The universe tries to discover itself

Dark matter

Around eighty percent of the matter in the universe consists of a substance that no one has seen before - dark matter. Overall, it should make up almost 27 percent of the energy density in space, while dthe baryonic matter of which everything we know consists of contributes only five percent. Scientists use various methods to find out what is behind dark matter.

Matter and energy distribution in the universe

The first indications of the existence of dark matter came back in the 1930s when the Swiss astronomer Fritz Zwicky investigated the movements of galaxies in the Coma galaxy cluster. These were much too fast for the visible matter - stars, gas and dust - to hold them in the galaxy cluster with its gravity. This phenomenon could only be explained by the assumption that there are vast amounts of invisible mass that provides additional cohesion among the celestial bodies. But what exactly does this matter consist of, which apparently only shows itself through its gravitational interaction with conventional matter and otherwise eludes observation?

So-called MACHOs (massive astrophysical compact halo objects, translated: massive, astrophysical, compact halo objects), which include brown dwarfs and black holes, for example, are not the only possible explanations. It must actually be a completely new form of matter. Theoretical physicists have already proposed a number of hypothetical particles that dark matter could consist of. For example, the lightest supersymmetric particle, the neutralino, has many suitable properties. The Neutralino is a possible candidate for the so-called WIMPs (weakly interacting massive particles, translated: weakly interacting massive particles), which many experimental physicists are now looking for. They are pursuing three different approaches.

  • Experiments in the air or in space
    It is believed that when two WIMPs meet, they annihilate each other and release energy in the form of a photon. In order to detect these photons or their secondary products such as electrons and positrons, one goes to great heights. Because in the lower layers of the atmosphere the particles react with air molecules, are simply absorbed or trigger particle showers so that they are lost for the measurement.

  • Underground experiments
    In order to demonstrate the interaction of a WIMP with an ordinary particle of matter in a detector, it must be shielded from cosmic radiation and other sources of interference as well as possible. Corresponding laboratories are therefore usually built in former mines or under a mountain. Since the interactions they are looking for occur extremely rarely, the researchers also need a lot of detector material and long measurement times.

  • Accelerator experiments
    In large accelerator facilities, attempts are made to artificially generate dark matter. This requires very high energies. In addition, you need sophisticated algorithms to filter out processes in which WIMPs can arise from the many events that occur during a particle collision. A typical indicator would be a lack of energy, for example, since the WIMPs are invisible to the detector when they leave the detector, but at the same time carry a lot of kinetic energy with them.