WHAT IS DARK ENERGY?
Dark energy is the name scientists give
to whatever is causing the expansion of
the Universe to accelerate.
It is not known to be a conventional
substance like atoms or ordinary matter.
Instead, it may be a property of space
itself or something associated with a
new field of physics.
THE UNIVERSE IS EXPANDING
The Universe has been expanding since
the early Universe.
For a long time, astronomers expected
gravity to gradually slow that expansion.
Observations of distant Type Ia
supernovae in the late 1990s revealed
something surprising: cosmic expansion
is accelerating.
DARK ENERGY IS NOT DARK MATTER
Despite their similar names, dark energy
and dark matter are very different.
Dark matter behaves as an unseen source
of gravity that helps form galaxies and
large-scale structure.
Dark energy is associated with the
accelerating expansion of the Universe.
THE COSMOLOGICAL CONSTANT
One leading explanation is Einstein's
cosmological constant, usually written
as Λ.
In this model, empty space itself has
a constant energy density. As the Universe
expands, this component continues to
affect the overall expansion.
WHAT WE KNOW ABOUT DARK ENERGY
ACCELERATED EXPANSION
Distant observations show that the
expansion of the Universe is speeding up.
COSMIC SCALE
Dark energy becomes increasingly important
as the Universe expands and matter becomes
more spread out.
SUPERNOVAE
Type Ia supernovae helped reveal that
cosmic expansion is accelerating.
COSMIC MICROWAVE BACKGROUND
Measurements of the early Universe help
constrain models of dark energy.
GALAXY DISTRIBUTION
The large-scale distribution of galaxies
provides another way to study cosmic
expansion.
BIG MYSTERY
Scientists still do not know whether
dark energy is a cosmological constant
or something more complicated.
DID YOU KNOW?
The expansion of the Universe is not
simply continuing — it is accelerating.
And the physical cause of that acceleration
remains one of the biggest unanswered
questions in modern cosmology.
THE EVIDENCE FOR ACCELERATED EXPANSION
Dark energy is the term used for whatever is responsible for the observed acceleration of cosmic expansion. Evidence developed from measurements of distant Type Ia supernovae and is studied together with observations such as the cosmic microwave background and the large-scale distribution of matter.
The name does not identify a known substance. A cosmological constant is one important model, but determining the physical explanation for accelerated expansion remains a major problem in cosmology.
Dark Matter · Supernovae · Cosmic Voids