Erwin Schrödinger, Mind and Matter
Chapter 4: The Arithmetical Paradox: The Oneness of Mind
The reason why our sentient, percipient and thinking ego is met nowhere within our scientific world picture can easily be indicated in seven words: because it is itself that world picture. It is identical with the whole and therefore cannot be contained in it as a part of it. But, of course, here we knock against the arithmetical paradox; there appears to be a great multitude of these conscious egos, the world is however only one.
There is obviously only one alternative, namely the unification of minds or consciousnesses, Their multiplicity is only apparent, in truth there is only one mind. This is the doctrine of the Upanishads.
The doctrine of identity can claim that it is clinched by the empirical fact that consciousness is never experienced in the plural, only in the singular. Not only has none of us ever experienced more than one consciousness, but there is also no trace of circumstantial evidence of this ever happening anywhere in the world.
Mind is by its very nature a singulare tantum. I should say: the over-all number of minds is just one. I venture to call it indesctructible since it has a peculiar time-table, namely mind is always now. There is really no before and after for mind. There is only now that includes memories and expectations. But I grant that our language is not adequate to express this, and I also grant, should anyone wish to state it, that I am now talking religion, not science – a religion, however not opposed to science, but supported by what disinterested scientific research has brought to the fore.