EVIDENCE FOR DARK ENERGY

Relic radiation

The CMB is the primordial ‘echo’ of the universe. Measurements taken by probes show that the universe’s geometry is nearly flat. For that to be the case, the total amount of matter in space must tally with the average density of matter to energy in the cosmos. But the CMB’s spectrum shows that this isn’t what’s happening – matter only accounts for 30 per cent of the density.

Exploding stars

Type Ia supernovae occur in binary systems when a white dwarf’s gravity pulls material from the other star onto itself, causing it to explode, briefly outshining all other stars in its galaxy. Their intrinsic brightness is known, so their distances can be calculated from how dim they appear. Using this, scientists were able to show that the universe’s expansion is accelerating.

The shape of the cosmos

Its shape is governed by the general theory of relativity, which describes how spacetime is warped by matter. Measurements of the CMB show that the universe is nearly flat, but there’s not enough matter to keep it that way. Since E=mc2 shows that matter and energy are two sides of the same coin, could dark energy remedy the shortfall?

The universe is expanding

The expansion rate of the universe is the time it takes to expand a certain amount. In a certain period of time, space will expand by a certain amount – whatever makes space expand doesn’t dilute or decrease in density. An expanding universe leads to a greater amount of space, and more of what caused the expansion. This suggests dark energy may be a feature of space itself.