The term ‘monolithic collapse’ is often used as an alternative to primordial collapse. In this theory for galaxy formation, all galaxies were formed at the same time through the collapse of a cloud of primordial gas.

In theory, however, a subtle distinction can be made between primordial collapse and monolithic collapse. Primordial collapse (by definition) involved the collapse of a primordial gas cloud early in the history of the Universe, while monolithic collapse could still occur today.