Suppose the universe has no observers, and the universe's dynamics is governed by the Schrodinger equation. What does the wavefunction represent now? Is it that parts of the universe keep "measuring" other parts of the universe and the wavefunction represents the statistical description of what measurements get recorded as the universe evolves?

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    The "observer" in quantum physics, AFAIK, IS any other particle that interacts. Isn't this a physics question, btw?
    – kutschkem
    Commented Aug 1, 2022 at 5:53
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    @kutschkem I asked this on the physics site too. I also want to know philosophers' ideas. An "measurement" in QM is some interaction between a macroscopic and a microscopic system. An interaction between microscopic particles is unitary, while measurements are non-unitary. This is why the measurement problem is popular. If you just remove all macroscopic systems, then all evolutions become unitary. But the problem is that the wavefunction now becomes meaningless, because probabilities are meaningless without measurements.
    – Ryder Rude
    Commented Aug 1, 2022 at 6:20
  • Ok, understood, I think. So the thought experiment here is a universe consisting only of an interstellar medium withoutany clumps that would count as macroscopic?
    – kutschkem
    Commented Aug 1, 2022 at 7:11

2 Answers 2


The wavefunction represents what is happening in reality. It is not a statistical summary since the square amplitudes only act according to the calculus of probabilities in some circumstances:


A measurement is just an interaction between physical systems that creates a record of the value of some physical quantity. It has nothing to do with conscious observers, which aren't required to explain anything in quantum physics:



The wavefunction represents what a measurement, were it to take place, would find as the statistics. Since we talk about it and compute it normally in a context before the measurement, it should make sense, in the same way, to talk about it in a universe where the measurement is infinitelly far in the future (or, in other words, never happening).

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