What is life?

Surely what this shows is that the word 'life' doesn't correspond to a category in reality except in the fuzziest of ways. So taboo it. What aspects of 'life' are you actually interested in?

Nature draws no line between living and nonliving.

-- K. Eric Drexler, Engines of Creation

Reminds me of Arguing By Definition; you can argue about the definitions of life and find one that includes (or excludes) prions or viruses. Does it really matter? When you call something 'life', all kinds of connotations come in; but of course the phenomena does not change.

Baby d-
[is killed]

-3 karma for a meeting report? Yeah, that's just the sort of incentive LW needs.

From the link: "If one star burned longer or brighter, that didn't affect the probability distribution of the next star to form." This is false, brighter stars die sooner and emit more stuff in space, including heavier elements, thus affecting both the probability of formation and the makeup of the future stars. You can even take this further, arguing that this amounts to reproduction (with synthesized elements instead of gametes), and that stars are a form of life (they self-replicate). This has been explored in science fiction, of course. In this way, stars also transform the interstellar space into more (or less) conducive to further star life. They also resist entropy, as long as there is some material to make more stars out of.

In fact, I dare you to argue that stars are not alive by your definition.

'Life' is a term used by biologists to describe that subset of chemical phenomena which is their purview.

Our intuitive concept of 'life' conflates two concepts: the ability to reproduce and complexity. Many would consider a machine made by an advanced civilization (but incapable of reproduction) as 'alive'; meanwhile, one might hesitate to call prions 'alive', despite their capacity to replicate, merely due to their simplicity.

'alive' relative to a specific environment

It's always relative to a certain environment. Human beings and most animals can't survive outside of the current biosphere. In that respect we're no less independent from certain peculiar conditions than viruses are. We both depend on other living organisms in order to survive.

Maybe redefine life against a continuum of how unlikely, complex the necessary environmental conditions are that sustain it?

Some autotrophic cells might rank at one currently known bound while higher animals would be on the other end.

what we're looking for is a population who search faster than the natural decay rate

Is this correct? Imagine a least-convenient-genome where every mutation causes instant death (but the mutation rate is low enough that some offspring survive). Then the decay rate is nonzero but the search rate appears to be 0.

My point is that "search" in this context seems to imply seeking out new innovations, not merely maintaining a stable population. The search rate only appears relevant to survival when the environment is changing.

"Rate of search divided by rate of change of environment" might be an interesting metric (where the "environment" obviously includes other populations of replicators who have their own search rates). Possible division-by-zero error if neither the phenotype nor the environment seem to be changing very much.

It seems to me that both a genotype and phenotype is needed to qualify for labelling something as alive. It's difficult to see how any form of natural selection could operate on inheritance and variation without a genotype. So that would rule out crystals and so forth.

Are other approaches to life any more productive at categorising whether an individual being is alive, such as Dawkins' "non-random survival of randomly varying self-replicators" or Lehninger's "living organisms preserve their internal order by taking Gibbs free energy from their surroundings" ?

The synthetic RNA in question was the family of ligase-polymerase ribozymes described here: http://www.sciencemag.org/content/332/6026/209.short