Is it possible to explain themain ideas of GR without complicated math? In particular, what is the relation of current model of universe (FLRW) and GR? what is the difference between spacetime and universe, spacetime is surely curved and universe can by flat at same time? both mass and energy bend spacetime, in what proportion? what is the max quantity of mass allowed, due to what? I read that neutrinos can't have more than 2 eV of mass-energy because there would be too mauch mass in the universe, it that is true, why so?