Is there somebody out there trying to make contact? If so, then how might we find them?
(Multiple galaxy image courtesy of NASA.)
Ask any science fiction fan or science junky about the Search for Extraterrestrial Intelligence, or SETI, and you will immediately get their attention. After all, as we read about a universe filled with aliens and a hopeful vision of humanity’s future among the stars, how can we not think about who else, or what else, might be out there? Within our galaxy alone there are at least 100 billion stars; within the universe there are an estimated 100 billion to 200 billion galaxies; giving a staggering total of about one billion trillion stars in the known universe. Surely, the argument goes, among that many stars there evolved other life forms like us who develop technology, explore space and seek to find others like themselves. If only a small fraction of them are communicating across the vast interstellar and intergalactic distances, then might we be able to hear them? Might we be able to decipher what they are saying and join in a conversation with them?
Thus was born SETI. The idea of listening for signals from distant civilizations goes back to the 1800s and early 1900s when astronomers thought that beings on other planets in the solar system might be using this newfangled discovery called radio. Various attempts were made to listen for signals from Mars and elsewhere and, as we now know these planets are likely lifeless, none were received.
Modern SETI began in the 1960s with astronomer Frank Drake’s Project Ozma (named after the Land of Oz in L. Frank Baum’s Oz series). Drake used existing radio telescopes to see if anyone in a few nearby stellar systems were broadcasting into space. No signals were detected. SETI continued in fits and starts with funded, canceled, and sometimes restarted projects like The Big Ear at The Ohio State University Radio Observatory, NASA’s Project Cyclops, Suitcase SETI, the Megachannel Extra-Terrestrial Assay (META) and Billion-channel Extra-Terrestrial Assay (BETA), and today’s Breakthrough Listen. Aside from a few spurious signals that were later shown to be either terrestrial in origin or produced by known natural sources beyond Earth, the result was again the same: no promising extraterrestrial signals have yet been received.
There may be a very good reason for this that has absolutely nothing to do with the existence of extraterrestrials or whether or not they use radio. It’s a matter of physics and practicality. For a radio signal to be heard at the Earth from a source as close as the nearest stars, the transmitter would have to be broadcasting with at least a few megawatts of power and it would have to be pointed in the right direction. That’s certainly possible, and we’ve even sent our own message. In 1974, the Arecibo Radio Observatory broadcast such a signal—but for only a few minutes and toward one particular and very small region of the sky. Even if someone is out there listening, what’s the probability they will be listening at the right frequency, at the right time and at the right place when the short duration message arrives? Approximately zero. For this reason it is assumed that anyone wanting to be heard must broadcast continuously, at high power, across the entire sky and for extremely long periods of time—think hundreds of thousands or even millions of years.
What would be required to establish a viable, radio-based interstellar communications system that was not just a shout in the dark? (And, if you listen to luminaries such as Stephen Hawking, shouting in the dark while in the middle of the jungle might not be such a good idea. Who knows who or what will hear you and how they might react?)
You would want to be selective in where you are broadcasting and listening. Setting up megawatt or gigawatt transmitting systems that blare our message across wide swathes of sky indiscriminately is a waste of energy. All you have to do is look at the history of telecommunications here on Earth and you will see the trend away from high power, wide area broadcast stations to targeted, narrow bandwidth yet highly efficient and very information-dense transmission options using cables and now optical fibers. To do otherwise is a waste of resources and primitive. Shouting across the full sky might be the best way to see if anyone is out there, but the identification phase is only the first step. And that first step is finally being taken in earnest with the Breakthrough Listen Project. Their stated goals include listening for such shouts from among the one million closest stars and even for shouts from some nearby galaxies. They are even planning to look for optical transmissions, not just radio.
Once you find out that ET is living around a specific star, then you will want to target your energies, literally, and set up your two-way communications to be as efficient and information-dense as possible. You will therefore most likely concentrate your future efforts only on where ET resides.
What if intelligent, tool-using life is common throughout the universe? What if technological civilizations like ours often arise from their own Dark Ages and find others with whom they wish to communicate? How would they efficiently communicate with each other? They would be unlikely to shout their calls across the whole sky for anyone or everyone to hear for both Stephen Hawking’s reasons and out of sheer practicality. How, then, would one set up a targeted, energy efficient communications network among these civilizations? For a possible answer, let’s look to one of our favorite sources: Albert Einstein.
Einstein gave us an understanding of the universe that’s counterintuitive in many ways and, unfortunately, placed some obstacles in our path that appear insurmountable. For example, that whole speed of light “speed limit” thing. His theories have been tested and retested and each time they come out stronger than before. Relativity, with its embedded understanding of space-time, appears to be here to stay. And that’s a good thing. It may give us a chance to get up close and personal with extrasolar planets and establish or connect to an interstellar communications network that my friend and colleague Dr. Claudio Maccone calls “The Galactic Internet.”
But first, as with all good scientific theories, we need to establish some background. Before Einstein, we were limited in our understanding of the universe to the theories of physicists like Isaac Newton and mathematicians like Euclid. In their worldviews, and, quite frankly, our modern “everyday” worldview, the universe is thought to be essentially flat and unchanging. It is a universe where drawing two parallel lines out to infinity continues forever without the lines ever growing closer together, crossing or diverging away from each other. It is a universe where one can continue accelerating forever; and where we can accelerate to many times the speed of light by simply adding more energy. And, it is a universe where time is independent of spatial coordinates (by “spatial coordinates,” I mean things like length, width and depth). It is also incomplete. (I will not say “wrong.” It just does not accurately predict what happens on a Solar-system-wide, interstellar or intergalactic scale. Newtonian physics often works very well in our everyday lives, where we do not travel at speeds close to the speed of light nor do we encounter ultra-dense matter like black holes.)
Let’s go back to that whole parallel line thing and consider light instead. To make it simple to visualize, imagine shining a laser beam across the room using your favorite laser pointer. To make it interesting, let’s fill the room with carbon dioxide fog from some evaporating dry ice so that you can actually see the laser light beam as it crosses the room like the Enterprise’s phasers when Captain Kirk is dueling with the Klingons. The light is not propagating through nothing to get across the room, it is crossing a room filled with air, and in this special case, water vapor and carbon dioxide. If we evacuate all the air (and dry ice fog), we may not see the laser beam but we can see the spot it produces on the opposite wall. And you can be sure the light traveled in a straight line from the end of the laser pointer to the spot on the wall. What did the light beam propagate through if all the air was removed? It moved through space-time, the stuff from which the universe is made. The light beam follows a straight line, not exactly in space, but in space-time.
But what is this stuff called space-time? To be blunt, from a physical, “can I touch it?” point of view, we have no idea. But, if we use one of the greatest abstract ideas ever created by the mind of humans, mathematics, we can describe its properties and then theorize how it behaves in ways that are testable in our so-called real world. By combining time into the description of space, creating a theory of space-time, and then using that theory to observe and predict how a universe made from it might work, Einstein was able to come up with theories that accurately describe how our universe works. Whatever space-time might be, it has properties that are mathematically predictable and physically testable—and we live within it.
When you treat space and time as space-time, interesting things begin to happen. For one thing, we now believe that the stuff we call matter either bends and distorts space-time or is actually distorted space-time and only appears as matter to our senses. (Take some time to think about that one; it might cost you some sleep or cause you to dig up a Pink Floyd song from your playlist.) For the sake of this article, let’s say that matter bends space-time and the more massive an object is, the more it bends. The best description I’ve heard to visualize the effect is that of a bowling ball sitting on a rubber sheet. The ball causes the rubber sheet (space-time) to stretch under the weight of the ball. The heavier the ball, the more stretched the rubber sheet becomes. If we instead consider a planet or a star instead of a bowling ball, then you can see how matter affects the local shape of space-time.
When we now think of our parallel lines or laser beams, we still need to require it to follow a straight line through space-time. But we now know that space-time can be bent by matter and, when that happens and the parallel lines or laser beam traverse the bent space, they too will appear to bend. If there is enough mass to radically distort the local structure of space-time, then the lines may actually cross all-the-while they are moving parallel to each other through their local space-time. Yikes!
As a science fiction reader, you probably aren’t unaware of this. You’ve read about how black holes, which are extremely dense and massive, distort space-time and bend it so much that they cut themselves off from the rest of the universe and create a singularity. For the topic at hand, we will not consider that singularity part but the radically bent space-time that does not cut itself off from the rest of the universe and is merely distorted. Light passing near this distorted space-time is bent but continues on, back out into deep space and away from the mass-bent space-time and, perhaps, toward us and our telescopes. The light that reaches us from near one of these gravitational space-time distortions has been bent. And this means it can act to magnify objects from which the light emerged. To understand how, think about a magnifying glass.
In an unrelated process called refraction, light that passes through a lens is bent by the lens and can be focused, providing magnification. This can be seen in Figure 1. The magnifying glass is thicker at the middle than at the edges. Light rays that pass through the lens are brought closer together until they cross at the focus. As you can see in the figure, all of the information and energy contained in the light beams that enter the lens from the left are concentrated at the focus. This is how eyeglasses work, how telescopes gather light from distant objects and magnify them so you can see them, and how we might be able to image planets around other stars. When a massive object bends space-time to act as an optical lens, it is called a gravity lens.
Figure 1. A convex lens like that found in a magnifying glass bends light rays so they converge, or come together, at a focus. This results in the image being magnified and made easier to see.
Astronomers validated Einstein’s prediction about gravity lensing by observing distant galaxies that are gravitationally distorted by massive objects between us and them—usually supermassive black holes in the centers of galaxies—and finding what are now known as Einstein crosses. The Hubble Space Telescope captured one such Einstein cross in Figure 2. In this image, several galaxies in the MACS J1149.6+2223 galaxy cluster create magnified images of the galaxies behind them. A large cluster galaxy bent the light from a supernova from an otherwise invisible (blocked by the galaxy in front of it) background galaxy into four separate images. Voila! One of nature’s magnifying glasses at work.
Figure 2. Einstein crosses have been observed by the Hubble Space Telescope. In this Hubble image, the light from an exploding supernova in a background galaxy was magnified and split into four yellow images (arrows) to form the Einstein cross. (Image courtesy of NASA.)
The key thing here is that any mass distorts and bends space-time. The Earth does. The Moon does. And, importantly, the Sun does as well. Given that the Sun is over 330,000 times more massive than the Earth, it can significantly distort space-time—but let’s stop calling it distortion. That is like saying that your contact lens distorts the light reaching your eye. While this may be strictly true, it is a useful distortion. For this reason we say your contact lens focuses the incoming light. So also does our Sun focus the light coming from distant objects.
Since 1992, scientists have found thousands of planets circling other stars. These exoplanets come in all sizes and are around many different types of stars. But they all have in common the fact that they are too far away and too dim, as compared to their parent stars, to see directly1. Recall that the only reason we might be able to “see” them at all is because they will reflect a very small portion of the light from their home star from their surface, through space, and into our telescopes. Imaging this very dim light is a huge problem. It is just not feasible to launch a primary lens or mirror big enough to capture enough light to focus onto a camera to form an image.
But we may not have to. Nature has given us a big lens, the Sun, which might just do the heavy lifting for us. If the Sun is aligned between our future, deep-space version of the Hubble Space Telescope and the extrasolar planet we wish to image, then it can conceivably capture and bend enough light into a focus for our telescope to see its image. The catch is that the Sun’s gravity lens focus is about 550 Astronomical Units (AU) away and it isn’t a point, but a region that extends well beyond 550 AU. An AU is the Sun-to-Earth distance or about 93 million miles. For comparison, the farthest we have yet sent a spacecraft is about 138 AU—reached by the Voyager spacecraft launched in 1977. If we can get out there with a telescope, then it is feasible to use that telescope to image many of these newly-discovered exoplanets so that we can see if they have oceans, continents and whether or not someone has the lights on during the night. Now that would be exciting!
But what does this have to do with a Galactic Internet?
Gravity lenses focus more than just light. They focus all forms of electromagnetic radiation, including radio. Including radio.
Dr. Claudio Maccone, Technical Director, Scientific Space Exploration, International Academy of Astronautics has written a technical monograph on the subject in which he looked at building such radio bridges between the Sun and Alpha Centauri. A spacecraft stationed approximately 51 billion miles on the far side of Alpha Centauri in direct line with both stars and a radio at our Gravity Lens region should be able to communicate with each other using a few tens of watts. (Compare this to the billions or trillions of watts that some estimate will be required for conventional interstellar radio communications.) Maccone has also calculated the gravity lensing regions of other nearby stars and examined the requirements for forming similar radio bridges between them: Sun-Barnard Star, Sun-Sirius, and, fantastically enough, Sun-Andromeda Galaxy! In all cases, the power requirements are significantly less than one would expect from traditional radio strength-over-large-distance losses and would not have the stringent pointing requirements that might be needed for the latest “hot topic” in space communications, optical laser links.
It is easy to now imagine that multiple sentient species have set up such radio bridges between their star systems to allow for easy radio communications at relatively low power. There could be bridges between Alpha Centauri-Sirius and Sirius-Barnard’s Star and we would never know it unless we were in the line of sight of these bridges and had our receivers appropriately placed at the Sun’s Gravity Lens—a highly unlikely scenario due to the distances involved and the propulsion intense requirements to align the spacecraft. Our SETI (Search for Extraterrestrial Intelligence) searches could never detect the signal because it is far too weak without the gravity lensing effect to enhance it. Our neighbors could be chatting away and we will never hear them . . .
This would not be the case if the sentient being on the other side of the link is trying to communicate with us—purposefully aligning our node with a cooperative alien’s node should be relatively easy. All we have to do is get their attention and put our transmitter/receiver at 550 AU.
The first step toward taking advantage of this fantastic opportunity provided by nature is getting there. 550 AU is a very long way from home (51,150,000,000 miles, approximately), which is four times farther than Voyager has traveled since its 1977 launch. We clearly need a better method of deep space propulsion. Then we need to fly there with a telescope capable of imaging many of the recently-detected extrasolar planets to see if any of them harbor intelligent life. From there, well, we’ll have to see what the next logical step might be.
1Astronomers are working on other ways to image distant exoplanets. One of the most promising has nothing to do with gravity lenses. Instead, an occulting shade will be placed between the observing telescope and the exoplanet to block out the light from the planet’s parent star in much the same way we use our hands to block the light of the Sun when we are facing toward it. By blocking the bright starlight, it should be possible to see an exoplanet. In theory, a telescope at the solar gravity lens will be capable of significantly better imaging than a star shade.
Copyright © 2017 Les Johnson
Les Johnson is a Baen science fiction author, popular science writer, and NASA technologist. His most recent science fiction novel from Baen, On to the Asteroid, was coauthored with Travis Taylor. He is also the author, with Taylor, of Back to the Moon. With Ben Bova, he is the author of Mars novel Rescue Mode. Les is the editor with Jack McDevitt of science fiction/science fact anthology Going Interstellar. To learn more about Les, please visit his website at here. www.lesjohnsonauthor.com.