alien life forms, do they exist?

Eyelegal

I think with the recent discoveries of so many extrasolar planets, its almost not a question we need to ask anymore. In my opinion there are likely to be at least a couple other planets with life forms, if not civilisations, within about 200ly of us. Evidence is pointing to places being fit for life to exist being pretty common, estimates as high as 10% of stars having planets in habitable zones? The real problem in my opinion isnt having the planets, its having the right elements and molecules developing organic chemistry. With the discovery of other organic things simply floating in a soup like this = http://www.tgdaily.com/space-feature...n-orion-nebula it really gives me the impression that us being alone is VERY unlikely. Have they flown here in rotating discs though? Probably not.

Chalnoth

Even with the most optimistic probability estimates, a civilization 200 light years from us is horrifyingly unlikely.

The real problem, however, is twofold:
1. We don't know how common the right conditions for life are.
2. Given the right conditions for life, we don't know how common life actually forming is.

It doesn't help that we know even less about the probability of the formation of a civlization.

Eyelegal

Well then you start asking the brain question, is the development of the brain into a thinking and reasoning tool a common occurance or simply luck that exist once in a thousand galaxys. You can be pessimistic about intelligence, but if the data being returned by planet finding missions like kepler and at the keck telescope are anything to go by, habitable zone planets are far more common than we thought, and now they have found organic compounds in star forming nebula? What more evidence do we need to deduce that life is probably fairly common? Intelligence might be a big stretch, but i dont think organisms are at all, and thats where it all has to start.

Eyelegal

No, its not...because we know Everest is the tallest mountain as a fact. We dont know the amount of stars in the milky way or the probabilities of habitable planets as a fact. Kind of a terrible analogy...

DaveC426913

I did not define Everest as the tallest mountain, I simply chose a parameter for mountains of interest: higher than 29,000 feet.

That there are uncountable thousands of mountains is not, in and of itself, a reason for there to be more than one matching a given set of parameters.

Eyelegal

You defined 29000 feet, the only mountain which fits that description on earth is everest. We know that as a fact? I thought things that we knew as truths actually exist? Your analogy didnt make sense because we have mapped earth, we know how high mountains are. We have not mapped the galaxy, so we do not know the amount of stars and planets, so we can only make guesses educated by the current level of knowledge about our galaxy. If its about chance...the chance of everest being the only mountain higher than 29000 feet on earth is 100% isnt it?

I see where you are coming from, in that there is no proof that stars other than our own should have life around them. But, arent we beginning to get proof which allows us to make observations like Snipermans? Hasnt the probability of other life gone up hugely?

Physics-Learner

does everyone think that intelligent life needs to be carbon and water based, with a chemistry similar to our own ?

Chalnoth

No. There are other proposals. But we don't know if any of them are viable at present.

Eyelegal

http://en.wikipedia.org/wiki/Hypothe...f_biochemistry

This is a fairly good list of different chemistry types that could exist. I think our deal here is the most stable one possible?

Oldfart

We seem to be interested in looking "outside" for alien lifeforms, but why not look here first? Here right on Earth we Have ideal conditions, and a variety of such conditions, for a different form of life to develop. Are we actively looking for it?

Along this line, I think that if some form of "alien" life cannot be found here despite an extensive search, the likelihood of finding it elsewhere is sharply reduced.

OF

Eyelegal

Alien life is life that didnt develop here...unless you mean life that is alien to us. In that case do you mean the tube worms that live next to black smokers spewing superheated water deep in ocean trenches where we would expect water pressure and heat to kill all life forms?

Perhaps the organisms that live in hundred degree geothermal pools full of sulphur?

There are many "alien" creatures you can find on earth. If thats what you mean.

If you mean actual alien life...im really not sure what your talking about. How alien life would get here unassisted is...alien to me.

Oldfart

Well, what I mean by "alien" is not life from somewhere else, but life which is different from the carbon based life that we are acquainted with at present here on Earth.

OF

Eyelegal

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

Is the only one I could find quickly, an example of partial silicon biochemistry...sort of.

The problem with silicon is that it exists in far greater numbers than carbon on earth, yet carbon developed as the basis for life on Earth, suggesting that silicon life is hard to develop.

The problem with any other organic chemistry is that, to our current knowledge, all of the possibilities just dont stack up with a great chance of success. Organic chemistry with carbon is simply the most stable and easy to produce. Its probable that if life exists elsewhere, it too is mostly composed of carbon, with the probable exception of a certain % of planets/moons with life.

http://en.wikipedia.org/wiki/Carbon#Organic_compounds

Rob060870

If intelligent life does evolve in the universe then the question may be when, how long does an advanced Civilisation last for?. Say it lasted for one million years on average before being wiped out through natural disaster, consumes its resources, or war etc.then life could have evolved many times before us and may do many times after us.

One Million years is such a miniscule slice in time since the Big Bangs 13.7 Billion year history. there has been ample opportunity for maybe a Billion years or more before us for advanced life to evolve(2nd generation stars to form and stable Solar Systems to evolve), where is it?. How come SETI haven’t detected any artificial radio waves leaking into space from other Solar Systems?

The dinosaurs lived for many millions of years very successfully before being wiped out through natural disaster and they didn’t need to be very clever in order to achieve this. And if they hadn’t been wiped out then us primates probably wouldn’t have evolved.
If you played out the history of the Planet Earth millions of times I don’t think that we would necessarily have ended up with intelligent space faring civilisations, and Planet Earth as we know is perfect for life.

*NOTE- there seems to be a glitch with this site as after I post the whole thing disappears! until I post again then the previous post reappears!.

Eyelegal

Well it would be logical to assume that if a civilization lasted for millions of years, it would be highly unlikely that they could be wiped out. Im gonna look at the Kardashev scale here, I know its not really that scientific but its the best model I know of.

Its estimated that in a million years, if we are still alive, we will have at least mastered numerous star systems. This is under the assumption that spaceflight can become a faster and safer method of transport. Once we master a few star systems we cannot become extinct, because one catastrophic event would not wipe all of us out. In my opinion this should be the ultimate goal of ANY civilization ever. You might ask, if a civilization had mastered the galaxy, where are they? Well...not here yet? If faster than light travel is impossible then it is going to take a very long time for a civilization to populate the galaxy. Im not sure what the limit for slower than light travel would be, but its gonna take at least slightly over 100,000 years for a civilization to travel from one side of our galaxy to the other, and thats constantly in a straight line with no stops. Faster than light travel could make it a little faster, exponentially faster, or instant. Plus at a point I think a civilization would conclude that expanding more is pointless, they have enough space? And you have to remember, if earth took 4.5 billion years to develop intelligent life, and the universe was created only 13.75 billion years ago, it could be logical to assume that other civilizations are only developed to a level comparable (+ or -) to us.

I thought that it had been discovered that radio waves dont actually travel as far as we thought they would before disappearing into noise, so it is highly unlikely that seti would pick anything up at all?

And if there had been a civilization like ours at some point in this planets history, would we not have evidence of it in the same way we have evidence of evolution from microbes to the creatures we have today? Its predicted that nature would take back the world fairly quickly, but there would still be alot for us to see underneath this.

I agree that if we simulated the earths development of species over and over we would only get intelligence a very small percentage of the time, then again it could be the eventuality for all life harbouring planets. We just dont know. Intelligence could be the rule or the exception.

Rob060870

thats a good point there could be other life processes that are not based on carbon.however Who is to say that if other intellegent life is found why would it be based on biology at all?, it could well be machine based .

Eyelegal

Its possible, though they would have to be created by another intelligent entity wouldnt they?
How can a machine come together by itself in the same way that chemistry brought us together? At what point does machine life start? I dont think a collection of inert pieces that perform a task can come together by chance. You cant really make a comparison to how we were created, because the process is very different to the concept of a machine.