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2:04 PM
A: Would there be no time in a universe with only light?

Pentcho ValevYou seem to presuppose that time slows down for moving objects and stops for light, but this contradicts any theory. For instance, special relativity predicts that time SPEEDS UP for moving objects/observers: http://www.people.fas.harvard.edu/~djmorin/chap11.pdf David Morin, Introduction to Cl...

Sigh. I don't know what motivates these people, I really don't.
Good morning folks
@heather How well do you need to know it? Like for a play or ...?
@JohnRennie What irks me far more is the other answer that throws around a lot of technical terms but doesn't actually make any technical sense as far as I can tell.
@ACuriousMind Lawrence's answer?
@JohnRennie Yes.
Can you parse it, i.e. tell me what it's actually saying in your own words?
@ACuriousMind "Parse" it? Are you a programmer now? Who touched you my child?
2:13 PM
@BernardMeurer I have many faces.
@ACuriousMind I haven't got the faintest idea what it means. I recognise the words, but not the way in which they are arranged.
@ACuriousMind I think that guy's answer is just an iteration of the infinite monkey problem
@JohnRennie Likewise. And this isn't the first time I notice that with his answers - whenever I actually know the subject well enough to know the technical terms, they just don't add up.
@ACuriousMind A universe with just light would simply be a radiation dominated FLRW geometry wouldn't it? Why is that complicated?
@JohnRennie True, radiation dominated FLRW is a good example
2:17 PM
Maybe I should post that as an answer ...
@JohnRennie DO ET
I don't see what there's interesting or complicated about the question either
@ACuriousMind It seemed interesting to me, I had never thought about that
But it's just a gimmick
@Danu I think your flag is appropriate, but I would have preferred it if you had edited the elaboration into the answer yourself instead of leaving that to us ;)
2:37 PM
Greetings to everyone; may I ask for some quick help: does it happen anyone of you to know how to evaluate the trace $Tr [p' \gamma ^μ \gamma ^5 p \gamma ν \gamma 6]$. Thanks.
2:50 PM
@ACuriousMind That's a common theme with that user.
Similar with e.g. Timaeus.
> In general relativity spacetime consists of patches of locally flat regions with Lorentz symmetry.
I mean that's just flat out wrong (no pun intended)
3:27 PM
In mathematics, an amenable group is a locally compact topological group G carrying a kind of averaging operation on bounded functions that is invariant under translation by group elements. The original definition, in terms of a finitely additive invariant measure (or mean) on subsets of G, was introduced by John von Neumann in 1929 under the German name "messbar" ("measurable" in English) in response to the Banach–Tarski paradox. In 1949 Mahlon M. Day introduced the English translation "amenable", apparently as a pun. The amenability property has a large number of equivalent formulations. In the...
This is not going to be comprehensible without some background in analysis and topology. Guess I will revisit this later
Also someone really need to make a glossary of mathematical adjectives cause remember what property is defined as what is starting to feel like remember arbitary organic chemistry reaction conditions without much logic behind them
@ACuriousMind nice try, janitor ;)
Seriously though, I get that point but I'm not going to collect and then summarize comment lectures
one reason I want to carpet search and read all abstract algebra articles on wikipedia is to see how each of those adjectives are related, so as to create a mental glossary that acts like a toolbox should I want to build some abstract algebra structure and thinking about what properties I want to assign to its elements and the structure's properties in a systematic way
so far "homo-" means "preserving the structure"
and "almost" usually means "except a set of measure zero"
and "free" means "the least constrained of a given object" or "possess a basis"
3:49 PM
@BernardMeurer, pretty well; it's for mock trial. I have to memorize it and gestures that go with it and tone changes and such things.
@heather Ha, fun, I was very much into mock trials and model UNs :)
There was a young fellow called Sank
Who dearly loved a good prank
His qubits he cohered
In ways totally weird
That boy, he could do with a spank
@JohnRennie Holy shit hahahahaha
=P that is fabulous!
Thank you, thank you :-)
3:51 PM
@heather I usually tried to somehow connect with the side I was representing. I recall one model UN where I was Mexico at Bretton Woods conference. All I did was read all I could on Mexico, and then all the things I theoretically "had to know" from the study guide came naturally since I understood the context of the country and had half a brain to make sense out of it
Although for a mock trial I don't know how well that would work. Getting someone to test you on it, i.e ask you questions, is helpful for memorizing things a lot
@BernardMeurer, hmm, yeah. that makes sense. I've been bugging my mom to help me. =P
There was a guy called Daniel
And he had a nice cocker spaniel.
His job at that date
Made others irate
^it is hard to rhyme with things involving quantum computing.
This brings me back to high school, yikes
Sank and prank don't rhyme.
@0celo7 Yes they do?
Ask Reb
3:56 PM
No, Sank has a soft a.
uh...soft a?
@0celo7 I'll show you my soft a...
What does "soft" applied to a vowel mean?
@ACuriousMind Don't y'all have that in german soft a vs hard a?
how about a word that rhymes with the correct pronunciation of Sank?
3:57 PM
I know soft s and hard s, or soft and hard consonants in general, but I don't know what a soft vowel is supposed to be
@ACuriousMind stank vs. ha
uh...maybe I've always mispronounced Planck then, because Planck in my mind rhymes with prank.
the a in the first is hard, soft in the second
@heather You're mispronouncing it.
googling the correct pronunciation
3:58 PM
"ai" vs "á" phonetically
Got it
What's a phonetic "à" then?
the a pronounced like in father?
@0celo7 Never heard that terminology. I think those are just two different sounds
@ACuriousMind oh sure, I just made it up
but the meaning is clear
4:01 PM
@BernardMeurer I think that should be æ or vs. ɑ
@0celo7, well, at least you can't say that Daniel doesn't rhyme with spaniel. Though that was a much worse poem to begin with.
My real question is how do you know the correct pronounciation of Daniel's name, @0celo7 ?
@MetaEd Where are you when we need you?
@ACuriousMind I looked at it?
4:02 PM
@ACuriousMind I heard he say it himself, and @0celo7 is right
@0celo7 I don't understand. How can you tell which sound the 'a' makes from looking at it? (I'd have rhymed it with prank, too)
creepy stalker moment...=P
Pronouncing his last name as sank $\cong$ prank would be silly.
It's Sank $\cong$ Planck.
I don't know about silly, more like phonetic
Daniel "Fuck, the ship" Sank would be silly.
4:05 PM
@BernardMeurer I'm not doubting he's right, I want to know how he knows he's right :P
@0celo7 Lol
@0celo7 There are so many silly names in the world that that's not really an argument
@ACuriousMind fite me
@0celo7, what does that have to do with anything? Though rather funny. I've heard sillier names
Like, for instance, Butterball. I kid you not.
@BernardMeurer Huh?
4:06 PM
If @DanielSank ever dies with an actual shipwreck I can't promise I won't make the pun "Daniel Sank"
@BernardMeurer u think I never heard that on the swim team?
@0celo7, I also enjoy the fact that you are using mathematical symbols $\in$ normal conversation =)
@DanielSank Lol, can we please go swimming?
@JohnRennie ::cringes::
4:08 PM
@JohnRennie You're british, you don't speak english
@JohnRennie What the shit?
Also before you get too invested shoveling hot air into JR's ego, scroll up.
"scroll up" is so unspecific
Oh dear, this is going to be the Euclid conversation all over again :D
@ACuriousMind, the Euclid conversation?
4:09 PM
@DanielSank Shoveling what into him?
@heather just...search the transcript for "Euclid" if you really wanna know ;)
8 hours ago, by DanielSank
There was once a man called John Rennie.
In his pocket was nary a penny.
But physics he knew
and his rep points grew
after questions he answered so many.
--Daniel Sank
@ACuriousMind, oh, dear
stop the madness =P
4:10 PM
Daniel Shankspeare
OG physics poet represent.
@BernardMeurer, wouldn't it be Daniel Sankspeare?
@DanielSank to be fair I linked that from my own limerick
Unfortunately I can't think of a poet's name that coincides nicely with John Rennie.
4:13 PM
@JohnRennie yes indeed
John Shakespreannie
@heather nice.
@BernardMeurer hahahahaha
@DanielSank At least I'm learning how to name shit like an engineer in school :p
@BernardMeurer uhhh
Okay, I've got it: John Rennieson (Alfred Tennyson)
4:15 PM
@heather :-)
@DanielSank Are you good with circuit design? I need some saving
@DanielSank, oh, good news: I was able to get my hands on a copy of Quantum Computing and Quantum Information by Nielsen and Chuang! So I'm reading through that.
@BernardMeurer, what sort of circuit?
@heather Very high voltage plasma arc
@BernardMeurer define "good".
4:20 PM
@heather He should be simply Sir John Rennie.
@MAFIA36790, hmm, yes, good point.
@DanielSank If you help me can we make me not die electrocuted?
@MAFIA36790 as I keep saying...
A physicist first name of Daniel
Had eyes big and brown like a spanial
His skin soft and fair
Caused women to stare
But his bathtimes were only biannial
I believe it is biannual
4:22 PM
Anna just dropped this:
There was a young man of Japan
Whose limericks never would scan.
When asked why this was,
He replied "It's because
I always try to fit as many syllables into the last line as ever I possibly can."
@heather details, details, Shakespeare just made up words so why can't I? :-)
@DanielSank Married a poet
@JohnRennie, very true =P
@DanielSank, she writes better than you ;)
4:23 PM
@MAFIA36790 Indeed
@heather apart from spaniel I don't know any other word in the English language that rhymes with Daniel ...
@JohnRennie The dog ?!
@MAFIA36790 Don't call Daniel a dog!!!
I love dogs :)
There was an english squire named Rennie
Who was so noble he was put on the penny
His reputation was so high
That all participants had to look to the sky
And whenever asked a question
A perfect answer added to the conversation
4:26 PM
Is this the beginning of another duel T__T
@BernardMeurer I'm tying up some analysis notes
do you want them?
@0celo7 I want them
@MAFIA36790 you too
@JohnRennie, not quite perfect, but how about

There once was a man named Daniel
Who was going to an event but had to cancel
Or maybe Daniel/mantel, Daniel/sandal
@heather the second one is clever
@0celo7, which one?
the second one
in the comment or overall?
sandal or mantel?
4:30 PM
@JohnRennie my eyes are green.
Bearing in mind the comments made yesterday about my Welsh ancestry:
How sad to see little John weep
Rejected in love by a sheep
Though John he did sue
The judge found for the yew
And John he got fleeced, so to speak
hey everybody
I have a doubt
@heather those all work.
@DanielSank proof?
@DanielSank details, details
4:32 PM
@JohnRennie wtf you tried to rape a sheep and he kicked you?
@JohnRennie oh excellent.
@0celo7, whoa, weird comment of the day =)
Okay, new line of thought here: shouldn't the singular of sheep be shoop and then the plural is of course sheep? and then you could have moose and meese...
@0celo7 she not he - there's nothing weird about me
That's good for I wanted some quick intro to Banach space. Thanks @0celo7.
why would the ray internally reflect?
4:33 PM
@JohnRennie, complete with a rhyme, very nice
@heather nah. Y'all need to read up on your linguistic history. Check "the great vowel shift".
@OsheenSachdev why wouldn't it?
@JohnRennie I think at the point when you're going for animals, sex ceases to be the weird thing.
if the angle is r and the refractive index is constant then I guess it should simply be refracted
@OsheenSachdev part of it is refracted, part of it is reflected
4:35 PM
@DanielSank, sounds like some kind of epic story or something. But anyway, what does it have to do with sheep/shoop?
same as you can watch reflections on any old piece of glass
@0celo7 u want a selfie, bro?
uhh no why would internal reflection take place
@OsheenSachdev again, it's only partial reflection
@heather English animal (and other things) plurals are weird because of history. In essence, it's all French's fault.
4:36 PM
at that angle, most of the energy will flow out
but some nonzero amount will undergo internal reflection
@DanielSank yes
@0celo7 what, Daniel is just too hard to google for?
so here do we not mean total internal reflection?
@OsheenSachdev precisely
okay thank you
4:38 PM
@EmilioPisanty how would I do that?
@0celo7 though admittedly you can't really see the eye colour
that thing is more condescending than ever
@DanielSank Looks hotter irl
4:40 PM
@EmilioPisanty exactly
honestly they look brown in that picture
@DanielSank pic for pic
I'll take a selfie if you do
@0celo7 Not of your haemorrhoids!!!
@0celo7 yeah, @DanielSank, imma side with 0celo7 there, the available evidence points to brown eyes
@JohnRennie Oh darn, you caught on to my plan :)
Hey @EmilioPisanty: Quickly stopping by, to ask something. Have u actually read anything by John Green? He wrote this excellent article about great teachers and how they've changed his life. Have u read that? NOT ABLE TO FIND IT!!
@Kaumudi no, I have not.
4:43 PM
@JohnRennie: Evening :-) Look how I changed everything by posting that one poem!!
@EmilioPisanty Aw, man :/
The temptation to write a limerick about haemorrhoids is now almost irresistible.
XD Oh, do write one!
@Kaumudi no, there are some things we should put behind us
@JohnRennie do it!
@BernardMeurer did you look at my notes?
they are coming along nicely
4:57 PM
@0celo7 Where did you send it to?
They are indeed nice and looking great.
@0celo7 Dude use GDrive for the love of god
@0celo7 Can't open that
Use GDrive
Use GitHub actually
Hlw and good evening everybody
@BernardMeurer why not?
5:04 PM
@0celo7 it just sends me to my dropbox folder
sucks to be you I guess
@0celo7 Use GitHub, I'll teach you how and You'll see why it's awesome
If I apply 98 N upward force on a 10 kg object ... would it ever come off .... consider there exist 9.8 ms^-2 of constant g .... ... :-)
@JohnRennie OK... (:|)
Off to bed. Bye :-)
5:08 PM
@BernardMeurer It opened comfortably for me ;/
@MAFIA36790 :/
@MAFIA36790 ... would you like to tell me :-)?
I have no idea where I am in the spectrum of quantum interpretations:
1) wavefunction evolves determinstically
2) measurement is probabilistic and such probabilities are given by the wavefunction (probabilistic outcomes). The wavefunction also get projected due to the measurement
3) Before measurement there are no predetermined values (nonrealist)
4) interaction that establish the entanglement correlates some parts of the wavefunction of the subsystems to form a wavefunction of a composite system that spans spacelike distance (nonlocalism), with relativity protected by no communication theorem
@Secret Most of this are sounding like Copenhagen?
It seems I am taking a very bizzare nonlocal, nonrealist approach and the wavefunction itself is a intrinsic physical property treated as a hidden variable that can be affected by measurement, and such wavefunction can spans spacelike distance
5:16 PM
Q: Are the new moderators running a different flag policy?

NumrokI have noticed that since the moderator election my flags are getting declined significantly more frequently. Specifically I placed 9 flags since the election, 5 of which got declined. What I find particularly annoying is that some of those post I flagged got dealt with even though my flag got de...

the holidays are coming up and my mom is already asking what I want. My answer, of course, will be books, many books. Specifically, though, I kind of want to know what some good books would be in the realm of math, physics, and computer science to ask for. does anyone have any suggestions?
@heather Want an analysis book?
@MAFIA36790, anything's cool.
I will not not mention Royden; but you can go with Rudin.
However, the real deal would be to buy some good calculus books.
5:19 PM
My favourites are Spivak and Apostol.
However, Apostol has typos; or at least the Indian version; but I can manage with that.
I think in short the gist might be:
1. The wavefuction is a determinstic, intrinsic nonobservable property *as real as electric charges* possessed by the system, and it dictates probabilities. It can span spacelike distance with superluminal communication forbid by no communication theorem
2. Entanglement establishes correlations within it at the time of the interaction, and not due to measurement
3. Measurement is probabilistic (with probabilities dictated by the wavefunction), and it changes the wavefunction via projecting it.
At your stage, a calculus book would be good.
You can get a good intro of vector analysis in Apostol 2.
However, there are more detailed books on multivariable calc; but that's another story.
5:22 PM
@MAFIA36790 no
Rudin is extremely difficult
But it is easier than Royden :(
It sounded very similar to Lubo's except that
> But this step, in which the original overall probabilities for the second particle were replaced by the conditional probabilities that take the known outcome involving the first particle into account, is just a change of our knowledge
is replaced by
> the probabilities and all the information are stored inside the wavefunction, which is physicaly possessed by the system, hence there is no change of knowledge
@MAFIA36790 Royden is also extremely difficult
5:24 PM
I agree.
You can go with some Analytic Geometry books too.
You can play with Euclid Axioms.
It's really interesting to do geometrical problems.
Unfortunately, I have no good name to recommend.
But dig at the Archive; you'll get many century old yet good texts.
5:28 PM
And finally buy some Flash comics.
so mine sounds like cophenhagan, except adding nonlocality and that the wavefunction is a real, physical object
@Secret kinda.
I have no idea what kind of interpretation is this
I would appreciate it if someone could explain-to-OP/mediate/step-in/vote-to-reopen/vote-to-close here.
@EmilioPisanty what evidence?
5:32 PM
@Qmechanic OP is now in a bit ranting mood.
For the 3 main interpretations I knew Evetts, Bohm and Copenhagen
I are aware of a guy mixing Bohm and Evetts to get many interacting worlds
But mine seemed to be mixing all 3 together...??
@Secret Bohm is a commie conspiracy; so nulled out.
Timaeus wrote many posts on MWI.
I think I should ask on PSE what is this weird nonlocal physical wavefunction copanhagen-like interpretation is after getting anna v and Bruce Greetham's reply on my current question
5:57 PM
Yes, its most similar to von neumann and copahagen, but it is not von neumann because the observer can be any interaction and not just a conscious entity
But otherwise no single interpretation fit this one
@DanielSank Einstein.
Hmm, only one man gives Einstein as the evidence.
Would he wear Einstein costume in Halloween?
6:07 PM
i have a question on solutions
what's the relationship between $|x-y|$ and $|x|-|y|$
does a salt usually dissociate spontaneously in water ?
@0celo7 Difficult.
this is not a chemistry chat
@MAFIA36790 not helpful
6:09 PM
this is physical chemistry
yes probably, but why?
oh never mind
it follows from $|x|=|x-y+y|$
@Vip, never mind; ask what you want. But there is also a dedicated chem chat room, just to remember.
@0celo7 Maybe.
and isn't there a dedicated math chat room ?
6:17 PM
@VIP yes


Associated with Math.SE; for both general discussion & math qu...
|x|<=|x-y+y|<=|x-y|+|y| then |x|-|y|<=|x-y|
Q: A brief history of plausible and possible candidates for Quantum Gravity

Naveen BalajiI just want to know that of all the theories that are present for quantum gravity (QG), which seems to have the best potential. I am no expert on field theories and QG, cause otherwise I would have understood the answer for the same, online. I would appreciate a simple and detailed explanation of...

Too broad?
yeh, very much.
6:57 PM
@Qmechanic I'm not keen to step into the line of fire but that was some good handling there.
1 hour later…
8:02 PM
@Qmechanic, with the question
Q: Space and Non-Euclidean Geometry

bassam karzeddinIt is quite simple in mathematics to prove theoretically this statement: “For any assumed four distinct points in 3-space (in stationary positions), which are not coplanar, lie exactly at a surface of a sphere with unique radius.” Which is easily can hold true always if we assume that the ...

I tried to explain why to the user why this all happened but looking at your previous comment I couldn't quite understand what you wanted to happen when you said "vote to reopen/vote to close" - should it be migrated to math se, or did you mean for something else to happen?
@Qmechanic, I also just want to make sure my comments make sense and are reasonable, if you don't mind skimming them real quick.
@MAFIA36790, @0celo7, thank you for the recommendations! I'll be sure to add them to my list.
@heather : Thanks for the efforts. If OP becomes combative (which I half expect), I recommend to walk away, and let other take over.
@Qmechanic, okay, I just wanted to ask about the "vote to reopen/close" comment you made a little while ago:
3 hours ago, by Qmechanic
I would appreciate it if someone could explain-to-OP/mediate/step-in/vote-to-reopen/vote-to-close here.
8:21 PM
@heather : My above previous comment (2 comments up) was meant as a reply to that.
@Qmechanic, oh, okay, I see.
on the question you marked as too broad, I voted to close and commented and I think the user understands. So that's good.
8:39 PM
@heather don't bother trying too hard with bassam, he's known to stir trouble every now and then...
@Danu, oh, I didn't know that he wasn't a brand new user. I just left those comments, and he hasn't responded yet, so I'm leaving it be.
He's posted on other sites before.
Oh, I see.
He always pushes his own stuff and gets real pissy if it (invariably) gets closed.
If you have a simple emf = E and a R1 the power dissipated is P1. Same thing with R2 (dissipated P2). I didn't understand why if you put R1 and R2 in parallel the power dissipated is P1+P2.
8:42 PM
I think the essence is that he's banned on math.se (I don't know this, but I think he said it sometime), so he posts his math stuff on other sites.
@Danu, oh, geesh.
I have a function math problem, and I kind of want to check it, the book I'm going through doesn't have the answers to the problems. It is

Describe the domain of each of the following functions:
1. $Q(t) = \frac{3}{1-2t}$
My answer was "all $t \neq \frac{1}{2}$" because if you plug in 1/2 you get zero in the denominator. I'm just not sure if that is the right way to write it.
9:17 PM
@Danu <3
@heather I think the way you wrote it is fine.
You could also write $\{ t \in \mathbb{R} | t \neq 1/2 \}$.
Oh, | means such that, right?
so then, for the next problem, finding the domain of $f(b) = \frac{\sqrt{2b-1}}{(b-4)(b+9)}$ would it be alright to write ${b\in\mathbb{R}|b\neq 0, 4, -9}$?
@heather I think so.
@heather Uh, depends... are you allowed to have complex numbers?
Also, why do you think 0 is not allowed?
@DanielSank, no, complex numbers aren't allowed. 0 is not allowed because that would give -1 under the square root, which then gives an imaginary number.
Ok, what if I put $b=-100$?
oh...good point. =)
So it'd actually be
$\{b\in\mathbb{N}|b\neq 0, 4\}$, right?
9:24 PM
Why $\mathbb{N}$?
Oh wait, what does $\mathbb{N}$ mean?
The set of natural numbers, right? So that excludes...oh, wait, that's wrong too. Okay, it'd be
$\{b\in\mathbb{R}|b>0, b\neq 4\}$ I think
$\mathbb{N}$ would exclude the numbers less than one, but it'd just be the integers, and I want the stuff inbetween.
Stick with $\mathbb{R}$ and conditions on top of that.
Yo @dmckee, what's up?
But then with $M(x) = \frac{1}{1-|x|}$ it'd be $\{x\in\mathbb{R}|x\neq 1, -1\}$ because those are the only two numbers that cause it to be zero in the denominator, with the absolute value. Okay, I think I'm starting to get it. Thanks!
You could also write $\{ x \in \mathbb{R} | x \nin \{-1, 1 \} \}$.
Dangit. \nin isn't a thing.
or $\{x\in\mathbb{R}|x\neq \pm 1\}$
9:31 PM
that's weird.
So the book is "The Cartoon Guide to Calculus" and it doesn't have the answers in it. So I googled to see if the answers were online (which is probably what I should've done in the beginning). They are, and it says the answer to the problem above, with $f(b)$, is "all $b$ except $b = 4$ and $b = –9$" which doesn't make sense, because of what you said with $b=-100$...
@DanielSank, oh, by the way, I think it is \notin $\notin$
9:46 PM
Does anybody know of a generalisation of a n-tuple pendulum for n -> inf?
I have been thinking about a floppy rod for the last 2 hrs but I can't seem to get my head around it
It seems to me there would be problems in terms of differentiation along this rod which is kind of a necessary condition for most formulations
But if your initial conditions along this floppy rod is a differential function would it still be the case after some forces are exerted
10:37 PM
Is there a four-vector equivalent of angular momentum?
@DanielSank That was always my favourite song ('cause Back to the Future).
@SirCumference Yes
@PhysicsGuy Called what?
4-angular momentum?
Neat, thanks
@SirCumference See the part "4d angular momentum as a bivector"
10:58 PM
@DanielSank It's \notin, not \nin
@ACuriousMind Yep.
Heather found it :D
@ACuriousMind, are there any limits on what numbers can be put into $\ln$? (I'm trying to find the domain of a function with a natural log in it.)
@DanielSank, =D
@DanielSank Oh, right
Once again, I should read the entire chat before commenting :D
@heather Well depends what you want really. There is no way to map zero using ln
However there are multiple ways to map negative numbers
Perhaps it would help to give the function
10:59 PM
Usually the principle branch is used

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