The h Bar

ManishEarth

2:22 AM

GTR assignment. Lots of mus and nus. Ended up making my rough paper totally indecipherable.

github.com/CourseResources/CourseResources/blob/master/…

(took some help from Mathematica because I got bored halfway through the calculation of a Christoffel symbol.)

/me shall extend mathematica so that it understands summation notation

user54412

3:20 AM

@ManishEarth for mathematica-ing GR, I always fall back to this assignment from a course here - it has a lot of the stuff worked out

Kyle Kanos

Man...I hate when I am stupid

The Sedov solution is fairly complicated to code, so I'm just using Frank Timmes solution (it's written in horrendous F77 syntax, not really worth reading)

And am going to interpolate the data for use in a test-case for my hydro code

I mucked around with the units for about 20 minutes, getting bunk data quite a lot

Turns out I wasn't changing the length scale into pc, so it was trying to compute as if I dumped $10^{51}$ erg into about 1/120 cm of space on a scale of 1.2 cm

dmckee

Good units documentation...or better still a unit-as-code system that takes care of that for you.

Simplifies your life.

Kyle Kanos

@dmckee I whole-heartedly agree. It should be read in at run-time, rather than hard-coded in too

dmckee

Because I, too, have spent many, many hours seeking out problems in code that was really just a units conversion issue.

Kyle Kanos

But it looks (and works) great now!

I have a physically correct model

dmckee

3:36 AM

Yeah!

Now the real work begins.

Kyle Kanos

And all this work for a stupid 1 hour lecture on radiative losses

And, if it works, maybe a paper

David Z

4:24 AM

0

Q: Is it possible to use induction ampermeter to measure power consumption of electric water heater and dryer?

I hope this practical question is not OT and not too trivial for this forum. I am renting an apartment in a duplex with a shared water heater and dryer. Turns out, both water heater and the dryer are connected to my meter. The neighbors seem willing to pay their share for the past 6 months, only...

Off topic or no?

Arafat

11:06 AM

yeap. @KyleKanos

Kyle Kanos

1:37 PM

5

Q: Why the speed of light is represented by $c$?

In almost every textbook, I've found that the speed of light is $c \approx 3 \times 10^8\: \mathrm{m/s}$. I wonder why it's just $c$ ?

speed-of-light terminology notation

Methinks it's off-topic

Waffle's Crazy Peanut

@KyleKanos VTC then?

Kyle Kanos

I'm thinking about doing so

Just wanted feedback from others if they felt the same

Waffle's Crazy Peanut

@KyleKanos Usually, mods do that... Our votes are already based on individual opinions :)

Kyle Kanos

@Waffle'sCrazyPeanut I've seen others (non-mods) do so too

IDK, maybe I'll leave it. We do have a terminology and notation tag, I guess it could be categorized under those

Waffle's Crazy Peanut

@Kyle: If your vote doesn't survive, the post just gets out of the queue. You may not be able to VTC the question again, and thereby get it into the queue... That's it!

Meh, only when our vote is the last vote, we should think a while about it... Else, we don't have to! :P

Kyle Kanos

1:45 PM

@Waffle'sCrazyPeanut I haven't yet come close to getting to the last. Lowest I've gotten is having something like 9 left

Waffle's Crazy Peanut

@KyleKanos I meant "5th vote" (which closes the question) :D

Kyle Kanos

@Waffle'sCrazyPeanut Oh. I understand now

Waffle's Crazy Peanut

Oh, fine... ;-)

Kyle Kanos

@kyle kanos again, you judged my question but never answered it. You apparently are not good at judging questions nor good at answering them. Several other gentlemen saw fit to answer the question even in its original form. You continue to argue my question is in the wrong place. I submit that if you can reason it is in the wrong place you too can then reason what i am asking. I then reason that the problem is that you just are not able to answer and thus want the question moved because you feel obliged to answer as long as it is here. Answer the question or not? — pjameslamar 9 mins ago

From:

-5

Q: everything in nothing

in my mind everything has to exist in nothing. There has to be such a thing as nothing. That nothing is where everything that is exists. Without nothingness then everything touches something else and would be one large mass with areas of lesser and greater density. Space then must be the nothin...

space

Is it just me, or is there no question asked here?

Waffle's Crazy Peanut

@KyleKanos Meh, you don't have to prove anything there... Others recognize it (well, you can see the downvotes :D). My suggestion would be to stop responding to such comments :)

Kyle Kanos

1:51 PM

Can't help it

I get pinged, read it, then get mad enough to respond

Waffle's Crazy Peanut

@KyleKanos Hehe, you'll get used to that eventually :D

Kyle Kanos

@Waffle'sCrazyPeanut I've been here for like 8 months

Still not used to it

Waffle's Crazy Peanut

@KyleKanos I've been here for 556 days (consecutive that is!)

And, I'm sure I got used to that only after 400 days or so... :D

Kyle Kanos

Which is just insane

I've been here 141 straight

Waffle's Crazy Peanut

@KyleKanos Honestly, at the start, I really felt happy to get as much as consecutives (even after earning the Fanatic badge) - so, there were days when I came to the site, just to get consecutives (No, seriously!) :P

Dunno what that gave me, except Happiness :D

Kyle Kanos

1:56 PM

I think it'll be easier for people to get the Fanatic badge now that there's the SE App.

Waffle's Crazy Peanut

After a few months, I lost that ugly desire and stopped coming for consecutives...

Nowadays, I visit my profile only when people take me into... (like you did now! :P)

I mean, in order to respond you, I checked my profile

Kyle Kanos

I check it every so often to see my helpful flags

I have 1 declined flag

And 74 helpful

Waffle's Crazy Peanut

I always get amazed when I see my profile still not losing consecutives :P

@KyleKanos You've still got more to go.... I have about 500 :D

Kyle Kanos

@Waffle'sCrazyPeanut Yeah, I rarely flag though. That's like 1 every other day

Waffle's Crazy Peanut

@KyleKanos I was just kidding... We have time ;-)

Waffle's Crazy Peanut

2:03 PM

Do anyone remember the XKCD comic, when two people have a chat (teasing philosophers I think) starting with some topic which eventually goes to terminologies at the end?

Kyle Kanos

3:15 PM

@Waffle'sCrazyPeanut Hah: jinawee thought the same as me. VTC now

Waffle's Crazy Peanut

3:50 PM

@KyleKanos I already did that! :D

dmckee

4:53 PM

Why do people flag answers a "not an answer" or "very low quality" but neglect to downvote them?

4

Anyone?

Bueller?

Waffle's Crazy Peanut

5:06 PM

@dmckee Maybe they don't wanna lost 1 rep. :P

Kyle Kanos

Yeah, I'll agree with Waffle here. Losing a point is a lot to those with <500 rep. We with intermediate rep don't care about 1 and will aggressively downvote

Waffle's Crazy Peanut

@dmckee: But, I should admit! No man downvotes/comments as you do!!! You take part in almost all the posts... Keep up the good work :D

David Z

5:57 PM

@dmckee I guess when you flag as VLQ or NAA the expectation is that the post will be deleted, so it shouldn't really matter whether you downvote it or not

Mostafa

@dmckee Because:1. They will probably be deleted soon. 2.when you downvote an answer you implicitly accept it as an answer, although wrong or misleading. At least that's the way I think about downvoting.

Mostafa

6:21 PM

@DavidZ I've flagged the recent computational question(http://physics.stackexchange.com/questions/98261/are-there-simple-ways-to-numerically-solve-the-time-dependent-schodinger-equatio) for migration to SciComp. But till now the flag'e status has remained *Active*. Is there anyone who disagree or a new policy?
(The same situation with Uncle Al's inappropriate post on meta(http://meta.physics.stackexchange.com/questions/5462/why-is-there-a-down-voting-option-on-this-website/5463#5463))

David Z

@Mostafa That just means we haven't handled it yet. Here waiting to see if enough people agree.

Kyle Kanos

As the answerer to the aforementioned post, I'd rather not lose the 120 points for the migration :(. I also agree with both parties: it is indeed a question that could/should be asked on Computational Science, but it is also a question that probably is useful for physicists

And it has been asked before: here, here and here

And, as ChrisWhite points out in the comments to my answer, is has been asked on CompSci before: scicomp.stackexchange.com/questions/6708/…

Perhaps it would best to just close it as a duplicate and keep the links to relevant questions in the comments?

Actually, there's quite a few Schrodinger equations on CompSci: scicomp.stackexchange.com/search?q=schrodinger

dmckee

7:17 PM

@Mostafa I disagree that you are accepting it as an answer, you are noting that it is poor content. And this is important, because in the case the case of dispute we (the mods) are likely to leave that content on the site.

jinawee

8:49 PM

@dmckee Last year I had to prove that after a Compton scattering, pair production is impossible, but I can't remember the proof. Now I've read that it's possible. Do you know which stament is correct?

David Z

9:10 PM

@KyleKanos I would argue that all of those should have been sent to Computational Science

dmckee

@jinawee Pair production by a photon requires a heavy spectator (i.e. it can not happen in free space).

I can imagine that this implies a difference in expectation for dense, atomic matter (where a Compton scattering event implies a nearby nucleus to serve as the spectator) and diffuse, highly ionized plasma (where there is no such guarantee).

However, I have never seen the question framed in relation to Compton scattering in particular.

Kyle Kanos

9:30 PM

@DavidZ I would concur, but it appears that those were asked before Computational Science was made beta (that it's still in after 3 years)

David Z

10:28 PM

@KyleKanos oh, that makes sense. But in that case, they shouldn't be used as justification to keep the latest question here. (They might be good candidates for a historical lock)

user54412

11:36 PM

@dmckee well, when adding my flag to things already in the flag queue, there's no interface for voting - I have to open the question in a new tab to do it

user54412

(which I sometimes but not always do, given that whether or not a post is an answer depends on what was being asked)

ManishEarth

@ChrisWhite True. But I think dmckee is talking about non-10k flags

we can tell when it's a single flag and when it's a 10k pile-on :)

tpg2114

I have a data analysis question if anybody is around

user54412

@jinawee a typical graph of cross sections, such as those on this page, shows that the Compton (e.g. Klein-Nishina) and pair-production cross sections are equal somewhere around 10^7 eV photon energy

hwlau

@tpg2114 whats that?

user54412

11:50 PM

given that the photon will be mostly forward scattered by Compton in that energy range, you'd expect it to still be quite capable of pair producing provided, as dmckee says, there's a way to dump momentum

user54412

this works if you have either (1) a nucleus lying around, (2) you are at around 10^8 eV so you can efficiently pair produce off another electron, or (3) you have strong magnetic fields (think neutron star) to carry away the extra momentum

user54412

@tpg2114 hi there - what's the question?

ManishEarth

@tpg2114 everyone's around, not that I'm good at data analysis

dmckee

Oh! Oh! Oh! I'm good at one or two kinds of analysis.

And total s&%t at a lot of different kinds.

tpg2114

Wow, full house

So I have a 2D simulation and at each point I compute the shear strain and the temperature

And the hypothesis in the literature is that shear strain causes temperature

But it's likely time-delayed

So I need to figure out how to correlate the strain to the temperature

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