Measurements of the cosmic microwave background indicate that the universe is very nearly spatially flat, and therefore according to general relativity the universe must have almost exactly the critical density of mass/energy.
Pengukuran pada latar belakang gelombang mikro kosmis mengindikasikan bahwa alam semesta hampir secara spasial rata, sehingganya menurut relativitas umum, alam semesta haruslah memiliki energi/massa yang hampir sama dengan rapatan kritisnya.