sir Cumference

I know the basics, why?

0celo7

1:39 AM

please explain

Sir Cumference

I hate ya. Well, here's to start: When ya travel faster and faster through space relative to something else, you travel slower through time relative to that object

0celo7

why?

Sir Cumference

Time and space are interrelated

0celo7

how

Sir Cumference

As I understand it, I'll give an analogy. Say I'm going across a country eastward with a car.

I'll get to the end in 5 days. However, if I put some of that energy into going norther and norther, I'll spend less energy going east.

So it'll take longer to get to the east side

Time and space work similarly. If I spend no energy going through space, I'll go through time at maximum speed

If I travel more through space, I'll be spending more energy on that and less on traveling through time

When I reach lightspeed (which I can't), I'll experience no time.

If I go faster, I'd be experiencing negative time (as in, traveling backwards in time)

So yeah, negative energy going through time

Make sense?

0celo7

1:42 AM

no

Sir Cumference

...

0celo7

where are the equations

Sir Cumference

SCREW IT

0celo7

all I see is hand waving

pls just answer

11

Q: Do light waves precisely follow null geodesic paths in General Relativity?

In special relativity one may show that a plane wave solution of Maxwell's equations (in a vacuum), of the form $A^a=C^a\mathrm{e}^{\mathrm{i}\psi}$ has the following properties: The normal $k:=\mathrm{d}\psi$ to the surfaces of constant $\psi$ is a null vector and the integral curves of $k$ are ...

Sir Cumference

Hand waving is an easier way to explain

0celo7

1:43 AM

@SirCumference please

Sir Cumference

In imaginable terms

You hate me, right?

If you know that there are equations involved in the process, why do you need me to explain the basics?

Which equation you want?

0celo7

@SirCumference no?

@SirCumference the ones that answer the above question

Sir Cumference

I'm no GR major... ;-;

But it seems we both got questions about light

22

Q: Could gravity accelerate light?

Gravity causes anything with energy to accelerate toward the source. Black holes, for example, have such strong gravity that they pull in light and don't let any escape. But can acceleration still apply to light? The speed of light is constant, of course, but why are photons affected by gravity y...

general-relativity gravity photons speed-of-light faster-than-light

0celo7

well

Sir Cumference

Mine is less equation-y

0celo7

1:47 AM

mine is about wave solutions of Maxwell's equations on curved spacetime

And mine?

null geodesics

Isn't that yours?

maybe

go learn calculus

Sir Cumference

ಠ_ಠ

Fine, you know what, okay, I will

Recommend me a darn book

0537

1:53 AM

Watch the damn lectures.

It's the fastest way.

Sir Cumference

What, should I learn that first or mathematical analysis?

How long'd it take you to get a good handling on calc, @0537

HDE 226868

Read The Road to Reality.

And with that, I'm out.

G'night, all.

0537

@SirCumference 3 days to learn it? 3 weeks to sink in fully?

I guess.

Sir Cumference

As in, calc 1-3?

0537

calc 1.

Sir Cumference

1:54 AM

Oh

And calc 2-3?

HDE 226868

Wait, no, I'm back. Calc 3 is fun.

0537

I learned each in 3 days.

From watching the lectures

13 a day

0celo7

Calc 3 is not fun

Sir Cumference

Learning ain't fun?

0celo7

not always

@0537 that has to be a record

why are you not a PhD yet

Sir Cumference

1:56 AM

I dunno, I thought it'd be awesome. Ya open more gates for other subjects

@0537 Can ya link me?

0537

@0celo7 It took a while to sink in fully, it is still kind of shaky.

I did finish learning it in 3 days though, I watched all the lectures in 3x speed 13 a day.

Over the holidays in sophomore year.

@SirCumference I linked you before.

Sir Cumference

Yeah, I'm lazy

Ya mind relinking me?

0537

@SirCumference I guess.

Sir Cumference

Is that the same as this? ocw.mit.edu/courses/mathematics/…

0537

yeah.

Sir Cumference

1:58 AM

Newer = better?

0537

what?

Sir Cumference

The ones I linked were older

0537

same thing.

Sir Cumference

Should I go with those or the newer ones?

K

@0537 So I start here? ocw.mit.edu/courses/mathematics/…

0537

I guess.

Sir Cumference

2:03 AM

How'd ya watch it in 3x speed?

0537

It's an involved process... to lazy to describe how I did it.

;-;

Figure it out?

Download the video?

Or use a browser extension that can do 3x speed.

Sir Cumference

2:05 AM

Like?

0537

I don't remember.

Sir Cumference

What video player is it?

0537

I don't think you will be able to do 3x speed though. You should be able to read at 500wpm to be able to effectively learn from it.

[Because you will rely on subtitles]

Sir Cumference

So...2x speed?

1.5x?

0537

You decide?

Sir Cumference

2:15 AM

@0537 You don't know what player it is?

0celo7

2:50 AM

@dmckee Dude what about Maker's Mark!?

Sir Cumference

4:24 AM

@0celo7 Alright, learning calc from @0537's lecture videos

Already liking it

Stan Shunpike

8:52 AM

@0celo7 that shits awesome. Might be old but definitely sick.

@0celo7 did u find it while cleaning out dups?

@0537 where did u watch these lectures? can u set YouTube to 3x speed? That would save hella time

@ACuriousMind ur current profile picture combined with the winter bash hat is hilarious.

@ACuriousMind $\text{Alien} \times \text{Football} \times \text{Unicorn} \rightarrow \text{ACuriousMind}$

Physics Meta

9:12 AM

0

Q: Up and Down Voting a Moderator

Do moderators know when you are down or up voting all their answers? Is it anonymity for all?

discussion support design

Physics Meta

10:33 AM

0

Q: The Laymon Answer Alternative

More than half of us probably are not even qualified to ask a proper physics question let alone answer one. Would it be ok to add Laymon answers or examples to harder answers?

discussion feature-request answers

0celo7

12:08 PM

@StanShunpike Since Noisecontrollers released their entire discography I decided to make a top 10

It's useless, I can't eliminate anything

Secret

1:45 PM

Hi guys, here's a weird question:

When we wrote down 3-vectors we often denote them as a 3-tuple
$$\begin{pmatrix}a\\b\\c\end{pmatrix}$$

In physics, we know we are dealing with a vector because its components change with the basis used (i.e. it is only invariant when considered as a whole, a summation of basis*components) thus it has a geometric meaning

Specifically, a vector $v$ obeys the following transformation law (where ' denotes the new basis)

$$\Lambda^{-1}v=v'$$

We also have examples of scalars such as the speed of light that are independent of coordinate systems being used

Qmechanic

2:18 PM

About 1250 users got hats during Winterbash 2015. This gives an indication of how many active users that Phys.SE has.

2

0celo7

@Qmechanic How many did Math.SE get?

Huy

5685

ACuriousMind

6:22 PM

@Secret If they behave like scalars, why would you organize them into a tuple?

@StanShunpike Seems legit. ;)

TanMath

@DanielSank you there?

DanielSank

6:49 PM

@TanMath yeah

DanielSank

7:23 PM

@TanMath That may be true but it doesn't make it the right choice. Suppose I throw two parties in two different rooms. On the door to one room I put a sign "BOYS" and on the other door I put a sign "GIRLS". People seeing this will likely enter the door for their gender. However, if we instead have a single party with a sign "EVERYBODY" on it, we wind up with a more fun party. — DanielSank 11 mins ago

ACuriousMind

You know how to party.

vzn

7:40 PM

Replacing Magic With Mechanism? / Anderson, Edge mag

via aaronson (blog), Edging in: the biggest science news of 2015

0537

7:57 PM

Do you think it's funny that physics is last to have the new profile design...

DanielSank

@ACuriousMind Hah, well...

Danu

10:22 PM

Heyo

@0537 We are?

HDE 226868

67

Q: List of communities with base css updates completed

The design team has been rolling out design updates to sites as part of network-wide update to a new base css framework. The updates allow us to: Use .svg sprites for retina displays Fix layout bugs globally More easily add new features to all of our sites in the future Synthesize healthy, n...

discussion design announcements

Physics is the only one still On Deck. Randomly, or so they say. . .

Danu

What's the difference, anyways?

HDE 226868

Snazzy tracking stuff. Softer edges on buttons in the interface. Easier to see progress towards badges and other things.

Oh, and more semi-helpful stats, I think.

I still like the look of the old one, though.

ACuriousMind

It might also be because we requested extra stuff :P

14

A: Can we have a font which harmonizes better with MathJax?

Ask and you shall receive. This site is in line for CSS conversion, and, while we're in there, we'll make sure that we match the serif font in the body like Chemistry SE and Math SE. Thanks!

Danu

@ACuriousMind Chem & Math already got that stuff though.

HDE 226868

10:37 PM

Is anyone here good with the basics of lasers?

Specifically, laser range?

Stan Shunpike

11:10 PM

@ACuriousMind I thought the "interaction" term in QFT lagrangians refered to particle interaction. But I googled the term "free field" and it seems from what I read that an interaction is like....an energy term in the Lagrangian that involves just the field alone or something. Am I understanding this correctly?

ACuriousMind

@StanShunpike You don't have a notion of particle on the level of the Lagrangian. Terms in the Lagrangian involve only the fields, and an "interaction term" is any term in the Lagrangian that deviates from the free Lagrangian (because it gives rise to non-zero amplitudes for processes where the particles of the involved fields turn into one another)

Transcript for