What is the definition of life?

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Alexander

Main Question or Discussion Point

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?
 
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  • #2
FZ+
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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.
 
  • #3
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The Heart of Reality

From the thread, https://www.physicsforums.com/showthread.php?s=&threadid=1649" ...

What is life, if not that which is held internally? What is essence, if not that which is contained within form? Doesn't this suggest that life is an "interior process," by which the external "material world" exists to serve? And, that perhaps we should spend some time focusing on our "interior selves" as well? Why doesn't science seem to get the idea? With its exclusive focus on material existence. Doesn't it know that the "heart of reality" exists within us?

It used to be religion regarded the truth about our "inner selves," but now we rely almost exclusively on science to provide "the truth," which is nowhere near providing these kind of answers. Why is that? And why are we so bound on material existence?
 
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  • #4
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Originally posted by Alexander
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?
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.
 
  • #5
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Originally posted by Alexander
Usually biologists use the following criterium to distinguish between live and non-live matter: ability to self-reproduce.

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).
Well, think about bits of data on your hard disks then too.
Btw, can resonance be considered as self-reproduction?
 
  • #6
drag
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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.
 
  • #7
Ivan Seeking
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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?
 
  • #8
drag
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Originally posted by Ivan Seeking
I tend towards the leap of faith that "alive"
means self aware...although I do eye my
goldfishies with great suspicion. Who knows?

So, leaps of faith, huh ?
 
  • #9
Ivan Seeking
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Originally posted by drag


So, leaps of faith, huh ?
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.
 
  • #10
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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.
 
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  • #11
Alexander
Originally posted by Ivan Seeking

I tend towards the leap of faith that "alive" means self aware...although I do eye my goldfishies with great suspicion. Who knows?
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?
 
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  • #12
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Originally posted by Ivan Seeking
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.
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).
 
  • #13
RuroumiKenshin
Originally posted by Ivan Seeking
I tend towards the leap of faith that "alive"
means self aware
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.
 
  • #14
Ivan Seeking
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Originally posted by MajinVegeta
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.
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.
 
  • #15
russ_watters
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Originally posted by Alexander
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?
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.
 
  • #16
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Originally posted by FZ+
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.
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.
 
  • #17
Alexander
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.
 
  • #18
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Originally posted by Alexander
Of course, chemistry is NOT simply a sum of atoms. It is INTERACTIVE sum of atoms, and those interactions are complicated -
Just like music and notes.
just because life usually consists of MANY mutually interacting atoms, not just 2-3. [/B]
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.
 
  • #19
Ivan Seeking
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Originally posted by Fliption
Just like music and notes.
So life really does imitate art.
 
  • #20
FZ+
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Originally posted by Fliption
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.
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?
 
  • #21
LogicalAtheist
Originally posted by russ_watters
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.
Flawed Logic, and flawed test.

How would such a warped scientist be able to document weather or not a praying mantic KNEW it was him in the mirror?

Just because it attacks it doesn't mean he thinks it's not him. You're making an assumption, warped scientist.

Never have I ever heard of this test being used to determin self-awareness.
 
  • #22
LogicalAtheist
"Life" is just another one of those terms humans used before we were able to take the line we'd drawn and slam it into a microscope.

Now, the line is a bit fuzzy.

BTW - A virus requires a few things to reproduce. DOn't ever forget there ARE viruses who have all the requirements, and can produce without any other parts outside of their own membrane.

Some viruses have very few things, and must get them elsewhere, but some have everthing they need.
 
  • #23
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BTW - A virus requires a few things to reproduce. DOn't ever forget there ARE viruses who have all the requirements, and can produce without any other parts outside of their own membrane.
Erm.. are you sure about that? Any examples? Because IMHO, that seems to go against the definition of what is a virus....
(and they generally don't have membranes, but protein jackets instead.)
 
  • #24
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Originally posted by FZ+
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?
Well yes and no. I'm not sure what is meant by the word "special" but remember that we are talking about being able to define the concept of "life". I didn't realize we were trying to classify it as special. I thought the argument was that since a clear line could not be drawn between life and non-life then perhaps there is nothing to life to define. But I'm arguing that this is the nature of a wholistic effect. It's always going to be difficult to draw the line.

The fact that combining notes creates a unique wholistic effect in most everyone is the reason we invented a concept to describe it. Sure, what is music to some people is noise to others but everyone finds music is something! This is really the main point.

Perhaps I have misunderstood what your argument was earlier but my only point is that just because the line of definition is not clear doesn't mean that the wholistic effect isn't a real "additional" consequence of nature to be studied. If the whole is greater than the sum of the parts then we should have a concept for this "additional" result.
 
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