The h Bar

Slereah

2:01 PM

0celo7

do people seriously have chewing tobacco in their pockets

Slereah

One of the slide from my master thesis presentation :p

0celo7

get your shit outta here

FenderLesPaul

jesus wtf

Slereah

"And as you can see, after solving that integral..."

0celo7

2:01 PM

lol, Jewish indices

FenderLesPaul

index game so strong even the census is jealous

Slereah

I RAN OUT OF LETTERS

0celo7

this is why no one likes GR

$\zeta,\xi,\omega,\pi$

FenderLesPaul

start using penrose notation

Slereah

what's a xeta

0celo7

2:02 PM

still plenty of letters left

Slereah

(also I wanted to have some index fun)

"Greek letters are used to indicate culture, Gothic letters are used because they're pretty, Hebrew letters are used for religious reasons, and Cyrillic letters are avoided for political reasons."

0celo7

seriously

Dr. Parsons tamed his beard

he looks less like a homeless santa now

0celo7

2:34 PM

Why is the chat so dead

Slereah

Do you want to talk about GR

Quick while JD isn't here

0celo7

In physics

Let's talk about pulleys

GR pulleys

Did JD get chat banned? Probably.

I wonder for how long.

Slereah

He was briefly chat banned yesterday

John Duffield

@0celo7 : how many time do I have to tell you mathematics is not evidence? Physics experiments provides evidence. You make photons intersect in a vacuum, and you get electrons and positrons. If your mathematics says it doesn't happen, your mathematics is wrong.

I had a half-hour break courtesy of some robot that detected an expletive.

NeuroFuzzy

good morning!

Slereah

2:44 PM

Hello

0celo7

@JohnDuffield I'm ignoring you because you're too smart and are making my cry from your smartness. I'm just a dumb kid after all. You win.

@NeuroFuzzy morning calibro

Slereah

Don't say it, just do it

that is the best way to ignore a bloke

The Dark Side

OMG. You guys are still stuck in the same loop!!

(Einstein and the Evidence)

0celo7

@FenderLesPaul I know you're into condensed matter stuff. Any book recommendations?

I'm not looking for stuff that jumps to TQFT and gauge theory in the first chapter.

ACuriousMind

Feel free to recommend that stuff, too, though ;D

0celo7

2:55 PM

I want something to learn more about basic structure and thermodynamics of solids.

@ACuriousMind Well, sure.

But I don't think ~~Maik~~ Lord Protector Prof. Dr. Herr Mr. Lang will know what I'm going on about if I read one of those

There's 80 pages of condensed matter books on Springer.

NeuroFuzzy

@ChrisWhite I like that POV! Not that I'd ever echo it in a physics classroom. I'd get marked wrong immediately :P

Section of the tensor bundle FTW though

The Dark Side

Looks like I completely missed the battle:

-2

Q: The electron is a 511keV photon going "round and round." How does this work?

I'm curious about the properties of the electron as given in this PSE post. I always thought the electron was an excitation in the electron field. Apparently that's not true and it is a photon going round and round in a Dirac's belt configuration. I have some questions regarding this: How does ...

But I am curious regarding why the question got a -2 (=+3-5), I think it is well posed.

0celo7

@TheDarkSide Thank you, I thought it was quite good as well.

I wonder who upvoted and who downvoted

Slereah

3:22 PM

obviously the trolls

0celo7

Did you vote

Slereah

I did not

I'm not a troll

0celo7

Wow you always vote your friends' questions

I wonder when the meta post will drop

I wonder what it's gonna be about

0celo7

3:38 PM

@Slereah is our universe globally hyperbolic?

Slereah

Who the fuck knows

0celo7

JD, Hawking

Slereah

Hawking only deals in pop science nonsense, doncha know

If there's an initial singularity it is not, I suppose

0celo7

Does the concept of "globally hyperbolic after some time t" exist

Also

How on earth do you get the initial data on a Cauchy surface

Is there a metric measuring device

Slereah

Well it's a math object

You're not required to measure it

Just be aware that it existzs

0celo7

3:46 PM

Ok but how does numerical relativity work if we can't measure the thing it evolves

Slereah

Well you can measure the metric I suppose

0celo7

How

Slereah

Interferometry

Though I think numerical relativity mostly suppose the metric from the mass distribution

0celo7

Has that ever worked

Slereah

Well it is what is used to detect gravitational waves

So no :p

You can also check light deviation

0celo7

3:48 PM

That's what I thought

Slereah

which does work

And you can check time dilatation

and recently we've been able to measure frame dragging

IIRC if you want the set of measurements used to check metrics and such, it is best to check the... post newtonian approximation?

Parameterized post-Newtonian formalism

Post-Newtonian formalism is a calculational tool that expresses Einstein's (nonlinear) equations of gravity in terms of the lowest-order deviations from Newton's law of universal gravitation. This allows approximations to Einstein's equations to be made in the case of weak fields. Higher order terms can be added to increase accuracy, but for strong fields sometimes it is preferable to solve the complete equations numerically. Some of these post-Newtonian approximations are expansions in a small parameter, which is the ratio of the velocity of the matter forming the gravitational field to the speed...

Parameterized post-Newtonian formalism

Post-Newtonian formalism is a calculational tool that expresses Einstein's (nonlinear) equations of gravity in terms of the lowest-order deviations from Newton's law of universal gravitation. This allows approximations to Einstein's equations to be made in the case of weak fields. Higher order terms can be added to increase accuracy, but for strong fields sometimes it is preferable to solve the complete equations numerically. Some of these post-Newtonian approximations are expansions in a small parameter, which is the ratio of the velocity of the matter forming the gravitational field to the speed...

That part especially

0celo7

I know about that

Weinberg has a chapter on it. Also Straumann but I skipped it on my first reading

John Duffield

@0celo7 : "I'm just a dumb kid after all. You win". Next time I give you a reference to some robust scientific evidence from a reputable source, pay attention to it instead of dismissing it because it doesn't tally with some maths in some junior textbook you've read.

@0celo7 : ask the question, and I'll answer to the best of my ability.

@0celo7 : I upvoted it. And voted to leave it open.

@Slereah : the metric is an abstract thing derived from measurement.

Slereah

4:05 PM

every value is an abstract thing derived from measurement.

John Duffield

Not true. I hold my hands up a metre apart, and the distance between them is real, not abstract. See this answer where I talked about the Riemann curvature depiction as per your PPN link and my avatar. You can plot this using equatorial light clocks. Your plot of measurements is curved, your metric is curved. But space isn't.

Slereah

Informer You know say Daddy Snow me, I'm gonna blame A licky boom-boom down

vzn

4:36 PM

Bell inequality violation finally done right / Aaronson

vzn

5:16 PM

@0celo7 how to make your own homemade clock that isnt a bomb / wired. sad commentary on STEM study vs terrorism paranoia in US. :(

dmckee

@vzn Finally something that ought to be stared in here. Seriously, guys, this is the sort of thing that should be hanging around in the sidebar.

John Duffield

@vzn : try explaining what the experiment actually did. If you struggle, you might want to take a look at the paper. Then ask yourself if you understand electron spin, or the two spins are prepared into the entangled state. Mighty oaks from little acorns grow. And grand claims grow from experimental results you can't actually see.

vzn

@dmckee agreed, a very impressive level of technical/ experimental sophistication but also at the theoretical level as well.

user54412

Sep 6 at 6:14, by Chris White

I never understood this loophole business.

user54412

Sep 6 at 6:14, by Chris White

I mean, I can always claim my wrong theory is correct by saying prancing unicorns in subspace are to blame for its erroneous predictions. But that doesn't really count as a scientific argument.

vzn

5:18 PM

@JohnDuffield JD have some sympathy for loophole proponents/ advocates (am nearly one myself). think there is something (long) hiding in this that hasnt been isolated yet. just said earlier, think it might be significant that its so hard/ difficult to close all loopholes simultaneously. wonder if weak measurement can be combined with bell tests. think someone might figure it out soon. wish it could be me :|

ACuriousMind

@vzn I wouldn't say this is theoretically interesting. The experimental achievements are impressive. The result is utterly expected by all but those who still don't think quantum mechanics is right.

0celo7

I've never understood why JD says I do "kiddie physics" and "popsci" when I don't own and have never read a popular science book.

vzn

@ACuriousMind the use of the eberhard inequality instead of CHSH is the theoretical finesse/ advance.

0celo7

@ACuriousMind still unconvinced ~~~

vzn

to me, Bell was not very aware of the concept of "fair/ biased sampling" loophole. eberhard inequality seems to be more careful. actually Bell tended to be rather removed from experimental subtleties. his original ideas might not even have been intended for photons in particular!

John Duffield

5:22 PM

@vzn : I have no sympathy for shut up and calculate or quantum mysticism or tedious handwaving explanations that don't actually make it clear what was measured and how. Make sure you read arxiv.org/abs/0707.0401 by Travis Norsen.

"Many textbooks and commentators report that Bell's theorem refutes the possibility (suggested especially by Einstein, Podolsky, and Rosen in 1935) of supplementing ordinary quantum theory with additional ("hidden") variables that might restore determinism and/or some notion of an observer-independent reality. On this view, Bell's theorem supports the orthodox Copenhagen interpretation. Bell's own view of his theorem, however, was quite different."

vzn

@JohnDuffield have read norsen years ago, think he has something to contribute.

user54412

Internet bonus points to anyone who can locate the (original, Russian) article "A difference scheme for numerical computation of discontiuous solutions of equations of fluid dynamics" by Godunov, Matematicheskii Sbornik, 1954

vzn

my own view, there are very intense/ deep subtleties in this area. think the two camps have become "polarized"...

ACuriousMind

@vzn The paper talks about Bell-CHSH violation. They cite Eberhard, but they do not explicitly talk about using an "Eberhard inequality", nor does the blog post.

John Duffield

@vzn : agreed. I was gobsmacked to see quotes like this:

"Indeed, Bell even went so far as to suggest, in response to his theorem and the relevant experimental data,17,18 the rejection of “fundamental relativity” and the return to a Lorentzian view in which there is a dynamically privileged (though probably empirically undetectable) reference frame: “It may well be that a relativistic version of [quantum] theory, while Lorentz invariant and local at the observational...

vzn

5:25 PM

@ACuriousMind huh? was just skimming it. they use eberhard inequality. maybe it was the nature article. there are multiple papers out now.

John Duffield

"...level, may be necessarily non-local and with a preferred frame (or aether) at the fundamental level."

ACuriousMind

@vzn Well, I just looked through the one Aaronson's blog post cites in the beginning. They definitely report Bell-CHSH violations.

vzn

alas, to state the obvious, bell has been dead for years. same with EPR. physics moves on. suspect it is soon that all Bell/ EPR/ Bohm/ Copenhagen/ Bohr will all be seen to be correct in the sense of the "blind men & the elephant".

its a very tricky elephant.

John Duffield

@vzn : I think the weak measurement stuff will sweep it all away.

Sorry, I have to go. Time for tea. And it's Wednesday. Time for a glass of wine!

vzn

@ACuriousMind Eberhard inequality is stronger/ more strict than CHSH & takes into account so called "undetected" events. if you can satisfy Eberhard inequality then CHSH is also satisfied afaik/ affaict.

FenderLesPaul

5:28 PM

@0celo7 idk any book that jumps into that stuff in the first chapter

but I really like Altland and Simons

"Condensed Matter Field Theory"

it's fucking amazing

0celo7

"field theory"

that's probably the wrong direction

vzn

@JohnDuffield agreed weak measurement is likely to be understood as a gamerchanger "soon". was just arguing that in this chat room.

0celo7

yes, that's the wrong direction

vzn

radical thought (recently musing on this): weak measurement restoring the concept of locality, in a very subtle way.

0celo7

@FenderLesPaul something like this

ACuriousMind

5:31 PM

I have no idea why some people think weak measurements will "change" anything. They are describable within the very same framework as strong measurement - quantum mechanics. Weak measurements are not an addition to quantum theory, they've been there from the start (albeit it took people a while to notice they might be interesting/useful).

vzn

@ACuriousMind show me the mathematical axioms for "weak measurement" in quantum theory.

0celo7

I'm tempted to buy this book

Slereah

I have a physics problem

I am cold

What do I do

0celo7

but my poor reading list

vzn

weak measurement theory/ survey/ overview, from this nice ref recently found by @Secret, Tamir/ Cohen

Sep 12 at 15:55, by Secret

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

0celo7

5:37 PM

::facepalm::

bible verse in an email signature

I've seen it all

vzn

p11 "Here g(t) is a coupling impulse function satisfying..." (eq11). now, where is this concept found in the standard QM mathematical formalism/ axioms?

ACuriousMind

@vzn There's no "axiom" for it. But you can write down a typical von Neumann measurement scheme that couples the pointer device to the state to be pre- and post-selected, and results in the pointer being shifted by the weak value, all inside the standard formalism

vzn

it appears that weak measurement meshes with prior QM theory, but is not derived from it. this section of the paper defines a new concept of weak measurement. std QM is about strong measurements.

ACuriousMind

The $g(t)$ is precisely the thing modelling the coupling of the device to the state to be post-selected.

vzn

the distinction is subtle to anyone who is not a mathematician. but its exactly what EPR were arguing for. incompleteness

ACuriousMind

5:40 PM

@vzn Yeah, weak measurement is a particular kind of quantum interaction. Just as strong measurements are another kind. Standard QM is, in no way, "about measurements", it is about having a valid theory of mechanics (i.e. the behaviour of systems).

vzn

QM is a physical theory and a set of axioms. those axioms are revised by weak measurement. its new theory.

ACuriousMind

And if you want to understand weak measurements, you have to study these pre-/post-selection interactions, if you want to understand strong measurements, you have to study decoherence/einselection.

But none of these add any new axiom to quantum mechanics.

vzn

@ACuriousMind are you familiar with the axioms?

axioms can be extremely subtle. it literally took millenia for mathematicians to realize/ demonstrate/ prove the parallel postulate is independent of other euclidean axioms.

ACuriousMind

@vzn Yes. (Although there are different formulations, typically one takes the Dirac-von Neumann axioms)

vzn

it appears to me this moment that weak measurement introduces an independent axiom to strong measurement (std) QM theory.

eventually, weak measurement may make predictions that cannot be made by std QM (but also do not conflict with it) and is nearly already doing so afaict.

ACuriousMind

5:44 PM

@vzn Again, weak measurement is described with in the standard QM formalism.

It can't make "non-QM predictions" because it is QM.

vzn

@ACuriousMind what is the std QM formalism? where is it defined?

ACuriousMind

@vzn E.g by the Dirac-von Neumann axioms I just linked

Note that they do not refer to any kind of measurement, strong or weak.

vzn

anything you want to point to as defining std QM does not refer to weak measurement

@ACuriousMind ofc it refers to measurement!

ACuriousMind

@vzn Yes, because weak measurement is just a particular type of an interaction between systems. There's no need to talk about particular types of interactions in the axioms.

vzn

@ACuriousMind lol QM/ axioms is about "interactions"

Dirac–von Neumann axioms

In mathematical physics, the Dirac–von Neumann axioms give a mathematical formulation of quantum mechanics in terms of operators on a Hilbert space. They were introduced by Dirac (1930) and von Neumann (1932). == Hilbert space formulationEdit == The space H is a fixed complex Hilbert space of countable infinite dimension. The observables of a quantum system are defined to be the (possibly unbounded) self-adjoint operators A on H. A state φ of the quantum system is a unit vector of H, up to scalar multiples. The expectation value of an observable A for a system in a state φ is given by the inner...

zip/ zilch/ nada about weak measurements

it refers to observables

ACuriousMind

5:51 PM

@vzn I've repeated several time now that you shouldn't expect there to be. The Hamiltonians of weak measurements like $H = g(t)PO$ for the weak interaction $g(t)$, some pointer thingy $P$ and an observable $Q$ are perfectly fine Hamiltonians within standard QM

And the predictions about weak measurements are again derived by the standard procedure of letting the Hamiltonian (as the observable for energy) generate time evolution and so on

vzn

agreed it does not conflict with QM, it meshes. its a subtle point. it will likely take (many) years for experts to realize it. :|

ACuriousMind

There is no need to add axioms, weak measurements are just the results of a particular choice of interaction

vzn

there seem to be experimental weak measurements that are not predicted by classic QM. it will take awhile to formalize/ unify them into a (new) theory. they are probably scattered as bits & pieces of eqns right now, unrecognized/ not recognized as coherent.

what does QM say about $g(t)$? maybe that is the crux of the new theory. genuinely new physics lurking in $g(t)$...

ACuriousMind

@vzn Nothing, it's something that describes the measurement/interaction and depends on the experimental setup/how the pre-/post-selection is done.

vzn

so QM says nothing about $g(t)$ but it can be measured somehow? hmmm, experiencing some cognitive dissonance on all this :|

ACuriousMind

6:02 PM

Like all other Hamiltonians/Lagrangians, it's something you have to (educatedly) "guess" until the theories predictions agree with experiment.

@vzn Already in classical mechanics, you can't derive from the theory that the Hamiltonian of a free particle is $\frac{p^2}{2m}$. It's nothing unusual.

(And it is nothing unusual because Hamiltonians have a large kind of freedom - many different Hamiltonians (and Lagrangians) may describe the very same system, after all)

0celo7

these QM discussions are quite boring

none of this crap in good ol Newtonian mechanics

ACuriousMind

That's where physics becomes different from mathematics - you need experimental input to decide the correct form of the Hamiltonian, or the correct expression for the forces in Newton's law, and so on.

0celo7

by Occam's razor Newtonian mechanics is a theory of everything

vzn

@ACuriousMind it feels like a clever "sweeping under the rug" to me currently. or a sort of quantum epicycle theory. it will take longer to pinpoint.

0celo7

my work is done, you can thank me now

ACuriousMind

6:06 PM

@0celo7 I think you just cut yourself with that razor :P

0celo7

Lang is not in his office

great

@ACuriousMind please locate him

ACuriousMind

@0celo7 wat

0celo7

use your German mental link

ACuriousMind

I do not know what you are talking about.

I must go.

Assassins have been dispatched to your location.

vzn

@ACuriousMind kinetic energy derived / wikihow

0celo7

6:10 PM

@ACuriousMind I've played enough video games to know how to dispatch European assassination squads

lemme get out my karambit and Five-seveN...

+1 for anyone who gets the reference

ACuriousMind

@vzn No...I don't want the derivation of kinetic energy, but that of the Hamiltonian. Contrary to popular belief, it is not necessary for the Hamiltonian to equal potential + kinetic energy (and in fact false for things such as constrained or covariant systems). Nothing in the axiomatization of Hamiltonian mechanics tells you what the Hamiltonians are, except that they generate time evolution.

0celo7

:(

no one likes the games I like

you and your constrained systems

QoGS has turned you into a broken record

vzn

@ACuriousMind so in your words then there seems to be a new physics of the nature of constrainedness/ covariance of weak measurements.

it seems to be a new type of constrainedness/ covariance.

vzn

6:54 PM

@ACuriousMind it seems in some sense that QM does not describe any interaction between some pre/ post selection measurements. ie they are randomly related. weak measurement seems to find some nonrandom correlation. "the devil is in the details"

user54412

7:39 PM

user54412

wut

user54412

arxiv's getting as shamelessly beggy as wikipedia

vzn

8:05 PM

@ChrisWhite billionaire sponsorship is just not enough these days :|

ACuriousMind

-2

A: Why does a gas inside a closed container experience atmosperic pressure when the gas itself is not in contact with the atmosphere?

deez nuts deez nuts deez nuts deez nuts

Great contribution.

0celo7

Indeed. +1

@ChrisWhite did you donate?

user54412

8:26 PM

@0celo7 No, but unlike certain universities in Tennessee, my school already donates :P

0celo7

@ChrisWhite we have no monies

they already hiked tuition 15%

and they're building a new nuke building

no monies, we're poor

bolbteppa

8:44 PM

re epicycle-bashing - epicycles were actually just Fourier approximations to elliptic orbits so they actually were correct if properly interpreted motls.blogspot.ie/2008/07/myths-about-epicycles.html physicsforums.com/threads/… ;)

vzn

@bolbteppa "correct" "approximation" mathematically but the problem is they ("the formalism") helped obscure/ hide the "interpretation" of a heliocentric universe for ~1½ millenia

getting past them as a mindset was partly key to the copernican revolution...

0celo7

Copernicus was a punk

he's up there with Luther on the list of greatest punks

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