Who's Pushing and Who's Pulling?

Is the expansion of the universe triggered by the repulsion force of dark matter or by the pulling action of a mysterious massive force originating in the outer boundaries of the universe? Such information is currently unavailable, but one thing is for certain: gravity is not enough to keep the galaxies and galaxy clusters together in the distant future, meaning that the very likely fate of the universe is that it will end in a Big Rip rather than a Big Crunch.

Back in 1998, for the first time astronomers presented a possible explanation for the universe's acceleration expansion effects, in the form of dark energy and dark matter. Ever since, researchers all over the world have been trying to explain the properties of this elusive form of energy by fluctuations in the energy of quantum physics or even by proposing that, in fact, the universe has an extra set spacial dimensions on top of the three ones we experience every day.

A new study conducted at the Brera Astronomical Observatory in Merate, Italy, suggests that the intensity of the repulsion force exerted by dark energy fluctuates with time, thus they went searching for evidence that dark energy had an influence on the matter in the universe ever since the Big Bang event.

The vast majority of galaxies in the universe move away from each other at phenomenal speeds, but in some cases gravity somehow overtakes the repulsion force and brings galaxies together into massive mass accumulation, commonly known as galaxy clusters. By measuring the velocities of the galaxies exerting strong attraction forces towards each other, Italian astronomer Luigi Guzzo has been able to study the rate at which these galaxies bundle together in the universe.

With the help of observations conducted with the VIMOS-VLT Deep Survey that had been studying more than 6000 galaxies situated at distances of about 7 billion light years away, Guzzo was able to determine that the measurements are not enough to provide with conclusive evidence that the influence of dark energy is affecting in any way the motion of the galaxies through space. On the other hand, the increase in space expansion rate is influencing the galaxies in their struggle to form galaxy clusters. The higher the expansion rate, the less chance there is that a galaxy cluster will form into the future.

Nevertheless, conducting measurements into determining the characteristics of dark energy, its nature and how much of the mass of the universe is attributed to dark matter are relatively hard. Enzo Branchini, one of the scientists involved in the study, says that future studies covering large areas of the universe could be able to unveil the mystery.

Other astrophysicists, such as those from the Princeton University, also conducting research in the dark energy field, mostly use observation techniques involving distant supernovae explosion in order to search for similar features that would show that the distribution of matter in the universe is mainly determined by the effect produced by the action of dark matter. The most frustrating aspect of such work is that scientists cannot know for sure which research technique would have the best chance in revealing the nature and characteristics of dark energy.

The VVDS program is scheduled to make measurements on about 50,000 to 100,000 galaxies only in the next five years, which would provide with preliminary data that could be used to make a distinction between different scenarios. Alternatively, by 2017, the ESA will launch the Spectroscopic All-sky Cosmic Explores, or SPACE for short, which will have the mission to analyze about 2 million galaxies.