If the universe is isotropic and the gravitational properties, which we observe in small objects such as planets, stars and even neutron stars and black holes, apply to large objects such as galaxies and even the universe as a whole. Can we then assume that as the universe is expanding it is becoming less dense? As gravity is dependent on both mass and the distance from the centre of gravity, as the universe expands its overall gravity must decrease. Gravity has a profound effect on time; experiments have demonstrated that the more intense a gravitational field the slower time passes within it. In an expanding universe where gravity is decreasing, it logically follows that time must accelerate. The basic formula for calculating speed/velocity is V=d/t if time is not constant then the very basis for calculating speed indicates that; all velocities (including the speed of light) are relative to our position in time (or distance, in time, from the big bang). I came to this conclusion when reading up on Mach's Principle. Is this logic sound or have I missed some important factor?