Quantum physics, also developed in the 1920s, shows that in the subatomic realm, particles take on a hazy, nondefinite character, behaving as if they existed in several places at once. Although we don’t yet have a theory of “quantum gravity,” we can still estimate the size of the region in which quantum physics and gravitational physics would merge. This ultra-tiny scale is called the “Planck length,” named after the physicist Max Planck, a pioneer in quantum physics. The Planck length is 10-33 centimeters, a hundred million billion times smaller than a quark. Another way to visualize the
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