The h Bar

15:00

and we also need the zeroth Law of Mechanics: motion makes sense

ACuriousMind

At least, that's what I always heard as the answer to "why is the 1st law not just a special case of the 2nd", and it makes sense. I guess in the end it depends on what statements exactly you think the three laws make

PhyMan

@Maxwell I would put D as my answer since if any 2 laws are equivalent, then those laws would have been treated as one!

rob

@ACuriousMind Possibly. Newton's audience was people who believed "the natural state of an object is to be at rest."

ACuriousMind

Sure, Newton had probably no idea of frames. But we're not teaching the original Newton today, are we?

AccidentalFourierTransform

yeah, the answer is always the D

Slereah

15:01

The fact that you can't derive conservation of momentum from the third law is easy, since there are systems that do not conserve momentum

and obey the third law

rob

@AccidentalFourierTransform Let's ... let's not go there, please.

ACuriousMind

At least, our textbooks are not full of the awkward (though brilliant) geometrical reasoning that passed for calculus back then

Maxwell

@rob, what is "velocity is constant absent force"?

rob

@Maxwell "If there isn't any force, the velocity does not change"

"absent" == "in the absence of"

Slereah

@ACuriousMind Euclid's axioms were the ZFC of the era

Everything had to be built on it

AccidentalFourierTransform

15:08

very nicely formatted for a first-time post

0

Q: Can two fermions with different energylevels be at the same position?

Suppose I have two fermions in a infinite square well potential, without spin or other degrees of freedom at $0 K$ temperature. Let $L$ be the width of that well. I used the two particle wave function in 1D for itentical fermions $$ \Psi_{nm}(x_1,x_2)=\frac{1}{\sqrt{2}}\left[\Psi_n(x_1)\Psi_m(x_2...

John Rennie

@Slereah What systems obey the third law but don't conserve momentum?

Slereah

@JohnRennie Any system with a potential depending on position

as in, absolute position

for instance, Aristotle's physics would not conserve momentum, for things are subject to forces depending on where they are

John Rennie

@Slereah But that's cheating because you are considering only part of the system. Total momentum is still conserved.

paracetamol

@Slereah @JohnR, what do you two make of this?

ericscerri.blogspot.in/2012/06/…

Slereah

@JohnRennie Not if there's no potential energy or whatever else you could put the rest of that system

That's just a simple application of Noether's theorem

Yashas

15:17

@Maxwell Must be another state level competitive exam where the paper setters don't know physics but are asked to set the physics paper.

If I could complain about the wrong questions in KCET, I would probably report half of them.

Either they are totally wrong or they miss important information or expects us to make insane assumptions, etc.

Use JEE questions for practice.

Slereah

At its core, Aristotle's physics isn't that matter is attracted by anything

There are no fields or anything

Grave matter is just attracted to the center of the universe

Because that is its natural place

John Rennie

@paracetamol the electronic structure of atoms is far more complicated than we dare let students know. For example atomic orbitals don't exist for any atom with more than one electron.

The fact the aufbau principle fails to give the correct structure for $Sc^{2+}$ is not something that keeps me awake at night.

Maxwell

@yashas, then what would be your choice?

Yashas

D

Maxwell

@yashas, Oh. I ticked the same, however

Yashas

15:25

I would honestly go and fight if the answer key told the answer was option A.

John Rennie

@paracetamol See:

21

A: Why do non-hydrogen atomic orbitals have the same degeneracy structure as hydrogen orbitals?

Polyelectronic atoms don't have atomic orbitals - though they are a very useful approximation for describing the properties of polyelectronic atoms. The 1s, 2s, etc orbitals are solutions for a central potential, and for any smooth monotonic central potential we'll get solutions of this form. Th...

rob

@ACuriousMind Reference frames seem to be defined by Newton, not in the First Law, but in a preceding discussion of absolute and relative space and time.

Slereah

"This paper replaces CTP#2117, “Gott Time Machines Cannot Exist in an Open
(2+1)-Dimensional Universe with Timelike Total Momentum,”"

Can you just replace papers like that

rob

@Slereah Sort of. It's easier to "replace" a paper in an online-only journal; you couldn't do that if you'd already mailed a bunch of dead-tree versions of the original to libraries.

But an erratum to a dead-tree journal might say "Figure 7 should be replaced with the one below", and the online versions of that paper might make it hard to find the original wrong figure.

Slereah

15:47

Can you replace someone else's paper

I want to put my name on Einstein's papers

AccidentalFourierTransform

why

everybody knows Einstein was wrong

just pick a random vixra paper

user228700

The single reason I use Twitter is so that I can reply to my favorite creators' tweets (if I have anything particularly interesting to say) and hope that they will reply/like it! It's happened twice so far so it's safe to say that it's going great!

user228700

(Sorry about the random tangent)

Maxwell

Hello @ACuriousMind

AccidentalFourierTransform

10

user228700

15:53

x'D

paracetamol

@JohnRennie :O

Shivers

@JohnRennie :D

ACuriousMind

@rob Hm, in that formulation, it does seem that the first law is just a special case of the second

@Maxwell Hello?

rob

@ACuriousMind I think so, too. On the other hand, it might be easier to convince a skeptical reader of the first, then the second, rather than the other way around.

ACuriousMind

@rob Strange, the mention of the circular motion of the planets seems to indicate that Newton thought the orbits of the planets don't need the centripetal force from gravity to keep going in circles?

Balarka Sen

@AccidentalFourierTransform They're buying poop for €275,000 tho

rob

15:58

@ACuriousMind No, that one he discusses when he defines a centripetal force.

Maxwell

@ACuriousMind, whose explanation do you find the best here? physics.stackexchange.com/questions/66057/… physics.stackexchange.com/questions/66057/…

ACuriousMind

@rob Then I'm puzzled why he seems to mention the circular motion of planets as an example for the first law

rob

I read Newton's First Law, in his formulation, as "drag and gravity are also forces."

Sir Cumference

Fun fact: MathOverflow predates Math SE by a year

Balarka Sen

MO are the old guys

ACuriousMind

16:01

@Maxwell I think all of them (except for the negatively scored one) contribute valid points.

Maxwell

@ACuriousMind, whose would be best to submit to a teacher?

rob

@Maxwell You should of course write your own answers to submit to a teacher.

ACuriousMind

None, you should of course submit an answer in your own words.

Heh, @rob, great minds... :P

Yashas

0

Q: question of Kinetics of particles

The question arises from this problem:

kinetic-theory

The OP removed the contents of the question in an edit :|

rollback?

It has ended up in the VLQ queue now.

rob

@ACuriousMind True fact: dmckee and I recently posted nearly-verbatim identical answers to a Meta question, ten seconds apart.

zane scheepers

16:05

Hi all. New here so forgive any mistakes. I'm just wondering why our subjective perception of reality is not considered to be a simulation.

Yashas

because a computer cannot represent irrational numbers

if we were in a simulation, then there must be something simulating it

you need infinite memory to store the exact value of irrational numbers

that is what they say

I am critical of it, though.

What if the value of pi repeats after quadrillionth decimal palce?

Balarka Sen

sounds like a metaphilosophical question

zane scheepers

I did not say we are in a simulation. I said our perceptions are a simulation of reality.

ACuriousMind

@Yashas Of course, what are you uncertain about?

rob

@zanescheepers Isn't it? Your brain constructs an incomplete model of your environment, and you try to guess how your actions will affect that model.

Yashas

16:08

The author had edited it. He might have wanted to delete it. It sounds bad to rollback in case they did not want the question to exist :/

Balarka Sen

@Yashas I don't know what "infinite memory" means but there's an algorithm for determining the nth digit of the decimal expansion of $\pi$ without computing the (n-1)th.

zane scheepers

@rob, apparently not. According to comments I received.

Yashas

@BalarkaSen Interesting. What is that called?

Balarka Sen

Bailey-Borwein-Plouffe

ACuriousMind

@Yashas So what? Once you post a question here and it receives an answer, you no longer have the right to delete it.

Yashas

16:09

nvm

need to sleep; brain isn't functioning normally

rob

@zanescheepers Well, your proposal is easily confused with "maybe we live in a simulation running on God's computer," which I think is a much sillier idea.

Reading carefully is hard.

Balarka Sen

Ah, I guess that's only base 16. I think there exists base 10 formulas.

Yashas

@BalarkaSen Suppose you had to use the value of pi, you would first have to get the value of it? I can think of digit by digit multiplication but the result would also be irrational unles you multiply it by 1/pi.

zane scheepers

@rob you mean grasping the context. We see what we understand.

Balarka Sen

@Yashas I can't parse that sentence. What do you mean "Suppose you had to use the value of pi"?

Use the value of pi for what?

Yashas

16:13

I meant if the simulation computer needed the value of pi to do something.

Balarka Sen

Okay. So you compute it upto some precision. You of course can never list all the digits of pi!

Yashas

yea if the simulation computer is doing it, then we should notice that approximation in nature?

Balarka Sen

What is this simulation computer? :P It seems I am talking about math, whereas you are going into metaphysics again.

Yashas

we could measure something up and find that the value of pi measured isn't equal to the value of pi obtained from a series.

@BalarkaSen That had to deal with the case if we were in a simulated world.

I gave a reason why such a simulator cannot exist if we can measure an irrational number to infinite places and find that it is equal to the correct value.

Balarka Sen

Sorry, I don't care about a simulated world. I was just talking about your argument that digits of pi cannot be predicted.

Yashas

16:17

I tried to make an argument that a computer cannot store an irrational number :P

to store all the infinite digits, it wud need infinite memory

ACuriousMind

@Yashas Of course it can, make it store the string "sqrt(2)" :P

Yashas

but you pointed out that one can find the digit without knowing the preceeding digit

@ACuriousMind but you can't express it in reality? :P

Balarka Sen

Depends on what expression means!

Yashas

if you construct sqrt(2) from a right triangle of sides 1 unit

then we are able to measure that sqrt(2)

if we can measure, it must first calculate the value of sqrt(2) ? :P

ACuriousMind

@Yashas I don't know what that means. But many CAS can do computations with irrational numbers - be they $\pi,e$ or $\sqrt{2}$ - perfectly well, so I'm not sure what your argument is supposed to be

Balarka Sen

16:19

What does "calculate the value" mean? You can write $\sqrt{2}$ as an infinite sum. Isn't that calculating the value?

You can write it as a continued fraction. That's a value to me.

Slereah

"Killing spectroscopy of closed timelike curves"

Damn it

Yashas

the infinite sum is a formula

Slereah

There was already a paper on the topic of the existence of CTCs based on their Killing vectors

Yashas

if you start calculating, you would be adding each sum

Balarka Sen

Define a value for me, man

Yashas

16:20

you would need infinite computational power to find the sum

Balarka Sen

It ain't a mathematical term you're using

Yashas

you could store the number as sqrt(2) but if the simulator has to allow us to measure sqrt(2) then it must first calculate the value of it

the hypotenuse of the right triangle can be measured

the length is sqrt(2)

Balarka Sen

I am asking what the hell "value" means

Yashas

value = 3.14....

up to infinite decimal places

Balarka Sen

That's a decimal expansion. That's an infinite sum.

$\sum a_n 10^{-n}$

Yashas

16:23

but it would need to compute the decimal expansion to show it in reality

Balarka Sen

What does computing a decimal expansion mean?

A decimal expansion is a decimal expansion is a decimal expansion

Koolman

@Yashas good night

lol

Yashas

@BalarkaSen you need to get 3.14... from the infintie sum

get the decimal expansion from the infinite sum

Balarka Sen

3.14.. is an infinite sum

3 + 1 x 10^(-1) + 4 x 10^(-2) + ...

ACuriousMind

I have no idea what this conversation is about :P

2

Yashas

16:25

tell me how would you calculate the circumference of a circle if the radius was given to you using a computer

Balarka Sen

@ACuriousMind i am doing a highly mathematical troll

Yashas

you would need a datatype to store the decimal expansion of pi

infinitly_huge_float pi = 3.14.....

@BalarkaSen I already guessed that you were logic/semantics/etc trolling

Balarka Sen

I still have no idea what you mean though, trolls apart. But that's fine I guess!

gotta run

Yashas

5 upvotes + 1 accept = 65?

I don't know if my brain is trolling itself or if ...

AccidentalFourierTransform

40+15

4 uv, 1 accept=5 events

Yashas

16:34

there are 6 items with the grey colour

ACuriousMind

So what? The +55 says it counts 5 events - 4 upvotes and an accept.

AccidentalFourierTransform

delete the post and undelete it

that should fix it

ACuriousMind

Don't try to understand the way events in the rep tab are grouped :P

Yashas

it fixed itself

I did nothing

Stackexchange is trolling me :(

paracetamol

@Acurious Mind a question?

hyperphysics.phy-astr.gsu.edu/hbase/spin.html

^ What does "g" mean in the relation for spin magnetic moment given there?

AccidentalFourierTransform

16:42

G-factor (physics)

A g-factor (also called g value or dimensionless magnetic moment) is a dimensionless quantity that characterizes the magnetic moment and gyromagnetic ratio of an atom, a particle or nucleus. It is essentially a proportionality constant that relates the observed magnetic moment μ of a particle to its angular momentum quantum number and a unit of magnetic moment, usually the Bohr magneton or nuclear magneton. == Definition == === Dirac particle === The spin magnetic moment of a charged, spin-1/2 particle that does not possess any internal structure (a Dirac particle) is given by ...

paracetamol

^ Thanks @Accidental! ^_^

AccidentalFourierTransform

👍

paracetamol

@AccidentalFourierTransform I can't see it ._.

AccidentalFourierTransform

emojipedia.org/thumbs-up-sign

paracetamol

^ I wasn't aware of that, thank you again :3

AccidentalFourierTransform

16:48

lol

paracetamol

55

Q: Is it possible to draw this figure using Mathematica?

The figure is See the how-to video or a speeded-up GIF. I believe it should be possible to draw this figure programmatically using some Random function, but I'm rather new to Mathematica, so I could really use some help here.

graphics generative-art

Sir Cumference

Anyone want to hear a joke?

paracetamol

^ Depends on the joke...

AccidentalFourierTransform

hey! Ive seen that post before somewhere

paracetamol

But go ahead! :)

@AccidentalFourierTransform Sure you have ;)

AccidentalFourierTransform

16:50

chat.stackexchange.com/…

4

Sir Cumference

@paracetamol Have you heard of updog first?

@AccidentalFourierTransform LMAO

paracetamol

No...sorry

AccidentalFourierTransform

whats updog first?

Sir Cumference

@AccidentalFourierTransform Godammit...

@paracetamol You really don't know updog?

C'mon man, everyone knows updog

AccidentalFourierTransform

whats updog?

paracetamol

16:51

Nope ._.

Sir Cumference

@AccidentalFourierTransform NOTHING MUCH, YOU?

ACuriousMind

I only know downgoat:

2

Downgoat, The Glorious California Bay Area

101 3

paracetamol

@AccidentalFourierTransform Hilarious :D

Sir Cumference

Ok, but updog is kind of like a henway, right?

...someone pls

paracetamol

^ You're asking me? ;)

Sir Cumference

16:53

Sure

paracetamol

Nope ._.

Sir Cumference

Entertain my stupid joke please

paracetamol

^ I wouldn't know...sorry

@SirCumference By all means, proceed with thy joke :3

Yashas

They are just quadrilaterals, not rectangles. :) (A rectangle is a parallelogram with a right angle.) — J. M. ♦ Apr 1 '16 at 13:43

lol @AccidentalFourierTransform

Sir Cumference

@paracetamol Well, you really don't know what a henway is?

paracetamol

16:54

@SirCumference I know what a henway is, I just don't know if your "updog" joke's a henway ._.

AccidentalFourierTransform

:D

Sir Cumference

@paracetamol Goddammit just ask what a henway is

paracetamol

^ That a part of the joke?

Sir Cumference

Yes

paracetamol

Okay...

Takes a deep breath

Exhales

Yashas

16:55

:D

Sir Cumference

...

paracetamol

@Sir What's a "henway"?

Yashas

:D :D

Sir Cumference

@paracetamol I dunno, 2 or 3 pounds

paracetamol

...

Sir Cumference

16:56

:D

AccidentalFourierTransform

paracetamol

Tickles @Pies

Sir Cumference

@paracetamol My name is SC :P

paracetamol

^ "Pies" it is then :3

user228700

@SirC: Do tell when u finish the book :-)

0celouvsky

16:58

@ACuriousMind I've only had three crashes so far. Seems like normal Skyrim stability

Sir Cumference

@Kaumudi.H Yup

paracetamol

@AccidentalFourierTransform Which reminds me... when's the last time anyone here saw a Jim Carrey movie?

AccidentalFourierTransform

about three updogs and a month

3

Yashas

13 stars in last 10 minutes

AccidentalFourierTransform

oh cmon

we need some cleaning of the starboard

we should program a bot to do that

paracetamol

17:02

@AccidentalFourierTransform That, or we could all star really offensive messages and let ACM see it :3

Yashas

lol

AccidentalFourierTransform

any room owner around?

ACuriousMind

Yes.

user228700

Oh, not this again!

AccidentalFourierTransform

do your magic

Sir Cumference

17:04

Ugh

Yashas

r.i.p stars

user228700

So. Nice.

ACuriousMind

@AccidentalFourierTransform Abracadabra.

paracetamol

Ah, a minute's ban...how moving :3

user228700

Yo, @ACu: Why u unstar beautiful Jim Carrey gif? ._.

ACuriousMind

17:05

@paracetamol I have no qualms about removing you from chat for longer if you insist on being offensive.

@Kaumudi.H Fat fingers, the UI to remove stars is not exactly user friendly :P

paracetamol

@ACuriousMind Let's just keep it at a minute, shall we?

Yashas

I found a bug with the star system!

user228700

:-|

paracetamol

0;)

Yashas

It is too late to undo this operation
click here to remove the notification bar

I can't star Jim's pic

ACuriousMind

17:08

@Yashas I think the star system may be one of the buggiest pieces of SE to begin with :P

paracetamol

Hey ~~@SirC~~ @Pies! Wanna hear a joke? :D

Yashas

That bug helped me to guess the code SE is using :P

ACuriousMind

There was that time where the origin of stars was accessible through the API and people wrote bots that loudly announced who starred what

Yashas

:|

ACuriousMind

@Yashas I'm not sure what you mean by that

vzn

17:14

@ACuriousMind le Pen! huffingtonpost.com/entry/…

Yashas

Trump in America; UK in political crisis; Erdogan in Turkey; now le Pen in France

ACuriousMind

@vzn If you read a bit upstream, that was precisely the context :P

paracetamol

@ACurious ಠ_ಠ

@Yashas Mmm?

vzn

@ACuriousMind Trump/ Le Pen seem to have some connections & ofc similar ideology ("far right") although with Trump its a total moving target...

Yashas

@paracetamol rip

paracetamol

17:18

@Yashas You missed Petry ._.

Winks at ACM

Yashas

She isn't having a big role, does she?

leader of some German political party, that's it?

ACuriousMind

@vzn What are you telling me that for, Slereah was the one who said "she's no Trump". I carefully avoided discussing specific politicians.

vzn

in other words, Le Pen is indeed a Trump-like politician running in france!

(didnt see slereahs quote re the opposite thx for pointing it out)

totally wild/ contradictory signals on Trump-Le Pen connection lately politico.com/story/2017/04/21/… washingtonpost.com/news/the-fix/wp/2017/04/21/… politico.com/story/2017/04/23/…

rob

→ 5 messages moved to Physics Meta

ACuriousMind

→ 2 messages moved to Physics Meta

Secret

17:42

Woa woa woa, what on earth has been going on here during the time of my absence

Slereah

Oh man

Another portugese paper

Tempa vojago kaj geodezioj en generala relativeco

paracetamol

@Secret A fist-fight escalated to a gun-fun and then to an arms race of sorts >_<

paracetamol

17:56

@Slereah You sure that's Portuguese? O_o

Slereah

I'm no geese

dropbox.com/s/dxb42qufdr4pmhw/biblio.html?dl=0

Enough bibliography for today

paracetamol

^ Agreed

Balarka Sen

it seems i'm beyond bored with classical, linear fictions.

paracetamol

@Slereah I can't seem to view it :/

Balarka Sen

time to either read real weird shit or karl marx

paracetamol

18:04

@BalarkaSen They're different?

HsMjstyMstdn

^

Balarka Sen

one's weird shit, the other's tough shit

big dif

paracetamol

@BalarkaSen But they're "excrement" nonetheless ;)

HsMjstyMstdn

hahaha

Cows

18:18

@ACuriousMind listen. . . . . I'm writing, an aswer to my question. You can comment on it when I put it up.

Anyone else can comment

too

paracetamol

I...see ._.

Cows

@Fawad hehe legend status is a miles a way :P

Slereah

18:48

Can it be made illegal to spell spacetime as "space-time"

Transcript for