Can you get rid of all the energy in the room in which you are reading this? Move the room far from the earth’s gravity, then toss out everything made of matter so you can cross off mass, kinetic, and potential energies. Also pump out the air, the cosmic rays constantly streaming in, and the fog of neutrinos that were made during the Big Bang. Next, kill the energy in photons: darken the room completely, and clear away the microwave radiation left over from the infant universe.
Now all that’s left in your room is empty space, and no energy – right? No! Your room still has “dark energy”. In a patch of space the size of your room, dark energy is so scant that it is nearly impossible to detect. But across the cosmos, which is full of space, it contributes a titanic 70% of all energy. Matter, in the form of stars, gas, and the mysterious dark matter, supplies most of the other 30%, while radiation in the form of photons and neutrinos chips in 0.01%.
