Spacetime in General Relativity

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© NASA/STScI.

In Einstein's theory of general relativity, space is warped by the presence of mass and energy, but is featureless on small scales. Quantum mechanics, on the other hand, predicts that if you zoom in on empty space and look at distances much smaller than an atom, you will find energy fluctuations large enough to create particle-antiparticle pairs. The quantum mechanical view is supported by laboratory experiments, so space cannot be smooth and featureless on small scales. On the other hand, tests of general relativity on astronomical length scales find that it is the correct theory of gravity as well as we can measure. The correct way to incorporate quantum ideas into the theory of gravity is one of the largest outstanding problems in theoretical physics. (Unit: 11)