The h Bar

Amit

00:03

Looking a bit more at the previous issue, it seems a further complication is that the twiddling with the units can be done either in the vector space or in the tensor components. So for example what I wrote about the time units of the metric tensor is actually not the standard, the standard is to add the required factors of $c$ to the time components of the vectors you work with...

so that for example the Minkowski metric still has $\eta_{00} = -1$ despite it being the $dt \wedge dt$ entry. and we add a factor of $c$ to contravariant four vectors, e.g. $v^0 = ct$

btw just for the record, the exterior derivative of the metric tensor isn't defined, it's only defined for totally antisymmetric forms, the metric tensor is totally symmetric

Amit

00:25

I think then it is also true for the Faraday tensor, it is probably standard to ensure all entries are the same units, and do the required units adjustments externally

Now how you do those adjustments in the context of the external derivative, I have no "hands on" experience with, lol

Silly Goose

00:37

What would yall describe the essence of electromagnetism as

@Semiclassical maybe unknowable?

With the implicit clause (within the context of this problem)

Semiclassical

@SillyGoose "unavailable" might work in the case of things which just aren't given in the problem

Amit

@SillyGoose gateway to relativity ◇

Cassie Swett

01:07

So I've got a question related to my little musings above. I'll probably flesh this question out and post it on the main site.

Suppose I've got a couple of ordinary permanent magnets. My understanding is that the forces they exert on each other can be explained by the idea of bound current.

Does the amount of bound current change as I move the magnets around?

Amit

01:23

@CassieSwett not really related, just from what you're saying I think you may be interested, see "A paradox" here: feynmanlectures.caltech.edu/II_17.html

WaveInPlace

Wait, they remade Quantum Leap? wtf

Cassie Swett

@Amit Huh, that is pretty interesting!

Amit

Glad to hear.. gnight all

WaveInPlace

Good night!

nickbros123

04:27

What are the prerequisites to study FNH Robinson's papers on the problems with HA Lorenz's procedure / ensemble averaging procedure for deriving macroscopic Maxwell's equations from the microscopic ones

naturallyInconsistent

04:44

Ooo, that is a topic I am also vastly interested in. It is incredibly difficult to actually get sensible macroscopic averages of the microscopic Maxwell's equations. I suspect the whole scheme is just impossible to pin down correctly.

nickbros123

Robinson claims his scheme is the best of the lot

I'm not able to find his book though.

naturallyInconsistent

05:06

If that is the case, then I definitely doubt it. There is a nice little newer book by TC Choy titled Effective Medium Theory, that goes into how every currently available scheme is flawed in various ways. I definitely enjoyed it in hardcover

Physics Meta

0

Q: flagging non mainstream comments in questions and answers

In this question Why doesn't a photon state have to be infinite in length? in the answer given by https://physics.stackexchange.com/users/364064/naturallyinconsistent there is a comment by user https://physics.stackexchange.com/users/346466/flattermann that is advertising his/her personal theory ...

feature-request

nickbros123

05:23

@naturallyInconsistent hmm, i see. What are the prerequisites to study this book? And does it cover these averaging schemes (basically teach me them) before moving on to prove that they're flawed?

naturallyInconsistent

You need to understand it about as good as the little section in JD Jackson on the averaging, and the scheme that is in Kittel's Intro to SSP. Then you should be able to understand what is being covered.

Oh, are you also aware of the horrible difficulties in finding out where the energies in the electrodynamical system is in? That is, the many different ways that we could define the terms, and then the location of the energies will change?

@nickbros123

Mr. Feynman

05:56

@nickbros123 is the book called "Macroscopic E&M"?

nickbros123

@naturallyInconsistent no, I'm not aware of this

@Mr.Feynman yes. Macroscopic electromagnetics

naturallyInconsistent

@nickbros123 https://en.wikipedia.org/wiki/Poynting_vector#Other_forms refers to the Abraham-Minkowski controversy, and it also talks about what happens if you choose between E D B H to define the stuff. Life is difficult.

https://arxiv.org/abs/2112.14643
Sebens included density plots of where the energies will be if you calculate with difference choices.

Please try to refrain from substance abuse when you learn of all these headaches

nickbros123

06:15

@naturallyInconsistent haha, thanks for the links. I'll be sure to stay away from such substances

naturallyInconsistent

Oh, you should look at Section 27-4 and Chapter 8 too of feynmanlectures.caltech.edu/II_27.html

Shikhar Chamoli

06:42

which quantity is conserved in the Bloch wavefunction?

naturallyInconsistent

There are too many possible answers. One should learn to ask questions sensibly.

John Rennie

@ShikharChamoli The Bloch states are eigenfunctions of the Hamiltonian for a periodic potential so they have a well defined energy and momentum, and any other operators that commute with the Hamiltonian. Is this what you mean?

nickbros123

07:42

@naturallyInconsistent i suppose this might be against chat policy, but could you answer my recent question (it's on the method Griffiths provides to bring the macroscopic fields from the microscopic by doing spatial volume averaging)

In hindsight this method of spatial averages is wrong, and Griffiths uses it, but within the details of the framework i have an issue

naturallyInconsistent

Where is the question?

nickbros123

1

Q: Issue in justifying the use of dipole potential in the calculation of bound charges in a dielectric

We have a polarised material, suppose. The goal, is to find the bound charges. DJ Griffiths (4th ed, section 2.1, page 173) "chops" the material into smaller infinitesimal chunks and writes: $$V(r)=\frac{1}{4\pi\epsilon}\frac{\vec p\cdot \hat s}{s^2}$$ and by writing $ \vec p = \vec P d\tau' $, h...

electrostatics polarization dielectric dipole

naturallyInconsistent

Oh, I had already commented there with the stuff that I just told you!

Actually, there is much more shit in there, and I am now reminded of the quantum shenanigans that is involved. Can I just not answer that? Pretty please?

nickbros123

08:04

Oh, you don't have to go into much detail, the question is just about a doubt i had within the method of doing the spatial averaging(Griffiths method) . I think i found a shortfall, so I just want someone to either tell me " nah, that's not exactly the issue" or tell me "yes, this is a shortfall of the Lorenz spatial averaging method "

naturallyInconsistent

Actually, it has been MANY years since I last touched this, and there are so many different schemes of it, that you should actually properly copy out the relevant procedure. You don't have to copy everything, just a summary of the steps involved will do

nickbros123

In my question I've basically just outlined the procedure Griffiths used, and by the end of it I've explained the conundrum I'm facing. My primary issue here is: at what scales are the polarisation defined? At what scales are we doing the spatial averaging of the field? If they are of similar order, what is the meaning/size of the infinitisemal volume element $d\tau$ ?

naturallyInconsistent

08:38

Oh, I saw your earlier post rather than this one. I will have to think about it again.

Relativisticcucumber

09:33

does anyone have recommendations for looking into intersections between quantum gravity and quantum information? i have been looking into entanglement entropy, but im curious about other intersections

Amit

All the latest black hole stuff that has QM no?

Mad

10:35

heý guys, can you find the mistake in my calculation?

I am trying to calculate hte electric potential of a point charge ,i u sed the definition of integratring over the field, however i am getting the same textbook answer different by factor of 3. here is my solutio, can you find the mistake?
$ \phi(\vec{r}) = k Q - \int_{\infty}^{\vec{r}} \vec{r}/r^2 d\vec{r} = kQ [ \int^{\infty}_x \frac{x}{(x^2+y^2+z^2)^{\frac{3}{2}}}dx + \int^{\infty}_y \frac{y}{(x^2+y^2+z^2)^{\frac{3}{2}}}dy + \int^{\infty}_z \frac{z}{(x^2+y^2+z^2)^{\frac{3}{2}}}dz] = kQ [1/r + 1/r + 1/r] $ with $r:= (x^2+y^2+z^2)^{1/2}$

the textbook answer is KQ/r

sorry it should be r^3 . but everything else is correct

I do not understand why i get the factor 3?

obviously i am integrating incorrectly

Amit

11:09

@Mad the last equality. Integration is incorrect

Ryder Rude

@Slereah Hello. I think Aristotle's model need not b first order differential eqns. E.g. we can hav $\frac{dx}{dt}=\frac{p}{m}$ $\frac{dp}{dt}=-p$. These r second order

Any free particle comes to rest in this model. It is translationally and rotationally invariant

Ooh but momentum only exponentially decreases in this model. It wud take infinite time to become zero

I think it's a misconception that Aristotle meant $F=mv$. His law can be second order. It's very hard to know what Aristotle meant

nickbros123

Is there a policy against plugging site questions in chat

I'd really like my most recent question answered

Ryder Rude

@nickbros123 I think it is allowed. I and Mr. Feynman have done it

ACuriousMind

Please don't post your recent questions unless you explicitly want to show it to someone here you think will be particularly interested in it

see physics.meta.stackexchange.com/a/11094/50583, also linked in the room description: "If you just posted something on the main site, give it some time, and don't tell people to go there and look at it."

also:

Mar 5 at 15:05, by ACuriousMind

@Rajarshi_Rit Please don't use chat to attract attention to your recent questions (if everyone did that, the chat would be flooded only with messages like that). People that want to answer questions watch the main site anyway.

Ryder Rude

Yes, I didnt do it with a recent question @nickbros123

I'm having a very hard time in getting the order of these concepts right

Mad

11:25

@Amit can you please elaborate

Ryder Rude

Like, what concept really underlies the fact that our universe has the equivalence of "constant velocity frames" rather than "constant position frames related by affine transformations"? What is the star feature of our model that leads to the former? @ACuriousMind

One could say that the star feature is the Galilean or the Lorentz group, but GR doesnt have those

ACuriousMind

@Mad this already starts out notationally weird: What ever you think $\int_\infty^{\vec r} \vec r / r^2\mathrm{d}\vec r$ means, it notational nonsense: Either $\vec r$ is a limit or it appears behind the integral sign, never both. Presumably $\phi(\vec r)$ is supposed to be a scalar value but $\vec r/r^2$ is a vector - how is integration supposed to turn this into a scalar?

Ryder Rude

What GR does have is the metric. Can we say that the this is actually a feature of theories with metrics :euclidean, galilean and minkowski?

ACuriousMind

there's less a computational error here and more that your starting point is already messed up

Ryder Rude

And other signatures too

But all theories with metrics need not have this feature. E.g. u cud couple such a theory to a 0-connection vector field, which would make the theory lose this "equivalence of frames" principle

ACuriousMind

11:33

What on earth are you talking about? The Galilean or Lorentz groups are simply the isometry groups for the metrics with the respective signatures in flat space

if you aren't in flat space, you get different global isometry groups

where's the mystery

Ryder Rude

Oh yeh

In GR, we dont hav the equivalnce of "constant velocity frames" in the first place. Becuz velocity is only defined locally

So I really have two questions : 1. in flat space theories, what really underlies the equivalence of "constant velocity frames"? 2. In general curved space theory, what underlies the equivalence of zero-proper acceleration frames? @ACuriousMind

ACuriousMind

define what you mean by "equivalence"

Ryder Rude

Identical experiments hav identical results

ACuriousMind

I don't know what that means

frames aren't real, they're just coordinate systems

the core problem with the equivalence principle(s) is really that it's pretty hard to formalize what you actually mean by it

hence why there's a bunch of different versions

Ryder Rude

there is this concept of "equivalence of frames" defined using experiments u cud perform. In this concept, we take frames to mean physical laboratories

Mad

11:40

@ACuriousMind i just used the textbook definition

naturallyInconsistent

@Mad And we are telling you that you must have read it wrongly.

ACuriousMind

@Mad If your textbook actually writes down that integral exactly as you wrote it here, you should throw away that textbook.

naturallyInconsistent

Is there no mathjax here in the chat rooms?

Mad

The definition if $\int E(r) dr from r_o to r_1 all vectors. i just applied it. can you maybe tell me what was the wrong thing that i did?

ACuriousMind

@naturallyInconsistent look at the room description in the upper right

Ryder Rude

11:43

@ACuriousMind Do all metric-ful theories hav an equivalence principle where u cud make the metric diagonal at any point and make the first derivative of metric vanish?

ACuriousMind

@Mad How do you think the line integral $\int E(r)\mathrm{d}r$ relates to what you wrote?

Ryder Rude

If yes, then the presence of a metric may underlie this feature of theories

But not so fast. Becuz we can still couple the metric-ful theory to a 0-connection, and make it lose the equivalence principle

So the metric isnt sufficient

ACuriousMind

@RyderRude Of course, that's (Riemann) normal coordinates.

Ryder Rude

Then I think we r really close to breaking the mystery. Assuming a metric gets us very close to the equivalence of "constant velocity frames" in flat space theories @ACuriousMind I'm thinking the metric underlies Newton's first law and puts a coffin on Aristotle's law

Amit

@Mad Also, you should be mindful of how exactly you do that change of variables there. And I don't know why you need to do it. This particular integral is much easier to carry out directly on the radial coordinate $r$ and its differential element $dr$

Ryder Rude

11:48

But we r not quite there. Becuz the dynamics could still depend on a 0-connection vector field to make it Aristotlelian @ACuriousMind

Mad

i understand it refers to line integral, but as far i remember, we did treat dr and r as vectors and took scalar product. anyhow, really didnt understand what i did wrong here.i was merly pointed out to the fact that i am wrong, which i already knew.. so thanks i guess

ACuriousMind

@RyderRude what is a 0-connection?

naturallyInconsistent

@ACuriousMind thanks, sorted with mhchem enabled chatjax bookmarklet

Ryder Rude

@ACuriousMind sorry i didnt mean 0-connection. I just mean a fixed vector field to which the dynamics are coupled. This would make the metric-ful theory lose equivalence principle

ACuriousMind

@Mad I'm just trying to understand how you arrived at the expression $\int^{\vec r}_\infty \vec r /r^2\mathrm{d}r$ - because that's already wrong. If you can't explain to me how you got that from the line integral prescription $\int E(r)\mathrm{d}r$, I can't point out to you where you went wrong!

Ryder Rude

11:52

Becuz experiments wud behave different becuz of this dependence on the vector field

ACuriousMind

@RyderRude Of course, a distinguished vector field singles out a preferred frame

that's why e.g. the VEVs of all non-scalar fields must vanish in a Lorentz-invariant theory

Ryder Rude

Yes. So I believe we need two principles to get rid of Aristotle in principle : 1. A metric-ful theory 2. Lack of such an absolute vector field

This underlies equivalence principle

In case of flat space, this gives u the equivalence of "constant velocity frames"

@ACuriousMind But it's really hard to make equivelance principle precise. e.g. the CMB effectively works like the ether background. In practice, experiments would behave different if u r moving wrt to the CMB frame

naturallyInconsistent

I am not sure how you are wanting to state a mathematically precise enough version of what Aristotelian, and really it is more Medieval vague conception of physics to refute them.

ACuriousMind

yesterday, by ACuriousMind

@RyderRude No, you wouldn't. Trying to mathematize Aristotle's very much non-mathematical conception of physics is already a category error.

naturallyInconsistent

Instead, I think Galileo's original argument against Medieval physics is the direction to go. Show that any attempt to bring logical consistency to Medieval physics is going to fail.

Shikhar Chamoli

12:00

@JohnRennie sir, I was looking for the answer 'momentum'. But I don't see how these have a well defined momentum. Operating the moentum operator directly doesn't give back 'k'.

Ryder Rude

@naturallyInconsistent i dont care about Aristotle. I just want to know why equivalence of "constant velocity frames" is more natural than equivalence of "rest frames related by affine transformations"

In our universe, we have equivalence of constant velocity frames and constant rest frames, but not of constant acceleration frames @naturallyInconsistent

ACuriousMind

"I don't care about Aristotle" | 20+ messages about Aristotle

Ryder Rude

Lol

naturallyInconsistent

@ShikharChamoli Because momentum in a crystal is not as obvious as just applying the operator naïvely.

@RyderRude notice that I specifically brought up the attack on Medieval conception of physics rather than Aristotle. And as I hinted, the fruitful attack is on what it means to describe free fall near the surface of our Earth, rather than your attempt to argue about equivalence of constant velocity frames v.s. rest frames.

Amit

@Mad I think this addresses your issue: physicsforums.com/threads/…

To summarize, apart from the notational inconsistencies ACM pointed out, the real problem you get the extra 3 is that you no longer have a well defined path for the charge when you transform to cartesian coordinates that way

naturallyInconsistent

12:10

@Amit That conversation spectacularly failed... lol

Ryder Rude

@naturallyInconsistent yes. I am also investigating what makes the curved space equivalence principle natural. For flat space, I am investigating the equivalence of constant velocity frames

Amit

lol @naturallyInconsistent... we need to be more optimistic I think... it's a pretty coherent one for a bar ^_^

naturallyInconsistent

meanwhile I shall mildly entertain what kind of stuff do people consider is a natural way to consider principles natural or not, and how they would naturally investigate naturalness of principles.

Ryder Rude

@ACuriousMind @naturallyInconsistent I have a story in mind for the flat space equivalence principle. We start by assuming a spacetime flat metric. Then we investigate symmetry transformations of this that mix space and time.

We realise that these transformations map straight lines on spacetime to other straight lines (this is a feature of Galilean, Euclidean and Minkowsky theories). This observation allows us to conclude the equivalence of constant velocity frames rather than constant acceleration frames

Amit

@Mad Also related: math.stackexchange.com/questions/2384963/…

Ryder Rude

12:23

@naturallyInconsistent The conclusion is based on 1. We r investigating symmetry transformations. Symmetry of dynamics leads to equivalence of frames (I am handvawing from "symmetry of metric" to "symmetry of dynamics. I'm assumign there's no dependence on a preferred vector field in the dynamics)

And 2. The transformation maps some straight line trajectory to the time-axis. This is a feature of Galilean, Lorentz and Euclidean boosts. This allows us to conclude the symmetries are for constant velocity trajectories

naturallyInconsistent

Anyway, @Mad, that whole thing is a great abuse of notation, and if we insist upon indulging that abuse, then the correct expression is $$V(\vec R)=kQ\int_{\vec R}^\infty\frac{\vec r\cdot\vec{\mathrm dr}}{\left|\vec r\right|^3}=kQ\int_{\vec R}^\infty\frac{x\,\mathrm dx+y\,\mathrm dy+z\,\mathrm dz}{(x^2+y^2+z^2)^{3/2}}$$ and then it is clear that if you only varied/integrated one coördinate and treated the others as constant, then your integral is done wrongly.

That is what the PhysicsForums post that @Amit linked was trying to convey but failed badly, and what his newer M.SE post is trying to convey with greater success.

Ryder Rude

To make curved space equivalence principle natural, we just need : 1. A metric-ful theory 2.Riemann Normal co-ordinates 3. Non-dependence on an absolute vector-field

1. Implies 2., so 2. is not really needed here

Amit

I don't think the latest PF post fails badly, but I won't fight for the dignity of posts made in 2009 lol

(not that 2009 doesn't seem like yesterday to me)

@RyderRude Are you working on a new GR sort of theory?

Ryder Rude

12:42

@Amit lol no. I'm just investigating y our universe has equivalence of constant velocity frames, rather than equivalence of constant acceleration or constant jerk frames. To investigate, this I have to consider fictional theories sometimes

naturallyInconsistent

Pardon, @RyderRude, but I think that scheme of yours has little chance of succeeding so please let me be excused from further interactions on the topic. You can just do you and continue the convo here.

Amit

@RyderRude Maybe it's something you'll find as fun

Ryder Rude

@naturallyInconsistent ok i wont bother u about this. But if u have some thoughts on this topic (some other scheme), pls share them. I also dont think i have a good scheme

@Amit i could investigate new theories. But i would like to first learn GR and QFT. Do you also have this interest of making new theories? @Amit

Amit

How many users under the name "Nullius in Verba" are there? lol

Ryder Rude

@Amit everytime i make a question about Many worlds, this user shows up. I thought it's the same guy creating multiple accounts

Amit

12:49

@RyderRude Yes, I'm in the same position as you, I also want to study more before I attempt something like this. OTOH, knowledge is prejudice

Ryder Rude

I thought Nullius in Verba is protesting against the reputation system lol

Amit

But it's just that I find it more interesting to know what people found out, rather than rush with exotic ideas

naturallyInconsistent

Oh, I do have something to share on that. One reason why I think it is very unlikely to succeed, is because in most other places in physics, the normal kind of response is $F=mv$, i.e. the observed rate of change is linearly proportional to the applied cause. Mechanics is always doomed to be confusing because it is the one rare case that has a non-trivial physical symmetry protecting the rate of change, and thereby the correct resultant effect appears in the 2nd order.

Amit

lol, but then I thought you can make posts without even registering can't you?

he does register multiple times

naturallyInconsistent

So, I think that any such attempts are doomed, and instead students should just be invited to do stuff on boats and trains, so that they can feel it in their guts rather than be convinced by some theoretical justification.

Well, maybe Nullius in Verba simply followed those tags, so if you write a post, he would be notified.

Ryder Rude

12:55

@naturallyInconsistent i didnt care about this theoretical justification until like 2 days ago. I shud probably let it go now

It is already very natural to see constant velocity frames as equivalent

naturallyInconsistent

Instead, I have been arguing with FlatterMann and John Doty; they have been going around all the posts that are even vaguely theoretically inclined, and repeating their mantra that maths is not physics, or there is no collapse (and they believe in Copenhagen, without realising the irony), or photons are not particles, etc.

Ryder Rude

I've also argued with FlatterMan. But now I find myself agreeing with him.

Not about everything. But about irreversibility of collapse

Amit

ah i'm wrong btw, he is never registered

Ryder Rude

Collapse is definitely real tho lol

Collapae being real is exactly what's irreversible about QM imo

Amit

FlatterMan and John Doty had an interesting conversation about related stuff

Ryder Rude

12:59

If collapse isnt real, u just get MWI

naturallyInconsistent

Collapse is a _interpretation dependent_ thing.
It is only real if you accept interpretations in which it is real.

Ryder Rude

So idk how they can reject collapse while accept Copenhagen lol

naturallyInconsistent

@RyderRude No, there are MANY interpretations in which it is not real.

Ryder Rude

@naturallyInconsistent what r these other interpretations?

naturallyInconsistent

@RyderRude Because there are so many variants of Copenhagen, and while they are in a minority, they actually have an internally consistent version of it.

Amit

13:01

There are people who seem to be on an anti metaphysics crusade: "if it ain't part of experiment, it's nonsense" lol

Ryder Rude

They buy the decoherence stuff rather than instantaneous collapse? I'm also in the same camp. But i think Schrodinger eqn needs to be modified

I think collapse is just decoherence, yes

But it is real, as in, it's not explained by Schrodinger eqn

naturallyInconsistent

@RyderRude Wiki lists a whole lot. de Broglie Bohm Pilot Wave is one, Transactional is another, Ensemble is closer to what FlatterMann believes, etc

Ryder Rude

U need a real modification of QM

@naturallyInconsistent yeah. I forgot about De Broglie. The other two I didnt know about

naturallyInconsistent

@RyderRude decoherence is decoherence. You can say that decoherence is the replacement of collapse, but there is no need for collapse when you have decoherence. After all, it already explained the stuff collapse was invented for, better than collapse does it

Ryder Rude

@naturallyInconsistent i just call decoherence as the "process of collapse"

But i dont buy the usual instantaneous collapse, yes

So i am replacing the traditional collapse

naturallyInconsistent

13:04

@RyderRude decoherence just follows Schrödinger evolution to the logical conclusion. This means that MWI, which also goes with decoherence, is actually assuming less than Copenhagen with collapse.

@RyderRude But it does not ever need to collapse. Each resulting branch is as real as the rest.

Ryder Rude

@naturallyInconsistent I dont think MWI works tho. It needs a preferred time slicing. And Born rule gets completely screwed up. I have a post about this

naturallyInconsistent

@RyderRude That is what Wigner's Friend and modern experimental work is showing to be false.

Ryder Rude

Yes, but modern experiments havnt been confirmed upto Human-level or Cat-level entanglements

naturallyInconsistent

@RyderRude All of decoherence have trouble with Born rule. It is ok: we can simply just assume Born rule. Copenhagen got to assume collapse, so why can we not assume Born rule?

Ryder Rude

I believe Schrodinger eqn stops working

naturallyInconsistent

13:07

@RyderRude I know that, but there is also no known upper bound. Which means we have no choice but to take it seriously.

Ryder Rude

@naturallyInconsistent i have a post about this. The problem with the MWI born rule is much sinister

naturallyInconsistent

@RyderRude Then you are one of the people believing in objective collapse, and then you have serious experimental challenges. The experiments have already shown that something is seriously wrong with, say, GRW style interpretations.

Ryder Rude

Even after we assume born rule in MWI, it is a very crazy theory

Amit

no collapse & no MWI are necessary imo

naturallyInconsistent

@RyderRude all of QM is crazy. I am quite sure its craziness is normal enough for me to accept.

Ryder Rude

13:09

@naturallyInconsistent yes. I am believing in one of those interpretations for now. I believe classical stuff cannot b in quantum superposition. But I believe we dont hav the righr objective collapse theory yet

This is my post : physics.stackexchange.com/questions/762350/…

It shows a massive problem with MWI. The only way the Born rule is consistent with MWI is the most trivial way

@Amit what is ur view about what happens at collapse?

Amit

nothing happens, it's a mathematical artefact

you reach the limit of what your equation can model

Ryder Rude

So u dont believe some other modified equation models the whole thing?

Amit

nope, i don't think that's necessary

naturallyInconsistent

@RyderRude Not possible. We already have macroscopically large stuff in quantum superposition. Say mirrors. And think of superconductivity and other shit like that.

Ryder Rude

As soon as they decohere with the environment, the evolution shud b irreversible. We hav not confirmed Schrodinger eqn for human scales like in Wigner's friend @naturallyInconsistent

naturallyInconsistent

13:14

@RyderRude I already read that. Was annoyed that there was so much noise already in that post, so I just left it.

@RyderRude It matters not that we have not reached human scales. Unless you believe consciousness has something to do with collapse, the fact that we have macroscopic systems in quantum superposition is already enough to show that we have to take the position seriously.

Ryder Rude

Notice how the top answer proposes that the number of worlds created for an eigenstate is proportional to the Born rule probability for that eigenstate. I think this is the only thing that can save the Born rule in MWI @naturallyInconsistent

@naturallyInconsistent i dont necessarily mean humans. I mean we dont know if Schrodinger eqn holds for the messuremenr device scales

naturallyInconsistent

And no, I do not agree that MWI trivialises Born rule. It is perfectly fine for us to have parallel twins. I dislike MWI, partly because of that, but it is not a showstopper.

@RyderRude Which is equivalent to just assuming Born rule. That is fine.

Amit

the problem i see is always: we extend the microscopic model to macroscopic case, this is fine, we must do that. but we don't know how to model a macroscopic case accurately with QM. it's just too difficult -- that's the most important case. has anyone modelled for example via QM in a complete way, a system like a photomultiplier as it interacts with a photon? if they did, then i am completely on the wrong track here. but my understanding is, no one did that

Ryder Rude

@naturallyInconsistent but i think it's extremely weird. The wavefunction has no information about the "number of worlds" created

naturallyInconsistent

@RyderRude But the experiments that are done are already bigger than measurement devices of old.

ACuriousMind

13:17

May 1 at 14:15, by Slereah

why must we be eternally cursed with talking about the intepretations of QM

Amit

lol, ACM, I held myself from quoting that again but thanks

naturallyInconsistent

@RyderRude Correct, which is why it is nicer to just assume Born rule and not expect it to come from MWI.

Ryder Rude

@naturallyInconsistent what r these experiments? R they not explained by irreversible decoherence?

ACuriousMind

I propose a rule that you should be forced to compute the anomalous electron g-factor from QED by hand to the currently best known precision before you're allowed to talk about "interpretations"

Ryder Rude

@naturallyInconsistent i just think it's an extremely philosophical solution to the Born rule. It's like superdeterminism.

naturallyInconsistent

13:18

@Amit There have been numerical simulations of decoherence with simplified versions of detectors, and they show that the results agree, only missing Born rule.

Amit

l m a o

@naturallyInconsistent cool, i didn't know that, can you point me at a paper?

the words "simplified versions" are already suspect but it's still interesting

naturallyInconsistent

@RyderRude I believe in decoherence. I am not sure why you have to add the modifier of irreversible in front of it, but I meant that you can already put macroscopically sized mirrors in superposition, and those mirrors are bigger than small detectors used for other stuff.

Ryder Rude

@naturallyInconsistent Also, what about the preferred time-slicing problem for Many Worlds? The wavefunction has a preferred notion of simultaneity built into it

naturallyInconsistent

@RyderRude And Prof Sabine seriously believes in superdeterminism. One has to learn to be impartial to all the potentially correct interpretations, despite how much disdain we may have of them

Ryder Rude

@naturallyInconsistent and these experiments require quantum superposition to be explained? How large is the degrees of freedom involved in these experiments? Is the environment coupling involved? If it couples to the environment, I believe things r explaines by classical mechanics

naturallyInconsistent

13:22

Ok guys, I am incredibly late for dinner, so I gtg. I'll try to find the famous physicist who wrote a big paper on decoherence that I was reading later.

Ryder Rude

It was nice talking to u :)

Amit

cheers @naturallyInconsistent have a nice dinner

Ryder Rude

I was a Many Worlder a few months ago

naturallyInconsistent

@RyderRude That is the point. It is very important to be able to control the noise from the environment. Not all noise, only relevant degrees of freedom, but yes, they have to be explained by superposition.

ACuriousMind

@RyderRude you've run through about a few dozen "beliefs" in the last months, maybe you should consider not being so easily convinced :P

Amit

13:24

I'm sure someone made that joke already: I'm not sure if the Many worlds interpretation is right, but I am sure this is a Many interpretations world

ACuriousMind

you can learn about something without having to immediately sort it into either "totally wrong" or "the best thing since sliced bread"

Ryder Rude

Lol

I always have some reasonable doubt in mind about the school I'm subscribing to

This is y i keep changing schools lol

I was extremely convinced by Many worlds, then by "consciousness causes collase". It was hard to move on

But i still have some doubts about "quantum classical divide" schools. I think it somewhat runs into the problem of preferred time slicing

And "simultaneity of collapse" issues

The best part about relational QM and "consciousness causes collapse" is that they avoid "preferred time slicing" issues by making the wavefunction relative

But i think these schools r wrong. They ignore decoherence

Amit

13:50

@RyderRude are you familiar with Mott's problem?

Ryder Rude

@Amit i just saw it. What about it?

Amit

it illustrates some conceptual problems with the process of "collapse", also now i'm reading on the related Renninger negative result experiment, very interesting

Ryder Rude

@Amit i dont think it reveals any problem. The wavefunction of collider particles is sharpy peaked in position and the expected value of position follows a straight line path

Negative-result measurements r also standard

It's called POVM iirc

Amit

I guess you could say that the first droplet already causes collapse or something, but it is very strange. How many drops exactly do you need to avoid a collapse then, or how many molecules of liquid etc...

ACuriousMind

Mott solved his own problem!

Apr 25 at 12:08, by ACuriousMind

the emergence of classical trajectories can be explained from the quantum behaviour, see rob's answer on Mott's classic derivation

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