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Author Topic:   Definition of Life
Jon
Inactive Member


Message 1 of 77 (333651)
07-20-2006 8:32 AM


I was reading a book: Galileo, Darwin, and Hawking: The Interplay of Science, Reason, and Religion. (Phil Dowe), which says, in regards to the formation of carbon atoms after the Big Bang:

...[T]he entire process is so improbable that it is overwhelmingly unlikely that there can have been enough carbon produced since the Big Bang for carbon-based life to have evolved. The fact remains however, that sufficient carbon was produced. How can we explain this improbable good fortune?
...
It's hard to exaggerate how fortuitous this is. If the energy levels involved in this process had been any higher or lower there would be no carbon, and therefore no life in this universe.

(Dowe 149)

The rest of the chapter is tied up in finding various scientific and religious explanations as to how this "improbable" event could have occurred. The problem I am having here is the insistence that carbon is required for life. A Wikipedia article on Alternative Biochemistry makes it quite clear that there are other chemicals available from which life (given the proper conditions) could form.

This, however, brings up yet another problem in my brain. How is it that we (Earthlings only familiar with carbon-based life forms) can decide what other life forms would look like, or be made of? The Wikipedia article seems to say that the only chemicals in consideration are those which bear resemblance to the ones we know of for forming life (carbon, water, etc.). This is no surprise, as the Wikipedia article on Life seems to offer a definition very much fitting with our observances of life on our own planet. A view, which to me at least, seems rather self-centred--and as it's been shown since we first realized the Earth is not the centre of the Universe, such views can often be wrong.

I feel there must be a more general definition for life, which could incorporate all possibilities of complexity, self-replication, etc. that make life different from non-life. And if such a definition is not found, then it does become rather unlikely that we will ever find life elsewhere in the Universe--if, after all, we are to only regard things fitting our own self-centred view of life as life. And in such a case, is there any difference between life and non-life? Indeed, this would make us much less special in the galaxy (which would be better-fitting with the fact that we are also not at the centre of the Universe).

It is my opinion that life/non-life is a subjective differentiation that we make; and that there is nothing more special about life, than there is about non-life.

Is there anything scientific to show that there is something drastically different from life and non-life, other than more subjective lines drawn to separate one thing (existence) into two separate categories (life/non-life)?

Jon


In considering the Origin of Species, it is quite conceivable that a naturalist... might come to the conclusion that each species had not been independently created, but had descended, like varieties, from other species. - Charles Darwin On the Origin of Species
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nwr
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Posts: 5544
From: Geneva, Illinois
Joined: 08-08-2005
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Message 2 of 77 (333656)
07-20-2006 8:46 AM
Reply to: Message 1 by Jon
07-20-2006 8:32 AM


How is it that we (Earthlings only familiar with carbon-based life forms) can decide what other life forms would look like, or be made of?

The simple answer is that we don't decide, we speculate. A lot of science starts as speculative hypotheses. These hypothesis set a direction for research. Sometimes they turn out to be wrong (phlogiston and the lumeniferous ether are examples) and sometimes they turn out to be right. But even the wrong ones can provide a useful guide that eventually gets us moving in the right direction.

I the case of life, what is observed is the importance of proteins and their wide variety. It seems that amino acids are a bit like lego blocks that can be combined in a huge variety of different ways. Since this seems important to biological life, it is reasonable to look to other possible components with similar combining possibilities. This might turn out to be a mistaken idea, but at least it sets an initial direction for investigators to follow.


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Annafan
Member (Idle past 2194 days)
Posts: 418
From: Belgium
Joined: 08-08-2005


Message 3 of 77 (333664)
07-20-2006 9:07 AM


I once read an author who argued that the ring system of Saturn could be considered as a form of life. If I remember right, he pointed out the role of the "shepherd moons", and how the whole system seemed to stabilize itself. Much like life maintains itself against the tendendy towards thermodynamic equilibrium.

Isn't it all just a matter of definition?


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Jon
Inactive Member


Message 4 of 77 (333776)
07-20-2006 3:56 PM
Reply to: Message 3 by Annafan
07-20-2006 9:07 AM


life maintains itself against the tendendy towards thermodynamic equilibrium.

Doesn't this "thermodynamic equilibrium" apply only to heat? I'm not sure if you're a Creationist or not, but they do have a tendency to apply thermodynamic laws to everything :rolleyes:.

Isn't it all just a matter of definition?

My point exactly. In which case, it doesn't make us much different than anything else out there. And if there is no different between life and non-life, then the chances of life arising elsewhere in the Universe become quite high!

However, I do realize the difference between me, and the desk I'm sitting at. I'm alive, the desk isn't. For this reason, I would have to guess that there is somehow an objective scientific way to determine whether or not something is alive; seeing as how there are so many different and unfamiliar ways things can come into living.

Jon


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NosyNed
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Posts: 8802
From: Canada
Joined: 04-04-2003


Message 5 of 77 (333786)
07-20-2006 5:19 PM
Reply to: Message 4 by Jon
07-20-2006 3:56 PM


Replication
It turns out you ask a really difficult question.

Life is one of those things that we can recognize in the extremes but gets difficult as we get into the grey.

It is clear that by whatever definition that would work for most people you are alive and your desk isn't. The challenge rears up as you get down to simpler and simpler things. A good example is viruses (viri). There are those who would argue they are alive and those who would argue they are not. So your definition has to decide what is it about them that makes them alive or not.

One suggested definition is something which is an imperfect replicator. In this case, some chemicals can fall into the living category. To exclude them you would have to add the idea of it maintaining a thermodynamic disequilibium. However, I think you then have to argue over "for how long? ". You can mess around a lot and still have trouble getting a really good definition.

BTW and off the official topic of this thread:

If the big bang produced zero carbon (and I think it did, in fact, produce very little if any at all) there is no problem for carbon based life. Close enough to ALL of the non hydrogen or helium elements were formed after the big bang.

It is not improable at all. We (the universal we more than I) understand the steller phyics of supernovae which is where the heavier elements came from. Stars are hydrogen "burning" engines and big ones end their lives by a sudden production of heavier elements in a supernova; both producing them and spewing them out into space.

All stars "burn" hydrogen into carbon.

I'd say if that is an example of the book in general you should get rid of it at a rummage sale.


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macaroniandcheese 
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Posts: 4258
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Message 6 of 77 (333789)
07-20-2006 5:23 PM
Reply to: Message 1 by Jon
07-20-2006 8:32 AM


i love how people latch onto the word 'improbable' as though that means anything real. improbable given enough time and enough chances is more than possible. it's not like we're suggesting it all heppened on the first go round.
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RAZD
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Posts: 19309
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.2


Message 7 of 77 (333843)
07-20-2006 9:32 PM
Reply to: Message 1 by Jon
07-20-2006 8:32 AM


robot life?
One site I ran across in my research into abiogenesis is

http://baharna.com/philos/life.htm

It discusses the different parts of the definitions with pros and cons. Rather interesting, if not too practical in the long run -- the definitions are too frought with problems when they:

(a) includes things that are not (normally) considered alive
(2) excludes things that are normally considered alive

If we can't define life, then how can we tell where it starts and ends?

For instance, if we create self replicating robots that use raw materials to build new ones and modify the results to {suit needs\fit tasks} etc ... have we created life?

(This can also touch on the issue of abortion -- It would be best if we steered clear of this aspect or lose the thread.)

Enjoy the quest.


Join the effort to unravel {AIDSHIV} with Team EvC! (click)

we are limited in our ability to understand
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RebelAAmericanOZen[Deist
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Dr Adequate
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Posts: 15987
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Message 8 of 77 (333992)
07-21-2006 1:12 PM


Re: the energy levels of carbon

Let's see if I can clarify this.

The process by which carbon is made in stars is known as the triple alpha process. It goes like this. First, two helium nuclei (also known as "alpha particles") fuse, making a beryllium nucleus and releasing energy to the tune of 0.09 MeV. This resulting beryllium nucleus is unstable and very short-lived, but during its brief existence, it may be struck by a third alpha particle. Now this association of a beryllium and a helium nucleus is also unstable, and in most cases, this unstable association will decay. However, it may instead turn into a carbon-12 nucleus at an excited energy level. This reaction, unlike most nuclear reactions going on in stars, is endothermic --- it requires energy, to the tune of 0.37 MeV, to get up from the ground state of the beryllium and helium nuclei to this excited state of the carbon nucleus. We shall refer to this amount of energy from here on in as the required energy. Once this has happened, the carbon nucleus will fall from its excited state to its ground state, releasing 7.65 MeV of energy. And a carbon nucleus is born. *

Now, we have said that the second transition, from beryllium and helium to carbon is rare: it only happens about four times in every ten thousand. We have also pointed out that this transition requires energy. These two statements are intimately linked: it can be shown in theory that the greater the required energy, the less likely is the leap to the excited state of carbon (and conversely, if the required energy was smaller, carbon formation would become more probable). *

And here comes the Fine-Tuning Argument. The difference between the ground state and the excited state of the carbon nucleus is, as we've said, 7.65 MeV. Now, if we could somehow change this figure --- if we could hold the ground state constant, and increase the energy difference by only 1% (i.e. 0.07 MeV), then, it is argued, the required energy to get from the ground state of the beryllium and helium nuclei to this excited state of carbon would also be increased by 0.07 MeV, making this transition virtually impossible. Hence, it is argued, the difference between the ground state and the excited state of carbon-12 is "fine tuned" to within 1% from the production of carbon, which is essential not only for the chemistry of life in itself, but also for the nuclear synthesis of heavier elements such as oxygen.

However, it has been argued that this is the wrong sum to do. The possibility of the reaction does not depend on the fact that the release in energy from the excited state to the ground state of the carbon nucleus is precisely of such-and-such a size, but on the fact that the required energy to get from the beryllium and helium nuclei to the excited carbon nucleus is fairly small. It is, therefore, this number that we should look at for evidence of fine-tuning, as has been argued by Nobel Prize-winning physicist Steve Weinberg:

Another question is about the fine-tuning. I, as I said in my talk, am not terribly impressed by the examples of fine-tuning of constants of nature that have been presented. To be a little bit more precise about the case of carbon, the energy levels of carbon, which is the most notorious example that’s always cited, there is an energy level that is 7.65 MeV above the ground state of carbon. If it was .06 of an MeV higher, then carbon production would be greatly diminished and there would be much less chance of life forming. That looks like a 1% fine-tuning of the constants of nature ... However, as has been realized subsequently after this “fine-tuning” was pointed out, you should really measure the energy level not above the ground state of carbon but above the state of the nucleus Beryllium 8 (8Be) plus a helium nucleus ... In other words, the fine-tuning is not 1% but it’s something like 25%. So, it’s not very impressive fine-tuning at all. (Here) (More from Weinberg on the Fine-Tuning Argument)

His point may be clarified by analogy: imagine a man standing on top of Mount Everest looking at a giraffe. “Such exquisite precision!” he exclaims. “Do you realise that if its head was just 1% higher above sea level, its neck would be nearly 100 meters long and it would snap under its own weight?” But the "fine-tuning" of the giraffe must be measured on the scale of the giraffe, not the mountain, and in the same way, the fine-tuning of the required energy should be measured on the scale of the required energy, not the purely arbitrary scale of the energy above the ground energy of the excited state of carbon.

Re: life

I'll go with : "Chemicals which, given the right environment, catalyze their own synthesis".

There is no point in arguing over whether a definition is correct : definitions are merely convenient. Now when creationists and evolutionists argue, it is convenient for both sides to distinguish between the process of evolution and the process of abiogenesis, and this definition permits us to do so consistently.


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RAZD
Member
Posts: 19309
From: the other end of the sidewalk
Joined: 03-14-2004
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Message 9 of 77 (334114)
07-21-2006 7:41 PM
Reply to: Message 8 by Dr Adequate
07-21-2006 1:12 PM


thanks for the info and welcome to the fray.

I have usually found "fine-tuning" arguments to be the ultimate post hoc ergo propter hoc arguments -- we don't really know what would have happened if they had been different in terms of what the ultimate results would be because that hasn't been "tested"

I'm not sure you could get a giraffe on top of mount everest to test the analogy though ... :laugh:

Re: life

I'll go with : "Chemicals which, given the right environment, catalyze their own synthesis".

So crystals are life? Peptides?
http://www.santafe.edu/sfi/People/kauffman/sak-peptides.html

I kind of wonder if we shouldn't be breaking the definition down into substeps rather than try to lump (essentially) the whole abiogenesis process into a single definition.

It's kind of like trying to define an atom without defining the parts that make it up.

I do think that evolution-ability needs to be included in the definition -- the {proto-"ur"-life} needs to be able to {react\respond} to the surrounding input {environment} and {select\be selected} for fitness or it is just static growth (like a crystal).

In this view it would then need to be ""Chemicals which, given the right sets of environments, catalyze chemicals very close to their own {synthesis\type}, but which can have slightly different results in slightly different environments".

This variation could be as simple as changing certain {atom\chemical} elements to better match the chemicals available in each specific case while keeping the overall ability to catalyze chemicals very close to their own {synthesis\type}. We see this kind of variation all the time in current living things, often in places that seem to have no effect on the result (perhaps being part of structure of the molecule and not active in the synthesis - proteins only "present" parts of their molecules to act on the environment, and the ones "inside" just make it fold that way).

Note that making a near copy is less restricting than making an exact copy.

And then I think there needs to be some {encompassing\enclosing\combining} element, otherwise there is no definition distinction between what is and what isn't life -- it's all still chemical soup with slight differences in degree and not in kind. The {wall\enclosure\barrier} distinguishes between inside and outside and allows preservation of beneficial environments for replication and adaptation inside even when the environment outside becomes more {hostile\unforgiving}.

Thus I have a minimum of three particles to my {proto-"ur"-life} atom :

  • near replication of basic chemicals
  • enclosure to concentrate chemicals and raw materials
  • adapting to change in the environment
But it can be argued that these are not necessarily "life" if they don't replicate the entire package.

Enjoy.

Edited by RAZD, : added


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we are limited in our ability to understand
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RebelAAmericanOZen[Deist
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Dr Adequate
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Message 10 of 77 (334126)
07-21-2006 9:00 PM
Reply to: Message 9 by RAZD
07-21-2006 7:41 PM


So crystals are life? Peptides?
http://www.santafe.edu/sfi/People/kauffman/sak-peptides.html

The crystals are not, since they are not "chemicals which catalyse their own synthesis".

And the peptides cited in your link are alive according to my defintion, yes.


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RAZD
Member
Posts: 19309
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.2


Message 11 of 77 (334133)
07-21-2006 9:33 PM
Reply to: Message 10 by Dr Adequate
07-21-2006 9:00 PM


The crystals are not, since they are not "chemicals which catalyse their own synthesis".

Some would disagree, but it is irrelevant due to

And the peptides cited in your link are alive according to my defintion, yes.

But they are not alive according to common definitions - they would be at or less than the level of prions (much less than a virus, and neither of which are considered alive ... according to common definitions) being combinations of amino acids but not as large or complex as proteins.

This is one of the reasons I think a multilevel definition can serve better -- these peptides could be considered "animations" rather than "life" -- they become animate and make copies of themselves under certain conditions.

And we can then talk about the formation of "life" from "animations" -- which conveniently excludes crystals and cars from the definition.

Now one could make the "Dawkins Selfish Gene" argument and claim that all the rest of life has evolved to assist peptide reproduction of themselves, but there are some real {logic} problems with this type of argument (begging the question, post hoc ergo propter hoc etc - I have the same problem with the Dawkins argument).

Enjoy.


Join the effort to unravel {AIDSHIV} with Team EvC! (click)

we are limited in our ability to understand
by our ability to understand

RebelAAmericanOZen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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2ice_baked_taters
Member (Idle past 3466 days)
Posts: 566
From: Boulder Junction WI.
Joined: 02-16-2006


Message 12 of 77 (334137)
07-21-2006 9:58 PM
Reply to: Message 11 by RAZD
07-21-2006 9:33 PM


Every day we discover we know less than we thought we did. Every question leads to more questons.
In the case of this topic many pompously assume we understand what life is. Dynamic systems may be life in a sense. To off-handedly assume we have the market cornered on all knowledge of what is a sentient being would be quite pompous indeed. Before we assume a boundary we must look to see if one even exists. I do not talk to rocks but I keep an open mind. :)
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RAZD
Member
Posts: 19309
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.2


Message 13 of 77 (334148)
07-21-2006 10:35 PM
Reply to: Message 12 by 2ice_baked_taters
07-21-2006 9:58 PM


I do not talk to rocks but I keep an open mind.

I knew a vegetarian that kept a rock garden ...

:D


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Jon
Inactive Member


Message 14 of 77 (334189)
07-22-2006 12:43 AM
Reply to: Message 9 by RAZD
07-21-2006 7:41 PM


I do think that evolution-ability needs to be included in the definition -- the {proto-"ur"-life} needs to be able to {react\respond} to the surrounding input {environment} and {select\be selected} for fitness or it is just static growth (like a crystal).

But then, as pointed out by the link you provided in your first posting, mules would not be considered living, since they lack te ability to evolve (seeing as how they cannot even reproduce). Yet, to exclude something so obviously alive as a mule from the deffinition of life makes the deffinition a little useless.

Jon


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nwr
Member
Posts: 5544
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 2.6


Message 15 of 77 (334190)
07-22-2006 12:52 AM
Reply to: Message 1 by Jon
07-20-2006 8:32 AM


My tentative definition
life: a system of processes that acts in ways that tend to increase the probability that these processes will persist.
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