Are we alone in the universe? Or is the cosmos teeming with life? And what difference would it make if we found the answer?

Part of me thinks that we can’t possibly be alone in the cosmos. Back in the day, before the discovery of the first exoplanets, when astronomers didn’t have a clue how to go about searching for them, it was an open question whether the formation of planets was a rare or a common thing. When we didn’t know the answer, it was much easier to believe that ours might be, if not the only, at least one of the few planetary systems in the galaxy.

But we now have reason to believe that the galaxy is teeming with planets. By conservative estimates there may be one hundred billion planets and perhaps two or three times that number in the Milky Way alone. If the Milky Way is typical, that means the universe contains a truly vast amount of planetary real estate. You would think that the odds of there being life out there somewhere or other would be very high indeed.

Unfortunately, that given how very big the universe is and given the laws of physics, it seems a pretty sure bet that we may never know the ultimate answer. We certainly shouldn’t expect E.T. to drop by anytime soon. I know that movies and television tell a different story. With warp drive in Star Trek and jumps through hyperspace in Star Wars, interstellar travel looks both cool and easy. But that’s all just science fiction not science fact. Still, I hesitate to undersell either the human imagination or our power to eventually achieve what we can at first only imagine. Think of early humans who gazed out over a vast ocean and imagined unknown realms they might someday reach. Or of the first people who looked longingly to the sky with dreams of flight. So, who’s to say ultimately that we will never ever travel to the stars or find evidence of life on other planets?

Some will insist that in one sense it doesn’t matter whether we are alone or not—especially if we think we never have any opportunity to encounter alien life forms. If we can never learn anything from or about the inhabitants of other planets, why should we spend any time trying to find out? It means that nothing that we can possibly discover about them could have any real practical significance. Moreover, there is a danger that our unfettered flights of imagination will blind us to what really matters. Life here on Earth! We’ve got so much work to do—diseases to cure, social wrongs to right, an environment to save. In that context, spending great sums of money on the tiny hope that there might be life out there—life that we almost certainly will never meet, even if it does exist—seems kind of scandalous!

The starry-eyed dreamer in me wants, however, to rebel against this kind of earthbound thinking. Even if we are destined never to have a close encounter with it, the bare discovery of alien life… any kind of life… microbes, mice, or little green men… would be one of the most impactful discoveries in the history of humankind. It would be right up there with the discoveries of Copernicus, Newton, Darwin, Watson and Crick, and Einstein. It would change everything. It would completely alter our understanding of ourselves and our place in the universe. Think of Christianity. It teaches that we are made in the image and likeness of God, that we’re central to his Divine Plan. If it turns out that the universe is teeming with intelligent life, maybe we’re really just bit players in the great scheme of things.

Now, a lot of us have already gone a long way in that direction. Thanks to modern astronomy and cosmology, we know, for example, that we inhabit one small planet around one insignificant star, in one galaxy in a universe that contains untold numbers of other galaxies and stars and, probably planets too. And I grant that there is a legitimate question about whether it’s worth spending the resources it would take to find out about them. Whether we’re all alone in the universe or it’s crowded with life, we humans will still live and love and fight and die just the same as we always have.

But human curiosity isn’t going to be satisfied just by earthbound answers to earthbound questions. Something deep within us wants to know what, if anything, is out there. I mean suppose you knew that evolution has had a million different chances, on a million different planets, to design intelligent life from scratch. Wouldn’t that blow your mind? Wouldn’t you want to know how humans compare to other intelligent life forms? Whether we’re at the pinnacle or nadir of all that evolution? I would.

On the other hand, we could also be in for some rather unpleasant surprises. Suppose that someday we do manage to make contact with advanced aliens. Think about it from their point of view. After all their efforts to reach us, all the excitement and wonder about the possible wisdom they might gain, all they end up with is... us. Would you really want to be around to witness their cosmic disappointment?