Michio Kaku must have been the most interesting kid on his block.

When he wasn't reading science fiction, or wondering how carp in the Japanese Tea Garden envision the universe, he was building his own "Betatron," an electron accelerator, with the help of very supportive parents. Kaku assembled it on his high school football field with parts scavenged from the electronic warehouses that dotted the Bay Area, where he grew up in the '60s.

Today, with degrees from Harvard and UC Berkeley, he is a professor of theoretical physics at the City University of New York and sometimes a visitor at Princeton's Institute of Advanced Study, where he wrote "Hyperspace: A Scientific Odyssey Through Parallel Universes, Time Warps and the 10th Dimension."

Einstein spent the last decades of his life at the same institute, searching, unsuccessfully, for a unified field theory connecting all of nature's forces. It was Einstein's spirit, Kaku says, that inspired him.

Kaku believes that he, along with his colleagues studying hyperspace, may well have found the theory that eluded Einstein.

The idea of hyperspace, he explains, originated in higher-dimensional geometry, a new kind of math unveiled in 1854 by Georg Riemann at a lecture in Gottingen, Germany. There Riemann introduced the idea of a "fourth dimension," a concept that reverberated for almost a century in the worlds of art and literature.

In science, Riemann's work was the realization that physical laws simplify in higher-dimensional space. These are dimensions beyond the familiar frame of length, width, depth and time--dimensions beyond what our brains recognize.

It is impossible for most, if not all of us, to visualize these other dimensions, even when they are described as folded over or curled up in a knot. We can only know them mathematically.

Riemann's geometry inspired one Englishman, Oxford mathematician Lewis Carroll, to write "Alice's Adventures in Wonderland."

It inspired another, Edwin Abbot, to write "Flatland: A Romance of Many Dimensions by a Square." This best-selling satire described a two-dimensional world where those who suggested that a third dimension might exist were immediately sentenced to life in solitary confinement. That was more than a century ago. Today, most theoretical physicists have accepted other dimensions. The 10-dimensional universe Kaku describes is not only different from what the carp sees, but is also different from what we experience in our workaday, three-dimensional lives.

Kaku has enriched these pages with references to stories that illustrate the weird ramifications of hyperspace and the paradoxes of time travel.

These are not fairy tales. Kaku is a theoretician, but he is also the teen-age betatron builder. He reminds us that quantum mechanics--which suggests that it is impossible to predict the precise position of any particular particle at a particular time--is essential to such innovations in microelectronics as the transistor.

Kaku works on the field theory of "strings," part of the larger discipline of superstring theory that galvanized physicists in 1984. At that time, John Schwarz of Caltech and Michael Green of Queen's College, London, published an article establishing superstrings as the only self-consistent theory of quantum gravity.

Kaku explains that the string theory knits together the four fundamental forces that explain all phenomena in the universe--the electromagnetic force, the strong nuclear force, the weak nuclear force and the gravitational force.

Moreover, he writes, "the essence of string theory is that it can explain the nature of both matter and space-time." These tiny strings, "about 100 billion times smaller than a proton," vibrate each subatomic particle at a distinct frequency. They are part of a universal orchestra of vibrations.

Taking the longest view, Kaku considers the day long after our sun has died, when the universe will end and the only hope for sustaining intelligent life will be to use the energy we have learned to control by mastering hyperspace to escape to another universe.

Because I am not a physicist, I cannot scientifically assess Kaku's theories. But knowing physicists, I suspect that many will disagree with his non-mathematical summaries of theories they hold dear.

But "Hyperspace" is not really written for them. It is for lay people excited by the possibilities of these discoveries. They will appreciate Kaku's good nature, clarity and respect for his reader's imagination.