Old ‘Ghost’ Theory of Quantum Gravity Makes a Comeback

The force we experience most intimately remains the most mysterious. Physicists understand how vast migrations of particles called photons light up our homes, and how swarms of “gluon” particles hold together the cores of our atoms. But they can’t say what gravity particles, if any, delight us as babies by enabling our spoons to plummet to the floor. The force of gravity has proved so difficult to…

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