The Arithmetic of Life and Death (23 page)

Since 1993, NASA scientists have been analyzing a rock, playfully nicknamed ALH, that was found in the Antarctic but is believed to have dropped in originally from Mars. It has small, bacteria-like constructs in it that look as if they
may have once been a primitive form of life. Some scientists apparently believe this, others disagree, some are on the fence awaiting more data, and some aren’t even sure that the rock came from Mars. However, even if low forms of past life on Mars are eventually proven (the rock is billions of years old), the question of intelligent life, which is an entirely different matter, will probably continue to persist for many, many years.

Back in 1961, a group of prominent scientists decided that they couldn’t wait anymore. So they got together at the National Radio Astronomy Observatory at Green Bank, West Virginia, to see if they could build some sort of model that would predict the probability of intelligent extraterrestrial life. They came up with a simple equation, now commonly referred to in astronomical circles as the Green Bank or Drake Equation, that attempts to estimate the probable number of planets in the Milky Way (our galaxy) that can support intelligent life. The equation is:

Although controversial, the values for each parameter that was initially put forward were: R* = 10 per year; fp = 0.5; ne = 2; fl = 1; fi X fc = 0.01; and L = 10. That means that N, the number of planets that support intelligent life in our galaxy, equals:

Thus, the Drake Equation would seem to conclude that we, as human beings, are in an intellectual league of our own in the Milky Way. However, the value of each of the unknowns in the equation has always been speculative, especially L (the peak lifetime of advanced, technical civilizations), which was forecast in 1961, the peak of the Cold War, to be a paltry ten years. Now, of course, we know that we are much more likely to destroy ourselves through pollution and overpopulation, which will probably take longer than ten years (although anything is possible).

If, for instance, we were only to increase the value of L to 100 years, then the Drake Equation would forecast a total of ten planets in the Milky Way that could support intelligent life. Carl Sagan, in fact, predicted that the number of planets supporting intelligent life could be more than 100, which does not seem to be a gross exaggeration in a single galaxy of some 200,000,000,000 stars. More recently, Frank Drake, the principal architect of the Drake Equation, has increased his estimate from 10,000 to as many as 100,000.

But there’s another factor to consider. The age of the universe, and our galaxy, has been estimated by Stephen Hawking and others to be around 15,000,000,000 years, give or take five billion. Thus, even if there have been 10,000 intelligent civilizations in the Milky Way, and even if each of them thrived for 10,000 years, then it would seem unlikely that an extraterrestrial civilization in our galaxy would exist at the same time as ours (10,000 times 10,000 is 100 million, which is just 1 percent of 10 billion).

Once again, it seems likely that we are alone in the Milky Way. However, there are lots of other galaxies. Based upon recent data from the Hubble telescope, NASA estimates the number of galaxies in the known universe to be at least fifty billion. Assuming that our galaxy is average, then this would seem to predict that the number of planets capable of supporting advanced, intelligent life forms in the universe could be as low as fifty billion, which is the original Green Bank estimate of one per galaxy (ours) times the estimated number of galaxies. On the other hand, it could be more than 500 trillion, which is the low end of the more recent Drake estimate of 10,000 such planets in our galaxy times 50 billion galaxies.

At this point, we pretty much ought to concede either that the entire universe was constructed for us alone, which means that billions of galaxies with billions of stars in each one are all currently without any television whatsoever; or we should conclude that there are millions, if not billions or trillions, of other planets in the universe that are capable of supporting intelligent civilizations, some of whom, if they are close enough (within forty-five light-years or so), could be watching original transmissions of
The Mickey Mouse Club
at this very moment.

The real difficulty may be in getting from our little outpost of life to their little outpost, or vice versa. If the closest surviving extraterrestrial civilization is somewhere in Andromeda, which is the galaxy nearest to our own, then we will need to traverse about 2.2 million light-years of space in order to visit our neighbors. A light-year is the distance that light travels in a year, which is approximately 5.88 billion miles. If our spacecraft travels at an average of 100,000 miles per second (which is about 54 percent of the speed of light and which would get us to the moon in around 2.4 seconds) on its voyage to Andromeda, it will get there in around 4.1 million years. Then it would take another 2.2 million years for the news of contact to get back to Earth.

Any alien civilization desiring to travel to planet Earth would have to confront the same distance and time problem, unless they have figured out how to travel faster than the speed of light. Based upon what we know today, though, the speed of light cannot be exceeded. Moreover, the closer one comes to it, the heavier he or she becomes, which means that an impatient space traveler could develop an infinitely serious weight problem.

Until we contact a species from another planet, or until an alien race contacts us, we cannot know for certain that there is life elsewhere in the universe. And the distances in the universe are so vast that the proof of the existence of extraterrestrial intelligence may be many, many years, perhaps even millions of years, in the future.

This uncertainty may be provident. Because the distances of space are so vast, and because the limitations of what we currently know of physics are so rigid, it appears that our species has been given plenty of time, those same
millions of years, to manage our own evolution without risk of external intervention.

Maybe that is, after all, the Divine Intention: that no race may contact another until it has proven that it can survive on its own for millions of years. Then again, there is periodic but unconfirmed evidence that Earth has been visited by an advanced alien race. If so, they were probably in search of intelligent life. It appears, however, that they have since departed, possibly due to insufficient evidence.

S
ometime around 400 A.D., seafaring Polynesians discovered the island of Rapa Nui in the South Pacific. Although Rapa Nui was more than two thousand miles from the nearest civilization, which made trade impossible, human life flourished there. The weather was almost perfect. There was abundant fresh water, and the volcanic topsoil, although lacking depth, was very fertile. At that time, much of the island was covered with a biologically diverse forest, the tallest indigenous species of which were palm trees that may have grown to more than eighty feet in height and six feet in diameter. Under the forest canopy, there was an abundance of plants and wildlife, including more than thirty species of fowl. And, although the island lacked easy access to large quantities of tropical fish like so
much of the South Pacific, there was an almost limitless supply of deepwater porpoise reachable by canoe.

Over the next thousand years, the population of the remote island rose to somewhere between four thousand and ten thousand inhabitants. But in the process of converting their raw, isolated paradise into a suitable human habitat, the tribes of Rapa Nui deforested the island. Rain and wind destroyed the exposed topsoil. Water resources and the supply of game and fowl were depleted. Because there were no more trees of sufficient size, canoes disappeared, making the fish supply inaccessible and escape impossible.

Thus, the people of Rapa Nui became trapped in an increasingly inhospitable environment of their own construction. As resources became even more scarce, the tribes resorted to warfare. Eventually they fell into cannibalism, and civilization on the island collapsed, just as its ecology had. By the time the island was “discovered” by the Dutch ship captain Jakob Roggeveen, on Easter Day in 1722, the population had crashed to less than two thousand. The remaining inhabitants of Rapa Nui were poor and hungry, eking out a miserable living on what was left of the land and what they could eat of each other.

Naturally, a burgeoning slave trade and the inevitable arrival of European missionaries accelerated the destruction of the island, including the written and spoken records of its fall from ecological grace. By the year 1900, there were only 111 people left on Rapa Nui, which, by that time, had been renamed Easter Island.

Gwendolyn Sharpe arrived on Rapa Nui almost a hundred years later. She did not come to see the famous
moai
, the great stone statues, some as tall as thirty-three feet and
weighing as much as eighty-two tons, that rim the ancient island. Instead, like so many anthropologists of modern times, she came to study the rise and fall of the civilization of Rapa Nui. But Gwendolyn quickly discovered that the great statues played a prominent role in the island’s sad tale.

The
moai
were quarried by the tribes of Rapa Nui in a caldera near the center of the island. They then had to be moved, one at a time, to their final observation posts on the island’s rim, as much as fourteen miles away. Since they were so large and so heavy, the process of moving them became, by necessity, an even greater engineering achievement than their creation. By using the island’s large, indigenous palm trees like bearings, the
moai
were actually “skateboarded” to their final destination, possibly standing up.

Over time, in what was apparently a sort of tribal competition that had been empowered by palm tree transportation technology, the
moai
became larger and larger. Hence, the moving process required more and more palm trees, just as the growing population required more and more land to farm.

Today, there are no great palm trees on Rapa Nui. There haven’t been for more than three hundred years, and they aren’t growing back. The people of Rapa Nui cut them all down. Every one. No forest canopy, no wildlife. No forest, no topsoil. No topsoil, no crops. No palm trees, no canoes. No canoes, no fish. No food, cannibalism.

Like any other sentient person who has encountered the story of Rapa Nui, Gwendolyn wondered at its portent. Unlike most others, however, Gwen was the daughter of an accountant. So she took out her Sharp (no relation) calculator and cut a few numbers: