Page "Observable universe" Paragraph 7

Both popular and professional research articles in cosmology often use the term " universe " to mean " observable universe ".

This can be justified on the grounds that we can never know anything by direct experimentation about any part of the universe that is causally disconnected from us, although many credible theories require a total universe much larger than the observable universe.

No evidence exists to suggest that the boundary of the observable universe constitutes a boundary on the universe as a whole, nor do any of the mainstream cosmological models propose that the universe has any physical boundary in the first place, though some models propose it could be finite but unbounded, like a higher-dimensional analogue of the 2D surface of a sphere that is finite in area but has no edge.

It is plausible that the galaxies within our observable universe represent only a minuscule fraction of the galaxies in the universe.

According to the theory of cosmic inflation and its founder, Alan Guth, if it is assumed that inflation began about 10 < sup >− 37 </ sup > seconds after the Big Bang, then with the plausible assumption that the size of the universe at this time was approximately equal to the speed of light times its age, that would suggest that at present the entire universe's size is at least 10 < sup > 23 </ sup > times larger than the size of the observable universe.