We are the first generation to realize our cosmic origins.

Telescopes with electronic eyes billions of times more powerful than ours have seen out to the far horizons of the universe. Merely a century ago scientists thought that our galaxy was the only “island universe.” It was about 30 million years old and contained about a million stars. Now we know the universe is 13.7 billion years old with at least 100 billion galaxies, each containing about 100 billion stars.

To date more than 140 planets have been found orbiting nearby stars. Some astronomers speculate that, based on this very preliminary survey, there might be at least a billion — or even 10 billion — rocky planets the size of Earth. But what fraction are habitable? Today that is anybody’s guess. Within a few decades, however, the answers may at last be within our grasp.

Are we alone?

Today, the world’s largest telescopes unveil this vast universe as a restless diversity of color, shape and dynamics. These celestial panoramas reach across an immense gulf of time and space. Images of iridescent nebulae, stately spiral galaxies, gaseous pillars and jewel box clusters of shimmering stars are inspirational.

But they are also a reminder of our cosmic isolation and loneliness. Is all this celestial real estate barren and sterile? Are we the only entities in the universe that behold the wonder and awe of cosmic creation?

Looking back in time

Powerful telescopes such as the Hubble Space Telescope, the twin W. M. Keck telescopes in Hawaii and the Very Large Telescope (VLT) array in Chile are allowing astronomers to look far enough back into time to see how the universe has evolved. This is possible because the light from the earliest objects in the universe is just now arriving, like a postcard from a friend in a faraway country.

Thomas Aquinas thought Earth was so unique it would be pointless for God to create other inhabited worlds.

We are the first generation to realize our cosmic origins. We are the first to understand that our planet Earth and its many forms of life are a result of energetic events unfolding over billions of years. We are just beginning to confront unexpected new complexity and diversity as to how planets around other stars form and evolve.

We may also become the first generation to discover we are not alone in the universe. If this ever happens, it will be one of the most defining moments imaginable in the history of our species.

Cosmic isolation

Daniel Defoe describes such a moment in his classic story Robinson Crusoe, when the castaway realizes he is not alone on a seemingly deserted island. One day he finds a footprint on the beach, which forever changes Crusoe’s sense of reality about his life on the island: “I stood like one thunderstruck, or as if I had seen an apparition. . . . Nor is it possible to describe ... how many wild ideas were found every moment in my fancy, and what strange, unaccountable whimsies came into my thoughts by the way.”

Our cosmic loneliness was felt long before telescopes were ever invented. Simply looking into the starry nighttime sky invites a humbling sense of isolation beneath a beckoning but stone-silent stellar tapestry.

Ancient musings

Nearly 25 centuries ago, the Greek philosopher Metrodorus wrote that considering Earth the only populated world in the starry universe was “as absurd as to assert that in an entire field sown with millet only one grain will grow.”

Our cosmic loneliness was felt long before telescopes were ever invented.

In the 13th century, Thomas Aquinas thought that Earth was so unique it would be pointless for God — who cannot act in vain — to create other inhabited worlds. His contemporary Roger Bacon took exactly the opposite view. He held that no reason could be found to justify the creation of a limited number of worlds. An infinity of inhabited worlds had to be assumed by us.

Three centuries ago the science writer Bernard Le Bovier de Fontenelle was a bit more tongue-in-cheek in his popular 1686 book, “Conversations on the Plurality of Worlds,” in which he explains the universe to a beautiful and intelligent lady friend: “There’s no indication that we’re the only foolish species in the universe. Ignorance is quite naturally a widespread thing.”

Contemporary thoughts

Fontenelle's contemporary Christian Huygens held that God’s wisdom and providence were clearest in the creation of life and that Earth held no privileged position in the heavens. Since the same natural laws operated everywhere, life had to be universal, and it could not differ much from life on Earth.

Contemporary astronomer Ben Zuckerman of UCLA best echoed our cosmic loneliness in the preface to his 1981 book, Extraterrestrials: Where Are They?, “To astronomers who work with giant optical and radio telescopes the universe appears to be a gigantic wilderness area untouched by the hand of intelligence.”

Earthlike orbits

Astronomers have just started down the road to finding out how common or rare habitable planets may be. We now know that Jupiter-sized planets are common. They continue to be discovered at a steady rate. Smaller, Earthlike planets should be out there, too. Within not too many years we should know what fraction of stars have Earthlike planets in Earthlike orbits.

The thought that our world is the only place for life has far-reaching cultural, philosophical, and religious implications.

Then the deeper and more profound research will follow: What kinds of atmospheres do they have? How did they give rise to life? What kinds of life do they harbor? If we ever do contact extraterrestrial civilizations, it’s a safe bet they will be even more diverse than aliens dreamt up in numerous science fiction stories.

“You have to be made of wood not to be a little interested,” said the astronomer Carl Sagan in a 1993 televised interview. “Are humans all there is? Or are there other beings on other worlds? Older? Smarter? Wiser?”

Unique phenomenon or natural result?

But if Earths are rare, we may never find one, much less intelligent beings. The thought that our world is the only place for life in the universe is sobering and has far-reaching cultural, philosophical and religious implications. If Earths are abundant, the ramifications are equally spellbinding. Then we will see that the stage is set for life to play out in an unimaginable symphony of complexity and variation.

Either way, solving this question will truly define us as a species. It will answer whether we are a rare concoction of physics and chemistry, or a natural outcome of 13 billion years of cosmic evolution. Until we can answer this question we can never truly understand the role of life in the evolving universe.