I do not think photons have mass or gravitational fields. There may be some link between the electromagnetic force and gravity at the instant of the big bang - but thus far no grand unification theory works for this.<br /><br />However, I do not know if photons are involved in the propagation of dark energy.<br /><br />Perhaps dark matter propagates dark energy along with gravity?<br /><br />I wouldn't want to make light of the matter - but then everything would be lighter if that was the case - Correct??? <br /><br />I.e. if matter is converted into energy, then gravity is reduced?<br /><br />Such that the gravity of our universe increased when energy was converted into matter????<br /><br />And therefore the universe expanded???<br /><br />Of course, that makes no sense unless one considers dark energy also.