**If there are so many advanced civilizations out there, where is everybody?**

The implication of this paradox is that we are alone in this universe. However, the question whether there is life in space is inherently more complex than this, and thought must be given to the massive distances involved, development of space travel technology, and other factors.

Astronomer Frank Drake penned an equation that approximates the probability of existence of technologically advanced life in space and that we will find out about it anytime soon.

**N = R _{*} * f_{p} * n_{e} * f_{l} * f_{i} * f_{c} * L**

N = Number of intelligent civilizations in space

R_{*} = Number of stars

f_{p} = Fraction of stars with planets

n_{e} = Probability of number of planets with habitable environments

f_{l} = Fraction of planets where life has originated

f_{i} = Chance of life evolving into a condition of intelligence

f_{c} = Percentage of life that has technology to send out signals into space

L = The "longetivity" factor, from 0 to 1, gauging the lifespan of the average intelligent civilization

Due to the number of unknowns in this equation that we will probably not find out within our lifetimes, it is still a mere conjecture on the subject. Estimates on the number of intelligent civilizations in the universe range from over the millions to zero.