It has always amazed me that a science field like Biology is so comfortable with so many definitions which are equivocal. (Life, Evolution, Species...) But that's just the way it is. Biology is the study of life, but biologists can't agree on a definition of life. In every text book that addresses this subject, they are all quite comfortable in stating that there is no unequivocal definition of life and they usually spend a significant effort in "proving" why we can't come up with an unequivocal definition.
I question your need to have a static, absolute definition of "life." Reality, more often than not, is more of a spectrum of blurred boundaries than absolute boxes which hold categorized objects and ideas. Definitions, and scientific definitions in particular, should be flexible to accommodate new data.
I suspect this indoctrination has led most Biologists to give up on the definition. But not me! I believe it is possible to create an unequivocal, simple definition of biological life or for simplicity sake an organism. I have created this definition over a period of years, and it has been tested by a number of personally know scientists.
How has this definition been "tested"?
Life, or a living organism is a self contained entity which uses ATP (adenosine triphosphate) for metabolism and synthesizes ATP with enzymes which are synthesized from a genetic process requiring the transfer of information from DNA to RNA.
That's a very parochial and rather arbitrary definition for what "life" is.
This definition covers all known life.
An absurdly tautological statement. "This definition of life...covers all known life." The perisylvian areas of my brain feel like bursting at this egregiously tautological statement. No -- what your definition covers is an arbitrary portion of the natural world, which presumably fits some pragmatic objective.
Anyways, here -- let me pick apart your idiosyncratic definition of life with some questions for you to ponder:
1. How many ATP molecules must be consumed in order for a self-contained entity to be considered alive? You may think this is an irrelevant question. It is not, because some biological entities need not consume any ATP at all, and some consume different and varying levels of ATP molecules. Your definition requires ATP consumption -- but how much and to what extent?
2. Why do you have the requirement for genetic transfer from DNA to RNA? What is your non-tautological reason for stipulating this requirement?
3. It must be a "protein factory," you say. But why? What is uniquely special about amino acid chains that somehow gives "life" to something? Why did you choose protein production, and not lipid production? Or carbon production?
No -- your definition isn't any more rigorous and "measurable" than other definitions of "life."
Enough ATP to metabolize the synthesis of the enzymes required for the synthesis of the ATP. Definitely more than one molecule.
1. Why did you choose ATP for your definition instead of the broader NTP? There are more biological entities that fall under the umbrella of using NTPs, so what was your reason for choosing ATP specifically?
2. So mitochondria, as discrete entities, are alive by your definition, as are hydrogenosomes and chloroplasts -- but not peroxisomes. If a mitochondrial analog was created out of diamandoid material (mostly carbon atoms, along with some hydrogens, maybe some metals, etc., making a completely non-biological entity), would it be alive? It could self-replicate, transfer information through a non-biological tape, perform nanosurgery on cells, consume energy, and would be bound by a diamandoid wall. But it's not alive by your definition, correct?
Don't you realize that every atom, molecule, and chemical combination has an architecture or shape associated with it?
So you don't think heat and light affect chemical reactions? Would you like to research this a little before I embarrass you?
The only embarrassing thing here is that you're ignoring the question marks at the end of Percy's sentences -- so his/her sentences are interrogative, not declarative, as you would have the reader believe.
This is a general, overarching reply because I think this discussion has taken a pedantic twist in the sense that it's becoming a back and forth match where the same points are being repeated ad nauseum.
And these points should be repeated ad nauseum, because AOk has -- if s/he has done anything -- demonstrated a gap in knowledge when it comes to chemistry and biology (very specific errors having been pointed out by MrJack and Tanypteryx).
The accusation of "groupthink" may be hurled at me at this point, but keep in mind that my views are quite non-conformist compared to the views of most members of this forum.
With this preamble being made, here's the thing: AOk, your definition and main argument is simply not very useful and also dances dangerously close to committing the reification fallacy. "Life" is an abstraction; reality -- the mesmerizing and intricate interaction between matter and energy (with a dash of anti-matter, etc.) does not really care what we call or label a certain portion of the chemical and physical universe. Reality needs not -- and it does not -- nicely fit into absolute boundaries.
So a definition for "life" should not seek to be absolute. It should, instead, seek to be pragmatic. AOk's parochial definition of what constitutes life is simply a personal opinion -- there's no reason why the field of biology (as a whole) should adopt this non-utilitarian view of what life is.
Now, since any good, scientific definition of "life" should strive to be useful in some sense, this also means that different (but largely overlapping) definitions of life will emerge. This is not a problem; definitions, in science anyway, are not intended to exist to score rhetorical points in a broader metaphysical debate.
For example, why does AOk not simply define life as self-replicating polynucleotides? The utter dismissal of defining life in this manner suggests to me that there is a clear agenda for adopting and asserting his or her chosen definition of life.
Others here have offered different definitions of life. That is all fine and good: the point is that each definition will reflect the particular research foci of different scientific and technological fields (AI, nanotechnology, molecular biology, and chemistry -- for instance -- would each have slightly varying definitions of life). Why should any scientific field favor AOk's definition over other (arguably less parochial) definitions?
Nor is this about somehow playing a rhetorical game so that abiogenesis is more realistic. Whether you define "life" as self-replicating polynucleotides or use AOk's definition, the arguments for abiogenesis do not change (of course, those familiar with my history on this forum will know that I very strongly question the validity of abiogenic hypotheses, but that's tangential).
So, go ahead, AOk. What's special about your definition? Why is your definition superior to other definitions for what constitutes life?
Here's a definition of life that I find more useful -- why do you think yours is more useful?
Living systems tend to have (a) continual integrity of overall structure amid ceaseless chemical change, with self-preservation through up-building of subsystems to compensate for down-breaking; (b) a metabolism that harnesses energy in an organized manner; (c) growth; (d) multiplication; (e) development; (f) evolvability, as a part of a greater population of similar units.