What is dark energy doing to our universe?
Dark energy remains perhaps the greatest unsolved mystery in cosmology, aside from the question of how the universe got started in the first place!
Currently dark energy has mostly benign effects, causing the universe to expand at a moderate, though accelerating pace. If dark energy’s properties remain stable in the future, or if dark energy is similar to Einstein’s famous ‘cosmological constant’, the universe will expand indefinitely.
There are, broadly speaking, two other possible alternative scenarios where dark energy’s density changes over cosmic time. Neither scenario is particularly hopeful. In one, dark energy loses its power, decaying to zero and causing the acceleration to stop. In some models, the decay of its strength can lead to a ‘Big Crunch’, the collapse of all the matter in the universe, perhaps leading to a ‘bounce’ that causes another Big Bang.
In the second alternative scenario, in the extremely deep future, dark energy’s strength increases with time, possibly causing the so-called ‘Big Rip’ where the force associated with dark energy’s acceleration dominates over all other forces, including the chemical bond forces that hold atoms in our bodies together. But don’t worry – that would not happen for another 70 billion years or more… so keep paying your taxes!