Science Behind the Fiction: What if, like Ad Astra suggests, there are no aliens?

On the surface, Ad Astra appears to be a sojourn into familiar science fiction territory. A look at the trailer promises space-faring technology which, while advanced, feels not far off. There are vast structures, explosions, and the promise of a journey to the edge of the solar system, but not before we get a road warrior rover battle on the Moon, the likes of which would make George Miller shiver.

The film, directed by James Gray and starring Brad Pitt, is dressed in all the things that make science fiction exciting, but underneath is something much more intimate and a whole lot more true. Something... lonely.

**Spoilers for Ad Astra below**

Roy McBride (Pitt) has always wanted to be an astronaut. Lucky for him, it isn't such an elite calling in his time (a nebulous near future). Humanity has expanded beyond Earth, setting up colonies on the Moon and Mars. And it helps that his father is a famous hero of the stars, leader of the first mission to the edge of the solar system. Roy's father led a team of explorers to Neptune-orbit, beyond the interference of the inner solar system, in search of extraterrestrial life. The mission lost contact in the deeps of space and the crew is presumed dead.

In the end, the great irony of Ad Astra is that, while humanity has advanced and expanded its reach, Roy is utterly alone. It's a point hammered home at the end of the film, when Roy finally finds his still-alive father and learns that, even after all these years, all they've discovered is that humanity remains alone in the universe.

Ad Astra certainly delivers action and some incredible visuals, it exists almost entirely on a stage of quiet contemplation and, when the thinking is done, you're left with an answer you might not have wanted. Humans are alone in the universe, meaning we'll have to live with each other, and perhaps more urgently, ourselves.

So, is Ad Astra's revelation that there are no aliens out there true, and if so, why is that fact so quietly devastating?

WHERE IS EVERYBODY?

One cannot embark upon this question without first discussing Enrico Fermi. In 1950, during lunch with some colleagues, Fermi, a physicist, made two seemingly obvious observations. First that the universe is very old, and second, that it is very large. He questioned, therefore, that given the age and size of the universe, it should have had ample time to fill itself with all manner of intelligent life. After all, we're here, and there's no particular reason to suspect we're unique. So, where exactly is everyone?

This became known as the Fermi Paradox, the two seemingly incompatible truths that the celestial neighborhood ought to be heavily trafficked while we appear to be alone on a deserted island.

It seems a foregone conclusion, especially when considering the rapid rate of technological advancement we're experiencing. In only a few decades we went from first flight, to walking on the Moon.

While it's difficult to imagine the technology of the next century or the ones that follow, it doesn't seem unrealistic (assuming we're still around) that we'd settle our own solar system and continue onward. What might we accomplish in a thousand years, or a million? The universe has existed for several billion years. Shouldn't we expect advanced civilizations with a considerable head start? Mightn't they already have explored and settled the stars, scattering their footprints and the evidence of their presence?

Yet, when we look to the stars, we find a stunningly beautiful, yet entirely empty arena.

CAN WE SOLVE THE DRAKE EQUATION?

Dr. Frank Drake made the question of "where is everybody" a little more concrete — and more complicated — while working at the National Radio Astronomy Observatory in Green Bank, West Virginia. Drake suggested an equation which, if all the variables were known, could calculate the number of advanced civilizations in our galaxy.

The actual equation is little more than a string of variables, including the average rate of star formation per year in our galaxy, the fraction of those stars with planets, the fraction of those planets which are habitable, the fraction of those that succeed in developing life, the fraction of those that develop intelligent life, the fraction of those that develop interstellar communication, and the average length of time such civilizations could survive.

If we knew each of the variables for this proposed equation, we could solve for (N), the number of existing intelligent life forms we could contact in the universe. The trouble is, we have almost no empirical data to go on. We've got a pretty good idea as to the first bit, the rate of star formation in the galaxy, and as we continue to discover exo-planets, our view to the next couple bits improves. In fact, when it comes to planets in the habitable zone of their parent stars, evidence suggests they exist around approximately one-fifth of stars in the Milky Way.

The rest, however, is pure speculation.

When it comes to the frequency of life in the universe, let alone our own galaxy, we only have one data point. Us. The best we can say is that life can exist, whether it does anywhere else, remains to be seen. Ultimately, when using the Drake equation, the results tend to say a whole lot more about the biases of the people plugging in the numbers than it does about reality.

Still, there's some inherent expectation in each of us that there must be other life in the universe. Paraphrasing Jodi Foster's character in Contact, if we are alone in the universe, it seems like an awful waste of space. But science demands that we examine the evidence, and right now all we can say is it appears as though we're on our own.

Scientists and thinkers have suggested an array of explanations for why that might be.

Maybe it's that the Earth truly is unique, though that seems increasingly unlikely. It might be that we're simply ahead of the curve. Life might be common but it hasn't yet had the chance to gain a foothold.

WE WEREN'T ALWAYS ALONE, BUT WE ARE NOW

There are also more bleak explanations, namely that intelligent civilizations tend to destroy themselves, something of considerable speculation given our own violent and misguided tendencies. It might also be that the universe wipes out life. The Earth has already had five known extinction-level events and another could happen at any time. We're one asteroid or gamma-ray burst from annihilation.

It might also be that we're just not addressing the problem in the right way. Perhaps life is common, but we're looking in the wrong places or for the wrong things. Maybe other intelligences are so advanced we can't recognize them when we encounter them. Or maybe we're being intentionally avoided.

There are any number of reasons to explain our lack of contact in an environment full of cosmic neighbors. The lack of evidence might not actually be evidence that we're literally alone.

It might be that we're just not smart enough, interesting enough, or important enough to be invited to the party.

Of course, it might be a matter of distance. We've only been looking in a concerted way for a handful of decades. The universe is large, insanely, astronomically vast, and it takes a while for our messages or the messages of anyone else to travel the distance. Though, that's another problem Ad Astra seems to have solved.

UNIVERSAL LONG-DISTANCE CHARGES

If human history has proven anything, it's that we're pretty good at looking at our natural limitations and casting them aside. We see vast oceans, seemingly impenetrable barriers, and we build ships to cross them. We looked at the sky and saw not a limit, but another realm to make our own. We looked beyond the boundaries of our world and determined to send our machines and ourselves beyond it.

We're not very good with respecting limitation, but there is one limit which defies even our ingenuity and spirit: light speed. It's the universal constant, the boundary around which everything else is built. To break it would be to undo our very understanding of the nature of our reality.

When we send our machines into the cosmos, when we communicate with them and with one another, we have to account for the limitations of the speed of light.

For instance, if one day we do create a colony on Mars, it will mean we've overcome some of the greatest technological hurdles we've ever encountered in order to conquer another world. But you still won't be able to place a phone call and have an ordinary conversation. The average distance to Mars is 225 million kilometers (140 million miles). Though that's always in flux. Because of Earth and Mars' respective orbits, the distance is always changing. At the closest distance, the two planets are 54.6 million kilometers (33.9 million miles).

Taking the average, Mars lies 12.5 light-minutes away. Meaning that a phone conversation would have a 25-minute delay between statements.

Any dreams we might have had for interplanetary cooperative video game sessions are out of the question. Even a game of chess could take days to complete.

Which makes it all the more curious that Brad Pitt's character was able to send a message from Mars to Neptune and receive a response in a few moments. The distances involved there are even more staggering. The average distance from Mars to Neptune is 4,273,060,000 kilometers (2,655,279,484 miles) for a light-distance of nearly four hours. That means once a message was sent, you couldn't expect a response for roughly eight hours, and that's if the recipient replied right away. Interplanetary communication would be a whole lot of hurry up and wait.

But in Ad Astra, it appears as though McBride's companions receive a reply almost immediately, suggesting they'd developed some form of communication capable of skirting light speed. Which means they'd be able to peer even farther into the cosmos in their search for life outside our solar system.

So, why, given this level of technology were Roy and all the rest of humanity still alone in the universe? It's anyone's guess, and it very well might be something we have to make peace with someday.

For reasons we may never know, we might ultimately conclude that we are all there is, at least within the sphere of existence we're capable of observing. Perhaps it's a reminder of Sagan's famous words in his Pale Blue Dot speech: "Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come to save us from ourselves… it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known."

Ad Astra is in theaters now.