Introduction:
What is life?
Life is considered a characteristic of something that preserves, furthers or reinforces its existence in the given environment This characteristic exhibits all or most of the following traits: Homeostasis, Organization, Metabolism, Growth, Adaptation, Response to Stimuli, Reproduction.
It is important as well to specify what kind of life we are looking for. One may search for intelligent life by looking for radio signals, but bacteria may just change the chemistry of a planet’s atmosphere.
Life outside Earth:
First, life exists on Earth, so we know it’s possible for complex life to evolve.
Second, the scale of the Universe. As they said in the movie Contact “The Universe is a pretty big place. If it’s just us, seems like an awful waste of space”
The Paradox: Why don’t we see life everywhere?
The simple answer is that we just haven’t been looking long enough. If you consider the radio signals we send out into space, our communications have only reached a few hundred or thousand stars, and they are too faint to really register.
But this does miss one key point. If a civilization slightly more advanced than us could make spacecraft that went 10% the speed of light (200 times faster than Voyager probes, 20 times faster than our fastest probe ever), which is quite reasonable with some effort, then it would be possible to visit most stars in the galaxy in a few million years. Since the galaxy is billions of years old, this really should have happened already if life is as common as the Drake equation implies.
What does it take for there to be life?
Liquid water
Complex chemistry
Stability
Energy
Gradients
Special thanks to Colin Vendromin for the music, also thanks to Zac Kenny for the logo!