The exasecond (Es) is a unit of time in the International System of Units, defined as 1018 seconds using the SI prefix system. The unit is equal to 31.7 billion years, but the universe is only 13.8 billion years old, meaning the age of the universe is not yet an exasecond old. However the current age of the universe can be expressed as a fraction of an exasecond, at 0.435 Em old.