2:00 PM
@ACuriousMind When I'm old people won't criticise me as much
No

Not for the good cinema but for the exuberant scifi cheesyness

I like Swedish movies about death

Mmh.. okay then
What, it is a genre? Swedish movies about death?

I'm just referring to The Seventh Seal
which is my favourite movie

I have a hard time watching old movies since maybe more than 50% of why I watch a movie is because of the scenery and special effects. I fully admit it.
The story is just the excuse for the images

2:04 PM
@ACuriousMind Yeah, $\dot H>0$ is, in fact, absolutely NOT necessary for a big rip scenario. The ideal scenario for a big rip is $\dot H=0$
because, if we define $a(t)=e^{Ht}$, then you can see that $\dot H=\frac{\ddot a}{a}-H^2=0$ implies $H$ is constant and, thus, $a(t)$ becomes truly exponential

@Jim But an exponential doesn't become infinite in finite time.

The big rip happens when the hubble horizon is decreasing in a way that limits to zero. The Hubble horizon is $\frac{1}{aH}=\frac{1}{\dot a}$, which really just means a necessary and sufficient condition is that $\dot a$, or using previously defined notation, $\dot R\to\infty$

I thought the definition of a Big Rip is that $a(t)$ becomes infinite at finite time.

@ACuriousMind Naw, $a(t)$ can go to infinity all it wants. The big rip is that space expands so fast that even atoms become causally disconnected from ezch other (even quarks too) and so they don't experience forces from each other and fly apart

why no mathjax

2:10 PM
@G.Bergeron Look in the upper right corner of the chat

Although, if it goes to infinity in finite time, then $\dot a$ must go to infinity to accomplish that

@ACuriousMind thanks
$\Delta:\mathfrak{osp}(1|2)\rightlongarrow 1\otimes \mathbb{Z}_2$

Correction, $\dot R\to\infty$ is not necessary, just sufficient. If $\frac{1}{aH}$ becomes finite but smaller than the scale of the Planck length, then it is effectively a big rip. Which is why $\dot H=0$ is ideal; that accomplishes it in minimal time (at least, minimal while still using realistic functions)

$\longrightarrow$
nice

@G.Bergeron try using \to to get $\to$

2:20 PM
$\to$
better?
$\rightarrow$
same

ah ok
I just like the long version more in function definition

fair enough

but inline, I use the short one and in the end in a chat room I don't care \to is probably better, I'm not writing a paper

it's especially better when you are character limited (like you are here) and each character in the mathjax code counts

2:25 PM
good point

@ACuriousMind indeed
@G.Bergeron \to is closer to the TeX spirit of say what you mean
A \to B
same with A \implies B
(a.k.a. $A\implies B$)
(though I'm not a huge fan of how that one is typeset tbh)

I always felt Tex was in the spirit of making you cringe... you must admit it has a nasty syntax
and I abuse this symbol in my life $\implies$

Any folks with Mathematica installed around, by the way?

yesç
@EmilioPisanty why?

2:44 PM
@G.Bergeron I thought Tex has great syntax. It's very intuitive and done seamlessly. It's not as forgiving as Wolfram Alpha, but you also don't run into the problem where it misinterprets

@EmilioPisanty yep
@G.Bergeron try working with word, then we'll talk about nasty syntax again :D

Ugh word, it's not installed on my computer

Word has syntax?

Actually there is no syntax in word, maybe that is the major problem

Unrelated side note: Everyone should be aware of Beall's List. It is a list of both publishers and standalone journals that publish any paper submitted to them without any actual peer-review process and use fake credentials to charge lots to the people that submit papers. They also make for great ways for people with works that should never pass peer-review to get published and then say "Look, I can reference a published work that supports my zany theory".

2:48 PM
@ACuriousMind of course it has
it is just usually hidden

It's a good reference list when checking a dubious reference

@G.Bergeron @Sanya Can I ask you to run ConstantArray[0, {}] and see what it says?

but ... let me get an example

and also what $Version you're using and your OS @EmilioPisanty sorry, Mathematica is busy at the moment, but as soon as the calculation stops (~1-2 hours) I'll try version 8, win 7 2:49 PM Ah ok... But I never pay to publish @Sanya OK, yeah, that's an interesting testbed "11.0.0 for Mac OS X x86 (64-bit) (July 28, 2016)" @Sanya you can't even start a new window or a new kernel? you're really working it to the bone there It says 0 @G.Bergeron the bigger problem is with them falsifying their credibility credentials and publishing garbage, thus giving false credibility to people and papers 2:50 PM @G.Bergeron thanks @Jim Yeah I understand your point a friend is running v9 over OS X and it returns unevaluated for whatever reason =| @ACuriousMind "{REF _Ref468714837 \h \# "0"}" is TeX's \ref{} Is it a newly introduced command? 0 I saw this patent: https://www.google.ch/patents/US3951134 And I was curious if there is way one can shield to avoid being monitored or conditioned by remote RF waves, since it could be used for malicious purposes. If possible, what would be the cheaper method for shielding? I am interested i... I have to resist the urge to post "Have you considered a tinfoil hat?" 4 2:52 PM @Sanya are you running mathjax? 'coz that comment looks way funky @EmilioPisanty "ConstantArray::ilsmn: "Single or list of non-negative machine-sized integers expected at position 2 of ConstantArray[0,{}]. "" WHAT! @EmilioPisanty nah, I'm not - but why does it render as Mathjax? @Sanya no idea, but: @Sanya and does it return the ConstantArray as-is? i.e. unevaluated Are there often questions like that? 2:54 PM @EmilioPisanty Out[28]=ConstantArray[0, {}] @G.Bergeron like what? like ACM's link? @Sanya cool, thanks. yes That's really, really bizarre @EmilioPisanty that's weird because there's no$ ... :|

@Sanya I know, but still.

2:55 PM
@Sanya I see the same
what was it supposed to be?

a \ r e f { }

@Sanya the documentation tags it as "Introduced in 2007 (6.0) | Updated in 2008 (7.0)", so there are not meant to be any changes between v8 and v11

@Sanya you should also be able to say \ref{}

@G.Bergeron I don't recall another one about brain waves, but we've had everything from how to unmask werewolves to how to shoot teenagers into space

2:56 PM
;-)

It outputs a naked 0 not in an array in my case
wow

by the way, I hate Matematica's graphic export >_< I've got a nice plot in the notebook, but if I export it as a pdf ... it looks horrible >_<"
@EmilioPisanty that's exactly what I wrote up there in the message to ACM

@Sanya He means you can use backticks to escape code
Like, you should write \ref{}
To get \ref{}

aah ... I didn't see the backticks :o

^ that

2:59 PM
'\ref{}'

@Sanya agreed, luckily, I output only equations, so straight to latex than editing in latex editor

@Sanya backticks, not apostrophes

@Sanya Backticks, not apostrophes

I see '???'


not
'

2:59 PM
lol, you're great, you two :D

@ACuriousMind you should send that guy here

\ref{}`

\ref{}

ah ...

> Consciousness remotely change output voltages of solar cell and a balance between Electrons and electron holes which is a negative balance of SDS. By the nuclear energy of spacetime, consciousness should change the orbit of the balance of SDS for avoiding impaction.

3:00 PM
@G.Bergeron I've always been too lazy to install mathjax

I just used the javascript link
since 1hour ago
@Sanya And luckily I use Mathematica only for symbolic calculations. How is it for numerics?

@EmilioPisanty Great

And i need to write a lot of handler code for non-commutative algebras

@G.Bergeron I am not sure whether it's better or worse than Maple ... but let's say it like this
it's "powerful" in that it allows you to quickly solve basic problems in reasonable time
but computation times explode quickly

@ACuriousMind I've got pictures of some of his slides if you're interested
it was... an experience, that's for sure

3:03 PM
@EmilioPisanty You actually attended that talk?

but last time I tried integrating something that was a pixel on an image I abandonned one day later
And coded everything in C

@ACuriousMind yes, I did

Awesome

@G.Bergeron which is really the way to go
if you have anything serious, numerically speaking, I feel that Mathematica is not a good fit

Yeeaahhh.... I don't claim I do good numerical routines

3:04 PM
while it is a great tool to help beginning with numerics and solve easy stuff

It's just that it was a nasty integral for the structure factor of a spin chain, but the integral was exact and nasty in the sense that it came from an exact solution using nasty maths
so mathematica was having a hard time trying to treat every possible numerical instability or something
need to go

well, you're kind of lucky if it didn't just refuse to calculate
see you around =)

never terminated
... as a colleague said : "If it's not done in an hour, it's uncomputable!" :p

@ACuriousMind It changed my outlook on a bunch of things. Now, when I see things like the Concave Earth theory my first reaction is "surely this is a joke, and no one could take this stuff seriously...". And then I remember that talk. The guy seriously believed all of that stuff.

3:10 PM
@G.Bergeron let's say 2-8h can work too ... :D

there really are people who are honest-to-god just that crazy.

hi! What you guys are talking about?

@EmilioPisanty Sounds to me as if that talk cost you a bit of your faith in humanity :/

@ACuriousMind replaced some of that faith with realism, I would say

@EmilioPisanty wow ... concave earth theory ... there's things that are ... really hard to believe

3:13 PM
@Sanya yeah. Also Hollow Earth Theory is worth a look.

the concave video looks like the trailer to a new series, though
2
I'd watch that
"Concave Earth - Duped By God"

I'd advised against faith in anything...
Why do I always mess up verb tenses?!?
...probably have to do with never having proper english classes

Pro tip: You can edit chat messages for 2 minutes after they're posted

^ extra pro tip: pressing the up arrow will cycle through your editable messages.

0

I get, I think, that all experiments show that the (two-way) speed of light is constant in all directions regardless of the velocity of the observer, and that if taken as a postulate this leads to verifiable SR phenomena such as time dilation, length contraction and non-additive velocity. I accep...

O_o~ this is always the type of questions that leave me surprised
I never understand what kind of understanding they are after

3:27 PM
@Sanya They want an answer to "why" but they never stopped to think about what that means.

@ACuriousMind maybe any natural science student should have to take a course in philosophy of science in the first year

It's unsettling how many people you can stump by pointing out that asking "why" in this fashion either terminates at something that has no reason or continues to infinitely many reasons.
@Sanya Yes, they should (but we have no guarantee that OP is a natural science student, so we'd still get those questions)

@ACuriousMind I'd like to give them Russel to read

I hope you don't mean the Principia ;)

now, I meant "on the notion of cause"
it's a fun short paper

3:34 PM
I like Norton's "Causation as Folk Science"
Can't remember what I read from Russell, it's been a while.

Norton looks promising ... I'll have a look later with more time :)

He's the guy from "Norton's dome", pointing out that Newtonian mechanics can fail to have unique solutions

3:54 PM
Wonderful terminology: A "nearly Kähler" manifold is different from an "almost Kähler" manifold.

LoL
0

I would know if it possible to alter characteristics of high frequency EM waves, ie altering the frequency, phase and/or amplitude. I found it is possible to change frequency of ELF waves: http://rexresearch.com/puharelf/puharich.htm If it is possible, what would be the simplest practical way ...

:D
engineering-flag? :D

Hi, everybody.

4:13 PM
@Kaumudi I take back what I said about curry
This is my favourite thing from India

4:24 PM
@BernardMeurer do you like indian songs :)

@koolman I like that one :P

Great
@BernardMeurer have you watched movies also

I watched a movie that had an indian guy on it once, does that count?

@BernardMeurer which is not an Indian movie

@Jim You still here?

4:28 PM
@SirCumference A little bit, yes

Awesome
So I got a few questions
@Jim Can we determine whether the deceleration parameter is positive or negative simply by knowing whether $k$ is $-1, 0$ or $+1$?

the deceleration parameter?

@koolman Nope :p

@BernardMeurer which movie was that

4:30 PM
@Jim Or by knowing the value of $\Omega$?

@Jim $q = -\frac{\ddot{a}a}{\dot{a}^2}$

Life of Pi

@BernardMeurer oh yeah

Uh, @JohnRennie, now that the question is deleted it doesn't matter, but asking whether the strings are entangled is not a duplicate of asking whether they are tangled.
The former asked about the quantum notion of entanglement (which doesn't make sense here), the latter about the actual geometrical situation being that the strings are tangled.

@BernardMeurer <3

4:36 PM
@DanielSank <3

@ACuriousMind I don't have the link to the question any more, but I'm fairly certain it was asking if strings can be looped through each other i.e. tangled.

@SirCumference Not entirely. If $q=-1-\frac{\dot H}{H^2}$, then k has no real effect on the sign of it unless it is $-1$, but even then it's possible that other influences can overpower $k$'s impact on $q$

@JohnRennie Hm, you may be right. From the one sentence in the question it'S hard to tell.

@Jim So knowing the curvature of the Universe won't necessarily tell us how it will expand?

@SirCumference no

4:40 PM
Well, it would if we were looking at an ordinary-matter dominated universe, right?

Reading introduction to a paper: "In section 3 we complain about the absence of a clear set of rules for computing M-brane instanton effects"...lol, you and me both, Harvey.

@SirCumference yes

Sigh...
All right, next question

@SirCumference correct. It's easy to show that $\dot a^2$ is shifted up or down by $k$, or rather, $\Omega_k$. But things like dark energy, excess matter, or simply small amounts of curvature could weaken the impact of $k$

Does anyone know a formula showing how scale factor changes as a function of time?

4:43 PM
historically? Under what model?
for what domination era?

@SirCumference ...did I not give you a link to a paper that solved for $a(t)$ in various models yesterday?

@ACuriousMind Oh right
...does anyone know how to show LaTeX in the transcript?

Starting ChatJax with the bookmarklet as usual works for me.

21

To calculate the Hubble constant we need the a scale factor, $a(t)$. This is a measure of how much the universe has expanded. We take the scale factor to be unity at the current moment, so if $a = 2$ that means the universe has expanded twice as much as it has right now. Likewise $a = 0.5$ means ...

I use ChatJax++ >_>

4:49 PM
lol, I love this paper, section 3 is a Salviati-Sagredo dialogue expressing all my frustrations about "M-theory"
Sadly, it doesn't bring me closer to understanding wtf is actually going on.

@Jim All right, next question

@Danu Look at 3.1 here, you might find it amusing.

@Jim Sigh, hold on, gotta look through my notes for the question

For anyone interested in organic chemistry

### organic chemistry

Discussion for organic chemistry

5:02 PM
@Jim All right, does peculiar motion refer to the motion of objects through a comoving coordinate system?

@SirCumference yup

K good

@koolman By that you mean "anyone interested in answering your questions about organic chemistry although you have been banned from chemistry.SE"?

at least, that term used in a cosmological sense means that

Good grief, now there are some memories - not all good.

5:09 PM
@Jim Oh wait, one more question

shoot

My book gives this equation for a universe dominated by matter and dark energy:
$$\rho = \rho_m (a)+\rho_{de}(a)$$
It says that $\rho_{de}$ is the "mass density of the dark energy"
Doesn't it mean energy density?

GR doesn't distinguish between mass density and energy density
They differ only by a factor of $c^2$

@JohnRennie But photons, for example, have energy without mass
Shouldn't momentum be important in that?

Momentum?

5:12 PM
Yes, as seen in the energy-momentum relation

In an FLRW universe we generally ignore the momentum so the stress-energy tensor is diagonal.

So energy is interchangeable with mass in the FLRW metric?

Yes

(besides the fact that they differ by a factor)

Well ... you do have a good point, it makes no sense to calculate an equivalent mass density for photons.
But note that the different types of matter/energy have different equations of state.
The main difference between photons and matter is the equation of state not what units we use for the density.
Likewise dark energy. The key feature of dark energy is that it doesn't dilute as the universe expands.

5:16 PM
@JohnRennie Yes, its density always remains constant, right?

@SirCumference Yes

Well that's kind of a given, since the cosmological constant is a constant
And if I recall it's a function of the density of dark energy

Caption: Trolling concave earth in a way that makes sense
It is perfectly fine to have a 2-sphere that is concave as long it is bent into a Pringle chip like shape in 4D

@Secret They will never get that joke

well, not necessary, as some monothesis groups do say that god is 4D
I like to make jokes that are superpositions of "this is absurd", "wait it kinda makes sense", "it is logical", "that's a troll"
Like a capacitor, short circuiting a joke is a very euphoric experience

5:28 PM
Example of joke short circuiting:
Here, drop bear is a famous australian made up story or urban legend used to scare foreigners as a prank
Just imagine what I felt when this news item poped out. The cool thing about joke short circuiting is it blurs the line between reality and fiction, making a joke richer than it used to be
It is nice when nature played along these jokes sometimes out of chance

5:42 PM
The only way to have a utopia, is to have causality to break down completely (and to a degree even more than required by time travel novels with malleable histories)
only then will A stop lead to B and so on for all possible interactions and events

wat

otherwise for every act of trying to achieve happiness, there must be at least one party that is unhappy
because of how the process to achieve it affects other process in the system

That's not "causality", that's viewing happiness as a zero-sum game.

Well I guess that descibes it better. Our world is not a zero sum game, thus utopia (based on this interpretation) is impossible

No, that's not what I meant.

5:48 PM
?

If you say "utopia is impossible because when trying to achieve happiness, there must be someone that is unhappy", then you're implying there is no way to achieve actions that only generate happiness. This doesn't force allocation of happiness to be a zero-sum game, but if it's a zero-sum game, then that statement is true (viewing unhappiness as negative happiness, of course).
If allocation is not a zero-sum game, then it's not immediately evident why you claim unhappiness must be generated.

I see, i agree, in that case we don't really rule out actions that only generate happiness or unhappiness (under some given philosophy in order to define happiness)

I wonder if if we need a canonical q/a covering exactly what is meant by a constant speed of light

Some clarification: Initially I thought of causality to describe that is because consider the scenario where there's a criminal trying to steal something. Normally by doing so there will be a victim. If the criminal is stopped, then in a loose sense he will be unhappy because his aim is not fullfilled. But if the criminal is not stopped, than the victim will be unhappy because he suffered a lost of some kind (emotionally, financially etc.)
I do not know of anything that allow the happiness of both to be fullfilled for all possible such scenarios, since at least one scenario must be mutually
Perhaps, that's not causality, but logic instead
Simply put, I do not know of any way such that the aim and dreams of every living entities can be fullfilled, without at least one group to suffer, due to how they are related to each other
therefore concluding utopia will be impossible

Utopia would be easy just so long as it doesn't have any humans in it.

5:56 PM
Well it is true in a large sense, given that we humans are responsible for a majority of ecological damage due to our resource exploitation.

@Secret that's not what I meant.

that's just one example. But anyway, you can clarify your statement

Actually you can keep utopia. I'd settle for anywhere that didn't have certain humans in it.

@JohnRennie Amen.
Utopia would be frigging boring. ;)

It will be, basically progress and change will be completely stalled. Stagnation will result, which in some way is scarier, I think...
Actually, when we thinking of utopia, do we limit that notion of happiness to only humans, or do we try to go for the most general example of it (any entities that has a capability to assign a notion of happiness to itself)?

6:00 PM
@JohnRennie I'm pretty sure we already have plenty of questions discussing the differences between "one-way speed", "two-way speed" and "coordinate speed".

@ACuriousMind not enough it would seem, though I doubt any number would be enough in these circumstances.

@JohnRennie No question or answer, no matter how canonical, will convince anyone who just shouts "NANANANA I CANT HEAR YOU".

@ACuriousMind Amen :-)

1 hour later…
7:25 PM
@Jim By the way, could you explain why a static universe would be unstable?

1 hour later…
8:51 PM
@ACuriousMind physics.stackexchange.com/questions/297464/… would you be willing to warn me if I've written nonsense?

@Sanya looks correct to me

:) that's nice to hear
thanks

@SirCumference No, I can't. Is it unstable? I've not heard that. We just know ours isn't static

9:23 PM
hello

heyhey

school's out (::old-fashioned bell rings::) =D

Do they still have bells anywhere?
My school had a boring electronic thingy
The only fun sound it could produce was the fire alarm :P

not real bells, no, we've got an electronic thing
you know, I was reading your earlier conversation about the question "why" and I was thinking: really, there's no infinite string of why's, it either goes back too (if religious) "because that is how God designed it" or (if agnostic/atheistic) "because that's how nature rolled the dice", right?

@ACuriousMind I have to tell you something...
I've been stalking you on Facebook and I'm in love with one of your friends

9:38 PM
@BernardMeurer wat

@ACuriousMind that was the only appropriate response to something like that =)
oh, funny side comment: I overheard the other day someone saying jokingly, "Yeah, I'll InstaTweet that on FaceTube" =P

@heather Eh, I don't see why one could rule out the infinite chain of reasons (beware of Zeno's paradoxa!), and "rolling the dice" implies there was randomness involved in the creation of the laws of physics, which itself would be a (meta)law.

hmm...rolling the dice was a metaphor for random chance, but I guess you could argue that chance is a law

@BernardMeurer Do you mean you stalked me and then fell in love with their internet presence (creepy!) or that you actually know one of them and have fallen in love with them (funny coincidence!)?
Also, why did you feel the need to tell me that?
So many questions

welp, off to try to fix pesky giant bug/fundamental problem #2

9:45 PM
@ACuriousMind Is Ocelo7 back here again ?

@PhysicsGuy Not yet. (Also, all information you need to determine that is public, no need to ping me about it :P)

Yeah, fine, thanks.

@ACuriousMind I stalked you, saw a friend who looked absolutely gorgeous and fell in love
and I stalked you because you showed up in Suggested Friends as per usual

@BernardMeurer Ah, the young still give their love away so easily... :P

10:02 PM
@ACuriousMind It happens at least 5 times a day :P
Note that I no longer remember her name, and I first found her like an hour or so ago

lol

Nevermind, I had it on my clipboard history :P

10:43 PM
@heather Neither corresponds to my worldview. I don't think there was any kind of dices, or maybe a one faced dice...
@ACuriousMind Wouldn't you characterize perfect randomness as precisely the absence of any laws? Precisely the most scrambling, precisely the highest entropy...

@G.Bergeron What does "perfect randomness" mean? All random variables are distributed according to a probability distribution, which, to me, constitutes a "law".

Hey guys ! I'm actually here trying to solve a real life problem and I'm no expert on physics, can anyone help me or did I come to the wrong neighborhood ?

if someone can/wants to help, they will.

Equal measure for all points in the probability space
or flat constant mesure

@Maks I suspect you've come to the wrong place, but go ahead and ask anyway, if someone can and wants to answer, they will

10:51 PM
Or of which a sampling string is a complex string in the Kolmogorov sense (my favorite)
Shoot away

I need to empty the water that's in my pool, but the water pump stopped working, so I was thinking in using a pipe to get the water to come out, I was thinking in the same principle that uses the soda shipons, is it posible ?
The place where I have to drop the water is actually 2 meters above of the water

@G.Bergeron Yeah, I'm afraid I don't see why I shouldn't see a uniform probability distribution as just another law according to which the variable behaves.

Is there a way to play with the pressures and get the water out ? Or is it too high and I need the help of a pump ?

Hi, everybody.

I'm looking for something to do manually aside from using buckets

10:53 PM
@DanielSank, hello =)

By the way, I hope I can blame it on lack of sleep, but I answered a question with a trivial fatal error... :( It is now entirely rewritten but, yeah...

@heather 'sup?

Also, there is no uniform distribution on the reals, so if your parameter space isn't a finite interval/compact, your "perfect randomness" doesn't even exist.

76

This is joked about all the time, but... Can tin foil hats actually block anything? If they can, what frequencies? Is there any research into tin or aluminum foil and radio blocking or amplifying abilities when shaped into a hat? If they really don't do anything, what would be better? Radio blo...

@Maks, siphons won't work in this case

10:54 PM
@DanielSank, not much, fixed one conglomeration of errors, now I'm working on another (for the python project), I feel like I'm making progress

@G.Bergeron I cant use the same principle but on a big scale ?

@Maks yes but the output points needs to be lower than the water level, this height difference is what makes this thing... actively suck

Correct me if I'm wrong, but siphons are filled with a gas, that when you pull the level escapes and the water comes out because of the pressure difference right ? Shouldnt it be the same with air ??

@ACuriousMind It is a law in some sense, but it is the poorest one that can exist in term of information content.

@G.Bergeron But in the siphon the output isnt lower than the water level, how does it work ??

10:58 PM
@heather Great.
Keep at it.

@Maks In the one I know, yes it is