Hyperspace (49 page)

It is highly likely that our civilization (if it successfully negotiates the uranium barrier and ecological collapse) will attain Type I status, and with it the ability to control the weather, within a few hundred years. If humanity reaches Type I status or higher before the next ice age occurs, then there is ample reason to believe that an ice age will not destroy humanity. Humans either will change the weather and prevent the ice age or will leave the earth.

On a time scale of several thousand to several million years, Types 0 and I civilizations have to worry about asteroid collisions and nearby supernovas.

Only within this century, with refined astronomical measurements, has it become apparent that the earth’s orbit cuts across the orbits of many asteroids, making the possibility of near misses uncomfortably large. (One way for a Type 0 or I civilization to prevent a direct collision is to send rockets with hydrogen bombs to intercept and deflect the asteroid while it is still tens of millions of miles away from the earth. This method has, in fact, been proposed by international bodies of scientists.)

These near misses are more frequent than most people realize. The last one took place on January 3, 1993, and was actually photographed using radar by NASA astronomers. Photos of the asteroid Toutatis show that it consists of two rocky cores, each 2 miles in diameter. It came
within 2.2 million miles of the planet earth. On March 23, 1989, an asteroid about half a mile across drifted even closer to the earth, about 0.7 million miles (roughly three times the distance from the earth to the moon).

In fact, it was also announced in late 1992 that a gigantic comet would hit the earth on exactly August 14, 2126, perhaps ending all life on the planet. Astronomer Brian Marsden of the Harvard-Smithsonian Center for Astrophysics estimated the chances of a direct hit as 1 in 10,000. The Swift-Tuttle comet (named after the two American astronomers who first spotted it during the Civil War) was soon dubbed the Doomsday Rock by the media. Soon-to-be-unemployed nuclear weapons physicists argued, perhaps in a self-serving way, that they should be allowed to build massive hydrogen bombs to blow it to smithereens when the time comes.

Bits and pieces of the Swift-Tuttle comet have already impacted on the earth. Making a complete revolution around the sun every 130 years, it sheds a considerable amount of debris, creating a river of meteors and particles in outer space. When the earth crosses this river, we have the annual Perseid meteor shower, which rarely fails to light up the sky with celestial fireworks. (We should also point out that predicting near misses of comets is a risky business. Because the heat of the sun’s radiation causes the comet’s icy surface to vaporize irregularly and sputter like thousands of small firecrackers, there are slight but important distortions in its trajectory. Not surprisingly, Marsden retracted his prediction a few weeks later as being incorrect. “We’re safe for the next millennium,” admitted Marsden.)

A NASA panel in January 1991 estimated that there are about 1,000 to 4,000 asteroids that cross the earth’s orbit and are bigger than a half-mile across, sufficient to pose a threat to human civilization. However, only about 150 of these large asteroids have been adequately tracked by radar. Furthermore, there are estimated to be about 300,000 asteroids that cross the earth’s orbit that are at least 300 feet across. Unfortunately, scientists hardly know the orbits of any of these smaller asteroids.

My own personal close encounter with an extraterrestrial object came when I was a senior at Harvard in the winter of 1967. A close friend of mine in my dormitory, who had a part-time job at the university observatory, told me a closely held secret: The astronomers there had detected a gigantic asteroid, several miles across, heading directly for the planet earth. Furthermore, although it was too early to tell, he informed me that their computers calculated it might strike the earth in June 1968,
the time of our graduation. An object that size would crack the earth’s crust, spew open billions of tons of molten magma, and send huge earthquakes and tidal waves around the world. As the months went by, I would get periodic updates on the course of the Doomsday asteroid. The astronomers at the observatory were obviously being careful not to cause any undue panic with this information.

Twenty years later, I had forgotten all about the asteroid, until I was browsing through an article on asteroid near misses. Sure enough, the article made reference to the asteroid of 1968. Apparently, the asteroid came within about 1 million miles of a direct impact with the earth.

More rare, but more spectacular than asteroid collisions are supernova bursts in the vicinity of the earth. A supernova releases enormous quantities of energy, greater than the output of hundreds of billions of stars, until eventually it outshines the entire galaxy itself. It creates a burst of x-rays, which would be sufficient to cause severe disturbances in any nearby star system. At the very minimum, a nearby supernova would create a gigantic EMP (electromagnetic pulse), similar to the one that would be unleashed by a hydrogen bomb detonated in outer space. The x-ray burst would eventually hit our atmosphere, smashing electrons out of atoms; the electrons would then spiral through the earth’s magnetic field, creating enormous electric fields. These fields are sufficient to black out all electrical and communication devices for hundreds of miles, creating confusion and panic. In a large-scale nuclear war, the EMP would be sufficient to wipe out or damage any form of electronics over a wide area of the earth’s population. At worst, in fact, a supernova burst in the vicinity of a star system might be sufficient to destroy all life.

Astronomer Carl Sagan speculates that such an event may have wiped out the dinosaurs:

If there were by chance a supernova within ten or twenty light-years of the solar system some sixty-five million years ago, it would have sprayed an intense flux of cosmic rays into space, and some of these, entering the Earth’s envelope of air, would have burned the atmospheric nitrogen. The oxides of nitrogen thus generated would have removed the protective layer of ozone from the atmosphere, increasing the flux of solar ultraviolet radiation at the surface and frying and mutating the many organisms imperfectly protected against intense ultraviolet light.

Unfortunately, the supernova would give little warning of its explosion. A supernova eruption takes place quite rapidly, and its radiation
travels at the speed of light, so a Type I civilization would have to make a speedy escape into outer space. The only precaution that a civilization can take is to monitor carefully those nearby stars that are on the verge of going supernova.

In 1980, the late Luis Alvarez, his son Walter, and Frank Asaro and Helen Michel of the University of California at Berkeley proposed that a comet or an asteroid hit the earth 65 million years ago, thereby initiating vast atmospheric disturbances that led to the sudden extinction of the dinosaurs. By examining the rocky strata laid down by river beds 65 million years ago, they were able to determine the presence of unusually high amounts of iridium, which is rarely found on earth but commonly found in extraterrestrial objects, like meteors. The theory is quite plausible, since a comet 5 miles in diameter hitting the earth at about 20 miles per second (ten times faster than a speeding bullet) would have the force of 100 million megatons of TNT (or 10,000 times the world’s total nuclear arsenal). It would create a crater 60 miles across and 20 miles deep, sending up enough debris to cut off all sunlight for an extended period of time. As temperatures fall dramatically, the vast majority of the species on this planet would be either killed off or seriously depleted.

In fact, it was announced in 1992 that a strong candidate for the dinosaur-killing comet or asteroid had been identified. It was already known that there is a large impact crater, measuring 110 miles across, in Mexico, in the Yucat’n, near the village of Chicxulub Puerto. In 1981, geophysicists with the Mexican national petroleum company, Pemex, told geologists that they had picked up gravitational and magnetic anomalies that were circular in shape at the site. However, only after Alvarez’s theory became popular did geologists actively analyze the remnants of that cataclysmic impact. Radioactive-dating methods using argon-39 have shown that the Yucatán crater is 64.98 ± 0.05 million years old. More impressively, it was shown that Mexico, Haiti, and even Florida are littered with small, glassy debris called
tektites
, which were probably silicates that were glassified by the impact of this large asteroid or comet. These glassy tektites can be found in sediment that was laid down between the Tertiary and Cretaceous periods. Analyses of five different tektite samples show an average age of 65.07 ± 0.10 million years. Given the accuracy of these independent measurements,
geologists now have the “smoking gun” for the dinosaur-killing asteroid or comet.

But one of the astonishing features of life on earth is that the extinction of the dinosaurs is but one of several well-documented mass extinctions. Other mass extinctions were much worse than the one that ended the Cretaceous period 65 million years ago. The mass extinction that ended the Permian period, for example, destroyed fully 96% of all plant and animal species 250 million years ago. The trilobites, which ruled the oceans as one of earth’s dominant life forms, mysteriously and abruptly perished during this great mass extinction. In fact, there have been five mass extinctions of animal and plant life. If one includes mass extinctions that are less well documented, a pattern becomes evident: Every 26 million years or so, there is a mass extinction. Paleontologists David Raup and John Sepkoski have shown that if we plot the number of known species on the earth at any given time, then the chart shows a sharp drop in the number of life forms on the earth every 26 million years, like clockwork. This can be shown to extend over ten cycles going back 260 million years (excluding two cycles).

In one extinction cycle, at the end of the Cretaceous period, 65 million years ago, most of the dinosaurs were killed off. In another extinction cycle, at the end of the Eocene period, 35 million years ago, many species of land mammals were extinguished. But the central puzzle to this is: What in heaven’s name has a cycle time of 26 million years? A search through biological, geological, or even astronomical data suggests that nothing has a cycle time of 26 million years.

Richard Muller of Berkeley has theorized that our sun is actually part of a double-star system, and that our sister star (called Nemesis or the Death Star) is responsible for periodic extinctions of life on the earth. The conjecture is that our sun has a massive unseen partner that circles it every 26 million years. As it passes through the Oort cloud (a cloud of comets that supposedly exists beyond the orbit of Pluto), it brings with it an unwelcome avalanche of comets, some of which strike the earth, causing enough debris that the sunlight is blocked from reaching the earth’s surface.

Experimental evidence for this unusual theory comes from the fact that the geological layers from the past, corresponding to the end of each extinction cycle, contain unusually large quantities of the element iridium. Since iridium is naturally found in extraterrestrial meteors, it is possible that these traces of iridium are remnants of the comets sent down by Nemesis. At present, we are half-way between extinction cycles, meaning that Nemesis, if it exists, is at its farthest point in its orbit (probably
several light-years away). This would give us over 10 million years or so until its next arrival.
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Fortunately, by the time comets from the Oort cloud streak through the solar system again, we will have reached Type III status, meaning that we will have conquered not just the nearby stars, but travel through space-time.

Scientists sometimes wonder what will eventually happen to the atoms of our bodies long after we are dead. The most likely possibility is that our molecules will eventually return to the sun.

Our sun is a middle-aged star. It is approximately 5 billion years old, and will probably remain a yellow star for another 5 billion years. When our sun exhausts its supply of hydrogen fuel, however, it will burn helium and become vastly inflated—a red giant. Its atmosphere will expand rapidly, eventually extending out to the orbit of Mars, and the earth’s orbit will be entirely within the sun’s atmosphere, so that the earth will be fried by the sun’s enormous temperatures. The molecules making up our bodies, and in fact the earth itself, will be consumed by the solar atmosphere.

Sagan paints the following picture:

Billions of years from now, there will be a last perfect day on Earth…. The Arctic and Antarctic icecaps will melt, flooding the coasts of the world. The high oceanic temperatures will release more water vapor into the air, increasing cloudiness, shielding the Earth from sunlight and delaying the end a little. But solar evolution is inexorable. Eventually the oceans will boil, the atmosphere will evaporate away to space and a catastrophe of the most immense proportions imaginable will overtake our planet.
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Thus, for those who wish to know whether the earth will be consumed in ice or fire, physics actually gives a definite answer. It will be consumed in fire. However, it is highly likely that humans, if we have survived that
long, will have long departed from the solar system. Unlike a supernova, there is ample warning of the demise of our sun.

On a time scale of several billions of years, we must confront the fact that the Milky Way galaxy in which we live, will die. More precisely, we live on the Orion spiral arm of the Milky Way. When we gaze at the night sky and feel dwarfed by the immensity of the celestial lights dotting the heavens, we are actually looking at a tiny portion of the stars located on the Orion arm. The millions of stars that have inspired both lovers and poets for generations occupy only a tiny part of the Orion arm. The rest of the 200 billion stars within the Milky Way are so distant that they can barely be seen as a hazy ribbon that cuts across the night sky.