The very first structures in the Universe

The first moments of the Universe can be reconstructed mathematically even though they cannot be observed directly. Physicists have greatly improved the ability of complex computer simulations to describe this moment, discovering that a complex network of structures can form in the first trillionth of a second after the Big Bang. These microscopic clumps have masses of only a few grams and fit into volumes much smaller than particles.

source https://www.sciencedaily.com/releases/2021/03/210325115351.htm