Our universe becomes less dense

Dark energy

By far the largest proportion of the total density of matter and energy in the universe - namely around 68 percent - is made up of an energy field that accelerates the cosmos: dark energy. This previously puzzling form of energy counteracts the gravity of the matter contained in the universe, which slows down the expansion of space. As far as we know today, dark energy dominates, so that the universe will expand forever.

Matter and energy distribution in the universe

While particle physicists and cosmologists propose concrete solutions to the question of the nature of dark matter, the situation with dark energy is considerably more difficult. In order for it to cause the observed accelerated expansion of the universe, its pressure must be negative. That alone runs counter to intuition, but is theoretically possible. Certain types of postulated quantum fields can actually create a negative pressure that acts as if it were causing repulsive gravity. Constructing models for this is the task of particle physics. However, there is still considerable room for maneuver because there are no specific experimental restrictions.

The negative pressure necessary for the accelerated expansion prevents the dark energy from forming structures. Nevertheless, it intervenes in the formation of the cosmic structure because it changes the course of cosmic expansion. Cosmic structures made of dark matter had to run against the general expansion of the universe when they were formed. Depending on the model for dark energy, these structures formed sooner or later in cosmic history, and accordingly the central areas of these structures also become more or less dense. Computer simulations have become an important tool for cosmologists here.

How can we learn more about dark energy? On the one hand, cosmologists want to find out more precisely how the expansion of the universe has developed since the Big Bang. Observations of certain star explosions, so-called supernovae of type Ia, and the weak gravitational lensing effect of large cosmic structures currently appear to be best suited for this. Furthermore, the study of the mentioned indirect effects of dark energy on cosmic structures will further deepen the connection between particle physics, cosmology and observational astronomy.