I always laugh when I see people say that the discovery of alien life will be the death-knell of Christianity.  It only makes Theism more attractive, not less.  You see, while water is integral to life, not all planets with water are habitable.  (at least by complex life; bacteria are probably all over the place.)  The probability of a planet coming into existence without any outside Intelligence directing it, and being able to support life any more complex than that found in Domain Archaea, is approximately 1/1000000000000000000000000000000000000000.  And that's a conservative estimate, by the way.  Meaning that it's unlikely enough for it to happen once.  That it would happen twice?  That is statistically impossible. 

And even once we have a habitable planet, there is no guarantee that it will have life!  There are a little over two hundred proteins necessary for life in the simplest bacterial cells.  Each of these has approximately the complexity of a Rubik's Cube.  It has been calculated that it would take a blind man 1.6 trillion years to solve a single Rubik's Cube.  So we once again find ourselves faced with the statistical impossibility of the wind and rain solving 200 Rubik's Cubes during the lifetime of a single star.  Once again, it is impossible that it happened once.  To have happened twice is all the more impossible, barring a directing Intelligence.

Unless alien forms do not use carbon and water as a solvent as their base biochemistry, we can assume some similarities between alien life and terrestial life, at least at a cellular level.

Wikipedia has this fascinating article about hypothetical biochemistries, definitely worth a read.

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

life outside of earth exists, the chances for atleast 1 other lifeform to exist (bacterial or intelligent) is closer to infinite then one can comprehend

just a curious thought:

some peopel insist that they have seen aliens.. some... rare cases even believe they have been abducted by aliens and even more rare cases of people that imply to have a alien husband and children somewhere out there in the universe

(lol)

now i dont wanna spoil the fun of aliens visiting earth... cuase y  i to agree that would be something...

but why would an alien species intend to visit earth?

would they spend countless years traveling through space to reach earth.. (which is olmost completely filled with idiots)

would that be, to say hello?   to trade with us?  perhaps  to abduct a few idiots... marry them and have chilren...

no,  i strongly doubt that they'd have any reason to come here in the first place,

maybe to destroy us?  build mini-deathstars to destroy our planet

our lovely earth  dominated by super-evolved monkey's (let's atleast keep SOME pride in that)

why spend resources on destroying something like that?

and we havent even started taking lightspeed in account..... (no im not talking about startrek)  im talknig about .. ofc the speed of light  the universe is huge,  jargantuos   and it's expanding...  getting even more jarguantuos..os..ish.. like..

how would they even be able to know we existed? if they'd use a giant telescope to look at earth  all they'd see is earth milions of years ago (or probably even an empty spot becuase earth wasn't created by the time the light they are looking at reached them)

though jsut to be sure.. what if they found us by accident?

just looking back at our own history

When Europe finaly discoverred the western continent, now known as the Canada,USA, and South America

what happend back there?

they found the native inhabitants there.  i have no idea what happened exactly, but i do know that it ended in war, why? Europe's technology was more advanced, it thought itself to be more important, smarter, better

just like the slave-trading in africa,  they looked different, apeared primitive compared to themselves and becuase of that they were considered slaves...goods

i sure hope we're never to be discovered by some alien race.  not before we have the means to communicate/defend ourselves...

so all together

we're not alone,  the chance = just so big for life to be created out there.. somewhere...)

chance of aliens finding us = around nil

chance of aliens visiting us = even smaller....

if aliens would ever visit us in your lifetime, then pray they come in peace, becuase we wouldnt have anything to say about our existance...  this compared to human behaviour in the past

How do we know this? The opponents claim the opposite it true (that the chances are closer to zero than one can comprehend).

I dont understand statistically there has to be other intelligent life out there. How could you possible argue that there isn't?

Did you walk up to every planet and ask, "do you have life?"

So far, we have no statistics.

. . . except maybe from SETI. And out of the heaven knows how many stars they've looked at, we're - well we've got a big, fat zero.

Problem with zero is no matter how many times you multiply it, you still get zero.

It's the Fermi paradox. Or, to put it bluntly: If they're really so probable, why haven't we found them?

Science loves to have evidence. Evidence is good, evidence is great. But we've got no evidence.

That's interesting, but rather meaningless.

sheer.

Problem is, it doesn't matter - as we don't have any idea what fraction of planets have life. It could be an exceedingly small amount. It could even in fact be just us - the issue is not how many planets there are, but the fact that we know nothing about the probablities of life, or even if life was an accidental event at all.

Water is necessary for life, but not sufficient. What you just said is meaningless in this context.

Sure it does. If somebody presents a hypothesis, and the evidence contradicts it, then we need a new hypothesis.

We have guesses about planet formation based on various things we see in telescopes.

We know what elements are in the star at the time. The composition of the planet is AFAIK still not directly observable.

Well, I guess that means Earth's atmosphere is made of mostly Hydrogen and Helium.

Strange. Never heard of organic compounds being discovered in stars.

Do I need to explain the difference between "sufficient" and "necessary" conditions?

Yelling won't make your logic any better.

That wasn't your claim. Your claim was:

Whether or not the hypothetical alien species is anything like us at all, it still must obey the laws of physics.  Using only one criterion (that there should be no deadly radiation), we can eliminate over 99 % of the stars in the universe.  Each successive criterion (and there are many: the recipe for life is much more complex than "just add water") takes away over 90 % of the remaining stars.  Further, why do we keep assuming that all stars have planets?  To be sure, we have planets, and we know of SOME other stars that have them, but as far as we know, the VAST majority of stars have no planets.  Further, we have this odd idea that all habitable planets are inhabited.  As I said before, the simplest life has a little over two hundred proteins in it, each of which has approximately the complexity of a Rubik's Cube.  A Rubik's Cube could be solved by a blind man in approximately 1.6 trillion years.  (If you're wondering, I got those statistics from The Blind Watchmaker, by Richard Dawkins.)  The life-span of your average star is about ten billion years.  So we are asking the wind and the rain to solve two hundred Rubik's Cubes in less than ten billion years.  This is difficult, to say the least.  And further, we must cut down the time allotted to the wind and rain by about four billion years, as that is how long it takes for intelligent life to evolve from the primitve bacteria.

As a side note, I noticed someone above saying that "[these creatures] might not be based off of carbon and oxygen. Perhaps they're based from nitrogon and argon?"  Who taught you chemistry?  Please let me know, so I can slap them.  There are many good reasons why all life must be based on carbon or some other element in column IVa of the periodic table, but even putting all of them aside, argon is a noble gas; it can't react with ANYTHING!  Meaning that NO other chemicals are derivative from it!

Without the survival of the fittest, evolution cannot occur: it is the driving force behind evolution.  Therefore, an intelligent being not produced by either survival of the fittest or the from-scratch fabrication of an Intelligence is a contradiction in terms.  As for war, war is the natural state of all creatures, and to be intelligent and have no conception of it is, again, quite impossible.  Whenever you have multiple individuals in one place, they are inevitably drawn into conflict, "bellum omnes contra omnia" as Thomas Hobbes put it.  It is only after intelligence arises that government and law can begin to make peaceful coexistence possible.  And even then, war is the natural state of the intelligent species.  Indeed, we have not made peace today: there has never been a time in all of human history without conflict!

And really, this approach, while valid, is altogether meaningless.  If we assume nothing about these hypothetical aliens we are encountering, we cannot usefully conjecture anything about what will happen if/when we do encounter them.  So unless we assume that these creatures are at least somewhat like us, this thread is pointless.

i am under the impression that carbon along with other forms of matter such as silicon and gold, are "base elements". which is partly why life forms are based on carbon as far as we know. but considering the other base elements, would it be so great a leap so say that a creature could not be based on silicon? i am interested to know if any of that was true. anyway, as you said, virtually all stars give off deadly radiation, including our own(it still does btw). But the great part about planets is that they can form massive magnetic fields that act to deflect harmful radiation. earth does this and so does mars(to a far lesser extent). as for the winds and rains arguement, its true that they could take trillions of years to form all the proteins. assuming they try it only once at a time. but even on a small world, there are billions, if not trillions, of instances when the combination could take place in a given minute.(im not quite sure i convayed the concept quite right with that so let me know if your not on the same page) in addition, impacts from other worlds could potetially send the organic compounds to the potential planetary parent. i could also bring up the arguement about the true definition of a planet, & that it could be possible for life to develop on something other than a planet (ive heard that there is atleast 1 mini-planet with a sustainable atmosphere but im unsure of this) but id rather not so ill let it go.

I like this. I am going to make a similar case.

Your in a room of unknown size and dimensions. your vision is limited to 1 milameter infront of your eyes. you have no sense of touch, smell, or taste. you can only hear sounds of specific frequencies and wavelenghts. even then you can only hear things that are very loud and very close to you. you position in the room is also unknown.

you search this room for other entities for 30 seconds. while stumbling around with no direction planning, or even knowledge of what your doing or what your looking for, you find nothing. based on your 30 seconds of blundering, you conclude that nothing else exists in this room.

thats the argument you just made. because humans have been looking for possibilities of life in an incrediably clumsy and crude way for what, 30-40 years at best, and since we haven't found anything that lack of evidence means that there is nothing to be found?

here is one more similar case. i am sitting at my computer desk typing this reply for 5 minutes, while typing i am also thinking about how i would almost rather be dead than thinking about this. since i have spent 5 minutes thinking about my on death (Note. a reletivly crude and ineffective way to kill oneself.) and have still not died, i can conclude that i will never infact die.

Ah, but the others are saying that stuff must exist in the room because you're inside a football stadium. Never mind if there is really anything in the stadium or not, something must exist because it's such a huge room!