What Is Dark Energy? More is unknown than is known. 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. Dark matter makes up about 25%. The rest -
everything on Earth, everything ever observed with all of our
instruments, all normal matter - adds up to less than 5% of the
Universe. Come to think of it, maybe it shouldn't be called "normal"
matter at all, since it is such a small fraction of the Universe.