Well I think scientists look for a certain amount of similarity simply because of the universality of the laws of physics.

The greatest example of this would of course be gravity, the concept of "up" and "down" in creature (or alien) designs must be taken into consideration.

An animal like a dog, lizard, or human has appendages on the bottom of his body for movement of the body against gravity. But they have no such appendages on the tops of their bodies because of the gravity it would be ridiculous and useless to have appendages on top of the body. Also birds have landing/take off gear on the bottoms of their bodies.

Of course, because their is no distinction between right and left on a planet with gravity then you would also see symmetry in most aliens probably, just like us they would have two eyes, two ears, two arms, or maybe not two arms but the same amount on each side.

Another universal sort of science that would limit alien conditions would be the amount of elements available for chemical compounds. There are more only around 115 elements and they all have very strict parameters in terms of whether they are metals or non-metals or what they can form bonds with, and their various properties.

But I think your question is an interesting one, and there are many ways alien life and conditions could be completely different then us. For example many scientists wonder why our dna is composed of 4 base pairs, what would life have been different if they were anything other than c,g,a,t?

Basically without writing a thousand page response I would also have to add the fact about the chemical composition of water and its relationship to life and the environment. My mind starts to tilt when I try to think of how much h2o has of an effect on everything. I simply have a very difficult time figuring out how life could exist as we know it without H2O.

Anyway I have given my amatuer two cents now, and I doubt it was very insightful, but those are my intial thoughts to your question, Im sure someone else knows more.


One more thing....A lot of scientists feel that ET would probably be microscopic in nature, like a bacterium, and I would agree that it would be more likely, but I have difficulty in thinking that any intelligent life forms would be that small simply because of the chemical reactions needed for a synapse and the space that is needed. But since we dont really understand how the brain works at its cognitive level it would be difficult to say much more.

How about this one ?

http://www.youtube.com/watch?v=rJo2SeNZRC0&feature=related

I was pondering this idea about life existing without water. it lead me to this conclusion. Humans only know what is needed to sustain human life, not alien life. it is quite possible, that on other planets in nearby galaxies, there is intellegent life that is sustained by other things. it is possible that we havent seen these life forms here because our atmosphere could be deadly to them, and they havent found ways to "breathe" on class-m planets. the scientific ego still has this belief that we are the "only" intellegent life in our solar system. the truth of the matter is, we are probably too primitive to other worlds, they might not want to interfere and break their "prime directive" of not dealing with primitive life forms, for fear they might overwhelm us. my next statement may offend someone, so i apologize in advance, but look at the history of ancient cultures, and look at different events in the bible, as well as the accounts of the sumerians, the first civilization. it was clear that there was alien life her on earth, some even theorize that we were put here on earth by an alien for a purpose( read the history of the sumerians, akkadians, and mesopotaimians), so the idea that the vatican acknowledging aliens could exist is not a big surpise. if you ask me, they knew all along.

thats exactly my point!

Maybe some other alien races sustain by helium and not by water.

Its a little bothering that we seek for planets capable of HUMAN life while we didnt think that maybe on some far away planet with different conditions, a totally different lifeform evolved that needs totally different conditions than earth has.

That is a chemistry thing. Hydrogen and carbon can form very very long molecular chains which have very special functions. At some point we call this things life. With helium you simply can't do this.
I allways hated chemistry so maybe someone has a better knowledge about this.
I don't know if it is possible to make large moleculs with somethings different, but i think it is not possible, otherwise we would have found some other type of lifeforms.
Living without water-> i think this is impossible
Living without oxygen-> probably yes, there are some germs which life near volcanos underwater which don't need oxygen or sunlight.

Impossible. Thats like saying that maybe some species survive without gravity.

Hydrogen only has 1 proton in its outer shell, helium has 2 protons thus making it a noble gas. It simply doesn't bond like hydrogen does. Its a noble gas and would not want to bond with anything.

No matter which end of the universe we traverse to, there will only be a fixed amount of elements and they will only have fixed amounts of particles.

Speculation is fine, but it is only a wild guess unless you can answer the question: how is it possible?

Until then I am afraid you are just a faith-believer (but there is nothing wrong with that-I am also a faith believer)




Its the same with carbon-based life forms,we are carbon-based becuase of carbon's atomic structure and bonding characteristics. We have extremely, EXTREMELY complex macromolecules within us, so complex that some of them and their physical interactions almost escape our comprehension. They simply wouldnt be possible if it were not carbon-based. There is only one carbon atom.

If you could change the very fabric of matter and the way atoms interact then perhaps you would be on to something but changing the fabric of matter is only for the holy men.

but which different conditions? You have to be specific, otherwise as spock would say...."captain, its illogical." Anyway I'll stop arguing with you now, you have great questions though.

edit:ChrisB was posting at the same time as me so sorry for the repetition.

Simple science. We know what we look like, we know what kind of planet lead to that life, and thus we search for that.

Since we don't know of any other life-form (silicon, gaseous, energy, etc), we would be piling assumption (that they exist) on top of assumption (how they exist) and that WOULD be a waste of time as we guess blindly at what other life looks like.

again, we are talking about conditions for humans to survive, not alien species. without proof there can be no certainty that it isnt possible, just as there is no certainty that it is. think outside the box a bit. there were scientists not too long ago that said anti-matter didnt exist, but here we are. black holes were thought of as non-existant, now wormholes may be real. entertainment(movie)companies the media, and the government, and the scientific community has perpetuated these "false truths" about aliens, ufo's and such for years, and we still hold on to them until something happens, they are proved wrong, and a different way of thinks is produced, and now someone has an explination for the new phenomenom. why not read the writing on the wall(or cave, whatever the case may be) and realize that the possibility is there. if the writers of the bible (i will point to scriptures if needed to prove my point)and other ancient civilizations talk about ufo's and alien's who are we to say they are wrong? maybe we arent as receptive to them as they were, too arrogant to accept them, maybe we live among them, who knows for sure? i have read some books and can point to some websites that would shower you with facts and references to alien presence on earth(including the NASA website to make the connection between plantet x aka nibiru from the cuniform tablets of ancient sumer, and the planet on the approach coming back into our solar system) and i bet there will still be a doubt in someones mind that it is impossible. let's look outside the box a bit. it is possible.

Regardless what people think of chance... if something is unproven or unknown it still does mean it's likely to have happened that way. So in a way labeling something as 'A possibility' might not have any real value.



Yeah, but once you're following that line of thought, there's no way back in terms of assumptions based upon assumptions as Fastlane said.

Just because something was thought of to may have happened or exist, doesn't mean it's a real possibility so much as just a theoretical one. In abstract thinking, sure it can be possible, in reality most of the craziest ideas never really are a real possibility.

Now the real question here is; how crazy is the idea of life elsewhere and that's where we/they should concentrate on. And as far as I can tell, that's also why UFOs and aliens so easily get ridiculed as well. I don't think the idea of alien life visiting us mixed with no credible evidence whatsoever mixes very well when it comes to credibility and possibility.



True, but there you are assuming that these alien species may have entirely different ways of 'living'. I think it's unlikely for various reasons (for example; same rules in the universe would suggest a higher chance of 'similar' kinds of life evolved under the same conditions, wouldn't you agree? Obviously it's guesswork nonetheless, but it makes (more) sense imho than something totally different under the same conditions). Needless to say until we actually find alien species we won't know for sure.

Still, if you look at life here on our planet, sure life has found many ways to evolve, yet the core systems all tend to use the same successful formula.

the helium thing was just a wild example, i didnt write it as a real example. just to show what i meant by "something different than water".... geez

edit:


because earth has given the restrictions for evolution here, anothr planet may set other "restrictions" how life may evolve there.