Nobody knows the answer to that particular question. The only way at this time to address finding any answers is probabilities and the maths say it is very likely. However I personally think we will never know . I hope I am wrong.

If there is intelligent life it will most likely be finding earth because it wouldn't seem that we have the technology to find their planet. If they do find us let us all hope they are kinder and gentler creatures.

Firstly to qualify my response: I believe that life on Earth evolved from single cell beings which developed over millions of years from chemical reactions from Earths tumultuous past.

Secondly, I have to consider if other planets in other systems in other galaxies have formed similarly to Earth? Obviously, I answer yes.

Thirdly, Mathematically, and conservatively, what chances would life form from the chemical reactions of planet? 1%? 0.5%? 0.0001%? Plug that into the number of possible planets in our known universe. Consider that our known universe is finite, but only because we can't "see" past the limits of the cosmic microwave background. So there's a large possibility that it is even bigger than our known universe.

Thirdly part 2: 0.0001% chance of life that would evolve from chemical reactions in 1 million planets comes out to 1 planet with life. That would be Earth! Would there be more than 1M planets in our known universe? Sure. Lets plug that number into a group of 5M planets: 0.0001% in 5M planets comes out to 5 planets with life. Would our known universe have more than 5M planets?

It is estimated that there are 10^24 planets in our known universe. That's 1 with 24 zeros after it.

By the way, the above is the Fermi Paradox.

In extension, they've added to the Fermi Paradox reasons for us not meeting any other intelligent life. One of those reasons is that: if we take our history and evolution into considerations, it's likely that intelligent life snuffs themselves out (through war, disease, or not developing the technology to harness energies required, etc.) before attaining interstellar technologies.

EDIT: As I stated in other discussions on this site, I believe that we will attain sub-space travel and colonise Mars and likely one of the giant's moon - Titan for example. However, I can't see us travelling outside our solar system. It's simply too huge and the energy required to power any ship to get to the nearest star, is it Alpha Centauri?, is unimaginable.

And I really can't see us achieving inter-galactic technologies. Apart from the energy required for space travel, every galactic group in the universe is continually moving away from every other galactic group. In the very very very very very far future, our night sky will not be covered with stars. Instead, we'll see pockets of groups of stars (the stars in our local group of our galaxy) in different parts of the sky with huge black gaps in between.

Your in agreement that we're alone....? The book , Human Universe, thier denial was your answer? We're just now getting smart enough to reason things out. Our technology is helping us make educated decisions. Have you read other books? Anything by Steven Hawkins? Everything is so spread out. How can you say were it and theres nothing else like us? Just asking...

The drake equasion clearly states that it is statistically impossible for us to be alone in the universe. That's some pretty good evidence for other life in the cosmos.

I believe we are not alone and ancient aliens have played a key role in our human race too..

At least we have each other.

Life elsewhere in the solar system is certainly possible, if not exceptionally likely. However, restricting the domain of the question from the universe to the solar system is a colossal restriction. We surely need to consider, at the very least, our galactic neighborhood. And judging by the number of exoplanets already discovered which are at least candidates for hosting life, there is likely to be life within some tens of light-years.Now we only need to think slightly farther afield, still within our own galaxy, and not beyond possible reach some day, and we are very likely to find other life forms, with some level of intelligence. Or they will find (or have found) us.

Apartfromthefactthat you do not place spaces behind comma's and dots, which makes your text harder to read, I actually think that the contrast you presume is quite bold. I mean the contrast between "are we alone in the universe?" and "if we restrict the domain of the question to, are we alone in the solar system".
The scientific knowledge in the medieval times was way more limited that it is nowadays. There was no radio at all, people moved on foot, by horse cart or on horseback and believed that the sun rotated around our flat earth (even nowadays some people still believe that). Why than presume that in 2018 we already know everything, that it is impossible to bridge distances beyond our own solar system. I'm not so sure about that. In my lifespan since the fifties so many discoveries have emerged that I am unable to predict what the future will bring. It seems to go faster and faster.
Having that said, I question if it is fair to equate the question "Are we alone" to the question "is there life outside our atmosphere". "Are we alone" in general points on the question: Are we the only intelligent species in the universe or are there more". It is quite fair that scientists limit themselves to the questions "is there life beyond our atmospheric limits?" and "can we find planets where we find the same circumstances that we find on earth and where life could have evolved in a comparable way as life has evolved on earth". The first question is part of the investigation of Mars, Jupiter and other planets in our own solar system, but also of the results of analyzing meteorites etc. If bacteria are to be found there, then it shows that life is not limited to earth. If so, it's the starting point of further investigations.
The question "are we alone" is more based on the thought that, if the universe is so huge, with so many stars and ditto planets, it would be quite plausible that there are quite some planets where intelligent life of some quality has developed. Although the assumption is quite fair, there is still no proof and a perfect base for science fiction writers (it's not called "science-fiction" for nothing). What, apart from SF, the practical use is of this assumption, I don't know. Probably the idea has motivated scientists to study the theories that are based on that.
I'm sure that if we could look some 100 years in the future, we would be amazed.

As is outlined other places in the thread, the shear vastness of the universe and the conditions we know that create life in only on scenario make intelligent life elsewhere in the universe almost a certainty. The problem is the question may be vacuous since the chances of communicating with them or even sensing them is next to nil. In that sense we might as well be alone.

That being said I would be excited if we found any form of life in our own solar system. It would be fascinating to see how life evolves on a completely different evolutionary tree.

In the solar system yes, we're alone when it comes to intelligent life. In the universe? I find it hard to believe it's only us. However in our search we are more likely to find a civilization that died billions of years ago then one existing today. The reason is by the time we would find a civilization we'd probably be looking at what it was billions of years past. But just by share probability I feel certain there is live in many places somewhere right now.

I think the problem is that everything is so spread out.. Even if one could travel at the speed of light, it could take millions if not billions of years to pay our fellow universe inhabitants a visit. Plus, life forms do not exist forever. It is fun to think of distant civilizations though.

In this solar system perhaps. I can't say with any certainty that we are in the universe. It's more likely that there are other solar systems with survivable environments that might contain life. We have barely begun exploring our own solar system to know what goes on beyond it with any real certainty but it would be pretty ridiculous to think this one planet and this one solar system would be the only one. Words in a book not exactly scientifically based answering a more scientific question isn't something I'd use as evidence. You may as well keep the bible if you do that.

We can communicate with extra-solar civilizations quite easily:Gravity warbles. Use gravity as morse code. The size of the universe guarantees that someone is already using gravity to communicate. Since gravity is an effect, and not a law...then the speed of the waves of gravity are near instantaneous.

I’m al it’s certain we’re not alone. But I just hope is e er out there, it’s not a homicidal maniac. I’d refuse to live in a universe like that.

If the nearest life is beyond our reach and it lacks the capacity to reach us, then for all practical purposes we are alone. If we lack the technology to communicate over these great distance or are so unlike the other life, then we are alone. Lacking evidence for now, we can accept that we are alone at this moment. Things can change, but without evidence or constructive engagement, we are alone.,Possible visitation in the past still seems to be just conjecture, present day encounters may exist, but lack creditable affirmation by our scientific folks. Given the vast number of variables in the billions of years available for life to evolve, we may currently exist in the midst of other life forms and not be aware of it. Still no discernible contact means we are still alone. Keep looking, maybe the answer will be yes or stop wasting time and other resources if the answer is really no.

Even if there are living beings in other places in the universe, they are so distant in time and space that their existence is largely irrelevant to the human species.

Of course we are not, imo only fearful, narrow minded people would think so, I don't mean to offend anyone.

We're not alone - We're just here by ourselves.

Would be speculation, those movies that have ET`s in them might not be far from the truth. Like you said is to vast for us to explore. If our societies could just get over the greed and hate emotions. The progress would progress faster technology would not be suppressed . Wont see in in our life times our children might get to see warp drive star trek space like adventure.

I'll grant that in the sense of sentient life, except for this planet, we are alone in the solar system. Dolphins & possibly other animals may be smarter & more aware than we now give them credit for, so we may have some company here. & tho the universe is huge & we are unable to explore it in its entirety, that actually is a factor in the probability that there is intelligent life "out there", somewhere. We may never meet up with any others, which would be a shame, but the vastness of the cosmos makes it highly unlikely that we are the only island of life in the void.