10 Biggest Unsolved Mysteries In Science

5. Where Is Everyone?

One of the biggest questions scientists face today, is where exactly are all the aliens?

The observable universe is 92 billion light-years across, stacked with billions and trillions of galaxies, stars and planets - all of which are apparently devoid of any signs of life. We scan the skies from a planet positively bursting at the seams with rich and diverse life and wonder just where all the aliens are at.

This is what is known as the Fermi Paradox.

Given the sheer size of the universe, and given what we know about the resilient and adaptive nature of life, there are those who think that extraterrestrial life forms are a virtual inevitability.

There are so many different possible answers to this question, from the Great Filter to the Zoo Hypothesis, that they could fill their own article, but whether the answer to "Do aliens exist?" is yes or no, either answer will change the world.