The answer to that is: if it’s a very basic life form we will only know it as living if it’s based on carbon and water. The reason for saying that is that you only have to look at the articles and comments on this subject here at Science 2.0 over the last few weeks to see that almost everyone has an axe to grind, or a hobbyhorse to display, or they are led astray by careless language.
Life, it seems, is a subject close to everyone’s heart, (no pun intended) except, of course, for those who consider the quest for certainty about its meaning to be mere pseudoscience.
But it’s not pseudoscience in the least. This is a question of utmost importance as we learn more about the universe in which we live.
And it’s not a difficult question to answer as I showed here. (http://www.science20.com/gadfly/what_life) No-one has seriously challenged that view of life even though it’s been out there for over three years. But if you’ve read What is Life? and are not happy with the explanation, please consider this summary of the argument.
Life exists at several levels – cell, organism, community, and perhaps even extra-terrestrial. So a theory of life, to be of any use, must hold true for all levels, including alien life, even though we cannot predict the chemical composition or physical form of organisms found elsewhere in the cosmos. But we can predict some of their internal processes.
Why is that?
Well, we recognise earthly life forms because they display growth, reproduction, metabolism and homeostasis. (Which is why communities can be recognised as “living”. Recognition is easy, it’s the definition that’s a problem.) It’s therefore virtually a truism to argue that alien entities must display these also, otherwise they might be something, but they won’t be living.
The underlying feature that all the earthly levels of life forms have in common; the essence of their processes of growth, reproduction, metabolism and homeostasis, is cooperation. It’s cooperation that is “the spark of life” and therefore the explanation of life. (See NOTES)
However, if we do find life elsewhere in the universe, we may encounter a form so unfamiliar that we do not recognise its internal processes. Growth and reproduction might be negligible, and metabolism and homeostasis might be based on unfamiliar chemistry. (Remember also, that the frequency and visibility of these internal processes varies hugely even among terrestrial life forms, so the problem of recognition might be compounded in the case of alien forms.)
If those processes are occurring though, we might be able to see the cooperation on which they are based and realise – “Yes, this is life!”
That sounds overly optimistic on the evidence presented so far, but it must be kept in mind that cooperation is merely an exchange of energy or material for mutual benefit. With that in mind, the key to finding alien life forms that are not glaringly obvious, will be to first find exchanges of energy or material, and then look further to see evidence of mutualism. What could be simpler?
Here’s another angle to the whole question of life.
Radu Popa stated in a recent article on this very matter: (http://www.jbsdonline.com/mc_images/category/4317/5-popa_jbsd_29_4_2012.pdf) “Assuming that a definition for life is needed and possible, it has to obey two basic requirements: to be coherent relative to what we already know about life, and the philosophy used to produce the definition has to be clear of systemic errors.”
The view of life given here satisfies those conditions. A definition of life IS needed so that biology can look the world in the eye. I’ve shown that a definition IS possible. That definition IS coherent relative to what we already know about life. And although I’m not exactly sure what Popa means by “the philosophy behind the definition”, (philosophy being the search for understanding, which I would have thought is a given for this discussion) I believe the analytical approach that has been used IS indeed free of errors. But here’s something particularly pertinent.
In the same article, when discussing Edward Trifonov’s “common vocabulary” approach to arriving at a consensus view of life, Popa stated this: “One example from the field of the origin of life is Kunin’s contribution, which was used to explain the initiation of a living system as a symbiosis between two molecular networks (e.g. a protein-made RNA polymerase cooperating with an RNA-made protein polymerase) This great contribution to understanding the essence of life would be considered “unworthy of mentioning” by a vocabulary-based method, simply because it is seldom cited in origin of life models.”
In that statement Radu Popa has used exactly the same language that I have used for over three years – “cooperation is the essence of life.” He had the secret of life staring him in the face but was put off by its great merits – its simplicity and concision.
And for those with an interest in certainty or proof, its universality is its proof.
How do we determine if an accident victim for example, is alive or dead? We look for “vital signs”. The vital signs are no more than an indication that internal organs or systems, or both, are working in unison. The detection of a pulse for example, tells us that the heart and nervous system are working together. Cooperating, in other words.