Part 10 (1/2)
”But do you really mean, sir,” said Peter, ”that there could be other worlds-all over the place, just around the corner-like that?”
”Nothing is more probable,” said the Professorwhile he muttered to himself, ”I wonder what they do teach them at these schools”
-C S LEWIS, THE LION, THE WITCH AND THE WARDROBE
listen: there's a hell of a good universe next door; let's go
-E E cumMINGS
Are alternate universes really possible? They are a favorite device for Hollywood scriptwriters, as in the Star Trek episode called ”Mirror, Mirror” Captain Kirk is accidentally transported to a bizarre parallel universe in which the Federation of Planets is an evil ereed, and plunder In that universe Spock wears abeard and Captain Kirk is the leader of a band of ravenous pirates, advancing by enslaving their rivals and assassinating their superiors
Alternate universes enable us to explore the world of ”what if” and its delicious, intriguing possibilities In the Superman comics, for example, there have been several alternate universes in which Superman's home planet, Krypton, never blew up, or Superman finally reveals his true identity as mild-mannered Clark Kent, or he marries Lois Lane and has superkids But are parallel universes just the doht Zone reruns, or do they have a basis inback to almost all ancient societies, people have believed in other planes of existence, the hohosts The Church believes in heaven, hell, and purgatory The Buddhists have Nirvana and different states of consciousness And the Hindus have thousands of planes of existence
Christian theologians, at a loss to explain where heaven ht be located, have often speculated that perhaps God lives in a higher diher dimensions did exist, ht becoht be able to disappear and reappear at will or walk through walls-powers usually ascribed to deities
Recently the idea of parallel universes has become one of the most hotly debated topics in theoretical physics There are, in fact, several types of parallel universes that force us to reconsider e mean by what is ”real” What is at stake in this debate about various parallel universes is nothing less than theof reality itself
There are at least three types of parallel universes that are intensely discussed in the scientific literature: a hyperspace, or higher dimensions, b the multiverse, and
c quantum parallel universes
HYPERspacE
The parallel universe that has been the subject of the longest historical debate is one of higher dith, width, height) is common sense No matter hoe move an object in space, all positions can be described by these three coordinates In fact, with these three numbers we can locate any object in the universe, froalaxies
A fourth spatial dimension seems to violate common sense If smoke, for example, is allowed to fill up a roo into another dimension Nowhere in our universe do we see objects suddenly disappearing or drifting off into another universe This her dimensions, if they exist at all, must be smaller than an atom
Three spatial dieometry Aristotle, for exanitude in one way, the plane in tays, and the solid in three ways, and beyond these there is no other nitude because the three are all” In AD 150 Ptoleher dimensions were ”impossible” In his essay ”On Distance,” he reasoned as follows Draw three lines that arethe corner of a room) Clearly, he said, a fourth line perpendicular to the other three cannot be drawn, hence a fourth dimension must be impossible (What he actually proved was that our brains are incapable of visualizing the fourth dimension The PC on your desk calculates in hyperspace all the time) For two thousand years, any mathematician who dared to speak of the fourth dimension potentially suffered ridicule In 1685 ainst the fourth di it a ”Monster in Nature, less possible than a Chimera or Centaure” In the nineteenth century Karl Gauss, the ”prince of mathematicians,” worked out much of the mathematics of the fourth dimension but was afraid to publish because of the backlash it would cause But privately Gauss conducted experieometry really described the universe In one experiment he placed his assistants on three e triangle Gauss then le To his disappointles all surees He concluded that if there were deviations to standard Greek geometry, they must be so small that they could not be detected with his lanterns
Gauss left it to his student, Georg Bernhard Rieher dimensions (which were then ieneral relativity) In one powerful sweep, in a celebrated lecture Riemann delivered in 1854, he overthreo thousand years of Greek geoher, curved dimensions that we use even today
After Riemann's remarkable discovery was popularized in Europe in the late 1800s, the ”fourth di artists, musicians, writers, philosophers, and painters Picasso's cubism, in fact, was partly inspired by the fourth di to art historian Linda Dalrys of wo forward and nose to the side was an attempt to visualize a fourth-di down from the fourth dimension could see a woman's face, nose, and the back of her head simultaneously) Henderson writes, ”Like a Black Hole, the 'fourth dimension' possessed mysterious qualities that could not be completely understood, even by the scientists themselves Yet, the impact of 'the fourth dimension' was far more comprehensive than that of Black Holes or any other more recent scientific hypothesis except Relativity Theory after 1919”
Other painters drew from the fourth dimension, as well In Salvador Dali's Christus Hypercubius, Christ is crucified in front of a strange, floating three-dimensional cross, which is actually a ”tesseract,” an unraveled four-dimensional cube In his famous Persistence of Memory, he attempted to represent time as the fourth dimension, and hence thea Staircase was an atte the ti down a staircase The fourth dimension even pops up in a story by Oscar Wilde, ”The Canterville Ghost,” in which a ghost haunting a house lives in the fourth dimension
The fourth dimension also appears in several of H G Wells's works, including The Invisible Man, The Plattner Story, and The Wonderful Visit (In the latter, which has since been the basis of scores of Hollywood movies and science fiction novels, our universe soel fro accidentally shot by a hunter Horrified by all the greed, pettiness, and selfishness of our universe, the angel eventually commits suicide) The idea of parallel universes was also explored, tongue-in-cheek, by Robert Heinlein in The Nuroup of four brave individuals who romp across parallel universes in a mad professor's interdi boy reads a book and gets the inspiration to build a machine that would allow him to ”slide” between parallel universes (The book that the young boy was reading was actually my book, Hyperspace) But historically the fourth dimension has been considered a mere curiosity by physicists No evidence has ever been found for higher die in 1919 when physicist Theodor Kaluza wrote a highly controversial paper that hinted at the presence of higher dieneral relativity, but placed it in five dimensions (one dimension of time and four dimensions of space; since time is the fourth space-time dimension, physicists now refer to the fourth spatial dimension as the fifth dimension) If the fifth diically split into two pieces One piece describes Einstein's standard theory of relativity, but the other piece beco revelation Perhaps the secret of light lies in the fifth dimension! Einstein himself was shocked by this solution, which seeravity (Einstein was so shaken by Kaluza's proposal that heto have this paper published) Einstein wrote to Kaluza, ”The idea of achieving [a unified theory] by means of a five-dilance, I like your idea enor”
For years physicists had asked the question: if light is a wave, then what is waving? Light can pass through billions of light-years of empty space, but empty space is a vacuu in the vacuum? With Kaluza's theory we had a concrete proposal to answer this probleht is ripples in the fifth dimension Maxwell's equations, which accurately describe all the properties of light, e in the fifth di in a shallow pond They ht never suspect the presence of a third dimension, because their eyes point to the side, and they can only swiht A third diine it rains on the pond Although they cannot see the third dimension, they can clearly see the shadows of the ripples on the surface of the pond In the sa on the fifth diave an answer as to where the fifth dimension was Since we see no evidence of a fifth dimension, it must have ”curled up” so s a two-dihtly into a cylinder From a distance, the cylinder looks like a one-dimensional line In this way, a two-dimensional object has been turned into a one-di it up) Kaluza's paper initially created a sensation But in the co years, objections were found to his theory What was the size of this new fifth dimension? How did it curl up? No answers could be found
For decades Einstein would work on this theory in fits and starts After he passed away in 1955, the theory was soon forgotten, becoe footnote to the evolution of physics
STRING THEORY
All this has changed with the co theory By the 1980s physicists were drowning in a sea of subatomic particles Every time they smashed an atom apart with powerful particle accelerators, they found scores of new particles spitting out It was so frustrating that J Robert Oppenheio to the physicist who did not discover a new particle that year! (Enrico Fermi, horrified at the proliferation of subato names, said, ”If I could remember the names of all these particles, I would have become a botanist”) After decades of hard work, this zoo of particles could be arranged into so called the Standard Model Billions of dollars, the sweat of thousands of engineers and physicists, and twenty nobel Prizes have gone into painfully asse, piece by piece, the Standard Model It is a truly remarkable theory, which see subatomic physics
But the Standard Model, for all its experimental successes, suffered froly and ad hoc” It contains at least nineteen free parath of their interactions with other particles), thirty-six quarks and antiquarks, three exact and redundant copies of sub-particles, and a host of strange-sounding subatos bosons, W bosons, and Z particles Worse, the Standard Model ravity It seemed hard to believe that nature, at its most supreme, fundaant Here was a theory only a ance of the Standard Model forced physicists to reanalyze all their assu
If one analyzes the last few centuries in physics, one of the most important achievements of the last century was to sureat theories: the quantum theory (represented by the Standard Model) and Einstein's theory of general relativity (describing gravity) Reether they represent the sue at a fundamental level The first theory describes the world of the very small, the subatomic quantu in and out of existence and appearing two places at the same tie, such as black holes and the big bang, and uses the language of smooth surfaces, stretched fabrics, and warped surfaces The theories are opposites in every way, using different mathematics, different assumptions, and different physical pictures It's as if nature had two hands, neither of which communicated with the other Furthermore, any atteless answers For half a century any physicist who tried to eneral relativity found that the theory blew up in their faces, producing infinite answers that ed with the advent of the superstring theory, which posits that the electron and the other subato, acting like a tiny rubber band If one strikes the rubber band, it vibrates in differentto a different subato theory explains the hundreds of subatomic particles that have been discovered so far in our particle accelerators Einstein's theory, in fact, e
String theory has been hailed as a ”theory of everything,” the fabled theory that eluded Einstein for the last thirty years of his life Einstein wanted a single, comprehensive theory that would summarize all physical law, that would allow hi theory is correct in unifying gravity with the quantu achieveo to when the Greeks asked what matter wastheory is that these strings can only vibrate in a specific dimension of space-time; they can only vibrate in ten di theory in other dimensions, the theory breaks down mathematically
Our universe, of course, is four-dimensional (with three dimensions of space and one of time) This means that the other six dimensions must have collapsed somehow, or curled up, like Kaluza's fifth diht to proving or disproving the existence of these higher dimensions Perhaps the siher diravity In high school we learn that the gravity of the Earth diravity diminishes with the square of the distance of separation But this is only because we live in a three-di the Earth The gravity of the Earth spreads out evenly across the surface of the sphere, so the larger the sphere, the weaker the gravity But since the surface of the sphere grows as the square of its radius, the strength of gravity, spread out over the surface of the sphere, must diminish as the square of the radius) But if the universe had four spatial diravity should diminish as the cube of the distance of separation If the universe had n spatial diravity should diminish as the n-1-th power Newton's fareat accuracy over astronomical distances; that is e can send space probes soaring past the rings of Saturn with breathtaking accuracy But until recently Newton's inverse-square law had never been tested at small distances in the laboratory
The first experiment to test the inverse-square law at small distances was perforative results Apparently there is no parallel universe, at least not in Colorado But this negative result has only whetted the appetite of other physicists, who hope to duplicate this experie Hadron Collider, which will become operational in 2008 outside Geneva, Switzerland, will be looking for a new type of particle called the ”sparticle,” or superparticle, which is a higher vibration of the superstring (everything you see around you is but the lowest vibration of the superstring) If sparticles are found by the LHC, it could signal a revolution in the e view the universe In this picture of the universe, the Standard Model si
Kip Thorne says, ”By 2020, physicists will understand the laws of quantu theory”
In addition to higher dimensions, there is another parallel universe predicted by string theory, and this is the ”multiverse”
THE MULTIVERSE
There is still one nagging question about string theory: why should there be five different versions of string theory? String theory could successfully unify the quanturavity, but there were five ways in which this could be done This was rather e, since ” Einstein, for exa the universe” His belief was that the unified field theory of everything should be unique So why should there be five string theories?
In 1994 another bombshell was dropped Edward Witten of Princeton's Institute for Advanced Study and Paul Townsend of Ca theories were in fact the same theory-but only if we add an eleventh die point of the eleventh dimension, all five different theories collapsed into one! The theory was unique after all, but only if we ascended to the mountaintop of the eleventh dimension
In the eleventh dimension a new , like the surface of a sphere) Here was the a observation: if one dropped fro theories would e theories were just different ways ofa membrane down froine a beach ball with a rubber band stretched around the equator I the beach ball twice, once above and once below the rubber band, thereby lopping off the top and bottom of the beach ball All that is left is the rubber band, a string In the same way, if we curl up the eleventh dimension, all that is left of aIn fact,can occur, leaving us with five different string theories in ten diave us a new picture It also meant that perhaps the universe itself was ain an eleven-dimensional space-time Moreover, not all these dimensions had to be sht actually be infinite
This raises the possibility that our universe exists in a multiverse of other universes Think of a vast collection of floating soap bubbles or membranes Each soap bubble represents an entire universe floating in a larger arena of eleven-dimensional hyperspace These bubbles can join with other bubbles, or split apart, and even pop into existence and disappear We ht live on the skin of just one of these bubble universes
Max Tegmark of MIT believes that in fifty years ”the existence of these 'parallel universes' will be no alaxies-then called 'island universes'-was 100 years ago”
Howfeature of string theory is that there are trillions upon trillions of possible universes, each one compatible with relativity and the quantuol of such universes (A googol is 1 followed by 100 zeros) Normally communication between these universes is impossible The atoms of our body are like flies trapped on flypaper We canour membrane universe, but we cannot leap off the universe into hyperspace, because we are glued onto our universe But gravity, being the warping of space-time, can freely float into the space between universes