1.9     Special Topic: Quantum Mechanics and Babies

We might imagine that molecular orbitals and quantum mechanics, so critical in the microscopic world, would have little real influence on our day-to-day lives because we really do live in a world of baseballs, not electrons. Or so it would seem. Yet it has been argued¹¹ that “a new-born baby becomes conscious of . . . the consequences [of the Pauli principle] long before he finds it necessary to take account of the consequences of Newton’s laws of motion.” How so? Ernest Rutherford (p. 2) told us long ago that an atom is essentially empty space because the nucleus is very small compared to the size of a typical atom, and electrons are even tinier than the nucleus. Why is it, then, that when “solid” objects come together they do not smoothly pass through one another, as they sometimes do in 3 A.M. science fiction movies?

The answer is that the apparent solidity of matter is the result of Pauli forces. When your hand encounters the table top, the electrons in the atoms of your hand and the electrons in the atoms of the table top have the same spins and nearly the same energies. The Pauli principle ensures that these electrons cannot occupy the same regions of space, so the table top feels solid to your touch, even though Rutherford showed us that it is not. Were it not for the Pauli principle, our apprehension of the world would be vastly different.

 

¹¹By Walter Kauzmann (1916–2009) in Quantum Chemistry (Academic Press, New York, 1957).