Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What is the definition of life?

  1. May 18, 2003 #1
    Usually biologists use the following criterium to distinguish between live and non-live matter: ability to self-reproduce.

    Now, viruses are not capable of self reproduction without external help. Thus, they are not life yet?

    On the other hand, if to broaden the biological definition of life from self-replication to replication in general, then computers or cars are alive too - because they too are capable of replicating (although with external help - like viruses).

    Or shall we say that cars and viruses are sorta 30% life and 70% not life?
     
    Last edited by a moderator: May 18, 2003
  2. jcsd
  3. May 18, 2003 #2

    FZ+

    User Avatar

    Viruses are thought not to be alive.

    As to self-replicating robots, and stuff like that, the rule used is an entirely arbitary one - the idea of "organic" matter.

    In the end, I come to the conclusion that our definition of life is entirely subjective, based on our understanding of ourselves and willingness to elevate ourselves from other matter. Our criteria for life is based on familiarity to ourselves, and there is in my opinion that there is no sign of the objective existence of the concept known as life. When we hunt the universe for signs of life, we are in fact hunting for signs of things that are like us.
     
  4. May 18, 2003 #3
    The Heart of Reality

    From the thread, The Heart of Reality ...

     
  5. May 18, 2003 #4
    Well, that's only one of the criteria for being considered alive: self-replication. There are many other criteria, which (IMO) should also be considered, when determining whether something is "living" or not.
     
  6. May 18, 2003 #5
    Well, think about bits of data on your hard disks then too.
    Btw, can resonance be considered as self-reproduction?
     
  7. May 18, 2003 #6

    drag

    User Avatar
    Science Advisor

    Greetings !

    I don't think there is any clear definition
    of life, currently. The simple and basic reason
    for this is the fact that the current scientific
    view is that life is no different than
    not-life - everything abides the same laws and
    has the same basic constituents. Hence, no clear
    distinction seems possible, for now at least.

    Live long and prosper.
     
  8. May 18, 2003 #7

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    When does a breeze become a wind?
    When does a tropical depression become a hurricane?
    When does a computer become self aware?

    The question could be one of complexity.

    Since we don't know what life is we can't define it. Big surprise eh?

    I tend towards the leap of faith that "alive" means self aware...although I do eye my goldfishies with great suspicion. Who knows?
     
  9. May 19, 2003 #8

    drag

    User Avatar
    Science Advisor


    So, leaps of faith, huh ?
     
  10. May 19, 2003 #9

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Well, I get real worried when I try to conceive of a self aware plant or bacteria, but since we can't define what consciousness is yet, I still have some maneuvering room.
     
  11. May 19, 2003 #10
    Einfuhrung in der dialektischen und historischen materialismus (Dietz Verlag berlin 1980).

    Kapitel VI
    Materie und Bewußtsein

    2. Das Bewußtsein als Entwicklungsproduct und Eigenschaft der Materie

    Widerspeigelung als allgemeine Eigenschaft der materie

    (...)

    "Der Organismus reagiert aktiv auf eine Einwirkung der Außenwelt und verbraucht dabei Energie, die er wieder aufnehmen muB. Diese Eigenschaft des Organismus, auf Umwelteinfluss zu reagieren, d.h. ihre Reizbarkeit, is die notwendige Voraussetzung ihres Stoffwechsels mit der Umwelt und damit des Lebens"

    (...)

    Translation:

    The organism reacts actively on the impulses of the environment and consumes energy, that needs to be reconsumed. This property of the organism, to react on impulses from the environment, is the necessary predecessor for its \Stoffwechsels\ with the environment and with life itself.
     
    Last edited: May 19, 2003
  12. May 19, 2003 #11
    What does "self aware" mean? Of course, gold fish is aware of its own existence - how else it can open it's own mouth to eat anything if it were not aware of its mouth existence?
     
    Last edited by a moderator: May 19, 2003
  13. May 19, 2003 #12
    Consciousness within a living organism, arises out of the ability and need for a living organism to interchange substances with the environment (for instance take food for energy) and being able to react according to outside stimuli. The reaction is directed in accordance with the need to sustain itself, and is therefore different then the reaction of lifeless matter.

    If I pinch a hole in a lifeless material form , the reaction is only mechanical. If I do that in the skin of an animal, we can see a reaction that counteracts the damage done (see it bleeding, and can see in a few days, the damage is undone due to processes within the organism).
     
  14. May 19, 2003 #13
    Incorrect. Self awareness defines consciousness. When you are subconscious, you are not self aware, but none the less, you are still alive.

    Heredity is the most basic criteria of life, I think. In order to replicate/reproduce, heredity is involved in the very heart of it.
     
  15. May 20, 2003 #14

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    True in one sense, but, even though I don't really mean to push this point too much, even if one is unconscious the mind still works on one's behalf to maintain vital functions. Also, based on reports from coma patients who often describe awareness without consciousness, and also near death experiences where it seems that some level of self awareness is maintained even without measurable brain function, I am really using the idea of self awareness in a broader sense than it might normally be used.
     
  16. May 20, 2003 #15

    russ_watters

    User Avatar

    Staff: Mentor

    There is a big difference between stimulus/instinctive response and self awareness. A goldfish is NOT self aware. The easy test of self-awareness is the mirror test. When presented with a mirror, does the animal recognize the reflection to be him/herself or just another animal? Higher level primates and a handful of unusually smart other mammals (every now and then a cat or dog) are the only organisms that pass this test.
     
  17. May 20, 2003 #16
    Well if life is what I think most biologists say it is, a wholistic result of a lot of complex chemistry then the line will obviously be difficult to draw. This is not unlike any other wholistic creation. Think of a song. It is made up of individual notes that are carefully put together to form a pleasing acoustic experience. How many notes do you have to put together for it to be considered a song? Two or three? Probably not. It is entirely subjective. Yet I don't think there is a person alive who would deny the objective existence of the wholistic concept of music or it's effect.
     
  18. May 20, 2003 #17
    Of course, chemistry is NOT simply a sum of atoms. It is INTERACTIVE sum of atoms, and those interactions are complicated - just because life usually consists of MANY mutually interacting atoms, not just 2-3.
     
  19. May 20, 2003 #18
    Just like music and notes.
    Exactly my point. The numbers 2 and 3 are just arbitary numbers to make the point that they probably DON'T make a song because they do not have the compexity required to create the wholistic effect.
     
  20. May 20, 2003 #19

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    So life really does imitate art.
     
  21. May 22, 2003 #20

    FZ+

    User Avatar

    But you see there is a difference here between accepting that living things, or music exists, and saying that a living object or music is "special" outside of what we consider it to be. While we can say that the sound of music (cue people dancing on hills) does exist whether we hear it or not, we can't say there is a special quality about music that puts it above other sounds. It is special to US, granted, as life is seen as special to us, but it is not objectively special. The music exists, but it's particular definition, it's understanding, it's separateness does not. While it dents the eardrums of both, what is meaningless noise to one person is music to another. Do you see?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: What is the definition of life?
  1. What is life (Replies: 14)

  2. What is a definition? (Replies: 27)

Loading...