Redefining Reality - The Intellectual Implications of Modern Science

sort of thing we need, but it isn’t there. It was then realized that
if we extend the standard model with , we can
explain WIMPs.
This tweaking of the theory worked so well that by the 1990s, it
ever since.
The only one of the four physical forces that works over long
distances is gravitation, and gravity is an attractive force. As
such, all the matter in the universe must be pulling on all the
other matter in the universe, opposing the expansion. It seemed,
then, that there were only two possible options for the large-scale
history of the universe.
If there is enough matter in the universe, this gravitational
pull will be strong enough to stop the expansion and cause the
universe to begin contracting.
If there is not enough energy to fully stop the outward
momentum, the expansion will slow, but it will continue until
the energy density becomes so low that it extinguishes itself;
the universe will become cold and dead.
But in 1998, Saul Perlmutter, Brian Schmidt, and Adam Reiss
found that the expansion of the universe is speeding up. If gravity
is a drag on the universe yet the universe is expanding, there must
be some kind of energy driving the expansion. If the invisible
stuff increasing the mass of galaxies is dark matter, then the
invisible energy driving the increasing rate of expansion would be
dark energy.
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