The h Bar - 2013-11-05 (page 1 of 4)

« first day (1097 days earlier) ← previous day next day → last day (3834 days later) »

12:56 AM

Ah, chat session coming up in 15 hours-ish!

Everyone in the US, don't forget that daylight savings time has ended so the chat session is now at 11 AM Eastern, 8 AM Pacific (but who wants to be awake at 8 AM ;-p)

1 hour later…

2:07 AM

@DavidZ So you consider Hawaii and Arizona not to be in the US? ;)

Anonymous

2:20 AM

@ColinMcFaul I don't care, but if you are, at least don't downvote the questions, so that they don;t' disappear, as they have a lot of times.

2:42 AM

@DIMension10 Dude, I haven't touched any of your answers, and I haven't touched any of the questions they're attached to. CHILL.

user image

Anonymous

@Sklivvz It is still misleading, as I've mentioned in a comment. It is a must to mention that the kappa is dimensionful.

3:23 AM

@ManishEarth @DavidZ Rather than having people try to reopen old, closed questions, would it make sense to lock them as historical like was recently done on meta? This question for example:

5

Q: List of Scattering Phenomena

While at lunch with my lab group we got into discussion of the different types of scattering phenomenon that we encounter in everyday life and physical experiments. We ended up listing about a dozen or so types of scattering that we see constantly, but I left unfulfilled. I want to compile a lis...

particle-physics classical-mechanics scattering

@tpg yes, done

@ManishEarth Thanks. That seems like a good enough compromise. "We used to allow it but don't anymore so don't use it as a model"

Fwiw when I get time (2-3 weeks), I plan on reanalyzing the current list policy to allow some types

Same as with the book policy

Works for me

Btw, those interested please volunteer for the book curation!

3:36 AM

How do we decide anything from that HW banning question?

There's upvoted answers on every possible side

@tpg I blame you

@ManishEarth I did my best to muddy the waters...

@dim It's pretty common for constants of proportionality to have dimension (sklivvz is talking about proportion, not equality). Nothing misleading if this isn't explicit.

We wait for more votes first, and then see

If no consensus, no consensus. I hope that doesn't happen though :/

We'll see I suppose

What's your own stance, O schizophrenic meta-user?

3:44 AM

I think the policy as presented isn't helping anybody. I think if we changed the "Yes you can ask but only..." to "No, you may not ask unless" might be clearer

But it's a tough one to enforce either way -- is a question "What's my next step in the derivation..." on topic when it deals with a string theory derivation but off-topic when it's about a newtonian mechanics derivation?

I would argue it's off-topic in both cases, but some may argue that the next step requires physical insight which is true for both cases most likely. It's just the newtonian one is more "obvious" to those who have done it before. But that's in the eye of the beholder

Usually not. However, ST qs can be made conceptual because usually such steps require insight

But is the insight any different than, say, remembering to include rotational kinetic energy when deriving equations of motion from Lagrange's equations?

I personally think that if we close all the hw by a semantically changed policy, and then handhold askers of tranformable questions, we may solve both problems

I mean, one is more advanced but to the person asking the question both seem hard

Hm. Remembering to do something is one thing, using insight is another

3:48 AM

@ManishEarth And also handhold the reviewers/other users to train them what to watch for

I guess

We may want to break the homework thing down to more precise questions, such as "Should we update the homework policy to say homework is not allowed?" and "Should we get rid of the homework tag?"

Meh, too early for the second one

If we get rid of it it can't be now

@DavidZ I would agree with that. The question we have serves to get the options people are looking at to solve the problem...

4:00 AM

Ooh, we have tons of stuff to discuss today

HW policy, and the other three (4?) recent metaposts

I'll try to remember to be on for it...

I always somehow forget and drop in just after it finishes

And I think it's about time we officially put that book policy in place

I agree with that

Yeah

I hope others pitch in though. It's not sustainable if it's just the mods.

Well, flagging can go a long way

And if they don't, it just means the community doesn't want to allow the book questions and we revert the policy

4:34 AM

in The Pod Bay, 9 mins ago, by Undo

Although I sometimes wonder if half the stuff on Physics.SE is just from people typing jibberish in between two dollar signs and adding in some authentic-sounding wording.

4 hours later…

8:31 AM

@ManishEarth wakey wakey!

hrm?

1

Q: seminal research showing how light is created?

Pardon me if asked before. I did not see this anywhere and I'm new to this forum. I'm not an astronomer but I'm very curious about how light is created. I'm trying to get back to some type of real understanding about why everything on the sub-atomic level vibrates and the implications for the ...

2pm, of course I'm awake

physics wanty?

@ManishEarth well ive only just got up where i am so sticks tongue out

I had good food today sticks tongue out and blows raspberry

@RhysW Not that good a question, I edited it and now it seems a bit more suitable.

8:36 AM

If its not fit for physics i wont send it over. Rule 1!

@RhysW It's OK now. Not ideal, but OK.

Ok ill sendy sendy

1

Q: How is light created?

I'm very curious about how light is created. I'm trying to get back to some type of real understanding about why everything on the sub-atomic level vibrates and the implications for the preservation of both the conservation of energy and conservation of momentum. How is light created at the a...

Apprecialted, thanks manish

user54412

that's a pretty broad question...

I think its broad if you know the answer, but not if you don't, if that makes sense?

it slightly irks me that migrated posts dont get a refreshed vote cont though

@ChrisWhite VTC it if you don't like, if it gets rejected it gets rejected

That's how we usually approach migrations.

user54412

8:42 AM

it's not at my personal VTC level, though I can't say what I'd do if I saw in in the queue

@ChrisWhite personal VTC level? O_0

If I was not a mod I would have VTCd it :P

But I was pretty aggressive with VTCing back in the day

user54412

it's interesting - if you look at the question I linked, you'll note that most physicists completely ignore the mechanisms behind emission

@ChrisWhite whoosh the sound of all the physics going over my head, this looks like my cue to leave

cya all later!

user54412

which is like ignoring kinetics and saying "thermodynamics tells us this is the equilibrium, so the system must be in this state"

hahaha I think I've seen similar things happening a lot

@RhysW cya

user54412

8:52 AM

abstract on astro-ph, titled Why is Astronomy Important?: "For a long time astronomers and other scientists believed that the importance of their work was evident to society. But in these difficult days of financial austerity, even the most obvious benefits of science have to undergo careful scrutiny. Eradicating poverty and hunger is a worldwide priority, and activities that do not directly attempt to resolve these issues can be hard to justify and support..."

nice!

9:13 AM

Interesting: princeton.edu/~pkrugman/interstellar.pdf

Anonymous

9:31 AM

@ManishEarth So? It is still misleading, especially given that the OP doesn't really seem to have learnt much GR.

No it's not.

Proportionality need not imply equivalence of units. That's pretty basic.

2

9:45 AM

3

A: Einstein Equation at the Singularity. Understanding the Dr. Michio Kaku's explanation

There are a few errors in your transcription. The first equation does not have an equal but a tilde. I think that Dr. Kaku means that there is a relationship of proportionality there. $$R_{\mu\nu}-\frac{1}{2}g_{\mu\nu}R\sim T_{\mu\nu}$$ This is Einstein's field equation. The second equati...

^^^ now with added screen caps

just saw that

his $T_{\mu\nu}$ reads as "Tau" to me at that angle :P

not that I will ever convince anyone of the unconvinced but...

10:00 AM

@Sklivvz Apparently D10 is saying that your answer may be construed to mean that the equation in the q is incorrect, and he is trying to tell you to ass a bit saying that "The equation in the question is correct if you are using natural units, but not so otherwise"

(we discussed it in the Tavern and it became clearer)

user image

(photoshopped together by a batchmate. He's more into pop-ph but rocks at drawing and all)

that. is. so. cool!

10:18 AM

@ManishEarth He's now editing my answer to add his comments. I've reverted for now, but...

which post is this @Sklivvz?

34 mins ago, by Sklivvz

3

A: Einstein Equation at the Singularity. Understanding the Dr. Michio Kaku's explanation

There are a few errors in your transcription. The first equation does not have an equal but a tilde. I think that Dr. Kaku means that there is a relationship of proportionality there. $$R_{\mu\nu}-\frac{1}{2}g_{\mu\nu}R\sim T_{\mu\nu}$$ This is Einstein's field equation. The second equati...

@ManishEarth want

@Sklivvz good answer!

ta

@Sklivvz Meh, I feel his point is valid, though he has expressed it terribly

In the current form, your answer may mislead some into thinking that the OPs equation is wrong. It isn't wrong if natural units are being used (and natural units are pretty common)

10:28 AM

@ManishEarth Although I disagree with you on a couple of levels, I've edited the answer in spirit to your criticism. I still don't see why his point on natural units is relevant at all though since Kaku is clearly not using reduced plank units and he is clearly saying what I reported.

Alright :)

IMO it's pretty obvious, but I think it could be misleading to others. You've had two commenters (D10 and another guy) who were misled, so that could be it.

fwiw, I was not misled

neither was i

I think that if you read Dim's answer first, then it might be a bit different. I make a completely different point

could you please nuke the comment thread as obsolete now? I can't really flag without nuking :-D

boom

10:37 AM

thanks

much better

@ManishEarth Yeah, it happens to me. I can't control myself sometimes :P

@Sklivvz Heh... The pic upgrade was nice :P

Thanks

@ManishEarth I need one... Mail me a google form (assuming it's free of cost, just like SE's) :D

If I can give any adivice, vote as much as you like (close, reopen, up, down, etc.) The system works on balancing votes not on single votes :-)

10:47 AM

@CrazyBuddy Doesn't exist, it's photoshopped.

No problem... You're an engineer right? Design me one..!!!

do you have a large image of the print?

It may exist later, but it would cost you and Somesh won't take the trouble to ship it elsewhere :P

cafepress or spreadshirt, we just need the img

Nope, that's all I have.

10:49 AM

@ManishEarth will you send a 4-man-tent-size shirt for me

wait gotit

user image

(was in the comments)

@ManishEarth where? ::D

@CrazyBuddy It's in our batch group. Hidden. You can't access.

@ManishEarth Hah..!!! Then, I'll publicize that immediately :P

(I was wondering, who might be the creator of that) :)

Be sure to credit Somesh for his work.

0

Q: Is it customary to express heat loss as a negative number?

In my chemistry class, we had a problem akin to the following: If an object with mass bla and specific heat bla is placed into a bla g calorimeter with an initial temperature of bla and a specific heat of bla, and the temperature of the calorimeter rises to bla at the end of the experiment, h...

Time for a Phy vs Chem fight

2

10:56 AM

ding ding

@Sklivvz BTW Sklivvz, the Physics community & SE supermods have done their best to explain what's really going on in Physics.SE. If he wants to say something, let him downvote or comment, or ping you in chat to fight with you. Or, if he wants to go around and shout elsewhere, he can do that. But, why should you care? You don't wanna go around and see what he's doing. Should you? ;-)

@ManishEarth I'll do that (Give him my best) :D

@CrazyBuddy hear hear! let them have their little soap box, I no longer read that myself, due to irrelevance

That's just fine... Neither did I :)

Anonymous

11:12 AM

@CrazyBuddy I did post a comment, but Slikzw immediately deleted/whatevered it.

@DIMension10 In such a case, I can safely tell that it might be rude/offensive or something that we don't encourage. Else, the mods would've put a rope around his necks :D

cafepress.co.uk/cp/customize/…

if its regarding the comments after @Sklivvz's Michio Kaku's reply - I believe all were flagged and deleted as being obsolete

Anonymous

@CrazyBuddy No, it wasn't!. It basically said something like [EDIT:Oops, I forgot, Slikzw just posted it below].

Anonymous

@UV-D No, before.

11:18 AM

no it's regarding this: "Huh? As I explained in my answer, it is an equivalence, since this constant of proportionality is dimensionfual, and can be set to 1"

It's off topic, it talks about Dim's answer, but doesn't really point out anything about mine

@CrazyBuddy the thread was deleted due to obsoleteness

ah... There ya go :)

Anonymous

@ManishEarth This is about a different comment.

Anonymous

The old one.

@ManishEarth no this is one i nuked by flagging as OT, dim is right.

11:19 AM

ah

OIC

i mentioned it in the physmod room

oh that one

Maybe shouldn't have been deleted then, but it is obsolete now

Anonymous

@Sklivvz It does; it explains why it is misleading (which I then called "incorrect", because I was mislead, too).

whats done is done

11:21 AM

@DIMension10 it does, but it doesn't say that the answer is misleading. it reads like "my answer is right and I disagree with yours", which is of course not what you meant...

@Sklivvz 21 Euros??? Damn..!!! Dear @Sklivvz, being a dev (and a Phys.SE enthusiast), please tell the SE team to design a swag like that. I'd just love to get it for free :P

yeah, it's too expensive and the print too small

@CrazyBuddy remember that the earning power in the US and UK is also significantly higher. What may come off as expensive on applying the exchange rate may not actually be so....but 20 pounds is a bit much. 5 seems more appropriate.

typical price in the uk would be around 15

hm

wait, what's the pound-dollar conversion rate

11:24 AM

15 pounds

what are you buying me now?

that's $24 ... still a lot, unless the shirt quality is really good

@UV-D a big huge bag of nothing

awesome!!! just what I always wanted

Then again, what I said about India and US/UK probably applies for the US and UK. No clue what the normal price levels are in the UK

@ManishEarth Yeah... 5 maybe good :)

11:28 AM

zazzle.co.uk/custom_large_t_shirt-235188229222196359

cheaper and better

@Sklivvz i just see a black shirt there

yeah o_O

fixing

zazzle.co.uk/kakus_playing_skills-235330697848212772

nice

£11.48 with the 25% off redeem code

£15.29 including UK shipping (not sure to india though)

Bought it :-)

11:40 AM

@Sklivvz Whaaaa??? o_O

i bought the tshirt

@Sklivvz niiice :D

3 hours later…

2:37 PM

Logging into chat now so I'm not late to the session... now if only I remember to look at my computer when it starts!

3:05 PM

What does "h" in "h bar" stand for?

Planck constant

{| class="wikitable" style="float:right; margin:0em 1em 1em 1em" ! Values of h ! Units ! Ref. |- | align=right | ||align=center | J·s || align=center | |- | align=right | || align=center |eV·s || align=center | |- | align=center |2π|| align=center | EP·tP || align=center | |- ! Values of ħ ! Units ! Ref. |- | align=right | || align=center |J·s || align=center | |- | align=right | || align=center | eV·s || align=center | |- | align=center | || align=center | EP·tP || align=center | def |- ! Values of hc ! Units ! Ref. |- | align=right | || align=center | J·m || |- | align=right | || a...

It's a pun

"h" is plank's constant. "h bar" is h/2pi

@Sklivvz Wait, "bar" means /2pi?

let me find an example

Not in general -- it's just a notation used in this case

3:10 PM

> In applications where frequency is expressed in terms of radians per second ("angular frequency") instead of cycles per second, it is often useful to absorb a factor of 2π into the Planck constant. The resulting constant is called the reduced Planck constant or Dirac constant. It is equal to the Planck constant divided by 2π, and is denoted ħ ("h-bar"):

ħ <- h-bar

That's actually pretty funny...

As a pun, that is

@tpg ill ping you ten times

Im in transit though, not sure if ill be around

@ManishEarth Good, that won't be annoying at all

@DIMension10 I proposed that the list post be locked as a compromise. It was asked years ago, closed months ago and had useful information on it. So rather than close it so it "disappears," I asked for it to be locked as historical because it was on-topic when it was asked, has good information, but is off-topic under current policy.

So if you would like to attack me or my voting record, at least do it somewhere that I can explain it. I have nothing to hide. The irony is you and I vote more similarly than I do with others.

Is there a internationally accepted way to draw different types of particles in Feynman diagrams? A certain tutorial said that photons, Ws, and Zs were all drawn with a wiggly line, while a different one said that Ws and Zs were drawn with dotted lines.

Integer spins with wigglies

Half integer with arrows

Higgs and similar zero spins with dashed, sometimes

I think

wigglywigglywigglywiggly

~~~~~~

3:27 PM

Should I trust Wikipedia to get the spins of bosons?

/signs of a bored Manish

Yep

ShuklaSannidhya

AAARGH...

Bosons are integer spin though

ShuklaSannidhya

SIGNS OF ANGRY SANNIDHYA.

....

3:28 PM

@shukla WARGH

Er...

Is there something I'm missing here?

Nope. I'm just bored. In a train and limited to a tiny phone screen

Carry on with your physics questions

ShuklaSannidhya

@Arc676 You're missing the fact that $\Delta G = 0$ always.

Still hung up on that?

ShuklaSannidhya

yeah.

3:31 PM

@ShuklaSannidhya ?

That's what the main site is for :>

ShuklaSannidhya

@ManishEarth I'll be banned.

@ManishEarth Do you go out? :D

@arc he seems to have reason to believe that entropy is delta H by T always because his book is confusing.

Isn't the symbol for entropy Q?

3:32 PM

Or S

Depending on field

Q is usually something else. Work maybe

My thermo is rusty

@crazy only to go back and forth from home. There is a special sealed train going from my home to iitb so that I need not be exposed to the ~~great~~ outdoors

Q is heat

ShuklaSannidhya

@ManishEarth My book is confusing?

@ManishEarth You're quite lucky that you aren't a day-scholar like me -_-

@ShuklaSannidhya wrote a book?

I hate to go out, while my family members want me to..!!! :/

ShuklaSannidhya

3:34 PM

@Arc676 haha...

@shu Sannidhya is confused, Sannidhya's source is the book, ergo the book is confusing

@ShuklaSannidhya I didn't know you wrote a book...

@ManishEarth Which IIT are you at?

Bombay

I got an email from somebody at another IIT asking about getting into my lab as a PhD. No idea how I was found, I don't really publicize. But it wasn't Bombay

ShuklaSannidhya

3:36 PM

user image

I think people from iits send out lots of emails

I didn't get an answer, should I trust Wikipedia to get the spin value of a boson if I were to need to know?

ShuklaSannidhya

I have this habit of ignoring the subscripts.

We've been advised by seniors to do thr same :p

@arc I said yes I think

Ah, I see. There was no @, so I didn't know it was the answer to my question :D

3:38 PM

@ManishEarth I guess if you send 1000, somebody is bound to reply :) I usually don't answer unsolicited emails... Especially when it comes to working for my ~awesome~ lab

Ah

Mostly because I wouldn't want to be responsible for subjecting anybody else to it

@ManishEarth If integer spins are wiggly lines, why should people draw gluon wiggly lines differently from photon wiggly lines?

They have identical spin...

(according to wikipedia that is...)

Gluon wiggly lines are paired

And usually the particle type is mentioned or implicit (context)

@tpg haha good policy

ShuklaSannidhya

this one is better. At least it wouldn't give me $\Delta G = 0$.

3:42 PM

@shukla now that makes more sense! (referring to the sybscripted pic)

@ManishEarth What do you mean "paired"

Gluons come in pairs. A lone gluon is never really observed.

Check out the wikipedia page for color confinement

Iirc I made one of the animations on that page ;)

So we usually draw two wigglies side by side

Is that why in some images gluons are depicted as a wiggly line with two spheres in the middle?

At least that's what I've seen, @davidz knows better

Never seen that

But it makes sense

you made the animation of the gluon tube splitting on that page?

3:48 PM

Yeah

Back when I was bored and was messing with Flash

It probably looks ugly, can't even remember now

@ManishEarth Nice ;-)

ShuklaSannidhya

hmm... I just read Feynman's Lecture on Physics (Chapter- Thermodynamics), didn't find anything like $\Delta S=\frac{\Delta H}{T}$. Conclusion: $\Delta S \not= \frac{\Delta H}{T}$

@ManishEarth The black circles represent quarks right?

ShuklaSannidhya

Does entropy of every isolated system keep increasing or is it just the universe?

@arc the diagram is actually of two quarks being pulled apart

The ring is a gluon "tube"

3:52 PM

@ManishEarth Right, so the black circles are the quarks being pulled apart

but how exactly would one do that?

How can you pull two quarks apart?

But it applies to gluon pairs being pulled apart too

@ShuklaSannidhya It could remain the same. Doesn't have to increase

Or is that a purely hypothetical "experiment"

Wait no

Im confusibg you

?

Doesn't apply to gluons?

3:53 PM

It doesn't apply to gluons, sorry

Gluons don't come in pairs

?

ShuklaSannidhya

@tpg2114 but second law says otherwise...

Gluons have two colors

Ah

So no pairs?

Well, they can I guess

3:54 PM

@ShuklaSannidhya A system in isolation undergoing no changes has no entropy change. I agree if anything interesting is happening that S will increase.

But a normal gluon with two wigglies means a single gluon with two colors

\Delta S = 0 if \Delta G/T = \Delta H/T = 0

@ManishEarth Is there a REAL ACHIEVABLE way to do what's in that animation?

ShuklaSannidhya

OIC.

> An event is starting in 5 minutes in The h Bar - "Physics chat session"

@ManishEarth ?

I was going to ask that too...

3:56 PM

@ShuklaSannidhya AFAIK entropy for an isolated system should eventually reach a maximum, which is achieved when one of the states with most equivalent states is achieved.

@arc basically what they do at the LHC, smash stuff together to give it enough energy

@ManishEarth And this can pull quarks apart?

But again David would know this better

@arc yes

"David" isn't in this chat room...

@sklivvz isolated system

3:58 PM

yes?

He's usually there for the session, comes in when it starts

What exactly is this "event" starting in 5 minutes

And who/what starts it when/how?

@crazy @tpg if david isn't around, you guys start the session, im on a teensy keyboard

@Arc676 Automatic ;-)

put together an empty box and a box full of gas. they will eventually reach equilibrium... or a cold and hot liquid, etc.

3:59 PM

@ManishEarth I'll do that (as I always do) :P

Oh that way

/me assumed equilibrium

« first day (1097 days earlier) ← previous day next day → last day (3834 days later) »

Transcript for

Nov '135

The h Bar

General chat for Physics SE (physics.stackexchange.com). For M...

join this room
about this room

00:00

06:00

12:00

18:00

all times are UTC

site design / logo © 2024 Stack Exchange Inc; legal

mobile