I agree with the comment regarding the Born Rule, which is indeed a deep objection.
A further objection is aimed ad the claim that "we can be in a superposition" and it is: "If we can be in a superposition, why aren't we aware of it?"
This is a general question that any interpretation of QM must answer, and none does, which comes down to: "Why is there a classical world at all?"
There is a sense in which every interpretation of QM is an attempt to answer this question, but none do.
Decoherence, for example, simply asserts that we cannot be aware of quantum effects except via interference phenomena. Why not? Why can't we be directly conscious of the various incoherent components of the wavefunction in the same sense of directly that I am directly conscious of my cat sitting beside me? [1] I don't have to do any fancy interferometry or statistical inference to be aware of the cat, so why do I have to mess about with statistics and interferometry to be aware of the wavefunction, given I myself am described by one?
The fact that my multiple incoherent states do not interfere with each other is irrelevant unless you have some reason to believe that it is only via coherent interactions (interferecne patterns) that the wavefunction manifests itself to consciousness, and why would that be?
When I measure a gamma decay why am I aware of an event at a moment in time rather than a continuous probability wave? Likewise, why can't I be conscious of the wholistic universe that Many Worlds implies?
I've focused on consciousness here because there is no doubt we are directly aware of the classical world but are only indirectly aware of the quantum world, but there is very little reason to believe there is anything particularly special about consciousness in this regard. More likely, the brain, body, planet, etc, all "partake in" classical physics, none of which makes any sense from a quantum perspective.
That is: if all you knew about was quantum mechanics, you would never come up with Born's Rule or anything like it because you would never have any reason to talk about the results of classical measurement. You would not be aware than anything like classical measurement could exist.
So if we believe that QM is somehow foundational or fundamental to the classical world (and who doesn't?) then the fact that it gives no indication that the classical world even exists is something of a problem.
[1] To belabour the point: I do not mean "direct" in any Cartesian sense, but simply that there is a perfectly ordinary causal relationship between my cat and my awareness of my cat, which is quite different from my awareness of wavefunctions, which can only be via indirect means. We might have any number of additional senses, but all of them would be direct in this sense: none of them would allow me the immediate, simultaneous perception of a photon travelling through both slits at once. As Feynman said: this is the fundamental mystery.
> A further objection is aimed ad the claim that "we can be in a superposition" and it is: "If we can be in a superposition, why aren't we aware of it?"
Sounds rather like the fish being unaware of water. What would not being in a superposition feel like?
> Decoherence, for example, simply asserts that we cannot be aware of quantum effects except via interference phenomena. Why not? Why can't we be directly conscious of the various incoherent components of the wavefunction in the same sense of directly that I am directly conscious of my cat sitting beside me? [1] I don't have to do any fancy interferometry or statistical inference to be aware of the cat, so why do I have to mess about with statistics and interferometry to be aware of the wavefunction, given I myself am described by one?
So "you" is a quantum computer or something behaving like one, right? For you to "be aware of" a wavefunction, you'd have to causally interact with it. And that's very hard because of e.g. the no-cloning theorem; all you can do is entangle a qbit in your head with the qbit you're trying to measure, but what does that actually get you? What does that subjectively feel like? What operation would you expect to be able to perform that you can't?
A further objection is aimed ad the claim that "we can be in a superposition" and it is: "If we can be in a superposition, why aren't we aware of it?"
This is a general question that any interpretation of QM must answer, and none does, which comes down to: "Why is there a classical world at all?"
There is a sense in which every interpretation of QM is an attempt to answer this question, but none do.
Decoherence, for example, simply asserts that we cannot be aware of quantum effects except via interference phenomena. Why not? Why can't we be directly conscious of the various incoherent components of the wavefunction in the same sense of directly that I am directly conscious of my cat sitting beside me? [1] I don't have to do any fancy interferometry or statistical inference to be aware of the cat, so why do I have to mess about with statistics and interferometry to be aware of the wavefunction, given I myself am described by one?
The fact that my multiple incoherent states do not interfere with each other is irrelevant unless you have some reason to believe that it is only via coherent interactions (interferecne patterns) that the wavefunction manifests itself to consciousness, and why would that be?
When I measure a gamma decay why am I aware of an event at a moment in time rather than a continuous probability wave? Likewise, why can't I be conscious of the wholistic universe that Many Worlds implies?
I've focused on consciousness here because there is no doubt we are directly aware of the classical world but are only indirectly aware of the quantum world, but there is very little reason to believe there is anything particularly special about consciousness in this regard. More likely, the brain, body, planet, etc, all "partake in" classical physics, none of which makes any sense from a quantum perspective.
That is: if all you knew about was quantum mechanics, you would never come up with Born's Rule or anything like it because you would never have any reason to talk about the results of classical measurement. You would not be aware than anything like classical measurement could exist.
So if we believe that QM is somehow foundational or fundamental to the classical world (and who doesn't?) then the fact that it gives no indication that the classical world even exists is something of a problem.
[1] To belabour the point: I do not mean "direct" in any Cartesian sense, but simply that there is a perfectly ordinary causal relationship between my cat and my awareness of my cat, which is quite different from my awareness of wavefunctions, which can only be via indirect means. We might have any number of additional senses, but all of them would be direct in this sense: none of them would allow me the immediate, simultaneous perception of a photon travelling through both slits at once. As Feynman said: this is the fundamental mystery.