Chapter 14 13. Parallel Universe
Are parallel universes really possible?They're a favorite setting of Hollywood screenwriters, as in a Star Trek episode called "Mirror, Mirror."Captain Kirk is accidentally teleported to a wacky parallel universe.There, the Confederation of the Stars is an evil empire held together by savage conquest, greed, and plunder.In that universe, Spock sported a scary beard and Captain Kirk was the leader of a gang of greedy pirates who worked their way up the ranks by enslaving their enemies and assassinating their superiors.
Parallel universes allow us to explore "what if" worlds, with their delicious, fascinating possibilities.For example, in the Superman comics, there are several alternate universes where Superman's home planet Krypton doesn't blow up, or where Superman eventually reveals his identity as the mild-mannered Clark Kent, or He married Lois Lane and had a Superman baby.But are parallel universes just a repeat of The Twilight Zone, or do they have a basis in modern physics?
Throughout history, in nearly every ancient society, people believed in other layers of existence, abodes of gods and spirits.Christians believe in heaven, realms and purgatory, Buddhists believe in Nirvana and various forms of consciousness, and Hindus have thousands of levels of existence.
At a loss as to how to explain the location of heaven, Christian theologians often speculate that God resides in higher dimensions.Surprisingly, if higher dimensions do exist, many of the properties believed to be possessed by God might be possible.A being in a higher dimension might be able to disappear and reappear at will, or walk through walls—an ability usually attributed to God.
Recently, the concept of parallel universes has been one of the most hotly debated topics among theoretical physicists.In fact, there are several forms of parallel universes that force us to rethink what "reality" means.Nowhere is more at the forefront of this debate about alternate universes than the very meaning of reality itself.
There are at least three types of parallel universes that are most hotly discussed in the scientific literature:
There is a kind of parallel universe that has been the subject of the longest-running debate—higher dimensions.It is common knowledge that we live in three dimensions (length, width, height).No matter how we move an object in space, all orientations can be represented by these three coordinates.In fact, we can use these three numbers to map out the orientation of any object in the universe, from the tip of our nose to the most distant corners of all galaxies.
The fourth dimension seems to defy common sense.For example, if we fill a room with smoke, we won't see the smoke disappear into another dimension.We don't see objects suddenly disappear anywhere in the universe, or drift to another universe.This means that any higher-dimensional spaces, if they exist at all, must be smaller than an atom.
Three-dimensional space formed the fundamental basis of ancient Greek geometry.For example, Aristotle wrote in his essay "On Heaven": "Line has but one quantity, plane has two, and body three. Quantities beyond these do not exist, since the total There are only three quantities.” In 150 BC, Ptolemy of Alexandria presented the first “evidence” that higher-dimensional spaces were “impossible.”In his essay "On Distance", he reasoned as follows.Make three perpendicular lines (like the three lines that make up the corners of a room).Obviously, he says, it is impossible to draw a fourth line that is perpendicular to the other three lines, so there must be no fourth dimension (what he proves is in fact that our brains cannot see the fourth dimension The PC on your desk is doing calculations in hyperspace all the time).
For two thousand years, any mathematician who dared to talk about the fourth dimension risked being ridiculed.In 1685, the mathematician John Wallis attacked the fourth dimension, calling it "a freak of nature, less reliable than a centaur." In the 19th century, "Prince of Mathematics" Carl Gauss ( Karl Gauss calculated a great deal of mathematics related to the fourth dimension, but was afraid to publish it due to the fierce attack they might provoke.Gauss, however, conducted experiments in private to test whether the three-dimensional Greek geometry of the plane did indeed describe the entire universe.In one experiment, he asked his assistants to stay on the top of three mountains, each holding a lantern, thus forming a huge triangle.Gauss then measures the degrees of each angle of the triangle.To his dismay, he found that the sum of the interior angles of a triangle is 180°.He concluded that if there were any inaccuracies in canonical ancient Greek geometry, they must be too small to be detected with his lantern.
Gauss left the problem to his student Georg Bernhard Riemann, who wrote down the basic high-dimensional mathematics (which was heavily introduced decades later in Einstein's general theory of relativity middle).In a whirlwind of backlash, in one of Riemann's famous lectures, he overturned 2,000 years of ancient Greek geometry and established the fundamental mathematics of higher, curved dimensions that we still use today.
After Riemann's remarkable discoveries spread across Europe in the late 19th century, the "fourth dimension" became popular among artists, musicians, writers, philosophers and painters.According to art historian Linda Dalrymple, Picasso's Cubism was in fact partly inspired by the fourth dimension (Picasso's painting of a woman with her eyes facing forward and her nose facing the other is a four-dimensional Attempts to visualize the angle, since the woman's face, nose, and back of the head can be seen simultaneously from the fourth dimension).Henderson wrote: "Like black holes, the 'fourth dimension' possesses mysterious qualities that cannot be fully understood, even by scientists themselves. However, the 'fourth dimension' is far more influential than black holes or other post-1919 phenomena." Newer scientific hypotheses are more far-reaching, except general relativity."
Other painters also created works on four dimensions.In Salvador Dali's Christus Hypercubus, Christ is crucified on an odd-looking, floating three-dimensional cross, which is actually a hypercube, an unfolded The four-dimensional cube; in Dali's famous "The Persistence of Memory" (The Persistence of Memory), he tried to represent time as the fourth dimension, so he used the melting clock as a metaphor.Marcel Duchamp's Nude Descending a Staircase attempts to show that time is the fourth dimension by capturing the time-shifting dynamics of a nude woman descending a staircase.The fourth dimension even makes an appearance in Wilde's short story "The Canterville Ghost," in which a four-dimensional ghost haunts a house.
Four-dimensional space also appears in some H. G. Wells works, including The Invisible Man, The Plattner Story and The Wonderful Visitation. Visit) (in the latter - which has since become the inspiration basis for a large number of Hollywood movies and science fiction novels), our universe collides with a parallel universe. A poor angel from another universe is accidentally shot by a hunter. Falls into the universe we live in. The greed, pettiness and selfishness in our universe terrify the angels and eventually commit suicide).
Robert Heinlein also explored parallel universes in a slightly wry way in The Number of the Beast.Heinlein imagines four brave men frolicing and adventuring in parallel universes in a mad professor's interdimensional sports car.
In the TV show Sliders, a young boy takes inspiration from a book and builds a machine that allows him to "glide" between parallel universes (the kid was actually reading my book — "Hyperspace").
But, historically, four-dimensional space has been considered by physicists to be nothing more than a product of curiosity, and evidence for higher-dimensional space has never been found.That all began to change in 1919 when physicist Theodor Kaluza wrote a controversial paper mentioning the existence of higher dimensions.He started with Einstein's general theory of relativity, but put general relativity into five dimensions (time is one dimension, space is four dimensions, because time is the fourth space-time dimension, physicists now put the fourth dimension is called the fifth dimension.) If the fifth dimension is compressed ever smaller, the equation magically splits into two parts.One of them describes Einstein's standard theory of relativity, but the other part becomes Maxwell's theory of optics!
This is a shocking discovery.Perhaps the secret of light is hidden in the fifth dimension!Einstein himself was blown away by the solution, which seemed to give the perfect unity of light and gravity (Einstein was so shocked by Kaluza's solution that he mulled over it for two years before finally agreeing to let the paper be published) .Einstein wrote to Kaluza: "The idea of a realization (of a unified theory) by a five-dimensional cylinder never occurred to me... At first glance, I like your idea very much... Your theory The unity of form is astonishing."
For years, physicists have asked the question: If light is a wave, what are the waves?Light is able to travel across distances of billions of light-years in empty space, but empty space is a vacuum and contains nothing.So, what are fluctuations in a vacuum?Using Kaluza's theory, we have a concrete solution to answer this question: the light is the ripple in the fifth dimension.Maxwell's equations, which precisely describe the entire nature of light, are proven to be exactly the equations for light moving in the fifth dimension.
Picture fish swimming in a shallow pond.They probably never suspected a third dimension, because their eyes were on the sides, and they could only swim forward or backward, left or right.The third dimension may appear impossible to them.But, next imagine the rain falling on the pond.Although they cannot see into the third dimension, they can clearly see the shadows of the ripples on the surface of the pond.Likewise, Kaluza's equations interpret light as ripples moving in the fifth dimension.
Kaluza also answered where the fifth dimension is.Since we have seen no evidence of a fifth dimension, it must be "rolled" so small that it cannot be observed (imagine rolling a two-dimensional piece of paper tightly into a cylinder. From a distance The cylinder looks like a one-dimensional line. In this way, a two-dimensional object can be rolled up to become a one-dimensional object).
Kaluza's paper initially caused a stir.But in later years, opposition to his theory emerged.How big is this new fifth dimension?How is it rolled up?There is no answer.
Einstein continued to work on the theory now and again over the course of several decades.When he died in 1955, the theory was quickly forgotten, becoming merely an odd footnote in the history of physics.
That all changed with the advent of a startling new theory called super string theory.Until the 1980s, physicists were drowning in a sea of subatomic particles.Every time they use a powerful particle accelerator to smash an atom apart, they find that a large number of new particles are ejected. J. Robert Oppenheimer's claim that the Nobel Prize in Physics should go to a physicist who didn't discover any new particles that year is so depressing!The proliferation of subatomic particles with Greek-sounding names terrified Enrico Fermi (“If I could remember the names of all these particles, I could be a botanist. ”) After decades of hard work, a system called the “standard model” was able to classify particles.Billions of dollars, the sweat of thousands of engineers and physicists, and 20 Nobel Prizes have all been poured into the hard-assembled Standard Model one by one.This is a truly remarkable theory that seems to agree with all relevant experimental data in subatomic physics.
But for all its experimental success, the Standard Model has been hampered by a serious flaw.As Stephen Hawking said: "It's ugly and temporary." It includes at least 19 free parameters (including particle masses and the strength with which they interact with other particles), 36 quarks and antiquarks, 3 accurate and abundant copies of subparticles, and many subatomic particles with oddly named tau neutrinos, Yang-Mills gluons, Higgs bosons boson), W boson (W boson) and Z particle (Z particle).Worse, the Standard Model makes no mention of gravity.It seems hard to believe that nature, at its most important and fundamental level, can be so disordered and terribly inelegant.It's a theory that doesn't appeal to anyone but its mother.The downright ugly Standard Model has forced scientists to reanalyze all their assumptions about nature to see what went terribly wrong.
If one analyzes the physics of the past centuries, the most important achievement of the previous century has been the summarization of all fundamental physics into two great theories: quantum theory (represented by the Standard Model) and Einstein's general theory of relativity ( describing gravitation), it is worth noting that together they represent the sum total of all knowledge of physics at a fundamental level.The former describes the world of the very tiny subatomic quantum, where particles perform a wonderful dance, coming and going, being in two different places at the same time.The latter describes the world of massive objects, such as black holes and the Big Bang, and uses language like "smooth surfaces," "stretched fabrics," and "distorted surfaces."The two theories are diametrically opposed in every way, using different mathematics, different assumptions, and different physical pictures.It is as if nature has two hands, neither of which communicates with the other.Furthermore, all attempts to unite the two theories have been fruitless.For 50 years, attempts to force the union of quantum theory and general relativity have yielded only prolific and meaningless results.
The advent of superstring theory changed all that.Superstring theory posits that electrons and other subatomic particles are nothing more than different vibrations of a string. It acts like a miniature rubber band. If you hit the rubber band, it will vibrate in different ways. different subatomic particles.Thus, while superstring theory explains the hundreds of subatomic particles that have been discovered so far in our particle accelerators, Einstein's theory is in fact just one of the lowest levels of string vibration.
Superstring theory is considered a "true theory of everything," the theory that Einstein is said to have baffled for the last 30 years of his life.Einstein wanted a single, comprehensive theory outlining all the laws of physics that would enable him to "read the will of God".If superstring theory can correctly unify gravitation and quantum theory, it may represent the highest achievement of science since the ancient Greeks posed the question of what matter is made of two thousand years ago.
But the odd feature of superstring theory is that these strings can only vibrate in a specific space-time dimension—they can only vibrate in ten dimensions.If one tried to create a string theory in other dimensions, it would break down mathematically.
Of course, our universe is four-dimensional (three dimensions of space and one dimension of time).This means that the other sixth dimensions must have collapsed in some unknown way, or rolled up like Kaluza's fifth dimension.
Recently, physicists have given serious thought to proving the existence of these higher-dimensional spaces.Perhaps the easiest way to prove the existence of higher dimensions is to find fault with Newton's law of universal gravitation.In high school, we learned that Earth's gravitational pull decreases when we go into space, or more precisely, that the gravitational pull decreases as the square of the distance.But this is only because we live in a three-dimensional world (imagine a sphere surrounding the Earth. The Earth's gravity spreads out evenly across the surface of the sphere. In this way, the larger the sphere, the smaller the gravitational force. Due to the relationship between the size of the sphere's surface and its radius proportional to the square of the radius, the strength of the gravitational force across the surface of the sphere will be inversely proportional to the square of the radius).
If the universe has four spatial dimensions, then the weakening of gravitational force should be proportional to the cube of the separation distance, and if the universe has n spatial dimensions, then the gravitational force should be weakened by the power of n-l.Newton's famous inverse square law has been tested and proven to be extremely accurate at astronomical distances, which is why we can fly space probes through Saturn's rings with astonishing precision.But Newton's inverse square law had never been tested in the laboratory over short distances until recently.
The first experiment to test the inverse square law over short distances was carried out at the University of Colorado in 2003 and came back negative.It appears that parallel universes do not exist, at least not in Colorado.But the negative result only whetted the appetite of other physicists, who hoped the experiment could be repeated with greater precision.
In addition, the Large Hadron Collider, which opened in 2008 outside Geneva, Switzerland, will be used to search for new types of particles called "sparticles" (or superparticles), which are higher vibrational forms of superstrings (you can find them in Everything you see around you is just the lowest vibration of the superstring).If superparticles are discovered by the LHC, it could mark a revolution in the way we view the universe, in which the Standard Model represents only the lowest quiver of superstrings.
Kip Thorne said: "By 2020, physicists will understand the laws of quantum gravity, which will be discovered as a variant of superstring theory."
In addition to high-dimensional space, superstring theory also predicts other parallel universes, which are "multiverses".
There's another troubling question about string theory: Why did there have to be five different versions of string theory?Superstring theory could successfully unify quantum theory and gravity, but there are five ways to do it.This is rather embarrassing, because most physicists want a unique "theory of everything."For example, Einstein wondered whether "God had other choices in creating the universe."His belief was that a unified field theory of everything should be unique.So why are there five superstring theories?
In 1994, another startling revelation exploded.Edward Witten of the Institute for Advanced Study in Princeton and Paul Townsend of the University of Cambridge reasoned that all five string theories are really the same string theory—as long as we add an eleventh dimension.From the point of view of the eleventh dimension, all five theories are merged into one!After all, this theory is unique, as long as we climb the peak of the eleventh dimension.
In the eleventh dimension, there can exist a new kind of mathematical object called membrane (membrane, such as the surface of a sphere).Here is an astonishing observation: if one drops from eleven dimensions to ten, all five superstring theories emerge, starting with a membrane.Therefore, all five superstring theories are nothing more than transferring a membrane from eleven-dimensional space-time to ten-dimensional space-time.
(To visualize this, imagine a water ball with a rubber band stuck in the middle. Imagine using a pair of scissors to cut the ball in half, with half on the rubber band and half under the rubber band. Therefore, the water ball What remains after the upper and lower halves are removed is the rubber band—a string. In the same way, if we roll up the eleventh dimension, all that remains of a membrane is its equator, then is a string. In fact, there are five ways such a cut can be achieved, giving us five different superstring theories in ten dimensions.)
The eleventh dimension gives us a whole new picture.It also means that perhaps the universe itself is a membrane, floating in an eleven-dimensional space-time.Also, not all of these dimensions have to be small; in fact, some could be infinitely large.
This raises the possibility that our universe exists within a multiverse of other universes.Imagine - a mass of floating soap bubbles, or membranes.Each soap bubble represents an entire universe floating in a larger ten-dimensional hyperspace.These soap bubbles can join with other soap bubbles, burst, or even briefly appear and disappear.We may be living on the surface of just one of these soap bubble universes.
Max Tegmark of the Massachusetts Institute of Technology believes that in 50 years, "the existence of these 'parallel universes' will no longer be more controversial than the existence of other galaxies was 100 years ago-when our universe was destroyed. Called the island universe."
How many universes does string theory predict?Superstring theory has an embarrassing feature-there may be trillions and trillions of universes, all of which conform to the theory of relativity and quantum theory.One estimate declares that there might be 1 Googol of such universes (1 Googol is 1 followed by 100 0s).
In general, communication between these universes is impossible.The atoms in our bodies are like flies trapped in flypaper.We can act arbitrarily in the three dimensions of our own brane universe, but we cannot jump off the universe into hyperspace because we are stuck in our own universe.But gravity as the curvature of space-time is free to float in the space between universes.
In fact, one theory holds that dark matter — the invisible matter that surrounds the universe — may be ordinary matter floating in a parallel universe.As in HG Wells' novel The Invisible Man, a person becomes invisible if he floats in the fourth dimension above us.Imagine two parallel sheets of paper with someone floating above the sheet above them.
In this way, it has been speculated that dark matter might be an ordinary galaxy in another brane universe floating above us.We will be able to feel the gravity of this galaxy because the gravity will slowly flow between the universes, but the other galaxy will be invisible to us because the light moves under the galaxy, so this galaxy will have gravity, but Invisible, which fits the description of dark matter (there is another possibility that dark matter may consist of the next level of vibration of superstrings. Everything we see around us, such as atoms and light, is just the lowest vibration of superstrings. Dark matter may be a collection of higher vibrations).
Naturally, most parallel universes are probably dead, made up of a gas of shapeless subatomic particles — such as electrons and neutrinos.In these universes, protons might be unstable, so all matter as we know it would slowly decay and dissolve.Complex matter made of atoms and molecules might not be possible in many such universes.
Other parallel universes may be just the opposite, with far more complex forms of matter than we can imagine.They may have not just one kind of atom made of protons, neutrons and electrons, but a bewildering number of other stable forms of matter.
These brane universes could also collide, creating cosmic fireworks.Some physicists at Princeton believe our universe may have been created 137 billion years ago when two giant branes collided.The shock wave of that giant collision made our universe, they think.Remarkably, when the results of experiments exploring this strange idea appeared to match those from the WMAP (Wilkinson Microwave Anisotropy Probe) satellite currently orbiting Earth (it's called the "Large collision" [big splat] theory).
The multiverse theory has one fact in its favor.When we analyze the constants of nature, we find that they are "tuned" so precisely that life is allowed.If you increase the strength of the nuclear force, the stars will burn out too quickly for life to arise.If the strength of the nuclear force is reduced, then the star will never burn and life cannot exist.If gravitational forces were strengthened, our universe would die quickly in a "Big Crunch".If the gravitational force is weakened, the universe will expand into a "Big Freeze".In fact, there are plenty of "chances" among the constants of nature that allow life to exist.It appears that our universe exists within a "habitable zone" with many parameters, all "fine-tuned" for life to exist.So we either accept the conclusion that there is some form of God who chose our universe to be "just right" for life, or there are billions of parallel universes, many of which are dead.As Freeman Dyson said: "The universe seems to know we are coming."
Sir Martin Reiss of the University of Cambridge once wrote that this precise adjustment is in fact the proof of the multiverse.There are five physical constants (such as different force strengths) fine-tuned for the existence of life, and he believes that there are infinitely many universes whose natural parameters do not meet the requirements of life.
This is the so-called "anthropic principle".The milder version simply holds that our universe is fine-tuned for life (since we're making that claim for the first time here).The more radical version is: Maybe our existence is a by-product of some kind of design, or intentional.Most cosmologists would agree with the milder version of the anthropic principle, but there is much debate about whether the anthropic principle is a new scientific principle capable of leading to new discoveries and conclusions, or whether it is simply a statement of simple facts.
In addition to higher dimensions and multiverses, there is a type of parallel universe that gave Einstein such a headache and still plagues physicists today: the quantum universe predicted by ordinary quantum mechanics.The contradictions in quantum physics seem so intractable that Nobel laureate Richard Feynman was fond of saying that no one really understands quantum theory.
Ironically, although quantum theory is the most successful theory ever proposed of the human brain (often accurate to within 1 part in 10 billion), it is based loosely on chance, luck and probability.Unlike Newton's theory, which gives an exact and firm answer to the motion of objects, quantum theory can only give certain possibilities.Modern wonders such as lasers, the Internet, computers, televisions, mobile phones, radar, microwave ovens, and more are built on protean possibilities.
One of the most poignant instances of this problem is the famous "Schrodinger's cat" problem (designed by one of the founders of quantum theory, who posed it paradoxically in order to crush the possibility of Existence explanation).Schrödinger objected to this interpretation of his theory, saying: "If anyone insists on this damn quantum jump, then I regret being involved in this business."
The Schrödinger's cat paradox goes like this: a cat is placed in a sealed box.In the box, a gun was aimed at the cat (the trigger was connected to a Geiger counter placed next to a block of uranium).Normally, when the uranium atom starts to decay, it starts the Geiger counter, which then fires the gun, killing the cat.Uranium atoms either decay or they don't decay.Cats live or die.This is nothing but common sense.
But in quantum theory, we can't know for sure whether uranium will decay.So we have to add two possibilities, a wave function for decayed atoms and a wave function for non-decayed atoms.But that means, to describe that cat, we have to add the cat's two states, so the cat is either alive or dead.It represents the sum of a dead cat and a living cat!
As Feynman once wrote, quantum mechanics "describes nature as absurd from a common-sense point of view. And it agrees perfectly with experimental results. So I hope you will accept nature for what it is—absurd."
For Einstein and Schrödinger, this was counterintuitive.Einstein believed in "objective facts," a common sense in which Newtonian objects exist in exact states, not in many possible states.Yet this outlandish explanation lies at the heart of modern civilization.Modern electronics (and the atoms in our bodies) couldn't exist without it (in our normal world we sometimes joke that being "kinda pregnant" is impossible. But in the quantum world, things are much more Outrageous. We exist in every possible physical form at the same time: non-pregnant, pregnant, child, old woman, teenager, working woman, etc.).
There are several ways to resolve this difficult paradox.The creators of quantum theory believed in the Copenhagen School, that once the box was opened, a measure could be made, and whether the cat was alive or dead, the wave function "collapsed" into a single state, and common sense began to take over.The waves have disappeared, leaving only the particles.This means, the cat is now in a definite state (either alive or dead) and is no longer described by the wave function)
In this way, an invisible barrier separates the weird world of the atom from the macroscopic world of man.For the atomic world, everything is described by waves of possibility, in which atoms can exist in many places at the same time.The larger the wave at a certain location, the more likely it is that a particle will be found at that point.But for large objects, these waves collapse, and the object exists in an exact state, so common sense wins.
(When guests came to Einstein's house, he would point to the moon and ask, "Does the moon exist because a mouse looks at it?" In a sense, the Copenhagen party's answer to this might be definitely.)
Most Ph.D.-level physics textbooks are devoutly loyal to the original Copenhagen School, but many research physicists have abandoned it.We now have nanotechnology and the ability to manipulate individual atoms, so atoms that come and go can be manipulated arbitrarily with our scanning tunneling microscopes.There is no invisible "wall" separating the microcosm and the macrocosm, but a continuous and unified whole.
Currently, there is no agreement on how to resolve this dispute, which attacks the heart of modern physics.At the meeting, there were many competing theories.A minority opinion holds that there must be a "cosmic consciousness" pervading the universe.Objects pop up when measurements are made, and the measurements are made by conscious beings.Therefore, there must be a universal consciousness throughout the universe that determines the state we are in.Some physicists, such as the Nobel laureate Eugene Wigner, have argued that this proves the existence of God or some kind of cosmic consciousness (Wigner writes: "It is impossible to formulate the [quantum theory].” In fact, he even expressed interest in the Hindu Vedanta philosophy, in which the universe is governed by an all-encompassing consciousness).
Another view of this paradox is the "many worlds" formulation, proposed by Hugh Everett in 1957, which states that the universe is simply split in two, with the living cats in one half and the dead cats in the other half.This means that whenever a quantum event occurs, parallel universes multiply and diverge in large numbers.This is true of every possible universe.The more absurd a universe is, the less likely it is, but these universes still exist.That means a parallel universe in which the Nazis won WWII, or a world in which the Spanish Armada was never defeated and everyone speaks Spanish.In other words, the wave function never collapses.It just keeps going, happily splitting into countless universes.
As MIT physicist Alan Guth puts it: “There is a universe where Elvis is alive and Al Gore is president.” Nobel laureate Frank Frank Wilczek said: "We often have this awareness in our minds that there are infinitely many slightly mutated versions of ourselves living their parallel lives, and that every moment more copies pop up and start a continuation. Our many 'other' futures."
There is an idea that is gaining traction among physicists, and it's called "decoherence."This theory suggests that all these parallel universes are possible, but that our wave function has decohered with them (i.e. no longer vibrates in unison with them), and therefore no longer interacts with them.This means that in your living room, you could simultaneously co-exist with the wave functions of dinosaurs, aliens, pirates, unicorns, all convinced that their universe is the "real" one, but we are no longer with them" coordinated".
根据诺贝尔奖得主斯蒂文·温伯格（Steven Weinberg）的看法，这就像在自家起居室里将收音机调到另一个电台。你知道自己的起居室充满了来自全国和全世界各地大量无线电台的信号，但是你的收音机只能调到一个电台。它与其他的电台都“消相干”了（总而言之，温伯格注意到“多世界”构想是“一个不幸的构想，除了所有其他想法之外”）。
因此，是否存在来自一个邪恶的、劫掠较弱的星球、屠杀自己敌人的星际联邦的波函数？或许有，但即便有的话，我们也已经与那个宇宙不相干了。
当休·埃弗莱特与其他物理学家讨论他的“多宇宙”理论时，他获得的是令他困感不解或是漫不经心的反馈。有位物理学家，德克萨斯大学（University of Texas）的布莱斯·德维特（Bryce DeWitt）反对这一理论，因为“我感觉不到自己分裂但埃弗莱特说，这是类似于伽利略对那些说自己感觉不到地球在转动的批评者们的回答（最终德维特胜过了埃弗莱特一方，并且被称为这一理论的主要反对者）。
数十年来，“多世界”理论在晦暗不明中失去了活力。它太奇异了，不像是真的。埃弗莱特在普林斯顿的顾问约翰·韦勒（John Wheeler）最终总结说，与该理论相联系的“额外累赘”太多。但埃弗莱特的理论如今突然风行起来原因是物理学家试图将量子理论应用于最后一块拒绝被量子化的领域——宇宙本身。将测不准原理运用于整个宇宙会自然得出多元宇宙。
“量子宇宙学”的概念最初似乎在名称上是自相矛盾的：量子理论涉及的是极小的原子世界，而宇宙学涉及的是整个宇宙。但想想这个：在大爆炸的那一刻，宇宙比一个电子还小得多。每一个物理学家都认同电子必须被量子化，即它们是由一个或然性波动方程（狄拉克方程）描述的，并且能存在于平行状态中。因此，如果电子必须被量子化，如果宇宙曾经小于一个电子，那么宇宙一定也存在于平行状态中——一种自然通往“多世界”的方式。
然而，尼尔斯·玻尔的哥本哈根解释在应用于整个宇宙的时候遇到了问题。哥本哈根解释尽管在地球上的每一门博士阶段的量子力学课程中都要传授，但它依靠的是一个作出观察的“观察者”和波函数的崩溃。定义宏观世界时观察程序是必不可少的。但是在观察整个宇宙的时候，怎么能置身宇宙“之外”呢？如果有一个波函数描述了宇宙，那么一个“在外面”的观察者如何能使宇宙的波函数崩溃？事实上，有些人将从宇宙“之外”观察宇宙的不可行视作哥本哈根解释的致命缺陷。
在“多世界”方法中，对这一问题的解答很简单：宇宙不过是存在于许多平行状态中，它们全都由一个主波函数定义，称作“宇宙波函数”（wave function of the universe）。在量子宇宙学中，宇宙是从真空的量子涨落开始的，即一个时空泡沫中的微小气泡。时空泡沫中的大多数婴儿宇宙都经历过—次大爆炸，并且随后立刻经历一次大挤压。这就是为什么我们永远都看不到它们，因为它们极小、寿命极短，在真空中时隐时现，这意味着，甚至“无物”也与婴儿宇宙一起沸腾和时有时无，但在一定比例上，这太小，无法用我们的仪器发现。但是出于某些原因，时空泡沫中有一个气泡没有重新坍缩、造成大挤压，而是继续膨胀，这就是我们的宇宙。根据艾伦·古斯的说法，这意味着整个宇宙就是一顿免费午餐。
在量子宇宙学中，物理学家们从一个薛定谔方程的模拟入手，它支配电子和原子的波函数。他们使用作用于“宇宙波函数”的德维特-韦勒方程。通常，薛定谔波函数定义的是时间与空间中的每一点，因此你就可以计算在时间和空间的那一点寻找到电子的可能性。但是“宇宙波函数”定义的是所有可能存在的宇宙。如果宇宙波函数碰巧在定义某个特定宇宙时很大，那就意味着那个宇宙很可能会是一个特殊的宇宙。
霍金推动了这一观点。他宣布，我们的宇宙是宇宙中特殊的存在。我们的宇宙波函数较大，而对于其他大多数宇宙则接近零。这样，其他宇宙存在于多元宇宙中就有了微小但是确定的可能性。事实上，霍金试图用这种方式得出膨胀率。在这幅图景中，一个膨胀的宇宙比不膨胀的宇宙更有可能存在，因此我们的宇宙是膨胀的。
我们的宇宙来自时空泡沫的“虚无”，这一理论似乎完全无法验证，但它符合一些简单的观测结果。首先，许多物理学家指出，我们宇宙中的正电荷总数和负电荷总数相抵刚好为零，这非常惊人，至少在实验的精确性之内是如此。我们认为太空中的引力是主导力量，这是事实，但这不过是由于正负电荷精确地相互抵消了。如果地球上的正负电荷之间出现最最微小的不平衡，那么它或许就足以将地球撕裂，战胜将地球维持成一个整体的引力。要解释正负电荷之间如此平衡有一个简单的方法：假设我们的宇宙来自于“虚无”，并且“虚无”没有电荷。
其次，我们的宇宙的旋转为零。尽管科特·哥德尔用多年时间试图通过累加各个星系的旋转来证明宇宙在旋转，但如今天文学家们相信整个宇宙的旋转为零。如果宇宙出自“虚无”的话这个现象就很容易解释了，因为“虚无”的旋转为零。
第三，我们的宇宙出自“虚无”有助于解释为什么宇宙的物质－能量内容总和是如此之小，甚至可能是零。当我们将物质的正能量和与引力相关的负能量相加，两者似乎完全相互抵消。根据广义相对论，如果宇宙是封闭的、有限的，那么宇宙的物质-能量总量应该刚好为零（如果我们的宇宙是开放的、无限的，这就不见得对了。不过暴胀理论确实表明我们宇宙中的物质-能量总量极小）。
这就留下了一些颇耐人寻味的问题：如果物理学家不能排除几种平行宇宙的可能形式，那么有可能与它们取得联系吗？有可能造访它们吗？或者来自其他宇宙的生物是否有可能已经拜访过我们？
与其他和我们的宇宙消相干的量子宇宙进行联系似乎非常不可能。我们与这些别的宇宙消相干的原因是我们的原子撞击周围环境中的无数其他原子，每当有碰撞发生，那个原子的波函数似乎会略有“崩溃”，即平行宇宙的数量减少。每次撞击都使可能性的数量减少。数万亿个这样的原子“迷你崩溃”的总数造成了我们身体的原子完全在一个有限状态中崩溃的假象。爱因斯坦的“客观实际”（objective reality）是一种幻觉，由我们的身体中有如此多的原子这一事实造成，每个原子都与另一个碰撞，每次都减少了可能存在的宇宙的数量。
这就像从一架相机里看一幅焦点没对准的画面。这与微观世界相符合，在那里一切都似乎是失真和模糊的。但随着你调整相机的焦距，画面就会变得越来越明晰。这对应了数万亿次与邻近原子的微型碰撞，每次都减少了可能存在的宇宙。以这个方法，我们能顺畅地完成从模糊的微观世界到宏观世界的转变。
因此，与其他和我们相近的量子宇宙相互影响的可能性并不是零，但是它随着我们身体内原子的数量快速减小。由于在你的体内有数万亿个原子，你能与由恐龙或者外星人组成的其他宇宙交流的可能性无穷小。你可以计算出，你或许要等待比宇宙的寿命还要长得多的时间才能等来这样的事件发生。
因此，与量子平行宇宙取得联系的可能并不能被排除，伹由于我们已经与它们消相干，这会是极为稀有的事件。但是，在宇宙学中，我们会遭遇一种不同类型的平行宇宙：一种相互共存的多元宇宙，就像是在一个泡泡浴里漂浮的肥皂泡。在多元宇宙中与其他宇宙取得联系是一个不同的问题。这无疑是一个非常难以完成、但对于III型文明而言有可能的任务。
如前文所述，在太空中打开一个洞或者放大时空泡沫所必需的能量相当于普朗克能量。在那个水平上所有已知的物理学定律都将失效。时空在那个能量水平上不稳定，而这就开启了我们离开自己的宇宙的可能性（假设其他宇宙存在，并且我们没有在整个过程中被杀死的话）。
这并不是一个纯粹的学术性问题，因为宇宙中的所有智能生命终将面对宇宙的末日。最终，多元宇宙的理论或许能成为我们宇宙中所有智能生命的救赎。最近，来自正围绕地球运转的WMAP人造卫星的数据确认了宇宙正在以越来越快的速度膨胀。有一天，我们或许将全部在物理学家称作大冻结的浩劫中灭亡。最后，整个宇宙将陷入黑暗，天空中所有的星星都不会再闪耀，宇宙将由死去的星体、中子星和黑洞组成，甚至连这些天体的原子也可能会开始衰变。温度或许会达到接近绝对零度，使生命无法存在。
随着宇宙向那一点接近，一个面临宇宙最终死亡的先进文明可以考虑踏上去往其他宇宙的终极旅程。对于这些生物而言，选择是被冻死或者离开。物理定律对于所有智能生命而言是一道死刑执行令，但在这些定律之中有允许逃脱的条款。
这样一个文明必须利用巨大的核粒子加速器和大如一个太阳系或者星团的激光束来将巨大的能量集中于一点，以实现传说中的普朗克能量。这么做可能足以开大一个通往其他宇宙的虫洞或大门。一个III型文明宇宙可能会在踏上去其他宇宙的旅程时使用可供他们利用的巨大能量打开一个虫洞，离开死去的宇宙从头来过。
尽管这些想法有部分显得令人难以置信，但物理学家已经对它们进行了严谨的考虑。比如，在试图理解大爆炸如何开始的时候，我们必须分析可能导致最初爆炸的条件。换言之，我们必须问：如何能在实验室里制造出一个婴儿宇宙？斯坦福大学的安德烈·林第（Andrei Linde）暴胀宇宙学说的创造者之一，他说如果我们能制造出婴儿宇宙，那“或许就是时候让我们重新将上帝定义为比仅仅是宇宙的创造者更为成熟的事物了”。
这个构想并不新颖。多年前，当物理学家计算出点燃大爆炸所需的能量，“人们立刻开始好奇如果将大量能量放置于实验室的一个空间中会怎样——同时让许多大炮开火。你能集中足够的能最启动一场迷你大爆炸吗？”林第问。
如果将足够的能量集中到一点上，所能得到的将是时空的一次坍缩，变成黑洞，再也没有其他的了。但是，在1981年，麻省理工学院的艾伦·古斯和林第提出了“暴胀宇宙”理论，它到如今已在宇宙学家中引起了巨大的兴趣，根据这一构想，大爆炸是从涡轮增压膨胀开始的，比过去所认为的快得多。（暴胀宇宙构想解决了宇宙学中的许多顽固问题，比如为什么宇宙如此均匀一致。无论我们看什么方位，从夜空的一部分到对面的一侧，我们看到的都是均匀单一的宇宙，尽管在大爆炸之后没有足够的时间让这些相距遥远的地区取得联系。根据暴胀宇宙理论，这一迷题的答案是时空的一小块相对均匀的碎片被放大成了整个我们可见的宇宙。）为了启动膨胀，古斯假设在时间的开端有微小的时空气泡，其中之一大大地膨胀，成为了今天的宇宙。
一下子，暴胀宇宙理论解答了大量的宇宙学疑问。除此之外，它符合所有如今从太空中WMAP和COBE人造卫星源源不断传来的数据。事实上，它无疑是大爆炸理论的主要候选者。
然而，暴胀宇宙理论提出了一系列令人窘迫的问题。这个气泡为什么会开始膨胀？是什么使膨胀停止，造成了如今的宇宙？如果膨胀曾经发生过，那么它还会再次发生吗？具有讽刺意味的是，尽管宇宙膨胀构想是宇宙学中的先锋理论，但关于是什么使得膨胀开始以及它为何停止却几乎一无所知。
为了解答这些令人不安的疑问，麻省理工学院的艾伦·古斯和爱德华·法利（Edward Fahri）于1987年提出了另一个假设性的问题：一个先进的文明会如何使自己的宇宙膨胀？他们认为，如果他们能够回答这个问题，他们或许也就能够回答为什么宇宙以膨胀开始这个深层次问题。
他们发现，如果将足够的能量集中在一点上，微小的时空气泡会自动生成。但如果气泡过小，它们会消失，回复到时空泡沫中去。只有当气泡够大的时候，它们才能膨胀成一个完整的宇宙。
从外界来看，这一新的宇宙的诞生不会有多骇人，或许不比引爆一枚50万吨当量的核弹更惊人。它看起来会像是一个小气泡从宇宙中消失，造成了一次小型核爆炸。但是在气泡之内，或许有一个新的宇宙膨胀而出了。想象一个肥皂泡分裂或派生出一个更小的气泡，造成一个婴儿肥皂泡。同样地，在宇宙内，你将看到一场时空的巨大爆炸以及一个完整宇宙的诞生。
自1987年以来，已有许多理论试图验证引入能量是否可以使一个大气泡膨胀成一整个宇宙。最被广为接受的理论是，一种名叫暴胀子（inflaton）的新粒子破坏了时空的稳定，造成这些气泡形成与膨胀。
最近的一场争论在2006年爆发，物理学家们开始严肃对待使用磁单极子点燃婴儿宇宙的提议。尽管只具有正极或者负极的磁单极粒子从未被发现过，但据信它们支配过最初的早期宇宙。它们过于巨大，很难在实验室里制造。但正是由于它们如此巨大，如果我们将更多能量注入一个磁单极子中，我们或许能够点燃一个婴儿宇宙，使其膨胀，变成一个真正的宇宙。
为何物理学家们想要制造一个宇宙？林德说：“从这个角度看来，我们人人都能成为上帝。”但是，希望制造一个新宇宙有更加实际的理由：最终，从我们的宇宙的死亡中逃脱。
有些物理学家将这一构想推广得更远，达到科幻的程度，以提问是否有智慧的存在参与设计了我们的宇宙。
在古斯/法利的图景中，一个先进文明能创造出一个婴儿宇宙，但是物理常数（例如电子和质子的质量，以及四种力的强度）是相同的。但如果一个先进文明能够创造出基本常数略有不同的婴儿宇宙呢？那么，这一婴儿宇宙将能够随着时间“进化”，每一代的婴儿宇宙都与前一代略微不同。
如果我们把基本常数看作一个宇宙的“DNA”，那就意味着智能生命或许可以制造出与DNA有细微差别的DNA。最终，宇宙们将会进化，并且能够进行繁殖的宇宙将会是那些具有允许生命存在与繁荣的最佳“DNA”的宇宙。物理学家爱德华·哈里森（Edward Harrison）在过去由李·斯莫林（Lee Smolin）提出的想法基础上，提出了一种宇宙间的“自然选择”。支配多元宇宙的宇宙恰恰是那些具有最佳DNA的宇宙，它们符合先进文明产生的要求，而先进的文明又反过来制造出更多婴儿宇宙。“适者生存”意味着最适宜产生先进文明的宇宙能生存。
如果这一构想正确，那它将可以解释宇宙的基本常数为什么是“微调”后适合生命的。这完全意味着具备适宜的基本常数的宇宙适合生命存在，是在多维宇宙中繁殖增生的宇宙。
（尽管这个“宇宙进化”构想颇具吸引力，因为它或许能解释人择原理问题，但该构想的难点在于其不可测试，并且无法被证明真伪。我们将不得不等到我们拥有一种完整的万物至理才能弄懂这一构想。）
当前，我们的科技远不足以证明这些平行宇宙的存在。因此，所有这些平行宇宙都算作“二等不可思议”——如今不可能，但不与物理定律相悖。在长达数千年到数百万年的时间中，这些推测可能会成为一个III型文明新科技的基础。
Notes:
Notes: