How to pronounce “mass density” in English

And fluids are defined by mass density, and velocity, and pressure, and so on.

And he posits that the initial mass density of the universe was fine tuned to one out of 10 to the 24th or a septillion.

And so the paper goes on "we report measurement of the mass density and cosmological constant density omega and lambda of the universe, based on the analysis

energy uh couldn't be much larger than uh the mass density in ordinary space

It's actually the initial conditions on which laws work, the initial mass density of the universe.