The h Bar

dmckee

00:16

Yes! We have a supercilious and self-righteous quote of Feynman on explaining things.

The last resort of the whiny snowflake.

Does that make the full set?

NeuroFuzzy

Heheh is he referring to the quote "to decide something as true or false you must have a framework in which to decide" (parapbrasing. Feynman on magnets or something like that). That one always comes to mind when explaining things to people...

dmckee

@NeuroFuzzy I know what he's referring to. That quote and the similar one by Einstein are the last resort of people who feel we should enlighten them without asking them to think.

They are, in my not at all humble opinion, always the marker of a taker and a poisonous personality.

HDE 226868

@dmckee Looks like he won't leave just yet:

I see. I will explore the site and learn the mechanisms instead of asking questions I could find the answers to. See that? Full circle AND accepting your reasoning, although if I become a regular to the site I will maintain my stance on approaching the uninformed, but I do understand the difficulty in disparate understanding. — Rigel Stewart 1 min ago

dmckee

01:06

Self-therapy regime of the night: write a short, scathing missive full of scurious adjectives beginning with "s", sharpen it to spiky perfection and then don't post it.

Joshua Herman

01:37

if you could pressurize something in space to one of the low temperature supercondutors that require around 100 pascals of pressure is that feasible to do?

dmckee

01:56

Been watching the lunar eclipse. Getting close to total.

@JoshuaHerman 100 Pa is .001 atmospheres. Any container would do. Your bigger problem is shielding it from the sun. That's a solved problem in a lot of ways, but always adds mass and complexity to the mission.

0celo7

02:20

@FenderLesPaul I'm down if you see this

Secret

04:36

Actually, this intended joke sparks an intriguing question:

We know that vectors and matrices have discrete and continuous versions (e.g. vectors in $C(\mathbb{C})$ are basically having an uncountably many components, and then there's continuous linear maps in matrices such as in expressions of nonlocal operators in quantum mechanics)

We also know that tensors are a generalisation of vectors, scalars and linear maps

Then surely it is logical to have tensor indices that take values in $\mathbb{R}$, $\mathbb{C}$ or possibly some more exotic sets?

isomorphismes

04:49

I'm not sure if I should cross-post this question

https://math.stackexchange.com/questions/1454350/connecting-physical-tensors-to-mathematical-tensors

but it's about connecting physics tensors to maths tensors, so maybe posting on both would be appropriate?

I don't really know what the etiquette for posting on both is, though I'm sure this comes up often as they're cognate fields.

dmckee

@Secret I'd love to sagely nod my head and say "Now you begin to see...". But in fact all that is over my head.

Actually, I think I can kinda see the implication of continously indexed vectors. Sorta.

But I wouldn't want to compute with them because I'm sure I'd make a fool of myself.

Shing

I remember that I have read Shankar once wrote that experiments recently done show extremely high intensity but insufficient freq turns out can cause photoelectric effect. but he did not mention the resources,

have anyone read anything about it, and have good resources?

Danu

05:25

I see. I will explore the site and learn the mechanisms instead of asking questions I could find the answers to. See that? Full circle AND accepting your reasoning, although if I become a regular to the site I will maintain my stance on approaching the uninformed, but I do understand the difficulty in disparate understanding. — Rigel Stewart 5 hours ago

I feel like we're at the "catharsis" part of a Greek tragedy :D

@Shing here

@JohnDuffield As I said, most of the unpleasant stuff will be either hard or impossible to find (by design). This is hard to test, but I suspect most of the persistent posters (e.g. posting essentially the same pet theory multiple times) tend to do so as answers rather than questions. I do think, though, that we have had a relatively quiet period lately w.r.t. disruptive, argumentative posters. — Emilio Pisanty Sep 22 at 13:26

Will

05:59

Today, I'm trying to "get" Rigid body dynamics, but instead I think I'm slowly going crazy. Take accepted answer to this question: physics.stackexchange.com/q/126766/58642 How do the first two sentences not violate conservation of energy? If both statements are true, it would seem to me that imparting a force on the end of the rod would add more energy to the system than pushing at the center of mass...

Danu

06:13

@Will Just a quick thought: The resolution could be that, in order to keep up with the rotational motion, you'd have to bridge a longer distance to keep applying the force in the second case (recall $W=\int F ds$)

Will

@Danu Interesting, thanks. That hadn't occurred to me yet.

Danu

I think it's a valid question to ask on the main site, though.

Will

I suppose it is. It's just that I have so many questions in my head right now...

Another one would be: Why is it okay to use the center of mass to calculate the Resultant Force-Torque, even when the axis of rotation passes through nowhere near that center?

Danu

06:56

@Will Maybe a book on theoretical mechanics would be good for you

Fowles & Cassiday was pretty decent as far as I remember

Will

07:08

@Danu Will look it up. Appreciated.

Slereah

"If action equals reaction, how is it ever possible to win in martial arts?"

Finally the real questions

Shing

Thanks, @Danu !

Danu

08:23

@DanielSank funny question. What do you think about my comment?

user54412

08:53

@isomorphismes Generally cross-posting is discouraged. I personally think it's only justified if you actually want two different answers from different perspectives. If you just decide another community is more likely to give any answer at all, you can flag for migration.

user54412

Also, I think the tensor product page is somewhat between the pages on monoidal categories and [physics] tensors.

user54412

Note that the $\partial$'s are just physicists' way of writing the basis vectors for the tangent space that are induced by the coordinate system on the manifold.

Slereah

09:07

0

Q: White Holes and Eternal Black Holes

Is there a definitive theory concerning the formation and structure of hypothetical white holes? Also, could somebody please explain the connection between the eternal black holes, the arrow of time and white holes please?

Looking at this, I wonder

Are stellar black holes even supposed to form singularities in classical GR?

Wouldn't that violate theorems on topology change

user54412

That user has asked 7 questions, at most 3 of which are distinct.

user54412

They seem really worried about white holes.

skill patrol

Perhaps he needs to start thinking about grey holes too :-)

user54412

And here I thought the only holes worth studying were black ones.

user54412

Sep 24 at 18:35, by skill patrol

There are other colours pal :P

skill patrol

09:16

:D

Slereah

White holes are just time reversed black holes

Not that hard :p

Just take a black hole and do $t \rightarrow -t$!

just a bunch of shit spewing from the singularity at minus timelike infinity

And once it's out the horizon, it can never go back in!

Although now I wonder

Does it undergo REVERSE SPAGHETTIFICATION

2

Atoms and particles cross the horizon, forming more compact pastas

user54412

Pancakification?

2

skill patrol

The singularity is multiplication by 1

Slereah

Hm

I wonder what Hawking radiation looks like in white holes

Is it infalling positive energy and outgoing negative energy

White holes are a purely Schwarzschild thing, no?

So no need for weird time reversed singularity

I mean

Spacelike, while kerr is timelike

Secret

10:57

Some "analysis"
http://meta.physics.stackexchange.com/questions/7114/why-do-many-users-on-this-forum-approach-laypeople-with-arrogance#comment27814_7115

It often perplexes me on why answers that are similar to HDE 226868 don't result in strong negative output, but the other answers do

What do these "safe answers" have in common, are they relatively emotionless, or are they not having the concepts that accidentally hit the berserk button of someone?

Mike Edenfield

11:16

HDE's answer is not making any judgement about the OP's opinion or claims; it merely gives two examples that demonstrate why the site is what it is. It also doesn't address the real meat of the OP's objection, that the users here have "air of intellectual arrogance"; it merely addresses the mechanical part of his question.

so I think there's less for the OP to object to.

the other answers are politely, but firmly, telling the OP "you have a mistaken impression about this site"... no matter how carefully you try to say that, someone's going to take it wrong.

Secret

is there an evolutionary advantage to held onto one's worldview and resistant to it being questioned?

Take for example back in the days of Galieo, peopel think the earth is the centre of the universe. They have held firm on this for some time until Cope(forgot) found that earth is just a planet in the solar system that the worldview is completely revised

Also take the now obsolete phostigen theory as a nearly model on heat, and then there's the lumminferous ether and old quantum theory etc.

Mike Edenfield

there must be such an evolutionary advantage because almost all humans do it, even in the face of overwhelming evidence to the contrary.

it's a pretty well studied phenomenon in psychology

it seems highly counter-intuitive to me; you would think being able to adapt your world view to new information would be better. but perhaps when your worldview is much simpler, new information just confuses things and makes you indecisive?

i dunno

Secret

I do have beliefs I strongly adhere to, but I always try to find how a new worldview fits into the existing picture, as this is what the scientific method taught me over the years

Carefully tested claims seemed to me, closer to the truth than adhere to a belief that is being contradicted by overwheming evidence

Qmechanic

12:08

@ChrisWhite : 11:15, restate my assumptions: 1. Food is the language of nature. 2. Everything around us can be represented and understood through food. 3. If you graph the food, patterns emerge. 4. The world is a universal food fight...

Slereah

Pi was a pretty dumb movie pretending to be a smart movie

basically math is wizardry

0celo7

Hello

Slereah

Hey

0celo7

@Secret You dare question the beliefs of the elder? Now we're gonna eat you!

It's a basic component of tribalism -- don't question and you don't get ostracized.

Or eaten.

ACuriousMind

12:40

@Secret Every infinite-dimensional Banach space is necessarily uncountable, so if you wanted to write the linear operators on such spaces with indices in the standard linear algebra way, you'd be forced to have at least $\mathbb{R}$ indices.

One usually has some kind of function space, and then the "matrix element" of the operator is just some function that is convolved (or otherwise integrated against) the elements of your space.

0celo7

@ACuriousMind What's up in Hberg lately?

Town still standing?

ACuriousMind

@0celo7 Uh...not much

And it's HD, not Hberg! ;P

0celo7

@ACuriousMind Except for one more string theory text in the dump.

@ACuriousMind Wrong!

Slereah

HDawg

0celo7

BJtown.

Does Hberg have a red light district?

ACuriousMind

12:55

@0celo7 No

0celo7

@ACuriousMind I see you've looked and been disappointed.

Not sure if Knoxville has one...I haven't looked.

Chat is böring.

FenderLesPaul

13:23

@0celo7 sorry dude just saw it

Secret

@Acuriousmind
https://i.sstatic.net/vRr2A.png
FYI: This is where I first learnt the existence of continuous matrices, and that is how it forms the basis of my question by generalising it to tensors

FenderLesPaul

sometime this week though?

I'm pretty free

0celo7

I have an assload of HW tonight.

@DanielSank Better approach to solve this problem?

FenderLesPaul

aw :(

but yeah anytime this week

@Slereah preprint today on the arXiv in GRQC that you might like

arxiv.org/pdf/1509.07683.pdf

0celo7

@ACuriousMind How's the Mun endeavor going?

I see you're hard at work.

NeuroFuzzy

13:42

@Danu :D That's terrible!

ACuriousMind

@0celo7 I've reached it. Now I'm trying build something that can land on it and come back.

0celo7

@ACuriousMind Good. I see you do have the rocket building skills of your forefathers.

NeuroFuzzy

@Will Just a note: The full general 3D rigid body equations of motion are a pain (you wind up with big nonlinear equations and they're generally only studied after you learn Lagrangian mechanics). So make sure you're studying the right thing. (2D rigid bodies, I guess)

Slereah

@FenderLesPaul neat :3

So I learned that there is a totally path integral method to determine that spinor fields must anticommute

When you do the wick rotation boogaloo thing, the action has to be positive

But that does not happen for commuting fermions

0celo7

Zee shows it using path integrals...

Something something zero point energy

Slereah

13:50

there is that too yeah

No ground state

With the negative action the path integral diverges, too

0celo7

I think the path integral diverges anyway.

QM is wrong after all...

Slereah

are we any closer to a non-euclidian version of the path integral btw

It is annoying that it is not well defined

FenderLesPaul

it's annoying to like 3 people :p

0celo7

@ACuriousMind What is the impact parameter $\vec\rho$ here? It says it's perpendicular to $\vec k_0$, but it does not look so in the diagram...

Nosferatu

14:07

hello

0celo7

hello

Slereah

Hello

Speaking of spaghettification

Nosferatu

how is everyone?

Slereah

Isn't there also the lasagna-state in neutron star physics

Like a monday

FenderLesPaul

For the first time this semester my GR group meeting is scheduled at the exact same time as my QG group meeting

now I know how Brad Pitt felt

ACuriousMind

14:12

@0celo7 Not exactly sure either

Slereah

time to make some sweet quantum gravity

0celo7

15:09

@Slereah how

you don't even know string theory :O

and now ACM has given up on ST

so sad

ACuriousMind

@0celo7 I haven't given up on ST. I've given up on learning anything about it from BBS. :P

0celo7

he's given up on ST :O

@ACuriousMind Lemme know when you embark on your next ST adventure

Hennes

15:32

Hums the chances of anything coming from Mars are a million to one.....

Slereah

@0celo7 String theory sux

boo

David Z

So, anyone else watching the NASA announcement?

Danu

@DavidZ Link plz

What was it about?

their "major" thing

ah, flowing water

Hennes

@DavidZ Trying to. I get about 5 seconds of stream per minute

David Z

LIVE NOW: Major Mars mystery revealed! Watch live on NASA TV & use #askNASA for questions: http://www.ustream.tv/nasahdtv http://t.co/BbbKOd4j8b

Tweeted by NASA on September 28, 2015 at 3:31 PM

Yeah, NASA is not very good at keeping a stream running

Hennes

15:40

Yup. Major overload on their servers though ?

David Z

No pun intended

Hennes

On the summers and ...
however....
before ... years .... has been......

pause

unable to explain

Danu

lol

Hennes

My 5 seconds per minute is holding....

David Z

I'm watching it on TV - BBC World, if anyone gets that

NeuroFuzzy

15:42

@Hennes I only saw your messages after @Davidz's "no pun intended" and was VERY confused for a second.

Hennes

No TV over here... To little control over the program (really, no pause, or watch when you want. People still watch that way?) and way too much advertiosing forcing you to continiously switch channels

David Z

They're showing an animation of the channels extending over the course of a Martian year

Hennes

In the past I used to use the VCR recorders. One to record, one to play whatever I was watching. But terrestial broadcasts have degraded so much that I no longer bother.

David Z

@Hennes yes, people still watch that way, pausing and on-demand viewing are luxuries :-P

Hennes

mutters 'pirate bay' and 'friends with portable harddisks' and 'ebook readers with thousands of book'.

David Z

15:45

Now showing a map of where these features have been seen on Mars - they have multiple locations

Hennes

Mow getting 3/4rd of tyhe stream.

Danu

Sigh... got a bit bored of it already :P

David Z

16:01

Well I think we got the gist

IMO Twitter is often a better source of information about these things

Hennes

Now at the 'is there life part'. Meh

Having water is a good thing though, we need it if (when) we go there.

Danu

@DavidZ Now that's something you don't hear every day ;)

David Z

Yeah, I don't know if what they're talking about is enough to be drinkable or usable for any practical purpose

Danu

@Hennes I'm calling that we're never going up there because of prohibitive logistics costs alone, let alone numerous other issues.

David Z

@Danu perhaps we should though. Twitter is a really good source if you follow the right people

Hennes

16:11

Meh, we just need more religion. And they will eventually colonise their eden.

Danu

@Hennes Finally, something sensible ;)

@DavidZ I'm not on Twitter

DanielSank

16:36

@0celo7 Cringe

0celo7

@Slereah literally the only correct thing

isomorphismes

@ChrisWhite It's definitely with the intent of getting two different answers.

@ChrisWhite That was more a comment about not being basis-free

Slereah

"HOW DOES OUR HAND ROTATE"

This seems to be an urgent question

ACuriousMind

@Slereah I think it's a robot/alien trying to pilot a human body.

Slereah

17:21

Possibly

NeuroFuzzy

18:22

Today I used $P_n(0)^2\sim \frac{n}{\pi}$, $\int_0^{2\pi} P_n(\cos(\phi))d\phi=2\pi P_n(0)^2$, and $n!\sim \sqrt{2 \pi n}n^n e^{-n}$ without having proved any of them. :(

($P_n$ being legendre polynomials)

0celo7

19:31

@NeuroFuzzy you dirty boy

skill patrol

19:44

Forgive me father for I have used without proof :P

0celo7

physics homework required a taylor series

what do people who haven't taken calc 2 do...

skill patrol

Fail

0celo7

@skillpatrol I'm trying to source the proof for this neutron scattering equation in my assigned reading...making me use it without proof is torture

skill patrol

Ask the experts on the main site pal.

Btw get used to that kind of "torture."

0celo7

if I want an expert to tell me I'd ask lang

although chances are, as an experimentalist, he doesn't know :O

skill patrol

19:50

Go for it

0celo7

/doesn't care

dmckee

20:08

Have you every wondered what it takes to get appointed to the Official Considerations Board of Physics.

I mean, is that like getting an endowed chair or something?

0celo7

what is that

skill patrol

Sounds...official ;P

dmckee

21:05

@0celo7 The guys who provide the official ruling on questions like

-2

Q: Can a sample of beta radiation be considered as the fabled philosophers stone?

Given that it is possible to produce gold in nuclear reactors (even if not economical), is there a natural source of beta radiation whose half life is similar to that of human lifetime and whose beta radiation can induce a change in atomic number in stable elements? From what I could find in ter...

radiation radioactivity

right?

I mean, someone has to do the considering, and to have only one answer it had better be someone official.

Mike Edenfield

someone in an ivory tower, one would presume.

Physics Meta

21:36

0

Q: design for up-down buttons

I am not entirely sure whether this can be asked here, however I will give it a go. I have seen that most of the SE sections have very pretty designs for the up-down vote arrow buttons, that are most of the times related to the subject the page deals with. Physics should pave the way for that, bu...

feature-request

0celo7

0

Q: Given the intervals of a punctured flat spacetime how to reconstruct the intervals of the complete flat spacetime?

A set $\mathcal S$ of events can be characterized as a flat unbounded spacetime through a function $s^2 : \mathcal S \times \mathcal S \rightarrow \mathbb R$ which assigns spacetime interval values to all pairs of events, and which satisfies certain additional properties. If one particular event...

special-relativity spacetime

@ChrisWhite How're the black holes today?

2

user54412

21:55

@0celo7 phdcomics.com/comics/archive.php?comicid=47 ;)

0celo7

:(

user54412

My next fellowship application is due in... 12 days :(

0celo7

What should I eat tonight?

Subway or Chick-fil-A?

You must decide, almost Dr. White.

user54412

there's a higher risk of vegetables at subway -- quite inappropriate for college students

0celo7

D:

I like veggies

user54412

22:01

TIL my campus stops serving salads at 4 pm sharp

0celo7

I could get a salad at the dining hall...but my stomach is already feeling funky. No need to exacerbate that.

@ChrisWhite You ready to meet that deadline?

0celo7

23:04

@ChrisWhite Got Subway

Nosferatu

23:14

ooh answered my 2nd one!

thank you for the catch @HDE226868

HDE 226868

@Nosferatu No problem.

Nosferatu

I fixed the statement in my answer to reflect that and on Custer's comment

the Cornell quote seems to shy away from the term themselves as well

0celo7

23:33

removed?

HDE 226868

@0celo7 I decided against starting a discussion. It had to do with liquid water on Mars.

0celo7

is there oil on Mars? can we deliver some freedom?

@DanielSank complicated QCD Color factor formula? at least this one has some info in the title

chmod 711 telkitty

Why is that only between 0-10 degrees Celsius that water is in liquid form on Mars? Atmosphere pressure?

obe

@0celo7 doing qft problem set, and I have a new one.

looks easy.

0celo7

pdf?

obe

23:44

you want the pdf?

0celo7

yes

obe

for 0celo7

0celo7

is that your GR homework

obe

yup.

it's a lot easier.

I can probably do it without help unless I'm retarded.

0celo7

the QFT one isn't hard either :O

obe

23:45

what are you trying to say D: lol

0celo7

(1) has a name

idk what it is off the top of my head though

@Slereah probably knows

I eagerly await your 1.3 (b)

obe

Do I have to draw it?

0celo7

that is what the problem is asking for

obe

Right, well it will not be impressive.

I do not know if I'm inept at drawing though.

0celo7

I also await 1.4

@obe isn't the QFT problem set due tomorrow?

or is it Wednesday

obe

23:59

@0celo7 the day after.

I haven't written anything down.

better do so.

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