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Living and Non-living

  1. Aug 26, 2012 #1
    I have learnt in my second grade that all things are categorised into living and non-living things. Living things breathe , grow, reproduce, etc., I don't really remember... and non-living things don't.

    I was thinking if there was something that isn't living or non-living; something entirely diiferent. I know about viruses: the threshold between living and non-living. Just asking, but what about stars? It is sort of like a living system, isn't it? It can't be 'completly non-living'.

    I know my question is vague but I would like to know your opinions.
  2. jcsd
  3. Aug 26, 2012 #2
    I often wonder what advanced ai in the way way out future will consider itself possibly it will not consider itself living but could have all the qualities of a living entity possibly that is kinda what your getting at???

    Also you might be thinking of an ecosystem sorta like how the earth is.
  4. Aug 27, 2012 #3
    I am not thinking of something like alien species. I meant something that we already know about but haven't categorised it properly.

    Come to think of it, I think it depends upon how we define life. Would you think the universe as a living entity?
  5. Aug 27, 2012 #4


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    By any reasonable definition stars are non-living. They are simply large balls of gas obeying the laws of physics. They do none of the things you mentioned above (breathe, grow, reproduce...).
  6. Aug 27, 2012 #5


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    You already answered your own question. It depends on how we define life.
    Have you read this article?
  7. Aug 27, 2012 #6
    A module I took recently had a definition of life as a system that contained 3 things - the ability to multiply, the ability to vary and the ability to pass on traits to offspring. This is a definition I hadn't heard of before, but it is an interesting one. A flame for example can multiply but cannot vary - the nature of the flame depends on the environment. However even with this definition there is a substantial grey area. Things like prions seem to be not alive.
  8. Aug 27, 2012 #7
    If you look in a dictionary every word has multiple definitions and that one for "living" is the one a biologist might use. However, other cultures like the ancient Chinese believed everything is alive and which meaning you might want to use for "living" just depends on how you want to use the word at any given time.
  9. Aug 27, 2012 #8


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    Yeah, but thinking of rocks as living is getting pretty far out into the metaphysical/philosophical and away from any kind of science.
  10. Aug 27, 2012 #9
    Our textbook used "stimulus response plus metabolism plus offspring" and then added "genetic material" because something like fire can match the first three, if one interprets the terms widely enough. The approach Rooted mentioned is certainly more elegant, but I'm not convinced it actually solves the problem, since there's no obvious reason for all physical processes to be governed solely by current external conditions rather than past and present internal traits, which is presumably what "vary" means.

    I have actually read a publication making the case for stars being alive. Unfortunately, it was too long ago for me to remember enough about to be able to track it down, it seems. What I do remember is that it was a more or less scientific argument, without any recourse to mysticism, and that I ultimately didn't find it convincing.

    That being said, it's not unusual for insect colonies to be considered life-forms. They certainly match the four criteria from my textbook, and they even in some ways display a higher form of intelligence than any individual insect, possibly not all that dissimilar from a multi-cellular organism displaying a higher form of intelligence than that of any individual cell. Furthermore, there doesn't seem to be any good reason to count only the insects themselves and not the nest they build and inhabit as part of that colony life-form, that I can see, just as one counts a snail's shell as part of the animal and not as clothing or housing.

    If one accepts all that, it doesn't take much mental stretching to make a similar case for human communities and their homes, which when taken to its logical conclusion means humanity as a whole and the Earth, it would seem. In this view, the objection "it's not the Earth which is alive, it's individual creatures" doesn't make any more sense than "it's not humans which are alive, it's individual cells". And if one accepts the Earth as alive, then why not anything which contains it, i.e. the solar system, galaxy, and universe?

    There's a non-mainstream cosmological hypothesis by Lee Smolin which posits that every black hole gives rise to another universe. Based on that idea, universes can be thought of as producing offspring via black holes. Coincidentally, or maybe not, the same conditions that favour the production of black holes also appear to favour the emergence of intelligent life. From there, it again doesn't take a giant leap to consider a universe in its entirety to be alive. I seem to recall Smolin discussing that himself - and if I didn't, the name of his pop-sci book, "The Life of the Cosmos", would be a bit of a giveaway.

    I'm not really saying that I subscribe to any of these views myself, but it seems clear to me that definitions of (life which don't take the drastic step of limiting life to the biological, terrestrial kind by adding some ultimately arbitrary criterion like "genetic material") tend to be a lot more inclusive than we ordinarily consider them to be.
  11. Aug 28, 2012 #10
    Variations in organisms(which we consider as living forms) occur due to environmental changes, radiations etc. So, they change as they depend on the environment. Can't flames be living, then?

    What about sterile animals like mules? They don't have the ability to multiply and therefore, cannot pass on any traits they have. But mules are living beings!

    I don't think the definition you mentioned is a right one.
  12. Aug 28, 2012 #11

    No, I agree. For example one rabbit by itself would not be 'alive', because you'd need 2 to reproduce. I think the definition was a bit more general than that. The actual term is 'heredity' - the passing on of traits from one to another. My impression was that it was a way to describe an informational process like DNA and the genetic code and to differentiate it from merely a chemical reaction such as a flame - dependent purely on local fuel, heat, and a reductive agent.

    There are many interesting books on the subject and here's a couple, I've read bits here or there but not cover-to-cover -
    'What is Life?' - Schrodinger, 1944
    'Origins of Life' - Freeman Dyson 1985
  13. Aug 28, 2012 #12
    I believe Erwin Scrodinger defined life as:

    "An organized genetic unit that is capable of metabolism, reproduction and division."

    Don't get confused by the definition. Personally I think that everyone can intuitively guess if something is living or not. Life or being alive is something we can't define yet we can sense and determine. If a large number of people were each asked to judge a variety of objects and determine whether the objects were alive or not, I think the responses would be very similar. And in my opinion no one would define a star as being alive.
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