By determining the rate at which the universe is expanding,
Hubble may have helped solve the mystery of how old the
universe is, but it unexpectedly turned up an even more
profound one -- the fact that the rate of the universe's
expansion is not slowing down or even constant, but is
inexplicably accelerating. The culprit behind this, dubbed
dark energy, is now thought to make up about 70 percent of
the combined mass-energy in the entire universe, and it
remains an utter enigma. Solving this mystery could
revolutionize physics as we know it.
Science Friday | Exploring An Ever-Expanding Universe (30 min)
The Nobel Prize in Physics 2011
The Nobel Prize in Physics 2011 was divided, one half
awarded to Saul Perlmutter, the other half jointly to Brian
P. Schmidt and Adam G. Riess "for the discovery of the
accelerating expansion of the Universe through observations
of distant supernovae".
Press Release | Written in the stars
What will be the final destiny of the Universe? Probably it
will end in ice, if we are to believe this year's Nobel
Laureates in Physics. They have studied several dozen
exploding stars, called supernovae, and discovered that the
Universe is expanding at an ever-accelerating rate. The
discovery came as a complete surprise even to the Laureates
In 1998, cosmology was shaken at its foundations as two
research teams presented their findings. Headed by Saul
Perlmutter, one of the teams had set to work in 1988. Brian
Schmidt headed another team, launched at the end of 1994,
where Adam Riess was to play a crucial role.
The research teams raced to map the Universe by locating the
most distant supernovae. More sophisticated telescopes on
the ground and in space, as well as more powerful computers
and new digital imaging sensors (CCD, Nobel Prize in Physics
in 2009), opened the possibility in the 1990s to add more
pieces to the cosmological puzzle.
The teams used a particular kind of supernova, called type
Ia supernova. It is an explosion of an old compact star that
is as heavy as the Sun but as small as the Earth. A single
such supernova can emit as much light as a whole galaxy. All
in all, the two research teams found over 50 distant
supernovae whose light was weaker than expected - this was a
sign that the expansion of the Universe was accelerating.
The potential pitfalls had been numerous, and the scientists
found reassurance in the fact that both groups had reached
the same astonishing conclusion.
For almost a century, the Universe has been known to be
expanding as a consequence of the Big Bang about 14 billion
years ago. However, the discovery that this expansion is
accelerating is astounding. If the expansion will continue
to speed up the Universe will end in ice.
The acceleration is thought to be driven by dark energy, but
what that dark energy is remains an enigma - perhaps the
greatest in physics today. What is known is that dark energy
constitutes about three quarters of the Universe. Therefore
the findings of the 2011 Nobel Laureates in Physics have
helped to unveil a Universe that to a large extent is
unknown to science. And everything is possible again.
Why the Runaway Universe Discovery Won the Nobel Prize in
Physics (4+ min)
Why the universe probably is "flat" (15 min)
Lawrence Krauss makes the case for a flat universe, where
the total amount of mass-energy in the universe is and
always has been zero.
A Universe From Nothing' by Lawrence Krauss, AAI 2009 (1+ hr)
In physical cosmology and astronomy, dark energy is a
hypothetical form of energy which permeates all of space and
tends to accelerate the expansion of the universe. Dark
energy is the most accepted hypothesis to explain the
observations since the 1990s indicating that the universe is
expanding at an accelerating rate.
NASA's Hubble rules out one alternative to dark energy
Astronomers using NASA's Hubble Space Telescope have ruled
out an alternate theory on the nature of dark energy after
recalculating the expansion rate of the universe to
Hubble Confirms Dark Energy's Clout
By the way, this work was made possible by a little-known
but astounding effort undertaken with the Hubble Space
Telescope called the Cosmic Evolution Survey, or COSMOS.
From October 2003 to November 2005, HST's Advanced Camera
for Surveys acquired 38-minute-long exposures of 575
overlapping fields, collectively covering a patch of Sextans
a full 1.3° square.
COSMOS took 1,000 hours of Hubble time to acquire -- making
it even more ambitious than observatory's famous, but much
narrower, "deep fields." At full resolution, the final image
is 100,800 pixels on a side -- imagine a page in Sky &
Telescope 28 feet on a side and you'll get the picture (so
Astronomy Picture of the Day Archive