The separation of experiment and environment is an artificial distinction. Decoherence is caused by random phase shifts, which may appear due to interaction wi

The separation of experiment and environment is an artificial distinction. Decoherence is caused by random phase shifts, which may appear due to interaction with the environment, but by the entropic definition of temperature, a sufficiently large and warm object will be disorderly enough to have this effect as well. You can not be hot and coherent at the same time, as the first implies a large degree of disorder and the other implies a large degree of order. > In fact, proponents of MWI believe that the whole universe, which is an isolated system, is itself a quantum system. MWI doesn't make any experimentally verifiable predictions as far as I'm aware, so is not particularly in this discussion.