Call it Physics for the Next Millennium. Just as researchers were announcing last week the first compelling evidence of the existence of the "top quark," the final subatomic building block of the atom and a key element in the scientific world's reigning model of physical reality (box, Page 60), a flurry of new books is heralding a new age in physics -- one in which the ordinary understanding of reality is literally being turned on its head and inside out.
Never have researchers conjured up a world so weird: It is a universe where space exists in 10 dimensions, where one can travel through time into the past, where holes in the fabric of space and time pop up and serve as shortcuts to other parts of the universe, and where the visible universe may be only one of myriad mini-universes that coexist like so many soap bubbles in a cosmic froth.
No fantasy fringe. Such notions no doubt would have shocked Albert Einstein, yet the new research is in fact a legacy of the great theorist's work. At universities and research labs around the world, Einstein's theories of space and time are being stretched and refined by the brightest minds in science today, some of whom will undoubtedly garner Nobel Prizes for their sober-minded efforts to make the ordinary world seem very strange indeed. "Most people think of physicists as people who wear white smocks and work with tuning forks or study friction," says Michio Kaku, a physicist at the City University of New York and author of the just published Hyperspace: A Scientific Odyssey Through Parallel Universes, Time Warps, and the 10th Dimension (Oxford University Press). "But in fact, we make our living discovering things that blow people's minds."
Much of the new research stems from the intellectual effort to make the cluttered and chaotic universe tidier and more elegant. The so-called standard model -- the mathematical formulation that predicts, among other things, the existence of the newly found quark -- contains some 60 different particles with a broad variety of properties. Though a tremendous achievement of modern science, this theoretical model is simply too complicated to be the ultimate description of reality, says Kaku. "It's like using Scotch tape to pull together a mule, a whale, a tiger and a giraffe." Many physicists today assume that there must be a deeper, more comprehensive theory that unites all the phenomena in the universe, from light to gravity to quarks.
There is now tremendous excitement over a theory that may achieve that goal, but it is a theory that requires a kind of multidimensional thinking that even many scientists are unaccustomed to. Kaku uses a carp pond as an analogy for the new physics, with the fish being analogous to earthbound cosmologists. If carp were to observe rain splattering the pond's surface, for example, they might construct theories explaining the motion of the ripples in the water -- yet never realize that what they observed was caused by actions in an unseen world beyond their grasp.
Similarly, physicists such as Kaku are exploring the notion that the universe contains higher dimensions -- known as hyperspace -- and that many of the long standing problems in theoretical physics can be simplified with such a view. For nearly a century, for instance, physicists have wondered how light can display the properties of a wave traveling through water, even though light is capable of traveling through empty space where there exists no medium in which to ripple. But if physicists regard the universe as having not the familiar four dimensions -- three of space and one of time -- but instead an additional spatial dimension, then the properties of light emerge naturally from the equations describing this five-dimensional world. Adding even more dimensions gives rise to still other forces of nature. Indeed, the number of dimensions that appears to best explain nature is 10; physicists say the world merely seems four-dimensional to us because the other six dimensions, present during the big bang, are now inaccessible -- like rain clouds to a carp.
The notion of a 10-dimensional universe may be impossible for ordinary folks to comprehend, but it is a key part of a newly ascendant model of the universe known as the "superstring" theory. This theory holds that all matter and energy are the result of the vibration of infinitesimally small loops that are some 100 billion billion times smaller than a proton. These strings are the fundamental blocks that make up the entire universe, according to the new physicists, who say that a 10- dimensional universe arises naturally from superstring equations. Though there are still many issues to resolve, many scientists feel that this new model is the most promising hope for a "Theory of Everything," in which all of the properties of the universe can be folded into one set of equations.
Resolving superstring theory will help settle the hot debate now going on in scholarly journals over the possibility of time travel. Several years ago, California Institute of Technology physicist Kip Thorne and his colleagues proposed that Einstein's equations describing space and time allowed for the possibility of tunnels in the fabric of space. These "wormholes" could theoretically connect one part of the universe with another, or even loop around to bring a time traveler to a point in the universe's past.
Though no one has actually seen a wormhole, they are theoretically possible because, as Einstein established, gravity twists and bends the structure of space itself. Around huge chunks of matter -- such as the superdense, collapsed stars that form a black hole -- the surrounding space could be bent in such a way that a wormhole might open up, allowing a time traveler to slip through. Other physicists, including Stephen Hawking, have since weighed in on the issue, suggesting that the radiation surrounding such a wormhole would annihilate a time traveler, or that the energy arising from activating a wormhole might cause it to collapse, or that the hole might open and close too quickly to allow anyone to pass through. In his new book, Black Holes and Time Warps: Einstein's Outrageous Legacy (W.W. Norton), Thorne points out that one of the biggest problems for humans wishing to travel through time is that the amount of energy needed to produce a wormhole is beyond the scope of anything known today. "Even if a wormhole could be created," says Thorne, "it would be as far beyond our present technology as space travel is to an amoeba." Still, when Newton described his laws of force and motion three centuries ago, he possessed the theoretical tools to calculate the energy required to go to the moon, even though he lived in the era of the horse and buggy.
The biggest objection to time travel may arise from common sense rather than theory. Physicist Hawking, whose collection of essays Black Holes and Baby Universes (Bantam Books) came out last fall, argues that time travel must not be possible, since if it were, modern civilization would already have been overrun by tourists from the future. More troubling for many physicists is the "grandfather paradox": If time travel were possible, what would happen if someone traveled back in time and murdered his grandfather, thereby preventing his own birth?
One way around this difficulty, argue a growing number of physicists, is to look to the concept of "multiple worlds." In the shadowy world of quantum mechanics, particles can only be described as a collection of probabilities. Scientists can say with precision, for example, that a given particle will decay within 20 minutes, but there is no way of predicting exactly when in that 20-minute span the decay will actually occur; this uncertainty is an intrinsic property of the particle. To escape this apparent randomness, some researchers suggest that in fact all the possible scenarios exist simultaneously, but in multiple, parallel universes that are independent of each other. Thus in one universe the particle will decay after one minute, in anot
