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[alway]

You know, most of these posts are making the unlikely assumptions the aliens would be anything remotely similar to us; which is fairly unlikely. Its just as probable they wouldn't even recognize us as alive, or if they did, sentient. Our patterns and languages, our mathematics, might be as foreign to their brains as the pheremones of ants to ours. Theres no cosmic law dictating all life needs to be the format we see on earth.

I see what you did there.

Another few problems is the assumption that this life will even be cellular in nature, the assumption that it will use generally the same methods of metabolism, and exist in relatively similar temperature ranges. And of course that alien life would even be recognized by us as life. Heck, we don't consider robots to be life forms, but, like virii, some can reproduce themselves with the aid of another organism (humans). Sure, that is stretching the definition of life, but why should we expect alien life forms not to either?

[Renault]

[quote author=kuro_suna link=topic=55636.msg1200975#msg1200975 date=1272330647]

You know, most of these posts are making the unlikely assumptions the aliens would be anything remotely similar to us; which is fairly unlikely. Its just as probable they wouldn't even recognize us as alive, or if they did, sentient. Our patterns and languages, our mathematics, might be as foreign to their brains as the pheremones of ants to ours. Theres no cosmic law dictating all life needs to be the format we see on earth.

Anything regarding the consideration of extraterrestrial life is going to be wild speculation since we only have a statistical sample size of one to work with. We really have zero evidence for or against the universe being filled with bipedal carbon based life versus something so enigmatic we can't even begin to comprehend it.
[/quote]

Right.Which is exactly why specific guesses that their form would be anything recognizable are statistically impossible. Its the number of forms we could recognize, which is theoretically a finite number--only the traits that we have seen on livign creatures on earth-- over all the possible forms life could manifest itself, infinite. Any finite number divided by infinity is a value infinitesimally larger than zero. Thats way under statistical zero. Thus, we probably won't recognize the aliens when we encounter them.

[Tarran]

Well, one of the best features of humans is the ability to learn almost anything in time. So even if we don't recognize them as lifeforms now, we will shortly after. Like, say; living clouds of gas. It would only take us until we realize that they can move, and think for themselves to realize that they are living, or at least intelligent, beings.

[Aqizzar]

Chemically speaking, it's entirely possible to make organic-styled life, i.e. life analogous to ours, from silicon.  All the same sort of biochemical processes would take place, just at a temperature many thousands of degrees hotter and density even great.  Conditions like the inside of a molten planet.  Theoretically, there could be an entire ecosystem, even civilizations, of silicon-based life floating around under the Earth's mantel, completely oblivious to the fragile, carbon and water based life clinging to their planet's frozen outer crust.

[Grakelin]

If the Mrrnmmmhrrmrmrm are any example, you can make life out of anything.

Also, Slylandro.

[alway]

IMO an interesting tale is the Replicator story arc from SG-1. The replicators were not "evil," nor were they neccessarily plotting to wipe out all other species. They were not hostile unless they perceived you as threatening their wellbeing, and they sought primarily to increase in number and progress technologically as rapidly as possible. And of course neither side really saw the other as being life forms fit to continue living, and so wiped one another out. Ya, we're pretty much screwed if technologically advanced aliens find us.

[Il Palazzo]

Chemically speaking, it's entirely possible to make organic-styled life, i.e. life analogous to ours, from silicon.  All the same sort of biochemical processes would take place, just at a temperature many thousands of degrees hotter and density even great.  Conditions like the inside of a molten planet.  Theoretically, there could be an entire ecosystem, even civilizations, of silicon-based life floating around under the Earth's mantel, completely oblivious to the fragile, carbon and water based life clinging to their planet's frozen outer crust.

I always wanted to grab some chemistry PhD person, and interrogate him if this is really so, or just a mytho based on layman's misunderstanding of chemistry. After all, silicon might have the same valence as carbon, but what about other properties?

[Kebooo]

I'm going to go out on a limb and imagine any life capable of reaching us here with technology is sentient and intelligent, thus analytical, and could detect signs of our intelligence.  This is making the assumption that they did in fact create advanced technology and are not simply life that can travel through space without technology (Galaxy's Child from Star Trek).  In that case, anything goes.

[Aqizzar]

I always wanted to grab some chemistry PhD person, and interrogate him if this is really so, or just a mytho based on layman's misunderstanding of chemistry. After all, silicon might have the same valence as carbon, but what about other properties?

Like time-travel, faster than light drives, dry-genengineering, and artificial intelligence, it's probably a lot of bunk pseudoscience, but grounded in just enough solid theory to hold the public imagination in a death-grip.

I'm hoping it's pseudoscience anyway.  It's not we don't have enough invading aliens to worry about without checking under out feet for the Invasion of the Magma Men.  I haven't smelted enough iron bars yet.

[Org]

Time travel scares me.

[alway]

Only slight differences. The biggest hurdle to silicon based life is that silicon has only about 1/8 the prevalence of carbon. Which means carbon based life forms would be much more likely, and if carbon and silicon based life abiogenesized on the same planet, the carbon life forms would almost certainly outcompete the silicon life forms out of existance.

Interestingly enough though, without water's strangeness, life on earth may not be nearly as complex as it currently is, if it existed at all. Water is strange in that it is the only known material which has a denser liquid form than solid form. As such, it really doesn't freeze all the way through as normal liquids would. In a normal liquid, the warmest part of the liquid flows to the top, speeding up heat loss. In water, anything below 4C rises to the top, and when it freezes, it insulates the water below. Earth has gone through numerous periods in which nearly the entire planet was covered in ice (due in part to the removal of greenhouse gasses from the atmosphere by photosynthesizing life). If our oceans were, say, ammonia, the earth would have been nearly sterile after those periods since everything would freeze for a million years at a time.

@Aqizzar: Hey, AI isn't bunk science... It just isn't HAL9000. Yet. 

[Il Palazzo]

Time travel scares me.

You'll get used to it, in time.

[Aqizzar]

Only slight differences. The biggest hurdle to silicon based life is that silicon has only about 1/8 the prevalence of carbon. Which means carbon based life forms would be much more likely, and if carbon and silicon based life abiogenesized on the same planet, the carbon life forms would almost certainly outcompete the silicon life forms out of existance.

I did mention these theoretical silicon lifeforms being inside the Earth for a reason.  The issue of "likelihood" can be easy put aside by just assuming unlimited time, and the Earth's core being more than four billion years old is pretty close to unlimited time.  Inside the Earth, there would be no carbon based like to compete with; indeed, only silicon-based life could exist.  That in mind, the only real question is if the chemistry works.  Then, as Jurassic Park reminds us, life will find a way.

[Tarran]

Time travel scares me.

You'll get used to it, in time.

I see what you did there.

[kuro_suna]

Right.Which is exactly why specific guesses that their form would be anything recognizable are statistically impossible. Its the number of forms we could recognize, which is theoretically a finite number--only the traits that we have seen on livign creatures on earth-- over all the possible forms life could manifest itself, infinite. Any finite number divided by infinity is a value infinitesimally larger than zero. Thats way under statistical zero. Thus, we probably won't recognize the aliens when we encounter them.

Although using only are own world as a example is usually flawed logic we can still observe that life often isn't as random as you'd think. If were talking about life on the surface of a ball of silicon, oxygen, hydrogen and carbon I believe their would be more than a few recognizable similaritys.

http://en.wikipedia.org/wiki/Convergent_evolution

EDIT:

For example by your logic we shouldn't be able to predict the shape or path of any other planets in the universe, but their geometry is similar since their the product of a emergent system governed by the same laws of physics.

EDIT2:

http://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment