Another common source of confusion is that the accelerating universe does not imply that the Hubble parameter is actually increasing with time; since H ( t ) ≡ ≡ a ˙ ˙ ( t ) / a ( t ) , in most accelerating models a increases relatively faster than a ˙ ˙ , so H decreases with time. (The recession velocity of one chosen galaxy does increase, but different galaxies passing a sphere of fixed radius cross the sphere more slowly at later times.)