The h Bar

@ACuriousMind :D I just brought it for the anecdote that this one guy in my classes has spilled his coffee no fewer than three times this year. Probably more when I haven't seen.

ACuriousMind

@NeuroFuzzy lol, nervous much?

NeuroFuzzy

no, just forgetful about where he put it I guess.

ACuriousMind

Heh, I can imagine that

I've got a friend whose notebooks are always coffee-stained

And I always hope there's some cool story behind it, but it's never exciting :(

Kyle Kanos

3:58 AM

So no one seems to have proved that the acceleration moves objects with speed 9.8 m/s

ACuriousMind

@KyleKanos We're all just sheeple believing that, yes.

NeuroFuzzy

@ACuriousMind ...cool story? Coffee stain?

Kyle Kanos

Also: annav is pretty good at making me feel a little bad about somewhat mocking new users.

ACuriousMind

@NeuroFuzzy Hyperactive imagination, I guess :P

NeuroFuzzy

@ACuriousMind Got in a car wreck in the middle of nowhere... had to hike for days to get help... sat up one night drinking coffee from a portable stove and my hands were shaking so hard I got coffee on my notebook?

ACuriousMind

4:16 AM

@NeuroFuzzy I...don't know. She had pretty good stories for the chocolate stains on her clothes once :D

@KyleKanos annav's heart is made of pure gold.

yuggib

8:47 AM

@KyleKanos Sage is an open source alternative for mathematica

Danu

10:51 AM

I think someone should write a serious answer here

0

Q: Technical question abou 2 forms

A technical question about the electromagnetic tensor, but before that, it is know if, say, instead of being $$F_{\mu\nu}=\partial_{\mu}A_{\nu} - \partial_{\nu}A_{\mu}$$it were $$F_{\mu\nu}=(...)_{\mu\nu}-(....)_{\mu\nu}$$ I am giving an example of the electromagnetric tensor because it is a 2-fo...

I'm personally a bit too lazy, but I think it's worthwhile to explain the difference of the concept of differential forms with the components that we use in physics.

Actually, the comment I wanted to leave is too long so I guess I'll post it as an answer, but I think a better one could be written.

alarge

11:03 AM

@KyleKanos SymPy can do some. Maybe Maxima has an external package?

user1581390

11:16 AM

What relativistic conservation laws are there in case the invariant mass is not conserved? apart from energy and 3-momentum

ACuriousMind

1:47 PM

"Many cereals (from the supermarket) are attracted by a magnet. This can be seen by crushing the cereals into a very fine powder and approaching a strong magnet."

How do you even get the idea to crush cereals and approach them with a strong magnet? :D

Jim the Enchanter

@ACuriousMind Do you not take a magnet to all things in your household?

2

ACuriousMind

@JimtheEnchanter Usually not. Their dark magic should not be toyed with lightly.

Jim the Enchanter

@ACuriousMind Not by mere mortals such as yourself. But I am Jim the Enchanter

Of course, there are some who call me..... Jim

0celo7

2:08 PM

@ACuriousMind Inconsistent with the language of the indices on purpose here?

ACuriousMind

@0celo7 What do you mean?

0celo7

@ACuriousMind You write $v=v^\mu e_\mu$ and then call the components $v^i$.

ACuriousMind

No, that's just a typo :P

0celo7

You do it again later in the post.

You keep switching.

ACuriousMind

Oh, I see it.

0celo7

2:12 PM

Unless you want to do it, I'll just fix it.

ACuriousMind

Hmm...that we are free to call the indices whatever the hell we want might be also a lesson to learn here...

0celo7

Nope.

Danu

Hey guys

ACuriousMind

Yeah, better this way

0celo7

Also, you didn't space the second index on the delta.

Danu

2:14 PM

Does anyone konw a pedestrian way to say something about the connection between extremal Reissner-Nordström black holes and the BPS bound in SUGRA?

ACuriousMind

@0celo7 Why would I need to? The indices on the delta do not care for the order.

0celo7

@ACuriousMind It just looks better.

ACuriousMind

I have created a monster :D

@Danu I don't know any way to say something about that. :P

0celo7

^^

Danu

Wasn't asking you (I know I know more about GR than you :P)

But I feel it's a long stretch anyways, because I'm not sure we have anyone who's into both SUSY and GR :(

@ACuriousMind thanks for writing a good answer to that question, btw!

Anyone here who would know anything about this?

6

Q: History of Coagulation of Milk by Short Waves

In 1968 NASA, through the assistance of the Israel Program for Scientific Translation, translated from Russian the 1964 book "The Earth in the Universe", with chapters written by top Soviet scientists. In a chapter written by Prof. A. L. Chizhevskii, who was honorary president of the first Inter...

chemistry reference-request

ACuriousMind

2:34 PM

@Danu lol...milk curdled by thunderstorms? Really?

Danu

Friggin' cool, right?!

ACuriousMind

It sounds so absurd

But if it really happens, it's cool as fuck, yes :D

0celo7

Sumbag HE. Those surfaces in the past light cone are supposed to asymptotically approach the light cone.

Jim the Enchanter

2:59 PM

0

Q: What is the principle used by mangalyan to place it in mars orbit with 0 fuel consumption?

Recently I came to know from a seminar that where most of the satellites need gallons of fuel to be consumed to get placed in one planet's orbit Mangalyan took 0 fuel and it waited for the 'right time' by using centrifugal force to get placed in the mars's orbit. My question is what principle did...

astrophysics

From Wikipedia: Mars orbit insertion burn time: 1388.67 sec

It used the principle of imagination to do it with 0 fuel consumption

Danu

:P

Physics Meta

3:55 PM

0

Q: How can I view the breakdown of votes on an answer versus the simple total?

I recently had a non-multiple of 5 rep points for an answer (specifically, 18). I assume that is due to 2 positive votes and one negative, but there was no comment explaining the down vote. When I look back at the answer, I see it has a total of +1, but there doesn't seem to be a way to view th...

feature-request

Kyle Kanos

5:06 PM

So I was going through the review queues and noticed a nice comment and tried upvoting it. Turns out the nice comment was mine from last night & I couldn't upvote it.

Kinda hate it when that happens :(

Jim the Enchanter

5:21 PM

@KyleKanos Wow, I'm not sure who this Kyle Kanos guy is, but I really like the things he says. Wish I could meet him and get inside his head.

Kyle Kanos

I rarely look at the names of the commenters

Jim the Enchanter

Well, take comfort in the knowledge that you have no internal contradictions in the way you see things

Kyle Kanos

That is actually a thought I hadn't had yet, thanks for that one

Jim the Enchanter

:)

Kyle Kanos

Okay...so this is weird:

On the android SE app, I can see a link to the posts where I gained +2 rep from a user deletion

But I can't seem to find out how to do so on the main site on the computer

It just says +4: User removed (learn more)

Humorous Mother Meta post whilst searching for the answer to the above oddness:

-6

Q: Freemarket reputation

On http://meta.stackexchange.com/questions/20420/countdown-app-for-devdays balpha comments, "I would be willing to donate 500 rep (on meta) to the first guy who does this with LOGO turtle graphics and this program actually gets used at one devdays venue." This got me thinking: why not allow peop...

feature-request reputation

Kyle Kanos

6:54 PM

@Danu: chesspastebin.com/2015/05/25/kkanos-brother-by-kkanos I thought I was dead in this game, but managed to eke out a win.

Danu

7:35 PM

@KyleKanos Hah, you play? Nice!

Interesting game :P

Kyle Kanos

@Danu I play kinda regularly with my brothers, but we both suck terribly.

I just suck less worse than he

Danu

Cool dude :)

I'll refrain from trying to give you tips and spoiling the fun with my know-it-all attitude :D

Kyle Kanos

Could I have mated earlier?

Danu

7:58 PM

@KyleKanos It's not so much about that as about the openings ;)

There was a nice tactic that you missed near the end

After 45. Ra2 Qb3

see if you can find it ;)

There was not really an earlier mate, as your mate depended on a blunder by the opponent only 2 moves earlier ;)

Jimmy360

10:28 PM

-5

Q: particle physics and the problem with understanding

Imagine a world that is watching ours, theory is theory , what if theory was real, why do we breath, physics is all theory until proven otherwise

particle-physics

Can we kick this guy out? And who is upvoting his questions?! He has a reputation greater than 1.

Icosahedron

Remember when user:Blah had more rep than me by commenting "Blah" 13 times?

Jimmy360

10:41 PM

XD

Obliv

Can moderators ban people? It's pretty clear that he's a troll. I lost my shit at "magnetism creates white holes!!"

Jimmy360

theory is theory

Obliv

what if theory was real

Jimmy360

have you seen his earlier posts

someone upvoted them

Obliv

no i'm afraid to lol

Jimmy360

10:43 PM

and our downvotes didnt cancel them

so he has rep above 1

Obliv

He does not deserve 16 rep lol..

whoah nvm he's a genius. "if we introduced magnets to cancel out inertia as we travelled at this speed"

never thought of cancelling out inertia with magnets

Jimmy360

XD

Obliv, it all makes since if we remember that "theory is theory".

Obliv

physics.stackexchange.com/questions/185970/… I don't understand this question.. How does he want a mathematical model of something so abstract?

Jimmy360

I'm not completely sure that I know what he's asking.

Obliv

He's asking how we define the present in a very convoluted way. It's relative isn't it? the present is relative to everyone because of inertial reference frames and special relativity?

Most people just leave it at "time is non-simultaneity" but he wants some principle or mathematical model..

ACuriousMind

11:01 PM

BTW, please do not upvote the non-answers to troll questions, either.

Also, please do not post non-answers, @Obliv!

Obliv

sorry haha won't happen again. Just wanted to have a bit of fun with the question. I did not expect to receive rep from it.

ACuriousMind

Some people are very liberal in giving out upvotes

0celo7

11:38 PM

@ACuriousMind Chapter 5 is actually pleasant.

ACuriousMind

@0celo7 They dial down on the vagueness?

0celo7

@ACuriousMind Nope - I just know what they are referring to when they're being vague.

ACuriousMind

lol, well, that's at least something

0celo7

The diagrams in this book are beautiful, except for Figure 13, which has two hyperboloids looking like paraboloids.

@ACuriousMind I was just about to ask how (5.13) comes from (5.10), and then I realized $a\log b=\log b^a$. Logarithms are crazy.

Also, that $4\pi$ is really misleading IMO. It just comes from the choice of the integration constant, but it looks like it has a purpose.

Maybe I'm just bad at ODEs.

user1667423

Anyone willing to offer quick help with this question?
http://physics.stackexchange.com/questions/185833/perfect-fluid-and-cauchy-momentum-equation

0celo7

11:54 PM

@user1667423 Just by glancing at it, a factor of $c^{-2}$ will make things vanish in the classical limit.

Formally the classical limit is $\lim_{c\rightarrow\infty}$.

@user1667423 A note on notation: In special relativity, use the symbol $\partial_\mu$ for partial derivatives. $\nabla_\mu$ is reserved for the covariant derivative of general relativity. The notation $\vec\nabla$ in vector calc is unfortunate.

user1667423

@0celo7 Of course, thanks. I suppose the relativistic equations still hold with covariant derivatives in GR (ignoring the three-gradients, which happen to have the same symbol)?\

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