Do you think scientists are qualified to define life

the only type of life that we know of is our kind, we know and understand up to a great margin the carbon based life form, we do not understand the life form which is uranium based or silicon based, the conditions( boundaries) we live in is also called the goldilocks zone(http://en.wikipedia.org/wiki/Habitable_z… so the basic idea is to search for something which has a high probability of existence, like us, because we already exist so there is a chance for something similar outside our earth. when you search for life you look at these parameters (parameters of life as we know it) water, oxygen, ammonia etc not clouds of sulfuric acid or nitric acid. its not that scientist think they understand life, but simply that they know life of only one sort. if at all we do discover some other sort of life form by accident( because we are not intentionally looking for this type) then we could redefine life, but until then we have to do the best with what we have.
coming to the next question, our galaxy is really huge, i mean its really really big, mathematically the probability of finding life is roughly 0.01 in 4 billion, so the probability drops as we look for intelligent life, but the universe is big, enormous so mathematically there has to be life else where because maths is right almost every time. but it all comes down to chance!!