New Scientist: "they found that the Universe's expansion began to accelerate about 6 billion years ago.
This agrees with the supernova and microwave measurements. All three methods imply that about 75 per cent of the energy in the Universe is in this repulsive form. 'It gives us much more confidence that dark energy is real,' says Allen.



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Weblinks

Chandra X-ray Observatory

X-ray Astronomy, Cambridge

Dark energy, NASA





Empty space

But what actually is dark energy? The new measurements are consistent with a kind of dark energy that is not changing very much with time. That could be an energy inherent to empty space, Einstein's 'cosmological constant'.
But the constraints are not tight, leaving numerous alternatives. These include a kind of weakening dark energy field called quintessence. Another option is a kind of energy that is getting more intense, which could eventually become so powerful that it tears everything apart, even atoms."