The h Bar

ACuriousMind

10:02

@Slereah What is a "long-range neutrino force" supposed to be?

Also, why are there so many crappy questions on the site this Sunday? :(

Slereah

@ACuriousMind You may recall that in the 60's, it was proposed that the weak force was mediated by neutrino exchange

ACuriousMind

Yes, I remember that through the genetic memory passed down to me by my parents :P

But yeah, I recall hearing once that neutrinos were speculated to be force carriers in some models

Yashas

What happens if I try to add a comment from the review queue to a VLQ post when there is already an exact same comment given by someone else?

Slereah

So it turns out, no, even in that model, black holes don't carry a weak charge

Yashas

0

Q: Time- the stubborn illusion?

BACKGROUND: As I was happily watching "Genius" tele-drama's teaser http://channel.nationalgeographic.com/genius/videos/time-is-but-a-stubborn-illusion/ , I came across this very popular and subtle comment "The past,present and the future all exist simultaneously. Time is nothing but a stubborn i...

Slereah

10:10

the real question, though, is

Do black holes carry a color charge

I'm not sure anyone bothered to check since classical chromodynamics is pretty much meaningless

Though maybe someone checked for generic Yang Mill fields

ACuriousMind

@Slereah How could they, given the universe is in the confined phase?

The fact that you need infinite energy to separate a quark pair doesn't go away just because you wave your hands and shout "black holes are magic" ;)

Slereah

Well I don't mean for real

Gerold Broser

Good morning every ~~bloo~~ body!

Slereah

Just in some scenario where you consider classical chromodynamics and throw in some color charge in the black hole

Throw some paint or something

ACuriousMind

Who would consider classical chromodynamics? :P

Gerold Broser

10:19

Is a little rant allowed here? Just meant as compensation for not going to church this sunday.

And, BTW, GOOD MORNING EVERYBODY!

ACuriousMind

@GeroldBroser Depends on what you rant about, and whether you stay civil during that or not :P

And good morning

Slereah

@ACuriousMind I WOULD

Gerold Broser

@ACuriousMind I consider "civil" as a matter of POV, isnt' it?

The Bushes, Obama, etc., for instance, most probably thougt they were civil...despite of dropping bombs on innocent children's heads.

Slereah

@ACuriousMind so it turns out a lot of vector bundle related things about non-Hausdorff manifolds was hiding in some old French paper

Quite a lucky break

ACuriousMind

@GeroldBroser It is to some extent, but there are many things that are unquestionably rude and unquestionably not-rude. Don't tread the line if you don't have to

Slereah

10:23

Although it's mostly related to one-dimensional manifolds

He calls the line with two origins the lasso manifold

ACuriousMind

@Slereah So you're not the first Frenchman to embark on this anti-Hausdorffian quest? I'm...surprised ;P

Gerold Broser

@ACuriousMind Well, I don't even have much to say...physics.SE speaks for itself...if you look at my rep development...Do you see the red number, too, or are they just visible to the profile owner?

@ACuriousMind *number_s_

Slereah

@ACuriousMind So it turns out one of the fellow involved was mister Reeb himself

Of reeb foliation fame

ACuriousMind

@GeroldBroser If they go looking for it, they can see reputation you lose from being downvoted, yes. (Not reputation you lose from downvoting, though)

I think your answer is downvoted because it just states the numerical equality of $1/H_0$ and the age of the universe without supplying any physical reason for it

Slereah

good old Reeb

John Rennie

10:27

@GeroldBroser I see:

Gerold Broser

@ACuriousMind Nono, It's always just the number 2...or 4...or a multiple of it, generalized.

ACuriousMind

Turns out, there is a good physical argument for why these are related, see e.g. this question, but you don't make it in the answer and so it looks like numerology rather than physics.

Slereah

"International Journal of Mathematics and Mathematical Sciences
Volume 2009, Article ID 891785, 4 pages"

Did they publish 2009 journals

One for every year since the Roman Empire

ACuriousMind

lol

Gerold Broser

@JohnRennie Hi John, I hope one of the reds isn't from you, :)

Slereah

10:29

I do wonder what's the oldest academic journal

I think some of the philosophy related ones go back to the 18th century

Yashas

@GeroldBroser You cannot know who downvoted your question unless you try to screw with data.stackexchange.com

Slereah

"Philosophical Transactions of the Royal Society was established in 1665 by the Royal Society and is the oldest scientific journal in the English-speaking world."

Nice

Yashas

I actually tried to search for users who flagged chat comments and I failed...

I think normal users cannot check those.

John Rennie

@GeroldBroser I am asleep at 23:35 :-)

Gerold Broser

@Yashas I know, apart from being quick enough and checking for a suspect's -1...but even then it's just a guess, you're right. But that's not my point. I don't care who it was. I'm disappointed that it is.

John Rennie

10:32

Though I have to say that I agree with ACM that I don't think the question and answer make a great contribution to the site.

Yashas

@GeroldBroser Success is not final and failure is not fatal; everybody gets downvoted once in a while.

Gerold Broser

@JohnRennie That's great, John, but sorry, I came home at about 5 am yest...today. I don't get the point why you tell me...yet.

John Rennie

There are some excellent Q/As about the Hubble parameter that go into fine detail of exactly what is going on. Your Q/A looks like you're just saying hey look what I discovered, when a search of the site would have given you that info anyway.

Yashas

Even John Rennie has a downvoted answer :P

John Rennie

I have lots of downvoted answers. Sometimes the downvotes are justified :-)

Gerold Broser

10:35

@Yashas Sure, it's not too welcoming, however, for a new contributor, like me.

Yashas

I got my "Ask Question" privilege suspended several times on stackoverflow 5 years ago.

It isn't welcoming either.

It does not depend on the failure; it depends on how you tackle the failure.

Gerold Broser

And, I thought it's bad on SO sometimes...but...it's worse on SU (I got banned there for a day for the first time in my 20-year Internet life)...and, sorry having to say that, but that's my perception, it's worst at ph.SE

John Rennie

@GeroldBroser I understand that being downvoted isn't pleasant and I don't like it either. But you need to consider whether the downvotes are a message that you should take away and think about.

In a way it's a bit like submitting a paper to a journal. The downvotes are telling you your submission was rejected.

Gerold Broser

@JohnRennie I searched for "hubble frequency" and it didn't give me what I expected...can it be that some texts here are a bit...well...over-sophisticated?

John Rennie

The solution is to improve your paper not just get annoyed.

Slereah

10:40

Apparently Krasnikov's paper "Hyper-Fast Interstellar Travel in General Relativity" was supposed to be published in Physical Review D but was never published

John Rennie

A quantity that has units of $[T]^{-1}$ isn't necessarily a frequency, and the reciprocal of the Hubble time isn't a frequency. In the absence of any periodic behaviour it's meaningless to consider it a frequency.

Gerold Broser

@JohnRennie Well, the next step of my rant is...there are downvotes but people are too lazy, too coward, too arrogant, too...whatever...don't know...to leave a comment why the decided so and what can be done better...this doesn't help anybody, IMHO.

@JohnRennie I described the periodic behaviour in my (self-)answer.

John Rennie

I sometimes leave comments explaining why I downvoted and I sometimes don't. If I don't leave a comment that can be because I don't have the time, or it can be that I can't think of a good way to phrase the comment without giving offense.

Or of course it can be that I find the post contemptible. That does happen, though not often.

ACuriousMind

@GeroldBroser See, that's exactly why people don't leave comments with downvotes - they don't want to be called "cowards" or "arrogant" for doing so and then not spending the rest of their day arguing about that single downvote.

Gerold Broser

@Yashas "Even John Rennie has a downvoted answer :P" ... Is this is an argument like: Because people are stupid at one place it's OK that they are stupid at another, too?

Yashas

10:46

If downvoting a post is done only by stupid people, there would be no reason to have such a feature. Downvoting isn't really a dumb move.

ACuriousMind

I didn't vote in your case at all, but I usually leave a comment with my downvotes if I think the post can actually be improved to a point where I would reverse my vote, and if I think the author would actually be receptive to said comment.

Oh, there are certainly people who downvote for strange or "stupid" reasons. But the number of people who upvote for spurious reasons is far higher, in my opinion

If your post manages to score a net negative vote total, then it's likely there is actually something wrong with it

Gerold Broser

@ACuriousMind Touche! That's a good point. But you know the saying in German that goes like: The sound makes the music. I one tells me in a civilized, polite, helping and welcoming manner what could be done better, I'm glad to hear, but...you know.

@Yashas This was just an analogy.

ACuriousMind

@GeroldBroser Yeah, I get why it's frustrating.

Slereah

a lot of people will upvote just on the ground that the answer looks alright

even if they do not understand it

ACuriousMind

I do wish people wouldn't burn out on helpful commenting on "bad" posts - but many do, since more often than not, a helpful comment earns you little more than an insult from the author, and so they tend to just leave a terse comment and move on, or leave none at all

Gerold Broser

10:51

@Slereah "The question shows research effort; it is useful and clear" ...the semicolon implies a logical or for me, is it?

@Slereah Correspondingly the same applies for answers, doesn't it?

ACuriousMind

@GeroldBroser I've always read an and there. Maybe that's why I sometimes feel my quality standards are too high :P

I mean, why would I upvote something that shows research effort, but where I can't tell what it is actually trying to say? Why would I upvote a crystal clear, useful question that can be answered by typing it into Google? I think showing research effort and being clear about what one wants to know must both be done in order to ask a "good" question.

Gerold Broser

@ACuriousMind I'm more of the lenient kind, that's for sure. Perhaps that's a matter of origin. :P

Slereah

The least fun part of writing a physics thing

Compiling the documentation D:

Up to 40 documents out of about 3000

hopefully I won't need all 3000

Gerold Broser

@ACuriousMind a) Because it can evolve, it can be improved...by everyone who has the privilege or who takes the hurdle of Proposed Edit acception?
b) Because nobody can comment or put another answer in addition at google search?

@ACuriousMind But that's getting a bit off-topic...the real point is...

SBM

What is drift velocity

John Rennie

11:01

@SBM of electrons?

SBM

yes

Gerold Broser

I have the perception that ph.SE is a snakepit like so many out there in the Internet...that's a pity.
It seems to be some kind of (pseudo-)elite's, old man's country club with just an other topic, physics

Slereah

It's like this

Best Drift Cats!

►

except electrons

Gerold Broser

Yes, this is exaggerated and this is intentional.

John Rennie

@SBM how much do you already kniow about the topic? For example have you read the Wikipedia page?

Drift velocity

The drift velocity is the average velocity that a particle, such as an electron, attains in a material due to an electric field. It can also be referred to as axial drift velocity. In general, an electron will propagate randomly in a conductor at the Fermi velocity. An applied electric field will give this random motion a small net flow velocity in one direction. In a semiconductor, the two main carrier scattering mechanisms are ionized impurity scattering and lattice scattering. Because current is proportional to drift velocity, which in a resistive material is, in turn, proportional to th...

SBM

11:04

yes

John Rennie

Can you give us some idea what parts of that article aren't clear i.e. where you are struggling with it?

SBM

What is a carrier scattering mechanism?

Gerold Broser

afk 10

John Rennie

@SBM The carriers are the charged things that move when a current flows. In a metal the carriers are simply electrons, but in a semiconductor the carriers are electrons and holes.

Let's keep it simple by just considering electrons.

SBM

oh I guess maybe that explains why semi-conductors have different variations in resistance compared to metals or alloys

John Rennie

11:09

If an electron in a metal is not scattered then it moves without feeling any resistance and in that case the metal will be a superconductor. Indeed superconductors work by preventing electrons from being scattered.

SBM

But for superconductivity shouldn't the temperature be really low for a metal

John Rennie

In a metal electrons are generally scattered by interactions with the atoms that make up the metal. That's what the article means by lattice scattering.

Ionized impurity scattering probably applies more to semiconductors than metals. It happens when atoms of contaminants in the semiconductor scatter electrons that come near them. I think in metals lattice scattering dominates though i wouldn't swear to that.

I wrote some stuff on superconductivity here that you might find interesting

ACuriousMind

@GeroldBroser I'm sorry you feel that way. I think that of the many places on the internet where you can discuss physics, physics.SE is refreshingly free of pointless discussions and has an unusually high signal-to-noise ratio. This is precisely due to our quality standards. It is difficult for a layman to ask or answer something here unless they take their time to learn what we expect from contributions. Heck, sometimes it's even difficult for professionals!

John Rennie

Particularly since it concentrates on the scattering.

Slereah

If the layman wanted the answer that bad why didn't he read that untranslated soviet paper unavailable online that contains the solution

ACuriousMind

11:15

If you think it's elitist to refuse to compromise quality standards...then I guess physics.SE is elitist. Which is funny because there are some people for whom we are not elitist enough, some who'd see us become a homework help service, others who'd rather see us crash and burn...each detractor has a different opinion about what's wrong with physics.SE, yet we continue to run rather smoothly and successfully.

Slereah

Really I think you should have to submit a thesis to SE before being allowed to join

John Rennie

@Slereah Please give the sarcasm a rest

Slereah

oh yes, I'll do it right away!

John Rennie

This site works because off the good will of the people who contribute their time for free. I don't think being sarcastic is a good way to reward their efforts.

user228700

@JohnRennie because off?

John Rennie

11:21

Damn, and now it's past the two minute edit window :-) Where were you one minute and fifty nine seconds ago? :-)

user228700

:-/ Thought u'd notice. I'll remove the star, then...

John Rennie

@Kaumudi.H I'm not that fussed about minor typos as long as the meaning of the post isn't compromised. My OCD tendencies have decreased steadily with time and these days I tend to shrug instead of obsess :-)

Gerold Broser

@ACuriousMind What about https://physics.stackexchange.com/help/be-nice ?

"**Be welcoming, be patient, and assume good intentions.**" in **bold** and it continues with:

"Don't expect new users to know all the rules — they don't. And be patient while they learn." and:

"We're proud to be a large, user-driven space" ...it's just 'user' not 'elite-all-knowing-close-to-Nobel-prize-jack-of-all-trades user'.

John Rennie

@Gerold I'm not sure why you're pushing this point. ACM has made it clear that, by your definition, he does indeed take an elitist view of the site, and I agree with him. All you're doing is telling us repeatedly that you disagree. Well we've got that message.

Slereah

amazon.com/Einstein-Equations-Behavior-Gravitational-Fields/dp/…

Oh great

Another book to buy

Gerold Broser

11:25

@JohnRennie That from Slereah is perfectly fine for me...have you read the About Me in my profile already?

John Rennie

@SBM I have to head off now. Are you OK with the scattering stuff or was there more you wanted to ask?

user228700

@JohnRennie Ah, wokay :-)

Secret

I don't have the stare of death (unless I am extremely tranquilly fury, which of this entire world only 2 things can trigger it). However I do have the stare of search:

Sometimes when I have a certain category of people with certain clothing, outfit mannerims etc. to be searched for, and I started scanning the streets for said person, they will coincidently looked back into my direction as if my stare makes them uncomfortable and they have too look back to check what is going on, and by doing so, make their faces visible to me so I can tally the observations

John Rennie

@Kaumudi.H there's a lot to be said for shrugging. Though admittedly probably not when you're studying for university entrance exams.

SBM

Yes, understood it. Thank You @JohnRennie Are the more resources about electrostatics and current?

user228700

11:27

@JohnRennie :-P

Secret

The coincidence have happened 70 times for every 100 stare of search, thus even if there is no causation, it is still very useful

Gerold Broser

Bye

John Rennie

@SBM searching this site is a good resource, though the built in search isn't as good as it could be. I generally search using Google eg something like electron scattering site:physics.stackexchange.com

Secret

why I kinda confident there is no causation is because they don't always look back after the search is done, but the correlation is very strong, thus whatever

John Rennie

And now, lunch beckons. See you all later.

user228700

11:30

Bye!

SBM

bye!

Slereah

the election is upon us

AccidentalFourierTransform

Slereah

Eh, Le Pen isn't that bad

She's no Trump

SBM

loq

AccidentalFourierTransform

11:41

@Slereah ...

Slereah

I mean sure, racism and all

But economic-wise, she's fairly left wing

And at least she's a competent politician

AccidentalFourierTransform

SO WAS HITLER

Reductio ad Hitlerum

Reductio ad Hitlerum (pseudo-Latin for "reduction to Hitler"; sometimes argumentum ad Hitlerum, "argument to Hitler", ad Nazium, "to Nazism"), or playing the Nazi card, is an attempt to invalidate someone else's position on the basis that the same view was held by Adolf Hitler or the Nazi Party, for example: "Hitler was a vegetarian, X is a vegetarian, therefore X is a Nazi". A variation of this fallacy, reductio ad Stalinum, also known as "red-baiting", has also been used in political discourse. Coined by Leo Strauss in 1951, reductio ad Hitlerum borrows its name from the term used in logi...

ACuriousMind

Man, AFT, that was quicker than I could type "Godwin's law" :P

AccidentalFourierTransform

^.^

hmmm Im hungry

what should I have for lunch today?

Slereah

People are pretty spooked by far right politicians but they forget that plenty of far right politicians governed before and were not Hitler

AccidentalFourierTransform

11:44

hmm

Slereah

Hell most politicians if you go back far enough in time would be considered fairly far right

And yet most of them were not Hitler

AccidentalFourierTransform

I guess people are spooked by far anything politicians

ACuriousMind

@Slereah "not Hitler" is a fairly low bar to pass, though.

Slereah

Sure, but apparently not low enough for some people

They all have to be Hitler

ACuriousMind

As if you were a stranger to hyperbole ;)

Slereah

11:46

Only for the hyperbolic plane

SBM

what

ACuriousMind

I mean, I'll give you that comparing politicians to Hitler is in almost all cases a ridiculuous argument, but establishing that they're not Hitler doesn't do anything to show they're not still a really bad choice.

Slereah

Well yeah, but I'd argue

Less bad than Trump

AccidentalFourierTransform

Slereah

I always find it a bit weird when people say that restricting immigration is unamerican and all that

ACuriousMind

11:49

@AccidentalFourierTransform smbc-comics.com/?id=3556

Slereah

Considering that until the 60's, it was always US policy to have immigration quotas

ACuriousMind

@Slereah Unless Trump is running for office in France, still not an argument :P

Slereah

You never know!

Who knows when the US army starts invading your country

ACuriousMind

Is there a French equivalent for the name "Donald"?

AccidentalFourierTransform

lol

hadnt seen that one

Slereah

11:51

There isn't.

Donald is a very Scottish name

So it's just Donald in French

ACuriousMind

@AccidentalFourierTransform I linked it because the red button contains a graph with "Decahitlers" :P

(never forget to click the red button)

AccidentalFourierTransform

WAAT

what is this red button and how come I didnt know about it?!?!

Slereah

lol

ACuriousMind

:D :D :D

You'll have to read all SMBC you ever read again

AccidentalFourierTransform

sigh... it seems Ill spend by afternoon reading SMBC comics

ACuriousMind

11:53

In the lower right corner of the strip, to the right of the > >>, there's a red button. Click it.

The newer comics (~ mid 2016 I think) also have xkcd style mouseover text

AccidentalFourierTransform

I knew about the mouseover (bc of xkcd)

but the red button is new to me

Slereah

Also if you put on special glasses, there is a secret joke

Among my bibliography there's a paper in portuguese

Analise de geometrias com curvas fechadas no tempo

Causalidade e Proteção Cronologica

A beautiful language

Maxwell

Hello @yashas

Yashas

Hi

Slereah

From the Universidade de São Paulo

Maxwell

11:59

@yashas, Could you please tell me how can I find the average velocity?

Yashas

Average velocity = total displacement/total time

"Very small organisms called bacteria have damaged their sensory receptors and they are unable to feel pressure, temperature, and pain. As they walk, their brain does not get information on how to adjust; and so their feet are easily injured." — Answers in Genesis - Kid's answers

Slereah

Oh right, I still don't have a copy of Tipler's thesis

Bother

Yashas

r.i.p science

Maxwell

@yashas, then if a body travels from A to B and then again returns to A. What would be the average velocity? Is it 0?

Yashas

yes

Slereah

12:01

depends how you define it

Maxwell

How? @yashas

Yashas

@Maxwell total displacement = 0

average speed is not zero but average velocity is zero

displacement = final pos - initial pos

as the final pos = initial pos, the displacement is zero

Maxwell

@yashas, then what is the average speed?

Yashas

total *distance*/total time

distance = total length of the path travelled

displacement = shortest distance b/w two positions

Maxwell

In such case, average speed=(2v1v2)/(v1+v2) . Is it true? How?

@yashas

Yashas

12:04

@Maxwell That formula asks for average speed not average velocity, so it is correct.

To derive that formula, you have to go to the definition of average speed.

Average Speed = total distance/total time

A to B distance = d

B to A distance = d

total distance travelled = 2d

A to B velocity = v1

B to A velocity = v2

Time taken for the journey A to B = distance/speed = d/v1

Time taken for the journey from B to A = d/v2

total time taken = d/v1 + d/v2

Average speed = total distance/total time = (d + d)/(d/v1 + d/v2) = 2/(1/v1 + 1/v2)

= 2v1v2/(v1 + v2)

Slereah

"O¨ zgu¨ r Sarıog˘lu"

Turkish physicists are really testing the limits of my keyboard

Yashas

You can type those letters using ALT.

Slereah

well sure, if I knew the Unicode value of all letters ever

There are GR physicists of all nations and they are conspiring to make my life difficult

They all have weird names full of weird letters

0celouvsky

When is the election @Slereah ?

Slereah

Today!

well, the first round, anyway

Isn't that right, Jan Jełowicki, Øyvind Grøn, Özgür Sarıoğlu and Héctor Vargas Rodríguez

My keyboard only has so many letters

0celouvsky

12:19

What is that modified g supposed to be?

Slereah

It's a Turkish letter

soft g sort of letter

I don't look forward to typing the bibliography of that paper that has 20 authors

who's your professor who did that Gödel proof, btw?

0celouvsky

Et al, no?

Slereah

yeah, probably et al

0celouvsky

@Slereah Alexandre Freire

Mostafa

@Slereah Here we have presidential election in 27 days :/

Slereah

12:23

I'll put him in '"private communications"

heheheh

Who will u vote for

Mostafa

The current president

Second term

When his presidential term started, inflation was around 25%, and growth was negative.
Now inflation's around 5% and growth is around 3% I think.

Slereah

For a moment, I thought that someone actually wrote about both general relativity and non-standard analysis

But so it turns out it's two different people named Todorov

0celouvsky

12:40

I saw Robinson mentioned yesterday

Can't remember where

Slereah

in what context

Yashas

2

Q: Why are lower energy systems stable?

Apart form the practical evidence that the systems that exist in nature try to attain lowest energy possible and hence, maximum stability, and atoms forms bonds to attain low potential energy but do we have any reason why is that ? Why low energy systems are stable? What happens when a system lo...

thermodynamics energy stability

Is there an answer to that question?

or is it some empirical fact

AccidentalFourierTransform

eh, basically $\dot p=-V'(q)$

any system wants to minimise $V$

Slereah

It is due to the Hamiltonian equation

Yashas

I am not smart enough to understand either of you lol

AccidentalFourierTransform

12:54

ok, back to the basics: $Q_\mathrm{BRST}^2=0$, right?

Yashas

Was that a reply to my comment? @AccidentalFourierTransform

I guess not

AccidentalFourierTransform

yeah but I was messing with you :-P

recall that $F=ma$

write $F=-V'$

and $a=\dot p$

so $\dot p=-V'$

so if $V'\neq 0$, the system will change its momentum

Yashas

Ah, I understood that.

AccidentalFourierTransform

ie, a non-zero V' implies that the system will change its state of motion

and the negative sing

Yashas

One can also argue in terms of $dU = -F.dr$ relation but that probably doesn't directly answer for the case of atoms. At potential wells, the system is stable because if it deviates from the local minima, the force acts in a direction to bring it back (unless you help it by giving energy to to overcome the potential barrier). If the system was at a potential hill at equilibrium, a small force would drive the system towards a potential well. Hence, systems have a natural tendency to end up in potential wells rather than hills. — Yashas 14 mins ago

AccidentalFourierTransform

12:57

sign

makes it want to move in the direction of decreasing $V'$

so systems always evolve so as to make $V'\to 0$

Yashas

it can get stuck at a well too, right?

AccidentalFourierTransform

when $V'=0$, the potential has a minimum, so systems minimise energy

yeah, a well minimises energy

Secret

(No news dump today. Sciencedaily is down)

Yashas

why do we say that a system with lower potential energy is more stable? Something at a lower well is more stable than something at a higher potential well?

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