Since life is such a ubiquitous and fundamental concept, the definitions of it are legion. —John D. Barrow and Frank J. Tipler, The Anthropic Cosmological Principle

Words are our servants, not our masters. For different purposes we find it convenient to use words in different senses. —Richard Dawkins, The Blind Watchmaker

What is life? And why should we care? Well to begin with, we are living beings, and that fact distinguishes us from most things in the Universe. Though humans are not the only living things, we are among the few, so understanding the nature of life might be an important step toward understanding ourselves.

As Richard Dawkins points out, people define life in different ways for different purposes. For everyday situations, it seems to me that we have a common-sense set of criteria, somewhat along the lines of:

Does it look like a person or an animal? If so, is it moving? Does it respond to being spoken to or touched? Failing this, is it breathing, or is its heart beating?

Does it look like a plant? If so, does it have green leaves? If not, could it be because it is winter? . . . Etc., etc.

The question is, can anything meaningfully be done to define life that would not simply be a repetition of such everyday notions. Once upon a time, philosophers like Plato believed that things in the everyday world are imperfect reflections of perfect forms or concepts in some type of higher realm. In defining a class of objects, we would be searching for an understanding of that mystical essence that inheres in all of them.

But as David Hume said, somewhat more recently,

Nothing is more usual than for philosophers to encroach on the province of grammarians, and to engage in disputes of words, while they imagine they are handling controversies of the deepest importance and concern.

Even more recently, the logical positivists have stressed the distinction between analytic and synthetic propositions. An analytic proposition is one that is true by definition, such as saying that "men are adult male humans." Such a statement is an assertion about words. On the other hand, a synthetic proposition asserts some new truth about the world that was not inherent in the words themselves. Synthetic propositions are subject to verifiability; we can perform experiments or other observations to determine whether these propositions are true.

A third class of propositions consists of statements that are neither analytic or synthetic, and to the logical positivist, such statements are simply without sense. The logical positivists sought to expose much of traditional philosophy as meaningless discourse, a sort of neurotic disease.

Which of these three types of statements—analytic, synthetic, or meaningless—am I planning to make about life? Well, neither of the first two. Whether my statements will fall into the third category remains to be seen.

I would argue that it would be a good thing to have a workable abstract definition of life, and that such a definition need not be wholly arbitrary, but can be defensible to a degree. However, the point is not to describe some sort of metaphysical essence of life. Rather, the point is to define life so that the term can be usefully extended to situations we have never before encountered.

For example, the legal definition of "death" now has to take account of situations that have only recently been made possible by medical science. Nowadays many comatose people can be kept on life support machines for years. But are we to regard this as life, or specifically as human life, with all the ethical considerations that we attach to human life?

In the following quote, Poundstone derives the following criteria for living things from Von Neumann’s work:

(1) A living system encapsulates a complete description of itself.

(2) It avoids the paradox seemingly inherent in (1) by not trying to include a description of the description in the description.

(3) Instead, the description serves a dual role. It is a coded description of the rest of the system. At the same time, it is a sort of working model (which need not be decoded) of itself.

(4) Part of the system, a supervisory unit, "knows" about the dual role of the description and makes sure that the description is interpreted both ways during reproduction.

(5) Another part of the system, a universal constructor, can build any of a large class of objects—including the living system itself—provided that it is given the proper directions.

(6) Reproduction occurs when the supervisory system instructs the universal constructor to build a new copy of the system, including a description.

—The Recursive Universe, Chapter 11

However, it is true, as Schrodinger points out, that all life activities increase entropy, and that the body must exhaust this entropy back into the environment (primarily by radiating heat).

To summarize, what have we learned from Schrodinger?

Living things are systems with a characteristic order that persists over time.

Living things are active. (Even if an organism appears to be sitting still, processes are going on inside it.)

Living things are open systems that exchange material and energy with their environment.

Living things increase the entropy in the environment around them.



The term phantasia in the passage is apparently an untranslated Greek word for imagination.

Now, all this is true but it does not follow that our actions are uncaused, or even uncaused by input from the outside. For even in the case where we are sitting thinking, and suddenly decide to do something, the mind that is doing the thinking has been progressively modified by many inputs over the years. What does follow is that these inputs are not the complete causes of action. You put a key in a lock to open the door, but the key could have no effect unless the lock were shaped to receive it. The door opening is caused not only by the key turning, but also by all the forces that shaped the lock that receives it. Our responses are caused not just by some stimulus, but also by all the factors that have shaped us, both genetic and environmental.

Men think themselves free inasmuch as they are conscious of their volitions and desires, and never even dream, in their ignorance, of the causes which have disposed them so to wish and desire. —Benedict de Spinoza, The Ethics, Appendix to Part I, trans. R. H. M. Elwes

While the considerations in this section are helpful secondary criteria for identifying life, they are not sufficient, either individually or in combination, to finally show that something is alive. For we might be able to create some mechanism that responds to inputs in some sophisticated and indirect way. But if its responses are not such as to promote survival, such as by avoiding threats and seeking out food, then it is not really behaving in the manner characteristic of life.

Assuming that life is a matter of degree, how might we measure the degree of life in something? Following are some possible considerations:

Since we have said that living things are systems characterized by some pattern or schema, we can ask whether patterns are something that can be possessed in varying degree. A useful concept in this regard is the following:
The intensity of a process relative to a given entity . . . is a measure of how much the process simplifies the entity — how strongly the process is a pattern in the entity. It has to do with the ratio of the complexity of the process to the complexity of the entity. —Ben Goertzel, Chaotic Logic

The quality of life in a system could be proportional to the intensity of the pattern or schema that defines the order in that entity.

You could look at the percentage of variation that occurs in the system on a daily basis. How many properties are there that vary, and over how wide a range do they vary? Assuming that this variation can be quantified, how does it compare with the elements that remain constant? The quality of life could be proportional to the ratio of the constant elements to the varying elements.
You could look at the percentage of variation that occurs over the course of a lifetime. In large organisms, there is a huge amount of variation since growth begins from a tiny egg and proceeds to gradually build something much greater. Yet it seems that the basic pattern of the organism emerges fairly soon, albeit on a smaller scale and with different proportions than characterize the adult form. More significant changes occur in the insect world, where you find such things as a caterpillar changing into a butterfly. The quality of life could be proportional to the degree of constancy in an organism over the course of an entire lifetime.
Since organisms live for widely varying lengths of time, you could say that the quality of life is proportional to the average lifespan of individuals in a species.
Since organisms always die eventually, and have continuance beyond death primarily only through offspring, you could focus on the differences in the ways that various organisms reproduce. The quality of life might be proportional to the degree of resemblance between a parent and its offspring. A virus reproduces more or less exactly, as do bacteria. Most higher organisms reproduce sexually, as a result of which none of the offspring exactly resembles either parent. So this criterion would have the unfortunate effect of establishing that a virus is more alive than you and me.
You could modify the previous criterion to reflect, additionally, the number of offspring.
On a species level, you could focus on how long the species persists, or on how many other species are descended from it. It the species the origin of a major branch of the evolutionary "tree," or is it an old dead twig?

What exactly is life and what is death, so afterlife can even be defined.

Hugs,
Nanner

Hi Nanner, dave, Members,



Thinking that perhaps this may have some relevance to the discussion:


"Life has an end.  Death has an end.  But Consciousness is endless."


- u