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12:59 AM
@Azmuth It's extinct in the wild :P
not completely extinct
 
 
2 hours later…
2:44 AM
Somebody posted the above as a question here: physics.stackexchange.com/questions/581423/…
I see two possibilities. The first is that this person has decided to write some avant-garde physics-themed poetry and post it as a question.
The second is that this person does not speak English and used Google Translate to translate from their native language to English, but mistakenly inserted line breaks in the original, and Google Translate translated each line separately.
I think you have to admit that the result is quite beautiful in its way.
 
3:27 AM
@BioPhysicist Nah,,, How;s it?
@SirCumference Oh okay, then it's good, we can revive them...
@Slereah So you are Kitty Meeks ?
 
 
4 hours later…
7:20 AM
@TerranSwett We do need more physics poets! Even if it's just Google's translation AI... :P
"A slippery horizontal plane. / It moves from silence, / And in five seconds it was moving away 250 ft." sounds extremely sad to me and I can't quite pin down why
 
8:09 AM
@ACuriousMind you could buy that GR poetry book
Also of course, Tonnelat did GR poems
 
I don't speak French so I can't judge that :P
it certainly looks like poetry
 
well it's song parodies
but close enough
 
8:25 AM
If we’re accepting approximate poetry, Morin has quite a few limericks physics.harvard.edu/undergrad/limericks
2
 
 
1 hour later…
9:48 AM
Hey all kids!
See this!
Official Kevin Pietersen liked my post!
Biggest Twitter achievement soo far!
 
Which computer software i can use to experimentally verify variation of z factor with increase in pressure of real and ideal gas?
 
@Azmuth Serously
Which post?
 
@Mayank click the link and check it!
He's still my favorite Batsman!
 
Can you share the post link?
 
9:52 AM
Oh got it
 
His Hindi is also sooo good. He shot a Nat Geo Documentary in Hindi....
 
I can't believe it.
 
Yep. When he was a kid, he came to India just to learn Hindi... He was also selected to do Hindi commentary in IPL. Probably later matches....
 
10:42 AM
I'm afraid it's not the one french song people know, no
 
@sheltonBenjamin What do you mean, "experimentally"?
REFPROP can give you the compressibility factor for various real gases.
 
 
1 hour later…
 
2 hours later…
2:53 PM
How did Elon Musk figure out people need electric cars?
 
what
 
not sure what that means
 
Elon Musk is not the inventor of the electric car!
 
the demand was for cars with less environmental impact, not specifically electric ones
 
I mean, why did he decide to put his money into electric cars. As far as I know, this wasn't a successful thing before.
 
2:57 PM
First two paragraphs of the Wikipedia article on electric cars:
> An electric car is an automobile that is propelled by one or more electric motors, using energy stored in rechargeable batteries. The first practical electric cars were produced in the 1880s.[1] Electric cars were popular in the late 19th century and early 20th century, until advances in internal combustion engines, electric starters in particular, and mass production of cheaper petrol (gasoline) and diesel vehicles led to a decline in the use of electric drive vehicles.

From 2008, a renaissance in electric vehicle manufacturing occurred due to advances in batteries, and the desire to re
 
Did he not begin developing better batteries first? Before cars
 
the lithium ion battery is not a Tesla invention, and the same article points out the first modern electric car in series production was a Mitsubishi
 
I think Tesla was started as a car company. I'm not sure if designing the batteries was always part of their plan; but I'm pretty sure the company always intended to make cars
 
Why did he decide to put his money there?
 
BRB installing my mindreader.
 
3:00 PM
lol
Is Tesla not ultimately a source of funding for SpaceX? I was always under the impression that Elon's main project was mars
 
1899 had a very different aesthetic for cars :P
 
@Charlie I just looked it up and learned this, apparently SpaceX was made a year before Tesla was founded...
 
Yeah, I think that's also the purpose of StarLink, which I'm very much looking forward to (if it lives up to the hype), same as paypal, just a way to pour money into SpaceX
 
Huh, turns out Python can cross match two 300 line lists in a flash
I was worried doing something that's like O(90000) or whatever would take an eternity and tried to optimize it before even testing it
 
3:15 PM
300 lines isn't that much even with the most poorly optimized algorithm on a modern computer
also, O(90000) is not how big-O notation works :P
that it went quick tells you nothing about the complexity of your algorithm - complexity is about how it scales when the input size gets larger/smaller
 
@ACuriousMind Can you migrate a question to MSE?
 
@Mayank I can, but please just flag the question you think should be migrated instead of asking here
there's an explicit off-topic flag for questions users think should go to math.SE
 
@ACuriousMind to be honest, I quite like this design :P
Ah. So this where my newfound usage of “:P” comes from! For the past week or so I have been (over)using that emoticon. Now I see where I picked that up from
 
@ACuriousMind This one “ in need of moderator intervention”?
 
3:28 PM
:P is definitely the most versatile text face
 
@Mayank no, it's a close flag - under "community-specific reasons": "This question belongs on another site in the Stack Exchange network"
 
3:41 PM
Sorry, I am new. I don't know where close flag option is.
 
oh, you probably don't have enough reputation to do that, sorry
 
Can't I simply delete it and post it on MSE?
 
oh, it's your question? Then sure
 
@ACuriousMind Thanks :P
 
Is there any sort of action that is taken against users who repeatedly post solutions to homework questions in the answers / comments?
 
3:50 PM
@BioPhysicist if we notice it (either on our own or because they get flagged for it) they can be sent a mod message reminding them not to do that. I don't know if we ever suspended someone over it off the top of my head, but at least that's not standard procedure
 
rob
@BioPhysicist Answer: yes, but out of respect we try to keep details of such actions out of the public view.
 
For sure, I don't think it needs to be visible
 
4:05 PM
I am taking AP Research this year, and the main thing we have to do is conduct a research study over a topic of our choice and write a (~4000 word) paper on it. I want to do a physics topic because I have some experience in competition physics and I think I would enjoy doing it.

However, I have no actual experience in physics research and I don't think I can do anything that would require assistance from University-level equipment because of the current pandemic. I need some help brainstorming, so any assistance will be appreciated.
 
4:22 PM
@BioPhysicist But if it's not visible, how can you tell if you're helping prop up the mainstream dictatorship?
 
@ACuriousMind yeah i expected i was gonna mess that up lol
been a few years since i used big O
@ACuriousMind i assumed doing a linear search for each member of one list to see if it's in the other list would be something like 300^2 computations
 
@SirCumference sure, it is, I stand by "that's nothing on a modern computer" ;)
@SirCumference I see you're not in the pocket of big O.
 
@ACuriousMind true, but my "modern computer" takes 15 seconds just to finish a basic mathematica computation :P
19 hours ago, by Sir Cumference
I'm prob stupid but does anyone understand why Mathematica is giving three surfaces?
 
symbolic computation is very hard for computers
all they can do is add numbers and compare bits :P
 
yeah, i guess i'm not too experienced in what's fast vs. slow for computers
i was genuinely shocked when bash sorted a file of 130,000 lines for me in an instant. expected my computer to crash
 
4:37 PM
Can anybody help in why I am not able to access pse website using my pc and i am able to acess the same website using my phone
 
Algorithms scaling quadratically - like your linear list search - can be the right choice if you know the input set is small enough your machine can handle it. For example, the naive multiplication of matrices is O(n^3), but there are specialized algorithms that are something like O(n^2.6). Unfortunately, the constant and linear factors in front of that n^2.6 that big-O omits are so large this becomes only actually better than the naive computation at truly gigantic n
 
All the websites which I use regularly are out of the reach now
I am confuse can anybody help in this please
 
@JackRod "I am not able to access pse website" is not enough information for anyone to help you. How are you trying to access it? What error are you getting? Do other websites work?
 
Using Chrome or any other browser
 
@SirCumference we didn't invent quicksort for nothing!
 
4:40 PM
It is saying ip address could not be found
Site cannot reached
 
...that would indicate your computer has no internet connection :P
 
It has I can access YouTube
And Google
Not specific sites which I use on regular basis
Including twitter
 
try clearing the dns cache, cf. superuser.com/q/203674
 
@ACuriousMind it's rare to find such convenient names as "quicksort"
 
it is not responding
 
4:45 PM
@JackRod maybe try a proxy or vpn (assuming they're legal in your country)?
 
like I opened the site
oh wait
 
How to compute $\left[\hat{U}, x]\right]$? where [] denote commutator
 
i just disconnected my lan from computer
 
@Yashas $\hat{U} \hat{x} - \hat{x} \hat{U}$
 
now they are running
@ACuriousMind @SirCumference
 
4:48 PM
@SirCumference yeah but I don't know what to do next
 
idk what's your goal
 
do I expand U as a series?
I need to arrive at something like $i\hbar \over m$ or something similar
 
what is $U$? A random operator? A function of $x$? Of $p$? Of both?
 
what has happened I am confuse?
 
@ACuriousMind probably time development
 
4:49 PM
@ACuriousMind it's the time evolution operator
 
@Yashas So do you want to do this for a specific $U$? Do you know the Hamiltonian?
 
and $H = \frac{\hat{p}^2}{2m}$ (sorry, I forgot to tell this)
 
like if i connect my dongle or lan to the computer the sites are inaccessible
 
@JackRod So your wifi works but your ethernet connection is blocking them?
 
@JackRod is this 'lan' your personal network or a public/employer/school whatever? Some will block access to certain sites (though why they'd block SE but not YT eludes me...)
 
4:51 PM
I think it's possible if I expand U but that's a lot of work. Is there a way I can avoid lot of math?
 
@Yashas What are you trying to do then - that commutator is zero without any further computation!
 
actually, I have a wifi dongle which I can connect using my
dongle
 
@ACuriousMind i remember my high school blocked the stackexchange imgur domain
i just assume they don't really know what they're doing
 
@SirCumference ah, they probably blocked *.imgur.com because they've heard it contains these "memes" young people like :P
 
no, I am connected to the same network using wifi
earlier I was connected using the cable
 
4:53 PM
@ACuriousMind how? It's not obvious.
 
@Yashas What is $U$ in terms of $H$?
(and sorry, it's not zero, forget that)
 
@ACuriousMind $\hat{U} = e^{-\frac{i\hat{H}t}{\hbar}}$
 
@Yashas right, so since $H$ is a function of $p$, $U$ is a function of $p$, too.
do you know how what $[f(p),x]$ is generically?
 
@ACuriousMind No, if that has a name, I will look it up and learn.
 
I don't think it has a name
 
4:55 PM
@Yashas usually with these kinds of things you're gonna have to series expand and use bad math to get the form you want
 
you assume $f$ is a series in $p$ and then do it order by order
 
It seems funny but I do not know what is happening the same wifi allow me to use that website and when I connect it using the lan it does not allow me
 
then you stare at the resulting series long enough to realise it's the series of $f'$ :P
 
@JackRod I think the top suggestion would be worth checking. forums.tomshardware.com/threads/…
 
i do not miss those problems in qm
the only worse notation than the ones used in QM are the ones I'm seeing in my GR class
i dunno how Einstein summation notation is supposed to make things easier for anyone
 
4:58 PM
@SirCumference What?! Have you tried writing out all the summation signs? It's terrible.
 
@@JMac thanks let me try
 
you'll waste half or more of each line just writing a parade of $\Sigma$s
 
@ACuriousMind i'm prob just not used to it, so i'm getting tripped up in trying to understand a lot of formulae
 
just don't use a basis :p
 
doesn't help when the book skips most derivations for some reason
 
4:59 PM
$$\mathrm{Tr}(Z \mapsto (\nabla_X \nabla_Z - \nabla_Z \nabla_X - \nabla_{[X, Z]}) Y) - \frac{1}{2}g(X,Y) \mathrm{Tr}(\mathrm{Tr}(Z \mapsto (\nabla_W \nabla_Z - \nabla_Z \nabla_W - \nabla_{[W, Z]}) W)) = T(X,Y)$$
The EFE without a basis
 
@JMac I just assume that I am always doing that
 
also using $d/dt$ for a convective derivative and using $\partial / \partial t$ for a Eulerian derivative is totally throwing off all the calculus i've used in the last 4 years
in my math classes it's so much simpler, just use $D$ for total derivatives and $D_x$ for partials
 
@Slereah What is the $Z\mapsto[...]$ bit here?
 
@Charlie To define a function
 
@BioPhysicist I find it a lot harder to redeem my points with the Secret Guild of Anti-Intellectualism and Mainstream Dictatorship when I don't have clear evidence. Maybe they're just more lenient with you.
 
5:02 PM
oh wait the $Z$ the vector field in $\nabla_Z$?
 
@Yashas it’s instructional to expand in terms of power series and compute the commutator.
 
I've never seen the riemann tensor written like that
 
@ACuriousMind I find writing $\Sigma$s oddly satisfying.
 
Actually it was quite trivial to expand. It took just 30s to get the answer. I spent 15 minutes googling on how to avoid the expannsion. facepalm
 
@Yashas i spent 4 hours trying to optimize a computation i later realized my computer could do in 5 seconds. i feel ya :P
 
 
1 hour later…
6:18 PM
In research, do people come up with new discoveries and ideas from the mathematics, or they first get the general idea and then write the maths down?
 
@JingleBells a combination of both
existing ideas in math can inspire new ideas
 
hmm, got it. I'm a bit confused about how it happens. Do you just sit and look at some formula that describes something and you suddenly decide to move the symbols around or?
How do researchers get ideas? Do they come up with the general idea first, and then write the mathematics for it, or do they somehow look at the mathematics and move symbols around?
 
6:50 PM
The process of "getting ideas" varies hugely I imagine.
Sometimes a problem is solved just by brute force, staring at it until the solution happens to cross your mind. Sometimes an idea that someone else has can inspire a solution. Historically a lot of people have claimed to see solutions in dreams :P
 
Is finding $\left[x(t), x(0)\right]$ same as $[U^*xU, x]$?
 
what context is this in @Yashas?
 
@Charlie This is a subproblem in a free particle problem I am solving. The star denotes conjugate transpose. $U$ is the time evolution operator and [] denotes commutator.
 
ok
Should that read $[U^*x(0)U,x(0)]$?
 
@Charlie yeah
 
6:55 PM
and fwiw the symbol $^\dagger$ usually denotes the conjugate transpose in physics
If you're working in the Heisenberg picture and $x$ is the position operator? I suppose so
 
@Charlie yes
 
Then unless someone wants to correct me, I would imagine the answer is yes
Out of curiosity, is perturbation theory applied to operators other than the Hamiltonian ever useful?
 
I reached here $\frac{t\hat{p}\hat{x}}{m} + \frac{t}{m}\hat{U}\hat{p}\hat{U}^\dagger\hat{x} + \frac{t}{m}\hat{U}\hat{x}\hat{p}\hat{U}^\dagger$ but I need to get $i\hbar t \over m$. Is further simplification possible here? I did cross-check once and everything seemed to be correct.
 
Could you put that in double dollars so it's a bit bigger?
 
$$\frac{t\hat{p}\hat{x}}{m} + \frac{t}{m}\hat{U}\hat{p}\hat{U}^\dagger\hat{x} + \frac{t}{m}\hat{U}\hat{x}\hat{p}\hat{U}^\dagger$$
 
7:08 PM
You're definitely going to have to use the commutator $[\hat x,\hat p]=\mathrm i\hbar \Bbb{1}$
I don't see how to progress from where you are though
Maybe you have made a mistake somewhere, or I am missing something
 
7:27 PM
@Yashas Do you know BCH identity?
 
@SuperfastJellyfish No but I will learn.
 
7:49 PM
@SuperfastJellyfish Thank You. I solved it and it helped simplify my original problem really close to the expected answer. There are two extra terms which are very close and should be cancelling but this might be a typo somewhere (dimensionally incorrect too). I will retry tomorrow. Thanks again.
hmm, do operators have dimensions? Am I supposed to be worried about $\hat{x}\hat{p} - \hat{x}$?
I think they should because $\langle\psi|\hat{O}|\psi\rangle$ should have different dimensions depending on the observable. But then $i\hbar \frac{\partial}{\partial x}$ doesn't have any dimensions. I need to check if position wavefunctions have momentum dimensions by default (I think they don't; at least not in particle in a box if I remember correctly).
oops, the $\hbar$ has dimensions. I should sleep and think about this tomorrow I guess. It's 1:30 AM now and I have spent 8 hours straight solving problems :P
 

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