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12:17 AM
@EmilioPisanty Truth be told...
 
 
4 hours later…
user54412
3:49 AM
@DanielSank So I'll be SB from noon this Sunday to Tuesday afternoon. I don't have any plans for Sunday so if you want to meet an internet stranger...
 
@ChrisWhite !
@ChrisWhite say I have $f:M\to N$ and $\phi:\mathbb{R}\to M$
and I have a chart $(h,U)$
 
user54412
ok...
 
and then I write $f(\phi(t))=(f\circ h^{-1})\circ (h\circ \phi(t))$
can I Taylor expand this like I would anything on $\mathbb{R}^n$?
because $f\circ h^{-1}$ is just a function on Rn
and $h\circ\phi(t)$ is a curve in Rn
 
user54412
i think so
 
hello!
 
4:04 AM
God save us
 
user54412
?
 
satan is here
 
ummm what?
 
user54412
good to see things make as little sense around here as usual
2
 
4:09 AM
does no one else see the pentagram
 
user54412
aren't pentagrams upside down?
 
it's a pentacle ancient-symbols.com/pagan_symbols.html - a Pagan symbol, not satanic sysmbol
 
Pagan = satan
 
incorrect
Paganism is not satan worshipping at all
 
4:25 AM
@ChrisWhite How do I show the pushforward is linear?
using Arnold's definition
I think I need to show that given two vectors there is an equivalence class of curves that gives a linear combination of these vectors
hmm, so I need to give the set of equivalence classes of curves a vector space structure
 
but given that I am an Atheist, the image is a series of geometric forms to me
 
user54412
@0celo7 what's arnold's def?
 
4:40 AM
Hail Satan!
 
@ChrisWhite if $\phi$ is in the equivalence class defining the vector $v$ then $$f_*v=\left.\frac{\mathrm{d}}{\mathrm{d}t}\right|_0f(\phi(t))$$
@Slereah exactly!
 
grow up
 
Random 2
https://en.wikipedia.org/wiki/Pando_(tree)
 
user54412
@0celo7 sounds right -- something like addition being concatenation
 
user54412
I'm assuming equivalence classes are just reparameterizations with the same images
 
user54412
4:45 AM
Also, I'm only 10% paying attention, and about 5% coherent
 
@ChrisWhite concatenation? no
that doesn't make sense
I think
 
@Ghost Yes, paganism and satanism are miles apart
 
@Secret except to the ignorant
 
though I still know very little about satanism other than it is often used in heavy metal.
To date I have still refused to read the wikipedia article on satanism for fear of getting my future screwed due to being exposed to some dangerous concepts
 
user54412
@0celo7 Mmm perhaps you're right. But now I don't really know what's going on. What are curves? Maps from R to a manifold? What equivalence relation do we have then?
 
4:48 AM
@ChrisWhite my coherence and attention match yours
how about we don't do this at 1 in the morning :)
 
user54412
agreed
 
user54412
especially after I was coerced into rewatching 2001 a few hours ago
 
user54412
that LSD feeling lingers on
 
@Secret I am an Atheist - and what I see is a pentagon, 5 isosceles triangles and 5 wedges - in a geometric pattern that is called a pentacle (or a pentagram to the ignorant) and is a symbol of Paganism (which is not satanism)
 
looks like 666 to me
 
user54412
4:51 AM
@Ghost I count 10 isosceles triangles ;)
 
I am agnostic, thus I see both the religious meaning and the straightforward geometric meaning
 
@ChrisWhite even better!
 
I see 666 triangles :o
 
@0celo7 whatever, kid
 
why are you calling me kid?
 
4:52 AM
My current belief system is:
when in doubt, listen to what all worldviews said, and the truth is usually the weighted average of the intersections plus some outliers
 
@0celo7 why are you calling me 'satan'?
 
@Ghost your Halloween costume suggests it
 
@0celo7 whatever amuses you
 
I was hardcore scientism back in 2013, and then become agnostic afterwards
 
scientism?
 
4:56 AM
Scientism is belief in the universal applicability of the scientific method and approach, and the view that empirical science constitutes the most "authoritative" worldview or the most valuable part of human learning - to the exclusion of other viewpoints. Accordingly, philosopher Tom Sorell provides this definition of scientism: "Scientism is a matter of putting too high a value on natural science in comparison with other branches of learning or culture." It has been defined as "the view that the characteristic inductive methods of the natural sciences are the only source of genuine factua...
basically someone who is way too into the scientific method and think it solves everything
 
@ChrisWhite Hells yes!
Wanna email me?
You can find my email via my Physics.SE profile.
 
user54412
sure
 
It's not a healthy attitude because it leaves no room for arts, culture , philosophy etc.
 
@ChrisWhite that makes my profile much simpler to write
 
Apparently @Ghost is rather sore at being thought a pawn of Satan
 
4:59 AM
@Slereah not really
 
Poor choice of avatar for this
 
the silver lettering has worn off of my Visa
now it's ghetto
@Slereah he's trying to attract attention
 
@Slereah not really, depens how you perceive it
 
You should have taken the opposite of a satanist avatar
Like a kitten
 
it is not a satanist avatar
 
5:01 AM
Sure, why not
The cross is also just a geometric shape
 
it's a pentagon, surrounded by 10 isosceles triangles, surrounding by a circle
 
Being an agnostic helps me to open to all possible worldviews.
This is how I learn a bit about Buddhism, Paganism, Hinduism, Sikhism, Taoism, Muslim etc.

However because of my inherently straw nihilistic dark personality, hence easy to get addicted to dangerous concepts, I don't think I am ready to learn about satanism yet, for fear of destroying my future
 
Satanism is mostly a religion of people who like to dress in silly costumes
 
I am an Atheist, I have no religion
 
5:07 AM
Within the scientific community, it gives me an asset and liability to consider alternate ideas seriously, which is why I often need help form other professionals and nature itself to tell me whether I am on the right track
 
Happy halloweeeeen
 
to me, God, satan, heaven, hell etc etc do not exist
 
while to me, all of these theological entities cannot be detected by science, but we are not sure if they are compeltely ruled out of existence
 
each to their own beliefs, observations, whatever
 
So in short, I am agnostic with a science core
which is why people often confused I am atheist
 
5:09 AM
@Slereah to me, it is
 
@Slereah we need to get together sometime
you coming to this side of the pond any time soon?
 
Not in the near future
 
O btw I have two physics questions
 
I am all about Science and Mathematics - so my avatar is a series of geometric shapes that I like - if others have a problem with it, too bad
 
No problem
Just a tad amusing to see you so defensive
 
5:14 AM
I wasn't the one that started with the childish 'satan' crap
 
Q1 Is there a maxwell boltzmann like distribution that relates rotational states J with populations in the rotational state?

Q2 I often heard that entropy in statistical mechanics is the no. of microstates that give the same macrostate. How is this different form the no. of degeneracy?
Q1 i.e. Given rotational states J, if there exist f such that $$\frac{N_J}{N}=exp(f(J))$$ ?
 
Degeneracy isn't for macrostates
Degeneracy is the number of states for a given eigenvalue of the Hamiltonian
 
user54412
you're all seeming particularly... weird tonight... in an adorkable sort of way
 
Maybe because it is HALLO
OWEEN
 
@ChrisWhite lol 'adorkable' - love it
 
5:17 AM
All sorts of spooks and goblins tonight!
 
user54412
I'm about to fall asleep, and now I'll probably dream about the personas in this chat room.
 
I think I'll be keeping this avatar - love the symmetry and how the shapes come together
 
It only has $Z_5$ symmetry
Pretty weak
Well also $Z_2$
 
So is degeneracy in some sense a "subset" of microstates, because of how you can have some configuration of some quantities that corresponds to some macrostates described not (or not just) by the same energy, but also other thermodynamic properties like pressure, volume?
 
user54412
$Z_5$ rotations $\rtimes$ $Z_2$ reflections = $D_{10}$?
 
5:24 AM
Wot
Well degeneracy will contribute somewhat to the number of microstates for some macrostates
 
i.e. Let's assume we have some system $S$ and it has the following degrees of freedom $(a, b, c, d \cdots)$. Therefore each state $i$ in this system is described by the ntuples $k_i=(a_i, b_i, c_i, d_i \cdots)$

So for degeneracy in i it will be the number of $k_i$ such that

$$\hat{H}|k_i\rangle=E_i| k_i\rangle$$ (1)?

But since a macrostate $Z_j$ can be described by some m tuples $(A,B,C,\cdots)$ e.g. P, V, T

So we can have some microstates $k_i$ that satisfy

$$\hat{A}|k_i\rangle=A_i|k_i\rangle$$ etc.
Thus showing that $degeneracy \subseteq microstates$ ?
typo: The 2nd set of $k_i$ s after (1) should be $k_j$
 
5:50 AM
@ChrisWhite Never heard "adorkable" before.
 
 
1 hour later…
user116211
7:15 AM
I wish each & every member of the community a great haunted Halloween:P
2
 
user116211
 
7:56 AM
Get out the Fadeev Popov ghosts and the skeleton diagrams!
 
8:31 AM
@DanielSank "Advanced level question plzzzz help"
best title
 
user116211
9:06 AM
@Danu: Really advanced!! How could he get such creativity??
 
user116211
I was thinking many things when I was about to click that question & then when I noticed it, to me, it was the greatest joke of the century! Really advanced:P
 
 
5 hours later…
2:42 PM
Hello?
 
probably everyone is too busy celebrating halloween
hence the silence
 
What time is it where you are
 
1:49, so australia probably has passed halloween
 
Eastern coast?
 
yup, sydney
 
2:55 PM
@KyleKanos and other reviewers: Concerning physics.stackexchange.com/q/215612/2451, I stopped the migration to Math.SE in accordance with the Don't-migrate-crap-policy.
 
@Secret I know someone near Brisbane so I know the time delay to the Aussie East Coast :)
 
3:27 PM
Qualitatively speaking can anyone explain the main differences between Dirac-Bergmann vs Jackiw-Fadeev approach to constrained dynamics?
 
4:12 PM
On an unrelated note does anyone have familiarity with Markov chain Monte Carlo? I am running a code I have written for global optimisation and part of the procedure involves MCMC steps. I set limits for the acceptable range that the variables are allowed to step within, I know roughly what are appropriate and I am just refining the values.
HOWEVER
...
Whenever I run this, all my variables tend to the maximum limit of their value. So I, initialise them, update them via Metropolis Hastings and they all tend to the maximum permissible value!!
Any ideas?
 
4:27 PM
@AngusTheMan Jackiw-Faddeev presupposes a first-order Lagrangian and is mainly interested in obtaining the correct quantized theory. Dirac-Bergmann is both an approach to quantization and the classical theory, and works with essentially arbitrary Lagrangians as starting point.
No idea for your Monte-Carlo thingy though, I suck at those.
 
@ACuriousMind Ah so only for first order Lagrangians then! Cheers that clears it up :) haha yeah me too actually come to think of it!
 
@AngusTheMan Difficult to say without seeing the code. What do you do at the boundaries anyway? Just reject the move?
 
@AngusTheMan Well, the "only" is not as restrictive as it sound, given a Hamiltonian $H(p,q)$ you can always make a first-order Lagrangian by Legrendre transforming, but keeping the canonical momentum as a configuration space variable, i.e. get a Lagrangian $L(q,p,\dot{q},\dot{p}) = p\dot{q} - H(p,q)$.
 
@alarge So its for replica exchange monte carlo, for structure refinement from diffraction data. We always have a rough idea of what the values of the crystal parameters (unit cell, microstrains, thermal ellipsoids etc = variables) to start with, so we need to keep them within a given physical limit. If I didn't put a limit on then the Monte carlo would take them way out of acceptable values leading to inefficient computation. I reject the update if it is outside them limits.
 
@AngusTheMan Well could it be that the values are somehow unfortunate and you are stuck in a local minimum of some kind?
 
4:42 PM
@alarge I could be, I mean I let it run for about 2 hours and I got several exchanges, and in general it was getting better. Maybe if I optimised it more then with more exchanges it would converge. Because it is the exchanges that allows it to get out of the local minima. \
@ACuriousMind So this is the phase space Lagrangian. Are we not inverting the conjugate momenta there?
 
@AngusTheMan Nope, the whole point is not doing that to keep the first order form. (First order means that the time derivatives only appear linearly, in case you thought something else)
 
@ACuriousMind So we generate mixed $p\dot q$ terms in these Lagrangians then? Just out of interest, surely such an object can't live in $T^*M$ for configuration manifold $M$? Maybe $T(T^*M)$?
 
@AngusTheMan Exactly. The phase space $T^*M$ is now the configuration space and the Lagrangian lives on its tangent bundle
 
@ACuriousMind Ahhhh... So if I had an $n$th order Lagrangian can I always create such first order one? Is this to do with higher order field dependence .. Ostrogradsky? etc..?
By taking successive tangent bundles to phase space - 'configuration manifolds'
 
@AngusTheMan You don't have to iterate - doing this once suffices: Take the Lagrangian $L(q,\dot{q})$. Legendre transfrom it, if the transform is singular add the constraints with Lagrange multipliers $\lambda$ to obtain the Hamiltonian $H(q,p,\lambda)$, now write $L(q,p,\lambda,\dot{q},\dot{p},\dot{\lambda}) = p\dot{q}-H(q,p,\lambda)$ which is obviously first-order.
 
4:55 PM
What on Earth are you guys talking about?
 
@ACuriousMind But what about higher order field dependence? $L=(q,\dot q,\ddot q,\dots, q^{(n)})$
 
@AngusTheMan Oh, who does that? :P
 
not field... discrete coordinates
@ACuriousMind Einstein-hilbert?
;)
(I think)
 
If you have dependence of the Lagrangian on higher derivatives, none of the usual procedures work. I'm not sure if one can obtain a Hamiltonian picture for those
 
Oh yeah, the whole instability thing.
 
4:57 PM
And you need a Hamiltonian picture for canonical quantization. Not sure if anyone has been crazy enough to look what the path integral does with those Lagrangians
Albeit using the path integral without a Hamiltonian picutre is also ill-defined because it is usually derived starting with $U(t) = \mathrm{e}^{\mathrm{i}Ht}$
 
srs what is this
 
hmm true! I think they are generally not physical systems, purely academic? But would be nice to develop a generalised approach which reduces to the usual for only second order. Cheers for the conversation Curious mind, you cleared a lot up in my mind :) normally I don\t get to talk about mechanics with people ...my friends being chemists and all ... ;)
 
@0celo7 How to generate the first-order Lagrangian for the Faddeev-Jackiw method for constrained quantization, not sure what's unclear about that ;P
 
@0celo7 I was asking how to reduce the order of a Lagrangian to $(n-1)$.
 
@ACuriousMind what does one need this for (and I've never heard about that, so)
 
5:05 PM
taking classical systems ---> Quantum description
 
yes, that's what quantization is
is this for gauge theory?
 
Yeah, the main use case of quantization of constrained systems is for gauge theories.
Some people might even use the terms "constrained system" and "gauge theory" interchangably
 
so is this in QoGS
 
They do not talk about the Faddeev-Jackiw method, no
 
well never gonna learn about it then
QoGS is on my list
but at this point physics is being pushed out of the way
@ACuriousMind so, there's an exercise in Arnold to prove the pushforward is linear. I can do this using the "western" treatment of vectors, but it's not clear at all in the equivalence class of vectors picture
 
5:15 PM
The "equivalence class of vectors" approach is not distinctly Russian, you can find it all over "Western" diffgeo, too. Sometimes it's convenient to think about derivations, sometimes about curves.
 
*equivalence class of curves
 
Huy
wat
 
what is your confusion, my son?
 
Huy
why is plex still not approved on apple tv 4 app store
i am angry
 
@ACuriousMind Right, so what I first want to do is show that the "equivalence class of curves" tangent space is a vector space.
So there has to be an isomorphism $\alpha:T_pM\to \mathbb{R}^n$
 
Huy
5:21 PM
is trivial m8
 
@Huy for you
 
Huy
4u2
 
So let $[\gamma]$ be the equivalence class defining the vector $v$.
So $\alpha(\gamma)=v$ where $\gamma\in[\gamma]$. Injectivity: Suppose $\phi\notin[\gamma]$ but $\alpha(\phi)=v$. But by definition, $\phi\in [\gamma]$. Contradiction, so $\alpha$ is injective. Surjectivity: For each vector $v$ there must be an equivalence class. To prove this, simply construct the equivalence class, starting with one vector $\gamma^i(t)=\gamma^i(0)+v^it+O(t^2)$ and all vectors in the class differ from this one by second order terms.
@Huy Good enough?
so, given this, we can define a vector space structure on the space of equivalence class of curves
@ACuriousMind Perhaps: Let $\gamma_1,\gamma_2$ be curves in equivalence classes defining vectors $v,w$. Above we defined how $av+bw$ can be represented by another curve $\gamma$. Then $$f_*(av+bw)=\left.\frac{\mathrm{d}}{\mathrm{d}t}\right|_0f(\gamma(t))=\cdots=Df‌​\cdot (av+bw)=\cdots=af_*v+bf_*w$$
@ACuriousMind Something like that?
there's some chart stuff missing + other details
 
5:42 PM
Since I don't know how you defined half of the things there, I can't say much more than "You seem to have the right idea".
 
what do you need defined?
@Huy plex?
 
@0celo7 Not really in the mood for nitpicking proofs, so nothing
 
@ACuriousMind is there a mood for them?
 
https://en.wikipedia.org/wiki/Consistent_histories
>However, Griffiths[4] holds the opinion that asking the question of which set of histories will "actually occur" is a misinterpretation of the theory; histories are a tool for description of reality, not separate alternate realities.
 
Huy
sory 0celo7 I'm trying to make some dinner with what's left in my kitchen since I couldn't be arsed to go groceryshopping today
 
5:53 PM
I must be misunderstood or soemthing, but after looking at the maths of consistent histories and then recalling the very brief introduction on the concept of path integrals and its relationship with action, it still give me an impression it is some kind of alternate reality
in particular, it seems the experimental outcome that we observed is the only set of histories that are consistent
out of all the possible histories, with some probability
 
6:06 PM
I'm always a little surprise to find out what basic questions we don't have a good answers for.
I'm offering a 250 point bounty on
3
6
Q: How do electrons "know" to share their voltage between two resistors?

jeffythedragonslayerMy physics teacher explained the difference between voltage and current using sandwiches. Each person gets a bag full of sandwiches when they pass through the battery. Current = the number of people passing through a particular point per unit time. Voltage = the (change in) number of sandwiches...

Get in while the getting is good.
 
...sandwiches? oO
What kind of analogy is that? What's wrong with the old "It's like water in a pipe"?
 
What's wrong with the old "virtual photons are whizzing back and forth"?
 
Random 4
https://www.google.com.au/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=multivalued+energy+distribution+in+time
 
6:48 PM
Is anyone here familiar with bundle methods of descent, as mentioned here? It links to a page on subgradient descent, but that's obviously not a descent method.
 
7:24 PM
Hefty bounty you put out there @dmckee
@dmckee I feel like @DanielSank would be into this? Not sure why... probably because something something circuits something something engineering ;)
 
I hear the circuits class is the hardest class in undergrad here
 
@ChrisWhite Might've been the LSD you were taking? :)
@0celo7 Because nobody manages to stay awake?
 
@Danu That's not entirely wrong :)
truth be told I'm having a hard time staying awake doing (inverse) Laplace transforms right now
who wants to inverse transform $$\frac{s+5}{s^2-4s+4}$$
partial fractions is too hard :(
 
Huy
sory
my students do partial fractions too
they were really good at it
better than integrating by parts
 
they hate you for it
 
Huy
7:31 PM
nah they love me
im the coolest teacher eva
 
no
did you take a look at my solution above?
 
Huy
nah I'm looking at a review of the Toyota Aygo now
I need to figure out which car to buy
 
bish
check it out, the proof is so elegant
 
Huy
lol
good one
 
ok I'd like to see you prove it more elegantly using the shitty definitions I was given
 
Huy
7:34 PM
I'm busy watching car reviews
that's a bit more important to me atm
sory bro
 
so you insult me and then leave
 
Huy
that's what she did
 
I see how it is ::sniff::
 
Huy
send me 10k to spend on a car and I'll look at ur proof
 
bank account?
I should send you like 1 cent :P
 
Huy
7:35 PM
i will report u
 
what?
why
 
Huy
for troling
u trol
 
you're crazy, you know that?
insane even
more so than the resident ayy lmao even
 
Huy
wat
I just want a car m8
why is that crazy
 
hey get your students to partial fractions $[(s+2)(s-2)]^{-1}$ for me
 
Huy
7:37 PM
lol
they can do that in less than 1 minute
 
teach me
 
Huy
ansatz
A/(s+2) + B/(s-2)
 
oh, no shit
 
Huy
ikr
 
I thought you had some super secret method
 
Huy
7:38 PM
no
that takes 1 minute
 
I've been on it for 5
 
Huy
wtf
you get
$\mp \frac{1}{4}$
enjoy
 
mind = blown
 
Huy
troll
 
why do you call me this hurtful word ;_;
 
Huy
7:40 PM
the truth is quite hurtful sometimes
 
great, I must have done something wrong...that's not the solution
 
Huy
because you forgot the numerator
 
I didn't.
The solution of the ODE is wrong
 
Huy
lol
 
Wrong form, even.
 
Huy
7:41 PM
nub
I'm looking forward to teaching complex numbers next year
then they will enjoy partial fractions a lot more
 
what's a complex number
 
Huy
one too complex for you to understand
 
ouch
 
Huy
involves vectors and equivalence classes
very abstract
but in the end it's just isomorphic to $R^n$
 
what!
 
Huy
7:43 PM
ikr
 
complex numbers are isomorphic to $\mathbb{R}^n$??
for any $n$?
 
Huy
yes
even $n = \infty$
that's the so called Riemann sphere
 
hory shite
tell me more
 
Huy
it's a compact space
 
is that the thing from string theory
 
Huy
7:44 PM
because whenever $n = \infty$, the space is compact
and thus all norms are equivalent
 
dude how much of this is BS
 
Huy
XD
 
in any case
 
Huy
wat case
 
the case of $y''+4y'+4y=0$ and a stupid student
$y(0)=y'(0)=1$
 
Huy
7:47 PM
wat
why did you need that fraction before
don't you just get $\lambda = -2$
 
uh, Laplace transform
because
I'm not that smart
 
Huy
ok
 
see I get an exponential in the answer
 
Huy
ok
 
but I can't get the $x\mathrm{e}^{-2x}$ part
 
Huy
7:49 PM
sory
 
I can solve it by eye using the characteristic equation method
 
Huy
but ?
 
but the directions of the problem are to use Laplace transforms...
 
Huy
then use it
 
aha! sign error!
 
Huy
7:50 PM
no
an odd number of sign errors
 
"a" sign error implies one, one is odd
 
Huy
I learned that joke from MO
very funny site indeed
don't ruin my jokes
 
aha! there's the three! omg no partial fractions! woooooo
 
Huy
would have been too hard for the other students
right ?
 
partial fractions is just about the most challenging thing there is math
 
Huy
7:53 PM
can you prove uniqueness and existence of it?
 
god no
 
Huy
I had to
in first semester
I was horrified
 
I have the mathematical maturity of a middle schooler, how many times do I have to say it
 
Huy
I'm looking at my old analysis exercises now
on the same exercise sheet there's Weierstrass function
I don't think I learned a lot from that proof
 
Huy
7:55 PM
hue
 
I could never do that
 
Huy
@0celo7: http://i.imgur.com/LvlIRga.png
recognize who the prof is
 
no
 
Huy
trol
 
sure, just call me that
 
Huy
7:57 PM
the other day u asked about a book for ergodic theory
 
yeah
 
Huy
I sent u a book
it's the same guy
ur bad with names
 
I think you're the troll
 

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