We must distinguish between the physical world of physics, and the physical world of our everyday experience. The physical world of physics, supposing physics to be correct, exists independently of my mental life. From a metaphysical point of view, it is solid and self-subsistent, always assuming that there is such a world. Per contra, the physical world of my everyday experience is a part of my mental life. Unlike the physical world of physics, it is not solid, and is no more substantial than the world that I see in dreams.
Source: Bertrand Russell : Mind and Matter (1950?)
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