Is there other life on other planet?

It is likely that life exists on other planets, at least in its simplest form, bacteria. What we do not know is whether intelligent life exists. It is unlikely humans will ever answer this for certain, it is one of nature's great mysteries. However, it is likely that there exists intelligent life somewhere out there. Think about it.... we live on one out of eight planets; in just one of over 170 billion galaxies. (A galaxy is typically about 1,900,000,000,000,000,000 miles in diameter, so multiply this by 170,000,000,000 and you'll have a good estimate of how big the universe is even not counting empty space [there are voids out there 19,000,000,000,000,000,000,000 miles big!] Compared to this, Earth is tiny, only about 7,917.5 miles in diameter!) Our 170 billion galaxies make up our massive observable universe. Our observable universe is only what we can see with present technology, who knows what small part of the whole universe this might be? If you consider the infinite vastness of space and planets, it is likely there is one planet out there that harbors living, breathing, thinking humans.

The calculation that is most commonly used for the probability of intelligent life in our galaxy is the Drake equation, which is normally given in the form:


N = R x F_p x n_e x f_l x f_i x f_c x L

where

N = the number of civilisations in our galaxy with which communication might be possible.

R = the average annual rate of star formation in our galaxy

f_p = the fraction of those stars with planetary systems

n_e = the average number of planets per star that could support life

f_ℓ = the fraction of the above that develop life at some point

f_i = the fraction of the above that progress to intelligent life

f_c = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space

L = the length of time such civilizations release detectable signals into space.

Current best estimates of these figures gives a 1/30 probability of intelligent life in our galaxy (but, before you get excited, remember that WE are one example of intelligent life, and are part of the calculation). More pessimistic figures give a probability of 1/15,000, while the most optimistic values give around 100 civilisations at any one time - even then, the problem is that the closest ones would be around 8000 light years away.

The Drake equation can be easily modified to give estimates of the probability of life elsewhere in the Universe, at which point (with 170 billion galaxies) it becomes very likely that there are other life forms out there.



BUT, the Drake equation is partially based on estimates where, in some cases, we have no real certainty at all about the values (particularly f_ℓ, f_i, f_c and L), so the margins of error in each are multiplied up and, in reality, are enormous.