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00:00
@0celo7 Learn to play your games without me, I don't have fun discussing ME mechanics.
2
lol
I've literally been eating continuously all day
this is the best part of being home
unlimited fooood
@ACuriousMind I don't want to
 
8 hours later…
08:02
https://www.youtube.com/watch?v=X_xR5Kes4Rs

whenever I ponder about this question, I tend to think from the opposte perspective (some kind of attempt to proof by contradiction???)

What does a physical phenomenon that cannot be described by mathematics look like. How can we understood it?
08:20
@FenderLesPaul thanks again for the link. Been going over Anna Kostouki algebra video lectures. 6 hours of algebra. I will start the next course 1st thing in the morning(special functions and differential equations)
hey @kevinTahN.
hey
I have been glued to my pc learning hardcore lol
hardcore?
I want to play Mass Effect some more...
Damn, I have not played that in a while lol
hmm, my bank is not happy that I'm logging in using some random European IP
08:24
lol, sometimes the security measures are counter productive
what type of transaction are you trying to do?
check my account before I buy DLC
gotta make sure I don't overdraw, no clue when I last put money on my debit card
ah I see, wait what is DLC?
expansion pack?
Downloadable content (DLC) is additional content created for a released video game. It is distributed through the Internet by the game's official publisher. Downloadable content can be of several types, ranging from aesthetic outfit changes to a new, extensive storyline, similar to an expansion pack. As such, DLC may add new game modes, objects, levels, challenges or other features to a complete and already released game. DLC and a content creating and sharing user base are essential long-term needs in more complex simulator products such as V-scale model railroading applications (such as Trainz...
lol, the abbreviation threw me off
oooh
I can buy all the DLC
08:28
nice
don't know if I want to, though
@kevinTahN. are you American/English?
probably not
DLC is a very common English word
I am American eh. . . I mean I grew up around though but was brought up in Cameroon. I live in US now though
It seems like getting DLC would be pretty cool
indeed...
09:01
still there?
09:25
@kevinTahN. yes
0
Q: Which field of physics is more evoloving and trendy?

CoderInNetworkI am a computer science student working on information evolution in scientific literature. Recently I found the APS data-set which seems to be appropriate for my works. the data-set includes the following journals : Physical Review A: Atomic,molecular and optics physics. Physical Review B: Cond...

09:43
was just trying to understand Grassman algebra. With all the multi-vector lingo, and exterior products and stuff . .
pretty wild stuff
Was working it from a math angle
10:07
@kevinTahN. Let $\mathcal{T}(V)$ be the tensor algebra of some vector space $V$. Let $I$ be the two-sided ideal generated by objects of the form $v\otimes v, v\in V$. Define the equivalence relation $v\sim w$ if $v=x+i$ for $v,w\in V, i\in I$. Then the Grassmann algebra is defined as $\Lambda(V):=\mathcal{T}(V)/\sim$.
@kevinTahN. That's about the best "math angle" you'll get.
10:27
@bolbteppa : I'm sorry, but what you said there is wrong on so many counts. Where did you get that from? The mass of a body is a measure of its energy-content. When you lift a brick you do work on it. Its mass increases. Ask a question about this and I'll answer it with references you can trust.
10:37
@0celo7 : Lubos is pretty much the best physicist according to Lubos. Not according to anybody else.
@FenderLesPaul : and so laughably wrong. I can tell you how GR predicts Lorentz violation, and how the equivalence principle is nowhere precisely realized in the real world, and how fundamental "constants" vary. As for 4+4=5, that's just garbage, as is the stuff about entropic gravity and information and swampland and SUSY. What a load of BS.
Typo: 2+2=5 not 4+4=5. Tut.
10:55
Hi @JohnDuffield
@skillpatrol : Hi. I'm afraid I've got to go out shortly.
@JohanLarsson we enjoyed your "merry X-mas" equation, thanks pal :-)
:)
was a ~re-tweet
I think I see it every year and every year I have to add on the restrictions.
11:28
2800 reached.
3100 is still a long way away...
 
3 hours later…
Huy
Huy
14:20
@ACuriousMind: sorry to bother you with this but will I need complex numbers to teach differential equations for anything apart from computing roots of the characteristic polynom?
(HS level)
Uh...I'd say no, but my knowledge of DEs really is only knowing the most common tricks to solve the ones one encounters as a physicist, so I could be wrong
Huy
Huy
sure, I just figured maybe physicists know more about DEs than mathematicians. :D
thanks for your answer anyways!
15:15
I don't think you will need complex numbers for a basic course, e.g. check Ince's old ODE's book, the first half is all real numbers, second half he re-does a lot of it with complex numbers
To solve DEs take the big handbook of DEs and go from there :p
vzn
vzn
15:53
@Secret math is both discovered & invented!
"complex systems" tend to only be approximated by math eqns. there are many examples. eg fluid mechanics. also fractal phenomena/ system seem to be on the verge of "outside math" at times. etc
@bolbteppa "Ralativity"?
16:10
@kevinTahN. I think it's best to just first learn some basic differential geometry. Get to differential forms. Then Grassmann algebra makes a lot more sense.
16:42
@kevinTahN. no problem dude!
 
1 hour later…
18:03
@vzn ?
18:22
@0celo7 I'm bored as fuck
I hate winter break
19:02
@FenderLesPaul sucks for you
@FenderLesPaul if you're bored answer questions on the Physics SE. It works for me :-)
@0celo7 fight me irl
@JohnRennie But that's woooork
@FenderLesPaul Work? Physics?
@FenderLesPaul The hordes of procrastinators on here beg to differ ;)
Work is having to cut chemical engineering code for the nuclear power industry.
Physics is PLAY!!
19:30
@FenderLesPaul Listen to music, read a book of fiction, learn about a new area of science, write a poem, go for a run, explore a new Stack Exchange site, learn to dance, do a 3D puzzle, . . .
@ACuriousMind hey
I promise I'll work out that proof eventually
it would go much faster if you helped me :(
Your whole answer is an attack on my use of the word "follow." This is a matter of semantics. If you're going to write an answer saying "no because you use a word I don't like," don't bother writing the answer. It's not appreciated. — 0celo7 22 mins ago
Too much?
I'm tired of JD's "there is no motion in spacetime" schtick.
@HDE226868 yeah I should find a library nearby
@FenderLesPaul I recommend the Everness trilogy for some physics-inspired science fiction steampunk fun. If you don't mind a teenage protagonist.
Although I have yet to read the third book. I should do that over break.
them young whippersnappers
@0celo7 Your comment seems spot-on.
19:34
problem is I live in a very suburban part of Long Island
so there's no library within walking distance :(
Maybe try an e-book?
@HDE226868 fucking teens
@HDE226868 should I put on me question
@0celo7 Hm?
@HDE226868 oh I meant as a place to work
/study
I have a hard time studying at home
AN ACCEPTABLE ANSWER TO THIS QUESTION INCLUDES A RIGOROUS ANALYSIS OF WAVE-LIKE SOLUTIONS TO MAXWELL'S EQUATIONS IN CURVED SPACETIME
I mean, I thought that was implied...
19:37
there's not even a starbucks nearby or any other coffee place
@0celo7 $$\mathbf{Yes!}$$
there's a Dunkin Donuts but it feels weird working in a DD
his answer is at -7
good PSE hivemind
If I need to work on something like a physics problem, I crank up Dire Straits on the speakers, close my bedroom door, lie on the floor and work it out. It hasn't failed me yet. Outside of the house, though . . . well, that's tougher.
@HDE226868 as a budding GRperson/astroperson/nerd, do you agree that "the particle follows a geodesic" is equivalent to "the path through spacetime of the particle is represented by a geodesic on spacetime"
PS there is no motion in spacetime because Ben Crowell said it once
PPS also see the Einstein digital papers
@FenderLesPaul that is pretty strange
19:41
@FenderLesPaul You're on a break! And now you're talking about studying again!
@HDE226868 Lie on the floor?
@0celo7 It beats clinging to the ceiling.
@0celo7 Kinda feels like he's arguing about semantics.
@ACuriousMind but it's for fuuuuun
@0celo7 I'm too tall for my bed.
19:41
@HDE226868 yes...
I'm trying to learn condensed matter field theory
@HDE226868 ...
but I'm not even sure about that (semantics)
if we consider the affine parameter $\lambda$ of the geodesic $\gamma(\lambda)$, then there certainly is motion in $\mathcal{M}$ as a function of $\lambda$
I don't even...
I talk about SR EM and he's talking about...electromagentic geometry? Huh?
@ACuriousMind is he talking about U(1) principal bundle shit
@0celo7 that sounds like an old spice commercial
curved like some broad's ass
> I'm sorry, there's seems to be some kind of circularity going on here. Space is either homogeneous or it isn't. If it is, spacetime is flat and light goes straight. Unless it interacts with something else. Such as an electron. Or another light wave.
@FenderLesPaul how can you be bored with a fender and a les paul ;)
19:45
and then he links the fucking Breit-Wheeler article
@AngusTheMan fenders are pretty boring
hmm I m actually selling my old jazz master next week
had it like 10 years
@FenderLesPaul tbh I've never seen an old spice commercial that talked about principal G-bundles
but maybe they have smarter commercials where you grew up...
@AngusTheMan unfortunately my guitars are back in my dorm
couldn't bring them with me home for break
too much to carry
I do have my acoustic though
:( oh that sucks
acoustics are no fun
no shredding there
haha true
but I think my shredding days are behind me, I've grown old
nowadays I mostly just play and sing folk music or pop rock from the beforetime
19:49
interesting
more of a stevie ray vaughn kinda guy
do you like jazz?
@0celo7 I don't know what Hammond's work contains, but I'm willing to bet a large sum that it has no relevance to anything said before or after that.
hmm a bit
@ACuriousMind why does reparameterization invariance of the action imply a vanishing hamiltonian
does it?
19:51
6
Q: Is there a Maupertuis principle for General Relativity?

0celo7The motion of a point particle in classical mechanics is given by Newton's equation, $\mathbf{F}=m\mathbf{a}$. Suppose all forces considered are conservative and we have a constant total energy $h$. Let $M$ be the configuration space of our system, $T^*M$ its cotangent bundle, $(\mathbf{q},\mathb...

Section VII)
Too tired and anti-sober to figure it out now
So unless @ACuriousMind tells me it will remain a mystery for a while
@Qmechanic I'm sorry, but I don't see what the conclusion of that answer is.
@0celo7 It vanishes for systems where $q$ and $p$ are scalars under time reparametrization.
You conclude that $U=0$?
But the whole point was considering systems where $U\ne 0$, @Qmechanic
@ACuriousMind Can that be generalized? In the way that Qmechanic uses it in his answer there
I think Qmechanic is saying that the restriction on the potentials are so much that a nice one can't be found?
I should learn more Cat Stevens
@0celo7 Qmechanic doesn't even relaly generalize there: $\lambda$ is the time there, and so $\lambda$-independence and reparametrization invariance indeed imply vanishing Hamiltonian on-shell.
20:01
@ACuriousMind if I ask you for the proof of that, will you say QoGS
what is QoGS
Quorum of Great Slipshod
@0celo7 Yes, although the proof is basically that you assume a non-vanishing Hamiltonian and just run into a contradiction when you assume such a thing has a reparametrization invariant action.
@ACuriousMind Isn't Lagrangian mechanics re-parametrisation invariant in general however? So it is the specific lack of time invariance in the Lagrangian function that causing the energy function to vanish?
Oh i just found this
@AngusTheMan Re-parametrization invariant basically mean you can do arbitrary transformations $t \mapsto t+\tau(t)$. The action is not generically invariant under that.
20:07
@AngusTheMan cool
night, all
if I get back on ignore me
I have a 4AM train to DE (and must therefore sleep)
@AngusTheMan @0celo7: The linearization as $\delta q =\dot{q}\epsilon$ in there is precisely what I mean with the assumption that $q$ transforms as a "scalar", or Qmechanic with that "q has not explicit $t$ (or $\lambda)$ dependence.
@ACuriousMind I recall reading in the following book (I'll look at my copy in a second) about parameter invariance and Lagrangians... I mean don't get me wrong I take your and Qmechanics word for it believe me ... global.oup.com/academic/product/…;
Well, you have already posted a proof up there that such an invariance implies vanishing Hamiltonian, and I'm sure you know that not all Hamiltonian vanish, so the only two options are that you remember it wrong or the book is wrong ;)
it would appear that way, hang on I have it upstairs ill go read it :)
vzn
vzn
20:21
@bolbteppa they misspelled "Ralativity" on the perimeter pg you cited :P
@AngusTheMan: That section is not saying that the Lagrangian or action are invariant under change of time parameter. All that it is saying is that the equations of motion of the Lagrangian with one parameter are equivalent to the equations of motion of the other.
oooooooooohhhhhhhhhkaayyyyy
i see now
may bad, thanks :)
hi guys, on a projective space one usually distinguishes between the inhomogeneous coordinates and the homogeneous ones. Am I right that only the inhomogeneous coordinates are a set of charts for the manifold $P\mathbb F^n$? The homogeneous are just the mapping $x^\mu\mapsto[x^\mu]$, which is not injective, so it's not a chart of the manifold.
20:40
Wait
@Bass Tell me what you think "homogeneous coordinates" and "inhomogeneous coordinates" are, exactly
(Also, $P\mathbb{F}^n$ not a manifold for fields other than $\mathbb{R}$ and $\mathbb{C}$, but that shall not bother us)
@ACuriousMind as I understand it, the inhomogeneous coordinates are a set of charts $\{U_i\}$ for the projective space $P\mathbb F^n$. The point $\xi^\mu_{(i)}\in U_i\subset\mathbb F^n$ is mapped to $[\xi^1_{(i)}, ..., 1, ..., \xi^n_{(i)}]\in P\mathbb F^n=\mathbb F^{n+1}/\sim$, where the $i$-th component is set to $1$.
@Bass Yes, then you are correct.
for example the inhomogeneous coordinates of $P\mathbb R^1=S^1$ are just the lines $x=1$ and $y=1$
@ACuriousMind so, when speaking of projective spaces as manifolds, it does not really make sense to call the homogeneous coordinates coordinates, because they are no coordinates in the manifold sense?
@ACuriousMind @0celo7 with reference to the vanishing energy function see Faddeev Popov ghosts.
@Bass Yes, they are not coordinates in the manifold sense. That doesn't bother the algebraist who wants to solve his equations in projective space, though ;)
@AngusTheMan What should I see there?
20:51
@ACuriousMind yep ok :)
@ACuriousMind there should be a common notation for a field that is either $\mathbb R$ or $\mathbb C$. There are so many definitions and theorems that make sense only in their context.
@Bass Yes, and in analytic contexts $\mathbb{F}$ is totally fine and used. I just like to nitpick :P
 
1 hour later…
21:59
1
Q: I cannot chat on the physics rooms

Alec TealPlease lets not make a big deal out of it. I can't communicate with the parties involved but I cannot talk anywhere now. Can a mod please work out what is going on?

22:57
Now searching for all known mathematical formulatiins of time in PSE...
Now the question is, if there is no time, but only a relation between configurations, then what trigger the transition from one configuration to the next?

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