What is the probability of life existing beyond the solar system?
Question:
Answer:
The short answer is:
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Yes I think it is fairly likely that there is life someplace outside our solar system. I have written a short historical survey, and then summarized some of the reasons behind my answer. They boil down to 2 points:
1. The universe is a big place
2. Life seems to be pretty common here on earth and start pretty easily.
The Long answer:
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A. History
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This is a question that people have asked for a long time. The Greek philospher Epicurius (341–270 B.C) speculated that there were an infinite number of other planets like earth, with life on them, in the universe:
“There are infinite worlds both like and unlike this world of ours...We must believe that in all worlds there are living creatures and planets and other things we see in this world.” Epicurius (c. 300 B.C)
The Dominican Monk and philospher Giodarno Bruno conjected in his 1584 work, "On the Infinite Universe and Worlds", that there were an infinite number of other worlds with intelligent life on them. He refused to recant this and other controversial beliefs, and was burned at the stake during the Inquisition for this.
The famous physicist Enrico Fermi formulated the Fermi Paradox (sometimes known as the Fermi Principle by skeptics), which states that if advanced intelligent life was widespread in the universe, we would have evidence of it already. Since we do not have good evidence, where are they?
This was later addressed by Frank Drake with his Drake equation (aka the Sagan equation or the Green Bank equation) for trying to estimate the probability of using coming in contact with an advanced extraterrestrial civilization.
Both a modification of the Drake Equation and the analyses associated with the Fermi Paradox can be used to try to estimate the likelihood of there being life beyond our solar system (the interested reader is directed to the references). Basically, depending on what is assumed for a number of parameters, it appears either quite likely that there is life outside the solar system, or quite unlikely. However, at least one has a better handle on what the quantitative factors are that go into estimating this probability by this kind of investigation.
B. Reasoning Behind my Opinion
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My own opinion, after having read this material and some of the links contained, is that it is quite possible that life exists beyond our solar system, or even possibly does or has in other places in our solar system than earth.
First, consider the very large number of stars even in our own galaxy (200-400 billion) and the large number of visible galaxies. This leads to about 7x10^22 stars in the visible universe (according to Dr Simon Driver of ANU). This is more than 10 times the number of grains of sand on earth. This is 100 billion times more than the number of letters in the 14 million books in the Library of Congress. If this is coupled with the seeming presence of a large number of exoplanets around these stars (170 found as of the end of 2005, and we have barely started looking), then this translates into a HUGE number of planets. With this extremely large number of potential planets, there are bound to be some like earth.
Life seems to thrive readily, since life started soon after the earth cooled and existing in environments that we can barely imagine, like miles underground, or near deep ocean vents, or under the Antarctic ice. It has been well known for years that there are amino acids, the building blocks of life on meteors in space. Scientists have also created amino acids in environments similar to deep space environments (see reference). The Miller-Urey experiments in the 1950s were also able to readily create amino acids in environments meant to duplicate a primordial earth environment (reference below).
With the evidence that there are probably many planets with earth-like conditions, and the suggestion that life is possible in lots of environments under lots of conditions, it would not be too big a leap to think that life might exist someplace else besides earth.
Note that these figures for the number of stars are just a lower bound, because we have suggestions from cosmological observations that the universe is far far bigger than even the visible universe. This is not counting the potential existence of other universe or other dimensions. And, this is also making the very conservative assumption that all life must be similar to life we know and on a planet like ours.
So given these factors, it does seem likely that there might be life in other places. However, it is likely that this viewpoint will be opposed by many. A major objection is based on the anthropic principle (see references),i.e., that the universe is created especially for humans. This appeals to some on a teleological basis (claiming that the universe has an intelligent design), which some feel is necessary to agree with their theological beliefs.
Zero. It doesn't exist past planet earth, unless some microsoft life survived the trip to Mars and touched down on that surface and survived.
Ask steven hawkings:
http://www.hawking.org.uk/lectures/life.
http://www.reasons.org/resources/apologe...
I think it does, if you think the universe is infinite
I say most likely there is life outside our solar system. With billions of other planets there has to be at least one more with life on it. I do believe though the life won't be some messed up alien looking creature. I think they would look like us.
only god knows
zero to none. just more planets, stars, and galaxies. the farther out we go the more we see of pretty much the same thing making any likelihood even less likely.
There are about 80 billion stars in the Milky way alone that, if a planet is there in the right distance with the right chemicals, could give birth to life as we know it. So the odds for life elsewhere in the universe, with its 50 billion or so galaxies, are pretty overwhelming...
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