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4:00 PM
But you don't need to.
=)
 
@ACuriousMind ?
 
user228700
Right, I understand that a "balance" is established in this way but I'm asking about the industry of breeding animals for the sake of killing them later on.
 
Britain has the toughest laws in Europe on animal welfare, i.e. not treating domestic animals badly, and I support those.
So I'm not totally disinterested in the animal. I don't want animals to suffer just so we can eat them.
But the principle of breeding animals to eat gives me no problems.
 
user228700
@JohnRennie Why not?
 
@Kaumudi.H I don't think that can be answered. It's, well, an axiom I suppose. A basic principle that we assume instead of trying to derive.
 
user228700
4:03 PM
I understand what u are saying, but haven't u ever thought about it deeply? Perhaps venture to derive it?
 
From what principles would you attempt to derive it?
What starting point would you assume?
 
user228700
That animals don't exist for our needs--they must be allowed the freedom of having their own animal lives.
 
@Kaumudi.H I don't believe animals exist for any purpose. Animals are accidental throws of the evolutionary dice and exist only so long as their niche allows it.
So I see no reason why we shouldn't exploit them.
 
@JohnRennie be aware some people will say it's animal abuse …blah blah
 
@JohnRennie are we not also?
 
user228700
4:08 PM
Whoa there, I don't want for this to snowball into a philosophical debate but are u suggesting that humans exist for a purpose?
 
@Kaumudi.H We were created to spread the word of the Lord Jesus Christ
 
@Kaumudi.H what your religion says about humans on earth?
 
good. this has become a religion debate.
 
user228700
^ And I'm not particularly interested to talk about this along these lines.
 
Hi @YouKnowMe :)
 
4:11 PM
@Kaumudi.H Now look what you've started :-)
 
user228700
:-(
 
...what did you expect when you started to talk about what animals exist "for"? :P
 
user228700
@ACuriousMind Certainly not this!
 
my side,iam stopped,I don't want to be suspended
 
user228700
^ This is not good.
 
4:14 PM
@Kaumudi.H you clearly do believe that animal life has at least some small purpose and therefore shouldn't be discarded just because I like bacon. And I don't want to attack your views.
 
user228700
Fair enough.
 
But I don't believe views like this can be derived in any useful way.
 
user228700
I will be quick to add, however, that I don't believe that any of us (including other animals!) have any inherent purpose.
 
You can discuss them and the consequances that result from them, and that can be an interesting conversation.
 
There're volumes on existentialist philosophy out there...
 
4:15 PM
@Fawad Sorry, what?
 
6 mins ago, by Fawad
@Kaumudi.H what your religion says about humans on earth?
@ACuriousMind I will not raise these ^ questions
It's not appropriate here I suppose
 
user228700
@JohnRennie Yes. I agree that to determine what is "right" or "wrong" doesn't give way for an interesting (and decent) conversation.
 
@Fawad What? Who said so? We've only recently hashed out that there won't be any topic restrictions here. If you can have a civilized discussion about something, it's fair game.
 
@Kaumudi.H if you agree that animals don't exist for a purpose then I can't be frustrating that purpose by killing them in order to eat them.
 
So OK, @Kaumudi.H answer it
 
4:18 PM
Note that people are not obliged to discuss with you, though.
 
@0celo7 and do genocides
 
user228700
@JohnRennie U aren't "frustrating" that purpose. It was my intention to understand why your conscience allows you to kill them and I understand it now--that u don't believe that they have an inherent purpose.
 
@Kaumudi Even if I believe they do have a purpose, why should killing them affect the conscience at all?
 
Basically yes. I am not making the world a worse place by paying others to kill the animals I eat (I rarely kill animals myself though I have done it).
 
Those two are not contradictory
 
user228700
4:20 PM
@BalarkaSen Again, "breeding for the sake of killing" not killing itself.
 
@JohnRennie Well, factory farming contributes to global warming, and takes up space.
=)
 
I still don't know how that changes anything.
 
@Kaumudi.H if the breeding process was causing the animals suffering I would be uncomfortable with that, but as I mentioned above the UK is very strict on this point.
 
So technically you are making it a worse place.
 
I can very well understand something existing for a purpose and can very well not care about that purpose.
 
4:22 PM
I just don't see any reason to contribute to the enslavement of animals just so i could eat something that my body doesn't need.
 
user228700
@BalarkaSen Ah.
 
user228700
@JohnRennie Right, OK.
 
Bear in mind that wild animals generally have an unpleasant and short life.
 
user228700
@Fawad Like I said, I'm not particularly interested to have this conversation at the moment. In any case, I don't even know if I have a "religion".
 
Most wild animals die, of cold or starvation, shortly after birth.
Of the ones who make it to breeding age none will die peacefully in their beds.
I don't believe there is anything special or noble about the wild state.
 
4:25 PM
@JohnRennie What is your point?
 
Consequently I don't see there is any loss in domesticating animals.
 
There are the GHGs from factory farming and habitat loss.
But yeah, my take on this is just that i don't see any need to kill animals for food.
 
user228700
I do understand the other side of this conversation.
 
Anyone who says, or implies, I am better than you is annoying. That's human nature.
 
user228700
4:29 PM
I urge you to resist judging the title of the video...
 
user228700
> "Why Are Vegetarians Annoying? (An Exploration of a Cultural Rift)
 
@NSNoob - sorry, I don't think I got you. There will be no way to revert. We are going to consolidate the design on other SE sites to match this new design. — Oded ♦ 2 hours ago
Re the new top bar on StackOverflow
Kurtis Beavers on February 14, 2017
You may have noticed that we’re sporting a new look today.
 
is it me or the discussion suddenly shifted from existentialism and purpose of life to vegan lifestyle
 
possibly coming soon to an SE site near you?
 
user228700
@BalarkaSen It has not shifted, this is where we began.
 
4:32 PM
@BalarkaSen There was a discussion of existentialism?
 
user228700
42 mins ago, by Kaumudi. H
@JohnRennie I see. Why have u continued to stay a non-vegetarian? Do u just happen to like the taste..?
 
I jumped in the middle and it seemed like it. I have no clue what goes around this chat
 
user228700
That is where this discussion began.
 
user228700
@ACuriousMind For a little bit, yes :-P
 
@EmilioPisanty Yeah, saw that. Honestly, most of those "user responses" sound completely made up to me, but what do I know?
 
4:33 PM
@ACuriousMind meh, who cares
nav comes nav goes
remember this?
14
Q: Help! There's a giant ugly thing on top of the page!

user10851As you probably noticed, there is a new top bar implemented on this site. This is part of a network-wide experiment in... UI design I guess? Details on The new top bar is out on meta. Consider it a beta I'm not complaining about or complimenting the way the features are implemented (not her...

 
@Kaumudi.H OK, I watched the video and I basically agree with everything said in it.
 
user228700
OK :-)
 
Did you think I wouldn't?
 
this, on the other hand, is weird
in PHP on Stack Overflow Chat, 2 hours ago, by NikiC
basically Github and StackOverflow swapped headers?
what on Earth happened to github?
 
user228700
@JohnRennie Er, sort of.
 
4:36 PM
@EmilioPisanty Nope, I signed up here four months after that :P
 
@Kaumudi.H Ah. Hmm. OK. I'm curious to know what you thought I might disagree with.
 
@ACuriousMind yah, well, it happened
top bar was different before that
 
user228700
@JohnRennie I didn't think that u acknowledge the fact that vegetarianism might be better for the planet.
 
Do they say anywhere if they're getting rid of the useless "total flags pending" indicator?
I hate that number
 
@ACuriousMind if this is a mod thing, I don't think it's very prominent
 
4:38 PM
@Kaumudi.H That vegetable protein production is more efficient than animal protein production is undeniable.
 
y'all're like 0.000001% of the population
 
@EmilioPisanty No, I mean the red number to the left of review
The mod flag indicator is useful.
 
@ACuriousMind oh, that
I don't think they are
 
imho there are much more serious things which would be better for the planet than veganism, if human beings implemented them
 
And as the world population increases there's going to be a point where it's unsustainable to breed animals to eat.
 
4:39 PM
in fact, I think it's gon' become a bit more prominent
look at that big Review gathingammy top right in the new SO design
 
user228700
@BalarkaSen Veganism $\ne$ Vegetarianism.
 
That point isn't now. I don't know when that point will come. Indeed it might never come.
 
whatever
the latter is what i meant
 
@EmilioPisanty Where?
 
anyways, @ACuriousMind I give you: the pre-2013 top bar
 
4:40 PM
@Kaumudi.H but does that necessarily mean I personally should stop eating meat?
 
between achievements and all sites
the link to review
 
@BalarkaSen are you vegetarian?
 
user228700
@JohnRennie Perhaps. I suppose it boils down to whether or not u feel that ur actions might have any significant impact.
 
nah man
 
Ah. I've got no problems with a more prominent review button, just the useless number annoys me :P
 
4:42 PM
@Kaumudi.H I am pretty confident my actions have a negligable impact.
 
user228700
OK...
 
@EmilioPisanty Interesting
 
@ACuriousMind note in particular that the inbox and achievements things were different
but you can't really see that in that not-logged-in view
 
user228700
Right, I'm off. Bye, everyone :-)
 
Bye :-)
 
4:44 PM
^ previous top-left look
note two clicks needed to 'inbox' and 'notifications'
can't remember what went into 'notifications'
 
I guess there's no chance they'll hide hot questions in a dropdown again, is there? :P
 
Suppose I have a pair of differential equations like this $$\ddot{X}_1 - A \ddot{X}_2 + \omega_1^2 X_1 = 0 \\ \ddot{X}_2 - B \ddot{X}_1 + \omega_1^2 X_2 = 0\, .$$
 
@ACuriousMind nope
very much nope
@DanielSank we suppose that you do
if they are in fact equations and not just expressions
 
Compare these against a second set $$\ddot{X}_1 - C X_2 + \omega_1^2 X_1 = 0 \\ \ddot{X}_2 - D X_1 + \omega_2^2 X_2 =0 \, .$$
 
@DanielSank of expressions or of equations? =P
@DanielSank sure, what 'bout 'em?
(Also @DanielSank have you visited github lately?)
 
4:52 PM
The second set can be rewritten like this $$ \left( \frac{d}{dt} \right)^2 \left( \begin{array}{c} X_1 \\ X_2 \end{array} \right) = \left( \begin{array}{cc} -\omega_1^2 & C \\ D & - \omega_2^2 \end{array} \right) \left( \begin{array}{c} X_1 \\ X_2 \end{array} \right) \, . $$
That matrix form is useful because I know that the eigenvalues of the matrix are the squares of the normal frequencies of the coupled system.
How do make a similar approach to the first form, where the coupling comes in through the double-dotted terms?
 
Might anybody here know how to approach the following question: math.stackexchange.com/questions/2144233/…
 
@EmilioPisanty Yes.
 
Basically, if we have a dynamical system with given initial conditions, what transformations of the initial conditions would leave the symmetries of the original Lagrangian unchanged?
 
@AidanRocke @Qmechanic would probably know a lot about this.
 
@DanielSank Is he here?
@Qmechanic Are you onine?
 
4:55 PM
I don't know. That's why I pinged him.
 
*online?
 
You don't need to ping him again.
 
Thanks.
 
@DanielSank oh, I see the difference.
 
@EmilioPisanty Any familiarity with the situation?
 
4:56 PM
change to $$\ddot{X}_1 - A \ddot{X}_2 =- \omega_1^2 X_1 \\ \ddot{X}_2 - B \ddot{X}_1 =- \omega_1^2 X_2 $$
 
Yeah, sure. Then what?
 
solve algebraically for $\ddot X_j$
result will be in the form of the second set
 
Oh, right.
 
Jeez.
You know, some times I wonder about myself.
 
4:57 PM
::grin::
 
::Sulks back to den and piles rocks in front so no other sea animals can see me wallow in self-pity::
 
ah, there we go, this is what it used to look like
top bar is huge now, too
 
Which part are you concerned about?
Yeah, they changed stuff.
 
I was just trying to remember what it used to look like
and failing spectacularly
 
Mostly, they made the top bar dark. I don't know why.
Not as spectacularly as I!
I can't even algebra!
4
 
5:00 PM
If you're going to do embarrassing stuff, it may be advisable to not write it up in single starrable chat messages =P
 
@EmilioPisanty I didn't! My question was written in several messages.
"I can't even algebra" isn't embarrassing... it's funny!
I'm proud of my star history. It strikes a good balance between rants and humor.
More linear algebra things:
The first set of equations above can be written as $$M \left( \begin{array}{cc} \ddot{X}_1 \\ \ddot{X}_2 \end{array} \right) = \left( \begin{array}{c} - \omega_1^2 X_1 \\ - \omega_2^2 X_2 \end{array} \right) \, . $$
Where $M$ is a matrix.
Therefore, $$\left( \begin{array}{c} \ddot{X}_1 \\ \ddot{X}_2 \end{array} \right) = M^{-1} \left( \begin{array}{c} - \omega_1^2 X_1 \\ - \omega_2^2 X_2 \end{array} \right) \, . $$
 
@AccidentalFourierTransform You are the man. Thank you.
 
I never actually had a linear algebra course. In my freshman year of undergrad, my math course was "Linear algebra, multivariable calculus, and differential forms". Therefore, we learned the lin alg we needed to understand differentiation in $\mathbb{R}^n$, but no more.
 
5:11 PM
@DanielSank $$\left( \begin{array}{c} \ddot{X}_1 \\ \ddot{X}_2 \end{array} \right) = -M^{-1}\begin{pmatrix}\omega_1^2&0\\ 0& \omega_2^2\end{pmatrix} \left( \begin{array}{c} X_1 \\ X_2 \end{array} \right) \, .$$
 
I skipped the "math for physicists" course because I expected it to be crap, and I skipped the linear algebra course because I thought it would be too much of a review.
@EmilioPisanty Yeah. Thanks!
 
also, you have anything against \begin{pmatrix}?
 
@DanielSank what a shame
algebra I and II were the best courses I took
 
@EmilioPisanty I didn't know about pmatrix. Will have to look it up.
 
^ agree
 
5:13 PM
Hahaha, just realized I'm talking to two different people.
 
@DanielSank \begin{pmatrix}a&b\\c&d\end{pmatrix} produces $$\begin{pmatrix}a&b\\c&d\end{pmatrix}$$
 
Feb 5 at 19:53, by 0celo7
@EmilioPisanty @AccidentalFourierTransform can one of you change your avatar pls
 
@EmilioPisanty Well that's useful.
Ciao
 
@EmilioPisanty What's with the minus sign on $-M^{-1}$?
 
5:24 PM
$-\omega^2\to\omega^2$
 
oright
 
@Qmechanic Does my question make sense to you?
 
@AidanRocke Im just a newbie, but the question does not make much sense to me
transformations of the initial conditions dont change the Lagrangian
 
@AidanRocke Point of advice: don't ping users more than once. They'll see the ping when they load the site.
 
the latter is independent of the fomer
 
5:30 PM
Pinging multiple times just puts extra junk in their inbox.
It's annoying and completely un-necessary.
 
@DanielSank @DanielSank @DanielSank @DanielSank
 
@DanielSank Ok. I'm just adjusting to this. :)
 
also, symmetries are independent of coordinates
 
@AidanRocke Online chat is an asynchronous communication protocol.
 
@AccidentalFourierTransform Changing the initial conditions would change the Lagrangian of course.
 
5:31 PM
you cannot lose/gain symmetries in a certain system by changing your coordinates
 
Think about the gravitational potential energy.
 
Qmechanic will see your ping at some time. Then he might write an answer to your question, or not. Then you might come online later and see the answer. It doesn't have to happen in real-time.
 
If you change the relative positions you get different potentials.
@DanielSank True.
 
@AccidentalFourierTransform Sure you can.
 
@DanielSank wat? how is that?
 
5:32 PM
$V(x) = x^2$ has reflection symmetry.
If I shift it, the reflection symmetry is gone.
 
It's note really gone, but you know what I mean.
 
its implemented t¡differently, but its there
 
yeah yeah ok we agree
 
Looks like after not doing them for 7 years, I'm gonna have to do Weyl algebras again
 
5:32 PM
Basically, I'm interested in perturbations of the initial conditions which leave the constants of motion unchanged.
 
Apparently free fields in AQFT are all about the Weyl algebras
 
@AidanRocke the constants of motion are independent of the initial conditions
 
How do you "do" Weyl algebra?
 
@DanielSank with some lube and coffee
 
@AccidentalFourierTransform Are you serious?
 
5:34 PM
-_-
 
@AidanRocke well, take a system that is invariant under rotations
you have a constant of motion, the angular momentum
whether your particle is initially at rest, or moving very fast, doesnt change the fact that angular momentum is conserved
and neither does it change the formula for the angular momentum, $L=r\times p$
 
True. But, would you preserve linear momentum?
 
@AidanRocke that depends on the Lagrangian, and whether it is invariant under translations or not
but it is independent of the initial conditions
 
The issue is that the initial velocities are not necessarily zero.
 
that's irrelevant to whether $p$ is conserved or not
the only condition for $p$ to be conserved is that the Lagrangian is invariant under translations
 
5:37 PM
If the initial velocities are not zero, a rotation would only guarantee that the potentials are unchanged.
So the angular momentum isn't guaranteed to be conserved.
 
hmm no, the potential is $V=1/r$
 
You would need to rotate the velocity vectors as well.
 
@AidanRocke The fact is simply that conserved quantities arise from symmetries of the Lagrangian by Noether's theorem. The initial conditions nowhere even begin to enter into it.
 
yeah, pretty much what ACM said
there are some technical assumptions for the action to converge, and to be able to drop boundary terms
 
What I don't understand in this discussion is that if I change one of the original positions in the initial conditions, the dynamics are different. Clearly the hamiltonian will be different.
 
5:39 PM
no, that's the point
the Hamiltonian is $H=T+V$
with $T=\frac12m v^2$ and $V=1/r$
where are the initial conditions there?
 
the intitial conditions would be r(0) and v(0)
*initial
 
Do we agree?
 
about what? about the initial conditions being r(0) and v(0)?
 
About the fact that if I change r(0) or v(0) I get a different Hamiltonian with different symmetries in general.
 
5:43 PM
@AidanRocke No, because neither r(0) nor v(0) appear in the Hamiltonian.
 
no, the Hamiltonian is always $H=\frac12 m v^2+1/r$
that is independent of r(0) and v(0)
 
The Hamiltonian is a function on phase space, not on paths.
 
Ok. Maybe I'm getting really muddled.
I have been simulating the n-body problem for several weeks now and I have gotten used to thinking in terms of initial conditions.
 
maybe this'll help
the form of the Hamiltonian is independent of the initial conditions
 
Ok. Maybe I should rephrase my question.
I think I understand you guys now.
 
5:46 PM
the actual value of $H$ for a certain trajectory depends on the initial conditions
but the general form of $H$ is always the same
 
0
Q: Do you care about (micro) typography?

mhchemWhile thinking about if and how my MathJaX extension could benefit Physics.SE, I had a look at some of your questions and answers. I realized that you (I mean the community, not individuals) seem not to be overly concerned with the fine details of scientific typography. I see that you write units...

 
My question was exactly that.
 
and most importantly, it is always conserved
 
I want transformations that preserve the value of the linear momentum, H, and angular momentum.
 
if you change the initial conditions, the actual value of $H$ will change
but the fact that it is conserved will not change
@AidanRocke that depends on the details of the actual system
for example, for a harmonic oscillator, $H=p^2+x^2$, any rotation in the $(p(0),x(0))$ plane leaves the value of $H$ unchanged
for more general Hamiltonians, I dont think that there is a general rule
 
5:48 PM
@AccidentalFourierTransform I'm thinking of the special case of the gravitational n-body problem.
Any isometry applied to the initial conditions leaves the values of linear momentum and H unchanged.
 
@AidanRocke n-body problems dont have analytical solutions in general
so I dont think that there is an explicit answer to your question
at least, I dont know it off the top of my head
 
Hmmm...
 
but yeah, edit your other MSE post to clarify your question a bit
 
@DanielSank very carefully
 
and if someone knows the answer, it'll be Qmechanic
 
5:51 PM
@AccidentalFourierTransform Thank you for your patience.
This discussion was very helpful.
 
@AidanRocke Im glad I could help :-)
 
$\mathfrak{fraktur}$
 
6:48 PM
From what I can divine the issue with non-globally hyperbolic spacetimes is the lack of uniqueness for a QFT algebra
Well there are probably more issues but that is one of them
Also I don't get QFT algebras
I thought distributions did not form an algebra
Although I did see a wavefront set passing by
Do we only consider reasonable operators as part of the algebra
 
7:04 PM
@Slereah operators form algebras
Or are you trying to get operator valued distributions?
 
Well that's how they are constructed, yes
 
Maybe you should read the book on electric algebras
 
8:04 PM
howdy folks
 
8:16 PM
I decided to get University Physics With Modern Physics by Sears, Zemansky, and Young instead of Feynman Lectures On Physics in the end.
I think SE should not ban Ron Maimon for ten years. I think he is a great man who is seriously misunderstood.
@skullpetrol I see you like to hang out here as well.
 
@JasperLoy I have that book
 
@0celo7 Great. That makes me not totally off.
I did not need it for a class, so I got the cheaper global edition for one third of the price.
I believe the content is essentially the same. At most trivial differences.
 
How much did you pay?
 
About 70 USD.
 
That's reasonable.
 
8:26 PM
your face is reasonable
 
-_-
 
I hope Chris's Sis will return to math chat. She is also a great man who is seriously misunderstood.
 
I hope Chis White returns here.
 
Me? I am also seriously misunderstood. But I am not a great man. I am only a banana.
 
@skullpetrol He won't
 
8:35 PM
Too bad @0celo7 why not?
 
@skullpetrol Shhh
 
You're never gonna forget that are you?
 
Ah, I need the energy of a dipole
google!
no, that doesn't help either
@EmilioPisanty are you present?
 
8:58 PM
Doesn't his avatar have to be "present"?
 
It was when I asked the question
 
@0celo7 I'm around
@0celo7 energy of a dipole?
 
@EmilioPisanty no
 
what, as in self-energy of an electrostatic dipole?
or what's up?
 
If I'm doing perturbation theory, and I have the energy to second order, can I get the eigenvector to first order without doing any extra work?
Or do I have to go and calculate the matrix elements of the perturbation as usual
 
9:12 PM
@0celo7 huh
no idea
I don't normally seek out pain for no reason
ditto for perturbation theory
=P
 
well, it was worth a shot
the recitation is in 18 minutes
I can ask there
The question wants me to compute an "expression for the dipole moment" of an electron in the ground state subjected to an electric field
but it wants me to do it in two ways, and that doesn't make much sense
the dipole operator is just $ez$, since the field is along the $z$-axis
So I need to compute $\langle ez\rangle$ in the perturbed ground state
and I did that
oh well
 
@0celo7 pretty sure you need matrix elements.
 
@DanielSank Right. So I'm not sure how knowing the energy to second order helps me with $\langle ez\rangle$
 
@JasperLoy you can always read the Feynman lectures on line.
 
9:39 PM
@0celo7 who said it would?
Oh I should read more
 
Does the chatjax work with Mac/Safari?
Happy Valentine's Day everyone
!!
 
10:42 PM
If an electron does not orbit a nucleus in the same way that a planet orbits a sun, then why do we still talk of the electron's angular momentum?
 
10:59 PM
@whatin1992 Theoretically, I think it should, but you'll probably have to try it
 
11:10 PM
hello
 
rob
11:20 PM
@0celo7 Howdy
 
11:43 PM
@rob Was Spanier here when you were?
 
11:54 PM
He failed 3/4 of the people in my modern physics class on the first test
It was not hard at all
How do people do the homework and then act surprised when the exact same questions show up on the test?
 
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