How can the universe be speeding up in its expansion? Since gravity is the only force that controls wouldn’t the universe ultimately always contract again over time because gravity would eventually win out over the initial acceleration caused by the big bang?

Question

How can the universe be speeding up in its expansion? Since gravity is the only force that controls wouldn’t the universe ultimately always contract again over time because gravity would eventually win out over the initial acceleration caused by the big bang?

In: Physics

Answer 1

This is frequently confusing, but . . .

There is a difference between the [expansion of space-time](https://en.wikipedia.org/wiki/Expansion_of_the_universe) (where space literally expands as described by things like the cosmological constant, or energy density of space, or dark energy) and expansion within space-time (like a chemical explosion that moves things further apart)

>The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe with time.[1] It is an intrinsic expansion whereby the scale of space itself changes. The universe does not expand “into” anything and does not require space to exist “outside” it. Technically, neither space nor objects in space move. Instead it is the metric governing the size and geometry of spacetime itself that changes in scale. As the spatial part of the universe’s spacetime metric increases in scale, objects move apart from one another at ever-increasing speeds