  The unexpectedly large radii of hot Jupiters are a longstanding mystery whose
solution will provide important insights into their interior physics. Many
potential solutions have been suggested, which make diverse predictions about
the details of inflation. In particular, although any valid model must allow
for maintaining large planetary radii, only some allow for radii to increase
with time. This reinflation process would potentially occur when the incident
flux on the planet is increased. In this work, we examine the observed
population of hot Jupiters to see if they grow as their parent stars brighten
along the main sequence. We consider the relation between radius and other
observables, including mass, incident flux, age, and fractional age (age over
main sequence lifetime), and show that main sequence brightening is often
sufficient to produce detectable reinflation. We further argue that these
provide strong evidence for the relatively rapid reinflation of giant planets,
and discuss the implications for proposed heating mechanisms. In our population
analysis we also find evidence for a "delayed-cooling effect", wherein planets
cool and contract far more slowly than expected. While not capable of
explaining the observed radii alone, it may represent an important component of
the effect. Finally, we identify a weak negative relationship between stellar
metallicity and planet radius which is presumably the result of enhanced
planetary bulk metallicity around metal-rich stars and has important
implications for planet formation theory.
