The h Bar

ACuriousMind

5:00 PM

@EmilioPisanty You and me both :P

Emilio Pisanty

@vzn well, I really liked Solo

I'll try to go to the Incredibles II if I can manage it

vzn

@EmilioPisanty no kidding eh? didnt do too well as far as box office

Emilio Pisanty

dunno what else is playing tho

@vzn yeah, so I've heard

enumaris

lots of things playing

vzn

star wars 4+ decades old now, kind of mindboggling, pop culture supervolcano

Secret

5:04 PM

Latest in the quantum research: There may be possible signs of the collapse field

vzn

> High accuracy measurements of the cantilever thermal fluctuations reveal a nonthermal force noise of unknown origin. This excess noise is compatible with the CSL heating predicted by Adler. Several physical mechanisms able to explain the observed noise have been ruled out.

...

Quantum Theory as an Emergent Phenomenon: Foundations and Phenomenology / Adler, IOPScience

> I review the proposal made in my 2004 book [1], that quantum theory is an emergent theory arising from a deeper level of dynamics. The dynamics at this deeper level is taken to be an extension of classical dynamics to non-commuting matrix variables, with cyclic permutation inside a trace used as the basic calculational tool. With plausible assumptions, quantum theory is shown to emerge as the statistical thermodynamics of this underlying theory...

enumaris

fancy

what theories don't predict wavefunction collapse?

like...what theories are gonna be ruled out if these results "prove" wavefunction collapse?

vzn

5:19 PM

havent heard of this specific theory before but have been "all over" emergent QM for years now. have similar questions & just now googling, this ref directly addresses your question. A proposal for the experimental detection of CSL induced random walk bera et al nature.com/articles/srep07664 ... CSL is a subtle modification of sch eqn dynamics & therefore is different than the following:

Secret

If objective collapse is real, epistemic models and Qbism will be out

and bohmian may possibly dies also

vzn

> These explanations can be broadly divided into two classes. The first class consists of those which modify the interpretation and/or mathematical formulation of quantum theory without altering any of its experimental predictions.
> These include the Copenhagen Interpretation, Bohmian Mechanics, the Many-worlds Interpretation, Decoherence-based explanations (typically accompanied by additional assumptions such as the environment being an open system, or the many-worlds assumption), and the Consistent Histories formalism.

this reminds me there are some new (somewhat radical) theories of gravity that predict its an emergent property of QM wavefn collapse...

enumaris

I though Bohmian mech was equivalent

Secret

tequantum.eu

enumaris

it's not actually equivalent to standard QM?

hmmm

Secret

5:25 PM

Bohmian is not entirely equivalent, because it has a nonlocal velocity field

Semiclassical

It's equivalent in terms of experimental predictions, hence why it's listed in there.

ACuriousMind

@enumaris Hm? Who says it isn't?

Semiclassical

in terms of its ontology it's certainly different

enumaris

but then if it's actually equivalent why can it be ruled out from showing "objective collapse"?

vzn

bohmian mechanics is "not exactly equivalent" in some sense because it doesnt reproduce "all" the predictions of QM, ie nonrelativistic ones... afaik its considered equivalent for relativistic regime...

Semiclassical

5:26 PM

Because objective collapse wouldn't be equivalent to standard QM.

enumaris

hmmm...standard QM has wavefunction collapse, is "objective collapse" something beyond that then?

Secret

QM is linear, but objective collapse has a nonlinear term to trigger the collapse

Semiclassical

the kind of 'emergent QM' being suggested by Adler is definitely different than standard QM

enumaris

so what...if the results hold standard QM can be ruled out?

ACuriousMind

@enumaris "Standard QM" has no collapse, having collapse or not is a property of interpretations, not of the formalism.

vzn

5:27 PM

@enumaris (reading quickly) CSL proposes a small experimentally measurable effect from collapse not predicted by the "straight" Sch eqn, the experimenters are announcing results consistent with it.

ACuriousMind

Unless by "standard QM" you mean Copenhagen, which...I discourage.

enumaris

so are we at the point of ruling out standard QM? :D

Semiclassical

I sometimes do conflate standard QM with Copenhagen, at least when talking about Bohmian stuff

enumaris

THE FOUNDATIONS OF PHYSICS ARE CRUMBLING

3

Semiclassical

but when I say that, I really mean something more like "the standard account of QM"

vzn

5:29 PM

CSL is also a (complex) classical theory where QM is emergent from its dynamics... (maybe not unlike what DS said he was searching for recently...)

enumaris

seriously tho, does this result rule out standard QM or what?

ACuriousMind

@Semiclassical I much prefer to distinguish clearly between the standard formalism - operators, wavefunctions, etc. - and any interpretation. Because some interpretations use the standard formalism but imbue it with different ontologies, while others like Bohmian mechanics actually also use a different formalism.

Semiclassical

@ACuriousMind that's fair.

though Bohmian mech does use wavefunctions and such

Secret

From what I understood, Qbism, Objective collapse and Bohmian all have different formalism from standard QM

Semiclassical

the way I'd put it with Bohmian mech is that it's standard QM + stuff

Secret

5:33 PM

Bohmian = Standard QM + quantum potential to generate trajectories
Objective collapse = introduce nonlinear term to S.E.
Qbism = some underlying POVM to reproduce density matrices in a bayesian fashion

Semiclassical

you still need wavefunctions in there; the wavefunction is what dictates the allowed trajectories of the particle

enumaris

sounds like vzn is saying this experiment rules out standard QM

ACuriousMind

@Semiclassical But the computations don't look quite the same. When you hand a Bohmian and a standard formalist the same task, they will agree on the result, but they don't arrive at it in the same way

Semiclassical

depends on the question

vzn

@enumaris (not exactly) it suggests QM is a high fidelity approximation...

Semiclassical

5:34 PM

for some things, like the evolution of a wavefunction from initial conditions, they'll arrive at it in exactly the same way: the unitary evolution of the Schrodinger equation

enumaris

But in a different way than QFT says QM is an approximation (i.e. non-relativistic approximation) amiright

Secret

anyway, if the collapse field is real, I hope they will figure out how to turn it off, cause frankly, I am tired of stuck in this classical body

enumaris

so is QFT also ruled out?

REKT

Semiclassical

well, it's like saying the results from the EM drive experiment "proved" that momentum isn't conserved

enumaris

I'm gonna go tell everyone the standard model has been definitively ruled out and now we have no foundation of physics to stand on.

vzn

5:36 PM

(lol) dont throw baby out with bathwater™

enumaris

"It's all just a theory" will be my new motto w.r.t. all of standard physics.

Semiclassical

there's always a balance to be considered: the likelihood that a lot of physics is wrong and has to be reconsidered, vs. the likelihood that the experimental results have been misinterpreted or sources of systematic error not accounted for correctly

vzn

new theories do not (exactly) reject prior theories.

ACuriousMind

@enumaris The abstract says very carefully that they have observed excess noise that is compatible with the noise Adler's CSL collapse theory predicts and that "several" explanations from known physics have been ruled out.

enumaris

It's published in a Phys rev. letter, I'm sure it can't be wrong

Semiclassical

5:37 PM

and when it comes to very small effects, the possibility of mistaking systematic error as new physics is high (c.f. OPERA)

vzn

@ACuriousMind in other words there is no other known explanation (so far) other than what Adler proposes, confirmatory evidence for his propositions/ theory.

Semiclassical

"several"

ACuriousMind

@vzn Just as there was no known explanation for CERN's FTL neutrino's other than neutrinos being faster than light at the time they announced it.

vzn

@ACuriousMind it could be nothing or it could be something. time will tell. but its got many years of research behind it and it meshes with other larger trends.

enumaris

So when/where's the death of QM party happening?

ACuriousMind

5:39 PM

Getting hyped on the results of a single measurement is always dangerous, especially in realms where lots of technical instrumentation is involved

enumaris

I don't want to miss out

ACuriousMind

Let's see if others can replicate it

vzn

agreed. & that could take awhile.

enumaris

Just like I didn't miss out on the death of Relativity party when the CERN results were published, and I didn't miss out on the discovery of the inflaton field party when the B-modes were discovered.

vzn

SL Adler has worked at IAS etc

Stephen L. Adler

Stephen Louis Adler (born November 30, 1939) is an American physicist specializing in elementary particles and field theory. == Biography == Adler was born in New York City. He received an A.B. degree at Harvard University in 1961, where he was a Putnam Fellow, and a Ph.D. from Princeton University in 1964. He is the son of Irving Adler and Ruth Adler and older brother of Peggy Adler. Adler was elected a Fellow of the American Academy of Arts and Sciences in 1974. He became a member of the Institute for Advanced Study in 1966, becoming a full Professor of Theoretical Physics in 1969, and was named...

enumaris

5:41 PM

I did miss out on the death of conservation of momentum party when the EM drive was discovered though...I just couldn't find where that party was being held :(

vzn

← intense FOMO on all the cool parties also, eg just missed this one due to scheduling conflict :P wired.com/story/…

enumaris

so much standard physics stuff gone!

vzn

poof

enumaris

evaporated

like grandma's perfume

her fortune has...evaporated

(Alex and Emma anyone? No?

Semiclassical

"Above all, this experiment neatly illustrates the fundamental challenge of collapse model testing. Negative results are robust, but positive claims require extremely careful and systematic work in order to exclude any conceivable alternative physical explanation."

enumaris

5:49 PM

just being overly cautious

they should title their paper "Quantum Mechanics is Dead - Here's Why"

vzn

May 11 at 1:27, by vzn

> Whether you can observe a thing or not depends on the theory which you use. It is the theory which decides what can be observed. ---Einstein https://en.wikiquote.org/wiki/Albert_Einstein

Semiclassical

I will say, I respect that they end their paper with the above.

vzn

@enumaris collapse :P

enumaris

We all know theory > experiment anyways

@vzn you're right "Quantum Mechanics Has Just Collapsed! - Here's Why"

better title

Semiclassical

collapse-bait :P

enumaris

5:54 PM

I'm totally for it

vzn

@enumaris lol in a radical mood at moment? ps have you ever heard of Tenev + Horstemeyer? spacetime fabric etc :P

enumaris

I have not

Semiclassical

one point that does make me cautious is that the citations to that article seem largely to be in papers by the same authors. (and the exceptions seem to cite the article in only a very slight sense)

that's not an entirely fair criticism, since the paper only came out last year

vzn

its a small but highly credible/ credentialed faction/ minority specifically working/ focused on the problem. not unlike many areas of physics. with this announcement it will likely expand "some," the only question is how fast/ much.

Semiclassical

so long as it's a result which is only cited in-network it's hard for me to know what credibility to assign it

bolbteppa

5:59 PM

@Blue no I did not use those 7 lectures, here are 16 following a mix of Landau and Goldstein to complement it mediacore.ictp.it/categories/classical-mechanics

vzn

@Semiclassical try looking at authors credentials...

bolbteppa

Lecture 1 | Classical Mechanics (PSI 16/17, Front End) - David Kubiznak (Perimeter) 2016.8.9 10:30

►

They are on youtube, easier than their site, wouldn't take them too seriously, they are supposed to be an overview

Semiclassical

Now I’m curious about the body with multiple handles in the background

Something something invariant torii?

I very vaguely remember those having to do with KAM theory

bolbteppa

Yeah it looks like the tori thing, but he was actually explaining manifolds and charts there, on the right you can see the transition between charts picture

danielunderwood

That's what that guy draws as a manifold in all his drawings

I guess to have more structure than a blob

Semiclassical

6:11 PM

ah, okay

bolbteppa

Semiclassical

right

Anonymous

@bolbteppa Oh, nice! You do seem have a lot of great resources up your sleeves :P

Anonymous

Thanks :)

danielunderwood

6:36 PM

Speaking of those lectures, he minimizes the action by writing $\delta L = \frac{\partial L}{\partial q} \delta q + \frac{\partial L}{\partial \dot{q}} \delta{\dot{q}}$ and takes the time to not be varying so $\delta{\dot{q}} = \frac{d}{dt} \delta{q}$. Is that correct?

Then I'd think that varying $L(q, \partial_t q, ..., \partial_t^n q, t)$ would lead to $\sum_{i=0}^n (-1)^n \partial_t^n \frac{\partial L}{\partial (\partial_t^n q)}$

Actually that isn't the case since the integration by parts in higher order terms would bring in boundary terms that wouldn't necessarily vanish

Though I am curious if that's at least on the right track

bolbteppa

No that means $\delta \dot{q} = \dot{q}(t + \delta t) - \dot{q}(t) = \frac{d}{dt} q(t + \delta t) - \frac{d}{dt} q(t) = \frac{d}{dt} [q(t+\delta t) - q(t)] = \frac{d}{dt} \delta q$

danielunderwood

So it's not the case that it only works for $\delta t = 0$ like he said?

And it looks like it would work for higher orders too? $\delta \ddot{q} = \ddot{q}(t + \delta t) - \ddot{q}(t) = \frac{d^2}{dt^2} (q(t + \delta t) - q(t)) = \frac{d^2}{dt^2} \delta q = \frac{d}{dt} \delta \dot{q}$ or am I missing something there?

Huh the diff eq I ended up with is on the wikipedia page for EL

bolbteppa

6:59 PM

The claim of the principle of least action is that the extremum of $S = \int_{t_1}^{t_2} L(t,q,\dot{q})dt$ describes the real world, thus varying $S$ we find
\begin{align}
\delta S &= \delta \int_{t_1}^{t_2} L(t,q,\dot{q})dt \\
&= S(t,q+\delta q,\dot{q} + \delta \dot{q}) - S(t,q,\dot{q}) \\
&= \int_{t_1}^{t_2} \delta L(t,q,\dot{q})dt \\
&= \int_{t_1}^{t_2} (\frac{\partial L}{\partial q}\delta q + \frac{\partial L}{\partial \dot{q}} \delta \dot{q})dt \\
&= \int_{t_1}^{t_2} (\frac{\partial L}{\partial q}\delta q + \frac{\partial L}{\partial \dot{q}} \frac{d}{dt} \delta q)dt \\

The formal justification for the last step is

Fundamental lemma of calculus of variations

In mathematics, specifically in the calculus of variations, a variation δf of a function f can be concentrated on an arbitrarily small interval, but not a single point. Accordingly, the necessary condition of extremum (functional derivative equal zero) appears in a weak formulation (variational form) integrated with an arbitrary function δf. The fundamental lemma of the calculus of variations is typically used to transform this weak formulation into the strong formulation (differential equation), free of the integration with arbitrary function. The proof usually exploits the possibility to choose...

Arnold proves it in his book, so does Gelfand

If you include higher derivatives in your action, $S = S(t,q,\dot{q},\ddot{q},\dots)$ you get higher-order EL equations as in the wiki

danielunderwood

So what I wrote is kind of the same but sloppy as far as the math goes?

bolbteppa

Last sentence looks fine

enumaris

just do it

danielunderwood

7:21 PM

Hey if I take "just do it" I get $\partial g_{\mu \nu} = \partial_\sigma g_{\mu \nu} \delta x^\sigma + \frac{\partial g_{\mu \nu}}{\partial (\partial_\sigma x^\rho )} \delta (\partial_\sigma x^\rho)$. Though I would be genuinely surprised if that's correct

And it probably makes people the people who actually know GR cry

Oh no that first was supposed to be $\delta g_{\mu \nu}$

bolbteppa

How did you get that for $g_{\mu \nu} = g_{\mu \nu}(x)$

Beta Decay

Hey guys. You know how you have the Schwarzchild Metric for a spherical mass. Is there an equivalent metric for Newtonian gravitation (i.e. you could use the Newtonian metric to model the Sun-Mercury system which would show no apsidal precession)?

danielunderwood

Oh right. I was thinking $g_{\mu \nu}(x, \partial_\sigma x)$, which doesn't really make sense. Then the second term would go away. But I was just taking what I thought I knew and throwing it at the metric. No clue if it's actually valid

Slereah

@BetaDecay Newtonian gravity typically doesn't use a metric

Beta Decay

@Slereah I know, but is there a metric which would model it?

Slereah

7:27 PM

Well it is the Schwarzschild metric

bolbteppa

The Schwarzschild metric should model it in the Newtonian approximation

Beta Decay

But that will show the precession of the orbit

Slereah

you can't model newtonian gravity in GR because the basic structure of space isn't the same

if you want you can use the Newton-Cartan model

Newton–Cartan theory

Newton–Cartan theory (or geometrized Newtonian gravitation) is a geometrical re-formulation, as well as a generalization, of Newtonian gravity first introduced by Élie Cartan and Kurt Friedrichs and later developed by Dautcourt, Dixon, Dombrowski and Horneffer, Ehlers, Havas, Künzle, Lottermoser, Trautman, and others. In this re-formulation, the structural similarities between Newton's theory and Albert Einstein's general theory of relativity are readily seen, and it has been used by Cartan and Friedrichs to give a rigorous formulation of the way in which Newtonian gravity can be seen as a specific...

bolbteppa

Well the Schwarzschild metric is literally defined by the fact that it reduces to the Newtonian $1/r$ case in the non-relativistic limit, so you can at least approximate with it

Slereah

I mean if you really want to push it

bolbteppa

7:29 PM

I don't know a definition of $g_{\mu \nu}$ involving $\partial_{\sigma} x^{\rho}$

Slereah

You can use an even simpler metric to simulate local gravity

$$ds^2 = -\alpha dt^2 + dx^2$$

This is just a constant acceleration

and it's just Minkowski space with different coordinates

danielunderwood

@bolbteppa Yeah I don't either. I just had varying the Lagrangian stuck in my head and put it in there for some reason

bolbteppa

Yeah it's confusing :p

danielunderwood

Huh apparently my school has a GR wiki grwiki.physics.ncsu.edu/wiki/Main_Page

gateprep

What is diffraction?Whay does it occur..

Why doesn't light pass through straight?

ACuriousMind

7:40 PM

@gateprep Have you tried reading e.g. the Wikipedia article on the subject?

Slereah

magic

gateprep

@ACuriousMind

Yes I have...

I dont understand why it bends...

Not convinced bright and dark spots is quite convincing

ACuriousMind

@gateprep So you might get a more useful response from us if you indicate what specifically you didn't understand about what's written there.

gateprep

Why does that light bend?

ACuriousMind

That's...not more specific, really.

Anonymous

7:42 PM

You're literally asking people to explain the whole chapter of a general physics textbook to you :P

gateprep

Ok first tell me why it bends

danielunderwood

Fermat said so

Oh right diffraction

Beta Decay

Huygens said so

danielunderwood

There we go. Different guys control different properties

Anonymous

Lol

ACuriousMind

7:46 PM

@gateprep I've told you thrice now to be more specific, since that is explicitly explained in the "mechanism" section of the Wikipedia article you claim to have read.

enumaris

uhhh

hoorah

Anonymous

8:02 PM

@enumaris How's the L&L reading goin? You were reading volume 1, right?

enumaris

yeah, I got busy tho lol

Anonymous

Is it nice? I only read the first few pages of it

enumaris

pretty succinct

not bad as a non-introductory text

Anonymous

Does it cover coordinate free stuff too btw?

Anonymous

@enumaris I see

enumaris

8:04 PM

in mechanics? Certainly there's talk of vectors and stuff...

it's not all expanded into coordinates

Anonymous

@enumaris I meant contact geometry, symplectic geometry etc stuff

Anonymous

@enumaris Oh, gotcha

enumaris

contact geometry?

Slereah

@Blue ew

danielunderwood

Does the Einstein-Hilbert action mean that gravity wants to minimize the total curvature of the universe?

Slereah

8:07 PM

If there is no matter and you mean the scalar curvature, then I suppose, yes

Also plz

extremize

not minimize

Anonymous

@enumaris Umm: en.wikipedia.org/wiki/Contact_geometry

Anonymous

@Slereah Why ew? :P Is it too bad?

danielunderwood

stationarize :D

enumaris

no, they don't go over differential geometry concepts in a mechanics text lol

Slereah

@Blue veryt bad

Anonymous

8:08 PM

My current understanding of CM is very superficial. So I'm trying to understand the differential geometry approach to it

Anonymous

I found a few lectures (recommended by bolbteppa and the Perimeter lectures)

enumaris

You're better off learning from a Mathematical physics text then

Anonymous

They seem to cover those stuff

Anonymous

Haven't reached to that part yet though

bolbteppa

I wouldn't recommend the symplectic approach to mechanics, I would recommend L&L vol. 1

Slereah

8:09 PM

symplectic approach, aka

hamiltonian mechanics

bolbteppa

Then read Arnold as a re-write of L&L with symplectic stuff thrown in mainly so you can prep to learn integrability

enumaris

Physics texts will sometimes touch on the symplectic nature of the Hamilton equations, but few will go into the geometric meaning of it

Slereah

overall there isn't much reason to

i think you can find that stuff in like

Hamiltonian mechanics in GR

or fiber bundle Hamiltonian stuff

enumaris

unless you're learning Mechanics in an applied math department

bolbteppa

That's like saying we should ignore second order ode's because first order systems of ode's are 'geometric'

Slereah

8:10 PM

where it's all abstract on a manifold

Anonymous

@bolbteppa I see. Makes sense

enumaris

I did learn about the symplectic manifolds and all that stuff

but it was in a math class

not a physics one lol

Anonymous

I really don't care about the physics...not at the moment at least :P

Slereah

I mean in the end you pretty much always use the same symplectic form anyway

enumaris

the prof was very obviously a mathematician first - who really just cared about the mathematics

Slereah

8:11 PM

There isn't much reason to get fancy with it

It's always $\omega = ((0,1), (-1,0))$

enumaris

$\Omega$

bolbteppa

If you learn physics like a mathematician you'll end up on ncatlab making no sense, you've been warned :p

Slereah

I do love papers that start like that

this is how u know

ACuriousMind

@Slereah There is - for gauge systems you have to care about whether or not there is a proper symplectic form induced on the constraint surface

Slereah

is that related to the regularity conditions of the constraints?

ACuriousMind

8:16 PM

Partly

But also to whether they are first-class or second-class

Slereah

I should get down with constraints at some point rly

What's the most non-henneaux book on constraints?

bolbteppa

Dirac's little book? :(

Emilio Pisanty

huh

14

Q: Community Promotion Ads - 2017

It is a bit late into this new year, being that we're already in the second month, but we are now cycling the Community Promotion Ads for 2017! What are Community Promotion Ads? Community Promotion Ads are community-vetted advertisements that will show up on the main site, in the right sidebar....

bolbteppa

I have Dirac's little book and one by Regge to go through, trying to pick up things on the side

Emilio Pisanty

I thought the Community Ads threads got dupeclosed by default when the new one got posted

but apparently not

it's always just been @Qmechanic hard at work behind the scenes

but it's nice that I get the chance to use my Dupehammer On Meta

Slereah

8:24 PM

@bolbteppa Lectures on Quantum Mechanics?

bolbteppa

Yeah, the Yeshiva ones

Slereah

Henneaux is fine and all, but

he's not big on examples

bolbteppa

They made more sense the last time I looked at the early sections a while ago anyway, seemed pretty readable and quick

Slereah

Well it's probably fine once you roughly know how it works

but for a first read

not great

enumaris

greato

hey friendo

bolbteppa

8:31 PM

Prof. Rabin Banerjee - Pedagogic Introduction to Constrained Dynamics 1 - 11.09.14

►

Slereah

thx

bolbteppa

Skimming the two lectures there, looks like they basically explain the first lecture of Dirac's notes, I should just go through them tbh to revise, look good

Anonymous

SN Bose center has a youtube channel, didn't know. Cool :D

bolbteppa

There's 4 not 2 lectures on the channel, cool

Slereah

8:49 PM

Is there like

A nice simple one dimensional example of constraint

enumaris

10:39 PM

wtf....

how are all these common words missing in nltk's words.words()...

danielunderwood

10:52 PM

Just for sanity, those words don't happen to be things like "a" and "the" do they?

Nevermind those are definitely in there

On a related note, I finally actually submitted something for a kaggle competition. Usually it's just joining it and forgetting about it lol

enumaris

"has" is not in there

"number" is not in spacy's vocabulary

so weird

weird stuff

so inconvenient

vzn

11:14 PM

Improved Noninterferometric Test of Collapse Models Using Ultracold Cantilevers-- experimental anomaly detected/ measured wrt standard QM favors Adler CSL emergent QM model reddit.com/r/quantum/comments/8zpzqa/…

Cows

11:58 PM

A few things. So during my post-coding walk I ran accross some kids(engineering students from ASU). They are working on their hyperloop pod. I spoke to one of them. I also inspected the tube a few times from a distance during commutes and exercise walks. It is now longer and epic

I hope ASU wins. The competition is Sunday if I remember correctly

Hehe

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