The h Bar

I'm reading this paper, and it states that we can define a set of lines on $\mathbb{R}^2$ by $$\mathbb{L}=\{[(a,b,c)]\subset\mathbb{R}^3|(a,b,c)\in\mathbb{R}^3,\,a^2+b^2\neq‌0\}$$

0celo7

12:13 AM

@ACuriousMind Technical German is really dumb!

DanielSank

@0celo7 o_O

HDE 226868

It then says,

> It is possible to show that $\mathbb{L}$ is a 2-dimensional manifold, sometimes referred to as the affine Grassmannian of lines in $\mathbb{R}^2$.

user54412

@HDE226868 it wouldn't be a physics lab without coax cables everywhere

Slereah

What is even that thing

Is that the Kundt paper

0celo7

no

Straumann book from the 80s

Apparently he proves something interesting

gotta chug through...German and...drawing

Really?

Slereah

12:15 AM

Something something coordinate chart

0celo7

That's a pretty long proof.

@Slereah Yup

That's the intro

Huh, this is just his GR book but hand written :D

Where the heck is FLRW...

what the heck is up with this bibliography

none of these books are what they're supposed to be

HDE 226868

ResearchGate should get rid of their lemniscate buffering symbol. It really does make it seem like loading takes forever.

dmckee

OK. Now I'm confused.

0celo7

Stop that!

Don't be confused!

dmckee

In looking through the flags that are currently active I see the summary:

"very low quality – [NamelessUser] 1 hour ago; added 1 comment; Vote Up"

If it s very low quality, why did you vote up?!?

HDE 226868

12:25 AM

@dmckee Could it have been a misclick, and the user meant to vote down?

dmckee

I hope so. But I don't know and its driving me crazy.

Slereah

Maybe he believes in positive reinforcement

0celo7

Damn, just skimmed a 400 page book

Did not find what I wanted.

dmckee

This post also has a flag from another user (with 10k+ rep) who didn't vote down or vote to close. More confusion.

HDE 226868

@dmckee What was the second flag? Also VLQ?

0celo7

12:29 AM

THE BOOK ONLY HAS EIGHT CHAPTERS HOW ARE YOU CITING THE NINTH

I might have to email him

This is criminal

ACuriousMind

@HDE226868 Observe that $a^2+b^2 \neq 0$ means just $a\neq 0 \vee b\neq 0$ for real numbers. Now, $[(a,b,c)]$ describes the line $y = \frac{a}{b}x + c$ where $y =c$ if $b= 0$.

HDE 226868

@ACuriousMind Right, got that.

0celo7

vertigocenter/straumann/norbert

^^won't open for me

can anyone else open it?

Terry Bollinger

@yuggib Thanks and no problem, I didn't even ask until after you left.

ACuriousMind

@HDE226868 So your question is? ;)

0celo7

12:34 AM

@Huy I require your assistance.

Terry Bollinger

Wow, do you guys ever leave the chat room?

0celo7

no!

HDE 226868

@ACuriousMind Ohhhhh. . . I had been trying to prove it from the definition of an affine Grassmanian, i.e connecting the basic description with other properties. I can't believe I overthought it.

0celo7

oh my god now the book won't download

my life is crappy

HDE 226868

Thanks so much for taking a look at it.

Terry Bollinger

12:36 AM

@0celo7 well, I admire your dedication!

ACuriousMind

@TerryBollinger I just got back, I was enjoying a nice get-together with other students who have the same stipend as I have

0celo7

@TerryBollinger I've been looking for something for the past hour

Scouring the literature.

ACuriousMind

@HDE226868 It is sometimes quite challenging to translate abstract mathematical definitons back into something that makes sense, don't worry about it :)

Terry Bollinger

Fortuitous timing...

ACuriousMind

Also, my sleep cycle is very...unusual

Not sure it's a cycle anymore

0celo7

12:38 AM

SHIT

I think someone bought the thing

I keep getting to this strange search engine

@ACuriousMind I need your help

ACuriousMind

@0celo7 Oh, what will you do when I ever stop slacking? ;P

0celo7

@ACuriousMind I need to write an email to Straumann asking him why these references either A) don't exist, B) don't show at all what they should, C) reference nonexistent chapters

ACuriousMind

@TerryBollinger I'm also using this chatroom as a procrastination tool ;)

0celo7

This is pretty maddening, because he supposedly shows something amazing.

I would like to write this email in the Germans

I need some help with that.

Terry Bollinger

@0celo7 for what searchest thou?

ACuriousMind

12:41 AM

Tell me about it, I almost wrote Witten an email about why the heck he thinks "It can be shown" is an appropriate phrase to use when no one has ever shown that :D

I eventually figured it out, but it was infuriating

0celo7

@TerryBollinger Apparently FLRW is uniquely fixed by requiring that group of isometries leaving the velocity of a comoving observer fixed contains SO(3)

ACuriousMind

In retrospect, if Witten had written out that proof, I'd never have joined phyiscs.SE

0celo7

Apparently

@ACuriousMind what was this?

ACuriousMind

@0celo7 Just look at my first two questions.

@0celo7 Write it and I will critique it

0celo7

@ACuriousMind ok, will eat, do homework and then search the literature some more.

then write the email

@ACuriousMind If you wanna do me a favor, pls triple check link.springer.com/book/10.1007/BFb0118135 doesn't have anything on FLRW

Terry Bollinger

12:45 AM

@HDE226868 random: I've been looking at a subset of the permutation group as a way of visualizing Clifford algebras...

0celo7

what's strange is that Straumann references 3 of his own works for the proof

but none contain it

or even mention the topic!

Terry Bollinger

@0celo7 whoa, I almost missed that one!

That's interesting...

ACuriousMind

@0celo7 Not gonna skim a fucking typewriter paper, sorry

0celo7

It's a 400 page book, not a paper.

ACuriousMind

Still typewriter

::shudder::

BTW, got two string theorists to consider coordinate-free math more today :D

Also had to face the fact that I can't explain anything I'm interested in to non-physicists :(

0celo7

12:53 AM

Aww

The math people I hang out with do PDEs and geometry, so GR means a lot to them

I don't think they get my other major, though

Terry Bollinger

Later gents I'm pumpkinifying, @0celo7 good luck on the search!

HDE 226868

@ACuriousMind Thanks.

0celo7

@TerryBollinger Thanks

HDE 226868

@TerryBollinger Ooh, cool.

Have fun with the pumpkins.

@0celo7 Didn't work for me, either.

0celo7

I think Straumann has a draft out there somewhere of a new book. I need it.

@ACuriousMind Vorlesungskopie?

Draft?

ACuriousMind

12:58 AM

@0celo7 More like "copy of the lecture notes I'm not comfortable with publishing"

0celo7

Damn.

There's one more reference.

If I can't reconstruct the proof from that, I'm sending an email

And by "I" I mean @ACuriousMind

ACuriousMind

Don't expect anything from me till tomorrow, and this isn't a promise I'll do it tomorrow :P

:25146037 Oh, sorry, it's supposed to be $x=c$ if $b=0$.

dmckee

@TerryBollinger I joined FaceBook under protest, but I discovered that I can keep track of my niece's emotional state by checking once a day. As in: she was posting "not a morning person" stuff and then "my co-workers are idiots" kind of stuff, then "here is whts a chick wants from a guy" stuff then "he broke my heart, I'll dig his out with a rusty spoon" stuff."

This chat room reminds me of that at times.. Only with finer granularity.

0celo7

Rust spoon?

Is that a spoon made out of rust

dmckee

Rusty and not good at typing.

0celo7

1:08 AM

Or a spoon made to spoon rust

ACuriousMind

The only person talking about their love life in here is @Danu :P

0celo7

^^

No one else has one

ACuriousMind

Well, DanielSank has a wife

0celo7

Fiance

ACuriousMind

KyleKanos, too

user54412

1:08 AM

Too true

0celo7

@ACuriousMind He left.

HDE 226868

@0celo7 Ehh. . . I have a girlfriend, if that counts.

0celo7

And @ChrisWhite could seduce @DanielSank 's fiance

and then something happens and he never gets on here again

user54412

Umm...

0celo7

car crash, etc.

I...I might have found something.

Handwritten notes from one of Straumann's classes.

Gotta figure out cursive technical German. Oh boy.

wtf are these notes about??

itp.phys.ethz.ch/education/articles/KT1

Aha! Einstein-Universum!

I recognize something!

@ACuriousMind ein was?

omgomgomg I think I found the proof

@ACuriousMind D: pls help

ACuriousMind

1:19 AM

@0celo7 dreidim. is an abbreviation for three-dimensional

@0celo7 Wachstum, i.e. growth

0celo7

ach so

I need help with the cursive, not so much the German ;)

I FOUND THE REFERENCE

HE PUT THE WRONG PAGE NUMBER FOR THE JOURNAL

::dances::

retro.seals.ch/digbib/view2?pid=hpa-001:1974:47::385

Found it.

@ACuriousMind You're off the hook for the email.

@ACuriousMind Thanks for the hint about lecture notes. It prompted me to check his webpage for his classes.

DanielSank

@0celo7 ಠ_ಠ

@HDE226868 The reasons for various sizes and frequency ranges in information transmissions systems is fundamentally an question of electrodynamics.

The practical aspects are important parts of many experimental physicists' daily lives.

In particular, the choice of coaxial wire as opposed to other shapes and topologies of conductor comes down to interesting questions of the mode structure of those various topologies.

This is the sort of thing that can be far more satisfactorily explained via a physics oriented discussion as opposed to a typically "engineering" style discussion.

As I've argued before, if someone posts a question like that here, they probably want the physics type approach. We should respect that rather than discouraging it.

HDE 226868

Okay, thanks. That clears it up.

0celo7

why is no one happy I found this paper

>referencing HE and Weinberg in the same paper

@Slereah How does that even work??

dmckee

1:52 AM

@DanielSank Also the cross-talk properties. Coax has vanishing cross-talk but it is complicated and expensive compared to, say, twisted pair. SO then you ask how to reduce the cross-talk in twisted pair and maybe come to mutually prime winding numbers or some such.

obe

I found recorded lectures on dynamical systems!!!

bless

0celo7

@ACuriousMind @Slereah do you know what he's referring to here?

WHAT

OH NO YOU DID NOT

AHHHHHHHHH

I give up.

@HDE226868 help me

www-personal.umich.edu/~wangzuoq/635W12/Notes/Lec%2019.pdf

Might be helpful.

DanielSank

2:08 AM

@dmckee Wat?

Mutually prime windings? Go on...

dmckee

I'm in particle physics. We often need to run hundreds or thousands of signal from the detector to the DAQ (less so these data, as a lot of CPU has been pushed at of the counting house and into the machine, but still). Hundreds of cables lying side by side of tens or hundreds of meter. Signal transmission between the cables is a risk.

Twisted pair reduces the risk a little, because now it is dipole--dipole, but over long runs it still matters.

DanielSank

@dmckee You're preaching to the choir. I'm very interested in how to run lots of high frequency lines with low crosstalk.

Please do go on...

dmckee

So, one pair twists 28 times in 10 meters, the next twists 31 times, the next 37 times...

DanielSank

@dmckee And that leads to low crosstalk?

dmckee

Big reduction in cross-talk. You can buy cable bundles with that property.

DanielSank

2:11 AM

What frequencies are we talking about?

@dmckee hah! Didn't know that.

dmckee

@DanielSank Yeah, because sometimes the relative direction of the signal-group dipole is the same and sometimes opposite.

@DanielSank Now that's a good question. I'm used to thinking about amplified PMT pulses. Rise times oround nanoseconds, fall times 10s of nanoseconds.

DanielSank

@dmckee Ok so maybe up to 300 MHz ish?

0celo7

signals geeks

DanielSank

@0celo7 Signal processing is very interesting.

You know the Dyson series? Any signal processor worth his/her salt understands that as the transfer function of a simple feedback system.

0celo7

trying to decipher differential geometry lecture notes isn't

DanielSank

2:16 AM

You'd be delightfully surprised at how many really complicated things in physics can be understood very intuitively in the context of signal processing.

dmckee

@DanielSank It's contain some components faster than that, but I suppose that's a good center for the band.

I'm not actually a signal guy. Someone else always worried about those issues (Big Science means you end up specialized), but I've sat through talks about many times.

0celo7

@DanielSank can you explain sectional curvature of 3-manfolds intuitively?

what is this "Big Science" you keep talking about

dmckee

@0celo7 Most of my papers have more than 90 authors. Some have more than 200 authors.

That's a small author list in particle physics terms.

0celo7

Damn

Who actually writes the thing?

dmckee

Well, experimental particle physics. The smart guys still publish in groups of two or three.

DanielSank

2:19 AM

@dmckee Yah. Don't you guys have some kind of canonical author list for each hardware system or something like that?

dmckee

@0celo7 Lots of people turn in drafts of various sections and a committee dumps most of the work on a post-doc. Then edits and sends them back and send the result out for collaboration approval.

DanielSank

I've been wondering if we should do that too. Our author lists are like 20 folks long. I wonder if we should just throw up a web page called martinis_group_authors.org.

0celo7

dmckee

@DanielSank Most of the experiments I've been part of didn't divide it up that way. The 1000+ ones do.

0celo7

Great.

Now I have to mess with that thing.

DanielSank

2:20 AM

@0celo7 Enjoy yourself.

@dmckee I see.

0celo7

Why can't I be normal

dmckee

But some papers are just signed by the collaboration and there is a web-page that lists who that means.

0celo7

@dmckee Holy shit!!

1000+??

dmckee

LHS experiments are crazy stuff.

0celo7

LHS?

Large Hadron ...Splitter?

Left Hand Spinel?

Love His ...Sh...uh

DanielSank

2:22 AM

@0celo7 Yeah, how do you think you build a piece of equipment that spans international borders? You can't just theory that into existence.

0celo7

@DanielSank Einstein and the Evidence, my friend.

DanielSank

You need a construction crew, a software army, instrumentalists, theorists, and people to make sure all those people's work goes in a coherent direction.

dmckee

Did I mention my typing? And my better half keeps dragging me into the kitchen to help with things.

DanielSank

@dmckee Ain't nothing wrong with that.

Good things happen in kitchens.

dmckee

@DanielSank IN this case we're straining the beef broth. That is a good thing.

0celo7

2:23 AM

I guarantee: sectional curvature of 3-manifolds has never happened in a kitchen

DanielSank

@0celo7 I used to do all my homework in the kitchen.

Easy access to snacks helps the brain.

0celo7

@DanielSank This is not homework, sadly.

I can't take geometry for another few years.

OH MY GOD THE BOOK I ORDERED PROVES THE THEOREM I NEED

Magic~~

Just gotta wait for it to arrive!

HDE 226868

@0celo7 Sorry, I'm in the middle of Macbeth. I'm in the wrong mode.

0celo7

@HDE226868 I think I figured it out. Maybe.

Since you're into astro I figured there was a shot you know something about constant curvature manifolds

HDE 226868

Not much.

0celo7

2:31 AM

It looks like Jost proves most of what I need.

I guess the thing with research articles is that I have to fill in some details.

DanielSank

2:55 AM

@ACuriousMind ?

0celo7

@DanielSank He objected

DanielSank

@0celo7 Yes. Why?

0celo7

I quoted Tony Zee

damn, I was doing something

you distracted me

now I have no clue what I was doing

DanielSank

@0celo7 Getting old?

0celo7

ah! I remember

DanielSank

3:01 AM

That's because I reminded you.

You were getting old.

BTW @0celo7, nice job articulating your point with JD.

0celo7

@DanielSank you the one who starred it?

DanielSank

@0celo7 Nope.

0celo7

@DanielSank why don't you star it then

DanielSank

I'm just always impressed when people clearly articulate their position on issues like that where it's so easy to just get annoyed.

@0celo7 Who says I didn't?

0celo7

@DanielSank uh...you?

DanielSank

3:04 AM

Oh, I guess I did.

XD

obe

there is no course on dynamical systems at my university lol.

:(

0celo7

@obe It's called "engineering"

DanielSank

@obe Isn't that usually called "Classical mechanics"?

Or maybe "Partial differential equations"?

obe

yeah

@0celo7 how is it engineering lol?

0celo7

@obe look at any of the upper division engineering classes

obe

3:05 AM

does that book i linked look like engineering to you?

0celo7

you'll find some crazy dynamics there

@obe probably

huh, there's class on fire dynamics here

0celo7

3:23 AM

TIL AEs use quaternions in error feedback for UAVs

obe

3:40 AM

look at this book amazon.com/Dynamical-Systems-Cosmology-Astrophysics-Science/dp/…

looks super difficult.

0celo7

basic civil engineering

obe

amazon.ca/Dynamical-Systems-Cosmology-J-Wainwright/dp/…

physics is scary.

0celo7

3:58 AM

you can only see like 3 pages of that

user685252

4:23 AM

Hi @ChrisWhite

:-)

0celo7

4:45 AM

all alone

doing homework

NeuroFuzzy

6:05 AM

Quantum Zeno effect

The quantum Zeno effect (also known as the Turing paradox) is a situation in which an unstable particle, if observed continuously, will never decay. One can "freeze" the evolution of the system by measuring it frequently enough in its known initial state. The meaning of the term has since expanded, leading to a more technical definition in which time evolution can be suppressed not only by measurement: the quantum Zeno effect is the suppression of unitary time evolution caused by quantum decoherence in quantum systems provided by a variety of sources: measurement, interactions with the environment...

neat

Huy

6:26 AM

@0celo7 what for my son?

Slereah

7:36 AM

@0celo7 well obviously

John Duffield

8:00 AM

@bolbteppa : I have seen some of them, and I'm not impressed. Leonard Susskind is the guy who will tell you that the infalling elephant goes to the end of time and back and is in two places at once.

user54412

8:56 AM

Finally got my code paper out. Now I can actually start doing science.

user54412

@ACuriousMind I put in as many indices as I could, just for you ;)

Slereah

After checking that metric does fail the Frobinius condition

Does it have to fail for all timelike vector fields or is one enogh?

Slereah

9:27 AM

Gödel just ised one but maybe he's a lazy shit

Secret

I saw you guys have a lot of awesome CTC discussion in the past 3 days. I wish I will be able to catch up later. My brain resources is currently 99% on my honours project, in particular some spectroscopy stuff

Slereah

10:04 AM

So I used the ansatz for klein gordon in that metric

It is less bad but still pretty awful

Basically it's the Mathieu equation but slightly worse

Mathieu equation that, if you recall, I struggled with for the KG in a Ellis Bronnikov wormhole

But worse

Bad sign

Although the goal isn't quite the same, so I can probably cheat a bit

Slereah

10:29 AM

"Solutions of the Cauchy problem for the wave equation on a non-globally hyperbolic spacetime, which contains closed timelike curves (time machines) are considered. It is proved, that there exists a solution of the Cauchy problem, it is discontinuous and in some sense unique for arbitrary initial conditions, which are given on a hypersurface at time, that precedes the formation of closed timelike curves (CTC)."

Oh boy

Slereah

10:42 AM

Also wait

Isn't Frobinius theorem just for first order PDEs

Slereah

10:55 AM

Gotta love when papers list their assumptions

"We conjecture that this well-posed nature of the initial value problem is true for initial data on a spacelike hypersurface (but not necessarily of data on $\mathcal{I}^-$) not only for our specific wormhole spacetimes, but also for any 4-dimensional, asymptotically flat, classical spacetime with topology of the form $R \times S - {p}$, where S is a closed 3-manifolds,

and we also conjecture that in such spacetimes the initial value problems is well posed, in the same sense as fpr $\Phi$, for all other non-interacting (linearly superposing) fields, classical and quantum"

That's a lot

Slereah

11:20 AM

imgur.com/gallery/3pf4SG3

user685252

11:36 AM

Too bad he turned out to be a pervert :(

Secret

12:43 PM

@Slereah If I simply look at this statement by itself, it seems somehow time earlier than the CTC region dictate the dynamics within the CTC.

Slereah

It's complicated

Secret

I might look at the maths later, but if my understanding is correct, it kinda makes sense to me

innisfree

@ChrisWhite you're joking aren't you? Now you begin answering email about bugs, fixing bugs, and email about how do I install dependency X for your program?

0celo7

What is the spacetime with the most singularities