The h Bar

Jack Clerk

02:48

Good night/evening/morning for everyone!

Well, I have a expository presentation based on powerpoint to do for my physics class, tomorrow.
The subject is: Great Experiments of Physics in Pre-Galilean Era.
Please, I appreciate any ideas that you might suggest, references and so on

Thank you!

heather

have you looked on the wikipedia article? the section on physics in the medieval islamic world seems pretty interesting

has a bunch of sections on physics before galileo.

Jack Clerk

@heather

@heather thanks!

Constantine Black

05:10

@Danu Thanks for the reply. 1) If such a transition has worked out for you( both in what you wanted for math education and regarding mathematical physics abilities and skill development) and mostly 2) if such a transition could be useful to someone currently interested in mathematical physics. Thanks again for any info.

John Rennie

@enumaris the other half of my prediction gets tested tonight! :-)

heather

@JohnRennie sportsball?

John Rennie

@heather football (soccer) world cup

England play Colombia tonight

heather

oh

what "level" is it (quarter-finals, semi-finals, finals ... ) at

John Rennie

The winner of this game goes through to the quarter finals

heather

05:20

ah, okay.

oh, i pulled up a bracket.

google is great.

John Rennie

If (and it's a big if) England win this game the next match will be against Sweden or Switzerland and we should be able to beat either of them. So effectively winningthis would get us to the semi-finals.

Then we'd face Russia or Croatia and we should be able to beat either of them. That would mean a place in the final.

Secret

meh...

heather

@JohnRennie nice

good luck =)

Cup Fever

@JohnRennie only IF the transitive property was true in sports :-)

John Rennie

But this is the England team we're talking about, so we'll undoubtably lose to Colombia and go home in disgrace :-)

Secret

05:25

although to be frank, if you have the 4th dimension, you simply rotate the sphere along its equatorial region by 180 deg and you already turned it inside out

Cup Fever

6

Q: South Korea defeated Germany who defeated Sweden who defeated Mexico who defeated South Korea

In the 2018 World Cup group F, South Korea defeated Germany who defeated Sweden who defeated Mexico who defeated South Korea and thereby took the most indirect revenge. Did such a long circular chain of defeats ever happened in any of the previous world cups?

heather

well, i need to go to bed

night all

Cup Fever

cya

Secret

Wait a sec... is that Poincaré–Hopf theorem?

It will be really cool to see this happen if we were living in a 4 dimensional space

Secret

06:16

0

Q: Does Bell's Theorem suggest both Nonlocality and "Temporal Nonlocality"?

My understanding is that the meter is currently defined as the distance traveled by light in vacuum in 1/299792458th of a second. The speed of light is in turn defined as 299792458 meters per second. This is, of course, a circular definition. However, it is a circular definition that lies at the ...

quantum-information equivalence-principle bells-inequality

Semiclassical

for my own serenity/disinterest in pointless frustration, I probably shouldn't look at that

Secret

don't worry, there's an answer to that already in the PSE

2

Q: Is quantum entanglement affected by time dilation?

Is quantum entanglement affected by time dilation? Let's say one of the entangled pair is accelerated to very high speed. When both the entangled particles are observed at the same time, will they have the opposite spin?

quantum-mechanics special-relativity quantum-entanglement

short answer: No, entanglement is independent of spacetime

Constantine Black

09:10

@Danu If I may rephrase: was a transition from physics to mathematics maybe to hardcore, considering having to study pure mathematics and not physics-oriented problems or did you somehow managed to combine both disciplines with mathematics in front? Thanks again.

knzhou

11:52

@Semiclassical Don't even bother! vzn's ranting provides proof of nothing, besides perpetual motion.

Danu

@ConstantineBlack 1) Sure, it worked out for me just fine. As I said, I managed to get a PhD position in math. In my case it wasn't too hard to combine physics and math, since I'm into geometry. If you learn some general relativity, string theory type things then you will already learn some basic geometry things. That being said, actually doing differential geometry is very different from doing physics, and you'll need a lot of time to adjust, probably.

I spent an extra year in my (mathematical physics) master's degree.

I think it's important that you first clear up what kind of mathematics you're interested in.

rob

12:08

@EmilioPisanty I see twenty significant reviewers this month. A year and a half ago I wrote elsewhere that there were about thirty, and that seemed reasonable. When I posted the starred message I think there were about ten.

Semiclassical

@knzhou for clarity, I was just judging by the title / thumbnail in the link (and on that basis decided not to look beyond that)

And I reserve judgment on what I haven’t looked at

Emilio Pisanty

12:24

@rob 404 =(

so I guess what I wanted is indeed available, but just for mods?

Cup Fever

12:49

nice try by mexico pal

rob

13:18

@EmilioPisanty yes, mods only, and limited history.

Physics Meta

13:41

0

Q: Is a good 'accepted flag ratio' defined?

What's a good ratio for $\frac{\text{Number of declined + disputed flags}}{\text{(Number of flags raised) - (Number retracted)}}$? Just an approximate... 1:50, 1:75, 1:100 or something rough. It obviously will only be even a little significant when you're considering a large number of flags (may...

discussion flagging

Emilio Pisanty

Folks, is anyone able to access nobelprize.org?

Balarka Sen

Emilio tryna hack his way to a Nobel prize

Slereah

@EmilioPisanty Running for one?

Semiclassical

14:02

@EmilioPisanty i am, yeah

Emilio Pisanty

14:13

@Slereah @Semiclassical huh

isitdownrightnow.com/nobelprize.org.html

IIDRN says it's down

I still can't see it

ERR_NAME_NOT_RESOLVED

@BalarkaSen sort of

Semiclassical

Huh.

Emilio Pisanty

I'm trying to get the lecture notes for a few Nobel Prize lectures

to cite in a paper

that will earn me the Nobel Prize

Semiclassical

Lol

Emilio Pisanty

actually

not really

if that work does earn a Nobel prize it'll be the first author that gets it, not me

vzn

14:42

@EmilioPisanty homepage just loaded for me but the isitdownrightnow link still says its down. maybe a geographical oriented (DNS?) glitch?

@knzhou trying to recall, have we ever had a harsh word before? on what basis do you make your judgement? you seem to have physics credentials and say/ announce in your profile youre a physics grad student + interested in "particle phenomenology," what exactly is that anyway? did you manage to catch that ref just posted by enumaris phd physics & quoted by me on exactly that subj?

23 hours ago, by Balarka Sen

vzn's reading of everything is so cursory and superficial that it's scary

↑ irredeemably superficial™

Anonymous

Man, you're famous now :P

vzn

@Blue am getting tired of the starred baseless criticisms (not pointing to anythign specific) some not unlike yours. lets just say sometimes BS is BS...

Anonymous

" am getting tired"

Emilio Pisanty

@Blue Life in this chatroom is much easier if you don't bother with messages from people who don't bother with grammar

Anonymous

@EmilioPisanty Wasn't really pointing at the grammar. Rather at the fact that it's ironical that it is vzn who's saying "am getting tired", whereas it should be the other way round (a 1000 times over) :P

Emilio Pisanty

14:54

@Blue well, that too

It's also a bit tiring to see extremely thorough explanations of why a given position is a cursory and superficial reading of a certain bit of science getting blown off

subsequently leading to claims that the criticism is 'baseless'

but oh well

I don't see much hope for change so I'm not going to argue

John Rennie

@EmilioPisanty no name servers are registered for the domain:

D:\temp>nslookup
> server 8.8.8.8
Default Server:  google-public-dns-a.google.com
Address:  8.8.8.8

> set type=ns
> nobelprize.org
Server:  google-public-dns-a.google.com
Address:  8.8.8.8
*** google-public-dns-a.google.com can't find nobelprize.org: Non-existent domain

Anonymous

@EmilioPisanty Oh, btw since you're around - Is it possible to experimentally distinguish between two composite qubit states like $|0\rangle_A \otimes (e^{i\theta}|0\rangle)_B$ and $(e^{i\theta}|0\rangle_A) \otimes (|0\rangle)_B$ ? I basically was having a bit of trouble understanding the physics justification for the "phase kickback" mechanism

vzn

← long chat record shows responds to constructive/ specific/ multitudinous criticism(s). some critics of the theory are not even bothering to cite specifics re Physics, only mounting ad hominem attacks, fixating on irrelevant superficialities etc, and nonetheless taken seriously by others/ even chat room authorities

Semiclassical

sigh. i really get tired of people using the spam/inappropriate flag as an alternative to debate

(I'm on the opposite side of vzn in this debate, and I've disagreed sharply at times. but labeling that message as spam/abusive is just silly imo)

Masked Man

15:09

Is everything fine here?

knzhou

I did read that paper, "there are no particles, only fields" a few years back. I think its central message isn't controversial, it's just saying what every QFT textbook says.

It's called quantum field theory for a reason!

Masked Man

Got a couple of flags, but doesn't look like there's any obvious trouble.

knzhou

However, I find it very annoying when papers adopt a conspiratorial tone, as if what they're saying is something physicists are trying to suppress. There are a few papers like this that end up cited here and on Phys.SE over and over again as evidence that all modern physics is a sham.

vzn

@MaskedMan thx for dropping by & not overreacting, honestly am surprised that got flagged. its a longstanding debate in the room drawing in many, am trying my hardest to keep cool under pressure :|

Semiclassical

I'm not entirely surprised, but I am annoyed.

but for that matter I think the spam/abuse flag gets used way too much

knzhou

15:12

I don't think there's anything usual happening right now! No need for flagging.

Semiclassical

(at minimum I wish the system required people to include a reason for said flag)

knzhou

The point is, there are a lot of papers that, perhaps intentionally, may be read as an indictment of modern physics.

Masked Man

@vzn No problem, it would be silly for me to enter some random chat room and start kicking people without knowing the context.

knzhou

But if you actually dig down there's nothing there.

vzn

← does not think modern physics is a sham & has said so repeatedly. however, some minority/ contrarian views in the field itself, written by top experts, are routinely denigrated by other experts from "other factions"...

knzhou

15:13

@vzn So that's basically my all-purpose response to whenever you bring up a paper and hint-and-wink that it overthrows everything. It just doesn't.

Surely there are unpopular ideas that deserve to be more popular!

But there is no conspiracy.

If anybody said something genuinely new, that was genuinely likely to lead to new physics insight, everybody would be racing to work on it.

Semiclassical

well, there are conspiracies. but typically the reason for a conspiracy is in order to profit from it

vzn

@knzhou my all-purpose response is that some of the all-purpose responses are not specific & are vague. have been accused myself of vagueness think its another utterly bogus charge. do not believe in physics conspiracies but do note how similar cognitive bias + groupthink are which are aspects/ elements of all human fields o_O

Semiclassical

and there's more profit to be had by physics discoveries than by suppressing it

knzhou

There's at least 3 Nobel prizes in it for any group that champions a new, correct idea!

Semiclassical

@knzhou verifiably correct, at any rate

knzhou

15:16

@vzn Well, you have to understand the other side of things. I've written a lot of takedowns, because the popsci press is constantly saying this or that paper overthrows everything.

vzn

@MaskedMan amen to that & yet alas/ much to my chagrin it is not a universal mod philosophy, we got lucky this time so to speak & other times have not been so lucky. :( there is a longstanding effort to deal with flagging in here, its a long complicated story. o_O

knzhou

If I investigated every paper that was supposed to be revolutionary I would have no time to do anything else!

2

Secret

mirror.dlib.org/dlib/october06/king/10king.html

There is just too many papers to read

Semiclassical

i feel like the knee-jerk response to flagging is a problem site-wide unfortunately

Secret

You need to be a supercomputer to read the whole human literature

knzhou

15:18

I do concede some people never seem to look at any unorthodox ideas, but not everybody has to.

Secret

and even then, no guarentee that dots can be connected even under machine standards

vzn

@knzhou understood, others say similar stuff aka "who has time for this stuff" (something my own dad says about my prjs over the years, or others say in a more harsh way in here on record) but then maybe dont argue that there can be no such revolutionary papers merely because you havent seen any.

Secret

I really really want a physical phenomenon that is truly retrocausal though

Semiclassical

For me it's more a matter of "how do I prefer to spend my time"

Secret

think about the possibilities you can do with such technology

Semiclassical

15:19

and I find it more interesting to apply the (experimentally tested and reliable) theories we already have to new problems, rather than pick some speculative theory and hope against hope that we'll find incontrovertible evidence in favor of it

knzhou

There certainly are revolutionary papers, but I'm not usually the first to hear about them!

If something might credibly be revolutionary it instantly becomes the bandwagon.

I know a bunch of people that skim through every abstract posted on the ArXiv in, say, hep-ph, things aren't going to be missed.

Semiclassical

I just don't find that kind of science very appealing personally

(But then, there's a reason I've got the name I do)

knzhou

@Semiclassical Are you also a grad student, postdoc, ...?

DanielSank

@EmilioPisanty That's the phase qubit.

That's one of the harder ones to understand.

Semiclassical

current-soon-to-be-former grad student (my phd should go through within the month)

knzhou

15:23

Oh nice!

vzn

@knzhou think that is true to some degree but its also circular reasoning aka "if something promising shows up a lot of people/ researchers will jump on that bandwagon" and actually there is a new distinct/ identifiable fluid paradigm bandwagon that many are jumping on and some of the arguments against it are along the lines there is no bandwagon here... increasingly simply bordering on denial of reality

DanielSank

@EmilioPisanty Dunno. Enlighten me.

knzhou

@vzn What exactly is the "fluid paradigm"?

vzn

@knzhou myself stand accused of the crime of "skimming," guess others skimming is superior to my skimming :P

bolbteppa

@vzn there is no fluid bandwagon

vzn

15:25

@knzhou lol let me start by citing an eminent phd on the subj :P ...

knzhou

@vzn If you have the background, it's much easier to skim and get the content out. Without the background, even a close reading is liable to lead to misconceptions.

vzn

@knzhou while/ conceding you have some point here, honestly again this seems to me to amount to nearly circular reasoning.

bolbteppa

I can't find any discussion of this fluid stuff as crank stuff yet though, so I will give you that ;)

knzhou

Isn't that true of literally every human endeavor?

vzn

@bolbteppa there is lots of discussion in here of it as crank physics quite a bit by you :P

heather

15:27

morning

knzhou

X is bad because it's illegal. We made X illegal because it is bad. That's blatantly circular, but no problem.

heather

@DanielSank hello, long time no see =) how've you been?

Secret

weweweweweweweweweweweweweweweweweweweweweweweeeeeeeeeeeeeeeeee

knzhou

Every shared societal judgment is "circular", we're doing just fine!

Semiclassical

uh

Secret

15:27

(what happens when one rides a circular roller coaster)

Semiclassical

ok

knzhou

Systems made by human consensus can adjust and correct themselves, is the point.

Semiclassical

@knzhou :/

vzn

19 hours ago, by enumaris

@vzn so the general gist of the principle is that the analogies between fluid mechanics and other fields is more than just formal, mathematical analogies, but can be taken as expressions of some underlying physical mechanism?

Secret

Shot of circular rollercoaster swaying back and forth.

►

knzhou

15:28

@Semiclassical yeah I know, law isn't the best example here.

@vzn Well I've heard a lot of that already, and the question is, what are the consequences?

You can write the same physical laws lots of ways.

You could write QM in the standard way. Or as fluids. Or as cellular automata. Or as tiny cats pushing yarn around.

It doesn't even seem that hard to write it differently, if you're willing to accept a super computationally inefficient embedding.

Anonymous

@knzhou I'd like to see the last one :P

Semiclassical

The clearest example I know of the fluid stuff is the bouncing droplet systems studied by Bush-Couder

knzhou

So when people are really devoted to a specific one of those, and say that one is definitely ontologically real, there's no clear basis...

vzn

@knzhou trying to keep this brief, but basically new formulations of QM are not entirely equivalent to the prior formalism, and ultimately potentially or already demonstrably open up new vistas ie cut to the heart of very deep/ longstanding debate on completeness

knzhou

That just identifies the person as a philosophical partisan.

Semiclassical

15:31

But the reason I respect the Bush-Couder example is precisely that they can actually say what they're doing in terms of equations and solid predictions

knzhou

@vzn So far I've only seen QM formulations that are either (1) exactly equivalent for all practical measurements or (2) not equivalent, but already experimentally ruled out since about 1920.

bolbteppa

Another potentially vicious criticism of this fluid stuff, is whatever fluid equations you're using were almost certainly derived from $F = ma$, even though I've already pointed out explicitly where your fluid equations assumed thermodynamics

knzhou

@Semiclassical Yeah! But I do have a grudge against how publicized it is.

vzn

@knzhou (not contradicting that...) and do you therefore reason that no such new formulations are possible because history definitively rules them out?

knzhou

@bolbteppa Oh yeah, this is like Feynman's rant about explaining why magnets repel.

Semiclassical

15:32

@knzhou of course, "practical measurement" is a bit of a moving target insofar as it depends on tech

knzhou

People want an explanation in terms of mechanical "stuff", but that doesn't actually make it simpler at all.

Semiclassical

well, insofar as mechanical analogies can suggest interesting intuition, they can have value

bolbteppa

Quantum fluid mechanics has to come from non-equilibrium statistical mechanics which I'm pretty sure hasn't even been theoretically established properly yet, still needs to be figured out I think

knzhou

@Semiclassical I mean stuff like, Copenhagen is not falsifiable if you define collapse to occur when your system gets entangled with a system with over 1 trillion atoms exactly.

No matter what technology we get!

Not until we can overturn the second law of thermodynamics.

Semiclassical

@knzhou oh, sure. Same with Bohmian mechanics, at least insofar as one doesn't countenance some possibility of quantum non-equilibrium

knzhou

15:34

@vzn New formulations are surely possible. Like the cat and yarn thing I just said.

Maybe wavefunctions are made of yarn. They collapse when a microscopic cat comes along and smushes them.

Same math as standard QM, radically new ontology.

vzn

@knzhou there are almost no simuations at this point and have been calling for them repeatedly over quite a few years! nearly ½ decade+

knzhou

You can't rule it out though!

Semiclassical

simulations require a specific theory, though

knzhou

@Semiclassical I actually really dislike that feature of Bohmian mechanics...

bolbteppa

It's clearly angels pushing wave functions along quantum epicycles

Semiclassical

15:35

@knzhou heh

knzhou

Like, yeah, it's not falsifiable. It just looks funny to me!

vzn

@knzhou the founders of QM ruled out "classical explanations" as codified in copenhagen interpretation and those intuitions, not LAWS, are now proven false and now bordering on falsifiable dogma wrt recent breakthru research, ongoing...

knzhou

Of course that's not grounds for anything, just a feeling.

@vzn Give me an example of something falsifiable!

Semiclassical

Proving an intuition true or false seems like the wrong way to look at it to me

knzhou

For example, I think the bouncing droplet thing doesn't do quantum entanglement right, for multiple particles. So I guess that's a prediction, but it's one that decidable favors Copenhagen over it...

Semiclassical

15:38

You can test a prediction. But intuitions are heuristics---they do not and are not intended to provide numbers

vzn

@knzhou double slit experiment + others. thought/ said to have no classical explanation by all 20th century QM authorities incl feynman. plz try eg starting here to understand the new theory vzn1.wordpress.com/2018/05/25/fluid-paradigm-shift-2018

knzhou

@vzn What exactly does standard QM not explain about the double slit experiment?

Semiclassical

@knzhou Well, what I like about it is that it's a consistent story with trajectories. they're not trajectories of particles subject to classical mechanics (and given the role of nonlocality, they really can't be) but it's internally consistent and experimentally equivalent to QM

Secret

entanglement is ultimately a correlation though, whether it spontaneously establish itself after measurement or the correlation is already encoded within some nonlocal entity

Semiclassical

so as a story about QM, I don't mind Bohmian mechanics

vzn

15:39

@knzhou 20th century authorities claimed there was no "possible" classical explanation & that is now proven false. what is true is that it was previously inconceivable (by humans! aka anthropocentricism)

Semiclassical

as an explanation for it, I'm far less sure

knzhou

@Semiclassical I get that too, but you're really paying a heavy price for it with the guiding field!

Semiclassical

not sure what you mean there. the guiding field is just the wavefunction

Secret

I like the quantum potential and nonlocality of bohmian mechanics, but I dislike that it is deterministic

Semiclassical

I don't really like the quantum potential, tbh.

knzhou

15:40

I guess what I really mean is the quantum equilibrium assumption.

Secret

determinism is sooooo overated

Semiclassical

feels like it more comes out by the fact of trying to force the theory to look classical, and seeing the quantum potential as a mysterious/arbitrary obstacle to such

knzhou

@vzn What, a classical explanation for the double slit experiment with electrons?

Secret

In fact, I don't really mind if tomorrow, suddenly we are all trapped in cauchy horizon, cause and effect breaks down,spacetime breaks down, gravity is no longer curvature of spacetime, unitarity is out of the window

Semiclassical

now, that may be useful from a computational POV

Secret

15:41

yadayadayada...

vzn

@knzhou lol yes newsflash

Semiclassical

but from a principled point of view I'm not a fan

knzhou

@vzn Well I don't see that anywhere in the thing you linked, what is it?

@Semiclassical From a principled point of view I'm a many worlds partisan all the way!

Semiclassical

ew

knzhou

But that's not something you show off in public!

Semiclassical

15:43

snerk

Secret

In fact, one of the main reason I love contradictory and nonintuitive phenomenon, is the very powerful ability to make people shut up and focus

Semiclassical

I do feel like the QEH is the key mystery of bohm for me

Secret

When people are presented something that shatters their very philosophy of how they live, they stall, and then they will carefully reaccess their place in the universe

vzn

@knzhou try the viral veritasium video 11/2016 on this pg think has been posted in here also vzn1.wordpress.com/2016/11/07/…

bolbteppa

Note there is an equivalent second order formulation of Bohm re yesterday's argument

Semiclassical

15:44

sigh

not in the sense of classical physics there isn't.

Secret

what is QEH btw?

Semiclassical

quantum equillibrium hypothesis

Secret

I see

bolbteppa

Slide 5 qmts.it:8080/sites/www.qmts.it/files/…

knzhou

I was 'taught' Bohm by this really partisan philosophy prof, and when I realized something like the QEH had to exist and he was sweeping it really hard under the rug, I got pretty annoyed!

That's my main beef with people who promote Bohm in the popsci sphere, they try their best to avoid talking about the weaker points of their theory.

bolbteppa

15:45

'minimalist = first order, causal = second order'

knzhou

Say what you will about many worlds, at least it's forthright about it.

It's in the name!

@vzn Well that isn't the same thing at all.

heather

@BalarkaSen when you're next around, would you mind talking a bit about how the h-principle connects to the inverse gradient? I'm trying to read through some stuff on the h-principle and it's rather over my head, as you may have noticed in the math chat...

Semiclassical

@bolbteppa sure, but note that essential to the second-order formulation is the quantum potential

and that's dependent on the wavefunction, not the particle

heather

(i should probably read up on topology a bit.)

knzhou

Classical electrons don't make a double slit interference pattern. A classical particle interacting with a classical field, as in this experiment, does make an interference pattern. And a quantum particle does as well.

bolbteppa

15:46

But I think my argument from yesterday against Bohm will still work in the first order case too, but am thinking about it, another vicious thing is the meaning of spin in Bohm

knzhou

That does not mean that quantum particles are actually classical. No matter how you formulate it, classical physics is different from quantum physics.

Semiclassical

Mmm noncontextuality

I'm of two minds with spin as far as Bohm goes

knzhou

@Semiclassical Oh yeah, does Bohm have an explanation for quantum tunneling?

What are the trajectories there?

vzn

@knzhou QEH = ?

Semiclassical

lemme find a picture

there's some nice ones

knzhou

15:48

quantum equilibrium hypothesis

Semiclassical

right, this preprint: arxiv.org/abs/1210.7265

bolbteppa

It seems very basic to me if you actually assume there is a true path, even if we can't observe it, then Bohm is literally just saying Newton's force laws are wrong, very different to what normal QM claims

Semiclassical

see figure 4 on page 8

@bolbteppa sure

I'm not sure why that's so strange, though.

knzhou

@Semiclassical Neat!

Semiclassical

normal QM doesn't claim that Newton's force laws are right either. if anything it claims they're not applicable in a basic sense

you recover them in the sense of Ehrenfest's theorem, to be sure

bolbteppa

15:51

Normal QM claims it's only wrong because we can't define the variables in the first place, if we could normal QM would claim it's right

Semiclassical

I think that's a dubious claim about usual QM

DanielSank

@heather Not well.

I'm sorry.

Semiclassical

and one I'd want to see sourced

bolbteppa

First chapter of this:

amazon.com/Quantum-Mechanics-Third-Non-Relativistic-Theory/dp/…

Why doesn't the cool amazon picture of the cover show up here, it used to

Semiclassical

lol

vzn

15:52

@DanielSank sorry to hear that :(

Semiclassical

Regardless, that is an interpretational claim

heather

@DanielSank i'm sorry, i hope you feel better soon!

Semiclassical

it's not one which is contained in the equations of QM

heather

(or things improve)

bolbteppa

That's what Bohr etc claim, the guy who wrote that was Bohr's student

You can't even define the equations of QM without this assumption that the classical variables don't exist

I want to find out if anybody gave a Bohm explanation of this kind of stuff

DanielSank

15:54

@heather Thanks.

Semiclassical

I'm not even sure what it would mean to say that, if x and p commuted, then QM would just be classical mechanics

enumaris

I need to find another front page question to answer so I can get some more rep...that last one earned me like 400 rep...

Semiclassical

x and p don't commute, so that's not falsifiable

bolbteppa

But why are x and p even operators in the first place

enumaris

xp <---makes an emoji px <--- not an emoji therefore x and p don't commute

Semiclassical

15:55

at the level of the wavefunction, it's the same as in regular QM

bolbteppa

Why is there even a wave function

enumaris

There isn't, a wave function is a mathematical object that helps us compute probabilities

Semiclassical

Let me approach it in the following way, setting aside for a moment the notion of trajectory

enumaris

you can do the calculations another way, e.g. with Feynman's path integrals, that don't involve a wave function

bolbteppa

The first chapter talks about the fact the variables not existing as the most fundamental 'negative' claim quantum mechanics makes, then spends the rest of the chapter setting up positive claims like the Born rule

Anonymous

15:58

@Semiclassical BTW I had a bit of confusion about that derivation of classical mechanics as a limit of QM where they consider $\hbar \to 0$ (using some path integral argument). I always thought that the $[r_i,p_j]=\delta_{ij}$ is analogous to $\{p_i,q_j\}=\delta_{ij}$ in classical mechanics

Semiclassical

@bolbteppa Suppose I claim that I've prepared a 1D quantum system in a known pure state at time $t=0$. How would I validate that ?

Balarka Sen

@heather The literature on $h$-principles is interlaced with technicality a little. The reason it came up is because Gromov's book has "inversion of differential operators" as a section, like I showed you.

That's apparently one of the ways to prove $h$-principles. I haven't read it, but plan to. I have a vague idea how it could relate.

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