Perhaps the explanation of quantum decoherence theory is the most convincing, and quantum decoherence theory has been confirmed experimentally, so it may be useful to explain it here.
What Schrödinger did not expect was that "Schrödinger's cat," an experiment of thought that would have been used to attack the satire of the Copenhagen School, would become a proposition that theoretical physicists would be studying for decades to come. The central purpose of this thought experiment is to refute the Copenhagen School's incomplete explanation of quantum mechanics in the microscopic field, and the bridge is connected at both ends of the macroscopic and microscopic, that is, cats and microscopic particles that may decay.
The decay behavior of the particles is a superposition, and through this bridge, then the cat's dead and alive are also in the superposition state, which is absurd and illogical. But Schrödinger overlooked a huge loophole in this experiment
That is, particle decay triggers the Geiger counter, which itself is a macroscopic object. That is to say, it is not as Schrödinger said: the act of opening the box causes the cat's dead and alive wave function to collapse, but is caused by the Geiger counter.
In short: the cat's life and death have nothing to do with whether the person opens the box or not, and whether it looks with the eyes. It is related to the Geiger counter (i.e. measurement behavior).
This also happens to be the Copenhagen School's explanation of Schrödinger's cat thought experiment, which seems invulnerable, but there are still some problems
That is, after the cat enters the box, does it exist in the superposition of dead and alive? The Geiger counter is also an object made of microscopic particles, so why does it cause the wave function of the particle decay behavior to collapse?
There have been countless theories to explain these two problems, including the most sci-fi "parallel universe" explanation, including the "hidden variable theory" explanation, and the most reliable and experimentally confirmed is the "quantum decoherence explanation".
What is quantum decoherence, in simple terms: the coherence of a quantum system (easily understood and considered a superposition state) becomes quantum entangled with the open environment, a process that transforms the quantum behavior of the quantum system into classical behavior (i.e., the collapse of the wave function in Schrödinger's equation). Quantum decoherence takes time, and at the macroscopic scale, this time is very, very, very short.
If quantum decoherence is explained in the Schrödinger's cat experiment, then the experiment looks like this:
A sealed box is placed in a quantum system (decay particles) whose decay behavior is superimposed, and next, all the other experimental equipment: Geiger counter, relay, hammer, poison bottle, cat are simultaneously put into the box and close the box.
Then the following happened in a very, very, extremely short period of time.
As the external environment of the decaying particle changes (the above objects are added), the quantum system of the decaying particle becomes quantum entangled with this environment, at which point all objects within the box (including the box) enter a superposition state.
Due to quantum decoherence, in this very short period of time, the superposition state of the system collapses as a wave function and enters an eigenstat (i.e., a definite state).
Assuming that the decaying particle enters the eigenstat state is the decay state, then the Geiger counter will trigger the relay, smash the hammer, break the poison bottle, and the cat will die. On the contrary, the cat is still alive and well.
This interpretation seems bland, and once similar to the "parallel universe" interpretation, which cannot be falsified. But in 1996, French physicist Arroche first quantitatively observed the phase coherence of the mesoscopic superposition of radiation fields gradually being destroyed by quantum decoherence. Arosh himself won the 2012 Nobel Prize in Physics for this remarkable achievement.
It seems that this mischievous kitten, which has plagued the physics community for decades, has finally been tamed by humans, but unfortunately, we still don't know the physical mechanism behind the phenomenon of quantum decoherence.