  Einstein's theory of general relativity describes gravity as the interaction
of particles with space-time geometry, as opposed to interacting with a
physical fluid, as in the old gravitational aether theories. Moreover, any
theoretical physicist would tell you that, despite its counter-intuitive
structure, general relativity is one of the simplest, most beautiful, and
successful theories in physics, that has withstood a diverse battery of
precision tests over the past century. So, is there any motivation to relax its
fundamental principle, and re-introduce a gravitational aether? Here, I give a
short and non-technical account of why quantum gravity and cosmological
constant problems provide this motivation.
