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7:48 AM
Hello
 
8:10 AM
@RyanUnger I hope you the best
'twas my wish as well but alas
here I am
 
In QM, is it possible to ask what the probability of finding a particle in a coherent state will be?

I understand it is possible to find the probability that a particular system is in a mixed state, but as far as I am aware there is no way to ask $Pr(\|{\Psi}>=c_1|{1}>+c_2|{2}>)$ ?
 
8:34 AM
@user400188 yes, but you need to say what the other options are
That is, is your measurement a binary "is the system in this coherent state or isn't it?"? Or is it something more complex? And if it's something more complex, then what?
The results can change depending on the answer
@user400188 this is the wrong way round. It is possible to query for superpositions, but not for mixed states.
 
8:57 AM
@EmilioPisanty I'm fairly its possible to find the probability that a system will be in a mixed state. Here is an example (that I may have misinterpreted)
Suppose the density matrix for a system is represented as the following:
$\rho(A,B)=\frac{1}{2}\left|\uparrow_{A}\right\rangle\left|\uparrow_{B}\right\rangle\left\langle\uparrow_{B}\left|\left\langle\uparrow_{A}\right|\right.\right.+\frac{1}{2}\left|\downarrow_{A}\right\rangle\left|\downarrow_{B}\right\rangle\left\langle\downarrow_{B}\left|\left\langle\downarrow_{A}\right|\right.\right.$
If we wish to know the probability of A possessing a particular state, we
take the trace over B
$\rho_{A}=T r_{B}\left(\rho_{A B}\right)$
$=\sum_{i}\left\langle i_{B}\left|\rho_{A B}\right| i_{B}\right\rangle$
$=\left\langle\uparrow_{B}\left|\rho_{A B}\right| \uparrow_{B}\right\rangle+\left\langle\downarrow_{B}\left|\rho_{A B}\right| \downarrow_{B}\right\rangle$
$=\frac{1}{2}\left|\uparrow_{A}\right\rangle\left\langle\uparrow_{A}\right|+\frac{1}{2}\left|\downarrow_{A}\right\rangle\left\langle\downarrow_{A}\right|$
This tells us there is a 50% chance state A will be up or down, obtained by
taking scalar product of the density operator on both sides by A.
@EmilioPisanty To answer your question though, I was supposing a simple ""is the system in this coherent state or isn't it?" query, but I would be interested in the other things you can ask.
 
9:39 AM
@user400188 that's not what the partial trace does
@user400188 this has no bearing on whether the system is in a pure state or a mixed state
There is no projective measurement onto mixed states
The question doesn't make sense in qm
 
Greetings to all. Does anyone know if areas like QCD phase diagrams and transitions, ultrarelativistic ion collisions, are good for one to work in terms of current research and employment? Also areas under the whole quantum thermalization scheme and possible applications in biology? Thanks.
 
9:55 AM
Trying to answer that question on solutions of the Misner space geodesics but turns out it is very unpleasant
I end up with stuff like $$\frac{c_2^3}{3} (-\frac{2}{v_\theta}+\tau)^7 + c_2^2 t_0 (-\frac{2}{v_\theta}+\tau)^4 - 4c_2(-\frac{2}{v_\theta}+\tau) < 0$$
let's just say it has an unreasonable number of possible solutions
 
10:22 AM
@ConstantineBlack if it involves QFT, and it's not in condensed matter, then it's not a fountain of jobs, that's for sure.
 
10:38 AM
@ConstantineBlack Probably not...
 
If you want the money makers just go in the industrial fields
Nanophysics, electronics, condensed matter, optics
That kind of stuff
 
10:57 AM
boring but full of gold
 
 
1 hour later…
12:14 PM
Is there a fate more cruel than having to program a topic obscure enough that the libraries are very poorly documented, but not obscure enough that you could just choose to write it yourself
I mean I guess I could be stabbed with a fork
A crueller fate
but still
 
Well there's the "we bought this product, so you must use their APIs/libraries" but it's terrible
Though I suppose it's about the same situation
 
I mean it's like data mining stuff
there aren't that many different libraries to choose from
 
Or their side is completely broken, but it's all business-side people communicating
Just import datamine
 
not quite
it is sklearn and keras
 
What obscure corner are you in? Most of the sklearn documentation I've seen has been excellent...not so much for keras though
 
12:29 PM
There are a couple of Python room regulars who are into data science / machine learning. eg Arne. There is / was a Machine Learning chat, but I think it died from a help vampire infestation.
 
For instance the nyoka library
 
1:09 PM
Never heard of it...though from googling, PMML looks like something potentially useful
 
1:28 PM
it would be if its standard covered all common algorithms properly!
 
@Slereah you misspelled "interesting"
 
nah fam
 
Spacetime is almost flat in every application u may find
very boring topic
and the topology is trivial too!
 
perhaps, it is an acquired interest?
 
1:45 PM
::crickets chirping::
1 year later...
 
what
 
@Slereah based on how much I spend on the steam sale, I might get those books
I want to learn about renormalization before I die
 
Renormalization is basically nonsense although there is a fancy renormalization which is proper
But it's hard to find stuff on it
gotta do symbolic sums or whatever
 
@Slereah that's why we need those spacetime engineers!
 
2:00 PM
I mean just doing a gravity experiment is a huge pain
even a classical one
like the Schiehallion experiment
Just need to have a mountain
 
Are gravitational experiments a common thing? I've heard of a couple, but it seems I hear about astronomical observations a lot more...though I suppose we can't really make galaxies in the lab
 
define "common"
I mean there's a bunch of them
 
although there's only so much you can do with local gravity experiments
Like there might be a dozen or so gravity experiments that have been done on the ground
well, different ones, anyway
probably more than that but I can't think of that many different ones
 
I mean I've never met a gravitational experimentalist, so they must not exist!
 
2:08 PM
Well you know
There's some current ongoing ones I think?
example
 
It'd be fun to measure the deflection due to the gravitational deflection of a pair of large pendulum bobs. Doing it with osmium or iridium would be a tad expensive, but I reckon you could get decent results using tungsten.
 
there's the Harold White one but obviously nonsense
 
2:23 PM
This guy is still going on about relativistic mass. :facepalm: physics.stackexchange.com/questions/481634/…
 
@Slereah the books are written for mathematicians
so presumably they do something correct
 
which books are they?
 
deligne
 
I finished Q is for Quantum and if I have to rate it from 1 to 5 it's a 3.
 
is it a Sesame Street thing
 
2:39 PM
It just uses weird analogies and terms such as rocky state, real state, misty state... I understand what they mean but it's just too much.
 
Any mods or 15k+ users lurking? This HNQ is starting to attract rubbish answers, so it may require protection. physics.stackexchange.com/questions/481634/… It's got 4 close votes, but I don't think it really needs closing.
 
Part I is perfect, but from the half of part II to the end... it's just messy
I learned some weird analogies with some weird rules and no idea how to apply them to the real world.
 
@NovaliumCompany I haven't read it, but maybe he's using the funny terminology precisely to get away from any faulty preconceptions the reader may have from less serious popsci treatments.
 
@PM2Ring Maybe. Maybe it's a book a person has to read multiple times to understand properly.
 
@Slereah reading about the Polyakov action rn
 
2:46 PM
Is it delightful
 
Also since it is a math book, do they actually write the Polyakov action in a coordinate free way
I've never seen it done
 
oh Im not reading that book
 
o
 
actually this might not be the Polyakov action
 
2:48 PM
This is the second time I read a book that I didn't enjoy :p
 
I've forgotten what that is
 
I'm pretty sure the Polyakov action action should be something like $$S[X, \gamma] = \int d\mu[\gamma] \det[X^* g]$$
With $X$ the embedding
 
the think I'm looking at is a log det of the Laplacian
 
Ryan how old are you? :P
 
2:53 PM
Oh I'm 8 nice to meet you :)
 
@Slereah I think the Polyakov action is just the Dirichlet energy for maps.
this can be given a coordinate invariant form
 
it does seem similar
 
do you want a reference
 
sure
 
chapter 8 of Jost's Riemannian geometry and geometric analysis
he defines the thing at a point using coordinates but then explains the right bundle you want to look at
and you get a proper norm on this
 
2:57 PM
thx
 
for $f:M\to N$ it's $T^*M\otimes f^*TN$
and you can define a metric on this in an invariant way
 
@RyanUnger I looked it up. What are those complicated stuff and what are they used for?
 
It does indeed seem to be the Polyakov action
 
"How to teach QM to your dog" Amazing book 5 out of 5
 
I have the how to teach relativity to your dog one
 
3:01 PM
@NovaliumCompany not used for anything
math is just cool
 
@RyanUnger lol that is just sad
 
@Slereah aha the log det ratio is the effective Polyakov action
 
Jost's Riemannian geometry and geometric analysis What is the book about? And how doesn't it have any application?
I mean, do people read that book to just go around and tell people how coplicated stuff they know?
 
the title describes it pretty well
 
So advanced geometry?
 
3:12 PM
it is how to draw squares and triangles
like all geometry
 
Yep, I looked it up. Those smooth manifolds look exhausting
I can only imagine the equations describing them...
actually, I can't
 
@Slereah wonder if witten teaches classes
 
Calculus is used to describe change (most often change through time), so thise differentiable manifolds should be like animations of complicated changing geometry of complicated 3D and higher dimentional models?
 
see this is why you need to go to school
 
??
What's so wrong about a 16 year old who doesn't understand complicates geometry? I'm just curious what it actually is.
I think my description of calculus in Riemannian geometry is pretty accurate. :D jk
But still, I thought calculus is used to describe change?
So the geometry of those manifolds should be changing?
 
3:22 PM
@NovaliumCompany it might
 
Or it might not. Is it like in a superposition XD jk.
nvm I'm going to make my roblox server now
if anybody wants to join, tell me
 
@RyanUnger probably famous enough that he only does if he so chooses
 
he has a non-teaching job at the IAS
but so does de lellis and I'm taking a class from him in the fall
 
I'm taking a class from him in the never.
Ok I'm getting a bit assholish, I'll go make my roblox server sorry
 
3:57 PM
Whoa! Numerology guy has returned, with a vengence! Check out his latest edit: physics.stackexchange.com/questions/481404/…
 
@PM2Ring what the hell is that??
 
@SDFG It's Uncovering the Secrets of the Universe by Totally Random Arithmetic. Check out the original version of that question for a much tamer version.
 
@PM2Ring Lol yikes. I'm not sure why he thought adding biblical references would encourage "us brainiacs" to help solve it.
 
Indeed. I thought we science types were supposed to be heathen sinners.
 
4:13 PM
he could at least have spared some time to break it into paragraphs. But looks like he was too excited with his discovery
 
@PM2Ring I assume so, since "proving god" often is just pointing to holes in scientific theories and saying "if not that, it must be god!" (and I have no real problem with people believing in god, but I have issues when people try to use faulty logic as a proof for one)
 
Looking for hidden numerical patterns in the Bible has a very long history. See en.wikipedia.org/wiki/Gematria
 
@PM2Ring Not to be a killjoy, but I kind of doubt this worked. There are lots of ways to get a force between two nearby metal balls that aren't gravity.
 
Just wanted to know this: When someone replies to a message which is waay up in the chat, how do I see which one it is?
 
@PM2Ring Makes a bit of sense, in the way that you assume the book might be holding more information because of it's divine properties. Makes less sense in the way that finding relationships and patterns in numbers and letters is trivial and something that our minds are wired to find significant patterns in. It's like the "new messages in the bible by taking every 3rd letter". It seems like something special might be happening, if you don't really understand the statistics
 
4:24 PM
@JMac I can agree with that. I know lots of religious people, some nice, some not so nice. But scriptural literalists, and people who claim that all important information can be found in ancient scriptures, tend to make me uncomfortable.
@SDFG Click on the little arrow at the left of the message.
 
Oh
Got it thanks
 
@knzhou Oh? Like what? Apart from obvious stuff like air currents, which Walker tried hard to eliminate.
 
in TeX, LaTeX and Friends, yesterday, by David Carlisle
Another question answered by not using one of my packages...
lolz
 
@PM2Ring Yeah same. I don't know if you've ever seen like "presuppositionalist" arguments; but I find those frustratingly hilarious. "The bible says god is truth and reason, therefore without god you cannot know truth or reason, therefore god exists."
 
@PM2Ring Electrostatic attraction? Residual magnetization? Humans wearing shoes can easily get charged to hundreds of volts. That could have ruined the experiment by him merely touching one of the spheres.
The Cavendish experiment was extremely difficult and it used weights that were hundreds of times bigger.
 
4:38 PM
@JMac Yes, I've heard stuff like that. At least it's not judgemental, like "You don't believe in God because you want to do sinful stuff".
 
@Danu yo @Danu, remember the Robert Cameron papers we went through a while back?
 
@knzhou He was using non-magnetic stuff, like lead. But yes, electrostatics could mess it up.
 
check this out
totally not intimidating
 
At least you can tell him you know about zilch!
 
@PM2Ring True, and as long as they are only using it for philosophical arguments, it doesn't really harm others, so that's a plus. The mentality of "sinful stuff" is a harmful one when people start using that logic for laws
 
4:42 PM
@ACuriousMind indeed I can
I can also push him to start working on $L+\gamma S$ angular momenta
speaking of which
Conservation of Torus-knot Angular Momentum in High-order Harmonic Generation, E. Pisanty et al., Phys. Rev. Lett. 122, 203201 (2019)
2
The other paper is in press and will appear shortly.
 
5:19 PM
welp, so finally read through the documentation for tf eager execution...it's exactly the same as pytorch lul...
 
 
1 hour later…
6:20 PM
@JMac for me the issue isn’t even whether the logic is consistent or not. It’s that the world they construct seems just terribly boring
 
@enumaris they have to keep up and completely rewrite it to be like pytorch!
 
pretty much...
srsly
 
This meme resonates perfectly with me
 
 
1 hour later…
7:57 PM
I wonder what happens to the guy at Google that goes "maybe we should try out pytorch"
 
lol
 
8:28 PM
ooo
they did improve one thing tho
if you make a list of layers or list of variables, it will automatically register all the stuff within that list
you don't need to specially call a nn.ModuleList or nn.ParameterList object
 
9:08 PM
ah I haven't used either of those yet
 
9:31 PM
It's useful for when you want to be able to build a model with a lot of identical blocks
I use it for my implementation of the transformer...that doesn't work... T_T
but now I can try implementing it in tensorflow I guess and see what happens lol
 
meanwhile, I'm sitting over here analyzing a language where data type type type. is a legal variable declaration...
 
uhhhhh....
 
@ACuriousMind how do you maintain sanity?
 
man, this dataset is actually pretty tough lol
even with a really dumbed down version, a vanilla rnn ain't working too great
 
@danielunderwood I never claimed that I do :)
 
9:43 PM
So which part of that is the variable name? data?
 
definitely the other data
 
@danielunderwood Wrong! data is the keyword saying that a variable is to be declared, the first type is the name of the variable, the second is the keyword saying that the type follows (often only a : in other languages, but the : is already taken for an even more horrifying construct...) and the third is the name of the type (which e.g. could have been declared to prior to be a synonym for integers by writing the equally beautiful types type type i.)
 
fun times
 
With syntax highlighting this actually looks not quite as bad, but even getting the syntax highlighting right is much more complicated than in most other languages...
 
sounds legit
 
9:47 PM
o.o
 
Oh, and it's case insensitive, so Data Type TYPE type. would be equivalent :P
 
That's when git blame comes in handy
Someone at work linked me to this goodie aws.amazon.com/blogs/apn/…
 
@danielunderwood This language and its change management ecosystem is older than git, and it is only slowly starting to become compatible to it. The vast majority of code does not exist in anything resembling a git repository.
 
all the snippets I've seen of cobol seem to suggest that the only case in cobol is upper case though
 
It's...really not that much like COBOL
But indeed everything is converted to uppercase internally
 
9:55 PM
Oh right I forgot ABAP is a different language
Sorry the brain link ACM <-> COBOL engineer is already there
 
hello
 
ahoi
 
hahaha
Ok so I've been reading this book on the Calculus of Variations
and I feel very comfortable now with like the math behind the lagrangian
just in terms of knowing about it rigorously
So I'm trying to understand now some concepts
I've struggled with
and one of the ones I just don't get is the idea of "virtual work"
when i hear it defined, it's referenced with respect to a "virtual displacement"
and i don't get that either. i understand what an action is and the principle of least action
 
@StanShunpike A "virtual displacement" is one that has no time component.(cf. e.g. this answer by Qmechanic), "virtual work" is just the work a force would do if acting along such a displacement.
 
 
1 hour later…
11:07 PM
guys any idea what compensation and dispersion voltages are?
 
11:21 PM
nope
 
So a virtual displacement is like thinking about changing space without changing time?
as far as non-relativistic situations are concerned?
@ACuriousMind ^
 
11:40 PM
-5
Q: Negative Quantum Space-Time?

pittsburghjoeWhat is the Uncertainty Principle telling us? Is it saying the power of observation/measurement of a quantum object is not enough to make it a genuine 3D + 1 space-time object? If something on our scale was partially fuzzy depending on how many measurements you made (at the same time) ..would yo...

>"Edit to the down-voters: guess you can't handle new ideas that will become mainstream soon enough ..and when it does I'll make sure you are held accountable for removing this. "
I find it somewhat telling that many people who post these theories all seem to think that they will eventually be proven right. The best part is that they think closing a theory proposal for being off-topic here would somehow make us look like huge fools
 
oh boy
 
@JMac I'd be scared if I were you.
 
11:57 PM
You're going to be held accountable
And it's obviously a conspiracy against his theory that 4/5 close votes were people starting with a J
 
@RyanUnger Yeah, when negative quantum space time is proven, they are going to dig up that question, show that I voted to close it and pointed out that it was an assertion. The negative-quantists will obviously track me down for this, using the clues I've left behind with my comment history to figure out who I actually am
@danielunderwood Delete that comment, you know too much.
 
Better you than me pal
I got out of the business of shutting those kinds of people down years ago
People around here probably don't remember my manifesto
maybe @Slereah does
 

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