The term life has a lot of generalities, such in biology, in chemistry, in philosophy, in religion... For example, from biology refers to what distinguishes the animal, vegetable, fungi, protists, archaea and bacteria kingdoms from the rest of natural realities. It involves the ability to be born, to grow, to metabolize, to respond to external stimuli, to reproduce and to die.

Although it can not be accurately stated, evidence suggests that life has existed on Earth for at least 3700 million years, although some studies date back to 4250 million years, or even 4400 million years , according to a study published in Nature.

Scientifically, it could be defined as the capacity to manage the internal resources of a physical being in a way adapted to the changes produced in its environment, without there being a direct correspondence of cause and effect between the being who manages the resources and the change introduced in the Medium by that being, but an asymptote of approximation to the ideal established by that being, an ideal that never reaches its complete attainment by the dynamics of the medium.

The term life has a lot of generalities, such in biology, in chemistry, in philosophy, in religion... For example, from biology refers to what distinguishes the animal, vegetable, fungi, protists, archaea and bacteria kingdoms from the rest of natural realities. It involves the ability to be born, to grow, to metabolize, to respond to external stimuli, to reproduce and to die.

Although it can not be accurately stated, evidence suggests that life has existed on Earth for at least 3700 million years, although some studies date back to 4250 million years, or even 4400 million years , according to a study published in Nature.

Scientifically, it could be defined as the capacity to manage the internal resources of a physical being in a way adapted to the changes produced in its environment, without there being a direct correspondence of cause and effect between the being who manages the resources and the change introduced in the Medium by that being, but an asymptote of approximation to the ideal established by that being, an ideal that never reaches its complete attainment by the dynamics of the medium.

some idea n different view.. best..

http://www.livescience.com/10862-life-great-mystery-life.html

Another perspective is Thermodynamics and physics (these books are seminal works within this perspective):

https://www.cambridge.org/core/books/what-is-life/A876185F2DB06FF5C2CC67C9A60DAD7F

https://ia802708.us.archive.org/17/items/elementsofphysic017171mbp/elementsofphysic017171mbp.pdf

Viruses and their host cells do share many common ‘needs’. They need to be able to produce RNA, protein, lipids and have access to the raw materials to generate these but a human cell is vastly more complex than even the largest virus, and viruses try to make use of this to compensate for their own simplicity but is that life?  Does life have to be complex to call it life, is that saying life can’t be simple? As a virus host cell already contains all the needed components to achieve virus ‘life’? A virus can simply provide its own instructions, in the form of the viral genome, and let the cell do most of the work. So life is based upon complexity of work or complexity of DNA?

Sure, a sperm is an essential step towards creating a person, but few people would argue that a sperm or unfertilised egg should be described as the finished product. Problem is, where's the demarkation line? what came before humans wasn't the finished product, with the principle of the blind watchmaker, at what point can one consider it as a life finished product?

Common sense tells us that only living things have an inner life. Rabbits and tigers and mice have feelings, sensations and experiences; tables and rocks and molecules do not. Panpsychists deny this datum of common sense. According to panpsychism, the smallest bits of matter – things such as electrons and quarks – have very basic kinds of experience; an electron has an inner life.

The main objection made to panpsychism is that it is ‘crazy’ and ‘just obviously wrong’. It is thought to be highly counterintuitive to suppose that an electron has some kind of inner life, no matter how basic, and this is taken to be a very strong reason to doubt the truth of panpsychism?

Also physics tells us nothing about the intrinsic nature of the entities it talks about, and indeed that the only thing we know for certain about the intrinsic nature of matter is that at least some material things have experiences, the issue of life looks very different if it's about experiences?

and don't get me started on Elon Musk telling me i might be in a matrix :0)

Ales, would you say your definition also covers a black hole?

Life is organisation of energy.

I would try and boil it down to as basic a level as possible, for example, at IGCSE level, students are taught that a living organism must have;

M Movement All living things move - to find food, escape predators or find better growing conditions

R Respiration Getting energy from food to carry out cell processes

S Sensitivity Detecting changes in the surroundings such as light levels

G Growth All living things grow

R Reproduction Making new generations of a species

E Excretion Getting rid of waste - including carbon dioxide from respiration

N Nutrition Taking in and using food as a supply of energy

Remembered by the acronym MRS Gren.

Hope this helps :)

Maybe a slightly edited version of something I wrote earlier, in reply to a question asking whether viruses should be considered as living, could add something to this discussion, in reply to one of Remi's earlier posts on this thread:

One might choose to consider that life is not a binary classification (living vs non-living), but perhaps it can be considered in terms of a range of conditions going (backwards) from intelligent life, via single-celled life, and such intermediate conditions as viruses and prions to biochemical molecules, and finally, cold inert matter as the "absolute zero" of life.

Might it prove useful to consider the different life-related characteristics as points in a multidimensional space that allows all the relevant characteristics (whether Earthly & chemical based, or "other") to be considered together, and perhaps a metric could assign a degree of life to various points in such a space.

My own interest in this question involves the relationship of various forms of life to information and decision making, which in a sense even simple life-forms having any sensori-response system engage in.

There is a deeper question, which I intend to post separately, relating to the emergence of life in physico-chemical terms.

Regards - PGE  

Are virus dead or alive? - ResearchGate. Available from: https://www.researchgate.net/post/Are_virus_dead_or_alive [accessed Mar 14, 2017].

The question is interesting. In old good times definition of life was just a biological problem - the definition was based on biological facts only (cell theory, etc). But now we have more knowleges and it is a self-evident fact: life is a more complex phenomenon and (theoretically) can be realized in synthetic forms - computer programs (a lot years ago I was trying to design some neural networks, it was interesting, but the real physics of living matter is more interesting :)), artificial chemical systems, hardware neural networks, etc.

I don't have any certain definition of life. It is possible to just name few fundamental atributes of it:

- self-organization

- replication

- self-reparation (some algorythms for prevention and corrections errors in reparation)

Bioinformatics looks as a very perspective way in this area - theoretically, it is possible to create a life in silico.

Viruses (biological) is an interesting example of life. They are all just obligate introcellular parasites. It means, they can replicate only in living cell without any other ways. Isolated virion (virus particle) is just a molecular (from proteins and (not necessary) lipids) container with nucleic acid. A good methaphor is printed code of computer virus - without a computer it is just a piece of paper and cannot replicate.     

Biological life as we know it is a mistake of nature created in the golden-lock zone of our solar system. There might be others in the universe but we sill don't have a prove. Why mistake, because during the millions of years of evolution, life was extinct during the dinosaurs age and flourished again. So to say the least, our Earth is an experimental lab for the creation of a Carbon based life. Is there something more complex or fundamental, I do not know. With the development of an Artificial Intelligence, we the life on Earth are trying to create similar human behavior using silicon microchips instead. Can we call it a Silicon based life. Is it more complex than ours or more fundamental than others. Elon Musk has said that there is only a “one in billions” chance that we’re not living in a computer simulation. Our lives are almost certainly being conducted within an artificial world powered by AI and highly-powered computers, like in The Matrix, the Tesla and SpaceX CEO suggested at a tech conference in California. As a computer scientist, I agree with him completely. Carbon based evolution will be replaced with a Silicon based one that is more sustainable and infinite. And maybe more peaceful...

The building blocks of life as we know it essentially consist of four groups of chemicals: proteins, nucleic acids, lipids (fats) and carbohydrates.

I’m not  a fan of intelligent panspermia because it leaves the problem of what started their life. And there are now extensive examples of how natural processes on Earth can convert simple molecules into these building blocks.

I suppose the same goes for us living in a matrix (how does the matrix builder know it’s not also living in a matrix?), or intelligent design falls into the ontological argument flaw.

What still eludes is the point in the process when a chemical stew becomes an organism. How did the first lifeforms become alive?

Although there is some debate about the definition of life, it is generally recognised that all life requires the formation of a sustainable cell, and cells must be capable of reproduction. Doesn’ that mean that if you want to concider other forms of life, one has to accept non-organic life, to get around the cell definition?

I remember being taught at school, “Living systems are chemically based and therefore must obey the laws of science.” But wasn’t brave enough to ask the teacher, “isn’t that true for everything else?”

But how did the very first cells emerge? Life appears to be just a series of chemical reactions – and we now understand how these reactions work at the molecular level. So surely this should tell us how life came about?

Why is the lifeless chemical activity transformed into organised biological metabolism extremely difficult to identify?

The assumption that early life forms must have been similar to what we see today may be preventing us from answering this question? It’s possible that there were many unsuccessful precursors that bore little resemblance to present-day life?

 A key trait that seems to sets life apart from inanimate matter is its reliance on organisation, aggregation. Molecules must be arranged in a specific way and replicate according to a detailed pattern. But the natural tendency of the whole universe is towards a state of equilibrium, or balance, Brownian motion or entropy – where everything is spread out and nothing is ordered. We need to understand how these properties combined to form a sustainable unit. Maintaining an ordered structure means life is constantly off-balance and this requires energy, which organisms must extract from their surroundings.

Ironically, paradoxically (maybe) organisms tend toward homeostasis: an equilibrium of parameters that define their internal environment.

 Chyba and Cleland argue that it is a mistake to try to define 'life'. Such efforts reflect fundamental misunderstandings about the nature and power of definitions. What we really need to focus on is coming up with an adequately general theory of living systems, as opposed to a definition of "life." I don't think that defining "life" is a very useful activity for scientists to pursue since it is not going to tell us what we really want to know, which is "what is life." A scientific theory of life (which is not the same as a definition of life) would be able to answer these questions in a satisfying way. Merely defining "life" in such a way that it incorporates one's favorite non-traditional "living" entity does not at all advance this project. It is possible that extraterrestrial life exists and that all life nonetheless has a common ancestor. I suppose it is always possible that life is not a natural category, and thus no universal theory of life can be formulated. But I doubt it.

Ralph, and All

Ralph wrote "Life appears to be just a series of chemical reactions – and we now understand how these reactions work at the molecular level. So surely this should tell us how life came about?"

As one progresses from considering pre-biotic chemicals to protocells to the earliest life forms and on up the tree of life, is there a point at which pure physics and chemistry is not enough to explain fully the properties of living systems? Are there "emergent properties"? 

Trained as a chemist myself, I have much sympathy with the reductionist viewpoint. 

Nevertheless, now that my interests include topics such as information, decision-making and consciousness, I am not so sure that we can simply reduce such phenomena to chemistry and physics alone.

(I do NOT mean that we have to introduce some extraneous or metaphysical notion.)

Let me phrase it this way: Are there properties of systems that are entirely dependent on the properties of their constituent components, but which could not even in principle, be predicted to occur from the properties of the components?

I used to think (in the late 1970s) that it would never be practical to predict protein structure from amino acid sequences, but clearly [1st link, below] this is now advancing.  

To take perhaps the most extreme example, consciousness as experienced by oneself (rather than being observed in another) seems like the strongest possible candidate for an emergent property. E.g. [2nd link]: 

“A number of philosophers have offered the argument that qualia constitute the hard problem of consciousness, and resist reductive explanation in a way that all other phenomena do not. In contrast, reductionists generally see the task of accounting for the possibly atypical properties of mind and of living things as a matter of showing that, contrary to appearances, such properties are indeed fully accountable in terms of the properties of the basic constituents of nature and therefore in no way genuinely atypical.”

My concern is simpler: information and decision making, as probably earliest-evidenced in chemotaxis [3rd]:

“... the movement of an organism in response to a chemical stimulus. Somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. This is important for bacteria to find food (e.g., glucose) by swimming toward the highest concentration of food molecules, or to flee from poisons (e.g., phenol). In multicellular organisms, chemotaxis is critical to early development (e.g., movement of sperm towards the egg during fertilization) and subsequent phases of development (e.g., migration of neurons or lymphocytes) as well as in normal function.”

While (virtually certainly) not involving consciousness in any form, chemotaxis seems to me to qualify as the simplest form of decision-making in that a simple organism acts to enhance its own survival or development by “sensing”, chemically, its environment and acting on this “information” in one of at least two alternative ways. This is not comparable to the simpler oscillations of the Belusov-Zhabotinsky reaction [4th] but seems to me to qualify as, in effect, the prototypical decision process. (The B-Z reaction is a response to a stimulus, but I think it’s fair to say that thereafter the dynamics are merely cyclic and closed, rather than thermodynamically open.)

My question thus boils down to the following: Is such an apparently-simple sensori-motor response as chemotaxis entirely physically & chemically determined, or do we need to invoke emergence to fully explain it? Does a proto-cell or a self-replicating bounded bag of chemicals display more properties than chemistry and physics alone can explain?

I have to admit that at this point I am starting to believe that I can imagine (without being able to explain in any detail) chemotaxis, and this possibly-earliest characterisation of “information”, being entirely accountable in terms of physical-chemistry.

Nevertheless, if consciousness (also intimately related to decision-making and the use of information) has to be admitted as an emergent property, then at what point in the evolution of the Tree of Life does emergence first occur?

Does it occur at the level of the cell, or only (perhaps) once there are nervous systems with specialised brain structures…?

Regards to all - PGE

(I‘m cross referring another thread [5th link] to this one as there’s less traffic on the other one.)    

https://en.wikipedia.org/wiki/Protein_structure_prediction

https://en.wikipedia.org/wiki/Emergentism

https://en.wikipedia.org/wiki/Chemotaxis

https://en.wikipedia.org/wiki/Belousov%E2%80%93Zhabotinsky_reaction

https://www.researchgate.net/post/At_what_point_does_an_association_of_chemicals_start_to_display_proto_biological_properties_that_cant_be_explained_as_pure_physical-chemistry#58c83e4fb0366d13cc79b423

“The answer lies in part with Lord Rees, astronomer royal of Great Britain. And one of his favorite sayings is, 'The universe is 100 percent malevolent but only 80% effective.'

So what does that mean? It means if you take any one of your bodies at random, drop it anywhere in the universe, drop it in space, you die. Drop it on the Sun, you die. Drop it on the surface of Mercury, you die. Drop it near a supernova, you die. But fortunately, it's only about 80 percent effective.

So if you want to start exploring [galactic] beaches somewhere else, or you want to see two-sun sunsets, then you're talking about something that is very different, because you have to change the timescale and the body of humans in ways which may be absolutely unrecognizable. And that's a Life Four civilization.”

Expanding the Genetic Code Floyd Romesberg, and one of the things that Floyd's been doing is he's been playing with the basic chemistry of life.

“We are working to increase the information capacity of DNA by developing a third base pair, for eventual in vivo application in an unnatural organism that can build proteins with unnatural amino acids. In addition, we are using an activity-based, phage display selection system to optimize the polymerase enzymes that mediate DNA replication so that they accept the unnatural nucleobases as substrates.”

 So all life on this planet is made in ATCGs, the four letters of DNA. All bacteria, all plants, all animals, all humans, all cows, everything else. And what Floyd did is he changed out two of those base pairs, so it's ATXY. And that means that you now have a parallel system to make life, to make babies, to reproduce, to evolve, that doesn't mate with most things on Earth or in fact maybe with nothing on Earth. Maybe you make plants that are immune to all bacteria. Maybe you make plants that are immune to all viruses. But why is that so interesting? It means that we are not a unique solution. It means you can create alternate chemistries to us that could be chemistries adaptable to a very different planet that could create life and heredity.

The other implication of this experiment, is that all of you, all life is based on 20 amino acids. If you don't substitute two amino acids, if you don't say ATXY, if you say ATCG + XY, then you go from 20 building blocks to 172, and all of a sudden you've got 172 building blocks of amino acids to build life-forms in very different shapes.

 And if that is true, then you can transplant memory and consciousness. And then the really interesting question is, if you can transplant this, is the only input-output mechanism is the body? Or could you transplant that consciousness into something that would be very different, that would last in space, that would last tens of thousands of years, that would be a completely redesigned body that could hold consciousness for a long, long period of time?

Juan Enriquez

Following is my definition of life.

Anything that move has a life. Everything between the fundamental particles of physics and Cell has life but does not have consciousness. When it comes to Cell and above, they have both life as well as consciousness.

“It’s tempting to think of the mind as a layer that sits on top of more primitive cognitive structures. We experience ourselves as conscious beings, after all, in a way that feels different to the rhythm of our heartbeat or the rumblings of our stomach. If the operations of the brain can be separated out and stratified, then perhaps we can construct something akin to just the top layer, and achieve human-like artificial intelligence (AI) while bypassing the messy flesh that characterises organic life…

…Now, it’s a bit of a leap to go from smart, self-organising cells to the brainy sort of intelligence that concerns us here. But the point is that long before we were conscious, thinking beings, our cells were reading data from the environment and working together to mould us into robust, self-sustaining agents. What we take as intelligence, then, is not simply about using symbols to represent the world as it objectively is. Rather, we only have the world as it is revealed to us, which is rooted in our evolved, embodied needs as an organism. Nature ‘has built the apparatus of rationality not just on top of the apparatus of biological regulation, but also from it and with it’, wrote the neuroscientist Antonio Damasio in Descartes’ Error (1994), his seminal book on cognition. In other words, we think with our whole body, not just with the brain.” (emphasis added)

It’s tempting to draw an analogy between computer scientists attempting to create intelligence in silico and the search for pain (or any experience for that matter) in the brain via fMRI. Disembodied ‘brains in vats‘, whether they’re made out of meat or silicon, will never provide the answers we seek.

Embodied approaches to minds and conscious experience seem to be a perfect fit for therapists of any stripe that touch others in attempts to alleviate pain.

Tim Cox

If the universe always contained the potential for life, does that make the universe "alive" is some fundamental sense?

Can we define "life" as awareness? Is the universe aware of itself only through the conscious life forms it gave birth to. Or is some kind of general awareness fundamental at the deepest layers of reality?

If so, everything is alive. Life and awareness permeate everything.

Alan,

You might be interested in the two items linked below, the first should give you the image, and the second relates to the corresponding ideas themselves of the late, great US physicist John Archibald Wheeler. 

Personally, I would agree with your view that the universe is "aware of itself only through the conscious life forms it gave birth to.".

Whether or not there is "some kind of general awareness fundamental at the deepest layers of reality" probably depends on whether you give credence to the wilder ideas of our universe being only some other entity's simulation...

Paul

https://www.google.co.uk/search?q=john+wheeler+participatory+universe&espv=2&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiUqLTNqe_SAhUrKsAKHWmGDoIQ_AUIBigB&biw=1164&bih=805#imgrc=TBYk5lGhayBTcM:

https://arxiv.org/ftp/arxiv/papers/1304/1304.2277.pdf

Now a new study has confirmed the “borrowed” nature of all these genes in viruses. The research uses the most advanced methods, named Next Generation Sequencing (NGS), to map out DNA extracted from a wastewater treatment plant in Klosterneuburg, Austria. In the last few years, NGS-based studies have uncovered myriad new types of lifeform, and in this instance NGS has revealed a completely new lineage of giant viruses, the Klosneuviruses.

Among all giruses, Klosneuviruses have the largest set of genes involved in making proteins. By comparing the genomes of different giant viruses and carefully reconstructing their evolution, the researchers persuasively show that the protein-making machinery in these giruses is a relatively recent genetic addition – not the scraps of a larger ancestral genome.

The study argues that the host cells these viruses tried to hijack may have evolved a defence strategy based on hiding proteins from the invaders. Then the viruses adapted by incorporating some of these genes into their genome. The researchers conclude that the giant viruses analysed in this study have evolved multiple times from smaller viruses, rejecting the idea they evolved from cellular lifeforms.

However, the new evidence doesn’t kill viruses completely. New gnarls in the tree of life are discovered every day, and a new finding could still provide a link between cellular and acellular life – or prove the opposite. Until then, we will keep thinking about the nature of life, the relationship between zombies and viruses, and wondering “what the hell is that?”

Jordi Paps Lecturer, School of Biological Sciences, University of Essex

Life is what we make it to be