Defining Life – The Current Working Definition

This is part of a series: Define Life

The first definition of life that I’ll cover is the current working definition used by NASA.

Life:

• Is complex
• Is highly organized
• Is diverse
• Takes energy from its environment, and uses it
• Tend toward homeostasis, where it is “normal” and “healthy”
• Grows
• Reproduces
• Reacts to its environment
• Adapts to its environment
• Has a control system/nervous system

Strengths:

• It works well for describing life as we know it
• It’s general enough that astronauts who use it will probably recognize any life that they find

Weakness:

• It doesn’t say what life is, it only lists characteristics

This is a good start, but it doesn’t clearly say what life is.  It only lists characteristics of life.  As the interviewee in the article above said, “in order to formulate a general theory of living systems, one needs more than a single example of life”.

We now have a chicken-and-egg problem:

• To create a proper definition of life, we need to study multiple kinds of life – not merely a gazillion types of creatures built on the same technology, but another creature built on a fundamentally different technology.
• Unless someone can find or build such a creature, it’s difficult, if not impossible, to correctly define life.

The standard that I’m holding each definition of life to, is how well it answers this question: “If an inventor says he’s created a new kind of life, is he right?  If so, why?  If not, why not?”

This definition will probably work for most, if not all kinds of life that can be created.  Under this definition, here are some things that are alive:

• All of God’s creatures here on earth
• Stargate replicators
• Self-replicating starships, including Von-Neumann Probes
  
• Clanking replicators
  I think that these will be created first, since they use current human technology, or a relatively small refinement of it.

Some things that would not be alive:

• Any kind of computer malware
  Software doesn’t take in energy, unless you call CPU cycles energy
• Viruses
  These throw a monkey wrench into any definition of life.  They’re built on the same technology as God’s creatures, but they don’t sustain themselves.  They also don’t have proper metabolism.
  Interesting question: if viruses aren’t technically alive, are other parasites?  If so, why?  If not, why not?
• Memes
  Ideas that spread
• Crystals They aren’t complex enough, and in particular have no control system.

Photo credit:
Disclose.tv – Alien Probes Could be Surfing the Galaxy