Originally Posted by
Dreamwoven
The SOCIETY for POPULAR ASTRONOMY
Electronic News Bulletin No. 458 2017 December 3
DO DARK MATTER AND DARK ENERGY REALLY EXIST?
Universite de Geneve
For close on a century, researchers have hypothesized that the Universe
contains matter that can not be directly observed, known as 'dark
matter'. They have also posited the existence of a 'dark energy' that
is more powerful than gravitational attraction. Those two hypotheses,
it has been argued, account for the movement of stars in galaxies and
for the accelerating expansion of the Universe respectively. But --
according to a researcher at the University of Geneva -- those concepts
may not be valid: the phenomena that they are supposed to describe can
be demonstrated without them. The research exploits a new theoretical
model based on the scale invariance of the empty space, potentially
solving two of astronomy's greatest problems. In 1933, the Swiss
astronomer Fritz Zwicky claimed that there was substantially more matter
in the Universe than we can actually see. Astronomers called that
unknown matter 'dark matter', a concept that was to take on yet more
importance in the 1970s, when the US astronomer Vera Rubin called on
it to explain the movements and speed of the stars. Scientists have
subsequently devoted considerable resources to identifying dark matter
-- in space, on the ground and even at CERN -- but without success. In
1998 a second problem arose: a team of Australian and US astrophysicists
discovered the acceleration of the expansion of the Universe, earning
them after some delay the Nobel Prize for physics in 2011. However, in
spite of much effort, no theory or observation has been able to define
the black energy that is allegedly stronger than Newton's gravitational
attraction. In short, dark matter and dark energy are two problems that
have stumped astronomersfor over 80 years and 20 years respectively.
The way we represent the Universe and its history are described by
Einstein's equations of general relativity, Newton's universal gravita-
tion and quantum mechanics. The model-consensus at present is that of a
big bang followed by an expansion. In that model, there is a starting
hypothesis that seems not to have been taken into account. That is the
scale invariance of the empty space; in other words, the empty space and
its properties do not change following a dilation or contraction. The
empty space plays a primordial role in Einstein's equations as it
operates in a quantity known as the 'cosmological constant', and the
resulting Universe model depends on it. On the basis of that hypothesis,
researchers are now re-examining the model of the Universe, pointing out
that the scale invariance of the empty space is also present in the
fundamental theory of electromagnetism.
When the researchers carried out cosmological tests on the new model,
they found that it matched the observations. They also found that the
model predicts the accelerated expansion of the Universe without having
to factor in any particle or dark energy. In short, it appears that
dark energy may not actually exist, since the acceleration of the
expansion is contained in the equations of the physics. In a second
stage, astronomers focussed on Newton's law, a special case of the
equations of general relativity. The law is also slightly modified when
the model incorporates the new hypothesis. Indeed, it contains a very
small outward acceleration term, which is particularly significant at
low densities. The amended law, when applied to clusters of galaxies,
leads to masses of clusters in line with that of visible matter
(contrary to what Zwicky argued in 1933): that means that no dark matter
is needed to explain the high speeds of the galaxies in the clusters.
A second test demonstrated that the law also predicts the high speeds
reached by the stars in the outer regions of galaxies (as Rubin had
observed), without having to turn to dark matter to describe them.
Finally, a third test looked at the dispersion of the speeds of the
stars oscillating around the plane of the Milky Way. That dispersion,
which increases with the age of the relevant stars, can be explained
very well by the invariant empty space hypothesis, while there was
previously no agreement on the origin of that effect.
