What is Life?

This might sound like a philosophical question, but I intend it more like a scientific question.  We’ve discussed this somewhat before, like in our post about the universe’s habitable zone, but I want to focus in a little closer on what life really is, on what makes one thing alive and one thing not alive, how we might go about defining the difference, and whether what we call life deserves the distinction we have hitherto applied.

Sententia Discussion Series 3: Habitability

The search for extra-terrestrial life tends to focus on the requirements for life on Earth: carbon, oxygen, liquid water, and so forth. There are arguments that support the idea that any life would have similar needs. Yet there are also arguments that life could be so alien that we might not even recognize it as life. Indeed, the biological definition of life can be interpreted to include things like stars, which are generally not considered "alive."