In the first chapter of The ABC of Relativity Betrand Russell points out most cogently that 'it is touch that gives us our sense of 'reality'. Some things cannot be touched: rainbows, reflections in looking-glasses, and so on. These things puzzle children, whose metaphysical speculations are arrested by the information that what is in the looking-glass is not 'real'. Macbeth's dagger was unreal because it was not 'sensible to feeling as to sight'. Not only our geometry and physics, but our whole conception of what exists outside us, is based upon the sense of touch.'
But Einstein discovered that 'much of what we learned from the sense of touch was unscientific prejudice, which must be rejected if we are to have a true picture of the world.'