The Great Filter

The Great Filter is a potential solution to the Fermi paradox that suggests the idea that all alien civilizations experience a "filter event" in which any sapient life is forced to go through an incredibly difficult challenge that could result in an Extinction Level Event and/or a technological retreat.

The Great Filter could have multiple separate scenarios, for example:


 * The invention of the first nuclear weapon or catastrophic antimatter-based, nuclear, or biological weapons that result in widespread war and conflict.
 * Global warming resulting in intense environmental shift that could potentially result in the loss of large groups of people to natural disasters.
 * The rise of nanotechnology leading to a potential "grey goo scenario" in which self-replicating systems consume all organic material on a planet, destroying any potential for life.

Although it is not known whether or not any existing alien civilization in our universe has passed The Great Filter, what we do know paints a dark future for the events that may unfold as a result of it. The Great Filter solves the Fermi paradox to a large extent, but it implies that the concept of civilizations that surpass type Type II or even Type I would be physically impossible and, as a result, ridiculous and improbable.