**4. Present value of light deceleration**
Finally, from the radius, the density and equation (9) is now easy to obtain the

**present value **of light deceleration, which results to be 2.2 10-10 m/s-2 , i.e.

**our model predicts that a decrease of 1m/s could be observed in about 140 years**. This very small value has not been observed, but could be hidden within the error bars in recent determinations of c.

**Very precise laboratory measurements of c could detect this deceleration in a few decades.**
In connection with this, it is remarkable that, using precision lunar orbital periods from 1978 to 1981,

**Van Flandern (1984) obtained a small deceleration in c**:

-c’/c = (3.2 ±1.1) 10-11/year. (23)

This result represents a light deceleration of about 3 10-10 m/s2 , in agreement, taking into account the error margins quoted, with our calculated value.

The variation of c should be tested with ‘mechanical’ clocks such as those based on mechanical vibrators, pulsars rotation or planetary revolution, because atomic clocks periods depend on c.