Thank you again for the thoughtful reply.

Your brain decoheres a zillion times per second. Your consciousness is far, far, far into the classical regime.

Observing does not cause collapse. Events which cause the wavefunction to split into dynamically separate parts do, and those happen at the same rate in a system regardless of how you cut it.

Eh? Observing is the only thing that causes collapse.

I agree that there are constant tiny thermodynamic events that, if observed, could cause decoherences a zillion times a second. But, usually these events are not observed.

Decoherence is me finding out which world I end up in, and this only happens as quickly as I think, once every ~1/10 seconds when I'm awake.

I'm guessing you would say that decoherence is my brain ending up in some world, and this happens every time any entropy-increasing chemical event happens.

How can I experimentally tell the difference between these? It's not obvious because even a high-speed detector requires me to read the readout with my (slow) brain. From my perspective, the detector doesn't collapse any wavefunctions until I look at it. I agree with you that if I looked at another brain I would see that brain decohering / doing thermodynamic stuff all the time. I also agree with you that if I looked at my own brain I would see my own brain doing a bunch of stuff really rapidly. You would say that my brain decoheres as quickly as a detector measures it. I would say that my brain decoheres only as quickly as I notice detector readouts. Until I look at the detector, my brain and the detector are in a superposition of states with different possible detector readouts.

I don't know how to test this.