The h Bar

ACuriousMind

20:02

@BernardoMeurer Newtonian mechanics, strictly speaking, is wrong yet we have many answers relying on it and nobody thinks something should be done about that

Bernardo Meurer

@ACuriousMind Indeed

But what if the old theory was deprecated in favour of a new one entirely?

David Z

Again, Newtonian mechanics was deprecated in favor of a new theory and nobody thinks anything should be done about that

ACuriousMind

@BernardoMeurer Note that, since our current theories match our observations, every "new" theory must necessarily have some sort of limit in which they become the old theory. "Entirely new" theories cannot arise; science is an incremental effort.

AccidentalFourierTransform

in short, no new discovery will ever prove that we were entirely wrong

@ACuriousMind I need help with inflation

$\phi$ is a real scalar field

BTW what happened here:

physics.stackexchange.com/posts/306222/revisions

I dont understand what anna tried to do

ACuriousMind

20:18

@AccidentalFourierTransform If you look at the other answers, she wanted to add something to her own answer and accidentally added it to another answer

Bernardo Meurer

@DavidZ @ACuriousMind Got it. It was just something that came to mind :)

ACuriousMind

@AccidentalFourierTransform What exactly do you need help with?

I'm not going to compute a Feynman diagram :P

AccidentalFourierTransform

@ACuriousMind but then she deleted something that was part of the original answer, right?

@ACuriousMind well, first of all how can a scalar couple to photons? =P

ACuriousMind

@AccidentalFourierTransform lol, good point

Well, a complex scalar could

AccidentalFourierTransform

@ACuriousMind the potential energy of the scalar is given as $V(\phi)=\Lambda\cos\phi/\mu$

so it is real

I wrote an email to my professor asking how could a scalar couple to the photon without breaking gauge invariance

and he told me that the coupling $\phi F_{\mu\nu}F^{\mu\nu}$ is gauge invariant

but then I told him that such a term has vertices with four photons and one scalar, and therefore the process $\gamma\gamma\to\phi\phi$ has no tree-level amplitudes

and then he told me that the vertex has two photons and one scalar, and that the diagram is indeed a tree diagram

ACuriousMind

20:23

But I'm not sure why they think the vertex should be scalar-photon-photon. By minimal coupling, the coupling should be scalar-scalar-photon-photon from the $D_\mu\phi D^\mu\phi$ kinetic term.

AccidentalFourierTransform

but that only works for complex fields, right?

ACuriousMind

Yeah, right

@AccidentalFourierTransform Why would it have four photons?

AccidentalFourierTransform

because $\phi F^2\sim \phi A^4$

ACuriousMind

...no, that's wrong

AccidentalFourierTransform

goddamit

ACuriousMind

20:25

$F$ contains only one $A$, differentiated.

AccidentalFourierTransform

yeah now I see it, thanks

ACuriousMind

In non-Abelian theories $F^2$ has three- and four-gluon vertices, but not for photons

AccidentalFourierTransform

also, what is the exact decay process? $\phi\to ?$

or maybe $2\phi\to2\gamma$?

ACuriousMind

What's wrong with $\phi \to \gamma\gamma$?

AccidentalFourierTransform

hmm

kinematics? =P

idk

that doesn't seem right for some reason

ACuriousMind

20:28

It's usually forbidden by charge conservation, but since $\phi$ is uncharged because of that weirdo interaction term, it should be admissible

AccidentalFourierTransform

screw renormalisability anyway

@ACuriousMind well thank you :-)

ACuriousMind

np, what do you call such a particle, anyway?

AccidentalFourierTransform

Walter

ACuriousMind

I'll call it the faxion - it looks like an axion but it's not, it's fake.

obe

@AccidentalFourierTransform did you listen to the album?

AccidentalFourierTransform

20:32

May 3 '16 at 18:58, by AccidentalFourierTransform

@user507974 then definitely Walter

@obe lol, I downloaded it and put it in my mp3 to take it to the gym

but, lazy as usual, didnt go

obe

@AccidentalFourierTransform ok lmk when you listened to it.

MartianCactus

I HAVE TRIED A MILLION TIMES but my ray diagram of a concave mirror when an object is over center of curvature is NEVER CORRECT!!

AccidentalFourierTransform

@obe will do :-)

MartianCactus

the object should be right under c

whats the problem here? :(((((((((((((

the diagram is correct

AccidentalFourierTransform

the problem seems to be that you are studying optics

MartianCactus

20:36

?

AccidentalFourierTransform

optics is a problem on its own

MartianCactus

lol

AccidentalFourierTransform

also, did I ever say that I hate cosmology?

MartianCactus

but seriously how do i make it?

AccidentalFourierTransform

did you try to make the lines thicker?

MartianCactus

20:38

nope

its all in one go

but the last one is accedentally divided in 2 but it doesnt make any difference anyway..

AccidentalFourierTransform

there you go, you're welcome

MartianCactus

THATS THE EXACT SAME THING MY TUITION TEACHER DID WHEN I SHOWED IT TO HER!!

god..

lol

AccidentalFourierTransform

the trick is to not give a damn

MartianCactus

are u on 9gag ?

anyway

lemme repost the question

I HAVE TRIED A MILLION TIMES but my ray diagram of a concave mirror when an object is over center of curvature is NEVER CORRECT!!

obe

what r u doing

MartianCactus

20:46

making a ray diagram

MartianCactus

20:59

]\

obe

21:18

@ACuriousMind 0celo7 asks - do a rotation and a parity transformation always commute?

heather

hello

ACuriousMind

@obe What do you think?

obe

22:27

@ACuriousMind he says if he knew what to think he wouldn't be asking.

ACuriousMind

@obe Not talking to him, talking to you

DanielSank

I find the discussion in the comments here rather interesting.

rob

@AccidentalFourierTransform Hmmm. Zooming way in, your upper-right corner reflection is taking place a little behind the mirror.

DanielSank

@heather ohai

Sasha

@DanielSank Thanks for the thorough answer :)

Skyler

22:40

howdy danny boyo\

hi heather, how do you do

@Sasha ive never seen you here before

DanielSank

@Sasha Sure!

Skyler

howdy

DanielSank

@Skyler Don't call me that. Or call me that if you can beat me in a Bo5 Smash Bros set.

@Sasha It was a good question. Did you see the discussion in the comments between @EmilioPisanty and me?

Sasha

I just got here. I'm new to stackexchange as a user in general... though I've used it for info many a time re:code snippets

DanielSank

@Sasha We're very happy to have you. Your question about the squeezed state cooling was good.

Sasha

22:44

@DanielSank Yes, I did see it.

DanielSank

It's interesting. I think it's interesting to see how different people think about the same issue.

Skyler

@DanielSank i might have some time this weekend

DanielSank

To me, the idea that the squeezed state cooling can "in principle go to arbitrarily low temperature" is an irresponsible and even foolish statement in a scientific context.

Sasha

Good points on both ends. I was nitpicking about their use of language, but you're right that it isn't definite that there's no theoretical limit on squeeze cooling.

DanielSank

The theory almost surely includes assumptions that fail at some point.

This is far, far too often missed by even very good physicists.

Skyler

22:46

@Sasha The article in your question reminds me of one of my final questions in stat mech.

Sasha

I agree. I expect grandiose misinterpretations of papers by journalists, but it irked me to see that on NIST.gov

DanielSank

I'm hypersensitive to this because a few years ago there was a big mystery in my fiend about why the quantum state measurement in superconducting qubits failed in a particular way.

Everyone was confused because the theory predicted that the state measurement should not fail. I got involved and eventually figured out what was going on, and it turned out that two of the major assumptions of the theory were just flat out wrong in the limit people we trying to apply that theory!

Sasha

I run into this a lot in fluid dynamics. which equations work here again???

DanielSank

Having experienced that, I strongly dislike statements about things working arbitrarily well in principle. Those statements are just lazy and kind of dishonest.

@Sasha Right!

Skyler

We were supposed to figure out the most cooling you could achieve with adiabatic cooling using magnetization on earth

DanielSank

22:48

@Skyler Nice!

That's a pretty simple calculation, yeah?

Sasha

supposed to lol, did you succeed?

Skyler

Yea

Sasha

Excellent :)

Skyler

sounds like my prof was shouldve quized the journalists

he'd tear them a new one, he's particularly savage old chinese man (im sure daniel knows who im talking about)

DanielSank

Zee?

Skyler

22:51

yep

AccidentalFourierTransform

si

Sasha

Speaking of fluid dynamics, if you glue a petri dish to a bass driver hooked up to a cheap two channel amp and strap a ring of LED tape around the edge of the petri dish, fill it with silicon, and get the frequency of the LEDs slightly out of phase with the correct frequency of the bass driver...

you have a ~$60 demonstration of quantum behavior that's visible to the naked eye ;)

Not that it's actually caused by quantum behavior. It just looks eerily like it.

Skyler

@Sasha (quantization intensifies)

AccidentalFourierTransform

Im looking for a new TV series to watch

any recommendations?

Skyler

so @DanielSank, advice

I bought this LED driver for a project Im working on, but theres a bit of an issue

how the heck do i solder that

Sasha

22:55

uhh... hope you have steady hands

DanielSank

@Skyler There are several ways.

You need solder-fu.

AccidentalFourierTransform

@Skyler with a hammer

Skyler

@Sasha ikr, as if my solder game was so good to begin with

DanielSank

@Skyler That's a surface mount part. Are you connecting it to a pcb? If so, please show image.

Skyler

@DanielSank na, i didnt realize its surface mount but it does electrically what i need

Sasha

22:56

@Skyler If your hands are shaky, do a single shot of vodka and wait ten to thirty minutes, if that's legal for you.

@Skyler you might I'm joking... but I'm really not

AccidentalFourierTransform

I had nothing better to do today

Skyler

@Sasha judging by the picture you look younger then me, then again ive rocked a beard since i was 14

AccidentalFourierTransform

getting drunk it is

obe

@ACuriousMind I haven't done physics in a while so I dunno :/

Sasha

@Skyler 25 as of a few days ago

Skyler

22:58

@Sasha uhh...how old am i again....

DanielSank

@Skyler You need to make a small pcb for that.

Skyler

ah yes...22

DanielSank

You can try to solder wires but it won't last.

Sasha

@Skyler He's right. It's to teensy to hitch wires to it securely.

DanielSank

For $30 you can order a bunch of pcb's from Advance Circuits on student special.

gtg

Sasha

23:00

they'd work temporarily if you were really careful

(wires, I mean)

Skyler

@Sasha ya, i guess i can at least get that done at home until someother solution pops up

i might be able to get a small batch done on university actually

AccidentalFourierTransform

Germany has legalised weed

we wont be seeing ACM around here anymore

Sasha

youtube.com/watch?v=Hopd-gKB1Xc btw, this was the setup I referenced

Skyler

so, @sasha, grad student right?

ACuriousMind

@AccidentalFourierTransform wait, what?

Sasha

23:12

@Skyler Nope, undergrad. I've temporarily checked out to get a series of medical issues sorted.

AccidentalFourierTransform

@ACuriousMind dw.com/en/…

but everything is medical if you try hard enough

Sasha

@Skyler you?

Skyler

@Sasha undergrad for ~9 more weeks

how long you been checked out for?

Kelthar

Hi guys, can someone advice me what subjects to pick in my Master's degree, I want to work in Quantum Mechanics, what would you advice me, besides grabbing all the QM I can ofc xD ?

ACuriousMind

@AccidentalFourierTransform I think it might actually be rather difficult to get the required prescription.

Skyler

23:15

it sounds like youll have to relearn things if its been a couple of years

Kelthar

What are some subject that are important and may not be that obvious*

Skyler

@Kelthar not sure if in US, but here usually people dont do masters physics

Sasha

I needed 3 major joints reconstructed because Ehlers-Danlos Syndrome. Also, was diagnosed with epilepsy, Hashimoto's, and a genetic immunodeficiency... so I've been out since 2013.

AccidentalFourierTransform

@ACuriousMind just stab yourself in the eyes, that should do the trick

@ACuriousMind physics.stackexchange.com/questions/306264/…

Kelthar

@Skyler, I'm from Portugal, I'm doing Engineering Physics now

AccidentalFourierTransform

23:16

@ACuriousMind the $\nabla$'s should be $\partial$'s, right?

Kelthar

@Skyler This is my course's program: fenix.tecnico.ulisboa.pt/cursos/meft/…

AccidentalFourierTransform

@ACuriousMind no wait, nevermind

Skyler

@Sasha wow, been a few tumultuous years for you?

they just all started hitting at once?

ACuriousMind

@AccidentalFourierTransform I don't that that's a "chronic illness" :P Faking any of the illnesses you can get the prescription for is probably harder and more expensive that just buying from you local dealer :P

@AccidentalFourierTransform hmm? Yes, they should, otherwise that's a pretty recursive formula :D

Sasha

@Skyler hehe, yeah :D but I've been working off and on in two cool labs, and am about to get co-author published in Cancer Research

Skyler

23:19

@Sasha noice, taking a little peak at the profil im guessing its related to metabolics of cancer cells

Sasha

@Skyler yes, but I just did a bunch of mass spec data analysis. I'm not a biologist at allll.

Skyler

no biophysics in there?

Kelthar

@Skyler I want to work in quantum computing*, lol, wrote QM by mistake...

Skyler

@Kelthar so experimentalist side

or engineering?

overlaps there

AccidentalFourierTransform

those friggin unpaired parentheses are making me really uncomfortable

Skyler

23:23

but i guess would you want to be working on the new method or implementing a functinoal computer from someone elses?

also @DanielSank is really rhe person to ask

ACuriousMind

@Kelthar Just...learn quantum mechanics well and thoroughly first, please. I see far too many questions on this site from people trying to learn something about quantum computing without actually learning QM

Sasha

@Skyler I did take one class in biophysics, but it's been entirely useless in metabolomics so far. It's OK, though... I'm a decent autodidact.

ACuriousMind

@AccidentalFourierTransform obligatory xkcd

Sasha

xkcd references? I'm home.

AccidentalFourierTransform

@ACuriousMind thankyou I'm stressfully cracking my joints because of that

Skyler

23:25

@Sasha yep, my biophsyics was a really amazing class but probably not useful

Kelthar

@Skyler I find the overlap quite cool actually, I'm not yet sure which of the flavors yet though xD
DanielSank?

AccidentalFourierTransform

@ACuriousMind obligatory smbc :D

Skyler

hes a q.comp guy(to say the least)

ACuriousMind

@Sasha I also do SMBC and abstruse goose references sometimes, for a little variety ;P

Skyler

first time ive heard of abstruse goose there ACM

Kelthar

23:27

@ACuriousMind I took this past semester my first subject in QM, 2nd next semester, but my masters starts in September so... I wanted to have an idea

@Skyler wow, that's cool. nice, I'll ask him when he's around

ACuriousMind

@Skyler Some questions on this site regularly make me think of this one, for example

3

AccidentalFourierTransform

xkcdref.info/statistics

nice ^

Sasha

@ACuriousMind One of my girlfriends recently asked me a bunch of questions about time. I almost taught her what K-space is before I realized her eyes had glazed over.

AccidentalFourierTransform

maybe I shouldn't ask... but... whats a k-space?

wikipedia is not helping

ACuriousMind

@AccidentalFourierTransform momentum space, I guess

Sasha

23:35

Now that I'm remembering, I can't recall how we got on the topic of topology.

AccidentalFourierTransform

K-space (magnetic resonance imaging)

k-space is a formalism widely used in magnetic resonance imaging introduced in 1979 by Likes and in 1983 by Ljunggren and Twieg. In MRI physics, k-space is the 2D or 3D Fourier transform of the MR image measured. Its complex values are sampled during an MR measurement, in a premeditated scheme controlled by a pulse sequence, i.e. an accurately timed sequence of radiofrequency and gradient pulses. In practice, k-space often refers to the temporary image space, usually a matrix, in which data from digitized MR signals are stored during data acquisition. When k-space is full (at the end of the scan...

?

Sasha

@AccidentalFourierTransform I was referring to compactly generated spaces.

OH, I was explaining what Minkowsky space is

ACuriousMind

...how did you get to compactly generated spaces from a question about time?

AccidentalFourierTransform

the time is gone, the song is over

Sasha

@ACuriousMind because she got confused when I said that Minkowsky space has a different metric from the one she's used to working with

and then I had to explain metric spaces, and so on

AccidentalFourierTransform

23:38

ah topology, youre so fun!

Skyler

@Sasha im surprised she made it to metrics

that sounds like a standard glazing point already

ACuriousMind

lol, you went full axiomatic on a layman question? Yeah, that tends to produce glazed eyes :D

Sasha

@Skyler she might be a political science/environmental science major, but she's very intelligent and curious

ACuriousMind

@AccidentalFourierTransform Topology is fun!

In what other topic is "find a gluing recipe for the three-holed donut" a legitimate exercise?

Sasha

@ACuriousMind topology is the point at which I start feeling like I need to deconstruct my brain just to wrap it around a concept

Skyler

23:41

@Sasha still, the prerequisite knowledge for metrics is pretty rare for people

Sasha

That reminds me of analysis. My introduction to analysis class was taught from the framework of metric spaces, which none of us had ever encountered before (professor was delusional).

During one lecture about open balls vs closed balls, someone had the audacity to ask him, "so, essentially, if I threw an open ball at your face, it wouldn't hit you?"

ACuriousMind

@Sasha Try mathematical logic if you ever feel topology is getting to comfortable ;)

It's incredible what mathematicians are forcing math to do these days...

Kelthar

XD

Sasha

Analysis from the perspective of metric spaces is fondly remembered as the math class where our lecture board looked more like a Jackson Pollock crossed with a Picasso.

@ACuriousMind I got lost in that world long ago, when I had to prove the existence of numbers as an initial homework assignment. Maths professors are jerks sometimes.

AccidentalFourierTransform

)

Sasha

23:50

() twitch

ACuriousMind

@AccidentalFourierTransform {[({{{[[(([

AccidentalFourierTransform

dude.

DanielSank

@ACuriousMind Yeah that happens a lot.

ACuriousMind

@AccidentalFourierTransform :)

DanielSank

It's amazing that some people actually manage to learn enough about what a quantum state and unitary transformation is that they do understand quantum algorithms, even though they've never seen a Hamiltonian.

This is a problem though, because they have no idea how to implement the unitaries they want for their algorithm.

AccidentalFourierTransform

23:52

@ACuriousMind oh no, now ascii smileys make me uneasy too

WHAT HAVE YOU DONE TO ME??

DanielSank

This is a problem in my field. Proposing beautiful quantum algorithms is fine but it's a lot more impactful to propose one that the experimentalists can actually run.

Well, perhaps I shouldn't say that.

I hope readers know what I mean here.

ACuriousMind

@AccidentalFourierTransform ::laughs maniacally::

AccidentalFourierTransform

:-($\phantom{)}$

ACuriousMind

@DanielSank I'm not sure I do.

AccidentalFourierTransform

a reference to string theory?

Kelthar

23:55

@DanielSank ! Someone told me you have something to do with quantum computing field! I want to work in that as well... Could you advice me on some important yet not so obvious subjects to learn for this?

Sasha

@DanielSank The programming is always far ahead of the hardware, it seems.

ACuriousMind

"impactful" is a wonderfully vague word with whose interpretation the whole sentence stands and falls

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