If you were stranded on a deserted island, you might write a message, put it in a bottle and cast it into the sea. What would you write? You might put down where you are and hope that someone quickly discovers the message and rescues you, but you wouldn’t have much hope that that would happen. It is more likely that your message is found long after you are gone. So instead, you might write about who you are and how you came to be stranded on the island. Your hope would be to have your fate known and recited by someone in the future. The bottle and your message are a means of not being forgotten.
The Pioneer planetary probes launched in the early 1970s have exited our solar system, passing into the great sea of space. Astronomer Carl Sagan advocated for including a plaque on the Pioneer probes. The plaques show where the craft came from and include a picture of a man and a woman. Later that decade, the Voyager probes similarly included a gold record that contained sounds and images from Earth. They, too, have left the solar system. We don’t expect to ever see these spacecraft again. At the rate they are traveling, it will be tens of thousands of years before they could possibly reach another star. Although the probes were not designed for the purpose of communicating with distant aliens, they are our first messages in a bottle.
They are mostly symbolic — not because of the time they will take to reach a potential audience, but because they will likely never be found. Space is so large, and the spacecraft are so small, that the chance they encounter anything is tiny. Still, it is comforting to know that these spacecraft exist, traveling through space right now. If our solar system blew up tomorrow, these plaques and records would be the only physical record of life on Earth. They would be our only legacy.
Today, there are initiatives to send spacecraft to nearby stars. One prominent effort is called the Breakthrough Starshot. It envisions using high-powered, space-based lasers to propel tiny spacecraft to our nearest neighboring star, Alpha Centauri. The primary goal of this initiative is to take pictures of the planets orbiting Alpha Centauri and beam them back to Earth. Under optimistic assumptions, the entire process would take several decades.
Like the Pioneer and Voyager probes, the Starshot craft will continue to move through space long after we are gone. If the spacecraft are discovered by intelligent beings elsewhere in the galaxy, then those beings would know that we once existed and were intelligent enough to send spacecraft between the stars. Unfortunately, this is a poor way to intentionally communicate our existence to other beings. The spacecraft are tiny and slow. They can only reach a minuscule portion of our galaxy, and even if they reached an inhabited star system, the likelihood of being discovered is small.
Leave The Lights On
The SETI Institute has spent years trying to detect intelligent life elsewhere in our galaxy. SETI assumes that other intelligent beings are broadcasting a signal with sufficient power that we can detect it here on Earth. Our radar, radio and TV broadcasts also send signals out into space, but these signals are so weak that we, using our existing SETI technology, couldn’t detect similar signals from other planets unless they came from one very close to us. Hence, right now, there could be millions of planets with intelligent life just like ours, scattered throughout our galaxy, and — if each planet had a SETI program just like ours — nobody would detect anything. They, like us, would be saying, “Where is everybody?”
For SETI to be successful, we assume that intelligent beings are purposely creating strong signals designed to be detected over long distances. It is also possible that we could detect a signal not intended for us. That is, we might just happen to be aligned with a highly targeted signal and unintentionally pick up a conversation. But, for the most part, SETI assumes that an intelligent species is trying to make itself known by sending a powerful signal.
It would be considerate if we did the same. This is referred to as METI, which stands for messaging extraterrestrial intelligence. You might be surprised to learn that quite a few people think that METI is a bad idea — like, the worst idea ever. They fear that if we send a signal into space and thereby make our presence known, more advanced beings will come over to our star and kill us, enslave us, do experiments on us or maybe accidentally infect us with a bug that we can’t fight. Perhaps they are looking for planets that they can live on and the easiest way to find one is to wait for people like us to raise our hands and say, “Over here.” In any case, humanity would be doomed.
This reminds me of one of the most common errors that first-time technology entrepreneurs make. They fear someone will steal their idea, and therefore, they keep it secret. In almost all cases, it is better to share your idea with anyone who might be able to help you. Other people can give you product and business advice and help you in numerous other ways. Entrepreneurs are far more likely to succeed by telling people what they are doing than by being secretive. It is human nature — aka old brain — to suspect everyone wants to steal your idea, where the reality is that you are lucky if anyone cares about your idea at all.
The risk of METI is built upon a series of improbable assumptions. It assumes that other intelligent beings are capable of interstellar travel. It assumes they are willing to spend significant time and energy to make the trip to Earth. Unless the aliens are hiding someplace nearby, it might take thousands of years for them to get here. It assumes that the intelligent agents need Earth or something on Earth that they can’t get any other way, so it is worth the trip. It assumes that, despite having the technology for interstellar travel, they don’t have the technology to detect life on Earth without us broadcasting our presence. And finally, it assumes that such an advanced civilization would be willing to cause us harm, as opposed to trying to help us or at least not hurt us.
Regarding this last point, it is a reasonable assumption that intelligent beings elsewhere in the galaxy evolved from nonintelligent life, just as we did. Therefore, the aliens probably faced the same types of existential risks that we face today. To survive long enough to become a galaxy-faring species means that they somehow got past these risks. Therefore, it is likely that whatever brain equivalent they have now would no longer be dominated by false beliefs or dangerously aggressive behavior.
For all the above reasons, I believe we have nothing to fear from METI. Like a new entrepreneur, we will be better off trying to tell the universe that we exist and hope that someone, anyone, cares.
The best way to approach both SETI and METI is critically dependent on how long intelligent life typically survives. It is possible that intelligence has arisen millions of times in our galaxy and almost none of the intelligent beings existed at the same time. Here is an analogy: Imagine fifty people are invited to an evening party. Everyone arrives at the party at a randomly chosen time. When they get there, they open the door and step inside. What are the chances they see a party going on or an empty room? It depends on how long they each stay. If all the partygoers stay for one minute before leaving, then almost everyone who shows up will see an empty room and conclude that no one else came to the party. If the partygoers stay for an hour or two, then the party will be a success, with lots of people in the room at the same time.
We don’t know how long intelligent life typically lasts. The Milky Way galaxy is about 13 and a half billion years old. Let’s say that it has been able to support intelligent life for about ten billion years. That is the length of our party. If we assume that humans survive as a technological species for ten thousand years, then it is as if we showed up for a six-hour party but only stayed for one-fiftieth of a second. Even if tens of thousands of other intelligent beings show up for the same party, it is likely that we won’t see anyone else while we are there. We will see an empty room. If we expect to discover intelligent life in our galaxy, it requires that intelligent life occurs often and that it lasts a long time.
I expect that extraterrestrial life is common. It is estimated there are about 300 million planets in the Milky Way alone that could support life, and life appeared on Earth billions of years ago, soon after the planet was formed. If Earth is typical, then life is common in our galaxy.
I also believe that many planets with life will eventually evolve intelligent life. I have proposed that intelligence is based on brain mechanisms that first evolved for moving our bodies and recognizing places we have been. So, intelligence may not be too remarkable once there are multicellular animals moving about. However, we are interested in intelligent life that understands physics and that possesses the advanced technologies needed to send and receive signals from space. On Earth, this happened only once and only recently. We just don’t have enough data to know how common species like us are. My guess is that technological species occur more often than you might conclude if you just looked at the history of Earth. I am surprised by how long it took for advanced technologies to appear on our planet. For example, I see no reason why technologically advanced species couldn’t have appeared one hundred million years ago when dinosaurs roamed the Earth.
Regardless of how common technologically advanced life is, it might not last a long time. Technologically advanced species elsewhere in the galaxy will likely experience problems similar to those we face. The history of failed civilizations on Earth — plus the existential threats we are creating — suggests that advanced civilizations may not last very long. Of course, it is possible that species like ours could figure out how to survive for millions of years, but I don’t consider it likely.
The implications of this are that intelligent and technologically advanced life might have sprung up millions of times in the Milky Way. But when we look out at the stars, we won’t find intelligent life waiting to have a conversation with us. Instead, we will see stars where intelligent life once existed, but not now. The answer to the question “Where is everybody?” is that they already left the party. There is a way to get around all these issues. There is a way to discover intelligent life in our galaxy and perhaps even in other galaxies. Imagine that we create a signal that indicates we were here on Earth. The signal needs to be strong enough to be detected from far away, and it needs to last a long time. The signal needs to persist long after we are gone. Creating such a signal is like leaving a calling card at the party that says, “We were here.” People who show up later won’t find us, but they will know that we once existed.
This suggests a different way to think about SETI and METI. Specifically, it suggests we should first focus our efforts on how we could create a long-lasting signal. By long-lasting, I mean a hundred thousand years or maybe millions of years or even a billion. The longer the signal persists, the more likely it will be successful. There is a nice secondary benefit to this idea: Once we figure out how to make such a signal, then we will know what to look for ourselves. Other intelligent beings will likely reach the same conclusions we do. They, too, will look for how to create a long-lasting signal. As soon as we figure out how to do this, then we can start looking for it.
Today, SETI searches for radio signals that contain a pattern indicating that the signal was sent by an intelligent being. For example, a signal that repeated the first twenty digits of π would certainly be created by an intelligent species. I doubt we will ever find such a signal. It presumes that intelligent beings elsewhere in our galaxy have set up a powerful radio transmitter and, using computers and electronics, placed a code in the signal. We have done this ourselves a few brief times. It requires a big antenna pointed into space, electrical energy, people and computers. Because of the brief duration of the signals we sent, the messages were more symbolic efforts than serious attempts to reach out to the rest of our galaxy.
The problem with broadcasting a signal using electricity, computers and antennas is that the system won’t run for very long. Antennas, electronics, wires, etc. will not stay functional for even a hundred years without maintenance, let alone a million years. The method we choose to signal our presence has to be powerful, broadly directed and self-sustaining. Once started, it needs to reliably run for millions of years without any maintenance or intervention. Stars are like this. Once started, a star emits large amounts of energy for billions of years. We want to find something that is similar but that couldn’t be started without the guiding hand of an intelligent species.
Astronomers have found many odd sources of energy in the universe that, for example, oscillate, rotate or emit short bursts. Astronomers look for natural explanations for these unusual signals, and usually, they find them. Perhaps some of the as-yet- unexplained phenomena are not natural but the type of signal I am talking about, created by intelligent beings. That would be nice, but I doubt it will be that easy. It is more likely that physicists and engineers will have to work on this problem for a while to come up with a set of possible methods to create a strong, self-sustaining signal that unmistakably originated with an intelligent being. The method also has to be something that we can implement. For example, physicists might conceive of a new energy source capable of generating such a signal, but if we don’t have the ability to create it ourselves, then we should assume that other intelligent beings can’t either, and we should keep looking.
I have noodled on this problem for years, keeping an eye out for something that might fit the bill. Recently, a candidate surfaced. One of the most exciting areas of astronomy today is the discovery of planets orbiting other stars. Until recently, it was not known if planets were common or rare. We now know the answer: Planets are common, and most stars have multiple planets, just like ours. The primary way we know this is by detecting slight reductions in starlight as a planet passes between a distant star and our telescopes. We could use the same basic idea to signal our presence. For example, imagine if we placed into orbit a set of objects that block a bit of the Sun’s light in a pattern that would not occur naturally. These orbiting Sun blockers would continue to orbit the Sun for millions of years, long after we are gone, and they could be detected from far away. We already possess the means to build such a Sun-blocker system, and there may be better ways to signal our presence.
Letting a distant civilization know that we once existed is an important first goal. But to me, the most important thing about humans is our knowledge. We are the only species on Earth that possesses knowledge of the universe and how it works. Knowledge is rare, and we should attempt to preserve it.
Let’s assume that humans go extinct, but life on Earth continues. For example, an asteroid is believed to have killed the dinosaurs and many other species, but some small animals managed to survive the impact. Sixty million years later, some of those survivors became us. Imagine now that we humans have gone extinct, perhaps due to a natural disaster or to something we did. Other species survive, and in 50 million years, one of them becomes intelligent. That species would definitely want to know everything they could about the long-gone human epoch. They would be particularly interested in knowing the extent of our knowledge and what happened to us.
If humans go extinct, then in just a million years or so, all detailed records of our life will likely be lost. There will be buried remains of some of our cities and large infrastructure, but pretty much every document, film and recording will no longer exist. Future nonhuman archeologists will struggle to piece together our history in the same way paleontologists today struggle to figure out what happened to the dinosaurs.
As part of our estate plan, we could preserve our knowledge in a more permanent form, one that could last tens of millions of years. There are several ways we might do this. For example, we could continually archive a knowledge base such as Wikipedia. Wikipedia is itself constantly updated, so it would document events up to the point where our society started to fail. The archive should be automated and shouldn’t be located on Earth, as Earth might be partially destroyed in a singular event. To overcome this problem, we could locate our archive in a set of satellites that orbit the Sun. This way, the archive will be easy to discover but difficult to physically alter or destroy.
We would design the satellite-based archive so that we could send automatic updates to it but its content could not be erased. The electronics in the satellite will stop functioning shortly after we are gone, so, to read the archive, a future intelligent species would have to develop the technology to travel to the archive, bring it back to Earth and extract the data. We could use multiple satellites at different orbits for redundancy. We already possess the ability to create a satellite archive and retrieve it. Imagine if a previous intelligent species on Earth had placed a set of satellites around the solar system. We would have discovered them by now and already brought them back to Earth.
In essence, we could create a time capsule designed to last for millions or hundreds of millions of years. In the distant future, intelligent beings — whether they evolve on Earth or travel from another star — could discover the time capsule and read its contents. If we do this, and it is read in the future, imagine how appreciative the recipients would be. All you have to do is think of how excited we would be to discover such a time capsule ourselves.
Is it worth the time and money to pursue initiatives like this? Would it be better to put all our efforts into improving life on Earth? There is always friction between investing in the short term and investing in the long term. Short-term problems are more pressing, whereas investing in the future has few immediate benefits. Every organization — whether it be a government, a business or a household — faces this dilemma. However, not investing in the long term guarantees future failure. In this case, I believe that investing in an estate plan for humanity has several near-term benefits. It will keep us more aware of the existential threats we face. It will propel more people to think about the long-term consequences of our actions as a species. And it will provide a type of purpose to our life should we eventually fail.
This is a modified excerpt from the author’s latest book, “A Thousand Brains: A New Theory of Intelligence” (Basic Books, 2021).