It’s a law of numbers, there’s no possible way the universe is this damn big and we’re the only ones out here in these streets. Hell for all we know there’s an exact copy cat version of us looking around but unfortunately all the planets we can see the light is billions of years old already so we could be staring right at our twins and not even know it (vice versa).we actually should be budgeting for that, especially with our nuclear weapons, It may seem like a waste to but with how big our universe is and how clueless we are to things out there simply put, that possibility will always be there for intergalactic invasion.