  Scalar radiation, represented by a massless scalar field in a
Robertson-Walker metric, is taken into account. By using a weak non minimum
vacuum definition, the radiation temperature as a time dependent function is
obtained. When the universe evolution is nearly but non equal to $t^{1/2}$, it
is possible to fit the temperature of the microwave background. A particular
massive case is compared with the massless one. When the mass of the matter
field is next to the Planck one and the time is going to infinite, a similar
result to the Hawking radiation of the blackhole is obtained.
