Decoherence and the Quantum Theory of the Classical - ICTP Colloquium

[@abhinavtripathi3119]

Didn't know Bob Ross did Physics on the side

[@DKshad0w]

lel, now I can't unsee it

[@JoaoMatrix]

I was about to comment that lol

[@xjuhox]

Dr. Quantum, David Schultz

[@ASLUHLUHC3]

I hope one day I can understand anything he's going on about

[@abanoubmikhail9632]

Great lecture.

[@schmetterling4477]

The quantum theory of the classical was already explored by Mott in his 1929 paper on the emergence of particle tracks from wave mechanics. It's basically just the result of conditional probability. It's amazing that some people still didn't get the message.

[@levk4321]

Thanks for great presentation. Just two comments which can be also seen as questions: 1. Quantum states of the measurement device A, |A_u> and |A_v>, still would require additional measurements in order to tell them apart, and I do not see how this process would end without a "classical device" and a "consuous observer" at the end. So, the postulate 4 is not really fully derived from 1 to 3 as a statement is still needed about the wave function collapse. 2. The Born's rule can be "derived" once the concept of probabilistic interpretation of the wave function (or general quantum state) is introduced. What shown in the lecture is the technicality of non-selfcontradictory asignment of the probabilities to outcomes. So, the postulate 5 is not really derived from 1 to 3, rather the consistency (and uniqueness) of probability assignment as |a|^2 is shown. The postulate 5 itself can be formulated as the statement of probabilistic interpretation of the quantum state measurements, for which Born got his Nobel prize. I did find the argument based on entanglement to be elegant.

[@chryles]

Wouldn't measuring the quantum states of the measuring device just add another level of complexity, because the device measuring the measuring device would then be part of the system and you would need to measure the device that is measuring the measuring device... Ad infinitum?

[@robmorgan1214]

@@chryles hello Feynman... yes. But the real question is can you truncate the series and if not does it converge? The answer to self interaction is yes. This effect has been measured to very high precision and is calld the lamb shift. To me this is ine of the coolest part of quantum mechanics since it points to more going on in the world than basic linear algebra.

[@robmorgan1214]

I'm no rocket surgeon so I can't say much about your first question however I think I know the answer to the second.

[@robmorgan1214]

Answer to question 2. Disclaimer: I probably need to watch it again more carefully...but... I think the whole point is specifically to avoid the assignment of a probabilistic interpretation to the theory but to arrive at one as a result of the other purely mathematical assumptions (which essentially boil down to something like... Dirac: "...qm happens in Hilbert space...ask me how!"). This guy takes that assumption and stretches it out to imply an orthogonality condition, then the probabilistic interpretation, and finally the born rule by manipulating the equations of an obviously valid (aka "trivial" in physicist speak) test case that eliminates any other consideration. It's an explicit proof by example, which by nature of its construction contains an implicit proof by counter example, namely: If this example exists then I am left with only one choice in how to proceed when using these primitive objects to describe this system... calling it the Pythagorean theorem of Hilbert space is a way to hammer home the geometric nature of the interpretation (which is basically the same thing as crack to most physicists). Essentially the whole talk can be summarized by paraphrasing gentleman with a nice beard: "...once you start down the road of Hilbert space forever will it dominate your destiny." When looking at physical theories you do math and that math, if it's descriptive, allows you to manipulate it; and then, if it's self consistent, you have to identify the things it says as concepts in the real world... assume this stuff is true using these mathematical ideas...the same math also says this other stuff stuff so how do we interpret it in the physical world...from there it's usually a straight shot to making testable predictions (typically called calculations) that the knuckle dragging wrench enthusiasts (aka experimentalists) can verify. A great example in classical physics is gauge transformations in electrodynamics. The classical theory said that the potential didn't matter and in the classical world it doesn't! Then berry, aharanov, and bohm said hold my beer the story isn't over! Turns out not only does the potential have a directly measurable physical effect...so does the uncollapsed wave function! Phase matters! Geometric topological etc. What else does Hilbert manage to smuggle into the theory? Ask Bell, Wigner, and Wheeler! In the process of doing this we have verified the second law of thermodynamics at work in the realm of education, effectively producing a state of monotonically increasing maximum entropy in the minds of physics students everywhere trying to make sense of a whole universe completly outside of the realm of direct experience! The state of confusion and uncertainty this induces usually wears off after about 50-60 years. While this violates both the letter and spirit of the university's IRB rules surrounding human experimentation, in this situation informed consent is technically impossible so the physics dept. usually gets a blind eye from the relevant committees.

[@David.C.Velasquez]

@@robmorgan1214 Great comment! LMAO

[@bjrnerikjuel1459]

Lecture starts 8 minutes in.

[@fivforfivfor]

I think With a little bit more information On what you are trying to get at (or to) I could not only answer your question(s) Professor But I could even show you How it can be done In an experiment type form Because I have done experiments That have solved lots of these quantum type questions 🙂🙂🙂 Excellent lecture !!!

[@eduardofrancosotelobazan9267]

I want translate this video, but I can't; could you activate the social contributions?

[@TymexComputing]

5:05 Prigozhin???

[@Zaekk]

This is such an awkward start but i'll stay with it.

[@Nicole72591]

Zaekk lmao 😂

[@thusspokeshabistari]

The pleasantries end at 7:14

[@itsbs]

*Objection:* Why can you use "Quantum State Superposition Principle" in this proof, when it also depends on Born's Rule of non-deterministic probabilities? In your proof of Born's Rule of non-deterministic probabilities, you exclude the Density Matrix, because it depends on Born's Rule. Your proof INCLUDES the use of Quantum State Entanglement, which requires the non-deterministic probability interpretation of Schrodinger's *deterministic* wave equation, and Quantum State Entanglement depends on Quantum State Superposition. In Dirac's Quantum Mechanics Manual, Quantum State Superposition Principle requires interpreting Photon polarization and Photon interference statistically. On page 9, section "The Principle Of Superposition" (3rd edition of Dirac's manual): _"The association CAN be interpreted only statistically,_ the wave function giving us information about the probability of our finding the photon in any particular place when we make an Observation of where it is." He is directly stating that to understand Quantum State Superposition of Photon interference, then you must interpret waves in a non-deterministic, statistical manner, i.e. via Born's rule). This is a direct challenge to the statement made at this timestamp: kzbin.info/www/bejne/bYTRZ2aqaKeYg8U

[@anywallsocket]

needs more simulations

[@Markoul11]

25:00

[@jacintopauloneto9841]

Ça commence 8:00

[@xjuhox]

What is this *intellectual jerking?* The Born's rule stems simply from the inner product structure of the (linear) Hilbert space. The spectral theorem is at the heart of time-independet quantum mechanics, since in that case the Schrödinger equation as an eigenvalue equation, and the Born's rule and state vectors are just necessary elements.

[@robmorgan1214]

Your comment about the spectral theorem is correct. However, the fundamentals community generally believes that Born's rule is an arbitrary imposition on the theory that hides physical dynamic processes. In this regard they think of quantum mechanics as a theory of scattering and other physical theories that could describe the mechanism that selects the final states. There's a subtle difference between this idea and "hidden variables" ideas (see bhomian wave stuff like pilotwave theory). In this talk, he demonstrates the fact that Born's rule doesn't hide any physical processes or additional physics. He shows that it is the same thing at assuming: Unitarity, repeatability (really just an assumption about the need for some sort of continuity, possibly analyticity), and Hilbert space. The result formally embeds both quantum and classical probability into the realm of physical law as a direct result the existence of orthogonal states in ANY THEORY that shares these assumptions. That's a big deal. It says to find new "quantum" physics, IT MUSY NOT BE EMBEDDED IN A HILBERT SPACE AND IT WILL STRONGLY VIOLATE CONTINUITY/REPEATABILITY OR UNITARITY! This means that to make progress you must throw away ALL of the math we currently use to describe quantum process or that it's mathematically consistent and as correct as it can be.

[@xjuhox]

@@robmorgan1214 It is as correct as it can be; for example, the electron diffraction pattern just emerges and we should not ask how a single quantum event turns out.

[@robmorgan1214]

@xjuhox quantum mechanics predicts that. This talk explains HOW. This interference pattern is a pure mathematical side effect of the wave functions that describe the particles existing in a Hilbert space. It's purely a result of the algebraic and GEOMETRICAL structure of reality that describe symmetrical objects in a Hilbert space... It's completely analogous to the way spherical harmonics describe the strange patterns that emerge when you put granular media on a horizontal screen on top of a speaker. (Edit this is hard to explain without math) i.e. the sound waves are spherical and get projected onto a 2 dimensional screen that's got its own modes of excitation. Similar things happen with "infinite dimensional" wave functions on a 2d screen. You're looking at objects that exist on trajectories and have properties defined by that space as it interacts with the totality of that space... this is NOT a dynamic process it's just the way the reality that defines our existence orders events. This order isn't reality it's only the reality that emerges in which we also emerged. Similar processes occur in condensed matter systems usually only observable in phase transitions in which local order suddenly becomes global order spreading out like a wave. Hilbert spaces don't need that order, and the processes we observe in them do not have it. Our frame artificially selects the direction of the scattering amplitude AFTER the fact. However, the transition is static and only orientable with respect to OTHER transitions. These individually are static events. The order parameter is usually entropic in nature and CONCEPTUALLY orthogonal to the underlying static processes. The dynamics exist in the system defined under the influence of that order parameter. For example, this is "WHY" chemistry happens, or why the Meissner effect can levitate magnets.

[@xjuhox]

@@robmorgan1214 All this is very interesting. To me QM is just a statistical recipe without metaphysical ontology, but maybe the future experiments allow us to go beyond the textbook QM.

[@robmorgan1214]

@xjuhox it's fascinating to me as well... but that's kind of the problem isn't it. One of the best theories we have can be derived from 3 basic assumptions. All the woo and weirdness including the constraints on what's knowable flow directly from them with zero exceptions. That means either one of these assumptions is wrong or this is how reality is organized at a fundamental level and it's a "fuzzy" reality at best with blurred edges and randomness as a first class citizens. The proof in this talk combined with the experiments testing the limits of QM slams the door on other possibilities. But NO ONE is looking at these realistic options and instead get their intuition from science fiction. As an experimental Physicist I find this upsetting. If we suspended or alter one of these assumptions can we construct a different theory? How can we test whether these assumptions are correct and to what level of confidence? etc.

[@sonarbangla8711]

There are groups that thinks that the quantum can be classical. Otherwise known as Bohmian mechanics (long debunked). This guy claims 'no cloning' and he will be glad to move on forgetting he didn't prove it.