What situation would we expect if the universe was perfectly uniform?

If the universe were perfectly uniform, it would imply an even distribution of matter and energy throughout space with no localized concentrations. In such a scenario, gravitational forces that typically pull matter together to form structures like galaxies would be absent. As a result, there would be no density fluctuations to initiate the formation of galaxies. Essentially, the gravitational interactions required to create the varied and complex structures observed in our universe would not take place.

The other responses check against this. If the universe were entirely uniform, options involving identical planetary systems and specific regions for star formation would not hold true, as random variations in density are essential for such diversity to occur. Fluctuations in the cosmic microwave background reflect the uneven distribution of matter in the early universe, thereby contradicting the notion of perfect uniformity. Thus, the presence of galaxies is a clear indicator of non-uniformity in the universe.