We at the Institute for Quantum Optics and Quantum Information - Vienna (IQOQI-Vienna) of the Austrian Academy of Sciences are committed to advancing knowledge and enhancing human understanding of nature and its laws. We also actively pursue the vision of quantum information science and the wide range of new possibilities it would open up for humanity. To this end, we conduct theoretical and experimental research on the foundations of quantum physics and the physics of quantum information and develop new quantum technologies. IQOQI-Vienna brings an information-theoretic perspective into physics questions and focuses on the development of quantum optics experiments for the coherent control of individual photons and atoms, exploring theoretical and experimental possibilities of constructing quantum-mechanical devices for quantum communication and computation.
Philipp says the reconstruction of quantum mechanics (QM) based on information-theoretic principles aims “at finding clear physical principles from which the formalism [of QM] can be derived or reconstructed.” He believes that “understanding quantum mechanics can be best achieved” in this fashion. He then points to special relativity (SR) as an example of the goal of the quantum reconstruction program (QRP). We agree wholeheartedly with Philipp. As it turns out, this precise goal can be achieved with QRP if you (re)spatialize the notion of measurement therein, as we explain in our book, "Einstein's Entanglement: Bell Inequalities, Relativity, and the Qubit" Oxford UP (2024). Let me summarize it here. Einstein defined a “principle theory” as one whose formalism is derived from an empirically discovered fact. SR is a principle theory and its empirically discovered fact is that everyone measures the same value for the speed of light c, regardless of their uniform relative motions (“light postulate”). Since c is a constant of Nature per Maxwell’s equations, the relativity principle says it must be the same in all inertial reference frames. And, since inertial reference frames are related by boosts, the relativity principle tells us the light postulate must obtain, whence the Lorentz transformations of SR. Likewise, QRP has successfully rendered QM a principle theory and its empirically discovered fact is called Information Invariance & Continuity (Brukner & Zeilinger 2009; other starting points are used of course). If you spatialize the notion of measurement, Information Invariance & Continuity entails that everyone measures the same value for Planck's constant h, regardless of their relative spatial orientations or locations (let me call that the "Planck postulate"). Since h is a constant of Nature per Planck's radiation law, the relativity principle says it must be the same in all inertial reference frames. And, since inertial reference frames are related by relative orientations or locations in space (rotations or translations), the relativity principle tells us the Planck postulate must obtain, whence the finite-dimensional Hilbert space of QM. Consequently, QRP has rendered QM as understandable as SR, per their desideratum.
From @31:10 the conclusion was underwhelming, "entanglement mediation by a Newtonian field provides evidence of existence of propagating degree of freedom of the gravitational field". So existence of gravity waves. LIGO said they already exist. The weasel words are "Newtonian field", since that's a fiction, there is only spacetime of GR, and that can have wormhole structure, or ER=EPR (nontraversable ER bridges). So of course gravity mediates entanglement, and there are only gravity waves. The whole pf spacetime does not ever get in a superposition. Gravity waves can, if localized sufficiently like solitions.
Question at 1:43:19 on establishing a common model. Poincare wrote about this interaction between subject and observer in his essay "The foundations of geometry" in 1898! It was published in English in _The Monist_ and is available online. That language, for Poincare was geometry and the model (i.e. the interpretation) was physical observations.
Take one entangled photon and move it up and down for zero's and ones and observe the output data on the other end. Use left and right for simultaneous bidirectional data output. No we can communicate across time and space without any delay.
I don't know about physics, never been educated in sciences, so my doubt may not sound scientific, but it stems from a logical intuition, so, if possible, help me understand this: why is it considered that there is a communication between both? Isn't it possible that it is not communication, rather their own natures, being perfectly opposite?
Why do we say "2 particles" when it's really just the one ?? 1 particle split in half - what's the big deal? I don't want to trivialize it, but don't we complicate the discussion by saying "2" ?? Using your complicated Maths it never goes from 1 to 2 so why do we not say it's just the 1 split in half?? using the term "indistinguishable" when your really trying to say its 2 faces of the same coin
If you think of it as 1 particle then there's nothing "spooky" about it - of course altering one half of it alters the other half - Are there really even 2 particles or is it just a "blind spot" in the way we see it at that weird dimensional angle - Like seeing gravitational lensing for the first time and assuming there's a circular hollow star ???? Please help - I only have a GED but I'm almost there with the understanding - SPINORS make sense to me if that helps
I assume this phenomenon is only of interest because some theoretician thinks they can devise an experiment that could transfer information faster than the speed of light using this "lensing" . We are a long way away from measuring the information change faster than the speed of light and PROVING IT. We can't SYNC two Particle detectors together and VERIFY the information between the two FASTER than the speed of light. Obviosly
Omg, no comments? Let me be the first to heap on praise! I haven't seen many lectures from Dr snopes, but I'm now searching for more. It seems like condensates exist at the intersection between classical and quantum mechanics.
This lecture was so wonderful. Wheeler is probably my academic hero, and his thoughts on the importance of measurement have occupied my mind for so long. I wish I had watched this years ago. I have so many new ideas now, this made so many things straight in my mind. Thank you so much for your irreversible act of amplifying Wheelers ideas!
Pauli spins are inadvertently complex objects. Not a good choice to refute the non-complex theorem. You should also make clear that you are dealing with non-stationary states. The latter description can always be done without complex numbers. Imagine a charge less quantum particle in a box. Clarification between a real number state description versus complex but Hermitian operators with observable states is important. In fact there are domain issues that plague the uncertainty principle derivations from QM.
I read through the two recently published papers cited in this talk, in PRX (theory) and Nature (experiment). I had several concerns not addressed by the questions during the talk, and not addressed in the papers. First, on the theoretical front, I get that one can model the classical variables with a stochastic PDF and even couple such a PDF into an evolution equation with quantum terms. However, the classical fluctuations are not arbitrarily large, there is some constraint. Backreactions are not arbitrarily large. Yet that is the conclusion reached, that one can obtain large classical stochastic fluctuations, which may be observable even for weak coupling such as gravity. The equations produced rely in part on Markovian quantum master equations, the Lindblad eq and the Kramers-Moyal expansion, all approximations that are often inaccurate. Yes, they give closed form eqs that can be solved, but at what tradeoff? Dropping nonlinear terms that constrain backreactions. Second, on the proposed experiment for “gravitational diffusion” - In the weak limit where gravity can be treated classically the strength of the coupling precludes any measurement of the effect of gravity on quantum decoherence, say over thermodynamical decoherence effects, even at low temperatures. Feynman had some solid examples in his lectures on gravitation, which is cited in the papers. For a gravitational perturbation on atomic dynamics, observing gravitational effects on the wave function phase would require a time equal to 100x the age of the universe. Gravity does not affect phase coherence in quantum systems in the weak limit. One can try to change that by introducing an unconstrained stochasticity as Oppenheim seems to have, but this would generate paradoxes beyond what he complains about from semiclassical gravity.
Atleast in the case I’ve been exposed to the Kramers-Moyal expansion (classics Fokker-Planck equations), the typical point of truncation occurs after the second order term, so it does go beyond linear there. The validity of the truncation is supported by Pawula’s theorem in that context, where KM coefficients of 3 or higher are zero.
@29:00 ok, but what I still find hard to grok here is why you need the stochasticity. Aren't you (implicitly?) _assuming_ gravity is well-described by gravitons? But that's not classical GR. Gravitons in GR are highly dispersive, and weak little blighters. To account for large scale gravity field effects you need the global spacetime of GR. This is what you're testing with the Feynman--Aharonov gedankenexperiments, right? But the classical GR fields is not a graviton, it has no particle-wave duality, it is all wave. So can superpose. So there's no inconsistency. I mean... right? The whole issue with which-way information from the EM fields was an issue only because the field is *_not_* a physical field, it's photons, which cannot be in superposition if they are classical particles. But they're not, and we know how to quantize the EM field --- namely with photons! We do not know how to do this for gravitons. And aren't Oppenheim's group saying there are no gravitons? Because GR is the thing! Feynman's argument was the interference when gravity is significant for giving up which-way information implied the gravity field has to have a "complex" amplitude (a non-classical probability amplitude). But surely that is only the case if gravity is the exchange of gravitons. If not, if gravity is spacetime curvature and gravity waves, then they _can_ be placed into (classical) superposition just like a hypothetical classical Maxwell-Faraday field. Then classical gravity defeats Feynman, no? I mean, help me out here! Imagine light was not actually photons, but pure Maxwell-Faraday waves. Then interference would not be a problem, it'd be classical. Similarly for firing probe light at diffracting electrons or neutrons or whatever, the classical light could not give you which-way information if in superposition, which classical light can be. But we know light is non-classical by other means, precisely because even when probing for which-way information, a large enough photon wavelength will fail to distinguish which way, regaining interference. What this means (imho) is the test should be of a different type. Not for stochastic gravity, but for superposed gravity waves (a very delicate experiment to be sure, impossible with current technology). I mean, do all test feasible of course, but if the stochastic gravity test fails, try the other. Implicitly here I've been assuming realism, that is, an electron or any other particle quanta, subject to two-slit interference or the like, does in fact go through both slits. It's a sum-over-histories type of realism. If that's the way QM works, then the _classical_ gravity field is non-zero around both slits, giving no immediate which-way information. That also means, to truly check for quantum gravity you're looking at the ultimate experiment: interfere actual gravitons (not classical gravity waves). Since Dyson and Feynman argued gravitons can _never_ be detected, this casts a terrible shadow over experimental physics, if this is all the case. Meaning these dodgy indirect test are likely all we're ever gonna have to test theories of gravity.
By gravitons? Quite the opposite! In fact, in the first (2018) version of his 1811.03116 ArXiv preprint, he even included this passage "and there are even some experimental hints pointing towards the absence of the graviton" citing these references: R. Lieu, "Exclusion of standard ℏω gravitons by LIGO observation", Classical and Quantum Gravity 35, 19LT02 (2018). R. A. Norte, M. Forsch, A. Wallucks, I. Marinković, and S. Gröblacher, Phys. Rev. Lett. 121, 030405 (2018). The context of the LIGO-related cite was, in fact, part of a direct reply to Feynman and Dyson that went: "Yes, we do have a way of seeing the sign of gravitons, with the aid of LIGO, we tried it and we saw nothing." The way this was framed made it look like a 2010-decade rendition of a Michelson-Morley "didn't see anything" experimental no go. Curiously, I don't see the references in the last (2023) version of the PDF. More curiously: there was no mention of leaving open any possibility of the hybridized framework being a possible "classical limit" to a quantum gravity in the 2018 version, either. Oppenheim? You have some explaining to do!
So if there is an upper limit on the coherence times of single particle quantum states, or if there is a lower limit on how quickly you can measure the gravitational field, those findings will prove gravity is both classical and stochastic?
Doesn't it need to be a bit of both? (see @1:03:00) The idea is if there is still interference, but gravity has dispersed too much so the (classical) gravity field can give up which-way information, then that's a total inconsistency. It would imply gravity has to be described by amplitudes, so is "quantum mechanical". Which is perhaps merely to say gravitons exist. It does not say spacetime is a fiction, so it does not say classical GR is false. It'd just say gravitons exist too. Then the goal would have to be to show *_all_*_ of the effect_ can be accounted for by gravitons, so then GR is redundant and is not an actual theory for our universe.
The lower limit in diffusion, I understand, must be the lower limit in the noise of the measurements of the mass in the cavendish experiment. The proposal is that by obtaining these limits they can rule out theories out of those boundaries.
I remember that part of Bohr Einstein debate was about a moveable slit and that the particle will influence the slit and thus the uncertainty principle has to be included for the slit. Is this part of the discussion?
No. That was about gaining which-way information through all the other mechanical forces. Oppenheim and Feynman--Aharonov et al., are talking about which-way information from the gravitational field and _only_ the gravitational field. The point being there has to be a non-classical amplitude for the field if it could provide which-way information, otherwise we'd never observe interference, and of course we do, observe interference routinely. But these are always incredible small masses, so with tiny gravitational field effects. You need about 0.00001 grams to get a significant effect with current gravity detection technology (I believe) and that's super damn heavy for elementary quantum coherent systems, almost impossible to presently engineer. So Oppenheim is still speaking at a gedankenexperiment level of discourse. The issue is that if we cannot detect gravitons or such weak gravity fields --- *_and_* maintain the coherence of the particle superpositions --- then we have no which-way information, so gravity _could_ be purely classical. Feynman acknowledged this, but said for gravity to not give up which-way information would require a new principle of physics, one that implies, for example, that too much mass involved will by pure principle destroy coherence. No one knows of such a principle yet. Oppenheim's candidate principle is that classical gravity has to have some sort of metaphysical noise.
There seems to have been a persistent aversion to the complex nature of the wave function among pioneers of quantum mechanics, rooted in their desire for an entirely physical formulation of quantum physics. The fact is, however, that the quantum wave function does not exist in 3D physical space, but is defined instead in complex-valued Configuration Space, an abstract domain of potentially limitless numbers of dimensions. In order to derive physically observable manifestions of the wave function, Hermetian operators must be applied to the Schrodinger equation to produce measurable eigenvalues. A key property of these Hermetian eigenvalues is that they are always real-valued quantities, indicative of solutions that can be manifest in physical space. Of course, the probability densities of these solutions are given by the conjugate square of the wave function, which likewise always produces real-valued results.
They don’t ever look like that. It’s the process of (quantum) ghost imaging that create an artificial image of the Yin and Yang diagram (the Taijitu) then the mass media claimed “it’s the visualization of two photons”
All versions / interpretations of QM are non local, at least in the " weak " sense ( i.e. that's compatible with Relativity). Some alternatives ( like Bohmian mechanics) are non local in a stronger sense ( they require some preferred reference frame, so , " behind the scenes" they're not really compatible with SR, although this characteristic does not have observational consequences, at least given some assumptions about the statistical distribution of the Bohmian particles). So far, so good. But I disagree about Everett: It's also "weakly non local" , just like the other interpretations of standard unmodified QM. It doesn't matter that the wavefunction doesn't collapse. Locality is, by definition, a "property" of the physical 4-dimensional Spacetime, not of abstract mathematical multi dimensional spaces.
decoherence is when the information contained in the wave function gets smeared out by environmental noise, or factors not considered to be inside the system of interest, and therefore results in some information being lost, and therefore a reversibility. blackholes as you have them here destroy correlations across the boundary, by preventing any ordinary reversibility, therefore erasing information relative to the outside system. all that said, the results elucidated here make perfect sense and should be seen to be intuitive by all members involved -- they are probably intrinsically skeptical of young people presenting new ideas lol.
19:10 That " dotted line " prof. Curiel is referring to, is a Cauchy horizon. A spacetime with a completely evaporated ( no remnant ) black hole is non globally hyperbolic.
I do see a simple "solution". We can all observe and set possibilities. That is, if I observe "spin up" and you observe "spin down", the alternative is identical, as in, it makes not physical difference the spin direction, but it does our correlation between them. As our correlation is a different physical interaction, we can have a nested observer setting some spin directions (cat alive or cat dead) while others are not set (the sum of observing the room with the scientist). As the scientist sets some spins, but not all, we should find a solution between us that agrees, even though some observations may not.
