pcalau12i

Isn’t the quantum communication (if it were possible) supposed to be actually instantaneous, not just “nearly instantaneous”?

There is no instantaneous information transfer (“nonlocality”) in quantum mechanics. You can prove this with the No-communication Theorem. Quantum theory is a statistical theory, so predictions are made in terms of probabilities, and the No-communication Theorem is a relativity simple proof that no physical interaction with a particle in an entangled pair can alter the probabilities of the other particle it is entangled with.

(It’s actually a bit more broad than this as it shows that no interaction with a particle in an entangled pair can alter the reduced density matrix of the other particle it is entangled with. The density matrix captures more than probabilities, but also the ability for the particle to exhibit interference effects.)

The speed of light limit is a fundamental property of special relativity, and if quantum theory violated this limit then it would be incompatible with special relativity. Yet, it is compatible with it and the two have been unified under the framework of quantum field theory.

There are two main confusions as to why people falsely think there is anything nonlocal in quantum theory, stemming from Bell’s theorem and the EPR paradox. I tried to briefly summarize these two in this article here. But to even more briefly summarize…

People falsely think Bell’s theorem proves there is “nonlocality” but it only proves there is nonlocality if you were to replace quantum theory with a hidden variable theory. It is important to stress that quantum theory is not a hidden variable theory and so there is nothing nonlocal about it and Bell’s theorem just is not applicable.

The EPR paradox is more of a philosophical argument that equates eigenstates to the ontology of the system, which such an equation leads to the appearance of nonlocal action, but this is just because the assumption is a bad one. Relational quantum mechanics, for example, uses a different assumption about the relationship between the mathematics and the ontology of the system and does not run into this.

Depends upon what you mean by “consciousness.” A lot of the literature seems to use “consciousness” just to refer to physical reality as it exists from a particular perspective, for some reason. For example, one popular definition is “what it is like to be in a particular perspective.” The term “to be” refers to, well, being, which refers to, well, reality. So we are just talking about reality as it actually exists from a particular perspective, as opposed to mere description of reality from that perspective. (The description of a thing is always categorically different from the ontology of the thing.)

I find it bizarre to call this “consciousness,” but words are words. You can define them however you wish. If we define “consciousness” in this sense, as many philosophers do, then it does not make logical sense to speak of your “consciousness” doing anything at all after you die, as your “consciousness” would just be defined as reality as it actually exists from your perspective. Perspectives always implicitly entail a physical object that is at the basis of that perspective, akin to the zero-point of a coordinate system, which in this case that object is you.

If you cease to exist, then your perspective ceases to even be defined. The concept of “your perspective” would no longer even be meaningful. It would be kind of like if a navigator kept telling you to go “more north” until eventually you reach the north pole, and then they tell you to go “more north” yet again. You’d be confused, because “more north” does not even make sense anymore at the north pole. The term ceases to be meaningfully applicable. If consciousness is defined as being from a particular perspective (as many philosophers in the literature define it), then by logical necessity the term ceases to be meaningful after the object that is the basis of that perspective ceases to exist. It neither exists nor ceases to exist, but no longer is even well-defined.

But, like I said, I’m not a fan of defining “consciousness” in this way, albeit it is popular to do so in the literature. My criticism of the “what it is like to be” definition is mainly that most people tend to associate “consciousness” with mammalian brains, yet the definition is so broad that there is no logical reason as to why it should not be applicable to even a single fundamental particle.

This problem presupposes metaphysical realism, so you have to be a metaphysical realist to take the problem seriously. Metaphysical realism is a particular kind of indirect realism whereby you posit that everything we observe is in some sense not real, sometimes likened to a kind of “illusion” created by the mammalian brain (I’ve also seen people describe it as an “internal simulation”), called “consciousness” or sometimes “subjective experience” with the adjective “subjective” used to make it clear it is being interpreted as something unique to conscious subjects and not ontologically real.

If everything we observe is in some sense not reality, then “true” reality must by definition be independent of what we observe. If this is the case, then it opens up a whole bunch of confusing philosophical problems, as it would logically mean the entire universe is invisible/unobservable/nonexperiential, except in the precise configuration of matter in the human brain which somehow “gives rise to” this property of visibility/observability/experience. It seems difficult to explain this without just presupposing this property arbitrarily attaches itself to brains in a particular configuration, i.e. to treat it as strongly emergent, which is effectively just dualism, indeed the founder of the “hard problem of consciousness” is a self-described dualist.

This philosophical problem does not exist in direct realist schools of philosophy, however, such as Jocelyn Benoist’s contextual realism, Carlo Rovelli’s weak realism, or in Alexander Bogdanov’s empiriomonism. It is solely a philosophical problem for metaphysical realists, because they begin by positing that there exists some fundamental gap between what we observe and “true” reality, then later have to figure out how to mend the gap. Direct realist philosophies never posit this gap in the first place and treat reality as precisely equivalent to what we observe it to be, so it simply does not posit the existence of “consciousness” and it would seem odd in a direct realist standpoint to even call experience “subjective.”

The “hard problem” and the “mind-body problem” are the main reasons I consider myself a direct realist. I find that it is a completely insoluble contradiction at the heart of metaphysical realism, I don’t think it even can be solved because you cannot posit a fundamental gap and then mend the gap later without contradicting yourself. There has to be no gap from the get-go. I see these “problems” as not things to be “solved,” but just a proof-by-contradiction that metaphysical realism is incorrect. All the arguments against direct realism, on the other hand, are very weak and people who espouse them don’t seem to give them much thought.

There is a strange phenomenon in academia of physicists so distraught over the fact that quantum mechanics is probabilistic that they invent a whole multiverse to get around it.

Let’s say a photon hits a beam splitter and has a 25% chance of being reflected and a 75% chance of passing through. You could make this prediction deterministic if you claim the universe branches off into a grand multiverse where in 25% of the branches the photon is reflected and in 75% of the branches it passes through. The multiverse would branch off in this way with the same structure every single time, guaranteed.

Believe it or not, while they are a minority opinion, there are quite a few academics who unironically promote this idea just because they like that it restores determinism to the equations. One of them is David Deutsch who, to my knowledge, was the first to publish a paper arguing that he believed quantum computers delegate subtasks to branches of the multiverse.

It’s just not true at all that the quantum chip gives any evidence for the multiverse, because believing in the multiverse does not make any new predictions. Everyone who proposes this multiverse view (called the Many-Worlds Interpretation) do not actually believe the other branches of the multiverse would actually be detectable. It is something purely philosophical in order to restore determinism, and so there is no test you could do to confirm it. If you believe the outcome of experiments are just random and there is one universe, you would also predict that we can build quantum computers, so the invention of quantum computers in no way proves a multiuverse.

It does not lend credence to the notion at all, that statement doesn’t even make sense. Quantum computing is inline with the predictions of quantum mechanics, it is not new physics, it is engineering, the implementation of physics we already know to build stuff, so it does not even make sense to suggest engineering something is “discovering” something fundamentally new about nature.

MWI is just a philosophical worldview from people who dislike that quantum theory is random. Outcomes of experiments are nondeterministic. Bell’s theorem proves you cannot simply interpret the nondeterminism as chaos, because any attempt to introduce a deterministic outcome at all would violate other known laws of physics, so you have to just accept it is nondeterministic.

MWI proponents, who really dislike nondeterminism (for some reason I don’t particularly understand) came up with a “clever” workaround. Rather than interpreting probability distributions as just that, probability distributions, you instead interpret them as physical objects in an infinite-dimensional space. Let’s say I flip four coins so the possible outcomes are HH, HT, TH, and TT, and each you can assign a probability value to. Rather than interpreting the probability values as the likelihood of events occurring, you interpret the “faceness” property of the coin as a multi-dimensional property that is physically “stretched” in four dimensions, where the amount it is “stretched” depends upon those values. For example, if the probabilities are 25% HH, 0% HT, 25% TH, and 50% TT, you interpret it as if the coin’s “faceness” property is physically stretched out in four physical dimensions of 0.25 HH, 0 HT, 0.25 TH, and 0.5 TT.

Of course, in real quantum mechanics, it gets even more complicated than this because probability amplitudes are complex-valued, so you have an additional degree of freedom, so this would be an eight-dimensional physical space the “quantum” coins (like electron spin state) would be stretched out in. Additionally, notice how the number of dimensions depends upon the number of possible outcomes, which would grow exponentially by 2^N the more coins you have under consideration. MWI proponents thus posit that each description like this is actually just a limited description due to a limited perspective. In reality, the dimensions of this physical space would be 2^N where N=number of possible states of all particles in the entire universe, so basically infinite. The whole universe is a single giant infinite-dimensional object propagating through this infinite-dimensional space, something they called the “universal wave function.”

If you believe this, then it kind of restores determinism. If there is a 50% probability a photon will reflect off of a beam splitter and a 50% probability it will pass through, what MWI argues is that there is in fact a 100% chance it will pass through and be reflected simulateously, because it basically is stretched out in proportions of 0.5 going both directions. When the observer goes to observe it, the observer themselves also would get stretched out in those proportions, of both simulateously seeing it it pass through and be reflected. Since this outcome is guaranteed, it is deterministic.

But why do we only perceive a single outcome? MWI proponents chalk it up to how our consciousness interprets the world, that it forms models based on a limited perspective, and these perspectives become separated from each other in the universal wave function during a process known as decoherence. This leads to an illusion that only a single perspective can be seen at a time, that even though the human observer is actually stretched out across all possible outcomes, they only believe they can perceive one of them at a time, and which one we settle on is random, I guess kind of like the blue-black/white-gold dress thing, your brain just kind of picks one at random, but the randomness is apparent rather than real.

This whole story really is not necessary if you are just fine with saying the outcome is random. There is nothing about quantum computers that changes this story. Crazy David has a bad habit of publishing embarrassingly bad papers in favor of MWI. One paper he defends MWI with a false dichotomy pitching MWI as if its only competition is Copenhagen, then straw manning Copenhagen by equating it to an objective collapse model, which no supporter of this interpretation I am aware of would ever agree to this characterization of it.

Another paper where he brings up quantum computing, he basically just argues that MWI must be right because it gives a more intuitive understanding of how quantum computing actually provides an advantage, that it delegates subtasks to different branches of the multiverse. It’s bizarre to me how anyone could think something being “intuitive” or not (it’s debatable whether or not it even is more intuitive) is evidence in favor of it. At best, it is an argument in favor of utility: if you personally find MWI intuitive (I don’t) and it helps you solve problems, then have at ya, but pretending this somehow is evidence that there really is a multiverse makes no sense.