TED: Questions no one knows the answers to

There's a new TED-Ed series that tackles questions that we don't know the answer to. In this first episode, TED Curator Chris Anderson asks: How many universes are there? And Why can't we see evidence of alien life? On the latter question, his answers are somewhat pedestrian and even outlandish, but Anderson takes a wide swath at the possibilities and includes some genuine solutions, including the Great Filter and postbiological existence.