The universe is out of control. Not only is it expanding but the expansion itself is accelerating. Most likely, such expansion can end only one way: in stillness and total darkness, with temperatures near absolute zero, conditions utterly inhospitable to life. That became evident in 1998, when astronomers at the Lawrence Berkeley National Laboratory and Australian National University were analyzing extremely distant, and thus ancient, Type Ia supernova explosions to measure their rate of motion away from us. (Type Ia supernovas are roughly the same throughout the universe, so they provide an ideal “standard candle” by which to measure the rate of expansion of the universe.)
Physicists, scrambling to their blackboards, deduced that a “dark energy” of unknown origin must be acting as an antigravitational force, pushing galaxies apart. The more the universe expands, the more dark energy there is to make it expand even faster, ultimately leading to a runaway cosmos. Albert Einstein introduced the idea of dark energy mathematically in 1917 as he further developed his theory of general relativity. More evidence came last year, when data from the Wilkinson Microwave Anisotropy Probe, or WMAP, which analyzes the cosmic radiation left over from the Big Bang, found that dark energy makes up a full 73 percent of everything in the universe. Dark matter makes up 23 percent. The matter we are familiar with—the stuff of planets, stars, and gas clouds—makes up only about 4 percent of the universe.
As the increasing amount of dark energy pushes galaxies apart faster and faster, the universe will become increasingly dark, cold, and lonely. Temperatures will plunge as the remaining energy is spread across more space. The stars will exhaust their nuclear fuel, galaxies will cease to illuminate the heavens, and the universe will be littered with dead dwarf stars, decrepit neutron stars, and black holes. The most advanced civilizations will be reduced to huddling around the last flickering embers of energy—the faint Hawking radiation emitted by black holes. Insofar as intelligence involves the ability to process information, this, too, will fade. Machines, whether cells or hydroelectric dams, extract work from temperature and energy gradients. As cosmic temperatures approach the same ultralow point, those differentials will disappear, bringing all work, energy flow, and information—and the life that depends on them—to a frigid halt. So much for intelligence.
A cold, dark universe is billions, if not trillions, of years in the future. Between now and then, humans will face plenty of other calamities: wars and pestilences, ice ages, asteroid impacts, and the eventual consumption of Earth—in about 5 billion years—as our sun expands into a red giant star. To last until the very end of the universe, an advanced civilization will have to master interstellar travel, spreading far and wide throughout the galaxy and learning to cope with a slowing, cooling, darkening cosmos. Their greatest challenge will be figuring out how to not be here when the universe dies, essentially finding a way to undertake the ultimate journey of fleeing this universe for another.
Such a plan may sound absurd. But there is nothing in physics that forbids such a venture. Einstein’s theory of general relativity allows for the existence of wormholes, sometimes called Einstein-Rosen bridges, that connect parallel universes. Among theoretical and experimental physicists, parallel universes are not science fiction. The notion of the multiverse—that our universe coexists with an infinite number of other universes—has gained ground among working scientists.
The inflationary theory proposed by Alan Guth of MIT, to explain how the universe behaved in the first few trillionths of a second after the Big Bang, has been shown to be consistent with recent data derived from WMAP. Inflation theory postulates that the universe expanded to its current size inconceivably fast at the very beginning of time, and it neatly explains several stubborn cosmological mysteries, including why the universe is both so geometrically flat and so uniform in its distribution of matter and energy. Andrei Linde of Stanford University has taken this idea a step further and proposed that the process of inflation may not have been a singular event—that “parent universes” may bud “baby universes” in a continuous, never-ending cycle. If Linde’s theory is correct, cosmic inflations occur all the time, and new universes are forming even as you read these words.
Naturally, the proposal to eventually flee this universe for another one raises practical questions. To begin with, where exactly would an advanced civilization go?
As it happens, physicists are spending billions of dollars on experiments to probe the nature of parallel universes. Since 1997, scientists at the University of Colorado at Boulder have conducted experiments to search for parallel universes perhaps no more than a millimeter away from ours. The experiments searched for tiny deviations in Newton’s inverse square law of gravity. The surface of a sphere in three dimensions is equal to 4π times the radius squared. Likewise, the surface of a sphere of higher dimensions is proportional to the radius cubed. According to Newton’s law, in such a sphere the measurable gravity should decrease as a factor of the distance cubed. So the Colorado physicists set about measuring the gravity within a small, defined space. If the gravitational force deviated significantly from Newton’s equation (the distance squared) and was more closely proportional to the distance cubed, the research team theorized, that would suggest the presence of a hidden dimension.
Newton’s inverse square law has been tested with exquisite precision by space probes, but it had never been tested at the millimeter level. So far, the results from these experiments have been negative, but other scientists are looking for even smaller deviations. A group at Purdue University has proposed testing Newton’s inverse square law down to the atomic level using nanotechnology.
Physicists elsewhere are exploring other possibilities. In 2007 the Large Hadron Collider, the world’s largest atom smasher, will be turned on outside Geneva, Switzerland. This huge machine, more than five miles in diameter, is capable of blasting protons together with a colossal energy of 14 trillion electron volts; it will be able to probe distances 1/10,000 the size of a proton, perhaps creating a zoo of exotic particles not seen since the Big Bang. One hope is that it will create exotic particles like miniature black holes and sparticles, or supersymmetric particles, which would indicate the presence of parallel universes in higher dimensions.
In addition, the space-based gravity-wave detector LISA (Laser Interferometer Space Antenna) will be launched sometime around 2012. It will consist of three satellites trailing Earth’s orbit around the sun and communicating with one another via laser beams, thereby creating a triangle with sides more than 3 million miles long. LISA is designed to detect faint gravity waves from extremely far away—gravitational shock waves that were emitted less than a trillionth of a second after the instant of creation. The instrument is so sensitive that scientists hope it will be able to test many of the theories that seek to explain what happened before the Big Bang and probe for the existence of universes beyond our own.
To journey safely from this universe to another—to investigate the various options and do some trial runs—an advanced civilization will need to be able to harness energy on a scale that dwarfs anything imaginable by today’s standards.
To grasp the challenge, consider a schema introduced in the 1960s by Russian astrophysicist Nikolai Kardashev that classified civilizations according to their energy consumption. According to his definition, a Type I civilization is planetary: It is able to exploit all the energy falling on its planet from the sun (10^16 watts). This civilization could derive limitless hydrogen from the oceans, perhaps harness the power of volcanoes, and maybe even control the weather. A Type II civilization could control the energy output of the sun itself: 10^26 watts, or 10 billion times the power of a Type I civilization. Deriving energy from solar flares and antimatter, Type IIs would be effectively immune to ice ages, meteors, even supernovas. A Type III civilization would be 10 billion times more powerful still, capable of controlling and consuming the output of an entire galaxy (10^36 watts). Type IIIs would derive energy by extracting it from billions of stars and black holes. A Type III civilization would be able to manipulate the Planck energy (10^19 billion electron volts), the energy at which space-time becomes foamy and unstable, frothing with tiny wormholes and bubble-size universes. The aliens in Independence Day would qualify as a Type III civilization.
By contrast, ours would qualify as a Type 0 civilization, deriving its energy from dead plants—oil and coal. But we could evolve rapidly. A civilization like ours growing at a modest 1 to 2 percent per year could make the leap to a Type I civilization in a century or so, to a Type II in a few thousand years, and to a Type III in a hundred thousand to a million years. In that time frame, a Type III civilization could colonize the entire galaxy, even if their rockets traveled at less than the speed of light. With the inevitable Big Freeze at least tens of billions of years away, a Type III civilization would have plenty of time to develop and test an escape plan.
Why not start now? On the following pages are experiments and plans to guide a civilization looking for a way out—a survival guide to the end of the cosmos.
Adapted from the book Parallel Worlds: A Journey Through Creation, Higher Dimensions, and the Future of the Cosmos, published this month by Doubleday. Copyright © 2004 by Michio Kaku.
SEVEN STEPS TO LEAVING THE COSMOS
1. Find and Test a Theory of Everything
Before an advanced civilization leaps into the unknown, it will need to study the pathways that make it possible to break through to the other side. Toward that end, scientists will need to discover the laws of quantum gravity, which will help to calculate the stability of wormholes connecting our universe to others.
At present, the leading—and, some believe, only—candidate for a theory of everything is string theory, or M-theory. This theory states that all subatomic particles are different vibrations or notes on a tiny string or membrane. These aren’t ordinary strings but rather strings that vibrate in higher-dimensional hyperspace. In principle, our universe might be a huge membrane drifting in 11 dimensions, which may occasionally collide with a neighboring membrane or universe. It is possible that our universe and a neighboring one hover only a millimeter or less from each other, like two parallel sheets of paper. To bridge even this tiny distance, however, we’ll need machinery of vast power.
2. Search for a Naturally Occurring Wormhole
Next, in order to escape from this universe into another one, we will need to find a suitable exit: some wormhole, dimensional gateway, or cosmic tunnel that connects here to there.
There are many possibilities, some of which may occur naturally. The Big Bang, which released a tremendous amount of energy, may have left behind all manner of exotic entities of physics, such as cosmic strings, false vacuums, or negative matter or energy. The original expansion of the universe may have been so rapid and explosive that even tiny wormholes might have stretched and blown up to macroscopic size. The discovery of such entities would greatly aid any effort to leave a dying universe; if they exist, we would do well to find them. Perhaps by the time the need arises, billions of years from now, an advanced civilization will have stumbled upon one of these gateways. In the meantime, we should consider a more proactive strategy.
3. Send a Probe Through a Black Hole
Black holes offer another possible avenue of escape. One advantage of black holes is that, as scientists now realize, they are plentiful in the universe. The one at the center of our galaxy has a mass more than 3 million times that of our sun. Of course, there are numerous technical problems to be worked out. Most physicists believe that a trip through a black hole would be fatal. Although Einstein’s equations permit the possibility of passing through a black hole, the quantum effects may be insurmountable. However, our understanding of black hole physics is in its infancy, and this conjecture has never been tested.
Before the probe falls into the black hole, it must radio its data to observers waiting nearby. Here a problem arises. To the observer, the probe seems to slow down as it nears the event horizon and eventually stops entirely. So the probe must send the last of its data early on; otherwise the radio signals may be redshifted beyond recognition.
5. Create Negative Energy
If Kerr rings prove to be lethal or too unstable for use as cosmic portals, an advanced civilization might instead contemplate opening up a new wormhole by using negative matter or negative energy. (In principle, negative matter or energy should weigh less than nothing and fall up rather than down. This is different stuff from antimatter, which contains positive energy and falls down.) In 1988 Kip Thorne and his colleagues at Caltech showed that with sufficient negative matter or negative energy, one could create a wormhole through which a traveler could freely pass back and forth between, say, his laboratory and a distant point in space or time.
Although no one has yet seen negative matter or negative energy in the wild, it has been detected in the laboratory, in the form of something called the Casimir effect. Consider two uncharged, parallel plates. Theoretically, the force between them should be zero. But if they are placed only a few atoms apart, then the space between them is not enough for some quantum fluctuations to occur. As a result, the number of quantum fluctuations in the region around the plates is greater than in the space between. This differential creates a net force that pushes the two plates together. Hendrik Casimir predicted the effect in 1948; it has since been confirmed experimentally.
The amount of energy involved is minuscule. To employ the Casimir effect to practical ends, one would have to use advanced technology to place the parallel plates at a fantastically small distance apart—10–33 centimeter, the Planck length (the smallest measurement of length with any meaning). Now suppose that these two parallel plates could be shaped into a single sphere, with the plates forming a sort of double lining, and pressed together to within this fractional distance. The resulting Casimir effect might generate enough negative energy to open a wormhole within the sphere.
6. Make a Baby Universe
If both Kerr rings and negative-energy wormholes prove unreliable, Guth’s inflation theory points the way to another, more difficult escape strategy: creating a baby universe.
As Guth points out, to create something resembling our universe would require “1089 photons, 1089 electrons, 1089 positrons, 1089 neutrinos, 1089 antineutrinos, 1079 protons, and 1079 neutrons.” However, Guth notes, the positive energy of this matter is almost but not entirely balanced out by the negative energy of gravity. (If our universe were closed, which it isn’t, the two values would cancel each other out exactly.) In other words, the net total matter required to create a baby universe might equal only a few ounces.
But what ounces! In principle, baby universes are born when a certain region of space-time becomes unstable and enters a state called the false vacuum. The false vacuum needed to create our universe is extraordinarily small, on the order of 10–26 centimeter wide. If one created this false vacuum from one ounce of matter, its density would be a phenomenal 1080 grams per cubic centimeter. Acquiring a few ounces of matter is easy; compressing it into the small volume necessary is not possible today.
The solution requires that a fantastic amount of energy, roughly equal to the Planck energy, be concentrated on a tiny region. Here are two approaches an advanced civilization might try.
Build a Laser Implosion Machine
The power of laser beams is essentially unlimited, constrained mainly by the stability of lasing material and the energy of the power source. Lasers that can produce a brief terawatt, or trillion-watt, burst are commonplace, and petawatt lasers capable of generating a quadrillion watts are possible. By contrast, a large nuclear power plant produces only a billion watts of continuous power. It is theoretically possible for an X-ray laser to focus the output of a nuclear bomb to create a pulse of unimaginable power.
At the Lawrence Livermore National Laboratory, scientists have used a laser to fire a series of high-energy pulses radially onto a single pellet made of deuterium and tritium, the basic ingredients of a hydrogen bomb, thus creating the conditions for thermonuclear fusion. An advanced civilization could create a similar device on a much larger scale. By placing huge laser stations on asteroids and then firing millions of laser pulses onto a single point, future scientists could generate temperatures and pressures that swamp today’s technology. Each laser could be powered by a nuclear bomb; however, such a device would be usable only once.
The aim of firing this massive bank of laser beams would be to either heat a chamber sufficiently high—about 1029 degrees Kelvin—to create a false vacuum inside or compress a pair of spherical plates to within the Planck distance of each other, creating negative energy via the Casimir effect. One way or the other, a wormhole connecting our universe to another one should open within the chamber, allowing us to exit.
6(b). Build a Cosmic Atom Smasher
One of the most powerful energy-generating devices currently available to scientists is the Large Hadron Collider, which, when it becomes operational in 2007, will be able to generate 14 trillion electron volts. Even that is one-quadrillionth the energy necessary to create a false vacuum.
But a particle accelerator with the diameter of our solar system might do the trick. Gigantic coil magnets could be placed at strategic intervals on asteroids to bend and focus a particle beam in a circular path around the sun. (Since the vacuum of empty space is better than any vacuum attainable on Earth, the beam of subatomic particles would not need light-years of tubing to contain it; it could be fired into empty space.) Fair warning: The magnetic field required by each coil to bend the beam would be so huge that the surge of power through it might melt the coil, making it usable only once. After the beam has passed, the melted coils would have to be discarded and replaced in time for the next pass.
Alternatively, it is worth noting that the Large Hadron Collider may be the last generation of giant particle accelerators to use radio-frequency energies to boost subatomic particles around a giant ring. Physicists are already attempting to build tabletop-size laser-driven accelerators that, in principle, could attain billions of electron volts. So far, scientists have used powerful laser beams to attain an acceleration of 200 billion electron volts per meter, a new record. Progress is rapid, with the energy growing by a factor of 10 every five years. Although technical problems hamper the development of a true tabletop accelerator, an advanced civilization has billions of years to perfect these and other devices.
In the interim, to reach the Planck energy with something like current laser technology would require an atom smasher 10 light-years long, reaching beyond the nearest star. Power stations would need to be placed along the path in order to pump laser energy into the beam and to focus it—a minor task for a Type III civilization.
7. Send in the Nanobots
Assume now that the wormholes created in the previous steps prove unworkable. Perhaps they are unstable, or too small to pass through, or their radiation effects are too intense. What if future scientists find that only atom-size particles can safely pass through a wormhole? If that is the case, intelligent life may have but one remaining option: Send a nanobot through the wormhole to regenerate human civilization on the other side.
This process occurs all the time in nature. An oak tree produces and scatters seeds that are compact, resilient, packed with all the genetic information necessary to re-create a tree, and loaded with sufficient nourishment to make colonization possible. Using nanotechnology, an advanced civilization might well be able to encode vast quantities of information into a tiny, self-replicating machine and send this machine through a dimensional gateway. Atom-size, it would be able to travel near the speed of light and land on a distant moon that is stable and full of valuable minerals. Once situated, it would use the raw materials at hand to create a chemical factory capable of making millions of copies of itself. These new robots would then rocket off to other distant moons, establish new factories, and create still more copies. Soon, a sphere of trillions of robot probes would be expanding near the speed of light and colonizing the entire galaxy.
Next, the robot probes would create huge biotechnology laboratories. They would inject their precious cargo of information—the preloaded DNA sequences of the civilization’s original inhabitants—into incubators and thereby clone the entire species. If future scientists manage to encode the personalities and memories of its inhabitants into these nanobots, the civilization could be reincarnated.
Mathematically, this is the most efficient way for a Type III civilization to colonize a galaxy, not to mention a new cosmos. If we ever encounter another intelligent life-form, chances are it won’t be in a flying saucer like the starship Enterprise. More likely, we’ll make contact with a robot probe they’ve left on a moon somewhere. This was the basis of Arthur C. Clarke’s 2001: A Space Odyssey, which may be the most scientifically accurate depiction of an encounter with an extraterrestrial intelligence. In the film version, this logic was originally articulated by scientists in the film’s opening minutes, but director Stanley Kubrick cut the interviews from the final edit.