Question

What is Dark Energy...?​

Answer 1

Answer:

In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales

Answer 2

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Dark energy is the name given to the mysterious force that's causing the rate of expansion of our universe to accelerate over time, rather than to slow down. That's contrary to what one might expect from a universe that began in a Big Bang. Astronomers in the 20th century learned the universe is expanding.