This fourth edition of selecta of my work on the stability of matter
contains recent work on two topics that continue to fascinate me:
Quantum electrodynamics (QED) and the Bose gas. Three papers have been
added to Part VII on QED. As I mentioned in the preface to the third
edition, there must be a way to formulate a non-perturbative QED,
presumably with an ultraviolet cutoff, that correctly describes low
energy physics, i.e., ordinary matter and its interaction with the
electromagnetic field. The new paper VII.5, which "quantizes" the
results in V.9, shows that the elementary 'no-pair' version of
relativistic QED (using the Dirac operator) is unstable when many-body
effects are taken into account. Stability can be restored, however, if
the Dirac operator with the field, instead of the bare Dirac operator,
is used to define an electron. Thus, the notion of a "bare" electron
without its self-field is physically questionable.