Do you believe that intelligent beings exist elsewhere in the universe?
We would have to define what "intelligent beings" are first.
We tend to think a lot of ourselves because we managed to put a probe on Mars.
But really, we aren't more "intelligent" then people were 4000 years ago. We have more
knowledge, which allows us to do more, but we aren't "more intelligent" imo then our homo sapiens ancestors.
Does homo erectus qualify as "intelligent"? They made tools so I guess that counts?
So I'll just use "toolmaking" and perhaps "language" (which implies being capable of abstract reasoning and ability to communicate ideas) as the "standard" of what an "intelligent being" is.
So when it comes to assessing the plausibility of extra-terrestial life, we'ld have to look at life on this planet and run the numbers, as it's the only planet with life that we know off.
(courtesy of an argument made by Neil deGrass Tyson, which makes lots of sense to me).
So, what is life? Life could be defined as the extreme expression of complex chemistry. Carbon based chemistry.
If we look at the top 5 elements that make up life, they match 1 by 1 to the top 5 of abundance of elements we observe in the universe. Hydrogen, oxygen, carbon,... Helium is very abundant in the univese, but chemically inert so it doesn't count since you can't do anything with it except sounding like micky mouse.
It's also not very surprising that life is carbon based as you can make more molecules out of carbon then
all other elements combined.
Next we can look at the building blocks of life like amino acids. These too seem to be very common in the universe - we even find them in random space rocks.
Next we can look at when life originated.
Earth formed 4.5 billion years ago. For the first couple 100 million years, earth was mostly a molten ball of rock being bombarded by asteroids, so we can ignore that as part of the "formation years".
Life originated some 3.8 billion years ago. Basicly within a time from of a dozen million years after earth was sufficiently cooled to allow such types of chemistry. On cosmic timescales, this is very fast. You could say that life formed pretty fast after the moment that earth was capable of sustaining it. This suggests that no matter how complex that chemistry was, it is relatively "easy" to have it occur. And if it happens here, it can happen elsewhere.
Now...the universe is BIG. Really really BIG. some 200 billion galaxies each holding an average of 200 billion stars, the vast majority of which has planets orbitting them.
Keppler has investigated only a fraction of a fraction of a fraction of these stars and already has PLENTY of rocky planets orbitting in the goldilock zone. So extrapolating that fact, we can safely say that there must be BILLIONS and BILLIONS of earth like planets out there with the potential of liquid water etc.
Considering all this, it seems almost pervers to assume that earth is the only planet with life on it. Considering these numbers, I'ld say it is near certain that there are planets out there with life on it. I can't for the life of me imagine that only earth holds life.
Now, as for
intelligent life... Let's look at earth again.
"intelligent life" as defined above and a bit less, only really surfaced in the last 2 million years on this planet - and that's including more homo species then just sapiens (like erectus and neanderthalis as well)
So it took some 3.798 billion years of evolution and bazillions of species... to obtain only a handfull of "intelligent" beings.
So clearly, right out the gates, it's clear that "intelligent" life is a LOT rarer then non-intelligent life.
So if we would encounter another planet with life on it, chances are rather enormous that this life will not be intelligent.
Yet, again considering the almost unimaginably big numbers of the universe....
If it happened once here on earth, it's quite unlikely that it didn't also happen at least a few times elsewhere as well.
So, in conclusion, based on the above, my answer here would be:
- non-intelligent life elsewhere in the universe: as good as certain
- intelligent life elsewhere in the universe: much, MUCH, less probable the non-intelligent life, but considering how huge the universe is, still quite likely
my 2 cents.