Any local decrease of entropy, you mean? Snowflakes and the contents of your refridgerator, for a start! Indeed, any instance of crystallisation, condensation or ‘organisation’. You could even call this post ‘alive’ since it caused ‘order’ in a manner of speaking.
Snowflake’s etc.:
Only the process of forming the snowflake changes entropy, and if you include the surrounding air that was part of that formation (energy exchange) then we are still ok. Once formed, the snowflake does not continue to decrease entropy, I don’t think, although with some updrafts maybe it continues to get larger, not sure.
Either way, the problem clearly becomes one of defining boundaries of objects/systems (i.e. where does the snowflake system end, same with a virus), which is obviously far from trivial.
One of the things I was thinking is that something alive “acts” on the environment, it doesn’t just “re-act”. Or at least it seems this way, maybe down at the lowest level of molecular interaction, it’s all reaction and no action.
For example:
The DVD proposed earlier does not act on the environment in any way. It merely reflects light, it does not move itself, it does not spin itself, it does not manuafacture complex proteins.
A cell, on the other hand, converts certain molecules into usable energy, it creates proteins, etc. etc.
Then if we include the sun in the closed system, the entropy decrease from any life is more than made up for by the entropy increase in the configuration of the sun’s constituents, and life no longer decreases entropy overall.
And, once formed, growing old constitutes an increase in entropy rather than continued decrease.
Well, we’d start with simple amoeba which do just react to local mineral concentration, temperature and other local conditions. Then we get simple vision in arthropods which again reduce to reaction although in a far more complex “algorithm”. Then simple neuronal memory in the first jawless fish - agin, itlooks like it’s acting “on it’s on” but it could also be said to be an enormously complex ‘reaction’.
Of course - bear in mind that I favour Varela’s definition in which cells are alive but computational entities aren’t. Indeed, I favour it because other definitions like the entropy-based one allows silly things to be alive.
Erratum: again, it looks like it’s acting “on it’s own” …
Agreed.
It’s entirely possible life began as a set of molecules that reacted to the environment in such a way that the set continued to exist and began making copies of itself, and the process continued into ever larger and larger structures reacting in more and more complex ways always with the simple result that generally the structure continues to exist and to create new copies.
If this is the case, then “life” is merely an abstract notion categorizing these sets of molecules, instead of the thing that it seems to be to humans intuitively.
Good article to read is the Koshland article on the Seven Pillars of life, or PICERAS. (warning, pdf file)
§rogram
(I)mprovisation
©ompartmentalization
(E)nergy
®eproduction
(A)daptability
(S)eclusion
Definately recommended reading.
Perhaps it is the case that there is no such thing as life in this sense; i.e., maybe a biological definition of life is as inappropriate as a theological definition of gravity.
Then perhaps there is no such thing as anything. Again, human language is necessarily imperfect in its precision and there will always be entities which fall on the boundaries of the set of entities which a given word applies to. We must always go along with the least worst in order to use language productively, and I nominate Varela’s biological definition as least worst.
Varela’s seems good but limiting (as MEBuckner mentioned, re: other chemistries).
It would be nice to get a decent (not perfect) definition that is not so focused on our form of life but that still captures the essence of what we consider to be alive (i.e. not a computer).
Not sure I have any other ideas yet, need to think about it.
Just out of curiosity, what is wrong with Koshlands defintion?
Only had a minute or two at lunch, didn’t get a chance to read that one. But I will.
PICERAS seems pretty good, although it would appear to include a properly programmed robot (which maybe is ok, not sure).
I wasn’t actually talking about precision (which was why I didn’t mention it. ;)) It isn’t a matter of how accurate the definition is — the definition of a unicorn is quite precise, but that doesn’t mean that there is such a thing as a unicorn.
You are suggesting there is no such thing as life? A horse with or without a horn is still alive, agreed?
You mean this wasn’t a totally original question? 
(Thank you for that reference.)
I’m not a microbiologist, but I think that viruses meet many of the criteria proposed in the article. The one that I am questioning is Energy. Does it apply to viruses?
That is exactly what I said: “Perhaps it is the case that there is *no such thing * as life in this sense; i.e., maybe a biological definition of life is as inappropriate as a theological definition of gravity.” That’s why your response startled me a bit. I couldn’t connect it with my assertion.
That’s begging the question, isn’t it? I understand that you’re satisfied with a particular definition of life, but maybe not everyone is. It’s hard to declare a horse alive or not without first defining life, unless we intend to define life by what a horse has.
I possibly agree with the “no such thing as life in this sense” if you take “in this sense” to mean the intuitive sense of “life” that I assign to myself and those things around me which we agree are alive (I say “I” in this but hopefully I’m not the only one with this intuitive notion, in other words, hopefully you know what I mean).
I had/have some poorly defined notion about what it means to be “alive” that I assumed would get better defined due to this thread. But just the opposite has happened.
For me I think I realized there are possibly 2 questions that I am trying to answer in my own mind, and the biological definition only feels like it answers one of them, here are the 2 questions:
- What rules do we use to classify “things” as alive
- What is the “magical” ingredient that differentiates sets of molecules that are alive from sets of those same types of molecules that are not alive.
I know, I know, question 2 assumes there is more to “life” than just the biological rules, and that may be a poor assumption, but emotionally it feels right.
I think your points are well taken, RaftPeople. The problem for me with biological definitions of life is that they are contingent upon perception. That’s a problem because humans have established ethical implications for life versus nonlife. If a thing is in fact alive, but we do not perceive it that way, then we have no moral qualms about treating it like a doormat or flatrock. That’s why I say that maybe life is not appropriately defined by scientists. Maybe it should be defined by ethicists. Besides, many scientists believe that biological life is too ambiguous to define. In addition, I believe that life has another, equovical, meaning that causes massive misunderstandings in discussions like these. There is a life that is not trivial, that is eternal and metaphysical. It is the life that matters.