This is a tricky question. Maybe you should be more accurate: you are referring to an "object" that makes the answer very difficult. For example. Is a virus particle considered an object? But those "particle" are for definition not a living "object".
There are few criteria which need to be full filled for one object to consider as living. These are :1) Growth (but even nonliving things grow eg mountains via accumulation), 2) reproduction (some living dont reproduce eg mule, worker honey bee though they are living), 3) All sum of metabolism (very important criteria as all living things show metabolism) and 4) Environmental response (another very imp criteria as all living respond to different environmental stimulus).
"struggle for survival" is the key feature for a thing to be classified as living, for survival an organism need to interact with different things in surrounding and possesses metabolic process within, that's how life continues. a non living thing has nothing to do with survival and so on. so in short "survival" is the exact base for differentiation.
life is a self-organizing bounded local environment that is at disequilibrium with its surroundings. When people die they become at equilibrium with their surroundings, the body will cool to the temperature of the surroundings and such. That is the chemistry definition of life. The philosophical definition is consciousness. If you do not know you are alive, are you really living?
As a geneticist, I prefer the following definition: Life is a complex and evolving pattern (the genetic material) capable of interfacing with its environment to ensure its own reproduction.
The meaning of life as we perceive it is derived from philosophical and religious contemplation of, and scientific inquiries about existence, social ties, consciousness, and happiness. Many other issues are also involved, such as symbolic meaning, ontology, value, purpose, ethics, good and evil, free will, the existence of one or multiple gods, conceptions of God, the soul, and the afterlife. Scientific contributions focus primarily on describing related empirical facts about the universe, exploring the context and parameters concerning the "how" of life.
To Elham Bilal: most of the criteria that you list would not apply to an amoeba (so far as we know), so is the amoeba dead? Also, re God and the soul: are atheists also dead?
I think this is more a philosophical question than anything else. Many ancient philosphers used to debate on the meaning of life and even today we cannot really define it by means of biology, chemistry or genetics (or else). Even a rock has life. It is subjected to weather erosion, therefore it interacts with the environment and it changes. It doesn't reproduce, not like other organisms do, but when it loses bits, could that be considered a sort of reproduction? I am being intentionally ridiculous now, with that, but the concept I am trying to put through is that life is really hard to define. For every definition we may find, there are others who could object with valid arguments. And that goes for the scientific community as well. Life can be defined differently, according to the field of specialization.
Re Valeria. This may seem like a philosophical question, but it actually has a practical side. Mankind is exploring space looking for life. In all probability, if we find life as we know it (Carbon-water based) then we will be able to recognize its signature. On the other hand, if it is 'Life, Jim, but not as we know it', we may not know how to look for it or fail to recognize or - more importantly - to respect it.
Andrew, you say that clays and crystals do not evolve. Crystals do change their structures from one generation to another, and carry unique surface microtopographies, so a moot point?
Roger, if the microtopology is 'heritable', then this is close to being an information system. If some microtopologies reproduce better under different environments, then the crystals would satisfy my definition of life. At that point I either have to accept that my definition is too broad or say that the crystals are alive.
Re Andrew. While I agree with you entirely, we constantly fail to respect life forms here on earth, at this moment in time (but this is another topic). In my opinion, it is still a philosophical concept, which has needs to be translated into practical applications, such as the ability to recognise life which might sustain itself in different combinations than carbon-water, as you put it. Unless you are suggesting that we consider any possible combination of systems which could be qualified as "life", I guess it will have to be a trial-error kind of thing. We should approach space exploration with Star Trek in mind. The principles expressed through the Federation of Planets, could work great! And who knows, we might have already encountered alien life, say on Mars, and we might have not recognised it. I don't disagree with you. I am just saying that we do not have specific parameters to apply and therefore, any reasoning is purely conceptual.
I think the only sensible approach to the question "What is life?" is taken from thermodynamics. Read Erwin Schrödinger's little book "What is life?", and/or the slim 1995 volume of expert commentary on Schrödinger's book, entitled "What is life? The next fifty years. Speculations on the future of biology", and edited by Michael P. Murphy and Luke A. J. O'Neill. The bottom line is that a living entity is one that decreases entropy in an environment of increasing entropy.
Re Gregg and Roger. I have a lot of time for the thermodynamic definition, though I think one should specify: living entity is one that decreases its own entropy in an environment of increasing entropy.
On the other hand: don't Roger's crystals do this too?
I acknowledge, and appreciate, Andrew's clarifying addition to the definition of life that I offered. As to the question of crystals, Schrödinger addresses that in his book, noting that crystals are periodic and living entities are aperiodic. It is this aperiodicity that leads to the complexity of living entities, versus the simplicity of crystals. This concept also led Schrödinger to postulate the existence of molecules in the cells of living organisms that were complex enough to encode information, years before the discovery that nucleic acids (DNA and RNA) serve that very function.
This leads to another addition to our proposed definition of life: A living entity is one that decreases its own entropy in an aperiodic form in an environment of increasing entropy.
But inability to grow (ie reproduce) does not necessarily indicate death in bacteria. We are familiar with viable but non-culturable bacteria. Also, the ability to "grow" depends on environmental factors: some bacteria reproduce only inside cells, etc
The definition of death for humans and animals is based on body dysfunctionality for any reason which can be checked medically. For bacteria death concept is different and hard to deferintiate a dead bacterium from alive. Inability to grow on suitable medium is an empirical approach.perhaps a molecular based approach would be more decisive.
Amin, I agree with you but the original poster didn't specify they were only looking at bacteria. Any appropriate answer is going to need to address the entire spectrum of "living" organisms.
An organism becomes dead or considered dead when it is no longer showing signs of life as metabolism, movement, sensing, and reproduction due dysfunctionality at molecular, cellular,or organs level.