SO..... dark matter is what is left inside the bell jar after you pump everything else out ?
In a way. Dark matter could possibly be made out of “ghost particles” that don’t interact other than gravitationally. In that case, the room you’re sitting in could be teeming with quintillions of then flying a few hundred miles per second. Not enough speed to escape galaxies, just cluster around them. Their density would be very low per square light year, of course, similar to dark energy. But overall, since there is a gawd awful amount of empty space compared to what we think as being normal, that adds up to a lot. And since these “ghost particles” travel below the speed of light, as they must for dark energy theories to be valid, they have mass.
Dark matter theories I mean. And cubic light years.