The h Bar

Slereah

9:00 PM

Well

The universe isn't heliocentric either

The point is that there is no center

Geocentrism makes just as much sense :p

vzn

... renegade! heretic! blasphemer! apostate! infidel! radical! rebel! contrarian! revolutionary! outlaw! etc... (sure are a lot of words for it!)

0celo7

see, the Evidence shows that the Earth is the center

ACuriousMind

@Slereah That has always irked me about this whole issue. Both "geocentrism" and "heliocentrism" are kinda wrong, even from simple Galilean relativity.

And yet people act as if heliocentrism is "correct" and geocentrism backwards and wrong.

0celo7

google on epicycles

copernicus is the first popscientist

bolbteppa

I wonder, I mean those epicycles were actually Fourier approximations to the true elliptic orbits with reference to the wrong place (the earth), whereas Copernicus claimed they were circular orbits around the sun when they should be ellipses, to a mathematician maybe the Church was more correct haha

0celo7

9:02 PM

then Newton came with his mathematical abstractions

and now no one thinks he's wrong

Slereah

The first popscientist is Eratosthene

A round earth???

0celo7

that's just plain cargo cult science

Slereah

Obviously it is flat

things would just fall off in space otherwise

obe

hello.

yuggib

@vzn I would say that the reference you cited as an introduction of weak measurements is so wildly inaccurate on a mathematical standpoint that it is hardly worth reading. Take this as a starting point for a rigorous analysis of the ideas behind weak measurements is not possible.

starting from equation (13) there are too much things that make me raise my eyebrow, and that are in my opinion wrong

if the level of rigor on the subject is like that, it is far from being something paradigm shifting. It seems more like a lot of conjectures badly supported by math.

bolbteppa

9:12 PM

Ptolemy's model in modern language is pretty amazing mathoverflow.net/a/201531/38721

yuggib

@vzn Anyways, the mathematical setting of QM is clear, and its "set of axioms" are simply the usual axioms of ZFC. In fact, with these axioms it is shown that non-commutative algebras exist, and quantum mechanical systems are models (@ACuriousMind mathematical style ;-) ) of non-commutative algebras.

0celo7

Just look at the evidence. It clearly implies that the Earth is as flat as Hawking's personality.

I haven't seen the Earth not be flat and neither have you.

Anything else is cargo cult science and pure math.

Math is not physics and any physics using math is suspect.

vzn

@yuggib seems like solid ref to me & authors presumably have good credentials. do you have a better one? at least its a mathematical treatment of weak measurement. agreed its a "young" area.

yuggib

even the measurement process fits inside the same axioms, at least as formulated by von Neumann, and discussed in modern terms in a paper by Ozawa

that sadly I do not have access to...

0celo7

bah, mathematicians have taken over

mathematicians wouldn't know evidence if it hit them in the tensor bundle

yuggib

9:16 PM

@vzn Equation (13) is wrong, for $H$ depends on $t$, and therefore the exponential is not straightforward

you are not assured that you can define it

(and anyways should have an integral wrt time)

vzn

@bolbteppa agreed that epicycles had a large degree of mathematical sophistication and could even be more accurate than a poor elliptical approximation. but isnt it fascinating that nobody ever realized for ages that "lots of epicycles = hint of ellipse"!

yuggib

such non-autonomous evolutions have all kind of troubles mathematically

it is possible to define them but hard

Slereah

"the geodesics around a black hope"

Why are there geodesics around Obama

vzn

@yuggib they are not claiming any paradigm shifting yet, few ppl are, but some of the weak measurement proponents are essentially now claiming that, but not with all the pieces tied together/ fleshed out out yet. its "early days". it hasnt escalated yet in Kuhian terms.

yuggib

In equation (14), it is not clear what $a_j$ is. It is the eigenstate of $A$? I agree that the exponential of $P$ is the $X$-translation, but only when there is not that time dependence in the exponential; and the rest is not an operator (even if in another space). If it is, then why there is $a_j$ and not $A$?

Equation (15) is, in my opinion, really wrong, whatever the interpretation could be...

vzn

9:22 PM

"wrong eqns"! interesting! the plot thickens! :D

yuggib

Yes, wrong. As in false

given the premises, it is hard to just believe in what they are saying.

ACuriousMind

@yuggib $a_j$ is defined shortly before eq. 9

yuggib

@ACuriousMind I know

ACuriousMind

So it's clear what it is. It's just not clear what the heck they're doing with it :P

yuggib

but it is an eigenstate of $A$, not a number

ACuriousMind

9:24 PM

@yuggib Well, $\lvert a_j\rangle$ is the eigenstate and $a_j$ is the eigenvalue, i.e. a number.

yuggib

ok, also given that, it remains to explain how it comes out of the blue when acting with $A$ on nothing

since $A$ commutes with $X$

scitation.aip.org/content/aip/journal/jmp/25/1/10.1063/1.526000

there

that is a rigorous paper on quantum measurement

usual one

I do not have acces, sadly

I would like to read it :(

vzn

does weak measurement fit into the ozawa theory? (1984 paper.) the mere phrase "weak measurement" is relatively new afaik/ct

yuggib

I don't think so. But you should start by knowing a rigorous definition of the usual measurement, to then understand the relevance of these "new proposed measurements"

vzn

@yuggib the paper/ theory (Tamir/ Cohen) is driven by experiment... the ideas of weak measurement seem maybe to be originating with experimenters to some degree...

yuggib

I think it originates with a proposal by some russian guy

ACuriousMind

9:32 PM

@vzn Not at all. The people who first developed it (according to Wikipedia) were Aharonov, Albert and Veidman, all three of them theorists

yuggib

journals.aps.org/prl/abstract/10.1103/PhysRevLett.60.1351

here it is

obe

@ACuriousMind This book I am reading defines spin as rest centre of mass angular momentum of a particle. Is that right?

ACuriousMind

@obe ...yes, one can say that. Provided you define angular momentum as "conserved charge under the rotation group" and not $\vec r \times \vec p$, which is the classical angular momentum.

vzn

ok... but Aharanov seems to be involved in experiments. from his page.

> In 1988 Aharonov et al. published their theory of weak measurement, which does not disturb the quantum state being observed. This work was motivated by Aharonov's long time quest to experimentally verify his theory that apparently random events in quantum mechanics are caused by events in the future (two-state vector formalism).

> Verifying a present effect of a future cause requires a measurement, which would ordinarily destroy coherence and ruin the experiment. He and his colleagues were able to make weak measurements and verify the present effect of the future cause.

Mike Edenfield

ugh. i have a question about mass and energy ... and levitation, in Harry Potter... but all Mos Eisley wants to talk about is people getting flagged. That's almost physics, right?

ACuriousMind

9:37 PM

@vzn "Trying to come up with a prescription for an experiment" is quite far from actually being involved in experiments :P

vzn

@ACuriousMind "He and his colleagues were able to make weak measurements and verify the present effect of the future cause."

ACuriousMind

Weird wording, nothing is verified because the TSVF is equivalent to the usual QM formulation, in which no one talks about "future causes". What they verified is that we can carry out weak measurements, and nothing else :P

yuggib

@vzn but they did not, apparently, write a paper about that

Slereah

Damn it people

Don't you know talking about QM interpretations is the best way to start a flamewar with physicists :p

you might as well ask them which theory of quantum gravity is correct

ACuriousMind

@MikeEdenfield Yeah. Also, it may not seem so lately, but being physics is not a prerequisite for being a topic in this room ;)

@Slereah Believe me, @vzn knows ;P

Mike Edenfield

9:40 PM

I don't think gravity exists. I think it's an emergent property of the Higgs Field.

0celo7

problem is, no one knows if you're kidding

Mike Edenfield

also, I know what at least 5 of those words mean.

0celo7

or not

Slereah

Isn't there a theory like that

Like tensor-scalar gravity

Mike Edenfield

it's a theory I made up in the shower trying to explain QFT to myself.

Slereah

9:40 PM

Where the scalar is the higgs field

0celo7

@MikeEdenfield well done

Mike Edenfield

and just assumed someone else smarter than me had already thought of it and proved it stupid.

vzn

@yuggib why do you think they didnt write a paper? (ps am enjoying Arahanovs association with bohm...)

user54412

@MikeEdenfield Well I'm sure gravity doesn't think you exist either. You're just an emergent property of some neurochemical signals.

2

Mike Edenfield

but now that I know there's real quantum physics words attached to it I feel way smarter.

yuggib

9:42 PM

@vzn Dunno. Maybe they did not actually do the experiments (wikipedia is not always correct); or they did but did not thought it was something worth a paper.

They are russians, maybe for them is trivial

vzn

@yuggib wikipedia doesnt say they didnt write a paper. it just doesnt seem to cite one.

Mike Edenfield

also, how come it doesn't take more energy to cast Wingardium Leviosa on a 100-kg object than a 1-kg chair? Someone's violating conservation of somewhere somewhere.

yuggib

@vzn I assume that either there or in the page about weak measurements they would cite such a paper, for it would be probably the first about a concrete weak measurement. Also, it should have been cited by the other papers on the subject

ACuriousMind

@MikeEdenfield They also can create (some) stuff (temporarily) out of thin air, can't they? That's much more worrisome, energy-wise.

yuggib

Nevertheless, it is not a very important point.

vzn

9:44 PM

@yuggib wikipedia is either strong or weak with citations :P

Mike Edenfield

@ACuriousMind i just figured that was highly improbably quantum fluctuations.

yuggib

:-D

ACuriousMind

But fortunately, just this once, the answer is actually: MAGIC!

yuggib

@ACuriousMind you forgot a "k" at the end..

ACuriousMind

@MikeEdenfield Mhhh...then why would you not think of the levitation as similarly improbably fluctuations?

yuggib

9:45 PM

I really prefer that version of the quote...

ACuriousMind

(Quantum fluctuations don't actually work this way)

@yuggib No, ancient and revered magick is different from the fancy modern magic kids today learn.

Mike Edenfield

hrm.... cuz levitation is permanent?

assuming you levitate it onto a higher shelf

ACuriousMind

Seems legit

Slereah

@MikeEdenfield It's LevioSA

vzn

@yuggib what point? about Arahonov being an experimentalist? agreed it is not crucial. looking over his pub list however he seems to have been involved in experiments for many decades. but maybe more of a theorist overall. not sure his own opinion; not all scientists are willing to be classified as one or another...

Mike Edenfield

9:49 PM

I think maybe it's because JKR is admittedly bad at math, so she might have had problems solving the DE's.

yuggib

@vzn The fact that he made or not the experiment is also not so important. Apparently, someone else later did the experiments anyways

Slereah

Hogwart is really a shitty school

Mike Edenfield

@Slereah true. except, it's actually LEGO Harry Potter, so its "mmmphmphpmh mpphmphpmMPPHHH."

Slereah

They don't learn math or english

Mike Edenfield

but they do learn chemistry!

Slereah

9:50 PM

They learn how to make poisons

Like a terrorist cell

Mike Edenfield

i wonder of polyjuice potion is an oxidizing reaction. I should go ask in The Period Table

0celo7

::fluctuates quantumly::

Mike Edenfield

great. now we have a mod "figuring out" how to freeze and unfreeze rooms... on our 25-person room.

ACuriousMind

@Slereah lol...interesting perspective

DanielSank

@0celo7 wat?

ACuriousMind

9:53 PM

Ah, we can ask @DanielSank! Will weak measurement revolutionize quantum mechanics?

0celo7

why would he know

DanielSank

@ACuriousMind Define "quantum fluctuations".

0celo7

he's an engineer

Mike Edenfield

@DanielSank obviously, it's how magic works.

DanielSank

@ACuriousMind That's a loaded question. May I ask what you have in mind.

ACuriousMind

9:54 PM

@DanielSank Yeah, that's the annoying part. I've never seen a definition of them that's not either trivial or non-sensical.

vzn

@DanielSank lol a nonstraight answer! a not immediate/ forceful denial! the best one could possibly hope for!

DanielSank

@0celo7 Ooohhh, you're cute! You think physics is all about reading books and getting an "A" on your exam. That's adorable.

0celo7

@DanielSank ...what?

idk why so hostile, it might not have been a good joke

vzn

he called you adorable, that is hostile? :P

DanielSank

@0celo7 I thought is was an excellent counterattack, actually.

ACuriousMind

9:55 PM

@DanielSank I have nothing in mind, but...some people seem to think there's something in them that QM can't yet really describe.

Or some kind of "deeper understanding"

0celo7

@DanielSank I'm not adorable though

DanielSank

Ok @ACuriousMind here's the deal: most people say "quantum fluctuations" and have no idea what they even think they mean by that. This is, unfortunately, particularly true in astrophysics.

0celo7

I need to shave

then maybe

ACuriousMind

@DanielSank I do not disagree.

vzn

@DanielSank see, the experimentalists are not so sure about weak measurement eh?

DanielSank

9:56 PM

@ACuriousMind, other people talk about it and do know what they mean: they mean that if you measure something in a system that's quantum enough, you'll see fluctuations in the measured result which you can't explain with classical physics.

0celo7

we all know that the universe is the way it is because of quantum fluctuations

Slereah

"Quantum fluctuation" just sounds nice

DanielSank

@ACuriousMind in particular, these fluctuations saturate at low temperature, so it's not thermal.

Slereah

Like "zero point energy"

Do people still use zero point energy

I rarely see it nowadays

They mostly just say vacuum energy or ground state or whatever

DanielSank

@ACuriousMind, interestingly, the theory does not have anything actually fluctuating until you make a measurement. Therefore, this idea of quantum fluctuations, like so many other things, is really the so-called measurement problem rearing its head once again.

@ACuriousMind does that help?

0celo7

9:58 PM

@DanielSank I have to break off the quantum computing endeavor for the meantime. Gotta learn about neutrons

I got like 20 pages into Nielsen & Chuang

Slereah

neutrons are the proton's boring brother

0celo7

wow, particleist

Slereah

Know what else I can't stand?

Mesons.

I have nothing against mesons

0celo7

you'd told us

over and over

Slereah

Some of my best friends are mesons

But there are too many of them

They need to go back where they came from

DanielSank

10:00 PM

@0celo7 Not surprised. Most of the time when a person is initially super interested in something that has no real relevance to their daily life they lose interest pretty fast. Combine that with being in college and I wouldn't be surprised if you don't come back to QC for a long time. I'm saying this so you don't feel bad.

ACuriousMind

@DanielSank You're essentially saying quantum fluctations are non-zero standard deviation of an operator not due to thermodynamics. I've heard that before, but this doesn't deserve such a mysterious name, imo ;)

DanielSank

@0celo7 When I was a student I carried some guilt for not following through on all my interests. It's impossible, so don't worry about it.

Slereah

"fluctuation" isn't a very mysterious term

DanielSank

@ACuriousMind The name isn't mysterious at all. It's as brief and descriptive as it could possibly be!

vzn

wow look at this from wikipedia weak measurement pg.

Slereah

10:01 PM

To be fair, I think particle physics would be better if we only had electrons and photons

vzn

> In 2010, a first experimental observation of trajectories of a photon in a double-slit interferometer was reported, which displayed the qualitative features predicted in 2001 by Partha Ghose[11] for photons in the de Broglie-Bohm interpretation.[12][13]

0celo7

I'm currently fluctuating quantumly...I don't see the issue

DanielSank

One adjective, one noun... what more do you want?

0celo7

@ACuriousMind imo it's not mysterious

DanielSank

So, what did you guys want to know about weak measurement?

0celo7

10:01 PM

do strings fluctuate quantumly

Slereah

well strings are just quantum objects

So they probably do

DanielSank

These guys have done some of the most amazing weak measurement experiments in history.

0celo7

i.e. how much sense does the standard pants picture of string interactions make

DanielSank

You can see %*(^*@ measurements of the path density of a quantum system!!!!!

OMFG!

Slereah

don't know too much about string theory

0celo7

10:02 PM

that was @ACuriousMind

Slereah

Isn't the pants cavalcade basically the string equivalent of a Feynman diagram?

0celo7

well I think the pants are literally what's happening

because string scattering is defined perturbatively

DanielSank

@ACuriousMind please at least skim this paper at some point in your life.

0celo7

>not the abstract

ACuriousMind

@DanielSank Uh...I guess the point in fact is: Is there something about weak measurement that cannot be explained/described by our usual quantum formalism? (I think that's what @vzn was saying)

vzn

10:03 PM

@DanielSank does QM fully predict all the physics being observed in weak measurement experiments?

Slereah

I should read more string theory, but

eeeeeh

DanielSank

@ACuriousMind What does "usual" quantum formalism mean?

Like, something you'd find in a grad course's book?

0celo7

@FenderLesPaul how mad would you be if I called off the GR talk

Slereah

the thing with string theory is

It's basically like a big bag of candy

0celo7

I forgot that the debate is tonight

DanielSank

10:04 PM

If that, then yes, weak measurement cannot be explained with "usual" methods.

Slereah

You know that if you start doing it

You'll have to eat it all

And it may not be fun

FenderLesPaul

@0celo7 I would be really mad

heartbroken

DanielSank

@vzn Yes.

Slereah

Because string theory is way too much shit

0celo7

string theory is ok but superstring theory is 90% SUSY model building and 10% actual interesting stuff

FenderLesPaul

10:05 PM

I baked cookies and everything

DanielSank

@vzn but you have to think more carefully then "herp derp I looked at it so the wave function collapses derpaherp".

Slereah

There's strings, there's supersymmetry, there's compactified dimensions

0celo7

SUSY sucks balls

Slereah

Probably a bunch of stuff I don't know about

Branes and whatnot

0celo7

no string theory text talks about it

FenderLesPaul

10:06 PM

@0celo7 which debate?

Slereah

I know a lil about SUSY

ACuriousMind

@DanielSank No, it can be research-level and difficult and elaborate all you want, it just has to be based on the usual QM axioms/concepts like Hilbert space, time evolution by Hamiltonian, etc.

@0celo7 As much sense as a Feynman diagram.

Slereah

Basically SUSY is about like

vzn

@DanielSank weak measurement seems to evoke something more than the Dirac-von Neumann formalism...?

Slereah

Symmetry groups that are spinors?

0celo7

10:06 PM

@ACuriousMind but string theory is defined by the pants, no?

DanielSank

@ACuriousMind Yeah, then weak measurement is nothing special.

Slereah

kinda

0celo7

so the pants are actually there

@Slereah yeah

freaking von Neumann again

Slereah

Because filthy mathematicians were unable to think of something so brilliant

Until physicists showed them the way

ACuriousMind

@0celo7 Yes, the string perturbation series is a sum over these worldsheets, just as the QFT perturbation series is a sum over Feynman diagrams.

0celo7

10:08 PM

ok but the diagrams are not physical, are they?

but the string ones are

DanielSank

@vzn weak measurement just means you didn't entangle your detector enough with the system under study to fully collapse its wave function.

^ That was a good description, actually.

Slereah

Does string theory have a perturbative definition?

DanielSank

::pats self on back::

0celo7

and are there "virtual strings"

Slereah

I thought it didn't?

vzn

10:08 PM

@DanielSank right. but doesnt classic QM have no concept of "not fully collapsed wavefn"...?

0celo7

@Slereah it only has one

ACuriousMind

@Slereah It has only a perturbative definition

Slereah

Oh

Hm, which one has none then

I remember a theory with no perturbative definition

DanielSank

@vzn If "classic" means the self-inconsistent nonsense they teach you as a freshman, then you are correct.

0celo7

$$\mathrm{string theory}=\sum_p\mathrm{string theory of genus }p$$

very roughly

the roughest of roughs

@Slereah QCD?

ACuriousMind

10:10 PM

@Slereah Oh, there are theories for which you have difficulty finding effective QFT Lagrangians that occur in some corners of SUSY and/or string theory, so you can't do perturbative QFT with them.

Slereah

QCD totally has a perturbative definition

DanielSank

@vzn "classic" QM was really loosey goosey about what "measurement" means.

Mike Edenfield

@ACuriousMind for the record, I knew that wasn't how "quantum fluctuations" worked, I just liked the sound. I have no idea how they work.

DanielSank

We've done better since then.

Slereah

It's just not that great because the coupling is strong

ACuriousMind

10:13 PM

@MikeEdenfield No worries, that wasn't about you

vzn

@DanielSank seems like new theory emerging, but theorists are not blaring it yet.

ACuriousMind

@Slereah Well, strictly speaking, none of the perturbative stuff is a "definition" because none of the sums converge in the first place!

DanielSank

@vzn It's not that new.

Lots of theorists know about it.

It just hasn't gotten into schools because writing books is hard.

Mike Edenfield

@ACuriousMind however, I did seem to think they worked in a way that @DanielSank claims they do now, so I learned something anyway!

vzn

the experimental precision is new. "new" is a slippery word.

DanielSank

10:15 PM

@vzn Ah yes.

We have had the pleasure of very excellent experiments in recent years.

vzn

cant put my finger on it yet but suspect it contains fundamental principles not contained in QM, maybe not yet fully identified.

0celo7

wait so is measurement defined properly now

DanielSank

@vzn As far as I know, that's not the case.

vzn

@DanielSank in a sense the textbooks have to be rewritten, exactly as kuhn talks about... :|

0celo7

@MikeEdenfield when you're done with Susskind's book, I highly recommend

amazon.com/Einstein-Gravity-Nutshell-A-Zee/dp/069114558X

DanielSank

10:17 PM

Weak measurement just means partial entanglement followed by projective measurement of half the system. It's not that amazing.

@vzn Who's kuhn?

Note however, that doing the experiments to really demonstrate this in the lab is pretty amazing and really hard.

vzn

@DanielSank ok. pretty much as ACM asserts. did not imagine others would say otherwise. but still think there are surprises in store. a marathon, not a race.

DanielSank

@vzn It's possible, but so far there's no evidence at all that makes me want to change quantum mechanics.

vzn

@DanielSank (briefly) kuhn is the guy that formulated the concept of paradigm shifts

@DanielSank in a sense, the heliocentric universe & copernican/ newtonian revolution did not change epicycles either :\

Mike Edenfield

@0celo7 Susskind's QM book was next on my list, but in his first book he implies that he's going to write a GR book as well.. do you know if he did?

vzn

since ppl are always hounding JD about predictions here is mine/ going out on a limb: weak measurements could (eventually/ subtly) restore locality to bell experiments.

DanielSank

10:22 PM

@vzn web.physics.ucsb.edu/~martinisgroup/papers/White2015b.pdf

:D

Slereah

Here is my prediction :

Future events such as these

►

DanielSank

@vzn put that in your pipe and smoke it.

@0celo7 I insist that you are adorable. Prove me wrong.

vzn

@DanielSank havent heard of BLGI. have you?

DanielSank

@vzn You must not have noticed my name in the author list... :-)

0celo7

@MikeEdenfield I don't.

@DanielSank Uh, what

You've obviously never met me

vzn

10:26 PM

@DanielSank touche/ way cool. anyway BLGI is violated with local realism is that the idea? the observation that violation is due to level of weak measurement is exactly what I was predicting...

DanielSank

@0celo7 You called me an engineer. I called you adorable. Game on.

@vzn :-D

0celo7

@MikeEdenfield Ok, after that QM book you should read Zee. It's fantastic and very accessible.

@DanielSank But...you are an engineer! I am too!

You're a physicsy engineer

DanielSank

@0celo7 Never said I wasn't. I simply posit that you are adorable.

0celo7

And I'm telling you that I'm not.

DanielSank