Could there be more than three?
A possible way of resolving the greatest problem of physics.
Open door #1 and scroll through our changing understanding of gravity...
To celebrate the recent centenary of the first major test of Einstein's general theory of relativity, we look back over how our picture of gravity has changed.
Does light have weight? Newton thought so. His laws predicted that gravity would bend light, two centuries before Einstein's revolution.
Most of us think that we have the capacity to act freely. Our sense of morality, our legal system, our whole culture is based on the idea that there is such a thing as free will. It's embarrassing then that classical physics seems to tell a different story. And what does quantum theory have to say about free will?