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A Workable Definition Of Life

  1. Mar 28, 2010 #1
    As far as I know, there isn't any definition of "life" that holds up to a physics standard.

    Sure enough, we can talk about (bio) chemistry and the specific arrangements of certain molecules, but what I'm missing is a simple, physical definition of life. I know that Erwin Schroedinger once stated that "life is a system that shows negative entropy" (and considering his bizarre cat thought-experiment, one would assume that this was a bit tongue-in-cheek), but I am unaware of any following-up on this subject.

    Enlightenment, please?
     
  2. jcsd
  3. Mar 28, 2010 #2
    Well, isn't biology and chemistry technically part of physics?
    what kind of definition are you looking for?
     
  4. Mar 28, 2010 #3
    A simple, matter-of-factly statement which defines life (in no uncertain terms) such that it won't need any "special" or "magical" ingredient to emerge.
     
  5. Mar 28, 2010 #4
    Ha, now that would be hard... =P
    i'd like to know too, till then i'll throw around schrodinger's definition it definitely is interesting and not to mention =P :D
     
  6. Mar 28, 2010 #5
    Well, while I am holding my breath waiting for that, I have chosen to think that "life" equals existence. That is to say, *everything* is alive - and our specialised niche here on earth is but one of many quadrillions of possible permutations when it comes to the question of how to organise basic quantums into larger systems.
     
  7. Mar 28, 2010 #6

    dx

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    Unfortunately, life is not that simple!
     
  8. Mar 28, 2010 #7
    Why not? We think of "gravity" as simple, so why not "life"?
     
  9. Mar 28, 2010 #8

    sophiecentaur

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    That's all very well but, if you were somewhere, elsewhere in the Universe and you bumped into some Gravity, you would recognise it and could test for it. Could you be sure of recognising 'life' if it wasn't quite "as we know it"'
     
  10. Mar 28, 2010 #9
    That's what my question is about!!!
    What, by a phycisists terms, is life?
     
  11. Mar 28, 2010 #10

    dx

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    Physics is not about inventing final definitions for everything. Our current understanding of life is simply not enough to characterize it in one or two sentences.
     
  12. Mar 28, 2010 #11

    mgb_phys

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    The trouble is you are trying to come up with a simple definition that encompasses a whole range of processes but only when they occur together.

    Try defining something simple like a star. Does you definition cover pulsars, neutron stars, brown dwarfs, should it include Jupiters and black holes?

    My favorite defn of life is the maths/computer science one - it's anything with inherited characteristics.
    It skips over the whole physics/chemistry phenomena stuff.
     
  13. Mar 28, 2010 #12
    I'd love to - except I don't see it as simple.
    To me, a star is alive - and able to shapeshift into other forms (over time).
     
  14. Mar 28, 2010 #13
    Self replication.
     
  15. Mar 28, 2010 #14
    I like that. A local state of negative entropy which increases the overall volume of (nonlocal) positive entropy in the universe. The question is; does "life" require mass?
     
  16. Mar 28, 2010 #15

    Vanadium 50

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    Are crystals alive? What about flames? You might argue this isn't self replication, but living things also require externalities like food.

    If the biologists can't draw a sharp line between living and non-living, why do you think physicists can?
     
  17. Mar 28, 2010 #16
    Which essentially boils down to "life" being a (self-contained, replicating and local) process which interacts with its surroundings by reconfigurating (parts of) them. Right?
     
  18. Mar 28, 2010 #17
    I think its actually the other way around. Our present knowledge and understanding about the complexities of life is to great to permit the formulation of a 2 sentence complete definition. The good thing is that we do not need one. A definition is a kind of tool that can be useful in some contexts but not always.In physics most of the time knowing the definition does not necessarily mean that we understand anything about the thing we are studying.The understanding comes by looking at how the thing behaves under different circumstances.The same is true about life. Observing the characteristics of life does give an understanding and helps generate new knowledge. A definition is useless.
     
  19. Mar 28, 2010 #18

    mgb_phys

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    That's why it's inherited characterstics not reproduction. A fire doesn't contain any information about the spark that made it.
    You could argue that crystals that set a certain arrangement dependent on the seed crystal are inheriting characteristics - but early life could have been as simple as self catalysing crystals/proteins.
     
  20. Mar 28, 2010 #19

    Q_Goest

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    It might be too obvious but all life we know has one thing in common; DNA. In fact, DNA seems to be a natural language of sorts, and the only language we know of that produces organisms that are alive.
     
  21. Mar 28, 2010 #20

    mgb_phys

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    Rather circular arguement though.
    If aliens appeared and had a different molecule would they be alive?
    There were also probably earlier forms of life on earth that had a different molecule by lost out to the DNA gang.

    There's also the extra question of whether RNA viruses are life.
     
  22. Mar 28, 2010 #21
    I would say that this only describes a very specialised "niche" of all possible life-forms.
    However, it is the anthropocentric one; i.e. the one which is about "things that are like us". What I miss is a comon denominator which covers all possible manifestations of "life", with or without DNA (which seems to be little but a database for the construction of a specific organism which can only exist under specific conditions). I am missing the basic vector, so to speak, the force (or field?) that makes molecules seek together and form proteins (as it were), and I am not at all happy with any religious approach of "faith".
     
  23. Mar 28, 2010 #22

    Q_Goest

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    If is a good question. Are there any others? Maybe... For one thing, it seems DNA is a language with just one interpretation. Would DNA for a human be the same anywhere in the universe, not just earth? Or might we find human DNA on planet X producing an aquatic life form with roots like kelp because it was interpreted differently? I don't think anyone knows the answer to that. Point being, we can speculate about alien life forms but we have nothing to base that speculation on.

    Same answer @ max faust.
     
  24. Mar 28, 2010 #23

    mgb_phys

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    Unlikely, there's nothing special about DNA.
    It's likely that another genetic coding molecule would be a double strand just because you can't get much simpler than that, although theres no reason not to have a triple or more.
    There's nothing particularly optimal about 4base pairs and of course the actual molecule structure is pure chance.
     
  25. Mar 28, 2010 #24

    Q_Goest

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    Yea, that sounds good. But I'm not convinced. In fact, I've heard others argue just the opposite.

    Regardless, the fact remains that DNA seems to be a natural language or molecular code as opposed to one that was invented.

    I've been meaning to start a thread on this in the bio forum... maybe I should. What do you think?
     
  26. Mar 28, 2010 #25
    I know you asked for a physicists definition but how about an Aristotelian mathematics approach?

    Define non-life.

    Everything that is not non-life is defined as life.
     
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