Accelerating expansion may
not be real but instead be an apparent effect, according to new research
published in the journal of Monthly Notices of the Royal Astronomical Society.

A new study by a group of
researchers at the University of Canterbury in Christchurch, New Zealand, found
the fit of Type Ia supernovae to a model of a universe devoid of all dark
energy to be a better fit than to the model containing dark energy.

Dark energy, proposed in
1998, has been assumed to form an approximate 70% of the present material
content of our Universe. This nebulous quantity is a popular, well known
component of unknown physics.

Current models of the
Universe require dark energy to explain the observed rate of acceleration in
the expansion of our Universe. Such measures are based off of measurements in
the distance of supernova explosions in distant galaxies that appear to be
farther apart than they should be if the acceleration of expansion were not
taking place. This brings a question to light... if dark energy is not the
explaining factor for such a phenomenon... then what is? What if our approach
has been incorrect this whole time?

In the past year, the
statistical significance of this signature cosmic acceleration has been a
common idea subjected towards heated debate. Previous debates have pitted the
standard Lambda Cold Dark Matter (Î›CDM) cosmology against a universe that is
empty, whose expansion neither decelerates nor accelerates. Both models take on
the simplified 100 year old cosmic expansion law-- Friedmann’s equation.

Friedmann’s equation assumes
an expansion identical to that of a featureless “coup” of a universe that has
no complicating structure. However, the present day Universe is actually one
that contains within it a complex cosmic web of breathtaking galaxy clusters in
sheets and filaments surrounding empty and vast voids.

The chart below represents
the difference in magnitudes of supernovae in the Î›CDM and Timescape
cosmologies paired with the magnitudes in which the supernovae would appear to
be in an empty universe (the horizontal, dashed line). Both models clearly
represent the recent acceleration that was followed by a deceleration. However,
in the Timescape model this is not a real effect and the curve is flatter than
in the case of the Î›CDM model. (Lawrence Dam, Asta Heinesen, and David
Wiltshire.)

David Wiltshire of the
University of Canterbury in Christchurch New Zealand, the leader of the study
said the following, potentially revolutionary words: “The past debate missed an
essential point; if dark energy does not exist then a likely alternative is
that the average expansion law does not follow Friedmann's equation."

Rather than comparing the
Î›CDM cosmological model with an empty universe, this new study compares the fit
of supernova data in the Î›CDM model to another model, Timescape cosmology. The
model is devoid of all dark energy. Instead, clocks carried by observers in
galaxies differ from the clock that best describes average expansion once the
lumpiness of our Universal structure becomes significant. Figuring out an
inferring acceleration is heavily dependent on the clock used.

Timescape cosmology turned
out to be a slightly better fit to the supernova catalogue than Î›CDM cosmology.
This reminds us of the words uttered during the OJ Simpson trial... “If it
doesn’t fit then you must acquit.” However, not enough statistical data has
been gathered in order to rule out one or the other and neither of the current
evidence is strong enough to rule out one or the other either.

Thankfully, future missions
such as the European Space Agency’s Euclid satellite will harness the power to
discern which of the models is real and aid scientists in their adventure
towards figuring out whether dark energy is real or not. Solving that cosmic
puzzle not only requires more data, but also a more thorough understanding of
the properties of the supernovae that currently limit the precision in which
they can be used as a ruler to measure large, cosmic distances.

With all of that in mind,
this new study shows significant, unexpected effects that are missed if only
one expansion law is applied. This is rolling out the carpet for greater
discoveries yet to come and sheds more light onto current questions physicists
have today.