How will you explain dark energy to a layman?

But let me try. Cosmologists, like astrophysicists, tend to keep things simple. For astrophysicists, everything that's not hydrogen or helium is a “metal”. For cosmologists, everything in the universe is reduced to dust, baryons, radiation and dark energy. Let me explain. read more

So the density of dark energy never changes. In an expanding universe, dark energy expands but it does not get diluted; the work done on it by gravity creates enough dark energy to make up the deficit. Meanwhile, other stuff (matter, radiation) does get diluted in an expanding universe. So ultimately, dark energy prevails. read more

Because there's no other way, currently, to *explain things* about modern physics--like how older galaxies stick together--without assuming that there's a *LOT* more mass to the universe than what we can see in light and heat (in electro-magnetic forms of radiation). read more

Dark energy has negative pressure, and so is more analogous to an 'inward pull' (on say, a piston on a container with water at negative pressure); there's no need for scare quotes on "pressure" because it is pressure. read more