Quote:Today, as a professional theoretical chemist, I know that Sagan’s statements failed to recognise some fundamental features of atoms and molecules.

Quote:Misconceptions feeding the idea of the empty atom can be dismantled by carefully interpreting quantum theory, which describes the physics of molecules, atoms and subatomic particles. According to quantum theory, the building blocks of matter – like electrons, nuclei and the molecules they form – can be portrayed either as waves or particles. Leave them to evolve by themselves without human interference, and they act like delocalised waves in the shape of continuous clouds. On the other hand, when we attempt to observe these systems, they appear to be localised particles, something like bullets in the classical realm. But accepting the quantum predictions that nuclei and electrons fill space as continuous clouds has a daring conceptual price: it implies that these particles do not vibrate, spin or orbit. They inhabit a motionless microcosmos where time only occasionally plays a role.

Quote:The interior of the protons and neutrons is likely the most complex place in the Universe. I like to consider each of them a hot soup of three permanent elementary particles known as quarks boiling along inside, with an uncountable number of virtual quarks popping into existence and disappearing almost immediately. Other elementary particles called gluons hold the soup within a pot of 0.9 femtometres radius. (A femtometre, abbreviated fm, is a convenient scale that measures systems tens of thousands of times smaller than an atom. Corresponding to 10‑15 m, we must juxtapose 1 trillion femtometres to make one millimetre.)

Quote:If atoms and molecules remained a collection of point-like particles, they would be mostly empty space. But at their size scale, they must be described by quantum theory. And this theory predicts that the wave-like picture predominates until a measurement disturbs it. Instead of localised bullets in empty space, matter delocalises into continuous quantum clouds.