I just saw a children's play (5-11th grade) rendition of To Kill a Mockingbird, and they left all the n-words in. As a Northerner, I was quite shocked.
@HariPrasad The whole blog thing has kind of died down network-wide, and no official per-site Stack Exchange blogs will be started. Most per-site blogs (if they exist) are stagnating, as @ACuriousMind alluded to. This would make starting an official blog affiliated and integrated with Stack Exchange impossible.
You could use a third-party host - as we've done on Worldbuilding using Medium, thanks to a suggestion by a CM - but our blog was supposed to build our community and get our name out there, where we can help worldbuilders online. Physics Stack Exchange has a different culture, and while some users do have their own blogs, the community doesn't have much of a vested interest in creating one, especially given that it will have to be done elsewhere.
I'd trust the assessments of ACuriousMind and DavidZ more than mine on this, as they know the Physics Stack Exchange community better than I, but I concur with them here. Those on Physics who would be best-suited to write for the blog might not have a vested interest in doing so, and I don't think the community would gain a lot from it.
It's still worth raising the issue on meta for a third-party host - I don't want to discourage you from doing that - but I highly doubt that it will be successful.
@HDE226868 I actually think writing more self-answered Q&A would be a good substitute for most things one might want on the technical side from a physics.SE blog, and chat sessions such as for the LIGO announcement can substitute for the "physics news" one might also expect from such a blog.
Alas, as I had to find out, if you don't actually have an answer sitting around waiting for a question, finding nice questions for a Q&A where you also give the answer is kinda hard
@0celo7 ahem ok. will try this. sincerely sorry for being too facetious about your sister. will try to avoid that. in my defense did not think it all that different than your mocking tone wrt the SJW in here (and rather mocking in general it would seem... yet funny nonetheless). and maybe other incidents. found your ref to your family interesting. also thought you said she had something to do with economics iirc. etc...
interesting. work at a fortune 250 company and we just did a big company-wide migration to git from clearcase. it was pretty tough at times. due to variety of factors wrt both packages... git is very impressive architecture... originally built by torvalds linux creator. have been using their new "gist" codesharing site quite a bit last yr or so (on my blog, math research).
@ACuriousMind That could work. I'd be concerned, though, that the posts would miss a substantial portion of the userbase. If the posts are continuously technical, that's 1) A fantastic thing, from the side of the person seriously studying physics, and 2) A fantastic way to go over the heads of most people. That poses a conundrum, in my view, because you should still go ahead and write the technical articles.
There are other arguments to be made about this - one of which being that I worry too much about minor things - but I still think that the community may not fully get many of the posts. Is that a bad thing? Maybe not.
@HDE226868 Yeah, they'll go over the heads of the "casuals". But I don't think we should cater any more to that portion of the userbase than we already do, to be honest.
@ACuriousMind I agree with that - and I'm not suggesting that articles be written to a lower level, for lack of a better phrase. But it might hurt community support a bit.
@ACuriousMind ah shew! lucky for me! but there does seem to be some kind of deep kirk-spock rivalry going on, exploited to big/ unprecedented level/ effect by eg Abrams. (ps have you seen his movies? also, did you know Shatner just wrote a new book/ memoir on Nimoy? some wild stuff in that...)
@HDE226868 Well, another advantage of the self-written Q&A is that you don't need community support to write them because they're not supposed to represent the community
@ACuriousMind yeah abrams changed the formula a lot. hey it cant be wrong if it makes so much $$$ right? actually was kind of shocked at how radical his 1st trek movie was. geez didnt spock/ kirk get into a near fistfight? over uhura-saldana? cant remember exactly... jaw dropping! did you see force awakens? havent seen it yet myself... are youa shatner/ nimoy fan or just a kirk/ spock fan?
@0celo7 hmmm... did she really understand your proof? uh, actually, maybe that really is a good sign if shes a music major & was willing to read it... :D
I am not sure, I always interpret entanglement as basically one object. Perhaps, the 3 barebears are one single entity that for some reason look like 3 dististinct entities?
@0celo7 too bad she couldnt just pass out of calc in college. some schools do have a way to "challenge" the tests or get credit. diffeq is pretty advanced generally, although a lot of engrs tend to have to take it... she probably could have found an easier math class... suggests shes got some major stamina there...
PS, this blog is where I got the idea that "entanglement is basically a single object" http://lesswrong.com/lw/q0/entangled_photons/
At the time I was reading that blog (2012), my physics level is probably not high enough to detect whether this compsci guy of the blog is saying nonsense or valid things
@0celo7 did she get college credit for that? that score is enough at many schools to actually get the college credits that apply toward the basic requirements... eg if a school has calculus as a requirement for the major, then passing the AP test can achieve that...
@Secret entanglement is still under active investigation/ research. its arguably not even fully understood by the experts "yet". its a decades-long project stretching to close to century now.
@0celo7 if she enjoys diffeq then no big deal, but if shes tired of taking math classes, she might have avoided it... at least at some schools, dont know details of yours...
So if entanglement is one object, then I won't be suprised why measuring one (and giving a random result) will determine the other (a result that correlates to the random result obtained form the first)
The only question is, why does it look separate to us
and then, the partial trace operation mentioned by Acuriousmind yesterday which gives the link between esembles and entagled states makes me ponder that entanglement might not really that simple, but I still yet to digest the maths completely
@Secret my opinion, the complex/ unintuitive math is obscuring some of the reality, but this is at best a small )( minority view these days (more accurately, contrarian). this is not an outlandish/ unique idea, its basically Bohmian ... "philosophy"...
Well, even for bohmian trajectories, there's still nonlocality in it. Is the nonlocality a fundamental thing, or is just a manifestation/projection of something that is basically just a connected whole.
If it is the latter, what is the mechanism of this connection, how does it form and why our detectors only see them as separate?
@Secret these questions are all under active research. did you hear about the recent "loophole free bell test(s)"? historic. anyway think that "weak measurement" will eventually/ finally resolve the theoretical conflict. leading to some big new theory.
@Secret trying to remember, are you in college? what major?
I'd like to let a message to @ACuriousMind . I once asked here whether "the number of photons of a system" is a lorentz invariant quantity and you (and fenderlespaul) answered me that no. After talking to a friend the question arose again so I posted it physics.stackexchange.com/questions/241522/… and the answer seems to be that it's invariant. I'd appreciate if you could comment on that or even reply.
Those questions are infinite rabbit holes. If you know the mechanism how something happens, you can always ask what the mechanism how the mechanism works is. At some point, physical theories *always* cut off this chain of questioning and postulate some mechanism as "fundamental", as note being composed of smaller units of understanding. The preliminary nature of human knowledge means that we can never be sure whether that point is really "the end of the line" or whether there is something to it we have not yet discovered. The chain of reasons is either infinite or terminates at something wh…
@ACuriousMind Perhaps among this chain, the really key thing I am interested in is "why does an entangled state look like a separate thing to us and our detectors"
@vzn I have a couple of honours friends working in that facility and yes, that facility is rapidly expanding. Right now it has consumed 1/4 of the physics building
@Secret way cool. ok wrt entanglement feel free to drop by my chat room anytime for ideas/ info. have a few intermittent cohorts into that stuff also. chat.stackexchange.com/rooms/9446/theory-salon (gotta go nice chatting all)
@Secret It doesn't really look like a "separate" thing. The point is the detectors are only sensitive to a subsystem, they cannot measure the whole system (because the state is inherently non-local (but this isn't really because of entanglement!), but every measurement is local).
"but this isn't really because of entanglement!" omg, now I am more confused. I must have mixed up nonlocality with entanglement, I should read more before get back to it
Why should the number operator be proportional to the Hamiltonian @ACuriousMind? That implies that all photons have the same energy. Under Lorentz transformation the occupation of photons at different frequencies changes but the total photon number is fixed. I would have commented on the original post but I am new to the community.
@JamesRowland The Hamiltonian is schematically $a^\dagger a + \text{zero point energy}$. In the single, non-relativistic harmonic oscillator, it's $H = N + \frac{1}{2}$. The difference between the number operator in that answer and the Hamiltonian is essentially just the choice of measure - spatial vs. Lorentz invariant one. I want to know why it is physically correct to choose the Lorentz invariant number operator.
I realize now that, physically, the photons get red/blueshifted through a boost, and it is probably really correct to choose the Lorentz invariant one. But how does one see this in the formalism?
@ACuriousMind I mostly mean that if you don't know who else wrote an answer you're more likely to try to write a good one. I know I definitely am way less likely to try to answer if there's even a moderately good one already there.
@ACuriousMind Regarding those "one more thing" answers... some times they really do add value, so I'm not sure what to think.
The number operator needs to satisfy $[a^\dagger(k),a(k)]=1$. If you make this choice than the Hamiltonian is $H=\sum_k E(k)(a^\dagger(k)a(k)+1/2)$ which is only proportional to $N$ is $E(k)$ is constant.
I just thought of an intuitive picture as well. The Lorentz transformation is a continuous transformation. Going from one to two particles in not a continuous transformation. If the Lorentz transformation could do this then there would be some special boost at which you jump discontinuously from one to two particles, etc.
@Secret There's an easy non-entangled "non-local" state: Consider a photon incident on a half-transmitting, half-reflecting mirror. Its wavefunction gets split up into two separate packets, whose separation gets larger with time. If you measure the photon on one side of the mirror, you won't measure it on the other. Ta-da, non-local correlation without entanglement.
@JamesRowland It can't be that easy because the Unruh effect in curved spacetime does transform the zero-particle state of the vacuum for one observer into a populated state for another, and the transform into an accelerated state seems to be continuous to me.
@DanielSank I don't know, if you couldn't see the other answers, you could end up with multiple answers that say pretty much the same, which would be a waste of everyone's time
So you mean when I start e.g. measuring the transmitted photon, the wavefunction get evolved by the measurement hamiltonian into a new one such that there is probability of 1 for the transmitted photon to be measured and zero for the reflected photon
That is, even though the wave packets became more separate over time, the interaction caused by the measurement will still be able to affect the whole wavefunction of the photon, hence the nonlocality?
But I don't quite get it, isn't that entanglement requires the states in the subsystems to be correlated somehow?
Here in the photon hitting the half mirror case above, there's clearly some kind of correlation because whenever you can detect a transmitted photon, you won't detect a reflected photon, and vise versa. Thus it seems that the transmitted photon and reflected photon can be considered as two correlated subsystem, thus leading the conclusion these two cases are entangled. What am I missing here in my deduction?
@ACuriousMind that reminds me. have always wondered if bell type experiments are the "simplest" entangled states possible. because theyre not so "simple" to produce experimentally. if they are, seems like it would be possible to prove it, and it would likely be an interesting proof. if not, it would be interesting also.
@ACuriousMind I just read the wiki page for Unruh effect. This is for accelerating observers. The Lorentz transformation connects observers at different velocities but not accelerating. Looking into this I found a post about the Unruh effect which made me remember that particles can be in a superposition of unoccupied and occupied, e.g., you can go continuously from zero to one particle.
@vzn They are the "simplest" in the sense that they work with two two-dimensional subsystems (spin up/down). You don't get smaller spaces than that, so the math is the simplest. I don't know whether you can measure experimental simplicity in the formalism
@vzn @Secret @ACuriousMind I have not been following the entaglement discussion. Has anyone brought up the fact that all Fermions are entangled by definition?
The Fermion anti-commutation relations enforce this.
@JamesRowland Yes, I know the Unruh effect is different and I now don't doubt that indeed the photon number is Lorentz invariant, I'm just saying the continuity argument alone is not enough.
Any one know a toy system that is (a) easy to analyze in Lagrangian mechanics if you use some generalized coordinates but (b) very difficult to do simply writing down the positions of the masses?
Will get back to that later, I am slow at typiing laTex (STILL TYPING) and yes you are right about the fermions, the electrons in a molecule is commonly regarded as entangled such that to compute the correct energy you have to consider all electron correlations in the molecule
@dmckee Atwood machines? I seem to remember those get pretty horrible in Newtonian mechanics, but the right choice of generalized coordinates makes them rather tractable in Lagrangian mechanics
Suppose you have a system of just two electrons. One in state a and one in state b. The state of the system has to be anti-symmetry under exchange of a and b so $\psi=a\ctimes b-b\ctimes a$.
I would struggle with the spinning thing in the thing
I don't see how that's clearer
user54412
I once had a mass attached to a spring anchored to a rod swinging around a joint off-center on a turntable -- not sure it was easy in any formalism though
@JamesRowland Yes, the antisymmetrization may be seen as just quotienting out the unphysical symmetry of interchanging two indistinguishable particles. (If you want to see TeX in chat, go to this page )
I am only clear that the hamiltonian cannot evolve the wavefunction into one that involve both D_1 and D_2 terms as otherwise both detectors will get a nonzero probability of detection
I need to figure out what form the final state has to take in order to ensure whenever D_1 detects something D_2 must be zero and vise versa
Please will someone explain what time dilation really is and how it occurs. There are lots of questions and answers going into how to calculate time dilation, but none that give an intuitive feel for how it happens.
By googling, I have found several different opinions about how to take one's own facial images more realistically:
Some said photos taken by cameras (smartphone's cameras, if specific) are more objective than images from flat mirrors, because it is close to what others see myself.
some said the...
@Danu Thanks for the tweaks. This was sort of a first draft - I rushed it out when I saw there was yet another question about time dilation. I think it could do with considerable polishing.
I'd be interested in opinions from the panel on whether it hits the right tone i.e. does it actually give a useful explanation of why time dilation happens?
@ACuriousMind: I am one of the close votes. The example in the book is bad physics and I don't think we really need an analysis of all the possible mistakes the author made/the possible attempts one could make on his behalf to rescue this nonsense. — CuriousOne2 mins ago
...that's not what "primarily opinion-based" is for...
How fast would a 1500kg, 1.4 m tall car have to be going to lodge a deer with a mass of 160 kg into the radiator or the bumper of that same car? I know that at most speeds, the deer will hit the windshield once it has been hit by the car but isn't there a velocity where the deer would get stuck i...
Please will someone explain what time dilation really is and how it occurs. There are lots of questions and answers going into how to calculate time dilation, but none that give an intuitive feel for how it happens.
