The h Bar

@0celo7 I view that as an attempt to somehow "salvage" some kind of notion of status, only to be used by those who know that they don't really have any.

ACuriousMind

At my school, you could tell which teachers hated each other, because only those called each other by their last names

Danu

Insisting on people "addressing you with respect" makes me instantly dislike you

0celo7

2:15 PM

If that makes you dislike me, I don't think I need you to like me.

Danu

@ACuriousMind I can one-up that: Leeb refers to his colleague Kotschick, who holds a chair in topology/geometry as well by "that other guy doing geometry"

@0celo7 Combo multiplier x10! :D

Secret

@ACuriousMind In chinese culuture, if someone really hates each other, they even call by their full names

ACuriousMind

@Danu how nice

0celo7

@Danu What?

Secret

@ACuriousMind it is actualy quite ambigurious, because closely related memebrs also refer each other by the full name

The key to differentiate between the two is the tone they use to say it

ACuriousMind

2:16 PM

@Secret I always thought that form of address was reserved for furious mothers :D

Secret

the hate case has very storng tone where each chinese letter is uttered sharply

Danu

@0celo7 Also...

> anarchist

Secret

while the frinedly and close case the words are uttered in a smooth phrase

Danu

don't you work for the government?

0celo7

I did, to see what it's like.

It's hard to form an opinion without some experience.

Danu

2:18 PM

Okay

Rigor

You need Einstein & The Evidence.

4

0celo7

OH MY GOD MY PACKAGE ARRIVED

Rigor

:O

Danu

yesterday, by 0celo7

Sen. Warren said my omelette smelled good

ACuriousMind

lol

0celo7

2:19 PM

::prays that post office is open::

Danu

I guess you were probing her* gastronomical intentions

0celo7

@Danu That is a fact.

ACuriousMind

@Danu That has to be some kind of euphemism.

0celo7

It's not!

Danu

@ACuriousMind :D

Great minds...

0celo7

2:20 PM

We were in the elevator by the Dirksen dining hall!

uh

Danu

(..or curious ones)

0celo7

shit

Ok that sounds even worse

A quick lil' omelet

lol

I see how it is

2:21 PM

there were a bunch of witnesses

ACuriousMind

@0celo7 kinky

Danu

@0celo7 Good ol' gangb*ng?

Rigor

-_-

0celo7

I woke up my roommate from my immature cackling

Danu

I think we need to tell missy Warren that her private life is being compromised

0celo7

2:22 PM

oh jesus this is how American lawsuits happen

Danu

Ocelot going to jail confirmed

Screenshot for evidence: Check!

0celo7

the state has a monopoly on violence

let this be a warning for all interns

Danu

Either bang a senator or get terminated!

0celo7

@Danu I swear if you don't get a ban for this

ACuriousMind

That's...not a good lesson :P

0celo7

2:24 PM

do you know what I got banned for yesterday

I bet you do

I bet you voted for my ban

ACuriousMind

Can mods even get banned?

0celo7

I bet you're the astronomer

Rigor

let's try

Danu

@0celo7 Do you think it's really offensive? It was pretty damn obvious that it was a joke.

@0celo7 There are no votes on bans

0celo7

@Danu ok, so you don't know what I got banned for yesterday, then

ACM can confirm it was ridiculous

Danu

2:25 PM

@0celo7 No, I didn't see it

ACuriousMind

@Danu Ocelot is a bit miffed because he was banned for a similar harmless joke

Or, at least, that's how it looks

Danu

Welp, sucks to suck? :D

0celo7

I got a 30 min ban, I think

Danu

If you were really banned for that, it was pretty ridiculous. I doubt that, though.

0celo7

I was on mobile and it said "room is read only"

well that's the message that got deleted

Danu

2:26 PM

No idea what that means---never got banned.

ACuriousMind

@Danu Well, it was removed, and he couldn't post for a while.

'Twas rather strange

Danu

@ACuriousMind OK. I guess some mods are very sensitive.

There are many...

Rigor

^

not

Danu

?

Rigor

:-)

0celo7

2:27 PM

not with a little hat, aww

not has a warm head now

Rigor

@Danu you are not sensitive

r u?

Danu

@Rigor Nope.

Ah, now I get it.

I am rather lenient.

0celo7

Danu doesn't give a flying f_ck if he calls some 80yo man "Karl"

he's a rebel

Rigor

or even old man

he tells it like it is

Danu

@0celo7 Karl?

Rigor

2:30 PM

use the first name

Danu

Oh yeah, of course.

I find lack of honesty/straightforwardness to be the greatest sign of disrespect.

Rigor

Danu

politifact.com/truth-o-meter/statements

lol

Rigor

:D

Secret

Random curious question: why state vector, but not state <insert mathematical object>
Is it because it is to address the linearity of quantum mechanics thus defining a state as a vector (or other linear mathematical objects) allow us to model it in terms of linear operators?

0celo7

2:48 PM

@Danu so you don't even ask?

Danu

@0celo7 Definitely not :)

0celo7

oh wow you'd get #rekt by Wes

(my department head)

Navy Captain

Danu

Told you, you belong in the military with an attitude like that.

I have no respect for people just for being in the military

0celo7

no

I don't either

but you'd get on his shit list so quick your head would spin

Danu

Good for him.

Why are you telling me this?

0celo7

2:52 PM

I can't comprehend your attitude

it physically shakes me

Danu

@0celo7 You must be frail.

0celo7

I could take Witten

@Danu so if you had a real job, you'd call you boss by his/her first name?

without asking?

Danu

@0celo7 I'd have to have a (non-trivial) conversation first, as I said.

After that, for sure.

ACuriousMind

@Secret I don't understand the question. If you modelled a state by a pflumt, you'd call it a state pflumt.

0celo7

pflumt?

@Danu ...

no wonder you think we're crazy

you're crazy

I'll ask Lang about this

ACuriousMind

2:57 PM

@0celo7 Could also be a wargletry.

0celo7

he's German, but maybe he's been tainted

Danu

You know that Germans are very formal, right?

0celo7

you go to a German school

and the physics dept is on a first name basis

and Lang is a German physicist

Secret

@ACuriousMind In quantum mechanics, we often represent the states as vectors in hilbert space, which obeys linearity, I am curious on what reason why we use vectors and other objects in vector spaces but not mathematical objects that don't live in a vector space.

My memory must be failing me because I felt like I have seen the answer, but I don't recall it

0celo7

@ACuriousMind wargletry?

ACuriousMind

3:01 PM

@Secret Ah, you're asking why states are modeled by vectors. Well, it works, doesn't it? Superposition of two states is achieved by adding them, etc...

0celo7

@Danu did you call your teachers in high school by their first names?

the mathematicians have invaded

Danu

@0celo7 Yes, and joke-y nicknames for most of them.

0celo7

@Danu ::ciringes::

holy shit

Danu

@0celo7 I'm cringing at you!

yuggib

@Secret states are positive and norm one, therefore do not form a vector space

ACuriousMind

3:03 PM

@Secret: Also, you don't always have to have a "vector" for a state. Look at the density matrix formalism, there a state is given by the matrix.

0celo7

oh my god I can't even imagine the shitstorm if I called my teachers by their first names

Danu

Anyways, I think I've had enough of this boring conversation.

0celo7

these are irreconcilable cultural differences

Danu

No, they're not. In the US it went just fine. I did it at Princeton.

You just need to get over something.

0celo7

you're telling me you could go into the average American high school and call teachers by their first names?

Danu

3:05 PM

I'm telling you that the people that deserve respect are not those that insist on enforcing it.

0celo7

at my school the new teachers didn't even refer to the old ones by their first names

I would not feel comfortable doing that.

that's that.

Secret

so in general, what physical property besides linearity that motivate us to use matrices and vectors (and tensors) (or in general, multilinear objects)) in quantum mechanics.

I mean, (forgetting about pictures for the moment), vectors and tensors are characterised by how they transform under coordinate transformations. What is the physical meaning behind the geometric meaning of a state vector or density matrix (since they obey transformation rules like a vector does)?

(putting in pictures in again) It is easy to see what the norms of these state vectors and matrices mean, but what physic…

Or put it simply, since states are modelled by vectors and other linear objects, they had some orientation relative to each toher, what does the orientation mean physically that is observed in experiments involving quantum mechanics?

ACuriousMind

@Secret The technical reason is that a quantum system is given by its $C^*$-algebra of observables, and that states are linear functionals on that (essentially the functionals that give you the expectation value for the state associated to them, I'd say). By the GNS construction, such algebras are naturally associated to Hilbert spaces.

@Secret The Hilbert space of quantum mechanics is abstract, and usually infinite-dimensional. There is no simple "geometric meaning" to it.

We don't observe the state vectors either, we only measure the values of operators. You can't really measure a wavefunction (there are tricks, but that's beside the point here).

user116211

@ACuriousMind: Your last profile pic was better, IMHO! Where did you get this?

Secret

hmm, I guess I have to understand $C^*$ algebra then to fully appreciate the motivation of using linear objects. I will check again once I have the knowledge

Like most people who learnt quantum mechanics, it amazed me why the maths worked so well, yet not everything inside the maths can be observed

ACuriousMind

3:16 PM

@user36790 Both are characters from the game Planescape: Torment. (Some of my other pics were as well)

@Secret Well, at the end, the motivation for using any formalism in physics is "it works".

0celo7

@ACuriousMind what tricks

Secret

@ACuriousMind Then I really think like a philospher and a mathematician then, because I often felt like being thrown into a black box given instructions on how to do things if I don't understand why it works

But why in quantum mechanics is a hard question, as everyone knows, just look at that sheer numbers of interpretations, to start with

yuggib

@Secret Hint: the interesting point about linearity is not so much that we use linear objects in QM, but that we use a linear evolution

Secret

time is linear, right?
I recall time is a parameter in QM

yuggib

@Secret time is linear, but that does not mean that the evolution must be linear

in classical mechanics, the evolution is often non-linear

Secret

3:23 PM

Oh

@yuggib remind me an example of nonlinear evolution in classical mech?

yuggib

@Secret the one generated by the hamiltonian $H=p^2/2m + x^4$

to mention a simple one

anyways, suppose that you have observables that you can sum and rescale

that is quite natural, it is something that you do in practice many times

linearity is simply the requirement that addition and rescaling of observables are preserved by a transformation

for states, it firs with the probabilistic interpretation: the evaluation of the sum of two observables on a state is reasonably taken to be the sum of the evaluations (and as @ACuriousMind said, it works)

also the rescaling of an observable corresponds to the rescaling of the evaluation on the state

therefore the states "inherit" the linear structure from the observables

now for time evolution, it is far less evident why it should preserve linearity

as I said, it is not true on the classical realm

I don't have an answer on this, apart from the fact that it is what is suggested by observation

Secret

http://www.acs.psu.edu/drussell/Demos/Pendulum/Pendula.html

nonlinear like the pendulum examples?

Well, the maths is needed to model what is observed in physics, and indeed, when I discuss with others, we found there is not really many mentioning about nonlinear phenomenon in quamtu mechanics.

I remember they say it is part of the postulate that the wavefunction is linear

yuggib

3:38 PM

one thing that is instead rigorously understood (at least in some cases) is why from a linear quantum dynamics you then obtain nonlinear dynamics as an approximation

the classical approximation is one, the mean field approximation is another

for Hartree, Gross-Pitaevski are nonlinear effective quantum evolutions utilized a lot in condensed matter physics

Secret

http://www.sciencedaily.com/releases/2015/09/150911224341.htm
I think this might be relevant

yes, take my honours project for example, we are using hartree fock and other methods to compute molecular dynamics

yuggib

@Secret well, you can obtain Hartree-Fock, as well as the other equation I said above, rigorously as an effective model of linear quantum many-body dynamics

(in the limit where the number of particles $N\to\infty$)

David Z

@Danu I think we're still at the point where more flags (on things that should be flagged, of course) are better, so yeah, flagging is appreciated.

0celo7

@ACuriousMind what tricks??

ACuriousMind

@0celo7 Some people are claiming you can measure the wavefunction with weak measurements.

0celo7

3:50 PM

meaning?

measurements of the weak force?

ACuriousMind

@0celo7 No, weak measurements are measurements by a weakly coupled measurement device so that the quantum state that is measured is not (or at least almost not) disturbed

Don't ask me for details, I've not read up on that.

Secret

If I recall that correctly, measure a little of e.g. the momentum, and then do the same for position for a large number of states, can allow you to learn a little bit more about the position and momentum without end up collapsing the state (at least that's how NewScientist puts in)

The idea is to measure just enough to gain a little bit of infromation, but not perturbing the state enough to colapse it

0celo7

@ACuriousMind darn

Secret

But I recall there's a compromise, except I forgot what exactly that is

0celo7

I need details!

Secret

3:53 PM

It allows you to bend heisenberg uncertainty principle at the cost of something

not brekaing it however

dmckee

@Danu About deleting comments. I have three modes.

Secret

@0celo7 http://quanta.ws/ojs/index.php/quanta/article/view/14/21
Ok this is WAY BEYOND MY HEAD for now

dmckee

(A) There are one or two out-of-the-blue rude ones. Scrub those exactly.

(B) The conversation has nothing to do with the post. Just kill it all.

(C) The conversation seems to have gone wrong somewhere. I work backwards looking for the place it went went from "clearly working to improve the post" to something else.

In that case I tried to go with (C), but it seemed that leaving your comments without leaving Michael's response would be unfair to Micheal. At the same time the pure volume of writing involved was a problem. There were four of your comments then four of his.

That said, I can ask another mod to look at what I did if you'd like.

vzn

4:15 PM

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

see sec [o] on Cavalcanti. not an expert but weak measurements seem to me to be some evidence for "incompleteness" in "classic QM" although almost nobody is claiming that outright now. the issue is that it seems to be some revision/ elaboration of classic QM measurement mathematical axioms.

Danu

@dmckee I think this response is at tension with what @DavidZ told me earlier; I had already proposed to move it all to chat, but David said that he didn't think that was the right thing to do.

I don't remember exactly what Michael's four first comments were like, but I think they were also still civil and on-topic.

Mark Mitchison

@vzn Actually it's just that undergraduate quantum mechanics courses notoriously treat measurement theory in an incomplete way.

Danu

Did I recall that incorrectly?

Mark Mitchison

But this is perfectly normal for any course in any field, to be incomplete

Actually it's impossible for a course not be incomplete, really.

Danu

I thought I made some important points in those four comments, so yes, I'd like it if someone looked into whether they can be restored.

0celo7

4:23 PM

MY MOUSE IS HERE

vzn

@MarkMitchison somewhat disagree. soft measurements are a genuine new theory initially being driven by experiment(ers).

Danu

@DavidZ I'll keep at it, then.

Mark Mitchison

@vzn Weak measurement theory falls entirely out of the quantum mechanics developed by Dirac.

vzn

QM was largely formalized by von neumann acting with his mathematical hat on. it does not appear a similar expert of large status has yet appeared to make sense of weak measurements afaik/ afaict.

Mark Mitchison

It is a relatively new topic within QM. It is not a new theory.

vzn

4:25 PM

@MarkMitchison dont think so. think that is possibly a fig leaf.

Mark Mitchison

fig leaf?

Danu

lol^

Mark Mitchison

Not familiar with that expression.

Danu

me neither

It's supposed to be something that hides the truth or something?

Mark Mitchison

ok, wiki to the rescue

Danu

4:26 PM

(it's clearly a reference to fig leaves in art)

vzn

QM dogma has been built up over close to a whole century now. nobody wants to claim they are revising it or they will be accused of heresy.

Danu

@MarkMitchison Yeah, but that doesn't apply here?

vzn

the new theory seems to be close enough to the old one for now that it is not raising alarm flags.

Mark Mitchison

But in any case, it is simply a fact that weak measurement theory is a straightforward application of standard quantum theory. There is no new theory required, it is a consequence of quantum dynamics and the standard von-Neumann projection postulate.

This is not really disputable

But of course the interpretation of what weak measurements signify is up for debate

vzn

but mathematically it does not appear to me to be equivalent. its "interpreting" old QM in new ways. aka QM v2.0

Mark Mitchison

4:28 PM

Mathematically it is equivalent, I'm afraid,

Or actually I'm not afraid, it would be weird if it was not

Of course the philosophical debate is quite interesting

vzn

it seems to predict outcomes of individual experiments so to speak. as forbidden by classic QM theory. am not an expert on this. think the paradigm shift will take longer to sort out. its not immediately apparent.

Mark Mitchison

But it is not correct to think that there is some new formalism here. It is about studying the evolution of coupled subsystems, a la standard QM.

vzn

it is not incompatible with prior theory but prior theory does not imply it. its an extension to an incomplete theory, exactly as EPR argued must exist.

Danu

@vzn I don't think there's a paradigm shift :P

vzn

weak measurement papers & authors are now using the language of a paradigm shift but not using the exact words "paradigm shift".

Mark Mitchison

4:30 PM

@vzn Sorry, but that's just incorrect. It is completely implied by the existing mathematical theory. The interesting questions are about how to interpret the weak values.

vzn

so as not to raise alarm.

Danu

@vzn Typically, the people writing papers are trying to promote the topic

vzn

some people mix up "promotion" and "research".

the mixup is related to too much adherence to the status quo at times.

Danu

(maybe you have fallen victim to this (referring to your first message) confusion?)

Mark Mitchison

@vzn I recommend that you work through the actual formalism, you will see that no additional "postulates" or anything else of the sort are required. It is about measuring one sub-system of an entangled pair and inferring information about the other subsystem.

vzn

4:32 PM

think there is genuinely new theory here but it will be difficult to sort out in the short run because it was discovered mainly by experimenters and not theorists. the theorists have not really noticed much yet.

Mark Mitchison

Such measurement techniques have been around for quite a bit longer than the current discussions on weak measurement.

vzn

will concede that my views are unconventional right now :|

Danu

@vzn Would you consider the possibility that it's more hype than real innovation? I didn't look into any of this so I'm not guaranteeing this is the case

vzn

science has hype at times. its a human activity. some discoveries are worth hype. esp paradigm shifting ones :)

Danu

I guess you see my point, though.

vzn

4:35 PM

all genuinely new discoveries are subject to a lot of noise & confusion at 1st.

Mark Mitchison

@vzn No offence, but your views are worthless if you don't understand weak measurement. You should really delve into it a bit, there is nothing there beyond the standard QM postulates. The interpretation is very interesting, but the predictions could have been made even in 1930. Just people were not working on these issues at the time. And as you say, experimentalists have been doing "weak measurements" since the dawn of science, so there was not much need to trumpet about it.

vzn

MM this debate will not be settled in a few lines in a chat room. lets both stay tuned.

Mark Mitchison

Agreed, but nevertheless it's worth learning about the formalism, it's very interesting.

vzn

can see that this might be the topic of my next blog post on subj :)

there are some papers now claiming that the wavefn must be "objectively real" & its somewhat tied to the weak measurement stuff.

Danu

@vzn I think the blogosphere already responded to this, and it was universally found to be uninteresting

vzn

4:40 PM

[Measurements of the reality of the wavefn](Measurements on the reality of the wavefunction](osapublishing.org/abstract.cfm?URI=FiO-2014-FW5C.1) / Ringbauer et al

lol rats messed that up, take2

Measurements on the reality of the wavefunction / Ringbauer et al

dmckee

Non-paywalled link: arxiv.org/abs/1412.6213

vzn

@dmckee thx :)

Danu

scottaaronson.com/blog/?p=822

dmckee

Assuming of course that the title is unique over those authors...

Danu

;D

vzn

4:50 PM

ah aaronson, yes, the chief quantum skeptic. slayer of dragons.

Secret

same paper?
http://www.nature.com/nphys/journal/v11/n3/full/nphys3233.html

vzn

am going to delve into Secrets excellent ref just posted. (Tamir/ Cohen) this is way beyond my personal capability to extricate this, but will tentatively start. p8:

> There are many motivations for generalizing quantum projective measurements into weak measurements: maintaining the initial state while gradually accumulating in- formation [5], determining the system’s state in-between two strong measurements [6] and revealing unusual weak values [7] are just three examples, others will be described below.

huh, "in between strong measurements," what a curious phrase. it sounds like QM "v1" is about strong measurements and this revision is what happens between those measurements.

ACuriousMind

@vzn What? It's just meant temporally - get information about the evolution of the state during the time between two strong measurements.

I don't see what's unusual about that phrase.

vzn

soft measurement seems to be making a stab for a "more complete" picture of the notoriously uninterpretable quantum states.

and what exactly are "unusual weak values"? nothing could be regarded as unusual wrt QM theory right? because its complete, right?

isnt unusual = anomalous?

ACuriousMind

Well, the answer to what "unusual" means almost certainly lies in [7] :P

vzn

4:58 PM

anyway, concede not having all the answers myself, & am continuing to delve into this myself, but think something is afoot so to speak.

ACuriousMind

I'd wager those are values that differ greatly from what a strong measurement would measure.

NeuroFuzzy

@Slereah Patriarch? I identify as RandomChoice[{"trigendered","foxkin","dragonkin","a paperclip"}] and I find that RandomChoice[{"offensive","insensitive","in very bad taste"}].

0celo7

trigendered cis scum

only us quadgenered have it rough

ACuriousMind

@NeuroFuzzy Why would your choice of identification change that Slereah is a patriarch?

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