Four-fifths of the matter in the universe is invisible. Nevertheless, this “dark matter” will determine the fate of the cosmos. But how is it distributed? That can be determined by measuring its gravitational effects. Gravity also changes the path that light takes as it travels from distant galaxies. The Hyper Suprime-Cam (HSC) of the Japanese Subaru telescope has studied these effects for approximately ten million galaxies. The farther away a galaxy is, the longer it takes its light to reach us, and the farther back we can see into the past. This allows us not only to measure the distribution of dark matter today, but we can also make statements on its distribution in the past.
The results confirm the expectations from other measurements – but not entirely. They show that the “lumpiness” has increased over billions of years. In the beginning, matter was largely distributed uniformly and then the existing deviations became more and more pronounced. The new measurements, however, also show differences with the data, for example, from the European Planck satellite. However, the matter is not as lumpy as expected. Currently, there is not enough data to decide whether this is a random deviation or whether the standard cosmology model is inadequate.