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cows

12:15 AM

Heading back home to be one with my code. Should be a super productive and exciting session.

Physics Meta

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Q: Is it possible to see how many times a particular tag badge has been awarded?

I'm curious because the main badges have a count associated with them (i.e., "altruist, 177 awarded"), but it's not apparent that you can find out how the number of times a tag badge has been awarded. I've been active in the acoustics tag for rather a long time (and will keep chipping away at t...

vzn

2:14 AM

@bolbteppa understand QED is highly tested. what is not well known is how close some fluid theories come to it. think its beyond mere coincidence, think its uncanny. the paper you cite actually supports that pov. its really just a matter of tinkering with parameters. almost nobody realizes it or is doing it... yet!

Secret

8:46 AM

(After get back on main comp, made a comment about "Surrealistic Bohmian trajectories do not occur with macroscopic pointers")

Captain Bohemian

9:22 AM

@vzn I thin that paper you claim to be your favorite isn't really counted as a research paper; it's just a note about personal thought about computing rather than research results.

Secret

@Semiclassical Couple of interesting points mentioned in that paper:

> 1. Nevertheless, at any time the motion of the pointer particle gives an information that is consistent with the present motion of the test particle: just after it crossed the slit, the position of the pointer moves in the corresponding direction; if the test particle later jumps from one wave packet to the other, the pointer also reverses its motion, providing an indication that remains consistent with the present trajectory of the test particle.

This is very different from the orthodox on how the non locality is very explicit, and I can imagine how that will cause difficulties with lorentz invariance especially when the pointer and the particle are spacelike separated. I do think however, a similar treatment on how entangled states transforms under the Lorentz group may be able to get around that. For example in the orthodox view, a pair of entangled states that are space like separated after brought into interaction

can have a timelike correlation when seen from a moving frame. I guess a similar treatment should be applied on the pointer and the the bohmian particle in order to transform it properly, but then my SR sucks so don't take my word for it

> 2. Interestingly, we have a case where it is not the “hidden variable” associated with the measured particle that determines the result of measurement, as often believed in the context of the dBB theory. What matters here is the initial values of the “hidden variables” of the measurement apparatus, which determine in advance which path will be taken by the test particle. This sort of “predestination effect”
is also a generalization of the “non-local steering of Bohmian trajectories” observed with photons in Ref. [24].

This is also an interesting point, but in a way it is also kind of expected whenever there is nonlocal influence as such influence can often constrain the future evolution of the dynamics in order to be consistent with the nonlocality

That we cannot use that for signalling is purely thanks to that the initial position of bohmian particles are unknowable thus we have statistical results instead

It is however, more interesting in a philosophical view: It basically shows how much the future is being constrained when nonlocal influences are present. This also reminds postselection somewhat, but it is different because in postselection, you choose events that satisfy a given constraint, then of course you only get the outcomes that correspond to it
(e.g. delayed choice quantum eraser experiment, depending on how you comb the data, you can reach the conclusion that the entanglement has projected away, or is ok and the interference is still intact)

but here in Bohm, in theory the nonlocal influence happens continuously as the particle pass through the slit and on their way to hit the screen

> 3. The morale of the story is that, when a trace operation is necessary in quantum mechanics to evaluate the decoherence induced by the pointer on the test particle, in dBB theory all degrees of freedom of the pointer that are traced out must be taken into account, including every Bohmian position.

This is also very different from the orthodox, in that decoherence occurs as the eigenstates get entangled with the environment and hence becoming non interfering pointer states and destroys the interference, thus require all the environment states to be averaged/traced out to determine the final probability, whereas in Bohm it is the internal degrees of freedom of the pointer device that controls the interference region.

Thus not only in Bohm the internal states of the pointer influences whether the interference occurs, it also influence its shape and hence the distribution of the trajectories in a predestination fashion, thus Bohm gives a more nonlocal treatment of the interaction of measurement with the quantum state

> 4. Actually, one can even argue that the trajectories in question are more real than surreal, since their characteristics (including the changes of directions) should be experimentally accessible by observing the successive positions of the pointer particles with sufficient accuracy.

But how are we going to measure that, as almost every measurement will perturb the wavefunction and hence changing all the initial conditions?

Nobody recognizeable

11:13 AM

Hey guys when on rolling motion the angular momentum will not be parallel to axis of rotation ? I just want an example or a reference.

Physics Meta

12:46 PM

0

Q: Why this question was closed?

I don't think that this question should be closed? A question on rigid body dynamics This was closed as unclear but I think that I explained it at my best! What should I do to edit it?

support specific-question suggested-edits suspensions

vzn

2:20 PM

@CaptainBohemian dont know what paper youre referring to

Captain Bohemian

@vzn you claimed at least two times that paper is your favorite; that's what motivates me to read it.

vzn

@Secret the idea that there are hidden variables "in the measurement apparatus itself" which interact with those of the particle being measured seems not fully explored to me. also note that detector dead time + detector efficiency etc are clearly apparatus hidden variables.

@CaptainBohemian have a few favorite papers do not limit myself to 1, thx for reading "whatever" :)

Captain Bohemian

you can go back to read the transcript.

I don't know how to cite message of transcripts.

vzn

@CaptainBohemian speaking of chat transcript have been chatting here over ~½ decade now did you notice? have an idea what youre referring to but why not just cite it? you can right click on the left msg section, "copy link" and paste it, yes this is a somewhat hidden feature.

> Nevertheless, the reader who is allergic to the very idea of particle positions in quantum mechanics can easily translate every statement in terms of the trajectories of the elements of the probability fluid.

↑ lol! :o o_O

PM 2Ring

2:44 PM

@ACuriousMind re: physics.stackexchange.com/questions/473959/… Fair enough. My guess is that they've noticed that the energy-momentum 4-vector has the same orientation as the 4-velocity.

ACuriousMind

@PM2Ring The part about the Compton frequency makes me doubt that.

PM 2Ring

3:35 PM

@ACuriousMind Ok. But I think that's just confusion, and that he's gotten mixed up trying to understand de Broglie waves. Anyway, he's commented & edited the question. It's still a bit mysterious, but he's verified that he's not interested in non-mainstream stuff.

ACuriousMind

@PM2Ring I could be convinced that it's not "non-mainstream", but I still think it's entirely unclear what the question is actually asking.

Even not thinking about the physics at all, the question uses the slope of the trajectory simultaneously as an angle. That's non-sensical.

PM 2Ring

@ACuriousMind True, it doesn't work so well when you have more than 1 dimension of space. :)

Semiclassical

4:31 PM

@vzn i suspect the point they're making is that a non-Bohmian can regard "probability fluid" merely as a mathematical description, not a physical reality

i mean, the continuity equation for probability density in QM does have the mathematical form of a fluid. but you also see that equation in heat, for instance, and we no longer believe in such a thing as a "caloric fluid"

I doubt most people would care to use the phrase "probability fluid", though. As a mathematical description it's fine, but if you buy into the orthodox view you'll balk at the suggestion of it being a physical thing

(As evidence of that, googling the phrase "probability current" yields about 10x as many results as "probability fluid")

vzn

@Semiclassical understood that. and think strictly speaking its wrong. but it will take a long time to prove it.

@Semiclassical yes physics sometimes reduces to a "belief system" o_O

Semiclassical

shrug

vzn

@Semiclassical its mere semantics. am highly aware of the orthodox pov, thx for keeping it straight.

Semiclassical

to the extent that it's an argument about metaphysics and not actual experimental results, it's not surprising

with "caloric fluids", they ultimately were experimentally testable and seen to be insufficient descriptions

vzn

@Semiclassical yes JR in a more friendly mood recently cited a SE question on that.

@Semiclassical it will take awhile longer to build awareness/ understanding/ insight & create experiments to prove the fluid idea and its very slow going at times, the Couder-Fort-Bush reversal shows "~1½ step fwd 1 step back"... its already over a decade old and the physicists are still arguing about it! at least now Bohrs grandson is in the mix lol! o_O :P

Semiclassical

4:46 PM

well, keep in mind: if you buy into the orthodox interpretation, then you're quite willing to acknowledge that "probability fluid" exists in a mathematical sense, and that the resulting equations will bear on physical predictions

ACuriousMind

@Semiclassical I think that the association of a continuity equation with fluids is an accidental effect because people usually see their first continuity equation in the context of fluid dynamics, but all conserved quantities have such an equation and an associated "flow", and the ones that correspond to actual fluids are probably in the minority.

vzn

@Semiclassical the orthodox pov downplays probability fluid as a mere abstract curiosity, a mere concept so to speak.

Semiclassical

@ACuriousMind agreed

ACuriousMind

Just take continuity for electric current: People don't really believe that there's an "electric fluid", yet the water analogy is popular to explain the basic properties of current.

vzn

@Semiclassical copenhagen interpretation/ "shut up + calculate" → "shrug" lol! :P

Semiclassical

4:55 PM

i'd say it's more a statement of "if you can make a prediction, calculate the prediction. if you can't make a prediction, shut up."

vzn

@Semiclassical understood, but which strictly speaking is not how science progresses, dont really feel its an entirely scientific pov/ position.

Semiclassical

depends on what you mean

i would tend to agree that "be quiet and dont' talk about it" is unhelpful. (whether that counts as "unscientific" is a subtler point)

but "i'm not interested in it if you can't make a prediction about it" is defensible

vzn

@Semiclassical my feeling is (and maybe have pointed this out before) that your stance wrt BM is (to put it mildly) not fully internally consistent. you embrace it exactly ~½ so to speak. it reminds me of the old expr dating to middle of enlightenment, a little knowledge is a dangerous thing...

Semiclassical

meh

I find it interesting but I see good reasons to not be dogmatic about it. (specifically when it comes to field theory and relativity)

and I find it interesting precisely because of the extent to which it, as an interpretation, is independent from the physical predictions

By contrast, I don't find endless speculation about what "could be found" very interesting

I'm more interested in exploring the stories we have.

vzn

@Semiclassical it appears you dont really take all of Bohms ideas seriously, feel that youve focused on a ½-baked version so to speak that is not what he intended, but something that has been reformulated to be as palatable as possible wrt existing orthodoxy etc.

Semiclassical

5:08 PM

I certainly don't find Bohm's views as interesting as I find Bohmian Mechanics.

the former is a historical question. it's not without interest

vzn

@Semiclassical right, and think at some pt it becomes a disservice to his real ideas.

Semiclassical

but I don't particularly care for Bohm's own presentation of it

vzn

@Semiclassical youre missing some of the presentation, glossing over some key aspects, some that am personally emphasizing.

Semiclassical

(whereas I'm far more sympathetic to Bell's presentation of it)

ACuriousMind

@JohnRennie Any idea how your duplicate comment here ended up as an "other" off-topic close reason?

Semiclassical

5:10 PM

But if I come to some conclusions about BM that run contrary to what Bohm would have thought?

Well, too bad for Bohm, but that's my judgment and I'm sticking to it

vzn

@Semiclassical like what? his ideas all fit together and theyve been selectively sampled by later physicists to (my pov) their own detriment. (but also, have long conceded/ underlined he doesnt have the complete story either.)

Semiclassical

like the idea that the right way to motivate the theory is to start from the Schrodinger equation, plug in $\Psi=Re^{i S}$, and deduce from that the continuity equation + the quantum Hamilton-Jacobi equation

there's an interesting story there, but I don't find it particularly convincing as a starting point

by contrast, I find it far more interesting to go from the Schrodinger equation to the continuity equation (in the usual manner). from the latter, deduce the velocity field $\vec{j}/\rho$

and finally take the extra step of viewing that velocity field as determining the allowed particle trajectories

I very much do not care for the idea of the quantum potential as being fundamental.

It looks too arbitrary for me to be very convinced.

vzn

am reminded a lot of a paper you cited, maybe it was cowritten by Hiley, trying to remember... gotta go look at it again... anyway was a bit gobsmacked, they mention madelung fluid! how many ppl tie Bohm to madelung fluid? nearly zilch it seems etc

Semiclassical

uh

quite a few people do

vzn

← (having trouble with my @#%& wifi/ internet right now) :(

Semiclassical

5:19 PM

as evidence of that, if you google the phrase "madelung fluid" you get about 5500 results

if you include "bohm" in the search, that gets you down to about 2000

the latter isn't a lot, but relative to the former it's pretty sbustantnial

vzn

anyway think that there is argument/ replication problems over the classical Couder-Fort-Bush experiments over 1 decade after they are formulated shows that this is an exceedingly subtle area of physics. feel a lot more humility is in order and that copenhagen is in a sense anti-humility/ curiosity so to speak... a ~~lot~~ ton of patience is required for this area. it seems few really have it.

John Rennie

@ACuriousMind I do that when I don't want to use the dupe hammer. The idea is to suggest it's a duplicate but wait for others to confirm the suggestion.

ACuriousMind

@JohnRennie The problem is that when the other close voters agree with your off-topic vote instead of casting a proper duplicate vote, the question ends up being closed as "off-topic" instead of as duplicate, so it doesn't get the link to the dupe target at the top and the close banner says "[...]not about physics[...]".

In this case, it confused both the OP and me

John Rennie

I see your point, but that's the problem with the dupe hammer

I wanted the op to have a chance to look at my suggested duplicate and agree or disagree

ACuriousMind

@JohnRennie Well, OP just raised a flag asking whether there was a bug in the close system because they only saw the question after it was closed and were confused at it being off-topic :P

Semiclassical

5:44 PM

@vzn well, my feeling is that: 1) the people who buy into the orthodox interpretation do have defensible reasons for not finding it useful to talk about this stuff, 2) it is nevertheless not helpful to tell people that talking about these things is inherently unscientific

vzn

@Semiclassical maybe we can agree the full "story" isnt known yet.

Semiclassical

i think a certain degree of pluralism is valuable. but pluralism also means that people can disagree, with reasonable arguments on both sides, and that's okay

bolbteppa

Naively I would have called those alternatives useless, however they actually do claim there is a whole world yet to be discovered, something QM claims is inherently impossible

Semiclassical

depends on the interpretation

bolbteppa

Right, BM and it's brethren for that comment

vzn

5:47 PM

@Semiclassical my point re unscientific is something like that the vernacular phrase "shut up" is not really seen in any scientific papers. o_O :P

Semiclassical

eh. depends on what flavor of BM you mean

if you mean a flavor that posits that quantum non-equillibrium should be observable, then yes

if you mean a flavor where equilibrium is a fact of life that you just have to deal with, then there's really no new physics to "discover"

vzn

@bolbteppa bohm calls it the "subquantum world"

Semiclassical

A theory of truly "hidden variables" is protected from experimental contradiction, but it's also not in a position of not being able to be experimentally distinguished

To me the more interesting question is not "what might we discover" but how best to utilize the tools we've already got

(hence my question from a few days ago about quantum computing)

vzn

@bolbteppa @Semiclassical think you guys + some additional flair have what it takes to move beyond the gridlock/ near stalemate but such an epic undertaking is not for the fainthearted/ casual :P

Semiclassical

and a difficult sell for someone who wants a job :/

bolbteppa

5:53 PM

I mean the quote from Bohm's paper about general hidden variable theories:

"Similarly, we suggest that if there are hidden variables underlying the present quantum theory, it is quite likely that in the atomic domain, they will lead to effects that can also be described adequately in the terms of the usual quantum-mechanical concepts; while in a domain associated with much smaller dimensions, such as the level associated with the "fundamental length" of the order of $10^{-13}$ cm, the hidden variables may lead to completely new effects not consistent with the extrapolation of the present q…

vzn

@Semiclassical lol seems to be a "difficult sell" for misc reasons, not all of which have been articulated. ps just think of it as much more meaningful/ substantial than a mere "job" :P

bolbteppa

The claim here is that a hidden variable theory "quite likely" is experimentally distinguishable from QM anyway

vzn

@bolbteppa think bohm slightly overestimated/ overstated how airtight QM is. it requires great sensititivity but suspect some misc experiments are already pushing into subquantum physics. eg recent quantum scarring results etc

@bolbteppa "quite likely" was used in the sense there that QM is nearly airtight and almost any LHV effects can be accounted for by it.

bolbteppa

His point seems to be that QM is to the theory he is trying to develop as 'stat mech' is to classical mechanics, so we should be able to find new phenomena if we go beyond the experimental limits of the day covered by QM arising due to the hidden variables

vzn

@bolbteppa hes saying something like we have to push into planck scale measurements to find any anomalies.

Semiclassical

6:03 PM

@bolbteppa this is a point that I'd tend to disagree with Bohm

bolbteppa

Expecting this starting from the non-relativistic Schrodinger equation is simply galling

Semiclassical

6:23 PM

at this point, i think it's not productive to expect a hidden-variables theory to prove its worth by experimentally distinguishing QM from it

what I find more productive is the idea that, by thinking about something like BM, that you gain a better intuition for how various QM setups should work

(that's my dream, anyways.)

bolbteppa

7:11 PM

If you take that view, the special case of the non-relativistic Schrodinger equation is handed down by religious fiat and can't be questioned, and has to randomly be twisted into ending up with some notion of paths for no reason which are hidden for no reason

Semiclassical

That's like saying that the non-relativistic Schrodinger equation has no experimental basis.

bolbteppa

7:24 PM

It's literally no different to calling non-relativistic Newtonian mechanics plus Einstein's Field Equations an axiomatic theory and then getting all of classical physics from your 'theory', any problems are saved by GR reducing to SR but one gets to pretend to think in a Newtonian world, all the logical problems this brings up are just ignored

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