The Observable Universe

This animation distinguishes the observable Universe from the total Universe. The total Universe may be finite or infinite (we don't know). The observable Universe is finite. It is a sphere centered on the Earth with a radius equal to the distance light could have traveled since the creation of the Universe (big bang). We cannot, even in principle, see anything outside our event horizon because light is the absolute speed limit and there hasn't been time for light to reach us since the big bang from points beyond the event horizon.

Other observers in the Universe have similar event horizons, with a radius dictated by the finite speed of light and the finite age of the Universe. Event horizons grow with time, since the distance that light could have traveled since the big bang grows with time. Thus, objects currently outside our event horizon can eventually enter our event horizon at some later time. Usage: Click "Play" to begin. Continue to click "Play" when action stops. "Step" moves forward one step and "Back" moves backwards one step. "Home" returns to the beginning from any point.