Three is the magic number, right? For most of our history, we've rested easy in the notion that there were three dimensions that have existed throughout time: length, width and height. Ah, the good old days. In the early 20th century, Hermann Minkowski and Albert Einstein connected our comfortable three dimensions with a fourth, time, defining special relativity using a spacetime continuum. This kind of worked, but still didn't explain a troublesome new theory of gravity called quantum mechanics that arose around the same time Minkowski and Einstein were working on their theories. Quantum mechanics had its own rules that contradicted the concepts behind the spacetime continuum. Scientists treated this incompatibility like the weather for decades, discussing it but not really doing anything about it. Who doesn't love (multidimensional) donuts? While higher theoretical dimensions began with Descartes in the 1600s, in the 1970s string theory expanded on this idea as physicists attempted to tie everything together in one elegant explanation of the universe. Variations of string theory require the existence of up to eleven dimensions and a slew of universes, with our universe forming a threedimensional membrane floating around some higherdimensional donut. According to this theory, each point in space has six higher dimensions wrapped up in supertiny geometries called CalibiYau Manifolds. One recent string theory suggests that the reason we only experience the three spatial dimensions is that all universes with higher dimensions got into some cosmic car accident and destroyed each other, leaving our measly threedimensional "brane" untouched. Who to believe? Seeing is believing, right? The problem is that so far it's all speculation without producing anything testable and these concepts are impossible for anyone to visualize. Given string theory's potential for explaining everything (literally), it's been given a lot of scientific leeway regarding the usual need for proof. That's beginning to change as some lose patience with the lack of evidence. But barring a better contender, string theory is still the favorite horse in the race. Everyone's Got a Theory Physicists aren't the only people trying to define additional dimensions. In 1975, mathematician Benoit Mandelbrot tied together, without strings, the work of a bunch of other mathematicians of the past several centuries when he introduced the wider world to fractals. Fractal equations and their elaborate visual representations can have any of an infinite number of fractional dimensions between zero and three. Tesseracts, another mathematical creation, carry the cube beyond three dimensions to a fourth spatial dimension. How do you wrap your head around these things, though? Even time, which we experience, cannot be represented physically. We can measure it, but not draw it. Edwin A. Abbott's classic book "Flatland," published in 1884, offers one way of thinking about unfamiliar dimensions by populating a twodimensional world with flat characters and describing how they react when characters from a third dimension interact with it. To answer the original question, it seems very likely that there are more than three dimensions. Defining them, however, is a matter of some debate. If nothing else, know that the next time you hear voices in your head, you're probably not going insane. An intelligent tesseract is just saying hello.

<a href="http://science.discovery.com/" title="[field_story_urltitle]">Science Channel</a>