Carl Sagan's Calendar Analogy of Time Since the Big Bang

Modified: 2010-01-30

Sagan (1977) created a powerful analogy, the cosmic calendar, to explain how much time has passed since the Big Bang, the primordial explosion that created the universe nearly 14 billion years ago. In his analogy, Sagan maps the time since the Big Bang onto a one-year calendar where January 1 is when the Big Bang happened and January 1 one year later is today. Let’s examine some of those dates:

I’m always amazed whenever I re-read Sagan’s cosmic calendar because it so clearly illustrates how little time humans have been living on Earth. Although this chapter will cover some 4,000,000 years of hominin existence, that enormous span of years is small in comparison to the lifespan of the universe and of the planet.

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