Constant electric fields are known to be unstable to spontaneous electron-positron pair production. Many experimental and theoretical efforts are focused toward observing spontaneous pair production, and there are opportunities to test today related phenomena by accelerating an electron with unit strength. Such experiments could help understand fundamental aspects of acceleration. The question I will focus on is: What is the relation between acceleration and temperature? There is a factor 2 disagreement between the Hawking-Unruh temperature obtained for an accelerated observer and the temperature of an electromagnetic field arising from its potential for spontaneous decay. Since the instability of the vacuum implies it has a finite excitation energy, a consistent understanding vacuum instability, temperature and acceleration may yield insight into the present accelerating expansion of the universe