It’s not a question of whether the ‘wave function’ is or isn’t mind-dependent. The equation describes the distribution of probabilities. When the measurement is taken the possibilities all reduce to a specific outcome. That is the ‘collapse’. Measurement is what does that, but measurement itself is not specified by the equation, and besides it leaves open the question of in what sense the particle exists prior to measurement. — Wayfarer
What might help is to consider that "the measurement" involves both preparing the coherent state and then thermally interacting with the system so as to decohere it.
A deflationary understanding of the collapse issue is that first up, we accept our experiments demonstrate there is something to be explained. Quantum physics shows that entanglement, superposition, contextuality, retrocausality (as time entanglement) are all things that a larger view of the real world, of Nature in itself, has to take into account. A classical level of description only emerges in the limit of a grounding quantum one.
But then what is going on to decohere the quantum?
To demonstrate the quantum nature of reality in the lab, we have to first prepare some particle system in a state of coherence. So the scientist makes what is then broken. Nature is set up for its fall by first that fall being prevented from happening in its own natural way – just by the fact there is always usually dust, heat, and other sources of environmental noise about at our human scale of physics – and then allowed to happen at a moment and in a way of the scientist's choosing.
So a pair of electrons are entangled in sterile conditions that quite artificially create a state of quantum coherence. The scientist's artfully arrange machinery – built with scientific know-how, but still a material device designed to probe the world in a certain controlled fashion – manufactures a physical state that can be described by a probabilistic wave function.
Now this wavefunction already includes a lot of decohered world description. It assumes a baseline of classical time already. In quantum field theory, the Lorentz invariance that enforces a global relativistic classicality is simply plugged in as a constraint. So a lot of classical certainty is assumed to have already emerged via decoherence starting at the Big Bang scale that now allows the scientist to claim to have the two electrons that are about to perform their marvellous conjuring trick.
A state of coherence is prepared by the larger decohering world being held at bay. A wavefunction is calculated to give its probabilities of what happens next. The wavefunction builds in the assumption about the lack of dust, vibrations, heat in the experimental array. Those are real world probabilities that have been eliminated for all practical purposes from the wavefunction as it stands.
Instead the experiment is run and the only decohering constraints that the electron states run into are the specific ones that the scientist has in advance prepared. Some kind of mechanical switch that detects the particle by interacting thermally with it and then – because the switch can flip from open to closed – report to the scientist what just happened in the language that the scientist understands. A simple yes or no. Left or right. Up or down. The coherent state was thermally punctured and this is the decoherent result expressed in the counterfactual lingo of a classicality-presuming metaphysics.
Out in the real world, decoherence is going on all the time. Nature is self-constraining. That is how it can magic itself into a well formed existence. It is a tale of topological order or the emergence of complex structure. Everything interacts with everything and shakes itself down into some kind of equilibrium balance. Spacetime emerges along with its material contents due to the constraints of symmetrical order. Fundamental particles are local excitations forced into a collective thermal system by the gauge symmetries of the Standard Model – SU(3)xSU(2)xU(1).
The quantum is already tightly constrained by the Big Bang going through a rapid fire set of phase transitions in its first billionth of a second. The wave function at the level of the universe itself becomes massively restricted very quickly.
So in our usual binary or counterfactual fashion, we want to know, which is it? Is the cosmos fundamentally quantum or classical. But as an actuality, it is always an emergent mix. The realms we might imagine as the quantum and the classical are instead the dichotomous limits of that topological order.
There never is a pure state of quantum coherence (and so indeterminacy) just as there never is a pure state of classical determinacy. The Big Bang quickly bakes in a whole bunch of constraints that limit the open possibilities of the Universe forever. Thermal decoherence reigns. The Universe must expand and cool until the end of time.
As humans doing experiments, we step into this world when it is barely a couple of degrees away from absolute zero. We can manipulate conditions in a lab to demonstrate something that illuminates what a pure quantum metaphysics might look like in contrast to a pure classical metaphysics. We can filter out the dust, heat and vibration that might interfere with the coherent beam of a laser or whatever, and so start to see contrary properties like entanglement and contextuality. Then we can erase that view by imposing the click of a mechanical relay at the other end of maze of diffraction gratings half-silvered mirrors that we have set up on a table in a cool and darkend air-tight room.
But the Cosmos was already well down its thermal gradient and decohered when we created this little set-up. And even our "collapse of the wavefunction" was bought at the expense of adding to that thermal decoherence by the physical cost of some mechanical switch that got flipped, causing it to heat up a tiny bit. Even for the dial to get read, some scientist's retina has to be warmed fractionally by photopigments absorbing the quanta of its glowing numerals. The scientist's brain also ran a tiny bit hotter to turn those decoded digits into some pattern of interpreting thought.
"Aha, it happened! I see the evidence." But what happened apart from the fair exchange of the scientist's doing a little entropy production in return for a small negentropic or informational gain?
What collapses the wavefunction? Well who prepared it in the first place. The Universe expended unimaginable entropy in its Big Bang fireball to bake in a whole lot of decoherent constraints into the actuality of this world. The needle on any quantum purity was shoved way over to the other side of the dial even in the first billionth of a second.
A complication in the story is that it is in fact right about now, 13 billion years down the line, that we are nearest a classical realm with its rich topological order. Matter has become arranged into gas clouds, stars, planets, and scientists with their instruments and theories. But in the long run, all that matter gets returned towards an inverted version of its original near-quantumly coherent state. The Heat Death de Sitter void where all that exists is the black body radiation of the cosmic event horizon.
But anyway, right now there is enough negentropy about in terms of stars and habitable planets to feed and equip the scientist who wants to know how it all works. The inquiring mind can construct a delicate state of coherence on a laboratory bench and run it through a maze that represents some counterfactual choice. Does the wave go through one or other slit, or both slits at the same time? A classical metaphysics seems to say one thing, a quantum metaphysics demands the other.
Which reality we then see depends on at which point we thermally perturb the set-up with our measuring instrument. If reading the dial and becoming conscious of the result mattered so much, then we would likely have to take greater precautions about keeping them well clear of the equipment too, along with the dust, vibration and other environmental disruptions.
The scientist of course finds the result interesting because it says both understandings of reality seem true. Particles are waves and waves are particles. Reality is quantum in some grounding way – the Big Bang and Heat Death look to confirm that's were everything comes from and then eventually returns as some kind of grand dimensional inversion. Hot point to cold void. And then what we call classicality is the topological order that arises and reaches its passing height somewhere around the middle. Like right about now. You get electrons and protons making atoms, which make stars, which make planets, which get colonised by biofilms that earn their keep by keeping planetary surfaces about 40 degrees C cooler than they would otherwise be if they were left bare.
And so there you have it. Mindfulness is life doing its thing of accelerating cosmic entropification – creating states of coherence and then decohering them down at the level of enzymes and other molecular machines. A scientist can play the same game on a bench top. Spend a little energy to construct a state of poised coherence. Report what happens when a little more energy is spent on decohering it within the contexuality of different maze configurations.
Well designed, a contrast between a quantum metaphysics and a classical physics can be demonstrated. We can take that demonstration and apply it to the entirety of existence as if that existence were entirely hung up on the question of which kind of thing is it really – pure quantum or pure classical?
Or we can instead look a little closer and see that the quantum and the classical are our abstracted extremes and what is really going on is an act of cosmic decoherence within which we can roll the decoherence back a little bit towards a dust-free and isolated coherence and then let it catch up again rather suddenly at the click of a mechanical relay. The almost costless informational transaction that still nevertheless has its thermal cost, as would be measured by a thermometer attached to the mechanical relay.