Ce Este Viu? Optiuni

[Blakut]

Totul a pornit de la discutia mea cu un prieten despre posibilitatea existentei vietii inafara Terrei si despre cum ar putea fi gasita ea. Si atunci m-am gandit: oamenii cand se gandesc la viata si la conditiile in care apare si se dezvolta ea, tind sa se gandeasca la viata bazata pe carbon, care ar exista si s-ar dezvolta in conditii oarecum asemanatoare cu cele in care traim.

Cum ne putem da seama ca un lucru este viu, mai exact, in explorarea noastra a lumii, cum putem sa realizam ce e viu si ce nu, ce este constient si ce nu? Oare omul poate sa inteleaga sau sa observe niste vietati care sunt total diferite lui? Pe Pamant pare simplu, dar in imensitatea Universului, cum ne descurcam?

De exemplu, de ce nu poate fi o stea considerata a fi o forma de viata? Aici discutia capatase deja aerul de gluma:

Adica putem sa acceptam ca o stea se 'naste' si 'moare'.
O stea (cel putin Soarele), are cicluri de activitate, care pot fi considerate ca fiind manifestarea unui 'metabolism'.
Cresterea unei stele este oarecum evidenta, pe masura ce hidrogenul din interior se consuma, steaua isi mareste volumul, consuma si fuzioneaza elemente mai grele.
Reproducerea, adaptarea si raspunsul la stimuli sunt problematic de discutat.

Desigur, nu vreau sa se creada ca spun aici ca o stea este cu adevarat vie sau mai stiu eu ce, ci doar sa arat ca modul in care privim viata este relativ, ceva viu poate fi definit ca fiind multe lucruri.

In clipa in care acceptam o definitie mai generala si mai cuprinzatoare a conceputlui de viata, putem sa realizam ca viata si organismul uman nu reprezinta decat niste sisteme bio-chimice, care reactioneaza si raspund la stimuli, fara nimic 'special', proprietatea de a fi viu neinsemnand decat o simpla organizare a materiei intr-un anumit fel...

[Erwin]

Dezbatere interesanta la cel mai inalt nivel (regret dar nu am timp sa traduc):

"At the Astrobiology Science Conference last March, Astrobiology Magazine organized a debate about alien life. Using Peter Ward's book, "Life As We Do Not Know It" as a launching pad, the participants debated everything from how to define "life" to what kind of strange aliens we can expect to find in our explorations. In part one of this seven-part debate series, Peter Ward tells how he was booed at a science fiction convention, and Neville Woolf has a conversation with his computer.
Lynn Rothschild: Welcome to this debate -- we have a panel of tremendously interesting astrobiologists of different flavors gathered to discuss the idea of alternate life forms.
We're going to start with Peter Ward, whose recent book, "Life As We Do Not Know It," is the impetus for putting together the debate. Peter is a geologist at the University of Washington in Seattle and the NASA Astrobiology Institute.
Peter Ward: After I wrote a book called "Rare Earth," I was asked to go to a science fiction convention to debate science fiction writers about the frequency of complex life in the universe. When I got in there, I looked about the audience and there were Wookies, and Klingons, and Vulcans -- everybody was in uniform! They started this low growling at me, and it got worse and worse. Someone said, "How can you take our aliens away from us?"
I didn't mind that, but someone else said, "You dumb fool, what about life as we don't know it? What about life that's chemically different from Earth life?" That's a very reasonable question, and hence I started thinking about this.
What do you really need for life? Right off the bat we have debatable elements. Certainly life on our planet needs membranes, it needs metabolic machinery, an information system, and reproduction.
We've had three and a half billion years of life at least, and maybe four billion years. My suspicion is that even our simple life is complex. There may be life that's much simpler yet. That is really one of the great frontiers.
How do we define life as we do know it? Life on Earth has DNA, a specific genetic code. It also uses only 20, and the same 20, amino acids. Life is always cellular according to some people, but I think not. I personally define a virus as alive.
As for other life, what could it be? Could there be non-DNA life? If such life does exist, what does chemistry permit? Certainly chemistry permits certain types of life on our planet and others not. But once we move out in the solar system, especially in the vast realm of cold, chemistry changes. There could be different information systems, different solvents, different membranes. And as we go from hotter to colder, when we go to Venus, out to Mars, to Europa, and to Titan, we really should expect radically different chemistries.
What could aliens be? They could have a different information system, a DNA equivalent. Joshua Lederberg said some time ago that there could be non-DNA life or non-Earth-like life on the Earth today, and we've just never found it.
DNA, I think, is a very important way to start looking at Earth life. DNA is so unbelievably complex, how in the world was it first synthesized? Are there different ways to make DNA? Was ours just the first out of the gate? Was there a whole zoo of DNAs out there, competing with each other? Is this the most efficient way to make it, or is this simply the way you make it under the conditions of 3.5 billion years ago, when we presumably first appeared?
John Baross once asked how we arrived at a unified genetic code on this planet. Why does all life have the same DNA? That's a very interesting question still unsolved. John has suggested the answer is easy -- viruses. Viruses go in, viruses go out, it is viruses that have unified the genetic code.
We can think about solvents. As we move from hot to cold, from Venus to Mars, to Europa, to Titan, we should expect that different solvents will work. A little antifreeze is a really good thing on a very cold day. And if you're a bug in Europa, a little antifreeze in your system would be a very good thing. Why can't we have ammonia working as a solvent?
What about structures? Chemistry in the cold can do things that chemistry on Earth can not. There's a possibility for silicon life, the great hope of science fiction. But we have the possibility now of seeing organic-like molecules being made out of material that is not Earth-permitted, but certainly can be permitted in alternate environments, especially cold.
In the book, I tried to take a controversial step by asking about the Tree of Life. I think the Tree of Life is outmoded. If you agree that a virus is alive, as I do, you've got to put it on that tree somewhere, but it doesn't fit anywhere. So, in the book I created a new taxonomic category above that of a Domain. I called this a "Dominion."
Let's say we go to Titan, and we find life that has had a separate creation, with no communication with Earth-like life ever. That's not just a separate phylum, kingdom, domain, or dominion, it's a separate tree. As taxonomists, we have to be ready to build a bigger house. Because it's coming -- either we'll find it or we're going to build it, but there will be life as we don't know it in a diversity of form on this planet in this next century. It's being built in many places right now.
Finally, I'd like to think about the implications, ethics, and dangers. We have made aliens. Not very different aliens yet -- we have made microbes that use a different amino acid than most of the Earth life does. But we should start and ask ourselves, "Should we be doing this? And if we do, why do we do it?"
I would wager that the Department of Defense has been thinking about aliens in ways that perhaps we don't. What could happen, what could go wrong? What might be the next kind of aliens that we'll see, and where should we go from here?
Lynn Rothschild: The next person on the panel is Dr. Nick Woolf, who is also a PI in the NASA Astrobiology Institute, leading the University of Arizona team. I asked him how he should be introduced, and he said, "Expert in everything else."
Neville Woolf: (Holding up a laptop computer) He's precocious, and he's going to help me tell you what life is. We're going to have a dialogue. We've got two minds about life, and I'm going to start talking first. Mirror, mirror, on the wall, which is the fairest life of all?
Computer: Congratulations! You are wonderful.
Woolf:Thank You!
Computer: I am even better.
Woolf:Are you sure?
Computer: Life works by chemical processes.
Woolf: Well, that's better, now we're getting there.
Computer: Life needs genes like yours.
Woolf: Good...
Computer: Life and you, must have water.
Woolf: Yes...
Computer: And the sun shines out of your...oops!
Woolf: Don't you say things like that! Let's go back to square one, and we'll start again explaining what life is.
Computer: Oh bother!
Woolf: Well, at least he doesn't cuss. Ok, go ahead.
Computer: Life properties: Birth. Death. Obtaining and using energy (metabolism). One eats another (predation). Life processes collaborate (symbiosis). Populations evolve.
Woolf: I think that he's got all that there are. Good job.
Computer: Stars have all of these.
Woolf: What?
Computer: They really shine!
Woolf: Hey, now! Let's try and lay it out properly. My idea is that life uses proteins and it has genes. There are things that are almost like it, such as viruses and prions, but they really don't belong to life. And of course, outside all that, there's chemistry.
But he thinks that there's something else -- that if something takes in energy and builds itself up, and it collaborates with or eats others, that's life, and that includes stars. I think we both agree that if you have things that merely build themselves up - such as fire and crystals -- they really don't have enough complexity to be called life.
So let's look at our different forms of life. A human child has a lot to learn, like how to do a job and pay taxes and have children. A Mars rover has to learn how to mine silicon and metals and build factories to reproduce itself, and maybe build rockets and fly away. So they've both got things that they hopefully will be able to do sometime, but they're not able to do them yet.
Computer: Which is better fitted for moon life?
Woolf: Hey, come on now.
Computer: For life on Mars? Which could live long enough to go to the stars?
Woolf: Is Jack Schmitt around? I need some help on this.
Computer: You dumb ass. You already know about other kinds of life. You're just too proud to think of them being like you. So you will only look for chemical life in a water medium.
Woolf: Look computer... he's not very amenable. I'll think about it.
Ok, I've thought about it, and I'm going to turn you off! (click!) There, that's better. You know, power may not be right, but it's sometimes very satisfying."

sursa:
Spacedaily.com