The h Bar - 2015-12-25 (page 1 of 2)

« first day (1877 days earlier) ← previous day next day → last day (3052 days later) »

12:26 AM

user image

12:54 AM

@DanielSank Measurements on the reality of the wavefunction / Ringbauer et al, Nature

am not an expert on this myself. they do not seem to claim it makes outside-of-QM predictions. the ideas seem to be connected to weak measurements. there does seem to be an emerging theory of weak measurements that is not predicted by standard QM. think details are not clear yet.

2 hours later…

3:10 AM

@DanielSank sorry, Christmas happened, I'll get back to you if I figure this out

3:47 AM

its only 4 more hours before its acceptable to wake everyone up and open presents :D I'm getting giddy! Have a good day everyone.

Pfft, weird tradition, we already got and opened our presents here ;P

3 hours later…

user54412

6:26 AM

Good ~~morning~~ ~~day~~ middle of the night, @FenderLesPaul

user54412

6:43 AM

10

Q: Are sophisticated Astrophysics Q's better asked in the Physics SE or Astronomy SE?

My interests primarily pertain to Astrophysics (and Astrochemistry). This subject appears to have two masters: Physics SE and Astronomy SE. How do I decide where to post, and how would you characterize the astrophysics sub-community on each SE? Does double posting of Q's make sense? I will be pos...

discussion scope questions duplicates

7:26 AM

@ChrisWhite mornin :p

@ChrisWhite how's life?

Also don't astrophysics questions tend to typically fall under physics anyways?

user54412

7:45 AM

yeah -- I think a good astrophysics question will always be a good physics question too

user54412

I'm not sure what's more wrong early Christmas morning: the fact that I'm coding, or the fact that I'm running the air conditioner.

8:43 AM

where are you located, @ChrisWhite?

9:37 AM

@Huy It amazes me that people ask that before checking someone's profile

@0celo7 I don't care enough to do so many clicks

The typing was far more effort

no

my hands are already on my keyboard

clicking requires more movement

9:53 AM

After a streak that lasted for almost two years, I missed a day on PSE yesterday :( Damnit, Christmas!

:D

Hi

everyone

happy christmas

Hey guys, I am reading Shanker, he says "when two states |w1>,|w2> are superposed to form a (normalized) state .... "

I am not quite sure what he means by "superposing two states."

sure he doesn't mean we put two particle together?

10:08 AM

I accidentally approved this edit: physics.stackexchange.com/review/suggested-edits/111177

If anyone can review it and reject it, please do so.

p.s. it is the chapter of postulates

10:23 AM

@Shing you just add the wavefunctions

(And then normalize)

10:36 AM

@ACuriousMind For whatever it's worth, it's possible that stating a probability distribution as $\delta(x^2 + y^2 - r^2)$ is bogus, as you suggested before.

However, I think it's not.

There are two ways to describe a manifold: 1) Via parametrization e.g. $x=R \cos(\theta)$ and $y = R \sin(\theta)$, and 2) As the solution set to a set of equations.

@Danu done

If we lack a parametrization, we have to use the equation system and I think that if I want to say that in a space of two variables we get a uniform distribution on a circle of radius $r$ then the only way to say that is $P(x,y) = \delta(x^2 + y^2 - r^2)$.

@vzn I can't access the full article at the moment. Did they measure anything surprising, i.e. anything I wouldn't expect?

Weak measurements are not unexpected. We've understood them for decades.

@DanielSank uh, the first is wrong

(at least, that's not a circle)

you need at least two charts to cover the circle

10:55 AM

@0celo7 Thanks, is there any physical interpretation for superposing the states? or just treating it as something I have to bear in mind when I do calculation?

@Shing (take this with a grain of salt, I'm not an expert) the interpretation is in the probabilities for measuring things

suppose we have a cat in a box

@0celo7 what do you mean?

and states $|a\rangle$ and $|d\rangle$ corresponding to alive and dead, repsectively

then we have the (normalized) superposition $\frac{1}{\sqrt{2}}(|a\rangle+|d\rangle)$

so if we measure the "life" of the cat, we get a 1/2 probability for alive and 1/2 for dead

@DavidZ there is no homeomorphism from the circle to the reals

@0celo7 Yes, so? It looked like Daniel was talking about parametrizations

@0celo7 oh yeah, that's right. I start to what is going on now. Thanks man.

11:03 AM

@DavidZ maybe, feel free to ignore me

ooooh, food

12:00 PM

My theory predicts that, at high enough energies, FRBs and perytons become indistinguishable because the detector burns out.

8

@ACuriousMind Do you know if Kretschman scalar is regular at some point $\Leftrightarrow$ there exists a coordinate system in which Riemann tensor is defined at that point?

1 hour later…

1:30 PM

Mh, no nice questions for Christmas. :( Why are so many people asking homework questions in a break?!

the best particle

1 hour later…

2:52 PM

I wonder how the energy conditions work in string theory

I should Investigate

I really need to read up on string theory one day

What is a string

what is a theory

Glossary of string theory

This page is a glossary of terms in string theory, including related areas such as supergravity, supersymmetry, and high energy physics. == Conventions == -bein A suffix indicating a frame, where the first part is a German word indicating the dimension (as in zweibein, vierbein, and so on). -ino The superpartners of bosons are often denoted by the suffix -ino; for example, photon/photino. s- The superpartners of fermions are often denoted by adding s- at the beginning; for example, quark/squark. == αβγ == α 1. Fine-structure constant 2. Regge slope, or inverse of the string tension 3....

So that's the famous Witten to English dictionary

It's always hard to get on a new book because there's always that first chapter that I've read a thousand times

"Here are the postulates of quantum mechanics!"

How novel

3:24 PM

@ACuriousMind I asked you a nice question a above...

Dump:
http://www.hep.lu.se/atlas/thesis/egede/thesis-node28.html

@Slereah it is a 1-brane

@Slereah something that tells you about strings

What is a brane

what is a brain

braiiiiin

Perhaps you need to upgrade your brain to a d-brain to understand string theory...

So Grimm and Jaffar says that along with integer spin commuting and halfspin anticommuting particles, there are parastatistics particles

Is it the continuous spin representation thing?

3:39 PM

@Slereah What's the most recent update about the 650 Gev particle?

Hell if I know

Here's my guess : The scientists all went home to celebrate Christmas

and so there are no updates

Also in the future : still no updates, because they will be celebrating the new year

@Slereah I don't think so. Parastatistics are just equipping the fields with uncanonical commutation relations with each other, but with itself, each paraboson and parafermion has still the ordinary commutation relations, and these fields are still just integer and half spin fields.

Oh so it's anyon shit

indeed

@Slereah Nah, anyons are different again, and arise from the rep theory of the "2D Lorentz group".

3:45 PM

https://xkcd.com/1621/

On a more serious note, I wonder what theoretical models that allow neutralisation of magnetic monopoles have been put forward by the community. From my knowledge, one of the ways is to have monopoles binding to each other to form monopolia, but are there other proposals?

While anyons evade the spin-statistics theorem by being 2D, I'm not actually sure whether the parafields just violate it and don't care, or whether they don't violate it because they have the correct relations with themselves.

"This elementary example appears in every book on quantum mechanics"

(memory of the monopole bibliography is now pretty hazy to me...)

Then why put it there, Jaffar

Aren't topological defects suspected of just having been strewn around far away by inflation

that's the common explanation. But I am wondering whether there are proposals that explicitly neutralise them

3:51 PM

Probably

as so far the only ones I am aware of is monopole bound states

That's the job of theoretical physicists

throw around theories

It's a weaselteats kind of season

It's a special holiday

The night air smells of sausage

And rancid curds and whey

The pickled chicken livers

Are all laid out with care

In hope that old Saint Weaselteats will rub them in his hair

He comes a-hurlin'

In his souped sausage cart

With a big old bag of pre-chewed gum and a hubcap over his heart

It's a Weaselteats kind of morning

And we jump out of our beds

Then we tumble down the staircase

Landing on our head

We wolf down meat byproducts

And choke down pre-chewed gum

Good old Stinky Weaselteats

He always leaves us some

His suit is made of donkey hide, and he smells like stinky feet

And that is how he got the name of good old Stinky Weaselteats

4:15 PM

@Slereah do you know the Kretschman thing

I do not

well ACM is ignoring me, and he'd probably know

you should ask him

What's a Kretschman thing

4 hours ago, by 0celo7

@ACuriousMind Do you know if Kretschman scalar is regular at some point $\Leftrightarrow$ there exists a coordinate system in which Riemann tensor is defined at that point?

Is that the Riemann tensor squared thing

4:19 PM

yah

@Slereah what's the dual of the Riemann tensor that wiki talks about here en.wikipedia.org/wiki/Curvature_invariant_(general_relativity)

The Biemann Bensor?

Might be just applied the Hodge dual

@Slereah Since when do scalars have 4 indices?

Also: the Riemann tensor is not a form.

Iunno then

Or does one take the dual of the spin connection curvature thingie

Although IIRC the Riemann tensor is a tensor of 2-forms

4:25 PM

An then pull off the components of that

@Slereah Yes, that's what I'm talking about

mb stop reading wikipedia like a wanker and get a real book on the topic

so Radiohead just released the song they wrote for Spectre but was denied because of Sam Smith's

what do you think of it @0celo7

personally I think both are superbad

I think we should let ISIS take over so that music can be forbidden

+1

@Slereah give me a book name on curvature invariants

4:29 PM

Alice in Wonderland

How about you do like a grown up and do Bibliographical Research

HINT : There are two references on that wikipedia page

wow you didn't think I tried to read that paper

it doesn't explain it either

and I don't have access to the other paper right now

mb read the papers in the bibliography of those papers

:(

the worst physics articles I've seen on wikipedia is probably the Misner space one

wikipedia is really useful tho sometimes.

4:40 PM

I'm too stupid to sign up for an AMS membership

mb I shouldn't be a member

well you're an engineer.

@Slereah wtf did you remove

^^

aha, found the registration button

Sliders - Professor Maximillian Arturo

WHAT IS THE LARGEST SYMMETRY GROUP OF A SINGLE DIRAC FIELD

4:46 PM

@Slereah $\mathrm{Mat}(4,\mathbb{C})$

He says U(4), but that is p. wrong

Dammit Gimli

check your math

Altho

Is it???

$\psi^\dagger \psi \rightarrow \psi^\dagger U^\dagger U \psi = \psi^\dagger \psi$

Could be!

Sliders taught me

what is $\psi^\dagger\psi$

One of the dirac bilinears

@ACuriousMind is the largest symmetry group $U(4)$

Is Sliders correct

@Slereah yah, well

is the Lagrangian invariant under that

Hm

If the symmetry is global, yes

5:01 PM

@Slereah I don't think it is. Also, isn't the "Dirac bilinear" rather $\bar\psi \psi$, not $\psi^\dagger\psi$?

yes

What is the commutator of a $U(4)$ matrix with $\gamma_0$ then, I guess

there is a journal of conformal geometry and dynamics

5:22 PM

@yuggib Do I have to prove to the AMS that I'm a math student?

I'm not getting my promised discount.

5:47 PM

Simpsons's CERN Illuminati Mathematical Predictive Programming EXPOSED

@DanielSank so then why are they showing up as major scientific advances in major/ top journals eg Science/ Nature? think there is "something" afoot with weak measurement that is not wholly predictable by std QM theory. but apparently no ("other") theorists are asserting that right now. cannot pinpoint/ put my finger on it at moment. but think it will continue to play out/ "emerge".

Science and nature aren't really science publishing journals

They're high profile but they are kind of pop science papers

@Slereah (somewhat) ridiculous assertion. they have some of the most rigorous peer reviews possible, to some degree even higher than those of the specialized fields they span (eg physics). it is not at all accurate to call it "pop science". it is only that they are scientifically crosscutting, but extremely rigorous.

Peer review only filters for wrongness, not for relevance :p

It's no Daily Mail but you're not gonna find a lot of math in Nature

@Slereah you think some of their articles on (eg) physics are not relevant? lol, whatever

5:58 PM

vzn is salty

@Slereah they cover every scientific field, in std mathematically rigorous ways.

I bet he's published in nature

@0celo7 lol this chat room is salty, you are salty :P

user image

@vzn what am I salty about

the fact that the AMS website is broken?

yes, very

6:00 PM

@0celo7 you dislike "new science" etc as much as many around here :|

@vzn what is "new science"

I don't even know what this thing is that I supposedly dislike

Oh no he's gonna say we hate daring new scientists trying to overcome the carcan of old science

we hate Einstein too

@0celo7 keep asking that zen question and you might someday find the answer :P

for the record, I am smarter than Einstein

he's a dumb thing

runs from people who want to pet him, etc.

6:01 PM

@0celo7 einstein died in 1950s. so we are all "smarter than einstein". QED :P

@vzn uh, no

he's still alive?

Are you smarter than the evidence, though

@vzn dude just tell me

@0celo7 ?!? maybe you are dumb then!

@Slereah evidence is not an agent of intelligence

6:03 PM

@0celo7 when the student is ready the teacher will appear (old zen saying)

@vzn what??

how does this fix the AMS bookstore being broken

You know what else an old zen saying says?

"If you meet the Buddha on the road, kill him"

Do not listen to those murderers

@0celo7 why do you "all hate einstein"?

If I ever murder someone, it will be with a karambit

@vzn because he was a quack who knew nothing about math or physics

@Slereah reminds me of the story of Angulimala

6:05 PM

i think he's talking about his cat einstein.

all he did was stand in the town square and scream about the variable speed of light and inhomogenous space

@vzn hello.

@0celo7 guessing, from your favorite video game perhaps?

@vzn good job googling

but yes

Splinter Cell has taught me how to take out terries with such a blade

I will extend the techniques to that asshole in physics lecture

@vzn dude just tell me what this new physics is that I supposedly don't like

6:28 PM

@0celo7 ok, have you heard of any "new physics" or do you think its a mysterious term verging on oxymoron?

do you want to be serious for a nanosecond, or should we have a nice long conversation about video games now?

6:40 PM

@vzn I have no clue what you are talking about.

@vzn I am being serious, the person talking about zen or whatever isn't.

@0celo7 zen is serious! do you think it isnt?

@0celo7 you use the phrase "new physics," what is that?

@vzn No clue.

You're the one who first used it.

Oh, "new science"

Replace "new physics" with "new science"

@0celo7 :(

@vzn I mixed up things

you said "new science" but I have no clue what that means

if you want seriousness, that's it

@0celo7 blades are cool like throwing stars myself, got to throw a few a few yrs ago at renaissance festival. they had axes too :)

@0celo7 are you talking about a teacher or student? is this a ref to earlier conversation here? if so missed it. ???

6:47 PM

@vzn there's a dude in physics who just makes me mad...

he'd look great with a karambit in him >:)

I do not think that "joking" about killing/injuring people is particularly good taste.

@ACuriousMind Oh, so that you comment on

7:05 PM

@ACuriousMind 0ce is the resident jester, am willing to "cut him some slack" :)

@0celo7 why does he make you mad? student, teacher, other?

@vzn student

@0celo7 hint, its related to so called "research." do you have any interest in "research"?

@vzn yes

@0celo7 great, what area(s)? :)

@vzn experimental physics, nuclear fusion, something like that

7:12 PM

@0celo7 fusion is a way cool area these days, posted a few links on that, did you hear the recent news in germany re stellarator?

@vzn yes

ok. ps happy holidays, merry xmas, are you celebrating in some way?

@vzn yes

you still have not told me what new science is

hi guys, for a pseudo-Riemannian manifold, under the variation $g_{\mu\nu}\mapsto g_{\mu\nu}+\delta g_{\mu\nu}$, why is $\delta g=gg^{\mu\nu}\delta g_{\mu\nu}$? $g=\mathrm{det}g_{\mu\nu}$. Nakahara proves it with the matrix identity $\tag{1}\mathrm{ln}(\mathrm{det}g_{\mu\nu})=\mathrm{tr}(\mathrm{ln}g_{\mu\nu})$. The LHS of this varies as $\delta g\cdot g^{-1}$ (which is fine), the RHS as $g^{\mu\nu}\cdot\delta g_{\mu\nu}$.

ah, this is easy

7:16 PM

I don't understand the last point. Why does $\mathrm{tr}(\mathrm{ln}g_{\mu\nu})$ vary as $g^{\mu\nu}\cdot\delta g_{\mu\nu}$ under the variation $g_{\mu\nu}\mapsto g_{\mu\nu}+\delta g_{\mu\nu}$?

you need the formula for the derivative of the determinant

note that $\delta$ is "in a sense" a differential operator on the space of metrics

Jacobi's formula?

yes, that works

oh yes

@0celo7 ok, fair enough, there is the general and the specific. how about starting with that nature link recently posted by me as a case study?

7:19 PM

@0celo7 thanks

@Bass wait do you accept the ln det formula

you don't need anything more than it

what is the derivative of $\ln M(x)$ where M(x) is some matrix, @Bass ?

@0celo7 I'm not yet done checking it fully, but your hint gave me something I haven't thought of yet.

@Bass you need to generalize $\partial\ln f=f^{-1}\partial f$

also it helps that the trace is a linear operator so derivatives commute with it

and $g^{\mu\nu}$ is the inverse of the matrix $g_{\mu\nu}$

@0celo7 I always imagine it this way: if you diagonalize the matrix, the logarithm is much easier since it's the logarithm of the eigenvalues at the diagonal. This "commutes" with many other operators, so you can calculate many logarithm things in diagonal form, for example my equation (1) above.

@0celo7 i faintly seem to remember that one.....

@Slereah Nasa used Santa Claus as a codename for THREE UFOs spotted during the lunar landings, claims former employee / dailymail

7:34 PM

>daily mail

The Daily Mail Song

wtf there are people who think UFOs are fake

UFOs aren't fake, they are just UFOs

Unidentified flying objects

if Mass Effect and Halo have taught me anything, the lmaos are all around us

That is what the name means

Not "saucer men from Mars"

SMM

7:35 PM

Aliens always look like what aliens look like on movies, for some reason

did you watch Prometheus

I have

My critique of that movie will be a noise

"Eeeeeeh"

I watched it with a friend

it felt like a slideshow of r/WTF

an SJW?

no but his GF seems to be one

just met her last Sunday

that movie though

when she gives birth

so yummy

7:38 PM

My favorite review of Prometheus

Red Letter Media talks about Prometheus - SPOILERS

birth fetish?

@0celo7 you should watch that part then you'll get a birth fetish as well

but maybe after xmas dinner

@Slereah bravo, brilliant! ps do you have a job right now?

Probably yeah

A company is writing a job contract currently

Probably a job for early january

sounds "promising"

7:42 PM

Well they asked for my paperwork

Probably wouldn't bother if they weren't gonna make me sign

whats it about?

What else

More web bullshit

That's pretty much the job market currently

web development? front end?

US/EU?

:(

Front end IIRC

7:44 PM

← know the feeling. "pays the bills"

Nothing too interresting but a man's gotta eat

do you want to work in physics again?

Would be nice

ok, this is personal, did you finish masters or PHD? trying to figure that out from transcript here

am reading a robotics book at moment...

*got a masters

No PhD tho

PhD topic wasn't financed

7:50 PM

come to my high school

1 physics teacher is quitting

China's a bit far

Oh, Zurich

Still a bit far

wow assume China just cuz asian

u fukin racist

you get 100k as entry wage without teaching diploma

@Huy China $\cong$ Japan dude

now come

mb pick a Swiss name

Hans Spatenberg

2

7:52 PM

Hans Spatenberg

lol

Happy christmas and merry holidays

Rudolf Haxengruber

that's not as good

Spaten is like an insult

@Huy DavidZ seems to like it, cant be all bad :|

@vzn: wat

7:53 PM

china

they seem to have a lot of $$$ for physics/ science, reading his blog

I hate China

he got a spiffy new topnotch mac etc

Not a lot of theoretical papers coming from China, tho

They're more into applied stuff

@Huy why?

cuz it's China

even PhD students get new topnotch mac etc

or is that different in your country

7:54 PM

@Huy wtf?

lol

My PhD topic was SUPERSYMMETRIC QUANTUM MECHANICS AND THE APPLICATION OF THE ATIYAH SINGER THEOREM TO KAHLER MANIFOLDS

@Huy not aware. davidz seemed to be impressed in his blog. china now has the worlds largest GDP by some measures. just passed US for 1st time in ~1½ Century.

It was not an easy sell

ok

it's still China

land of ****** if you ask me

7:57 PM

Which dynasty do u think is best

Tang Dynasty is top dynasty I say

@Slereah saw that in the chat transcript. sounds good to me anyway. and why does a Phd thesis have to be "sold" anyway? the curse of capitalism...

In France a PhD student is obligated to get paid

So he has to basically be hired by the university

So if there are not enough moneys for every students

IIRC there was enough money for 6 thesis

@Slereah sympathize. english expr: "it happens to even the best of them". have long noticed science and capitalism (sometimes) dont mix well.

« first day (1877 days earlier) ← previous day next day → last day (3052 days later) »

Transcript for

Dec '1525

The h Bar

General chat for Physics SE (physics.stackexchange.com). For M...

join this room
about this room

00:00

06:00

12:00

18:00

all times are UTC

site design / logo © 2024 Stack Exchange Inc; legal

mobile