> Consciousness comes indirectly into quantum mechanics through the measurement postulate. You have to assume something special about measurement which breaks unitarity. Not all physicist are convinced, but it is the traditional way quantum mechanics is taught (all of the "transition probabilities" are really measurement probabilities). The problem is that you can't tell if your apparatus caused the collapse or if it was you that measured the apparatus that then caused the collapse. And because you can only know that something was "observed" when a conscious physicist makes that final readout you end up with a solipsistic situation where the only thing you can be certain of is that it was that last conscious observer that could have for sure collapsed the wave function.
> Here we report matter wave interferometer experiments in which C70 molecules lose their quantum behaviour by thermal emission of radiation. We find good quantitative agreement between our experimental observations and microscopic decoherence theory. Decoherence by emission of thermal radiation is a general mechanism that should be relevant to all macroscopic bodies.
> We observe that at temperatures below 2,000 K the emission rate is negligible, whereas at higher temperatures the molecules may emit photons whose wavelengths are comparable to (or even smaller than) the maximum path separation of ,1 mm. They transmit (partial) which-path information to the environment, leading to a reduced observability of the fullerene wave nature. Around 3,000 K the molecules have a high probability to emit several visible photons
yielding sufficient which-path information to effect a complete loss of fringe visibility in our interferometer.
There are experiments that show decoherence in absence of conscious measurement. For example, https://www.physics.upenn.edu/~pcn/Course/250/Week.of.02.21/...
> Here we report matter wave interferometer experiments in which C70 molecules lose their quantum behaviour by thermal emission of radiation. We find good quantitative agreement between our experimental observations and microscopic decoherence theory. Decoherence by emission of thermal radiation is a general mechanism that should be relevant to all macroscopic bodies.
> We observe that at temperatures below 2,000 K the emission rate is negligible, whereas at higher temperatures the molecules may emit photons whose wavelengths are comparable to (or even smaller than) the maximum path separation of ,1 mm. They transmit (partial) which-path information to the environment, leading to a reduced observability of the fullerene wave nature. Around 3,000 K the molecules have a high probability to emit several visible photons yielding sufficient which-path information to effect a complete loss of fringe visibility in our interferometer.