> Observers are what deliver to us the results of randomly sampling from the probability distribution defined by the squared amplitude of the wave function by "collapsing" it, according to the Copenhagen interpretation. However, there is no particle that acts as an observer, they all just follow the Schrodinger equation, but nothing that exists isn't a particle.
This is why proponents of the Many-Worlds Interpretation claim that Occam's razor favours it: you don't need to posit "observers" or "collapses"; there's just the evolution of the wave function.
Occam's razor is not a scientific principle, it's just a rule of thumb. I have yet to see a proof that given a number of equal strength explanations for a phenomenon, the simplest one is always true.
One other thing that's often forgotten is that in Occam's opinion the simplest explanation for everything was God.
This is why proponents of the Many-Worlds Interpretation claim that Occam's razor favours it: you don't need to posit "observers" or "collapses"; there's just the evolution of the wave function.