2. Atoms

‘Atoms’ describes how humans discovered that the world is composed of atoms, even though they are invisible to the unaided eye. Starting with the prescient ideas of the Ancient Greeks 2,500 years ago there were, by the time of the Enlightenment, three ideas for a definition of matter: all matter is made of atoms, atoms take up space, and atoms have mass. The concept of atoms became more firmly rooted with the chemical experiments of the 19th century, but it was not until Albert Einstein’s interpretation of Brownian motion (the random jiggling of tiny dust particles) in 1905, that any last objections to the atomic hypothesis were finally quashed.

Radiokooistofdatering en teoiogiese refleksie

Radio-carbon dating and theological reflection. A brief description of radio-carbon and its implications serves as the context for a plea to extensively and radically revise "orthodox" Reformed theological discourse as practised in South Africa. Faith within a worldview determined by the atomic hypothesis is briefly explored by emphasising God-talk as moral discourse.

1997 Polanyi Award Lecture Why are there atoms in chemistry?

Dalton made a bold assumption in his atomic hypothesis by stating that atoms retained their mass and their identity in chemical combination. Its vindication had to await Rutherford's nuclear model of the atom. The continuing evolution of chemistry led to the realization that atoms exhibit not only a unique mass but also characteristic additive properties, thereby making it possible to recognize their presence in a molecule and to predict the molecule's static and reactive properties. The theoretical vindication of the model of a functional group as the carrier of chemical information had to await the work of Feynman and Schwinger. Their generalization of physics leads to a unique definition of an atom as an open quantum system and makes possible the renormalization that is required to account for the short-range nature of the forces that enable one to identify a given group in any environment. The lecture will demonstrate that the proper open systems predicted by the quantum action principle define the atom and that this definition accounts for the retention of an atom's chemical identity by enabling one to replace the quantum mechanical observables for force and energy with dressed, real space density distributions whose forms parallel the transferable topology of the electron density distribution.Key words: atom, action principle, atoms in molecules, functional groups.