第 1 章
When Science Fiction Becomes Science Fact
Imagine walking through walls, becoming invisible, teleporting across space, or traveling back in time. These fantastical abilities have captivated human imagination for centuries, appearing in everything from ancient mythology to modern blockbusters. But what if these "impossible" feats aren't actually impossible? What if they're simply waiting for the right scientific breakthroughs? This is the fascinating premise explored by renowned theoretical physicist Michio Kaku in "Physics of the Impossible." The book has become a cultural touchstone since its 2008 publication, praised by luminaries like Brian Greene and appearing on bestseller lists worldwide. Kaku, a co-founder of string field theory and frequent science communicator on shows like Discovery and BBC, approaches these seemingly magical concepts with both scientific rigor and childlike wonder, showing how yesterday's science fiction repeatedly becomes today's scientific reality.
第 2 章
The Impossible Is Merely Improbable
Throughout history, the word "impossible" has proven remarkably temporary. Continental drift, once ridiculed by the scientific establishment, is now accepted as plate tectonics. The theory that dinosaurs were killed by a meteor strike was once considered absurd fantasy. Even the atomic bomb was deemed "impossible" until it dramatically changed the course of history.
Kaku proposes a thoughtful classification system for these "impossibilities." Class I impossibilities don't violate known physical laws and might be achievable within this century or the next-technologies like force fields, invisibility, or certain forms of telepathy. Class II impossibilities sit at the edge of our understanding, requiring breakthroughs in physics that might take millennia to achieve-think time travel or faster-than-light travel. Finally, Class III impossibilities would violate the known laws of physics-perpetual motion machines or precognition. Surprisingly, very few technologies fall into this last category.
This framework helps us understand that what seems impossible to our civilization might be routine for a more advanced one. As Arthur C. Clarke famously observed, "Any sufficiently advanced technology is indistinguishable from magic." A civilization thousands or millions of years ahead of ours would appear godlike to us, just as our smartphones and airplanes would seem magical to people from the Middle Ages.
The history of science repeatedly demonstrates that studying the "impossible" often leads to unexpected breakthroughs. The search for perpetual motion machines led to the laws of thermodynamics. Einstein's "impossible" theories revolutionized our understanding of the universe. As physicist Freeman Dyson notes, "The purpose of thinking about the future is not to predict it but to raise people's hopes."
第 3 章
Force Fields: From Science Fiction to Science Lab
When Captain Kirk shouts "Shields up!" on Star Trek, he's invoking one of science fiction's most ubiquitous technologies: the force field. These invisible barriers could revolutionize warfare, construction, and transportation if they existed. But can physics actually produce such fields?
The concept originates with Michael Faraday, a self-taught scientist who began as a bookbinder's apprentice. In 1831, Faraday discovered that moving a magnet near a wire generated electric current without physical contact-revealing that invisible fields could exert force across empty space. This discovery powers our modern civilization, from electric generators to computers.
Unfortunately, none of the four fundamental forces in physics-gravity, electromagnetism, and the strong and weak nuclear forces-behave like science fiction's force fields. Gravity is attractive rather than repulsive and extremely weak. Electromagnetism can be repulsive but acts over large distances rather than forming thin barriers. The nuclear forces operate only at subatomic distances.
However, promising alternatives exist. Physicist Ady Herschcovitch created the "plasma window" in 1995-a sheet of plasma (superheated gas) that can separate vacuum from air, similar to the shuttle bay force fields in Star Trek. While current plasma windows aren't impenetrable shields, future versions could potentially vaporize incoming projectiles.
Magnetic levitation offers another path to science fiction technologies. Japan's maglev trains already reach speeds of 361 mph using conventional electromagnets. The real breakthrough would come with room-temperature superconductors-materials conducting electricity with zero resistance without requiring extreme cooling. If discovered, highways could be made from these materials, allowing vehicles with magnets to float frictionlessly above them.
Given these developments, force fields qualify as a Class I impossibility-potentially achievable within a century as our understanding of plasma physics and superconductivity advances.
第 4 章
Invisibility: The Vanishing Impossibility
Invisibility has fascinated humanity throughout history, appearing in myths from Plato's ring of Gyges to Harry Potter's cloak. While physicists long dismissed invisibility as impossible, revolutionary advances in metamaterials are forcing a complete revision of optics textbooks.
The science of invisibility begins with James Clerk Maxwell, who translated Faraday's experimental discoveries into precise mathematical equations. Maxwell showed that light consists of vibrating electric and magnetic fields-a revelation that Einstein considered the most profound advancement since Newton. This understanding explains why solids are typically opaque (tightly packed atoms block light) while gases are often transparent (light passes between widely spaced molecules).
The breakthrough came in 2006 when researchers at Duke University and Imperial College successfully made an object invisible to microwave radiation using metamaterials-artificial substances with optical properties not found in nature. These materials manipulate the "index of refraction" (how much light bends when passing through a medium), allowing light to flow around objects like water around a boulder.
Progress accelerated dramatically afterward. In early 2007, scientists created the first metamaterial working in the visible spectrum for red light. Later that year, Caltech physicists developed a metamaterial bending blue-green light using plasmonics technology. These advances could lead to "superlenses" capable of photographing microscopic objects with unprecedented clarity, such as components of DNA molecules.
The development of practical invisibility devices will accelerate as this research piggybacks on massive investments in photonic crystals and plasmonics aimed at replacing silicon technology. Within decades, we may see working invisibility shields emerge from laboratories, though early versions will likely be rigid cylinders rather than flexible cloaks like Harry Potter's.
Alternative approaches include projecting background images onto specially designed clothing (as demonstrated by Naoki Kawakami at Tokyo University) or using holographic projection. Given the rapid progress in this field, invisibility qualifies as a Class I impossibility-challenging but achievable within our century.
第 5 章
Phasers and Death Stars: The Science of Energy Weapons
Despite critics' claims that planet-destroying weapons like Star Wars' Death Star are impossible, physics places no fundamental limit on the energy that can be concentrated in a light beam. The dream of energy beam weapons dates back to Archimedes, who reportedly used solar reflectors to set Roman ships ablaze during the Second Punic War.
The development of practical energy weapons became possible through the quantum revolution. In 1900, Max Planck proposed that energy occurs in discrete packets called "quanta," while Einstein suggested light consists of particles called "photons." By 1925, quantum mechanics had emerged through work by Schrodinger, Heisenberg, and others, revealing electrons as both particles and waves.
This understanding led to the development of lasers in the 1950s, beginning with Charles Townes' "maser" (microwave amplification through stimulated emission of radiation). A laser works by pumping energy into a special medium (gas, crystal, or diode), exciting atoms' electrons into higher energy states. When a light beam passes through this unstable medium, it triggers electrons to release photons in a cascade effect, with trillions of photons vibrating in unison.
Today, lasers are ubiquitous in everyday applications from grocery scanners to DVD players. Military applications include chemical lasers powerful enough to shoot down missiles. However, practical handheld ray guns don't exist primarily because they lack portable power sources-a handheld ray gun would need a miniature power source with the output of a huge electrical station.
Creating a Death Star laser capable of destroying planets would require harnessing stellar-level energy. Current fusion research attempts to replicate star conditions by heating hydrogen to 50-100 million degrees centigrade. Systems like the National Ignition Facility can reach 700 trillion watts in brief bursts, but even this falls dramatically short of planet-destroying capabilities.
The most feasible approach would harness hydrogen bombs, which release 100 million times more energy than chemical reactions. Edward Teller pioneered X-ray lasers that use nuclear detonations to energize copper rods, focusing intense X-ray beams. A civilization thousands of years more advanced than ours might control thousands of nuclear-powered X-ray lasers firing simultaneously-technically feasible but far beyond current technology.
Even more powerful would be harnessing gamma ray bursters-natural phenomena that release radiation second only to the big bang. An advanced civilization might potentially aim this devastating power at any target, creating a true Death Star.
第 6 章
Teleportation: Quantum Leaps in Reality
Teleportation-the ability to transport people or objects instantly between locations-would revolutionize civilization. While seemingly impossible under Newtonian physics, quantum theory has revealed surprising possibilities that challenge our understanding of reality.
The earliest science fiction mention of teleportation appeared in Edward Page Mitchell's 1877 story "The Man Without a Body," but Star Trek popularized it as a budget-friendly special effect. Scientists initially objected that teleportation would violate the Heisenberg uncertainty principle, which establishes we cannot simultaneously know a particle's exact position and velocity.
However, at the quantum level, particles can make "quantum leaps"-disappearing and reappearing elsewhere or existing in multiple places simultaneously. This behavior forms the basis of chemistry, allowing atoms to share electrons in stable molecules. Without quantum theory, our molecules would dissolve instantly.
The key to quantum teleportation lies in Einstein, Podolsky, and Rosen's 1935 paper on quantum entanglement. If two particles initially vibrate in unison, they remain synchronized even when separated by vast distances. This "spooky action at a distance" (as Einstein derisively called it) was confirmed by Alan Aspect's experiments in the 1980s.
In 1993, scientists at IBM showed teleportation was physically possible at the atomic level. The process involves three particles: A (to be teleported), C (destination), and B (intermediary). Since B and C are entangled, A's information transfers to C when A interacts with B. The first demonstration occurred in 1997 at the University of Innsbruck with photons. By 2004, physicists were teleporting photons over 600 meters beneath the Danube River via fiber-optic cable and successfully teleporting properties between beryllium atoms.
In 2007, physicists proposed a teleportation method using Bose-Einstein condensates-substances cooled to near absolute zero where atoms vibrate in unison as a "super atom." This approach converts information from atoms into light, transmits it via fiber-optic cable, then reconstructs the atoms elsewhere.
While atomic teleportation exists today and complex molecules may be teleportable within decades (making this a Class I impossibility), teleporting humans remains a Class II impossibility that may take centuries, if possible at all. The challenge lies in creating quantum coherence with macroscopic objects containing trillions of atoms-a staggering technical hurdle.
第 7 章
Telepathy: Reading the Mind's Secrets
Telepathy has long fascinated humanity, with gods traditionally possessing mind-reading powers to answer prayers. Scientific investigation began with the Society for Psychical Research in 1882, where the term "mental telepathy" was coined by F.W. Myers. The first systematic American studies were conducted by Dr. Joseph Banks Rhine at Duke University starting in 1927.
While natural telepathy as portrayed in science fiction remains impossible today, technology is making remarkable progress in brain reading. The simplest form of "mind reading" would be determining if someone is lying. Daniel Langleben revolutionized lie detection in 1999 by using fMRI scans, discovering that lying creates increased brain activity in specific brain regions. His method achieved 99 percent accuracy in controlled experiments, leading to commercial ventures like No Lie MRI.
Scientists like Marcel Just of Carnegie-Mellon have managed to identify fMRI patterns for specific object categories with 80-90% accuracy, and computer scientist Tom Mitchell is using neural networks to identify complex brain patterns. However, a true "universal translator" like those in science fiction remains distant.
Traditional MRI machines are enormous and expensive, but physicists Igor Savukov and Michael Romalis of Princeton have developed technology that might enable handheld MRI devices by replacing huge magnets with supersensitive atomic magnetometers. These handheld devices could eventually be coupled with computers programmed to decode certain phrases or thoughts.
The human brain functions as a neural network that constantly rewires itself, with thoughts distributed throughout rather than localized in specific regions. This distributed nature means scientists may only ever compile a "dictionary" of thoughts-establishing correspondence between certain brain patterns and specific thoughts.
Projecting thoughts into another's brain appears possible in limited ways. Neurosurgeon Wilder Penfield discovered that stimulating certain areas of the temporal lobe caused patients to hear voices and see ghostlike apparitions. In the future, precisely targeted electromagnetic signals might elicit specific emotions or visual images by stimulating the amygdala and other brain regions.
Some scientists advocate a "neuron-mapping project" similar to the Human Genome Project that would locate and map connections between all 100 billion neurons in the brain. Such a project could potentially establish correlations between specific thoughts and neural pathways.
I classify general thought pattern detection as a Class I impossibility, while more precise mind-reading would be a Class II impossibility. Rather than using weak radio signals, directly tapping into the brain's neurons might unleash even greater power: psychokinesis.
第 8 章
Robots: The Rise of Artificial Minds
By 2035, advanced robotic systems might control everything from subway systems to household robots. Scientists predict that within thirty years, artificial intelligence may surpass human intelligence-but significant challenges remain.
The "top-down approach" to artificial intelligence attempted to program all rules of pattern recognition and common sense onto a single system. Despite early successes, this approach hit insurmountable barriers. While robots can see better than humans, they struggle to understand what they see, converting visual input into meaningless pixels rather than recognizing objects. Our brains unconsciously process trillions of calculations when we enter a room-evolutionary adaptations that robots cannot replicate through programming alone.
Due to these limitations, researchers turned to the "bottom-up" approach, mimicking evolution and infant learning. Instead of programming complex rules, these systems learn by interacting with their environment. At MIT, Rodney Brooks created "insectoid" robots that learned to walk through trial and error rather than elaborate mathematical computations. While neural networks have successfully mimicked insect behavior, they've performed poorly when attempting to replicate mammalian capabilities. Even the most advanced neural network robots contain only hundreds of neurons compared to the human brain's 100 billion.
Literature often portrays mechanical beings yearning for human emotions-from Pinocchio to Data in Star Trek. While some argue emotions represent humanity's pinnacle and are impossible for machines to possess, AI scientists view emotions differently. They see emotions not as humanity's essence but as evolutionary tools for survival. Future advanced robots might be programmed with emotions to bond with owners and function better in society.
There's no universal consensus on whether machines can be conscious, or even what consciousness means. Marvin Minsky describes consciousness as a "society of minds"-thinking processes spread throughout the brain with different centers competing for attention. Consciousness likely exists on a continuum from thermostats to humans, with robots potentially developing their own "silicon consciousness" that processes information differently from ours.
Robots could indeed become dangerous once they achieve monkey-level intelligence-self-aware and capable of creating their own agendas. The long-term solution might be merging carbon and silicon technology rather than awaiting extinction. Hans Moravec even envisions transferring our neural architecture directly into machines, granting a form of immortality. If we overcome Moore's law's collapse and the commonsense problem, thinking machines as smart as humans could become reality this century, making them a Class I impossibility.
第 9 章
Starships and the Escape from Earth
One day billions of years from now, the Earth will face its final day as our sun swells into a raging inferno. The oceans will boil away, mountains will melt into lava flows, and our planet will be consumed by flames. This isn't science fiction but inevitable physics-within five billion years, Earth will become uninhabitable. Eventually, we must leave Earth or perish.
With conventional rockets taking 70,000 years just to reach Alpha Centauri, we need radical new propulsion systems to survive as a species. Several promising technologies exist:
Ion engines work like TV tubes, shooting beams of ionized atoms such as xenon. While they produce thrust measured in mere ounces, they can operate for years in space. NASA's NSTAR ion thruster on the Deep Space 1 probe fired for 678 days, while more powerful plasma engines like VASIMR heat hydrogen to a million degrees using radio waves and magnetic fields.
Solar sails exploit sunlight's pressure to propel spacecraft, an idea dating to Johannes Kepler in 1611. For interstellar travel, proponents envision massive sails hundreds of miles across powered by lunar laser arrays firing continuously for years. Such a sail might reach half light speed, arriving at nearby stars in eight years.
The ramjet fusion engine would scoop hydrogen from space as it travels, then heat it to fusion temperatures. Robert Bussard calculated a 1,000-ton ramjet could maintain 1g acceleration, reaching 77% light speed within a year. In theory, time dilation would allow crews to reach the Pleiades cluster in 11 years of ship time and Andromeda galaxy in 23 years-though billions of years would pass on Earth.
Project Orion proposed using sequential mini-nuclear bombs to propel a starship on their shock waves. The largest version, "super Orion," would weigh 8 million tons with a 400-meter diameter, powered by over 1,000 hydrogen bombs. Despite promising calculations showing it could reach Pluto within a year at 10% light speed, concerns about nuclear fallout and the 1963 Limited Test Ban Treaty ended the project.
Space elevators could drastically reduce launch costs from $10,000 per pound to just $1. The concept involves a cable extending from Earth to a geostationary orbit. The development of carbon nanotubes in 1991 made this theoretically possible, as they can withstand the required 120 gigapascals of pressure.
Miniature unmanned probes using nanotechnology offer a promising alternative to massive crewed starships. Ionized nanobots could be accelerated to near light speed using ordinary laboratory voltages and electromagnetic fields, solving many problems plaguing larger vessels. These could be mass-produced by billions, with only a fraction needing to reach their targets.
Space travel presents enormous dangers beyond Earth's protective shields. Prolonged weightlessness causes severe physical deterioration-muscle atrophy, bone loss, reduced blood cell production, and cardiovascular decline. Micrometeorites traveling at tens of thousands of miles per hour require extra shielding, as even tiny impacts could be deadly. Radiation levels in deep space far exceed Earth norms, with solar flares during the eleven-year sunspot cycle sending potentially lethal plasma.
To overcome the decades or centuries required for interstellar travel, suspended animation offers a potential solution. University of Pittsburgh scientists revived dogs after three hours of clinical death by replacing their blood with a special ice-cold solution. Researchers have successfully placed mice in suspended states using hydrogen sulfide, reducing their body temperature and slowing metabolism tenfold.
第 10 章
Beyond the Impossible: Parallel Universes and Time Travel
Are alternate universes really possible? Throughout history, cultures have believed in other planes of existence. Today, parallel universes have become one of the most hotly debated topics in theoretical physics, with nothing less than the meaning of reality at stake.
The concept of higher dimensions beyond our three spatial dimensions has been debated for centuries. In 1919, physicist Theodor Kaluza placed Einstein's relativity in five dimensions and made a stunning discovery: the equations split into Einstein's relativity plus Maxwell's theory of light. This suggested light might be ripples in the fifth dimension, answering what was "waving" in empty space.
String theory revolutionized physics by proposing that subatomic particles are actually different vibrations of tiny strings, like notes on a rubber band. The theory's bizarre requirement is that these strings can only vibrate in ten dimensions, with six dimensions having "curled up" or collapsed. This theory suggests our universe might be a membrane floating in eleven-dimensional hyperspace, alongside countless other "bubble universes."
Beyond higher dimensions and the multiverse lies another type of parallel universe from quantum mechanics-one that troubled Einstein and continues to bewilder physicists. The Schrodinger's cat paradox illustrates this perfectly: a cat in a sealed box with a radioactive trigger mechanism is neither dead nor alive until observed, but exists in a superposition of both states.
Hugh Everett's "many worlds" theory suggests the universe simply exists in many parallel states defined by a master "wave function of the universe." Quantum cosmology suggests our universe began as a quantum fluctuation of the vacuum-a tiny bubble in space-time foam that, unlike most bubbles that quickly collapse, kept expanding.
Could we ever contact or visit parallel universes? Interaction with quantum parallel universes is theoretically possible but extraordinarily improbable. Contact with another universe in the multiverse, however, might be achievable for a Type III civilization. The energy required to open a hole in space or magnify the space-time foam approaches the Planck energy, where space and time become unstable.
Time travel presents paradoxical questions that challenge our understanding of causality. While Einstein proved travel to the future possible through relativistic time dilation, backward time travel creates logical paradoxes. Theoretical designs include wormholes connecting distant points in time, Godel's spinning universe solution, rotating infinite cylinders, Richard Gott's cosmic string model, and most promising, transversable wormholes using negative energy.
Three possible resolutions to time travel paradoxes exist: First, you simply repeat history with no free will; second, mysterious forces prevent paradox-creating actions; third, the universe splits into parallel timelines when you change the past. The multiverse approach solves radiation buildup problems that would otherwise kill time travelers or collapse wormholes.
In 1997, physicists Kay, Radzikowski, and Wald showed time travel was consistent with physics except at the event horizon-precisely where Einstein's theory breaks down and quantum effects take over. Only a complete theory of everything could calculate what happens when entering a time machine, making time travel a Class II impossibility.
