There is an interesting convergence going on these days, whereby aliens are back as the focus of attention.
Stephen Hawking's new series, Genius, airing on PBS, just had an episode titled Are We Alone? Presidential candidate Hillary Clinton recently revealed that she would be ready to release secret documents concerning the infamous Area 51, where, according to conspiracy theorists, remains of an alien corpse (possibly also of a downed spaceship, they say) is kept. She was quick to add that she would only make public those documents that do not compromise national security. Last but not least, Contact in the Desert, the huge alien fest taking place at Joshua Tree National Park, a gathering with dozens of talks, workshops and courses on aliens, is scheduled for June 3-6. Among the experts, expect to see Chariots of the Gods author Erich von Daniken, who still claims that aliens were here long ago and were instrumental in helping ancient civilizations in their massive building projects. Unfortunately, a quick scan of the speakers didn't reveal any practicing planetary scientist or astronomer of note.
As New York Times science writer George Johnson recently remarked, trying to make sense of the huge popularity of conspiracy theories involving aliens and other secrets: "The truth is out there or in there. Open the gates to the inner sanctum — whether it's the Vatican, the Federal Reserve, the Masonic lodges or Area 51 — and suddenly everything will make sense."
Amidst this excitement, it's good to bring back some scientific arguments to weigh in on the possibility that aliens exist or, even more dramatically, that they have been here before. (Or are still around in some sort of stealth mode.)
First, the big numbers argument. With some 100 billion stars in our galaxy, a large fraction of those with planets — and a reasonable fraction of those with moons (have to consider these, too, as possible harbors for life)-- there are trillions of worlds out there, each with its own history. That a fraction of these has conditions similar to Earth is a reasonable expectation, backed up by recent research in exoplanetary astronomy. Estimates indicate that one in five stars have Earth-like planets in the so-called habitable zone, the region where water, if present, would be in liquid form. That means some 20 billion Earth-like planets in our galaxy alone, a huge number. We must factor in that there are hundreds of billions of other galaxies in the visible universe, even if chances of having visitors from those distant spots are very remote indeed.
So, the potential homes are there. The next step is to consider the fraction of these potential homes that actually harbor some form of life. Here we quickly dive into obscurity. Even if the right ingredients are there (and we are only considering life as we know it, carbon and water based), there is no guarantee that life actually emerged. Like those who have tried to make a soufflé know only too well, having the right ingredients is far from seeing them rise into a beautiful dish.
Although we have some clues as to what would be the right initial steps, we don't know how inorganic chemistry self-assembled into organic, living creatures. What we know of life today, with the incredibly complex reproductive genetics based on RNA and DNA, is surely a far shot from the initial attempts at reproduction, which must have been much simpler. This means that of the huge number of Earth-like planets in the habitable zone, the fraction with some form of life is probably very small.
Still, some should have it. We then move on to the next step, which is to go from very simple unicellular creatures to more complicated ones, with multiple organs. On Earth at least, there was a huge jump in complexity when prokaryotic cells (cells where the genetic stuff just floats around) mutated into eukaryotic cells (cells where the genetic stuff is protected by a membrane and that feature a host of other fixtures, such as mitochondria and other organelles).
Again, there are theories as to how this happened, but the details still escape us. Moving from eukaryotes to multicellular organisms is yet another huge jump in life's complexity, one that appears to have been facilitated by the huge increase in the concentration of oxygen in the atmosphere, courtesy of photosynthetic blue-green algae. Amazing to think that we are here because of this curious change in the energy-gathering ability of the bacterial population during Earth's infancy.
Given the existence of complicated animals, like dinosaurs and butterflies, the next big jump is the development of high intelligence. Many mammals and birds are intelligent, and we can also consider the collective intelligence of certain insects as an amazing evolutionary feat. But human intelligence stands alone in its creative ability.
A common misconception is to think that if life takes root somewhere, it will be only a matter of time before it becomes intelligent. The fact is that life has no grand plan, no teleological blueprint to reach intelligence; life is about adaptability to the environment and reproducibility: All creatures want to eat and reproduce. Mutations are not going to create major changes in a species unless they are somehow beneficial. As coaches know, changing players in a winning team usually leads to disaster.
Wrapping this all up, even with the large number of possible life-harboring planets, odds are small that life exists in many of them, and exceedingly small that some of this life is intelligent. Even if there are intelligent aliens out there in the galaxy, it's unclear whether they actually have the technology to travel across interstellar distances in efficient ways.
Of course, we are only babies in the neighborhood, and what we know is still very limited. But stars and their planetary systems are really far away, and it would take something quite amazing to hop from one to another. As a comparison, with our current technology, it would take about 100,000 years for a spaceship to travel to Alpha Centauri, the sun's nearest star system. If super-intelligent aliens have the ability to travel at, say, one-tenth of the speed of light, the trip would still take 45 years. If they exist, and were interested in traveling (what do we know of alien psychology?), they would have had plenty of time to colonize the whole galaxy, an argument known as Fermi's Paradox. That being the case, why can't we find more convincing signs of their presence?
We love aliens because they are a reflection of who we are, representing both the worse and the best in humanity, from the plundering and killing types to the wise and caring. They are a repository of our deepest fears and hopes, just like, in the Middle Ages, those repositories were embodied in gods and demons. We want them to exist so that we don't need to confront the terrifying and awesome reality that if they don't, we are unique and alone as highly intelligent beings in this galaxy and, as such, responsible for our actions with no possibility of rescuing by any power from above.
In an age of science, aliens are the new gods. Fortunately, being an age of science also means that we may actually know one day whether they do indeed exist, or not, out there. After all, we will only find if we look. Meanwhile, evidence at hand — or the lack of it — points to the extreme unlikelihood of, at least, intelligent life.
Maybe it's time we accept the difficult reality that we are masters of our own collective destiny and take steps to preserve what we have without hoping for this highly elusive outside help.
Marcelo Gleiser is a theoretical physicist and cosmologist — and professor of natural philosophy, physics and astronomy at Dartmouth College. He is the co-founder of 13.7, a prolific author of papers and essays, and active promoter of science to the general public. His latest book is The Island of Knowledge: The Limits of Science and the Search for Meaning. You can keep up with Marcelo on Facebook and Twitter: @mgleiser