The h Bar

0ßelö7

20:00

@EmilioPisanty we have twitter oneboxing but not arxiv?

This site has strange priorities.

Emilio Pisanty

@0ßelö7 that is correct

@0ßelö7 indeed. they're "everyone but physicists" priorities

skullpatrol

~~site~~ network

People like g o h s set those priorities @0ßelö7 and he's the one who has the power to delete users.

0ßelö7

@EmilioPisanty or mathematicians

dmckee

@skullpatrol I doubt Gell-Mann spent much time thinking about nuclear physics—at least in the latter part of his career. He was concerned mostly with things at a more fundamental level.

geeky me

Hey my question is unanswered. PL try answering it.://physics.stackexchange.com/questions/357247/calculate-the-uncertainty-in-ve‌locity-of-electron

0

Q: Calculate the uncertainty in velocity of electron

I got this question in one of my periodic test in coaching, I (seemingly) solved the question but later recognised what mess I did. So, the question is : Calculate the uncertainty in velocity of an electron. If the uncertainty in its position is ${10^ {-15}} \; m$. By simple calculations one can...

skullpatrol

20:15

"Hey"?

geeky me

Hi

skullpatrol

Hey is for horses.

geeky me

Thanks emilo for editing

0ßelö7

You should be scared

geeky me

I am new here.... Maybe I don't know ur code words. ...

Going off..

1

Q: Calculate the uncertainty in velocity of electron

I got this question in one of my periodic test in coaching, I (seemingly) solved the question but later recognised what mess I did. So, the question is : Calculate the uncertainty in velocity of an electron. If the uncertainty in its position is ${10^ {-15}} \; \mathrm m$. By simple calcu...

homework-and-exercises uncertainty-principle

skullpatrol

20:19

hay is for horses

== English == === Etymology === From hay being homophonous with hey. === Phrase === hay is for horses (sarcastic) said as a retort to someone saying hey (any sense of the interjection), used to indicate that the speaker disapproves of the usage of the word "hey", perhaps due to a dislike of informal speech....

@geekyme^

geeky me

Hmm.... My bad.. English is not my first language

skullpatrol

Ok, np :-)

Emilio Pisanty

@geekyme done

Phase

Is there a way of assuming initial or boundary conditions and then generalising after finding the solution?

I'm trying to solve the wave equation using LP transforms

0ßelö7

20:35

@Phase what?

Just write down x_0

No need to pick an actual number

Phase

Nah I mean

I took the LP transform of u''(x,t)

w.r.t t

the dashes i mean

and I got something along the lines of s^2F(s) - f(0) - sf'(0)

0ßelö7

That's correct

Phase

But Im not sure if theres a way for me to ditch the last two terms and still keep some useful generality

0ßelö7

So what's the issue

Phase

Since the only case I can think of that has relevant initial conditions would be something like a string with fixed ends, and Idk if there's a way to take that solution and make it general

0ßelö7

20:38

@Phase oh. For a linear homogenous equation you can get away with setting f(0)=0

In theory...

For the derivative, no, I think that always matters

Phase

Why though? Is it because any periodic wave described by it could arbitrarily be moved left or right to have y=0 at the origin?

0ßelö7

Ah, no, still. You need your operator to annihilate constants. Forget what I said. No, you cannot set them to zero in general.

Phase

fug

I dont really feel comfortable going any further without being able to simplify it since I figure it's probably only gonna get worse as I carry on

I reckon if I was just doing it concerning standing waves though that it would end up working out since the last two terms vanish

0ßelö7

Don't simplify

It's good practice

You need to practice massive algebra calculations

Phase

But that's a sign error waiting to happen

0ßelö7

20:43

Then don't make one

Phase

By the way, when I've done my first year I'll have the chance to convert to mathematical physics

and thats what I feel I want to do since I find the maths more fun than applying it in some cases

and hate labs

But if I don't find a research program or something way down the line, is it as employable as standard physics just in case?

0ßelö7

Why even bother with physics?

Phase

wot?

Oh

you mean as opposed to maths

Idk, because I do like applying it. I just like it when you can apply it AND keep some depth to the maths side of the topic

0ßelö7

Cue @EmilioPisanty ranting

You will never, ever apply mathematical physics.

Phase

Thats why I like the idea of QM so much, physics seemingly done almost entirely mathematically. Granted the whole plancks constant thing means it cant be derived without experiment

oh

why not?

Anonymous

20:46

@Phase Maybe you'll like computational physics then

0ßelö7

@Phase you don't know what mathematical physics is...

Phase

I always thought the discipline itself was a sort of field where people develop mathematical analysis etc for Physicists to use

I get that the discipline itself is probably gonna be virtually all pure maths

but I mean I like the idea of being ABLE to apply it

Anonymous

@Phase What do you mean by "apply" ? :P

Phase

Well, the idea of being able to describe and analyse physical systems with what I'd learn

even if that's not necessarily something that would be in the course

0ßelö7

@Phase no

Phase

20:49

fugg

0ßelö7

Mathematical physics is mathematics based on physical problems

It is largely (almost completely) irrelevant to the physical problems themselves

Phase

I'm confused

Anonymous

@Phase I see. So you are looking for something in between theoretical physics and experimental physics?

0ßelö7

Many times one studies completely unphysical things too

Phase

I suppose so

I guess theoretical physics

I always assumed it was a subset of mathematical physics

rip

0ßelö7

20:51

Theoretical physics has a nonempty intersection with mathematical physics

Anonymous

That ^

0ßelö7

Neither of them are applied.

Phase

Side note:

"On the other hand, theoretical physics emphasizes the links to observations and experimental physics, which often requires theoretical physicists (and mathematical physicists in the more general sense) to use heuristic, intuitive, and approximate arguments.[4] Such arguments are not considered rigorous by mathematicians, but that is changing over time."

"but that is changing over time"

@0ßelö7 eat your heart out the worlds turning against you

0ßelö7

I don't know what that's supposed to mean.

And unless someone I know said that, it's a worthless opinion.

My heart is intact.

Phase

Damn. It's wikigod

how much of Mathematical physics is PDEs?

0ßelö7

20:54

I don't know any non-PDE mathematical physics.

Phase

huh

hey @0ßelö7 is Math. phys like a physicist deriving some sort of equation describing a physical system, but them being unable to solve it analytically? Is that when math phys comes in?

Like contextless problems

or am i gonna trigger by saying that

0ßelö7

No

Phase

I'm not so delicate you have to remove that btw

I was fully prepared to miss the point

0ßelö7

I misread what you said.

Phase

I may not have explained it well

I meant math physicists take over at that point

to analytically solve the equation without needing the context

lılostafa

21:05

@EmilioPisanty From it's Wikipedia article, another instance that Cassini's trajectory could pose a threat (this time to Earth!) was its initial trajectory toward Saturn. It's had several gravitational slingshot maneuvers including one fly-by pass of the Earth.

Phase

Could someone please inform me whether I'm justified in calling this answer nonsense

lılostafa

From the article:

The terrestrial flyby was the final instance when the Cassini space probe posed any conceivable danger to human beings. Had there been any malfunction causing the Cassini space probe to collide with the Earth [...] a significant fraction of the 33 kg of plutonium-238 inside the RTGs would have been dispersed into the Earth's atmosphere so that up to 5 billion people could have been exposed.

Phase

21:18

Ooo

this sounds ominous

"annihilation method"

If I have y'' - 3y' - 4

and then obtain (D-4)(D+1)y

well, how do I then know that -4 and +1 are coefficients in the solution?

That doesnt seem obvious to me at least

Sanya

y'' - 3y' - 4 = 0 ? And what's D?

Phase

the differential operator

Oh nevermind

I get it I guess

think i typo'd the signs for the coefficients tho rip

Emilio Pisanty

@lılostafa five billion people seriously endangered by 30 kg of plutonium in satellite fallout?

I'm skeptical of that claim

Nice find, though

Sanya

21:33

@Phase linearisation of the characteristic polynomial?

not linearisation ... linear factorisation

no clue how that's actually called in english

Phase

Its more that I was being dumb and probably wouldn't have even recognised that (D-4)y implied that 4 would be the k in $c e^{kt}$. I have really dumb moments sometimes.

Well, most of the time

NeuroFuzzy

@dmckee What's with these low quality answers by new users?? ( :P )

dmckee

Meh! Stupid track pad is so sensitive it sometime registers a click when I just come near it (or maybe I brush it so lightly that I don't notice it).

Sanya

@Phase the difference between "dumb moments" and "not dumb moments" is 98% experience

dmckee

^ That. And it is the experience of having tried out lots and lots of the ways to have dumb moments at that.

Phase

21:41

sad thing is I'm not even sure what my dumb moments are anymore

dmckee

@Phase IT reads to me like a jumble of partially digested pop-sci 'explanations'.

Phase

Im not sure if trying to solve the wave equation with Laplace transform is one of them, or one of my smarter ones

dmckee

Probably you could work up a justification for many of the statements therein, but that wouldn't make the whole thing "useful" as the vote-button hover-over text means it.

Phase

Thanks @dmckee that's the vibe I got but I'd never actually studied GR so I wasn't sure. The language seemed like a red flag

I was just on the mathematical physics wiki page

and the image they have is a gif of solutions of the oscillator

I haven't actually done the oscillator yet, just the well. There's a blue line and a red line and one lags behind the other by what looks like a 1/4 of a period, is that the real and imaginary parts?

here

dmckee

@lılostafa That is increasingly common. Galileo did two Earth fly-bys.

@Phase Not sure. The text associated with the figure says "oscillators" (plural) so that may be solutions for two different angular frequencies.

Phase

22:00

I hope recognition builds up over time

Beyond "Oh screw it I can't do this / do this quickly" I don't really know when to apply things like LP transforms

0ßelö7

22:25

@Phase no

we rarely solve equations arising in physical contexts

we prove equations exist, estimate properties of solutions, etc.

in pure math research we are sometimes very interested in exact solutions because they can display pathological behavior, help us classify solutions, find rigidity theorems

I went to a seminar about exact solutions of mean curvature today

but that's not mathematical physics

Jasper

22:39

Seems that almost nobody in this room is a physicist.

They are either mathematicians or chemists etc, lol.

Anonymous

@Jasper Where did you find Chemists in this room?

Jasper

@Blue I don't know. I think they mentioned long ago about the regulars in this chat.

@0ßelö7 You can be Green Ninja and I Blue Ninja.

0ßelö7

John and Secret

@Blue and @Kaumudi.H are engineers

@Jasper what?

Anonymous

@Jasper That's was probably a joke as we have quite a few theorists around here but less experimentalists .

Anonymous

@0ßelö7 I don't identify myself as an engineer. Formal degree is crap anyway.

Anonymous

22:48

:P

0ßelö7

We identify you as an engineer

Anonymous

@0ßelö7 That doesn't matter (to me). XD

0ßelö7

@ACuriousMind Hello

ACuriousMind

@0ßelö7 Hello?

0ßelö7

@ACuriousMind It's a common greeting

ACuriousMind

22:52

I may have used it myself occasionally :P

0ßelö7

@ACuriousMind So I went to two talks today (did you see my earlier message?)

One had no proofs and was very fun and interesting, and the other had some proofs and the audience was about to walk out

ACuriousMind

@0ßelö7 I just logged in to find it sitting in my inbox, so I suppose the answer is yes ;)

@0ßelö7 "was about to talk out"?

0ßelö7

typo, fixed

ACuriousMind

Ah, because the proofs were wrong or because the talk was impossible to follow? :P

0ßelö7

the talk was a bit insane. It was about asymptotic linearlization of the Navier-Stokes equations in an infinite dimensional sense

the speaker's English wasn't great and he kept forgetting to say things

also he never explained what the main hypothesis was about because "it would take too long"

Emilio Pisanty

22:55

0

Q: How can an electron have angular momentum when it doesn't orbit the nucleus?

Since electrons do not orbit the nucleus like particles, and instead have a probability to "exist" around the nucleus, how can they have an angular momentum as if they move at a certain velocity around the atom? Also, why does this force the electrons probability density into distinct shapes?

quantum-mechanics particle-physics physical-chemistry

↑ surely that's a dupe?

ACuriousMind

@0ßelö7 Ûh, okay

@EmilioPisanty I'm sure it is...searching...

@EmilioPisanty Close: physics.stackexchange.com/q/179476/50583

Also physics.stackexchange.com/q/105703/50583

0ßelö7

@ACuriousMind Do people practice chalkboard writing? Whenever I do it it looks awful and squeaks.

Anonymous

@0ßelö7 Buy a better chalk

Emilio Pisanty

@ACuriousMind no, you can probably get closer 'n that

0ßelö7

@Blue using the same chalk as other people

Anonymous

22:59

Some chalks cause too much squeaking

ACuriousMind

@0ßelö7 Pretty sure they do

0ßelö7

@Blue Not this one, I blame left handedness

I have to push the chalk instead of dragging it

Anonymous

Maybe you can buy a cheap chalkboard for practice, at home?

ACuriousMind

@0ßelö7 I'm also left-handed and I don't squeak while writing on a blackboard ;P

Anonymous

I have one at home

0ßelö7

23:00

@ACuriousMind you're a robot

ACuriousMind

::sad beeping::

0ßelö7

@ACuriousMind did you practice?

ACuriousMind

@0ßelö7 Not really - my writing was awful when I wrote on a board for the first time, though

I never had the squeaking problem

@EmilioPisanty What about the second one? Can't find more

Emilio Pisanty

@ACuriousMind it's close, not sure if it's a dupe

0ßelö7

@ACuriousMind mine has been awful for a decade!

Anonymous

23:28

@0ßelö7 If you plan to be a professor someday, please work on it. :P

0ßelö7

no one uses blackboards in class

Anonymous

@0ßelö7 What do they use?

Anonymous

Don't tell me that they teach from slides. I hate being taught using ppts/slides.

ACuriousMind

@0ßelö7 100% of the lectures I took were taught at a blackboard.

Phase

Could someone verify if something makes sense

my gut says it doesnt but my brain says I haven't actually got the qualifaction to say so.

"Let me put it this way: how do you define the speed of light? It certainky has nothing to do specifically with light in relativity. It simply is the maximum possible speed in the hyperbolic geometry."

ACuriousMind

23:33

@Phase It's...sort of correct? I mean, the "speed of light" has nothing to do with light specifically

Phase

I didnt mean that part

I meant about it being the "maximum possible speed in the hyperbolic geometry"

ACuriousMind

Well, depending on what the author means by that, it's true, false, or meaningless. "The hyperbolic geometry" is sorta vague :P

Phase

Unless they mean it to basically be a self-defining statement, i interpret it to mean that they mean there's a speed limit from pure maths rather than a physical one

If they're just saying "c is finite because thats how it is" then I dont really get why they said it

0ßelö7

@ACuriousMind that's european strangeness

@Phase they might be talking about rapidity

@Blue whiteboards or slides, like normal people

Phase

Depends on the Lecturer @0ßelö7

some make the blackboard great

Others make it ear-torture

Anonymous

23:38

@0ßelö7 Hmm whiteboard is still fine. I hate slides.

0ßelö7

@Blue slides are good in some classes

ACuriousMind

@0ßelö7 You should get rid of this notion that US-American customs universally define normalcy :P

3

0ßelö7

my controls/dyanmics professor does it right: important formulae on the slides, examples on the board

Phase

coloUr

actually no

America has a greater crime

0ßelö7

@ACuriousMind delete my account if that's how it's gonna be

Phase

23:39

"I could care less"

Anonymous

@0ßelö7 That sounds like a good approach. Very few professors would care to use both to ease the learning process.

0ßelö7

@Blue I'm too tall to use lots of board anyway

I have to bend over to reach the bottom half

ACuriousMind

@0ßelö7 That was friendly advice, not moderatorial command

0ßelö7

@ACuriousMind What is normalcy then? There are more Americans than Germans, so we're normaler than you...what do the Chinese do?

(in actuality normalcy is determined by GDP, but I won't get anywhere with that argument in here)

Phase

I think when the rest of the English speaking world knows how to spell a word

you need to take a step back and examine where you went wrong

0ßelö7

23:42

@Phase We streamlined the language

How on Earth does having more letters seem better to you?

Phase

I'll streamline the schrodinger equation

dont need this silly V term

Secret

@0ßelö7 O, and some exact solutions have pretty geometric interpretations

0ßelö7

yep

in MCF there's a "grim reaper curve" because it's a scythe sliding across $\Bbb R^2$

ACuriousMind

@0ßelö7 Normalcy is relative to where you are and who you are talking to - and the social context of this chat is not bound to any particular country.

0ßelö7

@ACuriousMind where is the company based?

ACuriousMind

23:46

The US, but I don't see what that has to do with the social context of the chat.

Anonymous

@0ßelö7 Well, looking at the "most popular American guy" at the moment....... if that's the definition of normalcy....I've nothing to say. :P

0ßelö7

@Blue he isn't normal

Secret

Curve-shortening flow

In mathematics, the curve-shortening flow is a process that modifies a smooth curve in the Euclidean plane by moving its points perpendicularly to the curve at a speed proportional to the curvature. The curve-shortening flow is an example of a geometric flow, and is the one-dimensional case of the mean curvature flow. Other names for the same process include the Euclidean shortening flow, geometric heat flow, and arc length evolution. As the points of any smooth simple closed curve move in this way, the curve remains simple and smooth. It loses area at a constant rate, and its perimeter decreases...

0ßelö7

@Secret Yes

Phase

@Blue he isn't normal, he's exceptional

Only one man could accidentally type "We" as a singular tweet, and have people actually start arguing over it

0ßelö7

23:49

He is

Anonymous

@0ßelö7 That's a clear indication as to why the US cannot be taken to be a "baseline" for normalcy. XD

0ßelö7

@Blue Any comment I make about American politics will involve me saying someone is insane, so I'll refrain.

Phase

I look to news outlets for my normalcy. Not that fake shit though, to me Alex Jones is the average American citizen

0ßelö7

Alex Jones is a decent normal human father

Phase

The tin foil hat wearing, working class man we can relate to

Oh yeah back to my original question I guess

0ßelö7

23:50

I distrust people who don't have tinfoil hats.

Better safe than sorry.

Phase

If I convert from Physics to Theoretical physics and can't find research positions, will it hurt my employability to have switched?

0ßelö7

if they don't have the hats then they must know something

Phase

Is Labwork something important that people look for?

ACuriousMind

@Phase What people?

0ßelö7

yes

Phase

23:51

If they don't have the hats, they must be the ones sending out the waves

Anonymous

@Phase Theoritical physicists can easily go to CS and software jobs

Phase

Idk, Job market

0ßelö7

@Blue Easily?

To be a theoretical physicist one doesn't need to know any programming

ACuriousMind

@Phase Sure, but it depends what sort of job you're looking for - the software industry certainly couldn't care less whether you've done labs, I think

Phase

I think CS is basically like voodoo science

0ßelö7

23:52

@yuggib got this beauty for $1.97, literally i.gyazo.com/914c0d36d59aaec11ca133762a82fe71.jpg

Phase

Normally to communicate to my computers I hold a seance

Anonymous

@0ßelö7 Well, real CS is more about algorithms and mathematics.

Anonymous

Coding isn't that difficult to learn

0ßelö7

@Blue how many "real CS" jobs are there that will take physicists over actual CS people?

ACuriousMind

@0ßelö7 True at least in Germany, software companies routinely look for people with degrees in CS, math or physics who know some programming

Phase

23:53

@ACuriousMind ideally I'd love to end up in research, but I'm pragmatic enough to be aware of how unlikely that will be

Anonymous

@0ßelö7 If you can do your job well they don't give a damn about what degree you have.

0ßelö7

@ACuriousMind I wasn't disagreeing with that, I was disagreeing with the premise that a theoretical physics background makes one immediately competitive for a CS job

ACuriousMind

And given the number of math and physics people I know who took such jobs, it certainly doesn't seem like they are outmatched by CS students

Anonymous

Yes, that ^

0ßelö7

@Blue You're assuming, again, that a theoretical physics background makes you good at those things

ACuriousMind

23:54

@0ßelö7 Ah, well, not in itself. But I've yet to meet a theorist who didn't at least have some programming skills.

(discounting the much older generation, of course)

Anonymous

@0ßelö7 There's obviously a large overlap in the required skill-sets.

0ßelö7

@ACuriousMind I'm disagreeing on principle here.

For some reason people come to college knowing how to work a Linux server nowadays

I don't even know how that happens

ACuriousMind

@Phase I also understand that. But whether or not lab experience will help you on the job market crucially depends on what sort of job you're looking for

@0ßelö7 Ask @BernardoMeurer :P

0ßelö7

@ACuriousMind He's crazy, but I'm talking about random people

And don't you dare flag that, he threatened to help my sisters sell my bone marrow

Phase

How much for 100g?

0ßelö7

23:57

like 23 grand

Phase

hm

ACuriousMind

@Phase ...how much bone marrow does a human have to begin with?

0ßelö7

you can safely donate enough per year to make 23 grand, but it's illegal

@ACuriousMind a lot, but one has to not die in the process

far more profitable to keep the person alive as a farm

ACuriousMind

@0ßelö7 It's illegal to donate or to take that sort of cash for it?

0ßelö7

@ACuriousMind to take cash

Phase

23:59

Hmmmmmmmmm

So I should raise a kid as a bone marrow farm and become a millionaire

He's a kid he'll grow more

0ßelö7

it's 23 grand per gram actually

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