The h Bar

12:00 AM

@0celo7 If you actually solve the constraints, you can just eliminate some coordinate from your phae space and arrive at a description that has no gauge symmetry (i.e. no constraints) left

On a bird's view, it's nothing else but quotienting out the gauge orbits from the constraint surface

0celo7

@ACuriousMind Ah yes, nothing else. Elementary.

ACuriousMind

@0celo7 Well, all that that is saying is: Identify all points that are related by a gauge trafo.

0celo7

@ACuriousMind That was sarcastic, but I fully understood what you meant :)

ACuriousMind

Alrighty then

And now, I'm off to get at least a minimum of sleep. Cya

0celo7

Bye

vzn

1:55 AM

via reddit

in Computer Science, 52 secs ago, by vzn

Filling in the Standard Model with a boost from computing / DOE

@Marcel inclined to agree, but do you have a ref for that?

0celo7

@ACuriousMind Prahar's comment on this post made me question something I thought I knew. We define the Levi-Civita tensor as $\sqrt{g}[abcd]$ where $[abcd]$ is the standard antisymmetric symbol. Then I've always thought this proof is straightforward: $\nabla_e\epsilon_{abcd}=\nabla_e\sqrt{g}[abcd]=[abcd]\nabla_e\sqrt{g}=0$, but as Prahar points out, $\nabla_e\sqrt{g}$ is ill-defined.

Pretty sure I'm derping, what's the catch?

vzn

@Martin which "post" are you referring to?

0celo7

@ACuriousMind Never mind, Straumann (once again the rigorous German saves the day) shows how to extend the covariant derivative to densities, including scalar densities.

vzn

2:27 AM

@Marcel did you finish it? masters or phd?

for those wanting to think carefully about bells thms & the issue of probability distribution "bias"/ "fair sampling" (the way it is sometimes identified), take a look at this paper

A local hidden variable model of quantum correlation exploiting the detection loophole / Gisin/ Gisin

the basic idea is that there exist hidden variable theories where the detection of the particle is influenced by the hidden variable, and bells analysis/ assumptions exclude those. this paper shows one for the singlet state; however, afaik, it has never been generalized. my personal intuition/ conjecture is that a full generalization exists.

in their paper they claim their theory must nec. have a detector efficiency of 75% but my suspicion is that this is a very subtle issue, and that LHV theories exist that control particle detection but which still can "fool" the experimenter into thinking they have high efficiency. the issue is that an experimenter can never actually "know" when a particle is not detected. its inherently unmeasurable.

detector efficiency measurement actually relates to (subtle) assumptions about "undetected particles"...

bell did try to take into account different types of probability distributions in some of his later derivations & conclude they dont matter, but it involves what is called a "fair sampling assumption"... but one would argue the use of the word "fair" here is an anthropocentricism...

Icosahedron

2:51 AM

A meteor appeared in the sky for a few seconds outside my window.

dmckee

4:28 AM

"its inherently unmeasurable." Er ... if I can know the number of pairs injected into the system to precision $\epsilon$ then I can constrain the non-detection rate to be no worse than a few times epsilon in the short term and more tightly than that as I accumulate statistics.

user1667423

4:42 AM

Electric susceptibility

In electromagnetism, the electric susceptibility (latin: susceptibilis “receptive”) is a dimensionless proportionality constant that indicates the degree of polarization of a dielectric material in response to an applied electric field. The greater the electric susceptibility, the greater the ability of a material to polarize in response to the field, and thereby reduce the total electric field inside the material (and store energy). It is in this way that the electric susceptibility influences the electric permittivity of the material and thus influences many other phenomena in that medium, from...

Am I understanding this correctly?

Is the rate of change of polarization density with respect to time equal to the product of the electric susceptibility and the electric field?

NeuroFuzzy

@user1667423 That's incorrect. If you differentiate $\int f(t) g(t')dt$ wrt $t$, then you get $f(t) g(t)+\int f'(t)g(t')dt'$

so you'd have another term there

vzn

5:01 AM

@dmckee if one looks at the bell experiments carefully, one cannot actually "inject pairs". often "only one" of the photons is detected at each arm. these "events" are mostly discarded... note that some of this confusion dates to the original EPR1936 paper which did not consider the (2020 hindsight obvious) case that one cannot consistently detect both pairs... (esp with photons...) wrt EPR, something got lost in the translation from particles to photons over the decades...

NeuroFuzzy

@user1667423 But try plugging in $\chi(t)=\chi_0 \delta(t)$, evaluating the integral, and then differentiating it.

vzn

admittedly there are some rare bell experiments done on mass-based particles, but am not very impressed with their setups. eg they might assume absence of + polarization (detected) is equivalent to - polarization, etc, a sort of theoretically acceptable idea (given the assumptions of QM) but experimentally quite nonrigorous/ "sloppy"/ "lazy".

@Martin my feeling is that these ideas have to be developed further with extremely careful attn to detail, but could be eventually pushed toward something "testable" / "falsifiable". sometimes one never knows unless one tries eh?

@Martin "does it really change a lot?"... who knows? couldnt a very serious/ rigorous/ expert physicist analyze/ answer that question? wouldnt they be particularly interested in the real answer? isnt that the kind of inquiry that drove Bell decades ago, and other great scientists? did QM "really change a lot" over classical physics?

Martin

5:37 AM

@vzn: Of course you are absolutely right - and that's exactly why I'm trying to understand Marcel's problem. What I'm saying is that I know a few of the world experts in the topic personally - they are not saying that everything is done, but Bell's paper is irrelevant in that sense, because it has long been surpassed by new results.

@vzn: What I'm saying is: If you want to get the experts' attention, you need to make sure they haven't yet addressed the issue years ago and you need to point out the failures in the current literature of the topic. Everybody of us labours under severe time constraints, so there is only so much you can do in a day.

user1064504

5:49 AM

hello anyone here
I have a doubt regading electrostatics

Physics Meta

7:43 AM

0

Q: fluid dynamics with external forces

Consider a one dimensional fluid flow in a rectangular tube. Typical streams are the poiseuille streams. Consider the case in wich we apply a force on the fluid. The Navier-Stokes equation (for incompressible fluids) is formally: $$\rho_f \frac{d \vec{v}}{dt}=-\nabla p+\rho_f \vec{f}+\eta \nabla^...

discussion

pZombie

10:14 AM

is there any experiment we can perform on a large number of entangled photon pairs where one of the photons of the pair would run through an arrangement of polarizers, such that we could tell with high probability (given a large amount of such photon pairs) if the photon pairs are in a superposition state still?

More precise. Would we be to assign a probability value on how many of those photon pairs are in a superposition state still after running one of the photons of every pair through a well chosen polarizer arrangement?

would we be able*

Danu

1:04 PM

Hi guys, I just read the following claim:

> Stationary black holes in Einstein gravity are axisymmetric

arxiv.org/abs/hep-th/0004098

ACuriousJim

What's the problem with that?

Danu

@ACuriousJim I don't know it, and no citation is provided

ACuriousJim

well why wouldn't they be axisymmetric?

Danu

1:20 PM

Lol, I mean to ask if there is a theorem

@ACuriousJim Because real stars arent

I would at least say it's a nontrivial statement.

ACuriousJim

I wonder if they mean the singularity or the event horizon

Danu

The event horizon

ACuriousJim

hmmm.... one second. I think this might actually be a trivial statement. Just let me check on something

I think in the case of an isolated stationary black hole, it's trivial to say it is axisymmetric. But if there are other bodies nearby, those could in theory affect the event horizon and undo that

So that statement needs to be taken in context. Are they referring to an isolated black hole?

Jiminion

Is a galaxy axisymmetric? Assuming a galaxy has a black hole at the center, do galaxy shapes assume black holes are rotating? (Does that even make sense?)

Danu

@Jiminion Obviously not perfectly

@ACuriousJim Why?

ACuriousJim

1:33 PM

@Danu Because then we could represent the black hole as a perfect Kerr-Newman black hole and the Kerr-Newman metric has cylindrical symmetry

Danu

@ACuriousJim Is that so? Any isolated black hole must be Kerr?

Why? *

ACuriousJim

@Danu A stationary black hole, by the no-hair theorem, has only mass, angular momentum, and charge

If it is perfectly isolated, then it exists alone in its environment

We can describe a black hole with mass, angular momentum, and charge perfectly by the Kerr-Newman metric

Danu

@ACuriousJim relativity.livingreviews.org/Articles/lrr-1998-6/download/…

> In particular, it has turned out that not all black hole equilibrium configurations are characterized by their mass, angular momentum and global charges

(note, I'm not trying to be a smart-ass. I'd just like to see some kind of uniqueness result)

ACuriousJim

Well then there you have it. This paper clearly establishes the existence of solutions where stationary black holes were not axisymmetric. I'd need to read further to see if those solutions were truly isolated or not, but it looks like the people who wrote your above paper may have overlooked this

One more reason not to trust everything posted on arXiv at face value

Danu

...but it was supposed to be a review article! Damn you, physicists!

ACuriousJim

1:43 PM

seems like the one you just linked is a much better review

Danu

But it's not about BPS black holes in N>4 dimensions :P

Maybe there's a Living Reviews thing on that though, I'll look

Remember me

2:06 PM

physics.stackexchange.com/questions/177780/… can someone have a look at this question of mine??

@ACuriousJim can you look at my question

Danu

@Rememberme So, ehh... did you just admit to sockpuppetry?

Remember me

what?

Danu

@Rememberme The poster of the question is not you

...or at least not by SE name

Remember me

Oh no no two accounts

Danu

Yeah okay (that's called sockpuppetry)

It's not necessarily bad or punishable, don't worry.

Remember me

2:21 PM

i didn't know that

Remember me

2:34 PM

@ᴇʏᴇs physics.stackexchange.com/questions/177780/… <-- this one

user41796

@Danu Sock puppetry is when you have two accounts and use those accounts to promote each other. It's not necessarily a problem to have two separate accounts for different sites. The concern is with gaming the system.

user41796

@Rememberme - I did notice that you have two accounts on Mathematics. Unless you have a very specific reason for keeping separate accounts on a single site, I would encourage your flagging a post of yours on the site and requesting the two accounts to get merged together. That prevents anyone from suspecting or accusing you of sock puppetry.

Remember me

How should i do that@GlenH7

How should i merge them

user41796

@Rememberme Pick any of your posts on Mathematics, select "flag" and then select "in need of moderator intervention". In the text box that opens, up, explain that you have two accounts, provide a link to the other user account, and ask for the moderator to merge them

user41796

Or you can pick the post from your other account: math.stackexchange.com/users/190906/sayan-chattopadhyay and flag that one instead. Doesn't really matter which you flag from - the point is to make sure the site mods know both user IDs in order to get the accounts merged.

Remember me

2:47 PM

If i dont merge them then ?

just saying

user41796

So long as your two accounts never interact with each other, probably nothing

Remember me

they haven't have they?

user41796

The moment you're caught voting for yourself, then it's at least a suspension and either a merge or destruction of one of the accounts

Remember me

I didnt vote even once

Or should i delete the other one?

user41796

@Rememberme I'm not a mod on the site, so I don't know. I do know that SE takes an exceptionally dim view of any potential sock puppet allegations. Not something I would choose to trifle with.

Remember me

2:50 PM

Coz i dont need it anymore

user41796

@Rememberme Deleting is an option as well; merging is preferred as the lower rep account has created content on the site. Deleted the account would destroy the content which negatively affects the site.

Gowtham

delete/ merge / dont vote each other account . pretty simple

David Z

@Rememberme it's fine to have multiple accounts as long as you don't use them to vote on each other, to evade a suspension, to create the appearance of more support for an issue than there really is, or so on. Basically, anything you can't do with a single account, you're not allowed to do with multiple accounts.

3

Remember me

Ok i have requested for a merge is that fine?

user41796

Yep, that's perfect.

Remember me

2:59 PM

When can i find that they have been merged

ACuriousMind

Ahhh, 17 things in the close queue. I would really be interested in knowing whether we get more bad questions or if people are just active flagging them more often.

ACuriousJim

@ACuriousMind I haven't been close reviewing lately. So that might be adding to a bit of the build up

ACuriousMind

@ACuriousJim If a single reviewer opting not to review - even if it is the king of Jims - causes such a buildup, we have a problem :P

ACuriousJim

@ACuriousMind Oh, I have no belief that I'm the sole cause. But I'm saying I might be contributing to the buildup. 2-5% might be due to me

ACuriousJim

3:38 PM

Hey, I just earned another yearling badge. Right now must be the anniversary of when I joined

Physics Meta

5:30 PM

0

Q: Is it inappropriate behaviour to post links?

preamble:- This is not related to my 1-year suspension which just expired, I understand the reasons for that, because my comments were really spam (because I posted links to PO threads before they were answered there. Note that I'm also not asking for the reasons for any suspension, but rather as...

discussion comments hyperlinks suspensions

vzn

@Martin "surpassed by new results"? huh? theoretical or experimental? the (math) defn/ analysis of locality has not changed a whole lot since bells papers.

12 hours ago, by Martin

@vzn: What I'm saying is: If you want to get the experts' attention, you need to make sure they haven't yet addressed the issue years ago and you need to point out the failures in the current literature of the topic. Everybody of us labours under severe time constraints, so there is only so much you can do in a day.

get the experts attn? for what purpose? yes ofc many issues have been addressed many years ago. as for "severe time constraints," yeah, everyone is busy! & one wonders is there any room for a tiny bit )( of (new) science in all of that?

> with all thy getting get understanding...

Loopholes in Bell test experiments

In Bell test experiments, there may be problems of experimental design or set-up that affect the validity of the experimental findings. These problems are often referred to as "loopholes". See the article on Bell's theorem for the theoretical background to these experimental efforts (see also J.S. Bell). The purpose of the experiment is to test whether nature is best described using a local hidden variable theory or by the quantum entanglement theory of quantum mechanics. The "detection efficiency", or "fair sampling" problem is the most prevalent loophole in optical experiments. Another loophole...

as mentioned marcel seems mostly focusing on the "fair sampling loophole" which is supposedly also connected to "detector efficiency" but as stated think that may be mistaken also.

and some further lol at the accepted physics terminology/ conventional wisdom. the term "loophole" is again an anthropocentrism.

0celo7

6:55 PM

"Mr. President, what if the unthinkable happens? What if the launch goes wrong, and Napoleon is not stranded on the Moon?" "Have Safire write up a speech."

0celo7

7:20 PM

@ACuriousMind Suppose I have an action with a symmetry generated by an antisymmetric matrix, i.e. $\phi^a\rightarrow \phi^a+a^{ab}\phi^b$, $a^{ab}=-a^{ba}$ and I want to find the Noether current. For a simple trafo one finds $$\delta S=-\int \mathrm{d}x\,j^\mu_a\partial_\mu a_a$$ but in this case we need $$\delta S=-\frac{1}{2}\int\mathrm{d}x\,j^\mu_{ab}\partial_\mu a_{ab}$$ right? (Note the 1/2.)

(Context: I am trying to derive the string angular momentum using the Noether method, but I have an extra 1/2 that I need to make disappear.)

Danu

7:48 PM

@GlenH7 Please note that I was not trying to imply that there was any problem

@ACuriousMind I haven't been reviewing much at all either lately. Not a lot of time :\

DanielSank

8:05 PM

If you were to see an equation like this: $\dot{\alpha}(t) = -i \omega_0 \alpha(t) - i \epsilon(t)$
and I were to tell you it's the equation of motion for a driven harmonic oscillator, could you tell me what $\alpha(t)$ represents?

pZombie

given two hollow tubes on wheels. One tube has a wind turbine in front whereas the other doesn't. Both have an engine which drives them forward. The tube with the wind turbine uses the energy generated by the incoming wind as a means to additionally power the "car". Which of the two cars will move further with the same amount of gas?

Marcel

@vzn It's a bachelor thesis. It's on german though.

@vzn I'm not aiming on "fair sampling". It's just a flaw within the assumption of the propability distribution, which seems to be general, but in fact is not. There is no experimental loophole involved. Just a false assumption, see this post

pZombie

Also, couldn't we instead of wasting the heat a car motor creates, rather have the motor itself inside a water tank to generate steam and use the steam to drive a steam engine?

vzn

8:42 PM

@Marcel hi. you are essentially arguing what is known as the "fair sampling" loophole which argues that the particles detected are biased. at least be reassured its recognized as a scientifically credible position eg as in the paper by gisin just cited.

DanielSank

@vzn @Marcel: Ever heard of the Bell-Leggett-Garg inequality?

NeuroFuzzy

@pZombie certainly the one without. Basically, the only difference is that without you are only accelerating the car, whereas with you're accelerating the car and dragging air along with you.

pZombie

@NeuroFuzzy but that air would hit the tube at a much higher speed if the wind turbine wouldn't have taken away some of the air's energy, hence higher air resistance

vzn

@DanielSank hi, no. kinda obscure. have seen most of bells own eqns/ derivations. have his book. read his papers. etc

DanielSank

@vzn Ok.

vzn

8:57 PM

hey when are you gonna do a chat talk on qm computing? :)

NeuroFuzzy

@pZombie in the frame with the ground stationary, the air has no energy to take away. Anyways, we are talking about a HOLLOW tube right? Are you asserting that a toilet roll paper tube has more air resistance than a toilet roll paper tube with some blades glued inside obstructing the airflow?

vzn

so what about bell-leggett-garg, are you gonna leave me hanging?

pZombie

@NeuroFuzzy ok, let the tube not be hollow, but be closed on both ends with a windshield in front. Does that change the outcome?

NeuroFuzzy

@pZombie any force on a fan blade will be realized as a momentum transfer to air. In the ground frame (w/ stationary air), this always increases the energy of the air. If you just stick a fan on, you increase the drag, and so transfer more energy to the air!

Martin

@vzn @vzn: But that's EXACTLY what I've been saying: It seemed from the discussion with Marcel that he had not read much of the current literature and I said that I could well believe that his issue had already been adressed sometime between Bell's paper and the present. You seem to understand more about the loopholes than I do, which is fine - I never claimed to be an expert - so great, you seem to have found it.

pZombie

9:07 PM

@NeuroFuzzy ever watched the video where someone straps a small turbine on a model car, uses some fan to blow air on that little turbine and then transfers this rotation into moving the car forward ?

vzn

@Martin there is always more literature to read. what is really interesting is stuff in the past that points to the future ;)

marcel seems well enough versed to me

Martin

@vzn: Phone call, I'll answer later.

vzn

@Martin when you say "already addressed" that is somewhat misleading/ inaccurate. certain issues have been "acknowledged by experts as not fully resolved/ closed"

ie not every loose end has been tied down so to speak.

pZombie

@NeuroFuzzy i forgot to add. He blew air from the front onto the turbine. Yet the car moved forward

NeuroFuzzy

@pZombie which is why I specified that I'm talking about energy in the ground frame with stationary air.

If there's wind blowing, you could make use of it, sure. You could also make use of solar, geothermal, or tidal power.

pZombie

9:14 PM

i guess the road moving relative to you is the problem here

NeuroFuzzy

Right, so what I'm doing is choosing the frame where the air/ground is stationary and the car is moving because things are much clearer there.

pZombie

there has to be a way to take that energy out of the incoming wind and pass the momentum into the road

Martin

10:29 PM

@vzn: granted - but I maintain: Given certain loopholes in certain settings, the issues have been addressed and the majority of researches that I have encountered seems to think they are closed (but the issues are hard). So "not every loose end has been tied down so to speak" is something I can agree with.

@vzn: "there is always more literature to read. what is really interesting is stuff in the past that points to the future ;) " I actually have to disagree in a certain sense: Hailing (for example) Heisenberg for his observations of error-disturbance relations doesn't get you anywhere outside history, because Heisenberg didn't have a proper understanding. You'll not gain much more than you can gain from reading good (!) papers about the issue today.

In my view, there are two types of research(ers), both of which are valid: One type has a very good overview of the current literature and combines it with new ideas to get new results in these directions. The other type likes to "go back to the roots" to rethink the problem. That is totally fine, but while you can always claim that the first research is new, in order to claim this for the second research, you will have to actually read the literature afterwards.

Martin

10:45 PM

I've already seen it a couple of times that something purportetly new was just reinventing stuff known for decades. It's all valid and important, but people might get bored.

Regarding the discussion Marcel and I had, this is what I thought: Marcel seems to definitely know what he is doing, in the sense that he knows the usual Bell derivation, etc.

I had however the feeling that he might not have a complete overview about all the possible experimental or whatever loopholes in existence (or he might just interpret some of them in another way, just as I would probably misinterpret some of them, if I had a good knowledge of them).

Therefore, it might be worth to look at it and see whether it's an issue that has been addressed (as you put forth) or that is actually not addressed in the literature, in which case it might be worth to help bringing it to the attention of the "scientific community". In any case, I was hoping to learn something myself ;).

vzn

@Marcel encourage you to translate it & share it. are you interested in challenging QM interpretations/ foundations over the long term? created a chat room to discuss alternative theories. always looking for participants.

@Martin alas despite pretentions & appearances, as a whole the "scientific community" is generally not so open to new ideas... this area interests me because its actively being researched & even revised, but by a small minority faction...

Jan 26 at 21:59, by vzn

in toy models of QM, 51 secs ago, by vzn

superclassical/ emergent QM, recent developments, rough outline/ overview/ leads / Tmachine blog

there are some newer/ recent refs to bells thm cited in that.

Alfred Centauri

11:31 PM

@DavidZ I would like to add that creating more than one account to vote against each other or to create the appearance of more disagreement on an issue than there really is also verboten. :)

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