In 1913 Niels Bohr proposed a model for the hydrogen atom in which
the electron moved in a circular orbit around the nucleus, with
the centrifugal force of the electron in the orbit just balanced
by the electrostatic attraction of the nucleus.
To the question "Why doesn't the electron radiate energy and fall
into the nucleus as electromagnetic theory predicts?", Bohr gave
the blunt reply "It just doesn't."
The theory of oscillating dipoles and radiation may apply to radio
antennae, he proposed, but not to things the size of atoms; just
as the separate categories of wave and particle do not apply at
For a cornerstone of his theory Bohr assumed that stable atoms could
exist with electrons in circular orbits.