The h Bar

Secret

00:00

For most classical things, they all have well defined causations thus a unique causal network can be drawn to describe them. Using this analogy, their causality is like a crystalline solid with an ordering

Meanwhile, possibly in some quantum systems, you have indeterminate causality where things are in a superposition of A cause B and B case A. These are like some kind of quantum state that are ordered

But can we have states where the causal network that describe it is stochastic and depends on some order parameters like an amorphous solid

or better, "liquid causality" where the underlying causal network keeps changing and does not have a settle form, similar to a spin liquid?

Sir Cumference

03:12

@Blue I'm pretty sure Abcd was joking

Or I hope (not trying to sound condescending)

vzn

04:15

@Secret try looking into (QM) "probability current" or probability fluid

Secret

04:44

Pretty sure a probability fluid is different from the notion where causal structure is dynamic

vzn

04:56

He just graduated from college and wants to be an astrophysicist. Oh, and he's 11 / cnn

↑ seems likely very interesting AMA guest speaker o_O

Jake Rose

05:20

Hey guys a question about SR. one of the assumptions of this is that you can't tell two inertial reference frames apart and that speed is just relative. But why couldn't you trace back to when one of the frames was accelerated? Then could you not deifniteively say that this frame was definitely the moving frame?

John Rennie

@JakeRose not necessarily. Both frames could have been moving and one frame decelerated to a stop.

Then the frame that experienced the acceleration would be the one that was stationary.

Jake Rose

So you couldn't tell if it was deacceleration or acceleration?

John Rennie

No

Jake Rose

Yeah I agree

So overall would it not be possible if you could trace back to all the forces which one was accelerating?

*moving not accelerating

John Rennie

Accelerating just means your speed has changed. You can tell how much the acceleration changed your speed, but you can't tell what your speed was before or after the acceleration.

Jake Rose

05:32

Oh I see

thanks for the help!

btw @JohnRennie experienced my first May ball

what a bloody party

John Rennie

@JakeRose :-) I never paid to go to a May Ball but I worked as security at a few of them

Jake Rose

Oh really how come? I had to leave town before I could work for any but hopefully gonna earn some quick money next year

Cows

finished v2 of code. It's in the cloud now

John Rennie

You just have to know the organisers. The deal is usually that you have to work for a few days setting everything up then again afterwards to clear everything away, then for half the night as security. Then you get to spend the other half of the night as a quest.

Jake Rose

@JohnRennie did you do pure physics second year?

Pretty good strategy

John Rennie

05:36

I don't recall being paid though

Jake Rose

May balls are extortionate

nearly cried after seeing what was left of my student loan

John Rennie

@JakeRose yes I agree. I was pretty broke as a student and paying to go to a ball was way outside my reach.

Just paying the rent on my digs was a stretch :-)

Jake Rose

The May balls employ everybody now adays. Unless you're on the committee you're strong paid (even if it's pretty poorly)

John Rennie

I guess that's a lot more professional, but it seems a shame

Jake Rose

Tell me about it. Magdalene accommodation is certainly not the best.

It's because all of the food and drink staff (not including the private vendors) are students. So it's probably a few too many people to let in.

John Rennie

05:38

No student accomodation is great. My brother went to Imperial College and some of the places he stayed were so bad the rats had left.

Cambridge is actually not bad compared to a lot of places.

Jake Rose

Imperial seduce you with the really fabulous first year accommodation then throw you out for the rest

Oh no trust me I count my lucky stars with my accommodation even if it is a tad expensive

Did you do pure physics in your second year? Or a bit of chemistry too?

John Rennie

I did advanced chemistry and ordinary physics in my second year. By then I had discovered quantum chemistry and decided that was what I wanted to do.

Jake Rose

Ahhhhh. Was it split into physics I /II and similarly for Chem back then?

John Rennie

Yes, for both physics and chemistry you had an advanced course for people who planned to specialise in the final year and an ordinary course for people who just wanted some knowledge but weren't going to specialise.

So I did advanced chemistry then all chemistry courses in my final year. The ordinary physics was very useful though and I'm glad I did it.

Jake Rose

Ah gotcha.

John Rennie

05:44

I would have been tempted to do both advanced chem and advanced physics but the timetable didn't allow it.

Jake Rose

I'm always interested to see what people who do a physics a chemistry and then do other random one

Could yo you part II physics without part I?

Cows

@JohnRennie what inspired you the most to get into Quantum chemistry

John Rennie

@JakeRose no

Well technically you could go to the lectures and sit the exam but I suspect you'd find it far too demanding

@Cows I've always been interested in applied science i.e. relating it to the real world, and quantum chemistry seemed like it did exactly that.

@JakeRose bear in mind my knowledge of the Cambridge courses is 35 years out of date :-)

Cows

The thing that makes me wish I really liked chemistry a lot is the fact that one could use it to create medical drugs. This to me is super magical.

I mean I like to see chem in action but I am horrible at it lol

Jake Rose

@Cows organic chemistry is da bomb. Just fun hexagons.

I found chemistry an overall pretty easy subject. At least first year it's a bunch of hand wavy-mess

Cows

05:58

@JakeRose I tried studying Ochem on my own some time ago, failed like a boss lol. But yeah Ochem and BioChem are essential to human survival

Captain Bohemian

chemistry in university level can only be easy for people with amazing memory power

Jake Rose

I found biochhem one of the more boring bits. Synthesis is what I found most interesting.

John Rennie

@JakeRose I agree. But quantum chemistry is very different. You're calculating molecular wavefunctions and from them the properties of the molecules.

2

Jake Rose

You can get through a surprising amount of organic with just a good conceptual understanding. Most of the basic mechanisms are just common sense then rather than memory.

Cows

what makes me marvel the most about life is drug action pathways

Jake Rose

06:01

Now geology. Theees a subject which was fun.

Cows

I can't even imagine how people think about these things

Captain Bohemian

my experience with chemical course is there are too many terms to remember in time so that I often don't know what the teacher is talking about when they intersperse their lecture with multiple chemical terms.

Cows

@JohnRennie not that I will understand :P , but what is planck data saying?

John Rennie

@Cows there's a good summary here

Jake Rose

I think our lectures went through them pretty well. If we talk about something we tend to talk about the idea more so than the name so you can still get by with knowing minimal terms. Sadly being a good (insert science branch here) does usually involve a bit of name learning.

Novalium Company

06:14

Hello everybody!

I've been working on my game recently and haven't got much time, but when I finish it, I'll be back regularly :-)

Sir Cumference

Howdy all

Cows

Helloooooo :-D

Sir Cumference

What's up?

Cows

just chillaxing

2

user2236

Chillaxing

:-)

user157860

07:28

@JohnRennie, hi, could you confirm your comment and give a judgement on the answers I got? I also found your formula $ v = \frac{at}{\sqrt{1 + (at/c)^2}} $ here, which one applies to my example? Thanks

P.S. When you can spare some time, could you give a short answer specifying the difference among those formulae?

John Rennie

@user157860 The two situations are very different.

user157860

which one applies to my case?

John Rennie

Suppose you have a spaceship with a steady acceleration i.e. it's firing its rocket motor with a steady thrust as measured by the people on board. That's when you get the equation:

$$ v = \frac{at}{\sqrt{1 + (at/c)^2}} $$

This happens because (a) time is dilated on the spaceship and (b) length is contracted on the spaceship.

user157860

So, I need the schwartzild radius? could I find the final velocity just finding the PE ?

John Rennie

So the observer on Earth and the observers on the spaceship disagree about the length of a second and a metre.

For the black hole you need to calculate the trajectory of a freely falling object.

user157860

07:34

No, I do not mean a black hole, just a massive planet or a neutron star

Cows

@user2236 :)

John Rennie

This is a fairly standard problem. In general you have to solve an equation called the geodesic equation, but for the Schwarzschild metric the symmetry allows you to take a number of shortcuts and you get the equation:

$$ v = \left(1 - \frac{r_s}{r}\right)\sqrt{\frac{r_s}{r}}c \tag{1} $$

Where $v$ is the velocity and $r$ is the radial distance as measured by an observer far from the black hole.

user157860

Consider the case of a neutron star, there is no Sr, a is just 3 Km/s^2, can I just add the PE and from the total, through SR work out the new velocity?

John Rennie

No

I assume you're asking for the velocity as measured by an observer far from the black hole, and that will be given by the same equation as for a black hole.

user157860

R is 10^8 cm,

John Rennie

07:40

Beta Decay has considered the case of a constant acceleration like the spaceship I described, though I don't recognise the final equation they got. It might be correct and just be in a more complicated form than the one I'm used to.

@user157860 the Schwarzschild metric describes the spacetime gemoetry outside all non-rotating spherical objects, not just black holes. So it applies to a neutron star.

user157860

So, I cannot just add the PE to the KE of F?

John Rennie

No

Neither PE nor KE are well defined concepts once you have to take spacetime curvature into account.

Computing the motion in curved spacetime is a lot harder than that.

user157860

so, the best way is your formula $ v = \sqrt{\frac{r_s}{r}}c \tag{2} $ ?

John Rennie

Careful, that's the velocity as measured by a shell observer i.e. someone hovering at a distance $r$ from the black hole.

But shell observers have their time dilated so the velocity they measure is not the same as the velocity an observer far from the black hole would measure.

user157860

Yes, that's what I need I am standing at hf (10^11 cm) where I want to record the velocity

John Rennie

07:50

@user157860 yes, in that case use $$ v = \sqrt{\frac{r_s}{r}}c $$

user157860

but does that formula take into account v at 10^12 cm? How can I fit that in?

John Rennie

It should be possible to show that this is approximately the same as the velocity you'd calculate using the change in PE as long as your far from the event horizon. I must admit I've never tried that.

user157860

Adding PE I found .9918 c, can you work out the value with your formula?

John Rennie

The equation I gave is for an object that falls freely from infinity starting with zero velocity i.e. at every point its speed is equal to the escape velocity. It's possible to do the calculation for an object that starts with a non-zero velocity i.e. it's speed is greater than the escape velocity but the resulting equations are more complicated. I don't remember them offhand though I have them somewhere.

@user157860 I'm not sure what you're asking. Your diagram is so cluttered I can't make out what you're trying to do. Can you explain it simply?

user157860

a comet F is at 10^12 cm from a massive star heading toward it at .99c it has 7.09 masses and 7.09-1 energy. it travels to 10^11 cm toward the star where it would reach c (+.01c), but considering relativity what is its actual speed when it impacts my ship at 10^11 cm from the star?

Secret

08:04

0

Q: Can particals such as tachyons and anti matter be detected looking backward in time?

Figuring moving faster than light goes forward and backwards in time hypothetically, maybe thats why tachyons and or anti matter cant be seen or studied because we are conducting experiments to the here and now, present, when in our reality it wouldnt be seen in present for that fact alone that m...

quantum-mechanics

If tachyons are detectable, it will be basically indistinguishable from some correlations in the data, since we can only look in the present direction below the speed of light

John Rennie

@user157860 I'm busy for an hour or so, but that's not a hard calculation to do.

Secret

as well we will expect a lot of chrenkov radiation to be in the vicinity

user157860

@JohnRennie, thanks, take your time, ping me the answer.

or, ifyou feel like it, post a short answer just with the right formula and the result

Secret

scientificamerican.com/article/what-is-known-about-tachy

old scientific american: Seems there is nothing in our imagination that cannot be produced by quasiparticles

Physics Meta

0

Q: How to write mathematical expressions in questions using android devices?

I posted a question at Physics Stack Exchange site, and I uploaded a photograph of the calculation I had done on that. But, I was asked to write all my calculations in the question(and not in the photograph). So, How to write mathematical expressions in questions using android devices?

support feature-request mathjax tex formatting

Secret

08:16

43

Q: Status of experimental searches for tachyons?

Now that the dust has settled on the 2011 superluminal neutrino debacle at OPERA, I'm interested in understanding the current status of experimental searches for neutrinos. Although the OPERA claim was a fun puzzle for theorists trying to find explanations, the claimed scenario wasn't anything li...

special-relativity particle-physics experimental-physics faster-than-light tachyon

Actually, what exactly do a tachyon signal look like (other than splitting into double images)?

Causality is overrrated, like everything else human

armaghplanet.com/blog/what-ever-happened-to-tachyons.html

> I have read some of the rationales and product descriptions on sites advertising this sort of junk and found only scare-mongering nonsense, aimed at extracting money from the unwell or anxious, proving that while space has a speed limit, there are no limits to folly and dishonesty.

There is only one thing that has the size of a proper class: Human Stupidity

Stupidity has no bounds

and bounds has no stupidity

and 2+2=5

Physics Meta

12:02

0

Q: Question deleted without a trace and without notice?

I'm somewhat annoyed that one of my questions just vanished like it never existed. Shouldn't there at least be some kind of notification in my account left? And why not keep questions that don't have an answer, yet? The question was related to quantum scars - a relatively recent research topic, w...

discussion

enumaris

16:01

hmmm

danielunderwood

16:14

mmmh

enumaris

had some insomnia last night

so now I'm pretty sleepy -.-

Sir Cumference

Huh, same

enumaris

we need a nap pod here...

Sir Cumference

Went to bed at 1, next thing I know it's 6:30...

enumaris

like a nap room with several nap pods...

6:30 and still awake?

Sir Cumference

16:19

Yeah, got classes :(

enumaris

Mine wasn't as severe lol. I think I was mostly unable to sleep cus it was too hot.

still...quite sleepy...

Sir Cumference

This is my life now

John Rennie

That's a lot of Starbucks coffee at $$$ per cup ...

Sir Cumference

@JohnRennie It's cheaper when it's affiliated with your uni

John Rennie

Cheaper still to make your own :-)

Sir Cumference

16:28

Fair :P

John Rennie

The amount of coffee I drink I would be bankrupted if I bought it all at Starbucks :-)

3

danielunderwood

If you make it at home, you risk it becoming an expensive hobby lol

Though I suppose not as expensive if you drink a lot

Sir Cumference

wait wtf

James Webb was postponed by three years?

John Rennie

@SirCumference huh? Jesus.

Semiclassical

another delay? daaang

Sir Cumference

16:39

2021 ;-;

enumaris

Who James Webb?

John Rennie

Yes, it appears to be true

Still, better safe than sorry I guess. If you discover a problem after it's launched it's a long trip to go and bring it back :-)

Sir Cumference

Since delays should get less likely closer to the launch, most astronomers in 2018 believed the expansion of the schedule was slowing, but by early 2020 new measurements indicated that it was actually accelerating.

2

John Rennie

:-)

vzn

← know the feeling, maybe will solve collatz on same day webb telescope launches (cf xkcd on it too) :| en.wikipedia.org/wiki/Collatz_conjecture xkcd.com/710

Sir Cumference

16:49

@enumaris Space telescope, successor to Hubble

enumaris

hmmm

Sir Cumference

Was supposed to come out this year, but ah well

enumaris

experiments are always like this lol

the NIF took forever to get going

(and never actually achieved legit "ignition")

the LHC had Helium tanks rupturing or something...

LIGO went through it's entire first phase without any detection events (had to wait for advanced-ligo)...etc...etc...

Dunno if the space-based LIGO is even gonna be built

I think it's called LISA

danielunderwood

LHC also had a squirrel problem or something like that

enumaris

I had a UCLA prof quit his professorship to go work on a European experiment on Fusion (can't remember the name)

Don't think it's produced fusion yet...

danielunderwood

16:56

I think space-based everything should be built. We do so much work just for vacuum systems

Though I imagine it would be an inconvenience to launch/retrieve all the associated equipment

Semiclassical

space elevator

vzn

(googling) there have been various significant failures at LHC over the years, think a documentary mentioned one of them: in 2008 was a helium leak + short circuit! + magnet damage. didnt exactly seem to announce this but repairs for that incident alone were around $29M. just part of Big Science. reuters.com/article/us-cern-repair/… press.cern/press-releases/2008/10/…

enumaris

I remember the news about the Helium leak

danielunderwood

Ahh it was a weasel, not a squirrel

> There have been previous incidents, including one in 2009, when a bird is believed to have dropped a baguette onto critical electrical systems.

> Nor are the problems exclusive to the LHC: In 2006, raccoons conducted a "coordinated" attack on a particle accelerator in Illinois.

Actually they say it may have been a marten instead of a weasel

enumaris

17:12

o.o

danielunderwood

I'll just assume birds dropping baguettes is a common thing in the area

John Rennie

The only big problem was the faulty soldering on the magnet connections, so when they tried to ramp up the power to max there was an explosion.

That caused the helium leak and magnet damage

That wasn't really Cern's fault as a sub-contractor was responsible for those joints and the subcontractor screwed up.

enumaris

gotta check those subcontractor's work tho

so it is still CERN's fault

aaaaaand comparison made

Cows

17:47

hehe :P

I look very sharp and formal today

nice!!

Eulb

lo

l

@SirCumference howdy

enumaris

what up with all the removed

Cows

hehe

:P

I was just mentioning how sharp and well dressed I was today

I am actually dressed like a corporate guy

:D

enumaris

nice nice

I hate dressing up

even though my work is ok with jeans and a dress shirt type deal

I still hate it

not dress shirt...button down shirt

I should switch to polos...

it's getting way too hot to wear button downs

Cows

yeah, I am trying to start taking care of myself and how I look and all again lol

enumaris

18:02

if you like that stuff, more power to you :D

I just feel totally uncomfortable in a suit and dress shoes...

Cows

I bought some slacks(dress) and full long sleeve button down shirt and shoes

enumaris

can't imagine being a girl and wearing heels all day...my dress shoes already hurt D:

Cows

One for each day of the week lol

enumaris

nice :D

I bought slacks but I never wear them cus jeans are acceptable at my work place lol

Cows

yeah, I don't know how girls wear heels. Does things must hurt

enumaris

18:04

and I got nice dress shoes but they hurt my feet so I also don't wear those >.>

yeah and then some girls get that weird curved toe... (is that due to heels, or is that genetics? I'm not sure, but it seems like it's due to heels...) D:

Cows

yeah

lol

danielunderwood

I work from home and end up in gym shorts and a t shirt most of the time lol

Anonymous

@enumaris What type of curved toe?

enumaris

@Blue like that big toe that curves towards all the other toes...

there's a medical name for it but I can't remember what it is

Anonymous

@enumaris Bunions?

danielunderwood

18:14

Oh I thought you were talking about the pinky toe. That one's definitely genetic, but no idea about the big toe

enumaris

uh...maybe bunions...

Anonymous

"There are many theories about how bunions develop, but the exact cause is unknown. Factors likely include:

Inherited foot type
Foot injuries
Deformities present at birth (congenital)

Experts disagree on whether tight, high-heeled or too-narrow shoes cause bunions or whether footwear simply contributes to bunion development.

Bunions might be associated with certain types of arthritis, particularly inflammatory types, such as rheumatoid arthritis."

enumaris

Apparently there's also Hammer Toe which has a similar kind of thing

Anonymous

health.harvard.edu/diseases-and-conditions/…

Anonymous

This looks interesting ^

Anonymous

18:16

"A bunion is most likely to develop when susceptible feet are repeatedly squeezed into narrow, pointed-toe footwear. "

enumaris

but it seems like a bunion is more close to what I was thinking of

Cows

What , there is research on this Thanks God

enumaris

lol

Anonymous

So it's less due to the high heels and more due to the pointed footwear :P

enumaris

It just seems to be more of an issue with girls (not that I've done any thorough research on the matter lol)

A lot of heels are pointy

Anonymous

18:18

But then your high heels will force the front end of your fit to slide more into the pointed footwear and thus squeezing it even more. So sort of indirectly related to heels

enumaris

Men's dress shoes are somewhat less pointy, though there are some pointy ones out there too

Anonymous

@enumaris True

Anonymous

I tried wearing my mom's heels once. It hurts like hell and more so, given that I have flat-foot

Anonymous

I should buy a bigger size for testing someday :P

Avnish Kabaj

@Blue thank gawd I'm not the only one

danielunderwood

18:22

I don't even understand how they do the really pointy ones that are basically a triangle at the end

Like my shoes hurt if they're slightly too narrow

Anonymous

@AvnishKabaj Pretty sure every teenage boy has done that at least once :P

enumaris

I can't wear European shoes...

they are too thin in front

Anonymous

I can't even wear thin jeans (those which stick to your body). Feels like they're choking my legs

Anonymous

I prefer the broader ones, especially near the legs

enumaris

you mean skinny jeans?

Anonymous

18:24

@enumaris Yep

enumaris

yeah I'm not a fan of those either lol

Cows

lolz

enumaris

astonomy stack exchange seems so small

but there's a lot of answers for how many questions it has

nothing to answer...

not fun

gateprep

18:44

Consider the following stress state imposed on a material:
� = [
ͻͲ ͷͲ Ͳ
ͷͲ −ʹͲ Ͳ
Ͳ Ͳ ͳͶͲ
] MPa.
If the material responds elastically with a volumetric strain � = ͵.ͷ × ͳͲ−ସ, what is its
bulk modulus?
(A) 150 GPa (B) 350 GPa (C) 200 GPa (D) 400 GPa

sorry

file:///C:/Users/RAJORSHI%20KOYAL/Downloads/GATE-Metallurgical-Engineering-Paper‌-2018.pdf

enumaris

wut

are homework problems allowed in chat? They aren't generally allowed on the stack exchange, but I dunno how different the rules are for chat.

gateprep

drive.google.com/file/d/15AUTJlHcSAzIt4zBjxlDqpZ8lOgzlKhU/view

check question 40

Its not bad to discuss homework problems

Anonymous

@enumaris Chat doesn't have any rules against homework, but we probably need one

enumaris

alrighty

Well, I dunno how to solve that problem lol

gateprep

No homework problems are important

Why should we process such rule

Discussion is important

At least we may segrate the chatroom sif necessary but one should be meant for Homework

Anonymous

18:50

Problem Solving Strategies

General chat for high school physics. For MathJax see meta.sta...

Anonymous

That room is specifically meant for those type of homework problems

Anonymous

But of course, you need to show your effort in trying to solve the problem. Or else no one would feel interested in helping

gateprep

Yes but i dunno how to deal with tensors..

Had this been young's modulus and linear strain there ud not have been any problem

Novalium Company

Evening everyone!

danielunderwood

From the little bit of stress/strain tensors that I've seen, you can just treat them as a collection of numbers sort of like a matrix

gateprep

18:55

yes now how to approach

Novalium Company

@Blue Hi, how are you doing?

Anonymous

@NovaliumCompany Hey! :) Unfortunately very busy these days :/ Packed with classes and lab assignments

Anonymous

I'm in the process of writing my first (two) papers. So that's a bit enjoyable, although I'm not getting much time to invest in that either.

Anonymous

How's it goin for you?

gateprep

19:11

@Blue Since how long have ur dept opened after vacation?

Sorry

Since when have u been going to JU after vacation?

Anonymous

@gateprep Since last week

gateprep

Today the second half was off right..

Hakim Douib

hi

Anonymous

@gateprep Nope. We had lab classes as usual

gateprep

Ohh Okk...

Novalium Company

19:13

@Blue I'm doing pretty good thanks. The game is going amazing and will be launched on Google Play after a week (maximum). What are you writing about? :-)

Anonymous

@NovaliumCompany Awesome! Will you make it free? :P Oh, and my first paper is on based on certain site percolation properties of square lattices which haven't been investigated before (very little literature available on it). One of the main parts is the variation of the percolation threshold in the infinite limit with diagonal connection probability. The other paper is mostly the circuit decomposition and simulation of the popular quantum algorithm for the solution of 4x4 linear equation systems

Anonymous

We're will try to extend it to higher dimensions though (in v2), but probably that won't be on arXiv until December

Novalium Company

Wow! Sounds complicated. The game will be free yes :D

Anonymous

@NovaliumCompany Cool! I'll download it :)

Anonymous

@NovaliumCompany They're complicated but I'm deeply grateful for the amount of help I received from some of the Stack Overflow and QCSE guys

Anonymous

19:20

It wouldn't have been possible without them

gateprep

My qquestion

Novalium Company

@Blue The stackexchange community is amazing, I know.

@Blue I wish you luck with the papers and I know you'll do it perfectly! :--)

Anonymous

@NovaliumCompany Thanks. I'll share when it's done :)

Novalium Company

That was a question requiring negative answer, and I don't like negativity :D.

@Blue I'm out for now, see you some other time :-)

Anonymous

@NovaliumCompany I'm trying my best to avoid introducing unnecessary jargon and make it as simple as possible :P Pretty sure you'll be able to read it

Anonymous

19:24

@NovaliumCompany Goodnight!

Novalium Company

@Blue I'll try my best.

Avnish Kabaj

@Blue I was 7 or 8

Weirdo

:P

Anonymous

@AvnishKabaj I used to apply my mom's lipsticks on my face at that age.

Anonymous

And by face I mean the face and not lips only :P

enumaris

hmmm

Avnish Kabaj

19:35

@Blue I ate lipstick

It was so tantalizing I bit a chunk off

Anonymous

Eww. Lip glosses taste better

Anonymous

Lipsticks taste pretty bad

Avnish Kabaj

Have you ever snorted chalk dust?

Like they snort cocaine in movies

I did

Anonymous

@AvnishKabaj Sure. I like the smell, when in small amounts :P

Anonymous

But haven't snorted cocaine yet XD

Avnish Kabaj

19:37

Waaaait

I meant I snorted chalk

Anonymous

@AvnishKabaj What type of chalk ?

enumaris

chalky chalk

Anonymous

I really want to buy some of those edible lipsticks though

Avnish Kabaj

@Blue the white chalk used by teachers

@Blue the candy ones?

Anonymous

@AvnishKabaj society19.com/…

Anonymous

19:43

"Bite Beauty’s edible lipstick line specifically uses twelve edible oils and freshly-pressed fruits to give the lipstick a delicious flavor; makes it that much better when you discover you’ve got lipstick on your teeth (which hopefully your friends make you aware of ASAP). "

user75916

guys please help me out

ana v used to claim that a black hole cannot absorb photons with wavelength greater than the black hole size. but does that mean that a common near black body object cannot emit photons with wavelength greater than their size? this seems wrong to me

Avnish Kabaj

@Blue how do you even know about this

Anonymous

@AvnishKabaj You get to know automatically when you have been randomly googling for edible beauty products, for the past few years (I'm pretty sure anyone would be traumatized if they see my browser history XD)

Avnish Kabaj

@Blue ok man

That is weird

Alex K Chen

Suppose I fill up a U shaped tube with water on one side and mercury on another side (the two sides are connected). Why the pressure at same heights must be same inside the tube?

Avnish Kabaj

19:51

@AlexKChen the forces need to be balanced in equilibrium

enumaris

20:01

most generic answer possible :P

I'm bored

dmckee

20:16

@AlexKChen In general there is no need that it should be. The requirement comes when you limit yourself to static conditions.

(Of course, in the case you name, the static situation comes in to being very quickly, but there is none-the-less briefly transient behavior.)

The argument gets made many ways, but it all come down to requiring that any given element of fluid be in equilibrium.

Now, before continuing let me ask you a question (or really two): (a) What is pressure? (b) What causes pressure in a fluid at the microscopic level?

enumaris

he has a different question asking about the nature of pressure

Sid

@Blue better than injecting it probably

And the nose hurts. So, yeah. Not a great feeling to be honest

dmckee

@enumaris I can see that from his questions on the site. But the right starting point is from the microscopic causes.

enumaris

20:33

@dmckee my only point was that asking him what is pressure might not help too much since he doesn't seem to understand the concept of pressure itself that well yet.

dmckee

@enumaris This is in the nature of one-on-one teaching. You have to probe carefully what is and is not known. How else could I know the right place to start?

enumaris

alrighty

Avnish Kabaj

@Sid o.O

bolbteppa

21:39

@vzn Lisi even in the comments quantamagazine.org/…

Right now I think I found a way to see why the Cartan-Killing form arises from Lie groups, I might be lying to myself, I want to, it's tempting, and I skipped a few things, and even if it's a lie it's still kind of okay,

The temptation to fool oneself is there at every second

motls.blogspot.com/2018/07/…

2

Things like this are a public service, scaring the heck out of you, even if it's caked in non-physics comments which one can disagree with (vigorously)

Problem Solving Strategies

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