Time has an arrow: It only ever seems to move in one direction. The future is always unknown to us, while the past forever remains locked and inaccessible. And yet, the vast majority of the laws of physics don’t seem to care about the direction of time at all. The equations that govern everything—from subatomic particles to the orbits of planets—can’t discern between forward and backward motion in time.
So, where does the arrow of time come from? A growing group of physicists believe that it originates in the force of gravity itself. But to get there requires a radical reshaping of Einstein’s General Theory of Relativity. The new idea is called Shape Dynamics, and it just may be our future theory of gravity.
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