What is life?

Question

I'm not talking about the philisophical implications of this question, rather, scientifically, what qualifies as life? What are it's characteristics? How would you know something is or was alive?

Okay, maybe you are right in that I was too strict in excluding the philisophical implications. All the answers so far are really good at explaining life as we know it on earth... carbon based...reproduction... metabolism etc. But when we are seeking life on other planets, we have to take a non-actualist approach.... life is just as likely to be silica based etc... nor do I accept reproduction as a requisite because there are many organisms that I would consider alive that do not reproduce. I also would not choose metabolism as a defining process because then there are many "self sustaining" systems that would qualify as life... (such as the earth itself in a broad sense)

Addendum et Ronin... First off... I do not reject the supplied answers, but as I stated, they do not take a non-actualistic approach that is REQUIRED when dealing with environments with which we are unfamiliar. While each stated charateristic is fundamental to life as WE know it... it is not necessarily the case to all life to which the question is directed. For example, reproduction, (as you mentioned) what I was referring to is as certain cross-bred life forms, such as a mule, is sterile.. but certainly alive... it is true that it is not capable of passing on it's genetic material, but that has nothing to do with the real question at hand... "What is life." I'm reasonably certain that a mule is alive. Is it not reasonable to assume that conditions may exist elsewere that "life" may exist, without an organisms ability to reproduce?

Answer 1

I think you have to be careful in declaring that "life is just as likely to be based on silicon." Biologists I've talked to say there are reasons to think it isn't just as likely. I've also wondered if liquids other than water could be the medium of life...such as the lakes of methane/ethane we think we have discovered on Titan. Again, I've been told that actual chemistry implies this would not be nearly as conducive to life as good old water.

That said, you are correct that we may have to think outside of the norm when considering life on other planets. I'm sure this aspect is not lost with most astrobiologists.

Answer 2

Life is a condition that distinguishes organisms from inorganic objects and dead organisms, being manifested by growth through metabolism, reproduction, and the power of adaptation to environment through changes originating internally. A diverse array of living organisms can be found in the biosphere on Earth. Properties common to these organisms – plants, animals, fungi, protists, archaea and bacteria – are a carbon and water-based cellular form with complex organization and genetic information. They undergo metabolism, possess a capacity to grow, respond to stimuli, reproduce and, through natural selection, adapt to their environment in successive generations.

An entity with the above properties is considered to be an organism. However, not every definition of life considers all of these properties to be essential. For example, the capacity for descent with modification is often taken as the only essential property of life. This definition notably includes viruses, which do not qualify under narrower definitions as they are acellular and do not metabolise. Broader definitions of life may also include theoretical non-carbon-based life and other alternative biology.

Answer 3

When the universe came into existence,it was an unknowing evolving beast that would run it's course according to the laws of physics.
Some where along the way the universe developed the capacity to become aware of itself.
We are the result,the eyes and ears of the universe.
We are one among billions that are burdened with this task.

Answer 4

You are basically rejecting all previous definitions of life and offering none of your own. Your idea that the earth has a metabolism is a cop-out. I go with science's definition myself.

What do you know of that's alive and does not reproduce?

Answer 5

The absence of death. It means that something depends on an intake of nourishment and air for growth and health and results in the excretion of waste by-products. If there are cells, there was once life in them. Dirt, minerals, and rocks don't have cells

Answer 6

The philosophical dimensions of your question are inextricable from the purely scientific, as the definitions rest on abstract ideas.

Answer 7

anything that can match these criteria:

undergoing metabolism, possessing a capacity to grow, responding to stimuli, reproducing and, through natural selection, adapting to their environment in successive generations.

Answer 8

life is a creative display of action, all comes from thought, and thought comes from an array of electrical impulses compiled into an intelligible and organized fashion, that explains intelligent life, but all other life forms are alive as well, but not producing as much in the collective life organization which aims to benefit humans, life comes in different levels of consciousness, as life and evolution, and life elsewhere, but that comes with an other set of questions, and I hope there are other intelligent life on other planets, as I believe the theory of evolution, but as a scientist I can not proclaim that as fact, until it is concretely proven, but are there other beings in the universe? Beings? To be or not to be=being, and at what level of consciousness? And what is consciousness? and how could we graph and display conscious levels to create a scientific chart to evaluate levels of consciousness, and is it linear and gradual from lower life forms such as fish, animals and humans for example, or fish don't have a clue why they exist, and monkeys are half way there and humans are the measuring rule for all other life forms on earth?, or is it sectioned into parts that are only partially understood? Do we have proof the fish became birds, and monkeys became man, do we have proof that we come from other planets? even if we do, that only moves the question to an other planet, and from the theory of the big bang, evolution originated from a center point and expanded, and more evoluted life forms exist in the outer circles as they have moved away from that center point before us, and if life as we understand it, grows and expands, why haven't we been contacted from life forms existing billions of years ahead of us in the expansion band? And why are radio telescopes not picking up even the faintest signal of life if advanced or transitional life forms, following the evolution process, should have sent intelligible signals? And why isn't it conceivable that the universe was engineered for the expansion of our species? Our expansion is endless. all these questions and a billion more, most of which are meaningless, why, because the human equation is not a black and white picture, because zero's and one's only dictate conditions that are safe to put away in an easy understanding box, and can be conveniently pulled out, in case of fundamental questioning to protect ego, but the fact remains, WE DO NOT KNOW, and any one seeking the roots of understandable truth can humbly exclude themselves from boastful claims that life exists or not on other planets , and know that the sum of all understandings only equal to a grain of sand compared to all existing grains of sand on earth, and even more, only one side of that grain of sand, how foolish and unwise to proclaim existence of any life form without careful scientific examination and proof, and as a track record, human's wisdom have certainly not exceeded their technology.