I have sort of a vague question. Am I right in saying that only mass and not energy cause space to curve and have gravitational effects (and other affects that only depend on mass)? Or does the "relativistic mass" of a photon cause similar but reduced effects? That's sort of just a lead in question ... I was thinking about how all the stars in the universe are coverting mass to energy all the time, which means the total mass of the universe it constantly shrinking and the energy of the universe is increasing (yes, I know that the mass-energy stays the same). My question is if this has any major effects on the physics of the universe? Is it it just too negligable to matter, or does the relativistic mass or other energy effects function the same as the missing mass in all relevant cases, or what?