The h Bar

Tuki

3:00 PM

hmm yes i know there is relation between mass and energy

0celo7

@BalarkaSen apparently Lefschetz lost both his hands before becoming a mathematician

one of my professors remarked that his propensity for hand-waving arguments was curious given this fact

Slereah

@0celo7 Burkhard Heim lost his hands and was blind and deaf

He still managed to do physics

0celo7

not as famous as ol lefschetz tho

John Rennie

@0celo7 he probably thought vague arguments were 'armless

Tuki

so $\approx 1 \text{ GeV}$ is proton rest mass ?

0celo7

3:02 PM

that only works in British

John Rennie

@Tuki yes, though we use the term invariant mass these days

Tuki

if it has velocity it's "mass" is greater ?

0celo7

@JohnRennie these types of things make physics distateful imo

John Rennie

@Tuki no

0celo7

who gives a poop which mass is correct

John Rennie

3:04 PM

@0celo7 these things matter oh potty mouthed one

Tuki

well does photon have "mass" when it's traveling at $\approx c$ ?

if $E=mc^2$

John Rennie

No, photons are massless

user42819

If we apply a force F on a sphere so that it undergoes pure roll, then why does not the opposite static frictional force cancel it out because static frictional force is equal to net applied force?

0celo7

What even is the definition of mass @JohnRennie

Slereah

@0celo7 $p^2 = -m^2$

John Rennie

3:06 PM

The thing that appears in $E^2 = p^2c^2 + m^2c^4$

0celo7

what is the definition of $p$

and $E$

Slereah

Depends on the theory

Either $p_\mu = \dfrac{\partial L}{\partial (\partial^\mu \phi)}$

John Rennie

@0celo7 conserved quantities relating to symmetries of the action

Slereah

or $p_\mu = \int d^nx T_{\mu\nu} V^\mu V^\nu$

With $V$ some observer

Or it's gonna be the expectation value of an operator similar to that

Busi

Hi

What is the best textbook for self-studying physics?

Slereah

3:08 PM

For most theories the definitions are equivalent, tho

Tuki

you could try to compute mass for photon even it's considered as massless $E=mc^2 \iff m=\frac{E}{c^2} \iff m=\frac{hf}{c^2}$ ??

0celo7

@JohnRennie but the action isn't symmetric in GR :(

Busi

I wanna know every concept in detail.

Physics Meta

0

Q: Tracking down an old question

A few years ago, there was a question posted --- and then soon deleted --- in the form of a brain teaser: A lockbox full of money had been transported to the moon, where, on a balance scale, the lockbox continued to balance against the same weight as it had on earth. The trick was to notice th...

discussion

Busi

Is there any textbook that you recommend?

Regards! :)

Slereah

3:09 PM

@0celo7 Then you just use the stress energy tensor

0celo7

@Slereah ...check your indices before you rek yourself

Slereah

@0celo7 w/e

Busi

@JohnRennie What's the best textbook for stuyding physics?

I wanna know every concepts of physics in detail.

0celo7

How do you even write down a Lagrangian. What's a field?

Slereah

You just take the spacelike part of projecting the SET on some observer

0celo7

3:10 PM

@Busi I can give you books

Let me get a stack going

Slereah

and then integrate it over a region of space

Busi

@0celo7 I'd be grateful! What are they?

0celo7

inb4 I stack all of my books

Busi

@0celo7 What do you recommend? I'd be grateful.

Slereah

@0celo7 Section of a vector bundle

0celo7

3:11 PM

but is spacetime really a manifold

also you mean principal bundle

Slereah

Well no

0celo7

well yes

Slereah

The principal bundle is the gauge, not the gauge field

Tuki

I would be interested too in some good textbooks about physics

Secret

what could spacetime be if it is not a manifold. I knew of nothing more general than a topologial manifold

Busi

3:12 PM

@0celo7 What kind of books do you recommend?

As I said, I wanna know every concepts of physics in detail.

0celo7

@Secret there's lots more general things

Slereah

There's plenty of theories with spacetimes as not-manifolds

causal sets

0celo7

@Busi For the hell of it I'm going to stack all of my physics books

Slereah

conifolds

etiological spacetimes

0celo7

this is going to probably break the table

hmm

Busi

3:12 PM

@0celo7 when lol

John Rennie

@Busi 0celo7's books are all far too advanced for beginners.

Busi

ooh :)

John Rennie

What stage are you in school?

Busi

Is there any alternative then?

@JohnRennie You mean what grade I am?

John Rennie

Yes. You're in the US?

Busi

3:14 PM

Oh, am not.

Slereah

I recommend this

amazon.co.uk/Manga-Guide-Physics-Hideo-Nitta/dp/1593271964

Busi

currently 9th grade

0celo7

@JohnRennie Not true

I have some basic books

Busi

and interested in physics

Slereah

amazon.com/Manga-Guide-Relativity-Hideo-Nitta/dp/1593272723/…

Busi

3:14 PM

as seen lol

Slereah

Man, I need to buy that one

0celo7

Well, one or two basic books

Busi

@JohnRennie So, I wanna know every concepts of physics.

How should I know every concepts of physics?

0celo7

ok @JohnRennie he wants to know everything

Tuki

which country your from @Busi ?

Busi

3:15 PM

I think just by reading books

@Tuki Italy

It will look great next to MTW

Secret

that's a very odd symbol, or is it 3 symbols?

Busi

3:16 PM

@0celo7 i was serious lol

Tuki

So in Italy 9th grade is considered as ? i mean how old are you if you are on 9th grade ?

Slereah

Remember that relations are sets

@Tuki am 16

now

3:17 PM

ok

Slereah

Busi

@JohnRennie Are you there

Secret

ah, so that's "$\subset$" subset relation, got it

John Rennie

@Busi I don't know what books are good for studying at that age I'm afraid.

0celo7

Hawking and Ellis requires basic algebra and calculus

Tuki

3:18 PM

the latex symbol for "existence" ?

Busi

@JohnRennie It's not that important to be 18 or something.

Slereah

The manga guide to relativity is on libgen

:D

Busi

If you're interested in physics, then there's nothing

physics is a field, not a subject.

Tuki

$\exists$

0celo7

@Busi start here i.gyazo.com/thumb/1000/4d5b30b41bea884d6bb9216dd6700c68-jpg.jpg i.gyazo.com/thumb/1000/a4287f9c68523539857a485239c15565-jpg.jpg

Slereah

3:19 PM

>Napolitano

Tuki

This is like set theory notation or what these symbols are called ?

Slereah

What is this ice cream man

@Tuki that is logic notation

It means "there exists"

Tuki

yes i know

Busi

@0celo7 Those all are about relavity

0celo7

there's like 8 quantum mechanics books there

Busi

3:21 PM

yeah but

I need mechanics, heat and others

0celo7

nah

just learn GR

Busi

Oh why?

0celo7

for the mathematics I have about 4 times as many books

you need to start reading soon

Tuki

I think there is no complications if you try to mix notation from set theory and ones used for logic ?

Busi

@0celo7 Do you have calculus textbooks for beginners?

0celo7

3:22 PM

No

Busi

Hmm

What about mechanics?

heat, circuits, electromagnetism?

0celo7

Only mechanics I have is Arnold

Busi

Hmm

Then I don't know what to do lol

0celo7

@Busi Those are for engineers

Slereah

Jesus

Busi

3:23 PM

still couldn't a book that explains everything

Slereah

That book is 200 pages

Most of it is pictures, still!

0celo7

@Slereah what book

Busi

@0celo7 Those all can help me for studying GR

Slereah

Manga guide to relativity

Busi

@0celo7 but not for studying others

0celo7

3:24 PM

all you need for GR is Riemannian geometry, elliptic and hyperbolic PDE, and geometric measure theory

Tuki

Well one good calculus book is "Calculus: A Complete Course by Robert A. Adams & Christopher Essex "

Busi

@0celo7 no need to study GR right now.

0celo7

@Tuki I have Adams' tome on Sobolev spaces, it's very good

Slereah

Busi

the thing I needa study is heat,mechanics,dynamics

Slereah

3:24 PM

Oh no

Busi

@0celo7 Isn't it possible to find a book which explains every concepts?

Tuki

Here is a amazon link

amazon.com/Calculus-Complete-Course-Robert-Adams/dp/0321781074/…

0celo7

@Busi of course not

Busi

@0celo7 Then what should I do?

0celo7

the CK theorem takes 500 pages to prove, how do you expect to fit that inside some other book

Busi

3:26 PM

@0celo7 cuz you know that I wanna know everything

Tuki

Well you should pick something you want to start with

0celo7

that's an unattainable goal

Busi

there should be some books that explain a concept and other concepts

0celo7

and you're not letting yourself get trolled, quite annoying

Busi

aight

am confused rn

n out of my mind

Slereah

3:27 PM

don't listen to @0celo7

he is a meme

Busi

I still couldnt a book

that explains mechanics lol

0celo7

@Busi come to me when you see the light

Busi

@0celo7 what u mean LoL

Slereah

Oh no

ACuriousMind

@Busi Physics is a vast field, and probably more than any single human can learn in their lifetime. Ask for something more reasonable, a book that explains a specfic subfield or concept, and we might be able to help you.

Tuki

3:28 PM

About that do you know good book about electromagnetism ?

0celo7

I gave him all the books on GR he'll ever need, so I have done my part

Busi

@Tuki For every concepts

like electromagnetism, heat, mechanics, circuits

relavity, modern physics

Slereah

Tuki

For that you would need more than a one book obviously as already mentioned multiple times ?

Busi

It doesn't matter.

the thing is to find the book

0celo7

3:30 PM

@Busi "University Physics" by Young and Freedman

Busi

@0celo7 I already had it

Anonymous

@JohnRennie Eh, that question was for @BalarkaSen . :P Anyhow, I was getting at the fact that the energy lost when a nuclides have less masses than constituting nucleons which form them, precisely because during formation there's emission of gamma particles. Many people seem to be confused about how exactly energy reduces when you bring together particles to form a system. So.

Busi

a month ago

0celo7

then what the hell are you asking for

ACuriousMind

@Busi Ah, and now I see that you are one of our more persistent sockpuppeteering trolls. Begone.

0celo7

3:31 PM

@ACuriousMind wtf?

did you just ban a curious kid?

mod abuse!

Slereah

The most kawaii I've ever seen Michelson and Morley

Secret

sockpuppet of who?

John Rennie

@Secret mods don't comment on these matters

Secret

ok

0celo7

@ACuriousMind Is there a Lipschitz retract of $\Bbb R^n\setminus \overline{B_R}$ onto $\partial B_R$?

Tuki

3:33 PM

Anyway how do you know if someone is moderator ?

0celo7

Cannot chat for 41 days!

John Rennie

@Tuki diamond next to their name

0celo7

@Busi whoops

ACuriousMind

@Tuki Our names are blue in chat and have a diamond beside them.

0celo7

@ACuriousMind I've never seen this diamond

WillO

3:34 PM

@ACuriousMind: Thanks very much for your attempts to help with my meta question. For the record, the solution was this: physics.stackexchange.com/questions/92619/…

Tuki

So the diamond doesn't show in chat but your name is blue got it

ACuriousMind

@0celo7 ...you have never looked at any of my posts on the main site after I was elected?

0celo7

@ACuriousMind I never go on the main site.

John Rennie

Master Yushi

problem solving room is dead

0celo7

3:35 PM

Yeah, I just saw that. I've never clicked on his name either

Master Yushi

I'm the only one there lol

John Rennie

@MasterYushi not dead, just sleeping :-)

ACuriousMind

@WillO Ah, huh. Out of curiosity, how did you find that? Standard users can't search deleted posts. Wayback machine?

WillO

I had apparently made a note to myself that I'd forgotten about.

Anonymous

The shape of a diamond really doesn't look like that though. :P

Anonymous

3:36 PM

They added some "curves" to it

Tuki

I wonder if there are books about just problem solving ?

ACuriousMind

@WillO Heh, alright then

Master Yushi

can anyone look at my solution?

Tuki

You can find plenty but the issue is you don't know which one is good and which one is bad

ACuriousMind

Funny thing: The diamond is orange for some reason in the SE mobile app

WillO

3:42 PM

@ACuriousMind: According to my notes, the user was named "Jitter". There seem to be two Jitters, neither of them active .

ACuriousMind

@WillO This Jitter is the one you want.

WillO

@ACuriousMind: Thanks. That's the info I was looking for.

ACuriousMind

@WillO No problem :)

Slereah

Apparently japanese for time dilation is the urashima effect

ACuriousMind

@Slereah Why are you still reading the physics manga? :P

Slereah

3:47 PM

@ACuriousMind to learn!

Oh no!

Anonymous

@ACuriousMind I was actually curious about something. Was your undergrad degree in physics or math? If it were physics, did you pick up all the advanced algebra, analysis, topology, diff geo, measure theory, etc. stuff in "physics for mathematicians" courses or in actual math courses? Also, how much of it did you learn in your undergrad and how much of it in your graduate degree? By the beginning of your graduate degree did you already know all those math topics in depth?

Anonymous

(If you don't mind me asking i.e.)

Anonymous

*I meant "math for physicists" courses there

ACuriousMind

4:02 PM

@Blue My undergrad was physics, but there's a lot of choice about which courses to take here - I filled a lot of the credit which others filled with other science courses like chemistry or biology with actual math courses.

I don't know measure theory, but the rest of the topics I'd say I already knew quite well after undergrad.

I haven't ever had a "math for physicists" course in my life - we are allowed to choose whether to take the three-semester analysis track or a two-semester "math for physicists" track, I chose the former

Anonymous

Interesting. That does give me a rough idea of how much I need to learn, or rather how much I don't know. Thanks. :)

skullpatrol

Do you have an "engineering physics" department at your uni

Anonymous

@skullpatrol Are you asking me?

ACuriousMind

@skullpatrol No, Heidelberg has no engineers (odd, I know!)

skullpatrol

yup

Anonymous

4:08 PM

@skullpatrol Nope. We have a separate physics department, but no "Engineering Physics" department

Anonymous

Some universities in India have that stream, though.

skullpatrol

Now, that is odd!

Both of you :-)

Anonymous

Why odd? Engineering Physics is not a very main-stream course

Prathyush Poduval

i always wondered whats special in engi physics

Anonymous

@PrathyushPoduval It's sort of Physics + EE + tiny amount of CS combo

Prathyush Poduval

4:11 PM

so you end up knowing little of everything

Anonymous

Not bad I'd say. A broad base during undergrad is helpful sometimes

Prathyush Poduval

yeah, but having only a broad base won't help

you need to have a specialization somewhere

skullpatrol

They say chemical engineers make the most money over their entire careers.

Anonymous

They do get some specialization during the last 2 years, I think. Electives and stuff.

Anonymous

Like we have an option for a CSE specialization in the last 2 years

Anonymous

4:14 PM

@skullpatrol Depends on the country. CE's here don't earn much

Prathyush Poduval

@skullpatrol money can be made if one wants to

for a good life, I don't think much money is required

dmckee

4:56 PM

@BernardoMeurer I've seen very few books that teach the technique and rationelle of free-body-diagrams well.

Certainly when I was learning (back in the late bronze age) I had to absorb that by osmosis, and I couldn't have explained it clearly even at the beginning of grad school.

Right now were using Knight Jones and Field for are algebra/trig based introductory courses and it does a better job than most.

Anonymous

@dmckee I've seen Engineering Mechanics (Statics and Dynamics books) do a better job of explaining it compared to Physics textbooks.

Anonymous

My favorite is Meriam and Kraige

Anonymous

"late bronze age" :)

dmckee

@Blue My wife's statics books did a passable job. I think the reason for this is that the process of calculating is (at least part of) the subject in those courses, while in physics courses the subject is the underlying principles.

skullpatrol

@dmckee How many lectures do you spend on it in that course?

dmckee

5:01 PM

@skullpatrol One dedicated hour-long lecture, with a supporting worksheet. Then we return to the subject of how and why to draw and use FBDs several times in the next few weeks. I'd estimate that this occupies about another hour of class time.

Anonymous

We had a nearly 4-5 month long course on Mechanics in high school if I remember correctly. As a result not much was new when we started with Meriam Kraige in college. It helped me to refine my knowledge a bit though.

0celo7

@JohnRennie I need a better CPU

Sir Cumference

WISE 0855−0714

WISE 0855−0714 (full designation WISE J085510.83−071442.5) is a (sub-) brown dwarf 2.23±0.04 parsecs (7.27±0.13 light-years) from Earth announced in April 2014 by Kevin Luhman using data from the Wide-field Infrared Survey Explorer (WISE). As of 2014, WISE 0855−0714 has the third-highest proper motion (8118±8 mas/yr) after Barnard's Star (10300 mas/yr) and Kapteyn's Star (8600 mas/yr). As of 2014 it also has the fourth-largest parallax (449±8 mas) of any known star or brown dwarf, meaning it is the fourth closest extrasolar system to the Sun. It is also the coldest object of its type found ...

The coolest star is cold enough for water to freeze on its surface

Anonymous

5:16 PM

@SirCumference Is that surprising? :P Not all stars are hot

Sir Cumference

@Blue Well yeah, but no other known star is literally freezing :P

Some are not hot enough to boil water, but darn, this is impressive

Anonymous

WISE 1828+2650

WISE 1828+2650 (full designation WISEPA J182831.08+265037.8) is a brown dwarf or rogue planet of spectral class >Y2, located in constellation Lyra at approximately 47 light-years from Earth. It is the "archetypal member" of the Y spectral class. == History of observations == === Discovery === WISE 1828+2650 was discovered in 2011 from data collected by NASA's 40 cm (16 in) Wide-field Infrared Survey Explorer (WISE) space telescope at infrared wavelength. WISE 1828+2650 has two discovery papers: Kirkpatrick et al. (2011) and Cushing et al. (2011), however, basically with the same authors...

Anonymous

This is close

Anonymous

There are some others too which are estimated to have <0C temps at some regions on surface

Anonymous

Too bad we don't have Black Dwarfs

Sir Cumference

5:20 PM

@Blue Ah, I stand corrected

@Blue Black dwarfs are an entirely different object from these brown dwarfs

0celo7

admitting you're wrong is very weak

Sir Cumference

@0celo7 Arguing when you know your wrong is pointless :P

0celo7

no, it's called dominating the competition

Anonymous

@SirCumference Eh, a white dwarf which doesn't emit light. Pretty much

Sir Cumference

@Blue Yeah, but these are brown dwarfs, which don't come from white dwarfs

Anonymous

5:22 PM

The time taken to form a black dwarf is greater than the age of the universe

Sir Cumference

@Blue Yep. It'd take quadrillions of years, or much more

Anonymous

@SirCumference That's true. Brown dwarfs are at the lower mass end.

Anonymous

What was that diagram thingy called?

Anonymous

Which plots masses and luminosities?

Sir Cumference

The Hertzsprung Russell diagram?

Anonymous

5:25 PM

Ah, yep

Anonymous

H-R diagrams

Sir Cumference

Yup, it technically plots luminosities and temperatures though

Anonymous

I should revise astro sometimes :P

Anonymous

@SirCumference Oops

Anonymous

Yeah

Anonymous

5:26 PM

Are you taking any more astro classes?

Sir Cumference

@Blue Same, I haven't visited it much since I became an undergrad. We don't have an astronomy major so I never learned much more about it here

@Blue Sadly not :/ They're been getting in the way of more important classes

Anonymous

I miss those days of rushing to the rooftop with my binoculars whenever I got a comet notification :P Could never afford a good quality telescope though. Maybe, someday...

0celo7

nerds

Anonymous

We had a Newtonian at school

Anonymous

I guess I'll get a refractor sometime

Sir Cumference

5:29 PM

@0celo7 How does your interest in math not make you a fellow nerd?

0celo7

because I never looked at comets

I don't even know of any

Anonymous

@SirCumference Ah. You can take up more classes in grad school

Anonymous

If you take up astronomy/cosmology

Anonymous

Unless you go hard-core math

Sir Cumference

@Blue Yeah, that's what I'm waiting for. I just hope I don't lose interest in these 2 years

Feb 2 '16 at 5:34, by user54412

One thing to note is that comet-hunting used to be at least 50% of astronomy (back a couple hundred years ago). Now there might not be 50 people in the world who research comets.

From the great Chris W

Anonymous

5:30 PM

@SirCumference Try taking part in some undergrad research projects if possible

Anonymous

Helps to keep in touch

0celo7

so Chris is saying that modern people think comets are boring

gotcha

I agree 100%

Sir Cumference

@Blue I genuinely love math, particularly analysis, and I enjoy the rigorous aspect of it. But I'm more interested in how the universe works

Anonymous

As a kid, that visual astronomy was more interesting. Who cares about the mad math people who spend their day writing weird symbols on paper!

0celo7

@Blue He has a legendary GR person at his school but he refuses to talk to him

skullpatrol

5:32 PM

The great Chris is not here to explain.

Sir Cumference

@0celo7 JS?

If not put the initials

0celo7

no

HL

Sir Cumference

@0celo7 This is a prof or grad student

0celo7

professor

Sir Cumference

@0celo7 Oh, this is a math professor

0celo7

5:36 PM

of course

Anonymous

Pretty much the first guy on your Math department faculty page

0celo7

the best physicists are mathematicians

Anonymous

PDE guy :P

Sir Cumference

@Blue I was looking aimlessly at physics for a while

Anonymous

Yeah, you should totally follow 0celo's advice and visit him :)

Sir Cumference

5:37 PM

I've already bugged 5 different profs for advice

0celo7

you just need to impress one

Anonymous

Doesn't matter. Profs normally like having enthusiastic students around.

0celo7

if you can read any of HL's papers you will impress him

we're doing some of his work in my hyperbolic PDE class right now, it's pretty insane

Sir Cumference

@0celo7 The only papers I'm capable of understanding quite well are astronomy papers

Anonymous

By the law of large numbers, the more number of people you contact, the more people you'll have who are willing to help you. :P

Sir Cumference

5:39 PM

Obviously math papers are out of the question

0celo7

I would link one of his famous papers but that would reveal you

Although I think everyone knows by now

Sir Cumference

@0celo7 Oh please, only a few people know

0celo7

How the hell did @Blue find out

Sir Cumference

He was there when you bought it up

Anonymous

I was lurking around

0celo7

5:40 PM

the other blue knows and he probably emailed people about it

skullpatrol

+ skill :P

0celo7

he's looking for you

Sir Cumference

Yeah I'm still wondering how obe found out

0celo7

he was lurking while banned

Sir Cumference

His ears must've rang when you brought up my uni

Does GR really involve that much PDE?

0celo7

5:43 PM

GR is a very large field

some parts do

Sir Cumference

Sigh, now I'm questioning my schedule again

0celo7

any PDE you could take now wouldn't help you with HL's work

is there a second year graduate PDE you can take?

Sir Cumference

Well at this point I'm just trying to figure out what math courses will help with cosmology

0celo7

probably none

Sir Cumference

Eh, cosmologists I've spoken with said complex analysis, some real analysis, and diff geo are helpful

0celo7

5:47 PM

Do those guys actually know what they teach you in those courses

Asking professors in other fields about math classes never works out

Sir Cumference

Well asking math professors about courses for cosmology doesn't seem more viable

0celo7

yeah

so the conclusion is to become a mathematician

Sir Cumference

>_>

skullpatrol

<_<

Anonymous

I think the best way to learn something is to get hands on experience. Cosmology is a really vast field, and you'd probably only be working on some parts of it, in the future.

Sir Cumference

5:49 PM

Yeah, but a strong math background gives me more options

Anonymous

It doesn't help to worry so much. You won't learn all the math needed for research level cosmology at college (undergrad) anyway. That's just the basics.

Anonymous

@SirCumference Sure

Sir Cumference

@Blue Meh, I have trouble believing that they'd waste our time and money telling us information we won't need

0celo7

lol

Anonymous

@SirCumference Heh

0celo7

5:51 PM

are you really that naive?

Sir Cumference