Parallel Worlds: A Journey Through Creation, Higher Dimensions, and the Future of the Cosmos

by Michio Kaku

Cosmology is the study of the universe as a whole, including its birth and perhaps its ultimate fate. Not surprisingly, it has undergone many transformations in its slow, painful evolution, an evolution often overshadowed by religious dogma and superstition.

Most of the universe is actually made of mysterious, invisible material of totally unknown origin.

According to the WMAP, 23 percent of the universe is made of a strange, undetermined substance called dark matter, which has weight, surrounds the galaxies in a gigantic halo, but is totally invisible. Dark matter is so pervasive and abundant that, in our own Milky Way galaxy, it outweighs all the stars by a factor of 10. Although invisible, this strange dark matter can be observed indirectly by scientists because it bends starlight, just like glass, and hence can be located by the amount of optical distortion it creates.

But instead of finding an elegant and simple framework, it was distressing to find that there were hundreds of subatomic particles streaming from our accelerators, with strange names like neutrinos, quarks, mesons, leptons, hadrons, gluons, W-bosons, and so forth. It is hard to believe that nature, at its most fundamental level, could create a confusing jungle of bizarre subatomic particles.

“Wormholes, if they exist, would be ideal for rapid space travel. You might go through a wormhole to the other side of the galaxy and be back in time for dinner.”

This is the key to the correct answer. The universe is not infinitely old. There was a Genesis. There is a finite cutoff to the light that reaches our eye. Light from the most distant stars has not yet had time to reach us. Cosmologist Edward Harrison, who was the first to discover that Poe had solved Olbers’ paradox, has written, “When I first read Poe’s words I was astounded: How could a poet, at best an amateur scientist, have perceived the right explanation 140 years ago when in our colleges the wrong explanation . . . is still being taught?”

time beats at different rates, depending on how fast you move. In fact, the faster you move, the slower time progresses. Time is not an absolute, as Newton once thought. According to Newton, time beat uniformly throughout the universe, so that the passage of one second on Earth was identical to one second on Jupiter or Mars. Clocks beat in absolute synchronization throughout the universe. To Einstein, however, different clocks beat at different rates throughout the universe.

(According to legend, Eddington was later asked by a reporter, “There’s a rumor that only three people in the entire world understand Einstein’s theory. You must be one of them.” Eddington stood in silence, so the reporter said, “Don’t be modest, Eddington.” Eddington shrugged, and said, “Not at all. I was wondering who the third might be.”)

The problem lies not in relativity but in assuming that our common sense represents reality.

First, the big bang was not big (since it originated from a tiny singularity of some sort much smaller than an atom) and second, there was no bang (since there is no air in outer space).

A supernova about ten light-years away could, in fact, end all life on Earth. Fortunately, the giant stars Spica and Betelgeuse are 260 and 430 light-years away, respectively, too far to cause much serious damage to Earth when they finally explode.

Carrying fifty people, the ship can attain velocities near the speed of light as it travels to a new star system. More important, the ship uses a principle of special relativity, which says that time slows down inside the starship the faster it moves. Hence, a trip to the nearby stars that takes decades, as viewed from Earth, appears to last only a few years to the astronauts. To an observer on Earth watching the astronauts by telescope, it would appear as if they were frozen in time, so that they are in a kind of suspended animation. But to the astronauts on board, time progresses normally. When the starship decelerates and the astronauts disembark on a new world, they will find that they have traveled thirty light-years in just a few years. The ship is an engineering marvel; it is powered by ramjet fusion engines that scoop the hydrogen of deep space and then burn it for unlimited energy. It travels so fast that the crew can even see the Doppler shifting of starlight; stars in front of them appear bluish, while stars behind them appear reddish.

By rights, the universe should appear quite lumpy, with one part too distant to have made contact with another distant part. How can the universe appear so uniform, when light simply did not have enough time to mix and spread information from one distant part of the universe to the other? (Princeton physicist Robert Dicke called this the horizon problem, since the horizon is the farthest point you can see, the farthest point that light can travel.)

Similarly, scientists believe the universe started out in a state of perfect symmetry, with all the forces unified into a single force. The universe was beautiful, symmetrical, but rather useless. Life as we know it could not exist in this perfect state. In order for the possibility of life to exist, the symmetry of the universe had to break as it cooled.

Since the inflationary theory is a quantum theory, it is based on the Heisenberg uncertainty principle, the cornerstone of the quantum theory.

Inside every black hole that collapses may lie the seeds of a new expanding universe. —Sir Martin Rees

Black holes may be apertures to elsewhen. Were we to plunge down a black hole, we would re-emerge, it is conjectured, in a different part of the universe and in another epoch in time . . . Black holes may be entrances to Wonderlands. But are there Alices or white rabbits? —Carl Sagan

plutonium-186

According to relativity, light beams, he showed, would bend severely as they whipped around the object. In fact, at 1.5 times the Schwarzschild radius, light beams actually orbited in circles around the star. Droste showed that the distortions of time found in general relativity around these massive stars were much worse than those found in special relativity. He showed that, as you approached this magic sphere, someone from a distance would say that your clocks were getting slower and slower, until your clocks stopped totally when you hit the object. In fact, someone from the outside would say that you were frozen in time as you reached the magic sphere.

The concept of time itself has evolved over the centuries. To Newton, time was like an arrow; once fired, it never changed course and traveled unerringly and uniformly to its target. Einstein then introduced the concept of warped space, so time was more like a river that gently speeded up or slowed down as it meandered through the universe. But Einstein worried about the possibility that perhaps the river of time can bend back on itself. Perhaps there could be whirlpools or forks in the river of time.

Anyone brave enough to travel around the cylinder would be swept along, attaining fantastic speeds. In fact, to a distant observer, it would appear that the individual was exceeding the speed of light. Although Van Stockum himself did not realize it at the time, by making a complete trip around the cylinder, you could actually go back in time, returning before you left. If you left at noon, then by the time you returned to your starting point, say, it might be 6 p.m. the previous night. The faster the cylinder spun, the further back in time you would go (the only limitation being that you could not go further back in time than the creation of the cylinder itself).

But physicists often quote from T. H. White’s epic novel The Once and Future King, where a society of ants declares, “Everything not forbidden is compulsory.”

What is really bizarre is that, if you look carefully at the left wall, you see that it is actually transparent and there is a carbon copy of your bedroom on the other side of this wall. In fact, there is an exact clone of yourself standing in the other bedroom, although you can only see your back side, never your front side. If you look below or above, you also see carbon copies of yourself. In fact, there is an infinite sequence of yourselves standing in front, behind, below, and above you.

chronology protection requires a fully developed theory of quantum gravity.”

TIME PARADOXES Traditionally, another reason physicists dismissed the idea of time travel was because of time paradoxes. For example, if you go back in time and kill your parents before you are born, then your birth is impossible. Hence you could never go back in time to kill your parents to begin with. This is important, because science is based on logically consistent ideas; a genuine time paradox would be enough to completely rule out time travel.

What is this mysterious force that prevents us from altering the past and creating a paradox? “Such a constraint on our free will is unusual and mysterious but not completely without parallel,” he writes. “For example, it can be my will to walk on the ceiling without the aid of any special equipment. The law of gravity prevents me from doing this; I will fall down if I try, so my free will is restricted.”

A second way to resolve the time paradox is if the river of time smoothly forks into two rivers, or branches, forming two distinct universes. In other words, if you were to go back in time and shoot your parents before you were born, you would have killed people who are genetically the same as your parents in an alternate universe, one in which you will never be born. But your parents in your original universe will be unaffected.

I think I can safely say that nobody understands quantum mechanics. —Richard Feynman Anyone who is not shocked by the quantum theory does not understand it. —Niels Bohr The Infinite Improbability Drive is a wonderful new method of crossing vast interstellar distances in a mere nothingth of a second, without all that tedious mucking about in hyperspace. —Douglas Adams

“There is nothing so absurd that it has not been said by philosophers.”

calculate this number. Miraculously, by adding up these numbers from all possible paths, you found the

Does this seem too strange to be possible? Nobel laureate Steven Weinberg likens this multiple universe theory to radio. All around you, there are hundreds of different radio waves being broadcast from distant stations. At any given instant, your office or car or living room is full of these radio waves. However, if you turn on a radio, you can listen to only one frequency at a time; these other frequencies have decohered and are no longer in phase with each other. Each station has a different energy, a different frequency. As a result, your radio can only be turned to one broadcast at a time.

When asked about the measurement problem in quantum mechanics, he says, “I am just driven crazy by that question. I confess that sometimes I do take 100 percent seriously the idea that the world is a figment of the imagination and, other times, that the world does exist out there independent of us. However, I subscribe wholeheartedly to those words of Leibniz, ‘This world may be a phantasm and existence may be merely a dream, but this dream or phantasm to me

worlds/decoherence theory

Heisenberg uncertainty principle

But scientists found a loophole in this argument in 1993, through something called quantum entanglement. This is based on an old experiment proposed in 1935 by Einstein and his colleagues Boris Podolsky and Nathan Rosen (the so-called EPR paradox) to show how crazy the quantum theory really is. Let’s say that there is an explosion, and two electrons fly apart in opposite directions, traveling at near light speed. Since electrons can spin like a top, assume that the spins are correlated—that is, if one electron has its spin axis pointing up, the other electron is spinning down (such that the total spin is zero). Before we make a measurement, however, we do not know which direction each electron is spinning.

Anyone who can tap into the fourth spatial dimension (or what is today called the fifth dimension, with time being the fourth dimension) can indeed become invisible, and can even assume the powers normally ascribed to ghosts and gods.

Imagine, for the moment, that a race of mythical beings can inhabit the two-dimensional world of a tabletop, as in Edwin Abbot’s 1884 novel Flatland. They conduct their affairs unaware that an entire universe, the third dimension, surrounds them.

Hovering in hyperspace has decided advantages, for anyone looking down from hyperspace would have the powers of a god. Not only would light pass beneath him, making him invisible, he could also pass over objects. In other words, he could disappear at will and walk through walls. By simply leaping into the third dimension, he would vanish from the universe of Flatland. And if he jumped back onto the tabletop, he would suddenly rematerialize out of nowhere. He could therefore escape from any jail. A prison in Flatland would consist of a circle drawn around a prisoner, so it would be easy to simply jump into the third dimension and be outside.

It would be impossible to keep secrets away from a hyperbeing. Gold that is locked in a vault could be easily seen from the vantage point of the third dimension, since the vault is just an open rectangle. It would be child’s play to reach into the rectangle and lift the gold out without ever breaking into the vault. Surgery would be possible without cutting the skin.

For some cosmic reason, our dimension and a parallel universe temporarily collided, allowing this angel to fall into our world.

The quantum theory is precisely the opposite—it describes the world of the very tiny: atoms, protons and neutrons, and quarks. It is based on a theory of discrete packets of energy called quanta. Unlike relativity, the quantum theory states that only the probability of events can be calculated, so we can never know for sure precisely where an electron is located. These two theories are based on different mathematics, different assumptions, different physical principles, and different domains.

Historically, the link between music and science was forged as early as the fifth century B.C., when the Greek Pythagoreans discovered the laws of harmony and reduced them to mathematics. They found that the tone of a plucked lyre string corresponded to its length. If one doubled the length of a lyre string, then the note went down by a full octave. If the length of a string was reduced by two-thirds, then the tone changed by a fifth. Hence, the laws of music and harmony could be reduced to precise relations between numbers. Not surprisingly, the Pythagoreans’ motto was “All things are numbers.” Originally, they were so pleased with this result that they dared to apply these laws of harmony to the entire universe. Their effort failed because of the enormous complexity of matter. However, in some sense, with string theory, physicists are going back to the Pythagorean dream.

String theory has to confront this same problem. We have to curl up these unwanted higher dimensions into a tiny ball (a process called compactification). According to string theory, the universe was originally ten-dimensional, with all the forces unified by the string. However, ten-dimensional hyperspace was unstable, and six of the ten dimensions began to curl up into a tiny ball, leaving the other four dimensions to expand outward in a big bang. The reason we can’t see these other dimensions is that they are much smaller than an atom, and hence nothing can get inside them. (For example, a garden hose and a straw, from a distance, appear to be one-dimensional objects defined by their length. But if one examines them closely, one finds that they are actually two-dimensional surfaces or cylinders, but the second dimension has been curled up so that one does not see it.)

Mathematicians are still trying to decipher the “lost notebooks of Ramanujan” found after his death.

since all subatomic particles are either fermions or bosons, a supersymmetric theory has the potential of unifying all known subatomic particles into one simple symmetry. We now have a symmetry large enough to include the entire universe. Think of a snowflake. Let each of the six prongs of the snowflake represent a subatomic particle, with every other prong being a boson, and the one that follows being a fermion. The beauty of this “super snowflake” is that when we rotate it, it remains the same. In this way, the super snowflake unifies all the particles and their sparticles. So if we were to try to construct a hypothetical unified field theory with just six particles, a natural candidate would be the super snowflake.

Mini–black holes were introduced again by Stephen Hawking, who proved that black holes must evaporate and emit a faint glow of energy. Over many eons, a black hole would emit so much energy that it would gradually shrink, eventually becoming the size of a subatomic particle. String theory is now reintroducing the concept of mini–black holes. Recall that black holes form when a large amount of matter is compressed to within its Schwarzschild radius. Because mass and energy can be converted into each other, black holes can also be created by compressing energy. There is considerable interest in whether the LHC may be able to produce mini–black holes among the debris created by smashing two protons together at 14 trillion electron volts of energy. These black holes would be very tiny, weighing perhaps only a thousand times the mass of an electron, and last for only 10-23 seconds. But they would be clearly visible among the tracks of subatomic particles created by the LHC.

Now, string theorists are trying to tackle the most difficult problem in black hole physics, the “information paradox.” Hawking has argued that if you throw something into a black hole, the information it carries is lost forever, never to return again. (This would be a clever way to commit the perfect crime. A criminal could use a black hole to destroy all incriminating evidence.) From a distance, the only parameters that we can measure for a black hole are its mass, spin, and charge. No matter what you throw into a black hole, you lose all its information. (This goes by the statement that “black holes have no hair”—that is, they have lost all information, all hair, except for these three parameters.) The loss of information from our universe seems to be an inevitable consequence of Einstein’s theory, but this violates the principles of quantum mechanics, which state that information can never really be lost. Somewhere, the information must be floating in our universe, even if the original object was sent down the throat of a black hole.

Last, there is a rather mysterious prediction of M-theory that is still not understood but may have deep physical and philosophical consequences. This result forces us to ask the question: is the universe a hologram? Is there a “shadow universe” in which our bodies exist in a compressed two-dimensional form? This also raises another, equally disturbing question: is the universe a computer program? Can the universe be placed on a CD, to be played at our leisure?

“Everyone complains about the weather, but no one ever does anything about it.”

the anthropic principle is one of the most compelling arguments for the multiverse. In the same way that the existence of Goldilocks zones for Earth implies extrasolar planets, the existence of Goldilocks zones for the universe implies there are parallel universes. Rees comments, “If there is a large stock of clothing, you’re not surprised to find a suit that fits. If there are many universes, each governed by a differing set of numbers, there will be one where there is a particular set of numbers suitable to life. We are in that one.” In other words, our universe is the way it is because of the law of averages over many universes in the multiverse, not because of a grand design.