We can mathematically guarantee that extraterrestrial life exists. Here's how. The first component to this equation: humans themselves. The fact that life, extraterrestrial or not exists is a factor in determining whether other life exists as will be made clear soon. Next, the rule of infinities. This rule states that given an infinite amount of time, materials and resources, anything that can happen will. Since the universe is always expanding, non-stop, and never will stop, this tells us that the universe is infinite. Mixing the two components, the fact of life and the rule of infinities tells us that since it is possible for life to happen (because it already has) it will happen again. It is mathematically impossible for there to not be extraterrestrial life out there. This goes hand in hand with the Drake equation, an equation that explains how many possible planets could contain and sustain life. The Drake equation however only takes into account the observable universe, and not at all the endless universe beyond the observable.