It's clear from your writing you don't understand the subject, much like the guy in the Quora link. The appeal to authority works here because unless you have a degree in the subject — TerraHalcyon
It's you who doesn't understand. I'm sorry to say because I'm not a solipsist either.
An observation is not an interaction. Every interaction is a virtual process and an observer looking at what he measures too. The photons reaching your retina are virtual ones too. They might have momentum and energy almost on shell (meaning the both obey the relativistic relation between them) but they are still not observed themselves.The system (process-observer-measuring device) remains in a superposition if it stays isolated from a second observer (which means the second observer is in a superposition too), the guy in your polemic. It could even be that there is
only superposition, without collapse. The talk about objective collapse, uttered by
some are put on your barricade just to back up your presumption. The claim to authority is just to hide your ignorance. Authority simply uses a priori assumption too. There simply
is no objective collapse when you stick to the basic principles. You can even consider the whole universe as a developing superposition, like is done in the many worlds interpretation, which was invented exactly to evade the problem of collapse (if collapse was objective, this wouldn't have been done, but collapse is problematic in the standard interpretation, giving rise to a non-unitary evolution of the wavefunction). And the guy is justified in using this interpretation. Let me explain.
If you observe a spin up thee is a second you observing a spin down. For the guy not observing you yet you are in a state of superposition of both outcomes in both parallel worlds (the one where you measured spin up and the one where you measured spin down). Simply because you always
are in superposition. In the world where you measured up, he is justified to see you as a superposition still because he is in superposition too. He is present in the world where you observed up, as well in the world where you observed down. Only when he observes you, the world will evolve in a new state that consists of four superimposed ones. Two in which you observed up and he observes up or down, and two where you observed spin down and he up or down. So you as well as him are
always in superposition, and observing causes the superposition to live happily after observing but in separate worlds. So either nothing is in superposition or all is. If he claims the world is in superposition if he doesn't observe it, he himself is in a superposition too.
To put it differently. If you observe a superimposed state of spin up and spin down, the superposition of you measuring up and down is still attached to the guy, in both the world where you measured up as in the world where you measured down. Only when the guy observes you, the two separate worlds will each split further in two separate states in which he observes you observing up and down. So in your world you might actually have observed up or down, but these two distinct outcomes will still be in superposition. For the guy, in both of these worlds with distinct outcomes for you, you are still in superposition and only when he observes you, he will see you have measured up or down. So from the state where you measured up, as well from the state where you measured down, two new states follow, because a superposition of you measuring up and down (apart from the actual outcomes you observe) is still contained in the both of them. Your observations might have caused two separate states (up and down), but the state of you observing the spin is still a superimposed one, and only the guy observing
you causes a split into two separate worlds in which he sees you observing up and down.
So the whole state is initially a superposition of the up and down spin of an electron
and you observing up or down spin. The total state is a product of these two states, with four outcomes, all superimposed firstly. If you observe firstly, there is a split between a spin up and a spin down state. From each of these two, up as well as down, the observation of the guy creates a split of you observing up and you observing down. This doesn't mean though that he observes up while you observed down. He will always observe the same spin as you observed.
To put it differently, for TG (the/that guy) you are still in a superposition of observing up and down. Your observation causes a local split, but only when TG observes the superposition of you observing up and down, the global splits in two distinct states. TG can't observe one of the two you's (one observing up and one observing down) if you did not actually observe. He can't observe something that doesn’t actually exist. The superposition of you observing up and down, is different from the superposition of the two spins, obviously. For TG you are still in a superposition, and you are, actually! Only when he observes you, from both the states with spin up and spin down, two new states will appear when TG observes you, one in which you have observed spin up and one in which you have observed spin down, no matter if the state it comes from contains up or down only. The states of spin up and down couple with the states of you observing up and observing down, and the product of these states gives rise to a state of four substates. One with spin up and you measuring up and down (which means you observe up while TG can observe you observing up as well as down) and one with spin down and you measuring up and down (which means you observe down while TG can observe you observing up as well as down). It may sound counterfactual that when you observe up TG can still observe you observing up as well as down, but that's exactly what the math tells us. There is a product state of spin up and you measuring up and down, as well as a product state of down with you measuring up and down. The sum of these two existed as a superposition first. Your observation of the spin led the separation of this sum into two distinct superpositions, the two products. Each product is a sum: spin up and you measuring up or down, and spin down and you measuring up and down.
So. At the start, the wavefunction is:
(up+down)(YOu+YOd),
Ignoring normalization factors. wher u is spin up and YOu is the state you observe (YO) up.ikewise for spin down.
Which can be written:
up(YOu+YOd)+down(YOu+YOd).
After you observed the spin, there are two states, each in a separate world:
up(YOu+YOd), and
down(YOu+YOd).
From these two worlds, TG's observation causes four worlds to come into play:
up(YOu) and up(YOd)
down(YOu) and down(YOd).
Now how the hell can a state whit spin up can go together with you observing spin down, up(YOd)? Following the rules we can nothing but conclude exactly that.
The only alternative: objective collapse theory or hidden variables.