Beyond: Our Future in Space (33 page)

The second possibility is that we’re isolated. Perhaps technological civilizations do exist and some of them are plying the galaxy or sending and receiving electromagnetic signals. But if such civilizations are rare, we might be unaware of their existence. The Milky Way is 100,000 light years across, so if there are only ten civilizations actively exploring at any given time, the average distance between them is 10,000 light years. Texting with a 20,000-year pause between replies makes for a very stilted conversation. The information being received is old news and the sending civilization may not even exist by the time the message or probe is received. So space might be littered with the runes of dead civilizations. However, the assumption that they will use radio waves might be wrong (
Figure 54
). Isolation applies to time as well as space. As we’ve been learning, interstellar travel is expensive and difficult, so large-scale colonization may be beyond the capabilities of all but a few species around the galaxy.

The third explanation is that the search isn’t good enough. Jill Tarter, the SETI pioneer who was a model for the Ellie Arroway character in
Contact
, has talked about the needle-in-a-haystack issue. The SETI haystack has nine dimensions: three of space and two each of polarization, intensity, modulation, frequency, and time. Tarter compared SETI to scooping a bucket of water from an ocean in the hope of catching a fish. That’s going to change as the Allen Telescope Array reaches its full potential. An irony of working in a field where detection capability improves exponentially is that each new search is better than the sum of all the searches that preceded it.
¹¹
The Allen Array will survey a million stars for artificial signals over a frequency range from 1 to 10 gigahertz.

Tarter refuses to be discouraged by the Great Silence. Rather, she thinks the search is only just beginning to get interesting. Our most powerful “send” capability is the radar transmitter at the Arecibo 305-meter radio dish in central Puerto Rico.
¹²
The Allen Array will be able to detect analogous technology beamed from a planet around any star out to a thousand light years. Optical SETI’s ability to detect pulsed lasers is also getting better. In twenty years, SETI could detect the equivalent of our most powerful radio and optical transmitters if they are beaming at us from planets around 100 million stars in the galaxy. At that point, surely, continuing Great Silence means we’re alone.

Or perhaps the search is ill conceived. We might be looking in the wrong part of the cosmic haystack. Denizens of other planets may be using forms of data modulation and compression that look to us like pure noise. Radio transmitters and laser might be fleeting technologies, so the window of time when they get used by a civilization is small. Seth Shostak, a senior astronomer at the SETI Institute, jokes about people who say he should wait until he has more powerful technology, noting that Queen Isabella of Spain didn’t tell Christopher Columbus to wait until he had a jumbo jet to discover America.

Another possibility is that all other life is already dead. When it comes to putative alien physiology and psychology, answers to the Fermi question proliferate like weeds. As we see ominously from our own history, galloping technology might render a civilization unstable. If the factor
L
in the Drake equation is on average no more than a few centuries or a millennium, SETI is likely to fail. It doesn’t matter whether the civilizations self-destruct or degrade to a preindustrial state—the effect on the search is the same. Silence.

It’s also possible that extraterrestrial life is unrecognizable to us. Aliens in films and on TV are amusing because they’re usually thinly veiled versions of us: bipedal vertebrates with extra appendages or bad skin. Occasionally, they’re amorphous and weird. But life elsewhere might be organized quite differently at the level of the organism. It might communicate at speeds that are too slow or too rapid for us to recognize. It might not be culturally inclined to communicate at all, or it might be disinterested in space travel even if it had the suitable technology. It might have passed from a biological to a post-biological or computational state. We can try to think outside the box, but anthropocentrism permeates all discussions of advanced life beyond Earth.

The Great Filter

Does the lack of evidence for extraterrestrial technology say anything about us and our future?

Yes, especially if spacefaring civilizations are very rare, as opposed to just hard to detect or recognize. In 1998, economics professor Robin Hanson presented an idea called “the Great Filter.” If any of the Drake equation factors is very low, it will act as a filter to choke off evolution toward life venturing beyond its planet of origin. A filter can lie behind us (in our past), or ahead of us (in our future).
¹³
In the past, the filter could be the transition from single- to multicelled organisms, or the steps required to develop a brain, or the instability of a technological species. When humans harnessed the power of the atomic nucleus in the middle of the twentieth century, it was in the unstable and destructive form of a bomb. For a decade, we teetered on the edge of nuclear holocaust. Regarding the future, this argument leads to the counterintuitive and unnerving conclusion that the easier it is for life to get to our stage of development, the bleaker our future chances for survival probably are.

Assuming that a Great Filter winnowed down billions of germination sites for life to zero observable extraterrestrial civilizations, it’s crucial to consider where the filter lies. If the filter is in our past, it means there is an extremely unlikely step in the progression from Earth-like planet to one that hosts a civilization with our level of technology. That step might even be the formation of life from simple chemicals. Whatever the filter is, if it’s behind us, we can explain the lack of observable aliens. Technological civilizations are intrinsically rare, so searches for them will fail.

On the other hand, if the Great Filter is in our future, it’s very unlikely that a civilization at our stage of development progresses to the large-scale colonization of space. One plausible scenario is that technology is the culprit because it includes the capability for self-destruction. Nick Bostrom, director of the Future of Humanity Institute at the University of Oxford, has done scholarly work on catastrophes. His partial list of existential threats faced by humanity includes nuclear holocaust, genetically engineered superbugs, environmental disasters, asteroid impacts, terrorism, advanced and destructive artificial intelligence, uncontrollable nanotechnology, catastrophic high-energy physics experiments, and a totalitarian regime with advanced surveillance and mind-control technologies.

Regarding existential threats that might act as a filter in our future, Bostrom makes another point. The requirement is not that it has a significant probability of destroying humanity. Rather, it must be able to plausibly destroy
any
advanced civilization. Asteroid strikes and supervolcanoes don’t qualify because they’re random events that some civilizations will survive and others won’t experience because their planet and solar system are different from ours. The technological innovations that drive the argument and act more effectively as filters are those that almost all civilizations eventually discover, where their discovery almost universally leads to disaster (
Figure 55
).

Bostrom has said: “I hope that our Mars probes will discover nothing. It would be good news if we find Mars to be completely sterile. Dead rocks and lifeless sands would lift my spirits.”
¹⁴
Why would he be so grumpy about one of our best pieces of technology?

If life is discovered on Mars or any other place in the Solar System, it suggests that the emergence of life is not an improbable event (and it doesn’t matter whether the life found is ancient or current). If biology emerged twice independently in our backyard, then surely there are many biological experiments in the galaxy. The same logic will apply if we one day find that a significant number of habitable exoplanets have had their atmospheres altered by microbial life. Either discovery would imply that the Great Filter is less likely to occur in the early history of planets and is more likely ahead of us. In other words, dead rocks and lifeless planets will be good news since they’d tell us we’d survived the tough part of our evolution.

This framing of the argument is a simplification. There may be more than one Great Filter. We might have cleared one, only to be faced in the future with another. Also, we should be wary of positing that life elsewhere has to follow the path traveled by life on Earth or that other civilizations progress with the single-minded purposefulness of humans. Let’s allow Nick Bostrom to have the last word. For someone who dwells on apocalypse and hopes that the search for life in the universe fails, he’s strangely optimistic:

If the Great Filter is in our past . . . we may have a significant chance . . . of one day growing into something almost unimaginably greater than we are today. In this scenario, the history of humankind to date is a mere instant compared to the eons of history that still lie before us. All the triumphs and tribulations of the millions of people who have walked the Earth since the ancient civilization of Mesopotamia would be like mere birth pangs in the delivery process of a kind of life that hasn’t really yet begun.

14

A Universe Made for Us

_______________________

Our Far Future

If we make it through our troubled adolescence as a species, what lies in store? We’re curious and creative but also prone to tribalism and needless competition. I’ve sketched a scenario for the next century, when we establish homesteads on the Moon and Mars, project our tourism and commerce off-Earth, and get used to traveling throughout the Solar System.

By overcoming our self-destructive tendencies, we might achieve the normal evolutionary lifespan of a mammal species, a million years or more. To see how hard it is to project ourselves forward that far, let’s play at “futurology.” Compressing time in orders of magnitude, we first look backward. Roughly ten years ago, there was no Internet. Roughly a hundred years ago, there was no mass transit and most people lived and died close to where they were born. Going back a thousand years, there was no medicine and life was short and brutal. Ten thousand years ago, agriculture would soon be invented but most humans were nomadic hunters and gatherers. Approximately a hundred thousand years ago, we hadn’t learned how to use tools or harness fire. A million years ago marks our emergence as a species. Leaping back in factors of ten quickly finds us in an unfamiliar and primitive state (
Figure 56
).

Now play the game forward. It’s fairly safe to predict that in ten years we’ll have sophisticated genetic engineering and a growing commercial space industry. In a century, we should have routine travel within the Solar System, robots doing our bidding, and artificial intelligence that rivals human capabilities. It’s very difficult to predict a thousand years hence, but I’m going to go out on a limb and assume that rapid technological progress will continue such that some of us will be heading for nearby stars. Ten thousand years from now, as far ahead of us as early civilizations lie behind us, the crystal ball is cloudy. A hundred thousand years and onward, it’s anyone’s guess. To venture further seems impossible. In the anthology
Year Million
, economists, science fiction writers, computer scientists, and physicists speculate freely, in tones that range from giddy to glum.
¹
The exercise is made more difficult by our position on the cusp of exponential technological change.
²
The far future, with all its potential for our greatness and failure, and the possibility that we might not exist at all, is as haunting as deep space.