The visible universe is the total volume of space within the universe that can be observed directly from a particular point in spacetime. The volume is determined by the distance that light could travel away from this point in all the time that light has existed, plus the amount that space in the observer's region has expanded in that time; this distance is the radius of the visible universe. Given that light has existed for approximately 13.7 billion Earth-years, the visible universe from any given point in spacetime is about 13.7 billion light-years plus the expansion of space around that point in 13.7 billion Earth-years. Earth's visible universe is roughly 93.6 billion light-years in diameter, while Tetro's is 74.2 billion light-years across. Although the visible universe represents a