The h Bar

Sir Cumference

01:25

@DeNiSkA I got your answer now

In a neutron star's core, there is neutron degenerate gas

The neutrons are being tightly pressed near each other

This leads to a pressure since they can barely be moved more

The neutrons also occupy the lowest energy levels, with two neutrons (of opposite spins) occupying each energy level

So all the energy levels up to the Fermi energy (difference between highest and lowest energy neutron) are filled. Now, these neutrons barely move, since they are at such low energy levels. In order to move, the neutrons would have to increase to a higher energy level — which is incredibly hard to do.

Thus, the star doesn't really compress, since the neutrons hardly move. To get the star to compress, you'd need to add more mass, which will cause stronger gravity. Then we can have them start moving. The Fermi energy would increase, and the star would become more compact while the degenerate pressure increases.

This pressure will fight against the gravity. However, in general relativity, pressure is actually a source of the gravitational curvature of spacetime, so increasing pressure increases gravity. This thereby increases the amount of pressure you need to fight off the stronger gravity. Eventually, there's a point at which increasing the pressure will only be counter-effective for the star. At this point, no increase in pressure will prevent the neutron star from becoming a black hole.

phew

dmckee

@0celo7 It's happened before. He writes a lot and sometimes it appears that he hasn't taken the time to make it shorter.

@ChrisWhite Absolutely over the top, but beautifully put none-the-less.

Sir Cumference

@dmckee Was what I said right about neutron stars?

Need to make sure

dmckee

@SirCumference Not completely. It's not really true to say the neutrons hardly move; some of them are in states of quite high energy and RMS momentum and angular momentum.

The trick here is that this is a fully quantum mechanical state of matter and a intuition built on Newtonian lines will lead you astray.

Sir Cumference

01:40

I thought they occupy all the lower energy states?

dmckee

They occupy the lowest available states, but that isn't the same as low in an absolute sense.

The Fermi energy is quite high.

Sir Cumference

Oh, really?

Then why is it that it takes so much energy to compress the neutron star?

dmckee

Wait, let me re-write that.

Because any reduction in the physical volume of the star must be compensated for with a equivalent increase of the momentum-volume; because the Pauli principle says how many identical fermions can fit into a phase-space volume ($(\Delta x) (\Delta y) (\Delta z) (\Delta p_x) (\Delta p_y) (\Delta p_z)$) of size $\hbar^3$ (2, for spin 1/2 particles like neutrons).

If you reduce the product of the spacial dimensions you must increase the product of the momentum dimensions.

But that means increasing their energy.

Sir Cumference

Oooooooh

I guess my source is a liar

@dmckee How about my part of neutron degeneracy pressure?

user116211

03:15

3

Q: Force distribution on corner supported plane

This question has been annoying me for a while. If you have a completely ridged rectangular plate of width and height x and y that is supported on each corner (A,B,C,D) and has force (F) directly in its center then I think the force on each corner support will be F/4. What I want to know is ho...

user116211

@Danu: Hey, why did you vote it to re-open? ^

user116211

This is definitely homework ;/

dmckee

There is, of course, a really interesting conceptual question hiding in there, and that conceptual issue is why the problem is often given as homework.

user116211

03:34

@dmckee Then OP should better highlight the underlying concept query rather than asking how to prove this mathematically; the later tastes like homework definitely.

Physics Meta

03:54

0

Q: Appropriate Response to Trollery

From time to time, I've written up substantial answers to naive questions about special relativity, sometimes illustrating them with spacetime diagrams and explaining how to read them. Some novices have found these answers helpful. At least one novice, though, has apparently found these answers...

discussion down-votes

0

Q: A Problem With a User

From time to time, I've written up substantial answers to naive questions about special relativity, sometimes illustrating them with spacetime diagrams and explaining how to read them. Apparently some novices have found these answers helpful. At least one novice, though, has apparently found th...

discussion down-votes

dmckee

@user36790 Well, of course.

user116211

@dmckee: BTW, why is only our meta named as Physics Meta while at the Periodic Table, it is known as Feeds?

dmckee

No idea.

user116211

@PhysicsMeta Tell OP not to publicise any user while alleging any complaint against him.

user116211

04:15

@dmckee: Is it good to name the user whom are talking about?

user116211

I've inserted [insert-here-the-user-who-shall-not-be-named] in place of the names; is it right?

dmckee

@user36790 We discourage it rather strongly. Questions on meta should be about policy (i.e. general rules) rather than about specific cases.

user116211

@dmckee Can I quote your statement to defend my action?

dmckee

@user36790 I'll take care of it.

user116211

@dmckee okay

innisfree

09:41

Any diphoton rumours?

Funny, I don't think we've had a single diphoton 750 GeV question yet, have we?

The Moriond diphoton session begins in about 6 hours

See indico.in2p3.fr/event/12279/other-view?view=standard#2016-03-17

Slides should be uploaded after the talks

Physics Meta

10:19

0

Q: Would having a second set of tags relating to the nature of the question make sense?

Yesterday I asked a question which was based on a conceptual confusion, as was revealed by the excellent answers I received. It made me think that it would be nice if that fact was visible straight away for anyone coming to the page. There would be a second line of tags, relating to the nature o...

feature-request tags

Nihal Jalaluddin P

@user507974@ACuriousMind@Slereah algebra,calculus or differential equation first?

Slereah

Algebra.

Nihal Jalaluddin P

then??

user116211

Wow! Completed reading Verhulst-Pearl Logistic curve.

Slereah

Then calculus.

Nihal Jalaluddin P

10:36

@Slereah after studiyng these how can compare these to real world physics?like QM

Slereah

First do classical mechanics

Nihal Jalaluddin P

how?

Slereah

2

Q: Physics books covering classic mechanics

I am going to be a high school freshman next year and I have acquired a strong interest in physics. I have a mathematical background, upto, but not including, Calculus. I am looking for in depth resources covering classic mechanics enough to move onto more in depth texts on relativity as well as ...

classical-mechanics soft-question resource-recommendations

Slereah

10:57

Nope

As can be seen by the different name

user116211

@Slereah Phew!

DeNiSkA

@hubot sorry i was busy yesterday at 8:00 pm(Europe time)!!

user116211

@DeNiSkA UTC?

DeNiSkA

well! he told me Europe time so i also told the same :)

Nihal Jalaluddin P

@DeNiSkA hi kid

who is older than me for 60030700 or something

DeNiSkA

11:09

@NihalJalaluddinP hahaha!!

how are you going to change the world?

Nihal Jalaluddin P

@DeNiSkA My net usage is gonna help a lot of people.

no "gonna"but it is

DeNiSkA

it is.....?

Nihal Jalaluddin P

helping now itself

DeNiSkA

i see!!

Nihal Jalaluddin P

so am gonna change the status

suggest one

DeNiSkA

11:17

keep status about your interest

Nihal Jalaluddin P

ok da

googling "da"?@DeNiSkA

DeNiSkA

i know in south india it is used ;)

Nihal Jalaluddin P

you are an indian?

DeNiSkA

well born in Germany!

but actually south indian

Nihal Jalaluddin P

How?

i was born in saudi

DeNiSkA

11:25

oh

user116211

I was born in.....

DeNiSkA

in.....?

user116211

India ;P

DeNiSkA

xD

Nihal Jalaluddin P

indians yay!!!!!

DeNiSkA

11:27

do you have any plan of going out of india!

user116211

@DeNiSkA Not now; as I said I want to do my graduation here.

DeNiSkA

oh! i see

user116211

@ACuriousMind: Am I still in your ignore list?

user116211

Damn, I'm still ignored by ACM ;(

ACuriousMind

@innisfree I think that's because no-one really has a good explanation for the excess, and no one knows really how significant the new analyses make it out to be. Without a snazzy headline like "model X confirmed!", "particle possibly detected which fits into hundreds of models but we don't know which one it is" is not really news of interest to non-physicists, I guess.

Nihal Jalaluddin P

11:38

@DeNiSkA you are in 12?

0celo7

Good morning chaps

@ACuriousMind Any thoughts on the car color?

user116211

@0celo7 o/

0celo7

hello

ACuriousMind

@0celo7 The only thought I have to offer is: "Why are you still annoying me with that?"

0celo7

damn.

user116211

11:45

@0celo7: Warning! ACM has still a place left in the ignore list ;P

0celo7

It would suck if ACM ignored me

The silent treatment is torture.

4

user116211

@0celo7 Now, feel my situation ;(

DeNiSkA

@NihalJalaluddinP no i am writing my 11th exams

@user36790 why he kept you on ignore list?

@SirCumference well the answer did not fulfill my question but it was cool written by dmckee

user116211

@DeNiSkA distasteful story ;(

DeNiSkA

i think i am also on ignore list!!

user116211

11:50

:(

user116211

Dark AGE ;/

DeNiSkA

let me check @ACuriousMind are you here?

user116211

........

DeNiSkA

hahaa!! as i told ;)

user116211

There must be a way, I believe, to have the ban get lifted......

0celo7

11:53

OP is just not ready for HE, I'm having to explain basic linear algebra

ACuriousMind

@0celo7 That's...your profile link.

0celo7

lol

ACuriousMind

:D

0celo7

A friendly word of advice, OP. If you feel like you're stumbling time and time again in a book, you might not be ready for it. I think Wald's book on GR treats this material more clearly for a beginner. (I will still answer this question when I have time.) — 0celo7 21 hours ago

There.

user116211

Any idea how?

ACuriousMind

11:56

You...recommended Wald to a beginner?

0celo7

@ACuriousMind I think my answer is very clear and he's just confused about what equivalence and isomorphism means

@ACuriousMind Yeah?

Wald is easier to read than Hawking, in general

At least as far as the geodesic congruence material is concerned

DeNiSkA

anyone knows about neutron degeneracy pressure?

ACuriousMind

Well, it's certainly easier, but does OP strike you as being able to read it? :P

0celo7

Maybe not!

user116211

@DeNiSkA This is related to Exclusion Principle, I guess; though I read it qualitatively while studying about stars.

0celo7

11:59

I don't know what to do, I don't want to spell out German middle school level linear algebra now

but I don't want to leave him hanging, either

DeNiSkA

@user36790 yes! it is do you know a lot about it so i will ask my question

user116211

@DeNiSkA No; but you can ask.

ACuriousMind

@0celo7 I would agree, apparently he just doesn't understand quotients and equivalence classes.

user116211

There are other users also who might help you.

DeNiSkA

@user36790 Who prevents neutron star from collapsing their is no repulsive force. (many people say it is because of exclusion principle but there should be some force to prevent huge attraction) john rennie in one way proved that their is a large force needed to compress it any further but i want to know which internal force is balancing external force

0celo7

12:04

@ACuriousMind Should I just tell him in the comments to think about it some more?

@ACuriousMind NB: the vectors are bolded because HE bolds vectors.

I'm not suddenly a heathen

ACuriousMind

@0celo7 Uh...I don't really have an opinion about that

0celo7

@ACuriousMind I know that if you were me and I were this guy, you'd tell him to think about it a while longer

because he's just refusing to read/understand the wiki article at this point

ACuriousMind

Nah, sometimes I also just wouldn't reply any more

0celo7

:(

the silent treatment

ACuriousMind

And sometimes I would indeed expand the answer to include a bit more basics. It highly depends on my mood and spare time

0celo7

12:08

speaking of mood, how do you feel about hiking

user116211

@0celo7: You don't ve to care too much for a user; you answered it correctly; tried to help.... that's a lot.

Nihal Jalaluddin P

@DeNiSkA cbse?

DeNiSkA

@NihalJalaluddinP yes!

ACuriousMind

@0celo7 With the right kind of friends, it can be really fun

...why?

user116211

@DeNiSkA: This might be related:

user116211

12:10

2

Q: What prevents a star from collapsing after stellar death?

When the star stops burning because heavier elements like Iron are formed in its core. Then the gas pressure stops and as you know the gas pressure helps keep a star in equilibrium because it provides pressure against the force of gravity. So Iron does not give off energy. So what stops the star ...

black-holes astrophysics stars stellar-evolution

0celo7

@ACuriousMind because a certain friend wants me to go hiking, haven't been in years

Nihal Jalaluddin P

@DeNiSkA I want to get into iiser or iit what sbt you?

0celo7

not my thing

Nihal Jalaluddin P

@user36790 me too

DeNiSkA

@NihalJalaluddinP IISc or IIT-madras but i will have my further education in Germany in think so?

ACuriousMind

12:11

Well...I wouldn't come up with a plan to go hiking on my own, either, but I tend to go with whatever plans my friends devise for trips/holidays

Nihal Jalaluddin P

How you get into south India?

DeNiSkA

@NihalJalaluddinP my parents are pure south indians!

Nihal Jalaluddin P

@DeNiSkA what are they doing?

0celo7

@ACuriousMind hmm

DeNiSkA

@NihalJalaluddinP breathing!

Nihal Jalaluddin P

12:13

Lol

I mean their profession

@ACuriousMind have you ignored me?

DeNiSkA

haha! all indians are being ignored by ACM

Nihal Jalaluddin P

You too?

0celo7

Yup, ACM doesn't like Indians

Nihal Jalaluddin P

Indians sucks

DeNiSkA

i agree but i am german-indian

Nihal Jalaluddin P

12:19

😉😉

innisfree

@ACuriousMind the wildest rumours are it's going to be ~<5 sigma (I've heard the number 4.9 and 4.5) and spin-2 is favoured by forward direction of photons

Nihal Jalaluddin P

I am an Arab Indian

Apparently

What's your relation with Germany ?

@DeNiSkA

ACuriousMind

@innisfree Spin-2 would be interesting as it's either composite or graviton. Is there some quark bound state/resonance we could feasibly expect to be responsible?

DeNiSkA

@NihalJalaluddinP i was born and for 10 years lived there!

Nihal Jalaluddin P

As electrons can be used for electricity,can gravitons be used for graviticity?

I coined a new word

@DeNiSkA Mm

innisfree

12:22

@ACuriousMind I don't know, scalar explanation was far more popular than spin-2. I didn't follow the literature in detail though.

After cms and atlas, Strumia will give a theory overview

DeNiSkA

@NihalJalaluddinP well that gravitons are totally hypothetical ! and there no such thnig gravicity

innisfree

which will be 1) very informative and 2) very amusing if strumia is his usual self

ACuriousMind

Are you there? Is there a stream?

DeNiSkA

@JohnRennie Who prevents neutron star from collapsing as their is no repulsive force. (many people say it is because of exclusion principle but there should be some force to prevent huge attraction)[ john Rennie in one way made me understand that their is a large force needed to compress it any further] but i want to know which internal force is balancing external force.

innisfree

I wish I was, I just read the schedule . No stream :( that sucks

Nihal Jalaluddin P

12:28

@DeNiSkA hypothetically thing do turn to real things.

ACuriousMind

@innisfree Sooo...we have to wait for the slides then. Hopefully they are good, like all physics slides are ;P

Nihal Jalaluddin P

@DeNiSkA you know linear algebra and all?

DeNiSkA

@NihalJalaluddinP yes!

Nihal Jalaluddin P

From where?

DeNiSkA

@NihalJalaluddinP books!

Nihal Jalaluddin P

12:30

School or Internet?

DeNiSkA

both

Nihal Jalaluddin P

Can you recommend some?please.

DeNiSkA

@NihalJalaluddinP some.... what?

Nihal Jalaluddin P

Linear algebra in which class? In cbse?

Books.

I am watching khan academy's video ,that is so helpfull

DeNiSkA

well i started in 8th standard i think with linear and in 9th with quadratic and polynomials

Nihal Jalaluddin P

12:33

I am in 8th

0celo7

@ACuriousMind what is wrong with people, she just said to pick a color that I like

that's 0 help

Nihal Jalaluddin P

That is linear equation on one variable.

ACuriousMind

lol, but that's how you pick colors

Or anything else for that matter

Nihal Jalaluddin P

@DeNiSkA what about QM

Slereah

If you don't know anything about physics, don't worry about QM for now

DeNiSkA

12:36

@NihalJalaluddinP well QM demands a flood of mathematics according to me, it needs damn lot application of calculus, if you want to understand it fully

0celo7

@Slereah uh

I learned Newtonian mechanics after GR and QM and was fine.

DeNiSkA

@0celo7 really?

0celo7

@DeNiSkA yes

user116211

@DeNiSkA That is typical

Slereah

Can you do basic step potential in QM now?

0celo7

12:37

@Slereah me?

Slereah

Yes

0celo7

of course?

Slereah

Well how am I supposed to know

0celo7

why

Slereah

You don't even know the quadratic formula

Nihal Jalaluddin P

12:37

which one is harder?

0celo7

because I'm not a dummy

...

DeNiSkA

@0celo7 when i read QM in my 14 i was blank without classical mechanics but now it is all set

Slereah

0celo7

:(((

DeNiSkA

hehe

Nihal Jalaluddin P

12:38

@DeNiSkA from where you studied QM

0celo7

@Slereah step potential is like page 100 in Shankar, hardly difficult

Slereah

Well yes, that's why i asked

DeNiSkA

@NihalJalaluddinP i used to go to library and at home i used feynman vol 3

Slereah

If u don't know how to do the basics

Then I could accuse you

of not rly being good

0celo7

@Slereah why don't you accuse me of not knowing GR

Slereah

12:40

Well

DO YOU KNOW GR

Nihal Jalaluddin P

Is PDFs available for Feynman vol3?

0celo7

I could not calculate the perihelion shift if you threatened an amputation

Slereah

Hm, what is the simplest GR thing that isn't trivial

K. N. O.

@0celo7 how much math do you know?

DeNiSkA

@NihalJalaluddinP yes

Slereah

12:40

Schwarzschild, i guess?

Schwarzschild with no horizon

0celo7

@K.N.O. basic linear algebra and calculus

K. N. O.

@0celo7 and you know QM?

0celo7

@K.N.O. yes

ACuriousMind

@0celo7 ...and a load of random differential geometry, don't forget that :P

Nihal Jalaluddin P

Is there any channel on YouTube which thoroughly explains all the f*****ing GR and QM

DeNiSkA

12:41

@0celo7 you know differential equations and calculus with 2 and more variables!

0celo7

@Slereah the perihelion shift is pretty much the easiest thing

but I have literally no idea how to do it :D

Slereah

I s'ppose yeah

K. N. O.

@0celo7 do you know functional analysis?

Slereah

Hm

0celo7

@K.N.O. no, no one uses that for QM unless you're a mathematician

Nihal Jalaluddin P

12:42

Leave it guys

Slereah

Can you do perihelion shift in linear GR

I wonder

0celo7

I don't know

Slereah

I think it's doable?

0celo7

CAN YOU

Slereah

Not sure

I can probably do like

0celo7

12:43

@ACuriousMind that's just calculus (on manifolds) ;)

Slereah

The Formula

Of an orbit in Schwarzschild

Showing a perihelion, maybe not

0celo7

@Slereah $$\frac{-b\pm\sqrt{b^2-4ac}}{2a}$$

Slereah

That is Good

0celo7

@DeNiSkA that's just calculus

Slereah

Quadratic formula you use p. much all the time

K. N. O.

12:44

@0celo7 physics is becoming too difficult for physicists! Hilbert (Space!) said! lol

0celo7

@ACuriousMind are you proud of me

ACuriousMind

@0celo7 no

0celo7

I memorized the quadratic formula for me PDE midterm

DeNiSkA

@0celo7 no you, told the basic one and in basic calculus we learn only one stupid variable

John Rennie

@DeNiSkA Was it you I was discussing this with before? I remember explaining how the exclusion force was generated, but I can't remember who I was discussing it with.

0celo7

12:45

@ACuriousMind wtf

DeNiSkA

@JohnRennie YES

0celo7

@DeNiSkA calculus is just metric spaces and limits

Nihal Jalaluddin P

@DeNiSkAhttps://www.google.co.in/url?sa=t&source=web&cd=1&ved=0ahUKEwjD9obw38fLA‌hUCWo4KHRQiBBcQFggKMAA&url=http%3A%2F%2Fwww.sci.buu.ac.th%2F~physics%2Fchainarong‌%2Ffundamental%2520physics%2FRichard%2520Feynman%2520-%2520The%2520Feynman%2520Le‌ctures%2520on%2520Physics%2520Volume%25203.pdf&usg=AFQjCNEQSjLl1trLOmiMARfqoBoX2y‌JDhA&sig2=vJAqJcvDVTChFlsN00tYqg is it this?

What about 1 and 2?

Sorry about the long link

K. N. O.

@0celo7 ?

Slereah

I mean the definition of a derivative is just like

⊢ D = (𝑠 ∈ 𝒫ℂ, 𝑓 ∈ (ℂ ↑pm 𝑠) ↦ {⟨𝑥, 𝑦⟩ ∣ [(TopOpen ‘ℂfld) / 𝑗](𝑥 ∈ ((int ‘(𝑗 ↾t 𝑠)) ‘dom 𝑓) ∧ (𝑧 ∈ dom 𝑓 ↦ if(𝑧 = 𝑥, 𝑦, (((𝑓 ‘𝑧) − (𝑓 ‘𝑥)) / (𝑧 − 𝑥)))) ∈ (((𝑗 ↾t dom 𝑓) CnP 𝑗) ‘𝑥))})

p. simple

DeNiSkA

12:47

@NihalJalaluddinP feynmanlectures.caltech.edu/I_toc.html

@JohnRennie did you get my question?

0celo7

@K.N.O. what

how else are you going to define calculus

it's just analysis

which is just metric spaces

DeNiSkA

@0celo7 for mathematician this is not a correct definition

ACuriousMind

@0celo7 I have no idea how serious you are.

Nihal Jalaluddin P

@DeNiSkA tnx buddy😘😘 sab bharathian bro and sis he

0celo7

@Slereah indeed

@ACuriousMind Completely, why are people acting weird?

Slereah

12:49

"Although the definition is valid for any subset of ℂ and is well behaved when 𝑠 contains no isolated points, we will restrict our attention to the cases 𝑠 = ℝ or 𝑠 = ℂ for the majority of the development, these corresponding respectively to real and complex differentiation."

Hm

So let's see

ACuriousMind

@0celo7 Ah, trolling, then.

Slereah

f is a function from a subset of C to C

0celo7

@ACuriousMind Screw you

Slereah

and it maps that function to...

ordered pair <x,y>

0celo7

I'm not trolling, and I don't know why you think so

analysis is the topology of metric spaces

Slereah

12:51

TopOpen is the topology extraction function

Not sure what that is

K. N. O.

@0celo7 I think calculus differs from analysis but i suppose we are talking about the same things!

Nihal Jalaluddin P

@DeNiSkA is this book complicated? Or simple?

Slereah

Cfld is the field of complex numbers...

ACuriousMind

@0celo7 How would differentiation be related to the "topology of metric spacs"?

John Rennie

@ACuriousMind I'm (mildly) curious to know who you're thinking of. There are some truly amazing (they amaze me) answers appearing in the review queues, but I can't think of any single worst offender.

Slereah

12:51

Blah

Not easy to read

I wonder if we could do this for GR

Generate proofs like that

K. N. O.

@Slereah whats the quotation about?

Slereah

the definition I posted earlier

DeNiSkA

@NihalJalaluddinP simple but you need to know calculus and algebra

K. N. O.

@Slereah its from which book?

ACuriousMind

@JohnRennie I can honestly think of only one user appearing so consistently in the VLQ queue, and so unable to write a single sentence without any error in it.

Slereah

12:54

No book

us.metamath.org/mpegif/mmtheorems.html

K. N. O.

oh got it

Nihal Jalaluddin P

@DeNiSkA ooh,let me study that.

DeNiSkA

@NihalJalaluddinP go for it!!

Nihal Jalaluddin P

Trigonometry?

DeNiSkA

@NihalJalaluddinP yaa! that is also quite needed in some places

Nihal Jalaluddin P

12:57

@user507974 I think mit ocw is a little complicated for 13 years old guy.

.@DeNiSkA have you read it?

When?

DeNiSkA

@NihalJalaluddinP yes!

K. N. O.

@Slereah they wrote all proof by their own or they used a program?

Slereah

Well the proof are written but they use a program to verify them

Transcript for