Marcel Luttgens wrote:


How do you explain that galaxies already existed 2 GY after the Big Bang,
and that some of them are nearly as large as the largest galaxies in the
universe today ?

Current models put galaxy formation at about a billion years after the initial
expansion. At roughly 300,000 years after the initial expansion, the conditions
in the universe were such that regions where gravity and pressure balance would
contain roughly 100,000 times the mass of the Sun. Exceeding this mass means
gravity wins and collapse can commence. Masses beyond a trillion times the mass
of the Sun would be unstable. So, you have lumps ranging in mass from 10^5
solar masses to 10^12 solar masses shrinking under gravity, which covers the
mass range of both globular clusters and galaxies.