I have read the papers of Verlinde, Jacobson, Beckenstein, Smoot and many other. They use the Unruh vacuum. It seems that Unruh vacuum is nothing but a thermal vacuum in the sense of thermodynamics. It contains vacuum fluctuations creating the virtual particle-antiparticle pairs. Verlinde wrote that gravity is an entropic force. Does it mean the gravitational field is an equivalent to the entropy of the vacuum with its virtual particles-antiparticles ? If the gravity is relatively measured what about the density of the vacuum (virtual particle-antiparticle pairs) ?