The h Bar

Physics Meta

12:17 AM

-2

Q: Can a new Pysics SE 093 for beginners be created?

Can a simple physics SE be designed for people who have little or no training who are enthusiasts none the less? That way moderators can instant migrate lessor questions there instead of instant close? Consisting Lamond of answers and questions it would provide a new Physics093.beta for beginners...

obe

@ACuriousMind I need your input on something

I feel like I learn better when I take notes in latex versus with pen and paper but all these modern studies claim that writing notes down (instead of typing) is better for learning.

dunno which to choose

do I listen to scientific studies or my own experience?

ACuriousMind

@obe Your own experience, of course. Consider whether your feeling is actually backed by facts, though (you might feel that you learn better but not actually produce better results, for instance).

obe

I think the reason is because when I type things I'm constantly re-reading them to see if I made any typos or mistakes, which is a form of repetition (helping me retain the information better) where as when I write I don't even re-read except for when I'm reviewing for a test or something.

also because my handwriting is the worst xD

I suppose those are facts to back up my experience so I'll type. Thanks :)

Bernardo Meurer

12:34 AM

Does anyone here know black magic? I have an Analysis exam tomorrow

ACuriousMind

@BernardoMeurer Relax :)

dmckee

@KyleKanos If I might say, I don't know the class of instruments at issue in physics.stackexchange.com/questions/308379, but my impression of the question is that the OP wants someone to give him step-by-step instructions for the particular tool in front of him.

In other words that this is a no-effort 'do my thinking for me' question.

Perhaps I'm wrong about that, but in that case the OP is doing a fairly poor job of communicating.

Bernardo Meurer

@ACuriousMind On a realist scenario I get 13/20, which is a passing grade

So i think I will be okay

Unless my asshole prof throws in some black magic question, like one year where to solve a primitive you had to know the derivative of the arctanh x

dmckee

@BernardoMeurer Using the exponential forms you can recover the trig and hyperbolic primitives long hand if you have to. But it burns up a lot of page and clock time.

Bernardo Meurer

@dmckee it was basically $$\int\frac{1}{1-u^2}du$$, that's $\tanh^{-1}(x)$

That was after you did some usub that I no longer remember, but that shouldn't matter

Problem is, we didn't even learn hyperbolic trig functions, lol

dmckee

12:43 AM

I never learned them either.

Bernardo Meurer

What are they useful for anyway?

dmckee

So I was reliant on those exponentials forms the few times they came up.

Anon234_4521

Can confirm that up to calc 3 we saw and glazed past them. Would probably learn them later if I kept going.

Bernardo Meurer

@dmckee How would I solve that having no clue that is has anything to do with the arctanh?

@Anon234_4521 They seem to be this hazy mathematical tool that everyone knows about yet no one uses :P

dmckee

@BernardoMeurer They show up in relativity (the Lorentz transform can be written that way) and as the general form of the wavefunction in classically-forbidden regions in SE problems.

ACuriousMind

12:45 AM

@BernardoMeurer You wouldn't. solving integrals is all about memorizing solutions, it's boring and I'll never understand why the people at math.SE seem to think it's an art :P

Bernardo Meurer

@ACuriousMind Lol :P

@dmckee I see, that's cool

dmckee

@ACuriousMind The art, such as it is, lies in solving as many integrals as possible after having memorized as few primitive forms and methods as possible. AKA the art of being a lazy, but clever bum.

6

Anon234_4521

In their defense, if you're solving the integral then you're not memorizing and using the solution. Some people like the process of determining how they should go about solving an integral, taking a derivative, etc. It's one of the reasons people find math fascinating; i.e. they get to feel smart, I guess.

Bernardo Meurer

Integrals are like picking wheat

No one likes it, but without it we can't have shit beer

Kristina L

Hello! In my physics class, we are beginning to learn about dark matter, and I asked whether or not dark matter existed only in the vacuum of space or if it was present in other parts of the universe, like on Earth. He said that it acts kind of like a ghost in a way and moves through Earth. Is this a good description? And if so, why does it do this?

Bernardo Meurer

12:58 AM

@ACuriousMind Since your heart is made of dark matter why don't you answer this one?

ACuriousMind

@KristinaL Since we don't really know what dark matter is yet no one can answer that.

Kristina L

Awh dangit. How do we know that dark matter exists in the first place? Is it just so the math adds up?

@ACuriousMind

Bernardo Meurer

@ACuriousMind You need new facebook pictures man, stalking you is boring

ACuriousMind

1:14 AM

14

Q: Is there evidence of dark matter in our galaxy?

Is there evidence of dark matter in our galaxy? How can we measure this, say, how many percent of the center of our galaxy is dark matter? I did not find the answer in the question What's Dark Matter and Who Discovered it.

astrophysics dark-matter

Bernardo Meurer

@ACuriousMind Can you bring Chris White back please?

ACuriousMind

@BernardoMeurer I'm afraid Summon Chris White is not on my spell list

Bernardo Meurer

@ACuriousMind :(

You know, the other day I was doing something with Boost's Multiprecision library

and it was hell on earth to work with

and I just missed having Chris White telling me I was a shithead for using Boost at all

So then I just switched to GMP on pure C to make him proud

Kristina L

Thank you @ACuriousMind

Bernardo Meurer

but then the project got too boring even for me and I went to have a beer

Sir Cumference

3:03 AM

@JohnRennie I'm more surprised that no one in the history of this chat has suggested that...

Sir Cumference

3:31 AM

@thoughtforfood Please don't bring politics here

7

Jan 12 at 8:37, by John Rennie

In the mean time please restrict discussions of politics to the Haven't You Got Anything Better To Do But Talk About Frakking Trump Stack Exchange

ACuriousMind

→ 3 messages moved to Trash

thought for food

ok np

David Z

@ACuriousMind I suppose we can consider it official policy to keep politics out of this chat room, then

thought for food

as of now

ACuriousMind

@DavidZ At the very least the sort of politics where the first sentence involves the word "troll", yes.

David Z

3:37 AM

@ACuriousMind good call

thought for food

Ok, sorry.

Have you guys seen this?

6

Feel free to move it to the Trash :P

vzn

Quantum Computing Progress Will Speed Up Thanks to Open Sourcing / Singularityhub

> This might be described as the probability a qubit is either 1 or 0, but it's actually more subtle than that and relies on a property intrinsic to quantum physics that is impossible to emulate using simple probabilities.

↑ (!) lol cites smbc/ aaronson cartoon, talk about "pop science"...! o_O

ACuriousMind

Please cast flags only on actually offensive content.

vzn

?!?

Meet the scientists affected by Trump’s immigration ban / nature

ACADEMICS AGAINST IMMIGRATION EXECUTIVE ORDER / notoimmigrationban.com

thought for food

3:57 AM

@ACuriousMind the system sent me an invitation to the Trash room?

Better to error on the side of niceness? @DavidZ

David Z

@thoughtforfood I'm not sure what you mean

thought for food

You said it was a "good" call.

"Good" in what sense? @DavidZ

David Z

@thoughtforfood In the sense that discussions of politics where the first sentence involves the word "troll" are not appropriate here

thought for food

Like I said

:-)

vzn

4:15 AM

@DavidZ science is made by humans. (hence) sometimes theres a fine line )( between science & politics.

thought for food

That's exactly what this president intends to test.

For the next 4 years.

vzn

@thought hi welcome, havent seen you around in here, what brings you to the room?

thought for food

Just browsing :-)

vzn

@thoughtforfood noticed you cited notoimmigration.com. & mentioned 0celo7. howd you notice him?

thought for food

4:31 AM

He's a legend.

vzn

@thoughtforfood really? how so? did you ever chat?

thought for food

Yup..he's out spoken and generally misunderstood.

In real life I know many people like that.

Sir Cumference

Back

Oooh, neat, a superstar :D

Howdy @Kaumudi.H

user228700

@SirCumference Hi :-) Wadup?

Sir Cumference

Nothing much, just studying right now

You?

user228700

4:42 AM

Same.

Secret

Last night dream (h bar section):

In physics stack exchange, I asked a question concerning the physics of powder game. I then get banned from h bar for 60 days by N(forgot). Later on, a mistake was found. David Z then commented I should wrote a small infographic explaining the intent of my question and N(forgot) will understood and unban me. Meanwhile, it seems some users are taking advantage of the situation. They (a user named Doctor and (forgot)) impersonate as me by changing their display name to Secret, and wrote some trollish comments. N(forgot) was initially fooled and responded that it is my choice to (forgot). Late…

user228700

Clearly, you spend too much time hereabouts :-P

Sir Cumference

I remember a weird dream I had, where this was an actual bar and 0celo was the bartender

But he wouldn't serve me a drink unless I solved one of his riddles, which was a math problem involving hieroglyphics.

user228700

If anything, Bernardo should've been the bartender.

Sir Cumference

^

obe

4:50 AM

@SirCumference I had a similar dream too.

how did he look in your dream? lol

Sir Cumference

@obe Like revolver ocelot :P

obe

lmao

Sir Cumference

I do recall that me and a few others here had to escape from the stack exchange network. HDE was there and had some weird portal to space, so someone else and I used it to escape to Jupiter

obe

in the dream?

Sir Cumference

John Rennie and ACM tried to strike us down with a giant laser

Yep

I guess that's what happens when I'm on this chat too late

obe

4:52 AM

was I in it?

Sir Cumference

Don't recall the dream too much :/

obe

damn

Sir Cumference

I think ACM was trying to show me that it was physically impossible for me to survive, but I escaped anyways

user228700

I am also annoyed that I may not have been present--you should've seen me eating or cooking or something. Food.

obe

reading through old chat logs, some conversations I bookmarked from before are really funny xD

Sir Cumference

4:56 AM

I had this dream that my professor was a snake, but because I couldn't speak Parseltongue I failed the class

obe

did the other students know how to speak it?

and that must have been a long dream since a class would be like 3 months long.

Sir Cumference

@obe Yep

Secret

Dreams spanning more than one day (in the dream's perspective) is quite common for me. It is quite interesting how in real life only a few hours have passed

obe

I remember the last time we had a dream conversation

Sir Cumference

You ever have a dream where something really good happens, but then you wake up and realize it wasn't real?

obe

5:02 AM

Jan 13 '16 at 22:57, by FenderLesPaul

I had a dream that @0celo7 was touching me relatively

Sir Cumference

@obe What the hell?

obe

taken out of context ofc. xD

lmao

oh wtf lol

Jan 13 '16 at 22:58, by FenderLesPaul

@0celo7 just told me it wasn't a dream

Secret

Very rare for me nowadays. My real life is quite steady atm, thus via Mechanism 1, my dreams tend to do things opposite to it.

Sometimes, I am aware I am dreaming thus I know whatever too good to be true thing is not real

Having said that, I once have a buffet dream where I have ate the best ever buffet (I cannot believe how my brain managed to simulate all the taste. The oxtail soup is the best one I ever had)

obe

@SirCumference or the opposite

most of the time it's something really bad for me.

but unreal ofc.

Secret

5:19 AM

Last night dream (Harry potter section):

In the Warner Bros Studio set for the Hogwatz grand dinning room (where there are now beds filled in it). A female professor (resembles professor Minerva McGonagall) taught the class some spells. Later on, professor Remus Lupin entered the hall to taught the kids some other spells. Having been through this scene before, I knew shortly after, some dark wizard will enter and terrorise the place. The dream, however played out differently this time. While yes there is still something bad is going to happen, this time it is the full moon and Lupin becomes a werewolf. He end up attacking the clas…

To understand why the 1st girl will not survive, the dream give an explanation that dark magic wound never heal. This is kinda surprising to me as in the dream I thought they can put a prosthetic on her to replace her lost leg. This suggests the werewolf's attack has some kind of toxic dark magic component in it, which will become irreversible if the wound is too deep.

DHMO

Level 1: x^2 y^(x+1) y' - y^2 x^(y+2) lnx y' = y^3 x^(y+1) - x^2 y^(x+2) lny
good luck solving it
and hope that I didn't make any mistakes

@anonymous @Secret ^

How Complex Can ODE Get? part 1

anonymous

6:27 AM

@DHMO I've forgotten all about differential equations :P I'll revise next week and solve it then:D

@BernardoMeurer You don't need to know hyperbolic functions to solve that. Just use logarithms!

Integration of 1 /(x^2- a^2) dx and its application

►

Secret

@DHMO Are you sure you get all the terms correctly? wolfram alpha failed to provide a closed form solution despite it seemed to be able to plot something

wolframalpha.com/input/?i=solve+x%5E2*y%5E(x%2B1)*y%27-y%5E2*x%5E(y%‌2B2)*ln+(x)*y%27%3Dy%5E3*x%5E(y%2B1)-x%5E2*y%5E(x%2B2)*ln(y)+for+y

ZeroTheHero

6:45 AM

@thoughtforfood thanks for posting the link. Amazing how quickly this got organized.

also interesting to note the order in which signatories are listed.

anonymous

@Secret Wolfram alpha isn't particularly good at solving differential equations. It failed on many occasions before even though I could find the solution from other sources.

Secret

For that equation, I tried to reverse the differentiation of $x^y$ and $y^x$ but there are extra powers of x and y that stopped me from doing so.

It is also quite intwined that I am not sure whether it is separable

Sir Cumference

7:07 AM

Question, is metallic hydrogen synonymous with degenerate hydrogen?

John Rennie

No.

The pressure achieved in the recent experiment is far, far lower than the pressure needed to create degenerate matter.

Sir Cumference

Hmm, Wikipedia says it is a type of degenerate gas

John Rennie

Indeed it does. I'm not sure what it means by that but it is most certainly not degenerate matter in the sense of the matter fromed in neutron stars.

Sir Cumference

@JohnRennie It doesn't need to be neutron degenerate

John Rennie

Ah, OK, I assumed that's what you meant.

Sir Cumference

7:14 AM

So I guess metallic hydrogen refers to electron degenerate hydrogen?

John Rennie

4

Q: Why is metallic hydrogen degenerate matter?

Why is metallic hydrogen considered a form of degenerate matter, akin to neutronium and electron-degenerate matter? I can understand that for the other two, degeneracy pressure is the only force countering inward gravity for very massive stars, but how does this concept also apply to super pressu...

astrophysics atomic-physics hydrogen

Ok, on Googling I see the phrase degenerate matter widely used in connection with metallic hydrogen.

Sir Cumference

I just really wish Wikipedia would cite its sources more often...

It says gas giants like Jupiter contain metallic hydrogen. I do know that gas giants like Jupiter are electron degenerate, due to their low temperatures

I guess I'll just ask a question

Secret

Is it possible to have some substance with a ridiculously high energy barrier that only high pressures can overcome, but a ridiculously low final state such that once it forms, it will stay stable even if you depressurise it?

Sir Cumference

Wait, can degenerate gases become liquids?

@JohnRennie Am I the only one in favor of this change?

John Rennie

7:34 AM

@SirCumference I would guess most people don't really care what the chat room is called and see no reason to change the name. However I like the idea and ten pople have starred my comment suggesting it.

I was going to propose it at the next chat session.

Secret

7:51 AM

0

Q: Are there reactions (physical or chemical) such that the product remains stable even after it is depressurised?

In transition state theory, the kinetics and thermodynamics of most reactions are controlled by the height of the transition state barrier and the difference in energy level between the reactants and the products. Some reactions have very high energy barriers such that extreme conditions are nee...

physical-chemistry pressure

DanielSank

8:07 AM

@KyleKanos Commented on the post.

DHMO

8:39 AM

(x^(y+1)xlnx - x^2 y^x)y' = y^(x+2)lny - x^y y^2

@Secret @anonymous ^ corrected

Level 2: 4x^2 y'' + 5x y' + 15y = 0

@Secret

sorry, 5 -> 10

user228700

Hey, everyone :-)

John Rennie

Morning :-)

thought for food

8:56 AM

Good morning :-)

John Rennie

@Secret Pressurise and heat graphite and it turns to diamond. At STP diamond is metastable but with a long lifetime.

thought for food

@ZeroTheHero you're welcome

Secret

@JohnRennie I know, but the question is trying to ask about a product formed from high pressure that end up being thermodynamically more stable than the starting material, analogous to products with exothermic reactions formed by heating and other means

thought for food

Chemists have always been interested in diamonds but their wives have been more interested :P

Secret

The energy profile of such reaction will have a very high energy barrier for the transition state, but the product is at a lower energy than the starting material

I am wondering why we seemed not able to have pressure driven reactions with this sort of energy profile, given how most pressured form products tend to explosively dcomposes after depressurisation (and for the case of diamond, it is actually thermodynamically less stable despite having a long life time)

John Rennie

9:08 AM

@Secret Start with diamond, heat it to not quite such a high temperature and it will turn to graphite. Then cool back to room temp and the graphite will be stable.

anonymous

@JohnRennie Really? Diamond turns to graphite on heating ? I thought diamond is inert even at high temperatures..

Secret

But that's heat, or is it basically the same as applying pressure in a thermodynamic point of view (NB its not ideal gas, thus I am not very certain on how the pressure will be related to energy input other than it will be in the form of work)

@anonymous No, it is actually possible to combust diamond at high temperatures

so diamonds are not forever, it just happens it is so metastable that it takes a long time (millions of years?) before it convert slowly to graphite at ambient conditions

anonymous

@Secret How high? Does combustion of diamond form graphite ?

Secret

@anonymous I forgot, it's more than 4000C, and if you combust it under oxygen, it forms $\ce{CO2}$ and all that usual stuff when you combust any carbon rich compound.

anonymous

@Secret What if I heat it in absence of oxygen ? Will it form graphite at 4000 C ?

Secret

9:15 AM

@anonymous Well, it should rearrange it to graphite

anonymous

Graphite to Diamond is an exothermic process. I don't see how heating helps here.

Maybe it needs some activation energy? I still can't believe that you can go from diamond to graphite by heating it. Do you have any source for it?

Yashas Samaga

1

Q: How covalent bonding lower the energy of potential energy?

Considering the potential energy of interacting particles, how does covalent bonding lower the energy of the system?

homework-and-exercises molecules binding-energy orbitals quantum-chemistry

that is so difficult to answer

anonymous

reddit.com/r/askscience/comments/1k2oj9/…

Secret

@anonymous Here's a relatively recent summary of it

the abstract is more than enough for the question

anonymous

@Secret Thanks. I think the heat needed is to provide sufficient activation energy for the reaction. The reaction is spontaneous but would normally take a long time. I see now!

Secret

9:26 AM

The question I asked in CSE, is then to find a spontaneous reaction which requires huge pressure instead of heat to activate it, so that the resulting product will be stable under decompression

anonymous

9:39 AM

@Secret Do you know about fullerenes ? Are fullerenes less stable than graphite or more stable ?

Secret

@anonymous most carbon allotropes are less stable than graphite at ambient conditions

@DHMO The best I can get it down to is $x(xx^y(y'\ln x)+yx^y (yx^{-1})))+y(yy^x(ln y)+xy^x(xy^{-1}y'))=0$ However, there are some extra x and y thus I still cannot reverse the product rule. I think I need a hint on what I need to do. Do I need some fancy substitution?

anonymous

@Secret So, what is it that makes graphite so stable? Is there anything special about its structure other than the aromaticity ?

Secret

@anonymous I have not read into much detail about that. However for the case of fullerenes, the ring strain could be a factor

DHMO

@Secret I have no idea how one would go about doing it straightforwardly

I constructed it from the solution

Secret

What does the solution look like. My final suspicion is that this might be an exact ODE, otherwise we pretty much exhaust most of the methods in analytically solving nonlinear ODEs

DHMO

9:50 AM

the solution is in the form of f(x) = g(y)

when I see ln x, I substitute it away

(I haven't tried. I'm just talking)

anonymous

@DHMO Where is your problem from? Any book ?

DHMO

@anonymous I created it

anonymous

10:06 AM

@DHMO In that case it might not be able to solve it...

thought for food

^

Secret

10:17 AM

The ODE is inexact, just checked their mixed derivatives they don't match up in any extent

There's still one more thing can be tried (which is too time consuming for me atm thus I will deal with it later)

Inexact differential equation

An inexact differential equation is a differential equation of the form M ( x , y ) d x + N ( x , y ) d y = 0 , where ∂ M ∂ y ≠ ∂ N ...

DHMO

@anonymous I mean, I have an answer

and I differentiated each side

anonymous

@DHMO You solved it ?

Tell me how :)

DHMO

@anonymous no, I created the question from the solution and I do not know how I would solve it straightforwardly

@Secret if you want a big hint: answer is f(x) = f(y)

anonymous

@DHMO Oh I see. In that case one needs to able to spot the exact differential which is sometimes really difficult.

Fermi paradox

11:20 AM

Isn't this answer rather problematic? It sort of implies that anything not follow that equation is "not exactly a wave". Am i misunderstanding it?

And since the Q title is "Do all waves of any kind satisfy the principle of superposition?", the answer should be a clear "No". Instead it feels like a "yes, unless it's not exactly a wave".

DHMO

11:40 AM

@Secret corrected: x (x^y ylnx - x y^x)y' = x y^(x+1) lny - x^y y^2

I am sorry for the confusion

@Secret wolfram alpha confirmed it, so please don't cheat.

@anonymous ^

user228700

11:54 AM

@JohnR: Interested in an embarrassing (if u get it wrong) tongue-twister?

John Rennie

Go on ...

user228700

"I'm a pleasant pheasant plucker and nobody's ever heard a pleasant mother pheasant plucker like me say the F-word"

John Rennie

I'm afraid I learned that one as a schoolboy decades ago :-)

user228700

Oh, is that one famous?

user228700

There's a song about it made by one of the vlogbrothers many years ago:

user228700

11:56 AM

Mother Pheasant Plucker - A Song

►

John Rennie

I'm not a pheasant plucker
I'm a pheasant plucker's mate
I'm only plucking pheasant
Cos the pheasant plucker's late

user228700

Oh, well, it's not the same. This one contains the word "mother", which will screw you if you get it wrong.

user228700

Try to say it 5 times faster than normal. You will find that u'll run into trouble soon enough... :-)

John Rennie

I know a Thai tongue twister (not obscene)

user228700

Yes..?

John Rennie

11:59 AM

@Rumplestillskin:hi :-)

@Kaumudi.H kai kai kai kai

Rumplestillskin

@JohnRennie hi there!

user228700

Are the pronunciations different?

anonymous

Rumplestillskin

I take it this is the main room? :) @JohnRennie

anonymous

@DHMO Any idea why H- attacks carbonyl carbon rather than abstract the acidic hydrogen ?

John Rennie

12:00 PM

@Kaumudi.H Thai is a tonal language so the meaning depends on the tone of voice you use. The four words have (a) a rising tone (b) a falling tone (c) a high tone and (d) a low tone.

anonymous

During reduction of amide by LAH

John Rennie

But unless you know to listen out for the tone the four words sound identical.

user228700

@JohnRennie Oh, that's interesting, I haven't heard a tongue-twister involving tones before.

DHMO

@anonymous the hydrogen isn't acidic

the nitrogen is basic

anonymous

@DHMO Why not? It is attached to electronegative nitrogen. Isn't it ? The hydrogen gains a partial positive charge

John Rennie

12:02 PM

It's not really a tongue twister - more of a test for non-native Thai speakers to check how well they can speak Thai.

Rumplestillskin

Is anyone interested in Kruskal Szekeres coordinates and how to obtain a Kruskal Szekeres diagram using CAS? I've updated my question with a poor effort of mine and would really like to see how it is done.
http://physics.stackexchange.com/questions/307630/kruskal-szekeres-spacetime

Any and all help is a welcome gift!

Secret

@DHMO Finally, I can reverse the product rule of this one: The answer is $x^y=y^x$

user228700

@JohnRennie Ohh, nice.

John Rennie

@Rumplestillskin the problem with your question is that it seems to be about plotting software i.e. how you would get a computer to draw the diagram. It isn't really a question about physics.

Rumplestillskin

I see what you are saying John! It is quite the conundrum!

DHMO

12:04 PM

@anonymous interesting question...

I guess N is not so electronegative anyway

@Secret how?

John Rennie

@Rumplestillskin I have no idea what software you would use to draw the diagram or how to program it. But why would you bother? The KS coordinates are very useful in understanding the causal structure of the Schwarzschild metric. Questions on that are on-topic, but just how to draw it?

That doesn't seem very interesting.

Secret

@DHMO oops sorry I mean: $y^x=x^y+C$, I forgot the constant.

DHMO

@Secret how?

Secret

The trick is to notice that the derivative of $x^y$ and $y^x$ is buried in the ODE. Therefore, after rearranging the 4 terms in the ODE, you get basically $(x^y)'=(y^x)'$

DHMO

hmm...

Secret

12:10 PM

That is, I am basically doing the product rule backwards

DHMO

I see

Rumplestillskin

@JohnRennie It's just one of them things that I would like to be able to do. There is a lot to be learned from the KS Diagram and some peculiar phenomenon going on. Also, I would like to give a short talk this year on Schwarzschild geometry and it would nice to display a cool image of KS diagram and show people how to do it! I guess I will have to keep battling!!

Bernardo Meurer

1:51 PM

Lol Wolfram alpha

4

Bernardo Meurer

2:29 PM

@anonymous QUICK

last help before exam

starts in 30 minutes

do you know about series?

Ramanujan

@BernardoMeurer @DHMO may help you quickly!

anonymous

4:01 PM

@BernardoMeurer Dammit! Sorry man, I was outside home. Didn't see your message earlier :/. Hope your exam goes well.

koolman

4:31 PM

Can anybody help me in this

I want to know what would be the angle between its velocity and string when it becomes taut

After that I will try myself

David Z

Well, if you show what you tried first, perhaps someone can help you work out what's keeping you from being able to do it yourself

koolman

@DavidZ I am not getting anything

Oh, I got it :-P

David Z

4:52 PM

Ah, good

DHMO

Jan 13 '16 at 22:57, by FenderLesPaul

I had a dream that @0celo7 was touching me relatively

Wdoctor123

5:59 PM

I'm doing some experiments on resonance frequencies of buildings and I just graphed one amplitude/frequency graph and it some how has 2 peaks?

Anyone have any idea why this might be happening?

anonymous

6:14 PM

@Wdoctor123 Can you show your graph and explain your procedure of graphing ? Remember that resonance occurs at integral multiples of fundamental frequency too.

Wdoctor123

how do i send images?

imgur.com/5IVrfgy

well that's the link to the graph

dmckee

@Wdoctor123 The "upload..." button right next to the "send" on.

I have to admit that I got to where I didn't see it anymore and had to ask, too.

Wdoctor123

I took 20cm ruler, and attached it to the vibrating machines and increased frequency little by little, each time recording the amplitude

there's no upload button

anonymous

@dmckee Wdoctor doesn't have enough rep to use upload option.

Wdoctor123

XD

dmckee

6:25 PM

Hm. Forgot about that.

David Z

@anonymous how much does it take?

Wdoctor123

did you see the image?

anonymous

@DavidZ 100 rep.

David Z

Ah, I forgot. Thanks.

anonymous

@Wdoctor123 See, notice that the peaks occur at 3 and 9 Hz approx

They are integer multiples

I'm not sure how accurate your values are

Wdoctor123

6:28 PM

0.01+/- cm

I should I explain that?

got other result with different height

imgur.com/sjxvhaI

0.1 +/- cm *

anonymous

@Wdoctor123 It seems like 3 Hz is your fundamental frequency from your first graph and 2Hz is the fundamental from your second graph

Also remember that the fundamental resonating frequency does not have the highest amplitude

(at least not always)

See physics.stackexchange.com/questions/31142/…

@Wdoctor123

I think this could be a good question

for the main site

I am not an expert on this topic...

Wdoctor123

wait so height amplitude isn't the resonance point?

anonymous

@Wdoctor123 Height amplitude is at the resonance point but there are multiple resonance frequencies.

Wdoctor123

I thought resonance frequency is when the thing vibrates most violently

so i guess it was just one of the harmonics i guess

anonymous

@Wdoctor123 It does vibrate "most" violently in a small region. There are several maxima present in the graph at integer multiples.

@Wdoctor123 Exactly.

Wdoctor123

6:36 PM

hmm

So explanation would be

There are more than 1 resonance frequencies

but there's one dominant one

anonymous

@Wdoctor123 And the dominant one may not be the fundamental frequency :) Anyway I would advise you to ask this question on the main site again. You may get much better answers!

Wdoctor123

ok thanks :)

vzn

7:49 PM

Substantial evidence of holographic universe / sciencedaily

Sir Cumference

8:48 PM

@vzn Sounds like a string theory thing

Sir Cumference

9:07 PM

@obe Just asking, does the background you're making include any public domain or creative commons graphics?

vzn

@SirCumference its been discussed for a few years in mostly theoretical terms. dont really think it originates in string theory much. it seems to be more an exotic area called "digital physics" that goes back decades... possibly roots more in CS...!

obe

9:24 PM

@SirCumference all original as of right now except the font for the title and other texts

Sir Cumference

@obe K, do you know the name of the font?

obe

alien league

or something like that

Sir Cumference

k

obe

why?

it's not official so who cares xd

Sir Cumference

Yeah but still, copyright is a little scary :/

@ACuriousMind Could you answer a question?

obe

9:49 PM

i thought everyone has been over this already

DON'T ASK IF SOMEONE WILL ANSWER YOUR QUESTION JUST ASK IT AND IF SOMEONE WANTS TO THEY WILL ANSWER!

:D

Sir Cumference

@obe Ok

Btw can I ask you something?

ACuriousMind

@SirCumference Dude, what about "just ask your question" is so hard to grasp that we have to do this routine of "Can I ask you something?" every time you have a question :P

Sir Cumference

@ACuriousMind Well, if no one here knows the answer, then I wasted my finger muscles typing it :P

ACuriousMind

...and how are you going to tell if they know the answer before you asked them the damn question?

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Sir Cumference

......huh...

Well, anyways, the question is about more cosmology...wooo

Specifically, can the observable universe ever shrink?

ACuriousMind

10:05 PM

@SirCumference Define "shrink"

Sir Cumference

@ACuriousMind Its radius decreases

ACuriousMind

Its radius as measured by whom?

Sir Cumference

By the person at the center of the observable universe

obe

centre?

Sir Cumference

yeah

ACuriousMind

10:08 PM

@SirCumference Eh, I'm not convinced that's a well-defined question, but depending on what weird shit the scale factor does, it may well be that the observer at one time will measure a larger radius than an observer at later times

Sir Cumference

@ACuriousMind The confusing thing is what wikipedia says in its Big Rip article

> A universe dominated by phantom energy is an accelerating universe, expanding at an ever-increasing rate. However, this implies that the size of the observable universe is continually shrinking; the distance to the edge of the observable universe which is moving away at the speed of light from any point moves ever closer.

> When the size of the observable universe becomes smaller than any particular structure, no interaction by any of the fundamental forces can occur between the most remote parts of the structure. When these interactions become impossible, the structure is "ripped apart". The model implies that after a finite time there will be a final singularity, called the "Big Rip", in which all distances diverge to infinite values.

This has a bunch of [why] tags on wikipedia, btw

Now I'm really confused. First, I thought the Big Rip occurs once the scale factor reaches infinity, rather than when the observable universe becomes too small?

Or do these occur at the same time?

ACuriousMind

10:24 PM

@SirCumference Thinking on it, the observable universe cannot shrink - its comoving distance is just $\int_0^t \frac{\mathrm{d}t}{a(t)}$, which is monotonically increasing.

See Wiki if you like Wiki quotes better :P (In this case, the statement "The observed size of the universe always increases" is sourced to two different sources")

Sir Cumference

@ACuriousMind Are you sure that isn't only for a universe with $w \geq -1$?

ACuriousMind

@SirCumference Why would the comoving distance of the horizon care for what value $w$ has?

Sir Cumference

No idea, otherwise Wikipedia is just flat out wrong

ACuriousMind

$w$ determines how $a(t)$ behaves, but once you have $a(t)$, the distances don't care what $w$ is.

@SirCumference Dude, the "particle horizon" article contradicts the Big Rip article. So one of them is flat out wrong either way, so don't get hung up on it :P

Sir Cumference

@ACuriousMind Oh fun...

@ACuriousMind Yeah, that feels kind of obvious...

Well, guess you can't trust anything these days

ACuriousMind

10:29 PM

In general, I tend not to trust Wiki articles with multiple [why?] or [citation needed] :P

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