The h Bar

By amount of substance you mean a mole?

user228700

Yep.

11:20 AM

Well one atom of a substance is obviously fundamental because it's an indivisble unit.

And n atoms of ... is just an extension to more than one atom. The value of n in this case happens to be Avagadro's number.

user228700

:S I don't understand that but it's okay. I think I should move on.

@Kaumudi.H Well one atom is a fundamental unit. Wouldn't you agree with that?

user228700

How is "one atom" a unit?

It's a unit of stuff. You need some units to measure how much stuff you've got, and you can't get much more fundamental than the number of atoms as a measure.

@JohnRennie I think K is asking about SI units

11:25 AM

@AccidentalFourierTransform Patience Grasshopper

Q: Why is the mole/"amount of substance" a dimensional quantity?

lol ok

user228700

@JohnRennie :-| I guess you're right.

user228700

Also, I just read this:

user228700

33

According to the BIPM and Wikipedia, "amount of substance" (as measured in moles) is one of the base quantities in our system of weights and measures. Why? I get why the mole is useful as a unit. In fact, my question isn't really about the mole at all; I just mention it because what little infor...

And ... ?

user228700

11:28 AM

I think it makes sense. I guess I just wasn't thinking right.

Everyone wonders about moles when they first learn about them. It does seem an odd unit.

But they turn out to be very useful :-)

user228700

It's been awhile since I first encountered Mr. mole but I wasn't able to make sense of why it's included as one of the fundamental quantities. I think I understand now.

> I think I understand now

Famous last words :-)

user228700

:-P

user228700

Ah, the resounding bell has just freed me from my work session and I can tell u about famous last words now! Are u an expert in this field?

11:33 AM

@Kaumudi.H No ...

user228700

> "Henry Gibson, born James Bateman, was an American actor, singer, and songwriter"

user228700

When his nurse said "You seem to be feeling much better today", he said "On the contrary" and then he died.

user228700

I see that was a poor attempt to bring some cheer :-|

They couldn't hit an elephant at this distance

user228700

That's... strange.

user228700

11:41 AM

Pancho Villa's last words were "Don't let it end like this, tell them I said something!"

"God is dead" - Friedrich Nietzsche, 1882
"Nietzsche is dead" - God, 1900

3

user228700

LOL x'D

user228700

Here, this man is my source:

user228700

Famous Last Words

►

user228700

And now I shall go back to my books :-)

11:43 AM

You do wonder about these famous last words. Some of them seem suspiciously apposite.

user228700

Yeah, no kidding.

I plan to die quietly in my sleep, not screaming in terror like the people in the bus I'm driving.

3

user228700

@JohnRennie Man, you must really love them buses--do you really dream about driving around buses?

Some people achieve immortality through their works.
I plan to achieve immortality by not dying.

user228700

11:46 AM

(Sorry. Wiping keyboard :-P)

@JohnRennie, you seem like old wolverine in your pic

IDK if I have typed the correct spelling

I think it is 50 years e old pic :D

And Wolverine is not gonna die

What I thought he is 90 or maybe more

@Kaumudi.H it's an old joke. As I first heard the joke it was something like "I plan to die quietly in my sleep like my father the airline pilot. Not screaming in terror like his passengers."

Because to have such knowledge, you have to be old

user228700

11:48 AM

@JohnRennie Ah, that makes a lot more sense :-)

I thought I couldn't really claim to be able to fly a plane.

@THELONEWOLF. but here is my hero google.co.in/url?sa=t&source=web&rct=j&url=https://… (child prodigy)

@THELONEWOLF. Yes,Hugh Jackman looks a bit like me :-)

user228700

@JohnRennie And u were correct to think that :-P

@Kaumudi.H I can fly a glider! Well, I got a gliding licence when I was in the RAF cadets at school. I haven't actually flown a glider for 38 years.

11:50 AM

Yeah @JohnRennie since you are older than Hugh so it make sense that he looks like you

Well, @JohnRennie, Despite of having a great physics background and knowledge, You like terry tao

I thought you would say someone like einstein or Maxwell

But leave terry for someone like me who does not need anything but a bit of mathematics

Terry Tao seems an all round nice guy. He goes to lots of trouble to explain maths on his blog.

Mathematicians will definitely say Euler :D

I would say Ramanujan

Not you @Ramanujan, the real one

@THELONEWOLF. why not Terre Tao ?

@THELONEWOLF. lol

Cuz I know the past thiing more than the present things which are going in maths

@Ramanujan, and also I m not a mathematician

:) :) :)

I just like doing maths

12:12 PM

Hey I just got a new hat :D

this is fun

Hey guys, have anyone of you got suspended for editing 25 questions in 20 minutes??

I have been banned for the same reason just now.

huh, that doesnt make much sense

Balarka Sen

@JohnRennie He's a neat fellow.

@THELONEWOLF. were the edits bad?

Balarka Sen

I can never wrap my head round the fact that he's actually a harmonic analyst slash PDE-theorist who does number theory, is an expert on combinatorics, but simultaneously knows how the Grothendieck-style abstract algebraic geometry works at the same time.

12:20 PM

No, they were like replacing dots by question mark, but they still make sense under those circumstances

@AccidentalFourierTransform

do you get banned for editing the questions?

@THELONEWOLF. welp, I dont know what to say

here in physics.SE I don't think anyone has ever been banned for that reason

but then again, I don't think anyone has ever edited 25 in 20 minutes :P

yes maybe, they say you have done so many edits that do not make a lot of sense.@AlanWatch

you should ask in the math.SE chat

Okay, I thought they have banned me from chatting too, but they haven't @AccidentalFourierTransform

12:24 PM

ban must be imposed by a moderator..it doesn't sound automated

yes mods banned me

for example, this is my one of edits math.stackexchange.com/posts/1124570/revisions

I think this was the badest

how long does the ban continue?

3 days

from the site?

A: Ice melting in a gravity-free room?

@THELONEWOLF. that doesn't seem to be a good edit

I would probably tell off a user that does that here

so yes, banning might seem excessive but your behaviour was not ideal either

user223506

12:29 PM

was I an idiot in answering this:

user223506

2

Just to add some experimental information that confirms your thought process from NASA SkyLab's Classroom in Space, where a similar quantity of ice was melted on SkyLab compared to Ground Control - as per the diagrams below: with the explanation: As water formed, it collected on the ice cy...

user228700

Does anybody have a better answer to this than the most upvoted one:

user228700

6

Q: Why do constants have dimensions?

I am just a beginner in dimensional analysis, and I see that $G$, the universal gravitational constant, is independent of everything. Speed, for example, depends on distance and time, but $G$ does not depend upon anything. Then why is $G$'s dimensions not $M^0 L^0 T ^0$, as it is not dependent ...

newtonian-gravity dimensional-analysis

@THELONEWOLF. maybe you should apologise in the chat and moderators might lift the ban

@Kaumudi.H I have a good answer

user228700

12:32 PM

Shoot.

ok let's consider a simpler constant as an example

the speed of light is always constant

user228700

Right.

user223506

i guess so...

despite it being constant, it is however a measure of the distance light travels divided by the time it takes light to travel that distance

user228700

Uh huh...

12:33 PM

thus it is measured in distance units divied by time units

or for example m/s

user228700

Right.

therefore, just because a quantity is "constant" doesn't mean it isn't a measure of something

and thus just because a quantity is "constant" doesn't mean it is dimensionless

user223506

apologies

user228700

@Kenshin But what are constants like $G$ a measure of?

user228700

@Doc What? To whom are u apologising?

12:34 PM

@Kaumudi.H a constant need not be a measure of anything.

user223506

@Kaumudi.H for interryupting with my question

user228700

Sure, but then @Ken's explanation doesn't account for why they have units then.

@Kaumudi.H G is a measure of the relationship between the gravitational force, and the masses of the respective objects producing that force (for a given distance between them)

user228700

I'm not buying it :-|

thus G is a measure and thus has units

it's the truth

user228700

12:36 PM

@Doc Oh, what? No problem!

user228700

@Kenshin :-/

think about the equation F = Gm1m2/r^2

@Kaumudi.H if I study some experimental phenomenom and write an empirical law $A(x)=kx^2$ for some magnitude $A$ that depends on some variable $x$

Sir Cumference

Question — just to clarify

isn't it obvious that G is a measure of how force varies with amss?

Sir Cumference

12:36 PM

The FLRW metric doesn't take into account dark energy, right?

it is to me anyway

then, depending on the dimensions of $A$ and $x$, the experimental parameter $k$ will have dimensions or not

user223506

@Kaumudi.H i was wondering if I was an idiot to answer physics.stackexchange.com/a/302645/140434

G = Fr^2/(m1m2)

if we choose units so that r^2 = 1, then

G = F/(m1m2)

user228700

Oh no, too many people, all at once! ::Panic!::

12:38 PM

So we can see G is just a measure of force divided by the product of the masses producing it

simplez

it just so happens this measure is constant as far as we are aware

(and invoking general relativity this law of gravitation is only an approximation)

G is no different to c

surely you don't think c is dimensionless?

and G, like c, is just another quantity that happesn to be constant

user228700

I'm still not buying it :-/ I understand that according to the equation, the "constant" will have units but I still don't get why, outside of the equation (And I don't think it's fair to compare $G$ to $c$). Hmm, maybe I should start a bounty on that question. Then again, I don't have much rep. to begin with :-{

user223506

i worry that an answer i wrote's question gets put on hold --> closed --> deleted --> loss of rep = waste of time

@Kaumudi.H G isn't a "constant" in the mathematical sense, it is "constant" in the physical sense that it is unchanging

@Kaumudi.H do you think all "unchanging" quantities should have no dimensions?

@Doc If the question is closed but it already has an answer it wont get deleted

@Doc the question amounted to calculating the radius of a sphere with a volume of 1 cubic cm, which seemed a blatant homework question to me. However I found your answer interesting as I didn't know the experiment had actually been done.

12:41 PM

you wont lose the reputation you got there, dont worry

@Kaumudi, e.g. If the mass of an electron never changes, should the electron have no dimensions?

user223506

@AccidentalFourierTransform really?

the fact the electrons mass is constant has no bearing on weather an electron's mass has dimennsions or not (it always does, dimensions of mass e.g kg)

user223506

@JohnRennie thank you!

user228700

@Kenshin Right. But if u can explain what $G$ even represents, I'll get the hang of it. U're using analogies in which the quantity itself has some physical significance.

12:42 PM

@Doc yep. Well, if the answer gets many downvotes it might get deleted, but in this case it wont

user223506

ahh okay!

@Kaumudi.H I'm only using analogies but earlier I did iuse the direct case

G has physical significance

it is the measure of how much force is produced per the product of the masses producing it

(for a given distance between the masses)

user223506

@JohnRennie I remember learning about that experiment when I was 5

user228700

I don't understand how that counts as being a "physical significance".

it just so happens that this measure is the same for all gravitational interactions

@Kaumudi.H well let's pretend for a moment that G isn't constant

12:43 PM

@Doc we tend to be a bit paranoid about homework questions because we get so many students taking the piss. However in this case the question was only borderline homework, and your answer was interesting.

user228700

Okay.

and let's say some elements, element A, have G1

and other elements, element B has G2

and the interaction between A and B has a G3 = 0

that is A and B don't interact

Now G1 and G2 do have physical significance. Because if G1 is greater than G2, then elements A attrract each other more than elements B attract each other

now it just so happens in our universe, G is constant for all elements

user223506

@JohnRennie i wonder if ice cream would melt the same way?

user228700

U mean for two A's it's $G_1$ and two Bs $G_2$? (Just to clarify)

that doesn't mean it doesn't have physical significance

@Kaumudi.H correct

user228700

12:45 PM

@Kenshin Dude, what is this physical significance?!

@Kaumudi.H the significance is, is that A elements attract each other more

and B elements attract each other less

if G1>G2

thus the value of G for these elements has phsyical meaning

user228700

I don't understand how "measure of how much force is produced per the product of the masses producing it" is a "physical significance".

the value of G thus has dimensions,

user228700

@Kenshin Ohh.

@Kaumudi.H hmmm, ytou agree physical significance means effects a physical behaviour?

@KA.

user228700

12:46 PM

No no, I get it now.

Swapnil Das

hi.

user228700

Alright, @Ken: Thanks thanks :-)

yay np

user228700

Also, @Sir: "Howdy" (:-P) I can see the "disable desktop notification" so long as I don't click on "Show 5 more" and that's good enough. Thanks for all the effort! :-D

Sir Cumference

1:07 PM

@Kaumudi.H Np :)

I'm still gonna try and fix it when I get the time, mostly because it's a pet peeve at this point

Slereah

1:39 PM

smbc-comics.com/comic/hiring-metrics

2

does that mean that I will never be a good physicist?

Slereah

You will be the best physicist

A: Lagrangian for a free Dirac field equal zero?

@ACuriousMind u busy?

can you please delete the (unrelated) comments here

1

Yes: the on-shell Lagrangian is zero. In the canonical formulation of quantum mechanics, the only role of the Lagrangian is to allow us to derive the equations of motion. But you cannot use the equations of motion before deriving them, of course. Once you know the EoM, you don't need the Lagrang...

can't u delete ur own comments

@AccidentalFourierTransform Just flag them as obsolete (or whatever fits), I'll get to it

1:53 PM

yes

@ACuriousMind ok. I thought that flagging them would alert all the moderators

I saw you here so I thought I could sidestep that

you know,

Dec 16 '16 at 12:18, by AccidentalFourierTransform

apologies to all moderators for wasting their time

@AccidentalFourierTransform Well, yes, it will, but it's not really an "alert" in the sense that it would be bothersome. Never refrain from flagging just because you think you'll "bother" the moderators unnecessarily

ok, I take note of that

btw, out of curiosity, how many daily flags are there on average here?

dozens? hundreds?

2:11 PM

@AccidentalFourierTransform It varies, I'd guess there are between 10 and 30 flags a day. It's a bit difficult to count because the VLQ and NAA flags go both to the normal review queue and the mod queue.

doesn't seem too many

in Ye Olde Hat Shoppe, Dec 31 '16 at 16:40, by Bhargav Rao

There's been 1000 flags today, And it's a "silent day".

lol

Q: The origin of Renormalization Group

Yeah, SO is several orders of magnitude worse

Qmechanic

2:51 PM

0

Polyakov remembers the development of Renormalization Group and Conformal Bootstrap as "With the use of the ingenious technique, developed by Gribov and Migdal [1] in the problem of reggeons, I found connections between phenomenological theory and “bootstrap” equations (Polyakov [2]). Sasha Mi...

quantum-field-theory renormalization conformal-field-theory history critical-phenomena

On-topic? The boldface question (v4) seems to be about persons rather than physics.

3:15 PM

@Qmechanic I would suggest to migrate the question to hsm.SE

Abdelmalek Abdesselam

@AccidentalFourierTransform is an intervention by the though police really needed here?

@AbdelmalekAbdesselam I dont understand why you see migration as something negative

its a good question and I'd love to read a thorough answer

and there is a site where people's expertise is to answer this kind of questions. Most people here can't and won't

Down-votes on questions are stupid.

I essentially never use them. I think that if a question isn't good, it needs an edit or a close vote.

Abdelmalek Abdesselam

@AccidentalFourierTransform so you think my answer is not thorough? The 1964 vs 1969 info I gave I think helps understand the question by the OP. I think this question is more of interest to theoretical physicists than historians of science because the OPE is quite technical. But if you still insist on migrating that's fine with me.

3:30 PM

@AbdelmalekAbdesselam to be honest I didn't read the answer (and I didnt even realise it was by you), because it thought it would get migrated rather fast

Secret

in Zero term algebra, 11 mins ago, by Secret

Theorem $\Omega_1$: Division by zero no-go theorem (Associativity): Finite associative division by zero is not interesting

@AbdelmalekAbdesselam to be honest I didn't read the answer (and I didnt even realise it was by you), because it thought it would get migrated rather fast

Secret

MAJOR RESULT!

@DanielSank Why? Contracy to the popular saying, there is such a thing as a stupid question, and we also get some questions, that, while not actually off-topic or otherwise closeable, can be answered with a trivial amount of research (typing the question into a search engine). These questions where OP evidently did no research and where the answers will jsut reproduce what's already written in dozens of other accessible places deserve to be downvoted.

@ACuriousMind Agreed. For example "What is Newton's second law", right?

> These questions where OP evidently did no research and where the answers will jsut reproduce what's already written in dozens of other accessible places deserve to be downvoted.

Aha. Is the information being available elsewhere enough to require a down vote, IYHO?

3:34 PM

jsut

@DanielSank It depends on its availability. If it's hidden in some obscure journal article (or even simply not on the first page of search results when typing in the keywords in the question), then there is value to that question being answered in a more easily found place like this site.

@DanielSank You see I really have to tell you

That it all gets so intense
From my experience
It just doesn't seem to make sense
Still... You turn me on

However, if the answer is already contained in e.g. the Wikipedia article on the subject, then I think the question deserves a downvote.

@AccidentalFourierTransform What?

@ACuriousMind Interesting. I disagree.

@DanielSank nvm im drunk

3:38 PM

@AccidentalFourierTransform k

Believe it or not, that's actually the first remotely sexual advance of which I've ever been the target on the internet.

@AccidentalFourierTransform the fraction of questions I have actually encountered which could be described as asking for easy-to-find information and aren't off-topic is very, very low.

@DanielSank On another note, closed unanswered questions will not be deleted unless they are negatively scored. So keeping questions with little hope of improvement at a negative score also has a janitorial aspect.

I was singing out loud

I have a great voice and I wanted to share it with you

Off-topic covers so much through the "too broad", "homework", and "unclear" close reasons.

@ACuriousMind That's interesting. Can't you guys just delete them though? Perhaps that's not enouraged.

@AccidentalFourierTransform Thank you.

man my internet connection sucks today

sigh

You're in Barcelona, right?

3:42 PM

im at my parents, in Madrid

for the holidays

cool

@DanielSank Yes, we can, but I think the idea is that an upvoted-but-closed question is assumed to have potential for improvement/reopening, and thus shouldn't be deleted.

@ACuriousMind maybe you have noticed but I've been downvoting regularly lately =P

I dont like it very much ^

what can I do to make it look better?

are the data points too thick maybe?

@AccidentalFourierTransform I can't (and wouldn't) track individual user's voting behaviour.

@ACuriousMind I mean, we discussed this here in the chat some time ago

you (and others) tried to convince me that downvoting was a good thing

3:49 PM

I think down-voting has a place in principle, and that the occurrence of that place is so low that down-voting has little to no use in practice.

::shrugs::

Apr 23 '16 at 13:47, by AccidentalFourierTransform

@Danu I dont know. If I think a question is off-topic, I vote to close it. If I see an answer that I dont like, I tend to think that I might be wrong and I prefer to comment

Apr 23 '16 at 14:50, by ACuriousMind

@AccidentalFourierTransform While it's of course your decision to not cast downvotes, I still stand by what I wrote in this meta answer. There are not enough downvotes cast to counteract the upvotes that even rather bad content gets.

@heather Physics question.

^ Actually the worst title in the history of the site.

We can all go home now.

@DanielSank let's downvote the heck out of that question ;-)

damn

7,890 results o.O

4:07 PM

@AccidentalFourierTransform Only 109 if you do the right query ;)

well look at me hurr durr the expert querent

4:34 PM

@DanielSank Emerson, Lake and Palmer. I doubt it was an expression of true love :-)

Im sorry, but to be completely honest, this is a shit site if you cant at least give me the formulas to go off of... — Justus Anton 14 mins ago

@AccidentalFourierTransform are you an ELP fan, or was that just a random song selection?

@AccidentalFourierTransform Heh, well... everyone's entitled to an opinion.

@JohnRennie Didn't say anything about true love. I said "remotely sexual advance".

@JohnRennie big fan of prog rock in general

@AccidentalFourierTransform Good man, we're a dying breed!

4:59 PM

@JohnRennie well I'm young and life is long and there is time to kill today ;-)

hanging on in quiet desperation is the English way

Living, if you claim that all
That entails is breathing, eating, defecating,
Screwing, drinking,
Spewing, sleeping, sinking ever down and down
And ultimately passing away time
Which no longer has any meaning

I see your gloomy pretentious lyrics and raise you :-)

wow, youre the first person that I know that likes VDGG :D

this is great, you made me happy lol

I have to be honest and admit I don't like all their albums. Some of them go on a bit. I do like Still Life and H to He though.

In fact I might just cue up Still Life ...

Sometimes you feel so far away
Distanced from all the action in the play

World Record is also very nice IMO

Pawn Hearts is the one that everybody seems to cite as a classic, but it kind of drags for me.

5:11 PM

I very recently discovered Renaissance

@JohnRennie do you know them?

I really liked "Song of Scheherazade"

They are at the soft core end of prog, along with Camel and erm lots of others I can't think of at the moment. I'm more at the VdGG, King Crimson end of the spectrum.

Camel kicks ass =P

but yeah, KC, Pink Floyd, Yes...

that is as good as it gets in this genre

There is lots of good modern prog around. It just doesn't get much publicity.

Porcupine Tree, The Pineapple Thief, anything involving Steven Wilson.

I had heard of them, but I haven't listened to them yet

let me see

BTW, do you know Tool? They are not precisely modern, but they are awesome :D