How do we define life?

  • #26
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The fact that life stores energy to do its functions is incidental (i.e. of little use) to its definition
You think? I would say that because life is obliged to store energy and use the store to find more energy (to store), defines it pretty closely. It has to grow (extend), and perhaps move around to do this. Also it necessarily must be able to determine (discriminate or measure) its environment to do this, and measure its own internal ´environment' simultaneously. Bacteria do this. Learning is the accumulation of this measurement and discrimination, and storage of this too (in DNA and protein). How does a car or a battery or a machine -a robot, do this?
 
  • #27
DaveC426913
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I have 47 gadjillion distinct objects on a (large) tray and I want to separate them into life and non-life. (The act of separating the two is the embodiment of having a definition. If we have a non-ambiguous definition of life vs. non-life we can do this, if we do not, we cannot.)


I keep all things that (metabolize and reproduce and grow and respond) on the tray, and toss everything else off the tray. I have 11 brazillion objects left.

I decide to enact your criteria and (from the remaining 11 brazillion objects) remove all that do NOT store energy for these functions.

How many do I have left? Exactly 11 brazillion.

"Storing energy" does not contribute to our isolating the set of things that are life from the things that are not life. Thus it is an irrelevant criteria in defining life vs. non-life.
 
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  • #28
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"Storing energy" does not contribute to our isolating the set of things that are life from the things that are not life. Thus it is an irrelevant criteria in defining life vs. non-life.
So there is no way to distinguish a battery or a jar full of some chemicals (that have a potential energy say, if someone opens the jar and chucks a lit match in), from a bacterial culture? There is no way to tell if a bit of wood or a rock is alive or not, because containing energy is an irrelevant distinction? How do you personally decide if something, say, is not alive? Just for argument´s sake, what criteria do you look for?
I keep all things that (metabolize and reproduce and grow and respond) on the tray
How can you hope to determine that things are metabolising or reproducing, for example, surely this must be impossible?

Frankly I think you are completely wrong, actually incorrect, and you definitely need to review what you know about this subject (you´re talking rubbish, in other words).

1. Things contain or store energy. All things made of matter can be converted to some kind of energy.
2. Life stores energy. It has to use energy to do this.
3. Life uses energy to find more energy, things can store energy (have or contain some), but only life (is obliged to) goes around looking for more of it. All by itself.
4. Life tracks its environment by using energy to maintain a map of external and internal information
5. Life grows (extends itself) by converting energy into more ´life´.
6. Life reproduces, this requires energy.
7. Life shares information with others. This sharing is not an energy-free process.
 
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  • #29
DaveC426913
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So there is no way to distinguish a battery or a jar full of some chemicals (that have a potential energy say, if someone opens the jar and chucks a lit match in), from a bacterial culture?
???

Of course there is - the four criteria defined: metabolism, reproduction, stimulation and growth.
 
  • #30
DaveC426913
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1. Things contain or store energy. All things made of matter can be converted to some kind of energy.
2. Life stores energy. It has to use energy to do this.
3. Life uses energy to find more energy, things can store energy (have or contain some), but only life (is obliged to) goes around looking for more of it. All by itself.
4. Life tracks its environment by using energy to maintain a map of external and internal information
5. Life grows (extends itself) by converting energy into more ´life´.
6. Life reproduces, this requires energy.
7. Life shares information with others. This sharing is not an energy-free process.
Again, I am not saying these things aren't true, I'm simply saying that the "uses energy" part doesn't help to distinguish life from non-life.

Take #6 for example:
"Life reproduces, this requires energy."

Do you know of any circumstance in the universe where a process "reproduces" without "requiring energy"? If there are no processes that reproduce without requiring energy, then this criteria does not narrow the choices by any. After applying it, you have the same number of items on your tray as you had before.


Or #4:
"Life tracks its environment by using energy to maintain a map of external and internal information"

Do you know of any process in the universe where a system "tracks its environment to maintain an external and internal map" - but does NOT "use energy" to do so? If you do NOT know any, then this criteria does not help narrow the definition any. same items on tray.

Simply put, you are confusing properties of life with definitions of life. What you are listing is properties that life has. But those properties do not help narrow the definition of life.
 
  • #31
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So what criteria are used to distinguish that something has "metabolism, reproduction, stimulation and growth" ?
How can we differentiate between something that "uses" energy, say some star, from something that grows, or metabolises. The key difference is the way life (is obliged) to use energy (for all the above reasons).

Also I don't think you can compare a nematode's, or a blue-green algae's internal "map of self" (whatever biochemical or neural representation it may have), with anything that doesn't have or maintain such a thing, or doesn't use it to exploit (to measure) the environment. Are you saying inanimate objects do this too (like the sun, say)?

It is a bit trite, I suppose, to just say "Life uses (and stores) energy", when actually it is more the way it does this, and how it depends on both its internal store and the energy (food) it finds, to store more of it, in an ongoing (teleological) process. I think that's succinct enough, because all the rest follows, more or less, from this "requirement". Telic processes are what ensues from Life having a unique "relationship" with its food (the environment).

Arguably, the distinction is that inanimate things don't have this teleological feature. Life appears to have a purpose, which is different from, say a fire. A fire can be said to have a purpose in that it "wants" to burn all the fuel it can, but there is no directed or purposeful (or intelligent) feature present after all, just our observation of its character or behaviour, which we tend to ascribe to some intelligence (because that's what we do -humans are incurable anthropomorphics, sorry about the big word...)
 
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  • #32
DaveC426913
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Life appears to have a purpose, which is different from, say a fire. A fire can be said to have a purpose in that it "wants" to burn all the fuel it can, but there is no directed or purposeful (or intelligent) feature present after all, just our observation of its character or behaviour, which we tend to ascribe to some intelligence (because that's what we do -humans are incurable anthropomorphics, sorry about the big word...)
Yes, I was about to raise the point that it is very common to anthropomorphize phenomena. Fire is often invoked as a loophole in definitions of life because it supposedly does all those things. But it does not. For example, fire does not reproduce unless one means figuratively.


But I disagree with your supposition that life appears to have purpose. I think that leads down a road to a philosophical definition of life, which I also think is of little use.
 
  • #33
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Your restrictions don't seem to leave a lot of room, though. How is the distinction made then (you said you could select things off a tray -what sort of criteria are applied when you do this?).
We can "tell" the difference between a bit of rock, and say some worms, or a bird (rocks don't move around "by themselves"). How do we make this distinction, or how do we discriminate 'dead' things from 'live' things - something we do continually?

If there is no use in distinguishing the way something uses energy, or appears to be directed to a purpose (unlike something inanimate, which has only its existence, but no awareness), then what do we use (what do you specifically use as a discriminatory feature, or set of features? I think you do use the same features I listed, like every other observer does).

Is awareness (thanks to a store of biochemical energy, a map, and so on) a unique property, perhaps?
 
  • #34
DaveC426913
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Your restrictions don't seem to leave a lot of room, though.
Isn't that the point?

How is the distinction made then (you said you could select things off a tray -what sort of criteria are applied when you do this?).

We can "tell" the difference between a bit of rock, and say some worms, or a bird (rocks don't move around "by themselves"). How do we make this distinction, or how do we discriminate 'dead' things from 'live' things - something we do continually?
Worms eat and excrete; we keep them on the tray. Rocks do not; we discard them.


Is awareness (thanks to a store of biochemical energy, a map, and so on) a unique property, perhaps?
Again, awareness is a property of some forms of life, but we can't use it to define life because it will rule out very simple lifeforms that don't have a meaningful amount of awareness. They do react to stimulation though, which is one of the criteria I listed. That might count as awareness, depending on how loosely you wish to interpret the term.
 
  • #35
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I think awareness is the ability to measure, or to observe, or to 'receive' messages (information), and to 'send' information too (to other observers).
All living things do this...
DaveC426913 said:
I disagree with your supposition that life appears to have purpose. I think that leads down a road to a philosophical definition of life, which I also think is of little use.
But teleology is an ergodic function, ergodics is certainly a scientific subject.
You claim that 'worms eat and excrete', presumably their use of energy, and the 'purpose' they exhibit doing this (as every living thing that exhibits trophism does), is irrelevant, or meaningless? Or just not very useful as a way to define or describe life?
 
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  • #36
DaveC426913
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I think awareness is the ability to measure, or to observe, or to 'receive' messages (information), and to 'send' information too (to other observers).
All living things do this...
Yes, this is embodied by the words stimulation/irritation, which is one of the criteria I listed. Living things in some way get information from the world around them (be it as simple as: it's very hot over here) and react to it (move away from the hot place). So we agree on this criteria.



But teleology is an ergodic function, ergodics is certainly a scientific subject.
You claim that 'worms eat and excrete', presumably their use of energy, and the 'purpose' they exhibit doing this (as every living thing that exhibits trophism does), is irrelevant, or meaningless? Or just not very useful as a way to define or describe life?
I don't follow your words but I do think we may be crossing wires here. I am taking your words of 'purpose' and 'meaning' at face value. I do not believe that life has purpose or meaning except that assigned to it arbitrarily by thinking creatures with philosophy or religion.
 
  • #37
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DaveC426913 said:
Living things in some way get information from the world around them
I would say that the "some way" involves energy, its "storage and usage" specifically. But this is irrelevant, according to your definition.
DaveC426913 said:
I do not believe that life has purpose or meaning except that assigned to it arbitrarily by thinking creatures
How do thinking creatures manage this? If the use of the energy store they all carry around, or the apparent purpose that thinking creatures 'observe' in other lifeforms (and other members of their own lifeform), is of no help, or is actually irrelevant?

I believe that both energy 'storage' and the teleology, are necessary features that 'thinking creatures' project onto them, to distinguish between living things, and non-living things. The projection doesn't create these things, they are intrinsic to all life, not created by an observer.

You can select things off the tray that are 'dead' because they do not exhibit either of these features (behaviours). A rock does not move around under its own power, or consume other things and then grow, or exhibit any sort of purposeful behaviour. We can distinguish between a rock and a bunch of insects, because of these behaviour distinctions. This is how you, me, and all living things see the world (to whatever extent they 'see', or measure it), surely?

BTW 'ergodics' is the study of evolving systems: complexity theory and emergent behaviour are included in this.
 
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  • #38
DaveC426913
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You can select things off the tray that are 'dead' because they do not exhibit either of these features (behaviours). A rock does not move around under its own power, or consume other things and then grow, or exhibit any sort of purposeful behaviour. We can distinguish between a rock and a bunch of insects, because of these behaviour distinctions. This is how you, me, and all living things see the world (to whatever extent they 'see', or measure it), surely?
How does one determine 'purposeful'? Does lichen exhibit more definably purposeful behaviour than a rock?
 
  • #39
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How does one determine 'purposeful'?
Are you saying that we, or you, are unable to make a distinction between "purposefulness" and "non-perposefulness", or that the distinction (if we make it), is irrelevant, or of no use to us?
Does lichen exhibit more definably purposeful behaviour than a rock?
Yes it does, if you observe it carefully or closely enough. A drop of pond water is teeming with lifeforms that we need a microscope to see; is something like that (or the bacteria living all over most organisms) not life, or not 'exhibiting' behaviour because we can't see it without some instrument?
 
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  • #40
DaveC426913
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Are you saying that we, or you, are unable to make a distinction between "purposefulness" and "non-perposefulness", or that the distinction (if we make it), is irrelevant, or of no use to us?

Yes it does, if you observe it carefully or closely enough. A drop of pond water is teeming with lifeforms that we need a microscope to see; is something like that (or the bacteria living all over most organisms) not life, or not 'exhibiting' behaviour because we can't see it without some instrument?
But it seems that the definition is circular.
Life exhibits purposeful behaviour.
How do you define purposeful behaviour?
Well, it's behaviour that life exhibits and non-life does not.

Purposeful is a judgement call.
 
  • #41
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Purposeful is a judgement call
What's a "judgement call", though? Is it the capacity of an observer to judge something (like whether there is enough light to make sugars, or enough heat, or too much)?
What else can observers do except observe --process the 'information' that is projected at them?
 
  • #42
DaveC426913
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What's a "judgement call", though? Is it the capacity of an observer to judge something (like whether there is enough light to make sugars, or enough heat, or too much)?
No, a judgement call means there's no objective, independent criteria for true or false, i.e. it's subject to the observer. You might decide something on my tray is exhibiting purposeful movement and who am I to say it's not purposeful? The first question I'm going to ask is 'what - in your judgement - makes it purposeful'?

Which means we're back to not having a definition.
 
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  • #43
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In which case, how do we, or any group of observers, end up making decisions (like whether something that's wriggling around might be good to eat for instance, or worth chasing, or as in our case, here on this forum)?
 
  • #44
DaveC426913
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In which case, how do we, or any group of observers, end up making decisions (like whether something that's wriggling around might be good to eat for instance, or worth chasing, or as in our case, here on this forum)?
?
What does this subjective, goal-driven action have to do with the task of creating a definition of life? We're talking pure academics here, not survival techniques.
 
  • #45
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?
What does this subjective, goal-driven action have to do with the task of creating a definition of life? We're talking pure academics here, not survival techniques.
What does this discussion (which I claim is also a "subjective, goal driven action" -and you appear to be claiming also that there is a "purpose" to all this activity, or maybe you are also claiming that there isn't any such thing as "purpose" at the same time, I can't quite figure this out) have to do with goals or purpose? We aren't able to make decisions based on this 'activity' according to you...
What's your definition of 'pure' academics btw?

Your definition does not seem to allow for the (observed) behaviour of life to 'preserve' itself. Without purpose, no organism would bother to expend energy looking for food, or move away from danger. We would simply stay inside a burning building, or remain 'unmoved' by an oncoming flood, or violent storm, or an attacking wild animal (a lion say); since we can't make a 'judgement', there is no point in having or even defining purposeful behaviour, because its an illusion; no lifeforms have this property, they simply sit around waiting for whatever might come along, but can't decide what to do if something does...
 
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  • #46
DaveC426913
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I think we've gotten mired in a meta-discussion; we're now talking about how our own discussion is an example of the topic we're arguing.

Hmm.

I'm going to go back to this point:

In which case, how do we, or any group of observers, end up making decisions (like whether something that's wriggling around might be good to eat for instance, or worth chasing, or as in our case, here on this forum)?
I don't see how the answer to this is directly relevant. It seems to be more about the application of our definition of life. We should first try to define life.
 
  • #47
Rade
On another thread I defined life this way, I think it works for all known examples of it that exist on earth:

life = entities with self generated action mediated by nucleic acid (either DNA or RNA)

see here:
https://www.physicsforums.com/showthread.php?t=114399

There are many other threads on this forum about this important question. If we do not know what life is, the word Biology has no meaning. So, if you study Biology, then I say you study entities with self generated action mediated by nucleic acid (either DNA or RNA). Of course how you can study such entities comes in many forms, which is what makes Biology such a great field of study, and so much more complex than any other natural science.
 
  • #48
DaveC426913
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On another thread I defined life this way, I think it works for all known examples of it that exist on earth:

life = entities with self generated action mediated by nucleic acid (either DNA or RNA)
That would be the definition of life-as-we-know-it.

But it still seems self-referential to me.
 
  • #49
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We should first try to define life.
I agree. This is supposedly the point of this thread, and I'm keen to see how well we do or how far we can all (as a group, say) agree on what each has to offer to the discussion.

First, I think it's probably important to define the question: what is it asking?
"How do we define" life, or how do we notice what it is, or what we are? How much of a problem is there with life trying to define itself (us, or any other organism)?
What about the possibility of being 'observed' --by something that isn't alive, as far as we can define, or 'notice'? How does the world 'see' life, in other words (or maybe that's a bit too obtuse or obscure for some).

Anyways, if you start with the assumption that you already know the answer --it's something you were born with, or some kind of innate knowledge (like knowing how to move around, or see or hear things)-- then it shifts to: What is this innate knowledge? Selecting live and dead things and sorting them (as on a tray), must involve some decision-making; what decisions get made, and why or how?

I don't personally think it's helpful to try to exclude things that are obvious characteristics; what's the point of doing that?
e.g. "moves around" (except for the life that doesn't, but this kind of 'non-motile' life isn't static, it is an active thing), or "has purpose", or "uses energy", etc.. Life does all this, so why is it 'important' to classify it as "irrelevant" --which I don't think is the case either? I don't see how something can be defined by describing what it doesn't do, except in a limited way; or that defining its characteristics away (as not meaningful) --so excluding them-- is going to get to any sort of useful goal here.
 
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  • #50
DaveC426913
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We strive for the most concise definition. If something can be expressed with one rule as easily as several rules, we go with the one rule.
 

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