very useful and clear talk!👍

Greatly benefited, thank you!

so yeah this is cool

First kudos for nice and realistic presentation. Having said that, I still see Tobias' talk as a "soft-landing" talk. Especially with the slide showing PsiQuantum predictions given in 2020 that in 2025 they will have 1 million qubits computer. They went big, they got big money (initially 1/4 $ Billion, later increased up to 1 $B) from gambling investors, and now they have postponed their computer for 2030. They hope more gamblers will be tricked in their promises.

yes

42:20. In fact, the observer's self-esteem in QM is underestimated to the level of the infamous ostrich. The observer is always involved in an unavoidable measurement process. It seems that there have never been any problems with QM already within the framework of GR (for example, in the case of the Schrodinger/Carroll cat). A live cat breathes and, accordingly, emits gravitational waves according to the formula GR with intensity: I(G)=(2G/45c^5)(M^2)(l^4)(w^6), where M is the mass of the cat, l is its characteristic size, w is its frequency breathing.The frequency of gravitational radiation should be on the order of w~ 2π/т where т is the characteristic time of accelerated mass movement (pulsation, rotation, collision, non-spherical explosion).It is clear that the dead cat is not breathing and I(G) =0*. In principle, all this lends itself to a certain (improbability) constant measurement without opening the "black box", since gravity is not shielded [w=w(m)]. Moreover, the behavior of the radiation source is also controlled, since it emits only in an excited state. ** Of course, Carroll's sleeping cat breathes, but differently (can be measured) than the waking one.*** Sweet dreams to you QM, on the interpretation of the Born wave function. P.S. Why didn't Einstein use this argument? He wasn't sure about the reality of gravitational waves and assumed only the presence of hidden parameters… --------------------- *) - By the way, a "smile" without a cat can be detected according to Einstein's equations. Raising one of the indices, substituting I=k and summing, we find: R=-(8πG/c^4)T, where T=T(n) is the trace of the energy-momentum tensor (~ "gravitational memory."). **) - If the cat is replaced with a detector, then with each absorption its state will change (which makes measurement possible). It is clear that this will also cause additional radiation of gravitational waves, since the included detector is already a source. ***) - The formula can be given in the following form for a photon: I(G)={[w/w(pl)]^2}ħw^2. Of course, this approach is also applicable to the case of entangled particles. "When physicists offer metaphysical explanations for physical phenomena, I start swearing." (Raymond Tallis). Frame of reference in GR: "In the general case of an arbitrary variable gravitational field, the metric of space is not only non-euclidean but also changed with time. This means that the relationships between different geometric distances change over time. As a result, the relative position of the "test particles" introduced into the field in any coordinate system can not remain unchanged." ( Landau-Lifshitz, II). It turns out that since the Big Bang, all the particles in the universe speak, hear and listen to each other in the language of gravity (= irreducible spontaneous measurement). Addition The main misconception in the interpretations of quantum mechanics is that the equally probable nature of phenomena implies their equivalence.* Moreover, not only at 50/50, but also at 99/1. However, equality and equivalence are completely different things, even if they are causally related; for example, all inertial reference systems are equal in SR or QM, but far from equivalent. Obviously, if a dead or a living cat, the spin of entangled photons up or down, pairs of socks or letters marked + or - in different parts of the world are equal, then they are not physically equivalent; and also, branched universes. When an tails falls out after a coin toss, then they talk about the collapse of the wave function, when tails and heads are just equal, but not the same even not only for numismatists.That is, these are physical parameters of different physical phenomena, and their representation by a single wave function according to Born is ridiculous. For example, when energy E=mc^2, then mass m=E/c^2, since they are parameters of the same physical entity, and therefore equivalent. For comparison: in GR, in a gravitational field or in an equally accelerated frame of reference, all events are not only equal, but equivalent, so Einstein criticized QM for not being as radical as RT.** Moreover, RT is even more radical: "Two world points located at zero distance from each other do not necessarily coincide." (Pauli, RT, paragraph 7, Four-dimensional world). That is, even with a repeated loss of heads (or tails), both of these phenomena are not equivalent. Moral: a particle cannot even be in one state at the same time. Finally, we can say that the concept of "frame of reference" was self-sufficient, and the introduction to physics of the concept of "state" was an unsuccessful attempt to describe reality. "A good joke should not be repeated twice."(Einstein).*** --------------------- *) - In logic, this is the basic law: the law of identity. **) - For fans of the multiverse: the equivalent Universe can only be the accelerating Universe itself. ***) - It seems that the uncertainty principle is the result of a misunderstanding of probability/equivalence. In the Heisenberg inequalities, the mathematical apparatus was formed before the interpretation of their physical essence. It is funny that these inequalities indicate that there are no exact values of coordinates and momentum vector in the states of microobjects at the same time; and thus exclude the equivalence of these parameters. If in RT the choice of a reference frame is essentially an experiment (mental or real) that produces a certain splitting of space into spatial and temporal "projections", then in QM there are "two types" of observations: using measuring instruments to measure coordinates and to measure the momentum of microparticles. There is no such separation in the observation process in QG, because instead of "rulers and clocks" in RT or "multi-functional" devices in QM, only a quantum counter (detector) is required, which catches gravity quanta (if the self-action) of physical bodies; without affecting them ("touch" or "illumination"). That is, an observer with a conventional detector is a "quantum reference system". Thus, in the general case, the observer is an evolving (- when measured, his state changes) researcher of the spontaneous evolution of the Universe and not measurement, but "Interaction is the ultimate cause of everything that exists, beyond which there are no other, more fundamental defining properties." (Engels). That is, the result of the measurement is a change in the state of the measuring device; a change in the physical state of the observer; and, finally, a change in the intellectual state of the observer.

Or in other words: all experiments done to date have not ruled out that Nature is local and no experiment that can be explained by any non-signalling theory can rule it out. This seems like a very fundamental insight.

Hi! I was watching the recording of "Efficient quantum algorithm for deterministic port-based teleportation" which was uploaded recently as well. Somehow it became private...May I ask if it's possible to make it accessible again? (Sorry for commenting on an unrelated video here!

The introduction of error tolerance and bias in communication complexity appears disconnected from the earlier discussion about the one clean qubit model, making it difficult to follow the logical flow of the presentation.

A summary of professor Brassard's paper is given at [51:20]. I would like to know a little about how probabilities are handled in this theory. Presumably Alice can manipulate her apparatus in any way she pleases. In particular, she could ensure that a series of experimental runs is such that P(she chooses banana) = p for any valid p. So P(she chooses rabbit) = 1-p. Suppose she arranges the setup so that p = 1/pi. It is unclear for me how the splitting of the universe into branches at each individual run would occur. Wouldn't it have to divide into an infinite number of branches? If so, how does one retain the concept of probability? In any event, it wass an excellent talk.

Very nice video - thank you. I am still trying to understand it all. But perhaps you can help: I have been asked whether CIG Theory survives the Frauchiger-Renner scenario. Perhaps you can lend some insight. I am offering a new Quantum Interpretation. Here is an introduction: www.youtube.com/@thedouglasw.lippchannel5546 Does CIG Theory survives the Frauchiger-Renner scenario? Does it have to in order to become a complete theory?

This feels a lot like Godel’s theorems - am I crazy?!

excellent talk

Great info

In my understanding of QM and the FR's argument, the crucial points are the notion of what constitutes a measurement (which is astride of theory and interpretation, and unsuspectedly linked with the measurement problem...) and the relation between decoherence and its purification in the encompassing entanglement. Measurement is here intended as distinct from observation, where the first is objective, and the second is subjective. The question is what constitutes in-principle-unobserved measurements, or at least if such notion is legit. I would count at least 3 distinct notions of "measurement" in traditional/usual QM, with distinct impacts on the measurement problem. The more "Copenhagenian" is that measurement and observation coincide, and they are formalized as projection (collapse). This can be read in the strict sense that measurement as objective is not defined, thus meaningless, which is the Qbism's reading, and probably Bohr's, or in the implicitly objectivist perspective leading to the conclusion that the subject's observation affects the reality "out there" (and I cosciently avoid adjectives for this latter stance, because I am polite, I just suggest to be consistently operationalist when adopting the operationalist's approach). In contrast, von Neumann, and a lot of theoretical physics, have been using the notion of measurement as the dynamics of entanglement establishing interactions. Then, there is the notion of measurement as the dynamics of decoherence establishing interactions. Respect to the first stance, entanglement and decoherence are analytically part of the theory (and the "unitary", plausibly objective, part of it, which is what we want for the notion), the question is if any, then which, of them has the right properties to be narrated as measurement. The distinction of the latter two notions might be subtle in some perspectives (abstract/theoretical?), after all, decoherence is a property of the internal structure of entanglement, but crucial and physically quite distinguishable: crucial because decoherence yields emergent classical logic within quantum logic (which renders conditionalization legit and implies emergent determination, by analysis of the logic), and physically relevant because it makes all the difference in the world in respect to our expectations to be presented with either a statistical operator or a pure state, and it also makes all the difference to our quantum, or not so quantum, computations. Curiously, the original Wigner's argument was based on the observation that we need to use a statistical operator and cannot use a pure state to describe our friend, on purely empirical considerations about the different statistics of the two states. Wigner failed to make the same argument for the notion of unobserved measurements, notwithstanding the fact that the reasoning is identical, he could have anticipated decoherence by decades if he did (and avoided "half backed" ideas...). Note that with decoherence we fix the question of entropy with measurement, and the other question of the decoherence scope, i.e. the fact that we need an observer to be presented with the decohered system for she/he to use the statistical operator formalism, rather than the pure one, means that the observer-system needs to be in some adequate sense co-decohered (within the same decoherence scope) with the observed system. This also means that "facts" and "conclusions" are relational, i.e. emergent from the (cor-)relation established by intercations between observed and observer systems (and their environment, usually). In contrast, measurement=entanglement is prone to be considered in abstraction without implying a factual relation between observed and observer, or agent, systems. This perspective clarifies that what is relevant to the FR argument is the decoherence scope in respect to its purification in its encompassing entanglement. To establish the contradiction with the B assumption, the external observer needs to access, interact with, the entanglement encompassing its (of the entanglement) internal decoherence, what is needed is decoherence AND its encapsulation, or accessing the multiverse of the specific decoherence scope from the outside. Which is why the argument is extreme for human-observers, and isolated laboratory is euphemistic for human-containing-laboratories. This, partially, mitigates the portent of the conclusion, which doesn't affect the consistent use of the theory, since the relation observer-facts is well defined by the theory, and physically it predicts that we do agree about facts. But the argument has merits, and I fully agree with Dr. Renner's consideration that quantum information and computation have foundational/interpretational implications, and can be used to study and test problems of this latter field. I also auspicate theoretical studies on the analysis of internal (within entanglement) decoherence, since the current state of our treatment of this property is not nearly adequate for what we could envision and expect for the implications of decoherence (for GR and cosmology). This said, which is my opinion, the tradition from Deutsch to FR doesn't follow the notion measurement=decoherence but rather measurement=entanglement, I think that this makes things less clear. You can see this in the consideration that certainty by Born rule constitutes a "conclusion" about a result. For the decoherence perspective this is insufficient, Born rule is counterfactual, it's about the result if that measurement occurred, but no decoherence, then no entropy (indicating the feeding of the epistemic ignorance of the observer), no measurement, no conclusion. In view of the measurement problem, I deem measurement=entanglement is also insufficient. Here one of the main issues is the gap between measurement and observation. Contrary to what is often considered it is not projection (collapse) the core of the measurement problem, there is not much that can be done around what is the correct formalization of conditionalization for quantum probability logic, and thus QM in general, which is indeed projection (it is projection, in the appropriate form, for classical probability logic as well!). The problem is from the gap, because the question is when conditionalization becomes legit. It is surely legit when it is purely epistemic, so that if we get epistemically interpretable probabilities we are good. Entanglement in general doesn't fill the gap, it is decoherence that does the trick, precisely because it is emergent classical logic, which is what renders the epistemic (ignorance) interpretation of probabilities legit, and consequently conditionalization as purely epistemic/subjective (somehow anticipated by Heisenberg's intuition that "probabilities", meaning epistemic, come from/start with the "divide"). PS: of course one of the reasoning of the FR argument is that You can use the 3 assumptions to classify interpretations by which of the 3 they violate, You can see that my use of decoherence is a (in practice weak/mitigated) violation of the B (determination is relational, and such are conclusions about facts), although in a way that does not preclude the consistent description of the use of the theory.

a great presentation, thanks for sharing this invaluable info

If each computer contained a description of the entire system (the experimental setup) wouldn't they all then predict that the red computer has a 1/12 probability of seeing w = ok just as we have done? Perhaps some subset of the computers are misapplying quantum mechanics by extending their limited knowledge of the systems they've measured to a system that they have not.

Of course this had something to do with consciousness. How does he think these computers will be programmed? How does he think these computers are made? Computers are an extension of consciousness and wouldn't exist without it. It always amazes me that these Scientist try to go out of their way to say this has nothing to do with consciousness when they don't even know what consciousness is.