Doomsday argument

The Doomsday Argument is a way of thinking about how long our world has been around. It suggests that there is a limited number of people who will ever be born in the world and that based on the number of people already born, we can estimate how many people will be born in the future. So if we can count the number of people who have already been born, we can figure out how long the world has been around and how long it might last. It's like trying to figure out how many people have left a party by counting the number of people who are still there.