The h Bar

Looking for opinions on my answer physics.stackexchange.com/a/203748/12029 since I'm really just sharing stuff I tried to figure out when looking at FTL

0celo7

@obe what QM do you know?

obe

That's not important right now.

Remember me

Well I have a question :
Can we say stuff about smog by thinking on the lines of Brownian motion?

obe

@0celo7 Ask that question in 10 days, and test me too.

NeuroFuzzy

4:25 PM

@Rememberme wiki page says "this smog contains soot particulates". The particulates would follow brownian motion, yep.

ADG

hello

book recomendation needed here

Remember me

So what all can we say?@NeuroFuzzy

ADG

quantum mechanics

0celo7

@obe if your QFT notes don't cover scattering, I highly recommend chapter 3 of Weinberg Vol. 1

NeuroFuzzy

@Rememberme But most mixing and "diffusion" properties would be dominated by fluid dynamics/wind

0celo7

4:26 PM

it gives you a "real world reason" (in a sense) for wanting to learn QFT

NeuroFuzzy

@Rememberme I don't know, that the path of a particulate would follow brownian motion. Not much I'd imagine :p

Remember me

Oh. I have a talk on smog tomorrow and want to include brownian motion in it @NeuroFuzzy

0celo7

@obe spin and identical particles are hugely important in QFT

obe

@0celo7 Tell me that in 15 days.

Right now I'm going to binge read these notes and shankar.

0celo7

lol

you're not going to remember anything

obe

4:29 PM

Then I'll do it 3 times.

0celo7

lol you said you can't stand reading shankar once

now you want to read it thrice??

obe

;<

ADG

my course includes these: pastie.org/10389955

please help me find a book to study from

0celo7

@ADG Did you ask the instructor?

ADG

he says beiser sakurai and zettili

but i want something more better and deep

but suitable for an undergraduate like me

0celo7

4:40 PM

Sakurai is graduate level, but very good.

Shankar hits most of those topics.

ADG

ok

0celo7

@ADG Personally, I don't know of a book that covers everything there.

ADG

beiser does actually

and the intstructor teaches it in class and it is very boring i doze off 99% classes and so do my 99% classmates

0celo7

Concepts of Modern Physics?

ADG

yes

0celo7

4:43 PM

Too much undefined there.

ADG

ok

bye

0celo7

Wow that's actually kinda comprehensive.

Physics Meta

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0celo7

@ACuriousMind How to remember what pathos means: emotion is a pathological plague on humanity.

NeuroFuzzy

5:41 PM

now with $\infty$% more pretty pictures physics.stackexchange.com/a/203748/12029 seriously if someone can tell me whether they agree or not that would be great

NeuroFuzzy

6:06 PM

:(

0celo7

@ACuriousMind Asking how "magic" would change physics is not a physics question. I'm totally not a fangirl, but that's an awesome line!

@NeuroFuzzy you and your hyperbolic rotations

the fun thing about the universe is that it doesn't care what you think is pointless or not

#rekt

John Duffield

6:40 PM

@0celo7 Fine, don't listen. Knock yourself out.

0celo7

@JohnDuffield With your confirmation, I am proceeding to knock myself.

Slereah

Nooo

Do not knock yourself

It is a poor way to learn

John Duffield

7:00 PM

@0celo7 Your choice. Just be aware that sometimes there's no evidential support for something, but people believe in it just because it's been around for a long time. Things like heaven and hell and sweet baby Jesus. And things like M-theory and Hawking radiation and quantum computers.

0celo7

@JohnDuffield I'll make the evaluation after talking to some professionals who work in the field and reading a book or two on it.

(To dismiss it just because you tell me to is no better than an appeal to authority!)

Slereah

(you can still do it though)

(it's a pretty good heuristic)

0celo7

(If the source has authority ;))

Slereah

I meant dismissing Duffield out of hand

He is like the guard that always lie in logic problems

0celo7

lol

John Duffield

7:09 PM

No, I'm, like both of them. You get the truth from me. Backed up by "Einstein and the evidence".

Slereah

you're both the guard that always lies and the one that always tells the truth?

I'm not sure I am reassured

0celo7

He lies sometimes?

John Duffield

Tsk. You ask one guard what the other guard would say, then you know the truth.

Slereah

well yes but you are both

Tricky

0celo7

He's in a superposition of truth and falsehood?

Slereah

7:14 PM

Ahahah

Is gamma the phase space

0celo7

It's from that mathy quantum information book.

Slereah

I gathered

The fuck are all those spaces

John Duffield

Of course, you could always dismiss Einstein and the evidence because you think you know better. LOL.

0celo7

Ask me in like three years.

I will read this book.

The equations are so ridiculous.

Slereah

Ever read like

Standard model in curved spacetime written by mathematician

That shit is insane

0celo7

7:17 PM

Slereah

They give you like 12 fucking bundles

0celo7

source?

Slereah

Lemme see

I think I have a paper on it somewhere

arxiv.org/abs/gr-qc/0703076

0celo7

eye twitch

@Slereah holy shizzle

John Duffield

@Slereah Of course it is. The mathematician has no regard for scientific evidence, and he probably doesn't understand gravity or classical electromagnetism or QED, so he goes wrong from the off, and before you know it he's "lost in math". Sadly a lot of people who think they're being taught physics aren't. They're actually being taught mathematics, and the physics content of their course is slim.

Slereah

7:23 PM

that's how you start a paper

and that's just for free fermions

it's even more fun when you have the electroweak bundle thrown in

look at all those sweet bundles

0celo7

D:

My ignorance of such things is immense!

I know some of the words at least?

@ACuriousMind Make it home OK?

Uh, avatar thing glitched out.

@Slereah Do you understand that arXiv paper?

Slereah

7:38 PM

eeeeeh

somewhat

I don't know what the fuck those slashes are supposed to be

0celo7

what paper is that

@Slereah Dirac slashes!

Slereah

not even!

arxiv.org/pdf/math/0603611v1.pdf

0celo7

email the author?

santiago

@0celo7 no problem

0celo7

@Slereah I blame Russian TeX for the slashes

Did the physics librarian die or something? It's been like 30 hours since I placed my order.

Amazon would have delivered quicker!

0celo7

7:58 PM

At least I'm consistent

0celo7

8:11 PM

One of the first questions studied was whether quantum mechanics imposes any limits on what a computer can do, and it was shown by Richard Feynman that it does not.

Feynman!

Slereah

you know what does, though?

General relativity.

0celo7

Too much info and you get a black hole?

Slereah

No

But the expansion of the universe makes it so that you cannot have a computer arbitrarily big that can still communicates with all its part

Although yes there is also a limit for information density related to black holes

Beckenstein bound, IIRC

DanielSank

@0celo7 I really don't think I'm missing anything, bro. Where did you get the idea that you can "never" learn to program or work in a lab?

0celo7

@DanielSank I can never do that as high school student.

Slereah

8:17 PM

Bekenstein bound

In physics, the Bekenstein bound is an upper limit on the entropy S, or information I, that can be contained within a given finite region of space which has a finite amount of energy—or conversely, the maximum amount of information required to perfectly describe a given physical system down to the quantum level. It implies that the information of a physical system, or the information necessary to perfectly describe that system, must be finite if the region of space and the energy is finite. In computer science, this implies that there is a maximum information-processing rate (Bremermann's limit...

0celo7

@Slereah That's cheating.

@Slereah Derivation?

Must one look towards the literature?

Slereah

Hell if I know

Hm

From what I can see, maybe it's just

The entropy is just the Hawking entropy

DanielSank

8:46 PM

@0celo7 So wat?

0celo7

@DanielSank So I won't get any internships my first year.

DanielSank

@0celo7 just go around to the labs and tell the grad students you want to help them.

It's really hard to refuse free help.

That's roughly how I got into my grad school lab, and that turned out well in the end.

The conversation went like this:

Me: I can haz work in ur labz?
Adviser: Meh, I don't have $$ for you.
Me: 'sokay. I can work for zero dollars.
Adviser: Welcome to teh labz.

6

0celo7

you're waaaaay too old to pull off that kind of language

DanielSank

@0celo7 Fine

Me: Can I work in your lab?
Adviser: Wellll, I don't really have any money for students.
Me: That's ok, I'll TA and work for free.
Adviser: Welcome to the lab.

@0celo7 you calling me old?

0celo7

@DanielSank Yes.

DanielSank

8:52 PM

@0celo7 jerk

0celo7

@DanielSank sorry

NeuroFuzzy

@JohnDuffield so re our faster than light arguments, what exactly do you think I assert that's wrong?

@JohnDuffield because I don't assert that SR doesn't hold, nor that FTL communication is possible, nor that causality paradoxes hold, nor that the animation is changing spacetime.

@JohnDuffield so most of what you told me was just totally irrelevant. I'm asserting two things: 1. If you imagine a universe in your head where almost all of SR holds, but there's one specific correct coordinate system where you allow instant communication, then you can actually make things consistent, but that 2. if you have two such frames, then you can get causality paradoxes.

@JohnDuffield If "X" is, "you have FTL travel in a consistent universe in SR" and "Y" is "you have a privileged frame", I'm trying to build the picture of "If X, then Y". In fact I basically make the argument in the post that "not Y, therefore not X."

@JohnDuffield and you're telling me, "not Y and not X". And I agree! There's no argument to be had, so why have we spent so many keyboard taps on it?!!

Slereah

9:14 PM

You can totally have FTL travel in a consistent universe in SR

It just happens that we do not have it in our own

NeuroFuzzy

Erm, I used the phrase "build the picture" because I realized I didn't prove it. But how do you mean, @Slereah ? I think the various time travel paradoxes show that with certain innocuous looking rules of physics you get flat out contradictions

"rules of physics" like "If Earth gets message A it sends message B"

Slereah

Well that's only a problem if tachyons and regular particles can interact

NeuroFuzzy

:P

Well that hardly counts!

Slereah

You asked if it was possible, not if you could have cool spaceships!

NeuroFuzzy

Okay okay, and a tachyonic universe would be pretty cool.

Slereah

9:22 PM

we are already in a tachyonic universe!

The Higgs field is tachyonic, technically

(emphasis on technically)

ACuriousMind

@0celo7 Yes :)

DanielSank

@0celo7 I was joking.

Slereah

tachyons aren't very threatening to causality in the real world for a variety of reasons

DanielSank

@Slereah What does "causality" mean?

ACuriousMind

We have a good post on tachyons:

9

Q: Do tachyons move faster than light?

I am trying to understand whether or not tachyons travel faster than light. The linked Wikipedia page shows some seemingly contradictory statements, and they are confusing. For instance, the first sentence states that tachyons "always travel faster than the speed of light" whereas, in a later se...

special-relativity faster-than-light tachyon

Slereah

9:25 PM

A variety of things.

In this case it means that you can only be influenced by your past light cone

DanielSank

@Slereah What does "influenced by" mean?

0celo7

Causal curves can only come from your past light cone.

Slereah

It means that, if you have a differential equation dealing with whatever matter you are dealing with, to know the behaviour at that point, you will only need knowledge of the initial conditions in the past lightcone

0celo7

And that.

DanielSank

@Slereah Ah. Thanks.

0celo7

9:28 PM

@DavidZ Well then I was joking too. You're really old.

DanielSank

@0celo7 Check your ping, bro.

0celo7

Ping?

ACuriousMind

@0celo7 Check whom you pinged

DanielSank

@0celo7 Never mind. I'll let the wrath of @DavidZ explain it in due course.

0celo7

Oh

Why do I keep doing that!??

DanielSank

9:30 PM

^ 'cuz you're a freshman.

Rigor

Not THE wrath :O

Slereah

In QM it also means that the commutator of two operators that are spacelike separated is null

ACuriousMind

Aug 18 at 18:02, by 0celo7

I am an idiot

0celo7

@ACuriousMind grumbles

Slereah

that is, a measurement outside of your past light cone does not influence your own measurement

DanielSank

9:31 PM

@Slereah Indubitably.

Rigor

What do you mean by "measurement" :P

DanielSank

@Rigor Something that starts with a bra and ends with a ket, probably.

Slereah

@Rigor : Lookin'

Eyeballin'

dmckee

@DanielSank Some one-time volunteer lab help at UC Berkeley sued the university over the matter and won. Since then more than a few Universities won't let people take on free lab help for fear of unexpected cost much later on.

0celo7

Scopin' out the hood

dmckee

9:34 PM

That's a shame because I, too, got my first real taste of that sciency goodness working for free.

0celo7

@dmckee I've heard that's not an issue at my school.

DanielSank

@dmckee Yeesh.

user54412

I also did my first research for free.

Slereah

I wanted to

user54412

How can an undergrad with 0 experience justify the cost of ~grad student salary otherwise?

Slereah

9:36 PM

But it's illegal in France :(

DanielSank

@dmckee I'll say that some university departments abuse the $%*^ out of their grad students, but not accepting a consensual volunteer relationship seems odd.

Slereah

So no PhD for me!

dmckee

The night we realized we'd tracked the light curve of a micro-lensing event (with a 14" CCD backed Celestron) and got the same overall change in magnitude and duration as the big boys was huge.

Slereah

That's the problem really

If you force the university to pay, they will often just not take students

dmckee

@DanielSank Yeah, it does. But that's because legal opinions are involved.

DanielSank

9:37 PM

@dmckee Why is this site so popular with astrophysicists?

dmckee

No logic survives contact with a lawyer.

4

@DanielSank Don't know. I went on to be a particle type. That was the only astro project I ever did.

DanielSank

@dmckee Tell me about it. Try working for a company so big that it's worth everyone's time to sue over nothing just for the off chance of a settlement.

dmckee

Ah. The great American past time: deep-pockets law suits.

Slereah

The American dream

Ambulance chasing

0celo7

I considered doing pre-law.

No logic survives contact with me either

Rigor

9:41 PM

What changed your mind?

DanielSank

@Rigor Logic

0celo7

@Rigor Too much reading.

I am doing debate club though.

Rigor

Cool

DanielSank

@0celo7 Why? Can't you argue with people here enough?

Call up @Danu if you need a good debate.

He'll even test your ability to focus in the presence of name calling!

P.S. I <3 you, Danu.

user54412

In other news, it's September 1, meaning postdoc job season has officially begun for me :(

user54412

9:46 PM

just sifted through 60 new job postings from today

0celo7

I'm sitting in a job info session

John Duffield

@NeuroFuzzy if you've got a question to ask, ask it. Meanwhile appreciate we've spent keyboard taps on this because you're peddling time-travel woo. Also appreciate that a frame isn't something you can see or touch, it's just an abstract thing associated with your state of motion. And your state of motion has got nothing to do with whether very fast communication occurs, or what happens on some distant planet.

0celo7

Oh Jesus

Huge wall of text appears!

@DanielSank Do you agree with JD that quantum computing is not worth looking into because it's all popsci?

DanielSank

@0celo7 Who's JD?

Also, don't you think that's kind of a null question, given that you're asking someone who works in the field? If I thought it were all bunk I wouldn't be doing it.

0celo7

@DanielSank John Duffield

DanielSank

9:50 PM

@0celo7 Oh goody! Do I get to argue with @JohnDuffield about this?!

I've heard that's popular.

Hey, @JohnDuffield, do you think my field is bunk?

John Duffield

@0celo7 : seeing as you said causal curves can only come from your past light cone, you might want to check out the question.

ACuriousMind

::gets popcorn::

John Duffield