NASA announced in may 2004 new results from the Chandra telescope
that offer independent confirmation that 3/4 of the universe is made up of dark energy.
26 galaxy clusters (1000-8000 million light-years away) has been measured,
to determine the distance to the galaxy clusters and the amount of hot gas in each one.
Plotting the results over cosmic time, the scientists determined this:
dark energy started speeding the universal expansion 6000 million years ago.
Dark energy was first proposed in 1998. Observations of distant supernova explosions
suggested the expansion of the universe to be accelerating, not slowing down as expected.
"Dark energy is perhaps the biggest mystery in physics, as such,
it is extremely important to make an independent test of its existence and properties."
Steve Allen, Cambridge, England.
"Until we better understand cosmic acceleration and the nature of dark energy,
we cannot hope to understand the destiny of the universe."
Michael Turner, University of Chicago.
May 2004