The Well-Tempered Cosmological Constant: Fugue in B$^\flat$
  Zero point fluctuations of quantum fields should generate a large
cosmological constant energy density in any spacetime. How then can we have
anything other than de Sitter space without fine tuning? Well tempering --
dynamical cancellation of the cosmological constant using degeneracy within the
field equations -- can replace a large cosmological constant with a much lower
energy state. Here we give an explicit mechanism to obtain a Minkowski
solution, replacing the cosmological constant with zero, and testing its
attractor nature and persistence through a vacuum phase transition. We derive
the general conditions that Horndeski scalar-tensor gravity must possess, and
evolve in a fugue of functions, to deliver nothing and make the universe be
flat.
