Cosmology is currently focused on learning more about three different things: inflation, dark matter, and dark energy. Inflation was the process that drove the early expansion of the universe—it is used to explain why the universe is basically the same in every direction. Dark energy is the label given to the apparently accelerating rate of expansion the universe is experiencing. Dark matter explains the huge amount of apparently invisible matter observed throughout the universe. These guys are seemingly very different, yet a key feature of physics has been the unification of seemingly different concepts. Could it be possible that inflation, dark matter, and dark energy are all aspects of a single underlying phenomenon?

Apparently so, according to new research published in Physical Review D. The idea that dark energy and inflation are somehow linked is not exactly new. They are both used to describe periods where the rate of the expansion of the universe is increased, and there have been a few attempts to find models that can link dark energy and inflation. Dark matter, however, was considered to be something else entirely. Now, a new look at inflation has proposed a set of dynamics that would lead to the universe we observe today and unite the three phenomena under a single conceptual framework.

We start off early in the universe, where there is lots of energy sitting in a field that drives inflation and bit of radiation in the form of photons, electrons, and quarks. The universe expanded quickly and, at a certain point, the inflation field density dropped below that of the radiation density, at which point the field decayed, releasing energy and heating up the universe in a process called re-heating.

After a while, the energy density would become high enough to drive a new epoch of inflation, called thermal inflation—this is analogous to the expansion of a high pressure gas that breaks its container and expands. After this occured, the universe was once again cold, and now symmetry breaking in the inflation field would drop even more energy into the radiation field, reheating the universe and resulting in a light-dominated universe. This would leave only nucleosynthesis and star formation to do before we humans could turn up to poke around.

The key points are that the inflation field is not completely exhausted at the present and, if certain parameters happen to be in the right range, it could play the role of dark matter. Furthermore, dark energy is exactly like inflation except on a much smaller scale, meaning that a residual inflation field could play the role of dark energy.

So, how does that work? Well, the average density of the inflation field is non-zero and, as a result, keeps the rate of expansion of the universe increasing. However, the density of the inflation field will fluctuate about this average value and, in places where there is a deficit, there will be less expansion, which will look just like a dark matter concentration.

Its a nice idea, but it has some way to go before it can gain acceptance. For instance, dark matter explains a large range of different phenomena on length scales ranging from a single galaxy through to the entire universe. This work has demonstrated that density fluctuations in the inflation field can mimic dark matter at the very largest scales. However, they would have to show that it can do so at every scale if it is to replace dark matter. By then, the Large Hadron Collider will have started turning up new particles, several of which are dark matter candidates. If that happens, physicists will be left to wonder why this new theory now predicts too much dark matter in the universe.

Physical Review D, 2008, DOI: 10.1103/PhysRevD.77.121301