BBC
Article On Dark Energy
Over the past five years, the mysterious tale of dark
matter has been taken yet another bizarre twist. Just as
cosmologists decided that the Universe is full of a strange invisible
matter, they then realised that space was even weirder than they had
thought.
After a full census of all the galaxies visible in the Universe,
astronomers calculated that their total mass (including their hidden
dark matter) only made up about one-third of the critical density needed
to satisfy the best current theory about the early Universe [known as inflation].
At first, cosmologists thought that inflation must be wrong. But then
further data from measurements of the cosmic
microwave background showed that the total density of the Universe
did add up to this special critical density, so inflation could be
reinstated and another solution had to be found. So even after their
best attempts to renovate our cosmic home, most of the Universe still
remained elusive.
The problem is that this new component seems even stranger than dark
matter. Not only is it invisible just like dark matter, but it must have
a repulsive force, otherwise it would get sucked into galaxies and
affect their motion. So this mysterious stuff has been labeled 'dark
energy' and is a kind of cosmic antigravity force that counteracts the
attractive force of gravity. This means that instead of the expansion of
the Universe slowing down, in fact, it is speeding up. Recent
measurements of distant supernovae agreed with this conclusion, finding
that the Universe was indeed expanding with increasing pace.
Interestingly,
this had already been foreseen in a botched sum. But this wasn't the
sloppy homework of a spotty student, this was a calculation by Albert
Einstein no less! It was 1917 and he was trying to reduce the dynamics
of the whole Universe into a set of mathematical formulae. His results
insinuated that the Universe was expanding. However like the vast
majority of people at the time, Einstein assumed that the Universe was
static. So to stop his model Universe from growing, he invented a number
he called the 'cosmological constant' to insert into his equations,
restoring the safe, steady nature of his static Universe.
After Edwin Hubble found that the Universe was indeed expanding,
Einstein quickly retracted this number, calling it his 'biggest
blunder'. But he needn't have been so hasty because now, nearly 80 years
later, it has been reinstated to account for this mysterious dark energy
that is overtaking gravity. These new findings are helping cosmologists
look into the future and foresee the destiny
of the whole Universe.
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