Simulations of the dense cosmic forest in intergalactic space illuminated by distant quasars have revealed new insights into the properties of dark matter that have recently been published in Physical Review Letters. The study and its results further support the theory of Cold Dark Matter, which is composed of particles that move very slowly, while, for the first time, they highlight the incompatibility with another model, the Fuzzy Dark Matter (FDM), for which dark matter particles have larger velocities.In order to study these dark matter properties, COSMOS Consortium investigators analysed the interaction of the “cosmic web” – a network of filaments made up of gas and dark matter present in the whole Universe – with the light coming from very distant quasars and galaxies. Photons interacting with the hydrogen of the cosmic filaments create many absorption lines called the “Lyman-alpha forest”. The atomic interaction of photons with the hydrogen present in the cosmic filaments is used to study the properties of the cosmos and of the dark matter at enormous distances. On the basis of the results obtained, they were able to infer some of the characteristics of the particles that compose the dark matter. In particular, evidence showed for the first time that the mass of the particles, which allegedly compose the dark matter according to the FDM model, is not consistent with the Lyman-alpha forest observed by the Keck telescope (Hawaii, US) and the Very Large Telescope (European Southern Observatory, Chile). The data, instead, support the scenario envisaged by the cold dark matter model.