-----|| DARK ENERGY ||-----
Much is unknown than is known abt the DARK ENERGY.
We know how much dark energy there is because we know how it affects the Universe's expansion.
Other than that, it is a complete mystery. But it is an important mystery. It turns out that roughly 70% of the Universe is dark energy.
One explanation for dark energy is that it is a property of space.
Albert Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood.
The first property that Einstein discovered is that it is possible for more space to come into existence. Then one version of Einstein's gravity theory, the version that contains a cosmological constant , makes a second prediction: "empty space" can possess its own energy.
Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear. As a result, this form of energy would cause the Universe to expand faster and faster.
Unfortunately, no one understands why the cosmological constant should even be there, much less why it would have exactly the right value to cause the observed acceleration of the Universe.
Another explanation for how space acquires energy comes from the
quantum theory of matter. In this theory, "empty space" is actually full of temporary ("virtual") particles that continually form and then disappear.
But when physicists tried to calculate how much energy this would give empty space, the answer came out wrong - wrong by a lot.
The number came out 10 times too big. That's a 1 with 120 zeros after it. It's hard to get an answer that bad. So the mystery continues.......