[____tom____]

The standard definition of life is too restrictive.

I suggest

  If it can reproduce and mutate heritably, it's alive. 

Or, in other words, things that can evolve.

I find the idea that viruses aren't alive ridiculous.

[jakobnissen]

That's an interesting definition, but it does have some issues.

Is an infertile animal (which can't reproduce) dead? What about a nerve cell (which have differentiated too far to become a reproductive cell)? Or a red blood cell (which has no genome)?

From the other end, is a genetic algorithm alive? What about a manuscript? Manuscripts are copied (so they reproduce), and have frequent copying errors, which propagate.

[3cats-in-a-coat]

Atoms and sub-atomic particles fit this definition.

Machines fit this definition.

Fire fits this definition.

Truth is "life" is not a distinct category. We just think of life as complex life. A complex system that mines energy gradients to preserve and replicate its forms.

But there's no hard boundary. It's just in our head.

[halestock]

How do any of those things fit that definition?

[____tom____]

No, none of those can mutate, that's the point of "and mutate heritably"

Crystals can "reproduce", but it's always the same (there can be errors, but they don't inherit), so they don't count.

And atoms don't reproduce, so I'm missing your point there.