Rocket often produces that effect. The assumption of homogeneity and isotropy results in solutions (not explicit closed form solutions but a categorization of possibilities) of the Einstein field equations that permit a decomposition of 4-dimensional spacetime as a 1-parameter foliation of 3-dimensional space-like hyperspaces of constant curvature. Originally Posted by Cyberia The hypersphere (a 4D sphere) works best for an expanding universe. Nothing will have any mass and the universe will become ‘conformally invariant’ which mathematically is a valid state from which the next big bang can occur thus the universe cycles through aeon after aeaon indefinately. Spheres are compact.To understand the origin of lumpiness (galaxies and such) you need to understand the theory of inflation.
Flip a coin ten times and it is possible that you will have ten heads or ten tails or anything in between. Where these needles penetrate the balloon is where there are galaxies. At time C, the balloon is now 18 feet across and the galaxies are much further apart, but all in exactly the same position with the needles still held steady and penetrating them exactly as before.The universe is anything but smooth.