Look at a few numbers that we will assume to at least be in the ballpark, and roughly correspond with scientific consensus: 1. The Universe is assumed to be 13

Look at a few numbers that we will assume to at least be in the ballpark, and roughly correspond with scientific consensus: 1. The Universe is assumed to be 13.7 billion years old. 2. Nothing can move faster than c, so light years are an effective measure of the maximum distance anything can travel since its inception. 3. Our Sun is about 4.6 billion years old. 4. The universe is 13.7 billion light-years across. Now, from these, I'm going to make a few propositions, given the lack of obvious extraterrestrial intelligence: 1. Stars stable enough to create life didn't appear until fairly late in the game, around the 9 billion year mark. 2. 5 billion years is a better-than-average time for a star system to stabilize and evolve life. 3. Stars stable enough to create life are still fairly sparse, as life in this universe is still fairly young. 4. Assuming 7 billion years as a bare minimum for the starting point for this process, and assuming the Earth is fairly quick, a reasonable upper bound for the distance that a civilization must be from us to have contacted us is 2 billion light-years. Of course, there are a lot of variables here, and it's highly probable that maximum reasonable speed for a life-form to travel is as low as .1c, which means that even a civilization that sprung into existence at 6 billion years (assuming a star system stabilized very early in the game and then also evolved life in the better-than-average time of 5 billion years) would only be able to travel 1 billion light years, cutting off a fair amount of the universe from contact. While the numbers involved in the time since the big bang are large, the distances a hypothetical civilization would have to travel are probably larger, especially given that evolving life, in our solar system's case, took well over a third of the time since the big bang, and that's not counting the circumstances that brought about the formation of our solar system, which took the remaining 2/3rds.