the change in the rate of the expansion of the universe, Everyone expected
to see, a deceleration due to the effect of gravity, instead astronomers discovered the universe was accelerating its expansion. Some mysterious force is acting like anti-gravity pushing galaxies (actually
super clusters of galaxies) ever further about from each other.
There are a number of theories explaining dark energy, very few of
which are well motivated by particle physics. But i believe the Axial force
offers a well motivated cause of the repulsive effect of intergalactic space.
In General Relavity both energy and pressure create gravititional pulls, and
while energy is always positive, pressure can be either positive (like gas
in a balloon pushing outwards), or negative when an attractive force is
pulling particles towards each other. It turns out that a negative pressure
causes a repulsive gravitional force. So in order to produce a negative
pressure in intergalactic space, we need a substance with very little mass-energy, but a strong attractive force between its constitant particles.
My (rather rough) calculations show that the attraction between the spins
of neutrinos in plasma of neutrinos, is enough to cause dark energy, if
the neutrinos feel the axial force (with strength 1/60 of the electromagnetic
force).
In fact it give the current measured energy density of dark energy, provided
the lightest neutrino has a mass of about 0.15 meV (milli-electron volts)
and the next to lightest has a mass of about 8 meV. The mass difference
is that measured in solar neutrino oscillation experiments, so only
the lightest mass, is a prediction of the axial force theory.
If this neutrino plasma is responsible for the dark energy of the universe
then, we can be safe knowing that the big rip will not occur. Instead
eventually the neutrino plasma will become sparse enough to decay
back into another axi-photonic background radiation that will disperse
away.
(wikipedia)
