Here’s the thing, though… Normally I suspect we are prone to thinking of life-forms as carbon-based and oxygen-consuming (exceptions notwithstanding), but there is nothing in the above that includes those as necessary pre-conditions. If we really push the boat out, *lots *of things could be ‘objects that have signaling and self-sustaining processes’. If we were to analyse certain patterns of gas clouds in the planet Jupiter (say…). would we not find certain arrangements (objects) of gas/liquid which move and distribute in such a way that ‘signal’ ‘self-sustaining’ processes?
Could it be that, actually, there is quite a lot of ‘life’ (including intelligent life) out there in the universe which we simply don’t recognise as such because it doesn’t resemble the ‘little green men’ archetype’? If we accept the wikipedia definition above, then couldn’t vast swathes of the universe be considered to be ‘alive’ in some sense or another?
Many thanks - and apologies in advance for my drunkenness.
There are approximately 137 science fiction novels, as well as 42 episodes of Star Trek, that deal with this very idea.
Of course, we probably wouldn’t recognize the vast majority of life in the universe as such if we applied our parochial carbon-based life form standards to our observations. To go even further, we probably couldn’t definitively say that any object we encounter isn’t alive. Is that rock sentient? What if its metabolic processes are so slow that it takes five thousand years for it to draw a breath? How do I know that that DMV employee is dead, just because I haven’t seen her move for an hour? (Sorry, the unmoving rock metaphor clashed unpleasantly with how I spent most of yesterday afternoon.)
Erwin Schrödinger wrote a book with the same title as this thread. He muses in various directions but does emphasize, as many before and after him did, that life is characterized by decreasing entropy, i.e. extracting free energy from the non-living surroundings.
(Some non-living machines, e.g. refrigerators, extract free energy but these are often created and maintained by living organisms.)
Well, this appears to be one of Wikipedia’s crappier efforts, and the citations do not support the definition as given. To start off the discussion on this basis is to start it on the wrong foot. We had quite an extensive discussion of the nature and definition of life in GQ not that long ago.
Traditionally there are 7 necessary and sufficient characteristics that something must have in order to be considered alive, although there is some disagreement as to the details of what should be included on this list. Here is one version, my first Google hit for “seven characteristics of life”.
Of course, there do not really have to be seven, that is just a traditional “magic” number. The point is, however, life is a complex concept, and there is no satisfactory definition of it to be given in terms of just one or two succinctly stateable characteristics. Attempts to provide such short definitions always wind up including all sorts of things that are obviously non-living, and/or ruling out lots of things that seem to be pretty clearly alive.
What I feel, I can’t say, but my love is there for you anytime of day. What I know, I can do, if I give my love now to everyone like you. What I feel, I can’t say, but my love is there for you any time of day. But if it’s not love that you need, then I’ll try my best to make everything succeed. Tell me, what is my life without your love? Tell me, who am I without you, by my side?
The attempts at defining life that we have so far have tried to distinguish life from non-life, as we see it around us right now. They’re not attempts to define all possible imaginable variations of what we might consider life; they deal with the reality of our planet, here and now. If and when we run into some kind of stuff that might challenge the definition, we’ll wrestle with new definitions then. Science, generally speaking, doesn’t spend a whole lot of time in imaginary classifications.
With that cat thing Erwin apparently hit the peyote now and then. Did he also answer that other favorite of dopers (small “d”) everywhere, “What is reality?”
There are a couple of reasons to suspect that life of our own general kind (that is, discrete, C+H+O-based organisms) will exist elsewhere, and perhaps be the predominant sort of life:
Firstly, Carbon, Hydrogen and Oxygen permit a very wide range of possibilities in terms of their chemistry - water is quite unique in its useful properties, for example, and Carbon forms chemicals that are gases, or soluble in water - the analogous silicon chemicals are insoluble solids - gases and soluble things are more easily exchanged, ingested and expelled than solids.
Nextly, it happened here, so we know it can happen.
Back to the topic: When we say ‘life’, we’re really talking about organisms somewhat similar to those we know about - the whole “Hey man, what if rocks are like, alive?” thing is interesting philosophically, but if it turns out they are, it changes the definition of ‘rock’, not ‘life’.
Or to put it another way, it’s like saying “maybe there are different shades of blue out there in the universe that don’t look blue, and would be undetectable as being blue by any of our instruments, yet are still somehow blue”. Actually, they’re just not blue.
How do we classify a virus? It looks like a crystal. However it invades cells and then replicates. Is it life? Crystals divide and replicate too in a saturated solution. But they don’t cause the common cold or AIDS.
Viruses are a good example of how much we don’t yet know.
This is like asking what is a country. You’ll notice only other countries are allowed to decide if something is a country, which seems rather elitist to me.
“What is life?” and “How would we recognize life?” are separate questions, but they shed light on each other.
In addition to the obvious requirement of locally decreasing entropy …
Life may require a relatively large, stable and cool assemblage, perhaps composed of the molecules Schrödinger calls aperiodic solids:
[QUOTE=Schrödinger]
Only in the cooperation of an enormously large number of atoms do statistical laws begin to operate and control the behaviour of these assemblies with an accuracy increasing as the number of atoms involved increases. It is in that way that the events acquire truly orderly features. All the physical and chemical laws that are known to play an important part in the life of organisms are of this statistical kind; any other kind of lawfulness and orderliness that one might think of is being perpetually disturbed and made inoperative by the unceasing heat motion of the atoms.
[/QUOTE]
Even bacteria rely on chromosome fission, a rather complex chemical process.
The organisms would also presumably need fluid environment to serve (in Lovelock’s words) “as conveyer-belts for raw materials and waste products.”
Lovelock points out that life would often reveal itself to a cursory examination of a planet’s atmosphere. Venus and Mars each have CO2 atmospheres; Earth’s mixture of oxygen and nitrogen would be impossible, at least in the long term, without life.
ETA: Viruses might be treated similarly to refrigerators! Both are non-living creatures which are present only on planets where they have life to co-exist with.
