2-8
Dark Energy
Dark energy
is a hypothetical form of energy in the universe that would be
responsible for accelerating the expansion of the universe. Dark
energy is
everywhere and evenly distributed in the universe. It behaves
as if it were
exerting negative gravity.
In 1917,
Albert Einstein had already introduced a cosmological constant
into his field equations. As Einstein assumed a static universe,
he did this to
prevent the universe from collapsing due to gravity, according
to his theory.
After the discovery of the expansion of the universe, Einstein
withdrew the
idea of this anti-gravity and called it “his greatest blunder”.
Distribution of dark matter and dark energy in the universe relative
to
visible matter according to WMAP measurements
In the
1990s, the study of distant supernovae, the Supernova Cosmology
Project, discovered that the expansion of the universe began to
accelerate
some five billion years after the Big Bang. The only way to explain
this was
to introduce an unknown force that behaved like a cosmological
constant
and acted like negative gravity.
Careful
analysis of the WMAP data in March 2003 revealed that 74% of
the total energy of the universe consists of dark energy. In the
meantime,
observations from the Planck Observatory have reduced this proportion
to
68.3%. The mass energy of ordinary (baryonic) matter amounts to
4.9%,
the remaining 26.8% is explained by dark matter. Cosmologists
do not yet
have an explanation for this dark energy.
They think
about the energy of the vacuum itself, the so-called zero-point
energy. However, this causes very big problems for the theorists
when this
energy is calculated according to quantum mechanics. The outcome
is much
higher (as much as 10120 to 10140 times) than the observed dark
energy.
