Spacial dimensions

People assume the world is what our senses tell us. That the universe has 4 dimensions - three of space (up/down, left/right, forward/back as we know it) and one dimension of time.

This simple 4 dimensional universe doesn't jive that well with gravity however. Gravity is extremely weak compared to the other forces of nature which affect particles (aka the strong & weak nuclear forces and elctro-magnetism.) A number of theories which could potentially explain why gravity is so weak involved the idea that space has more than the 3 spacial dimensions that we know.

Forces are conveyed by particles. The photon is the conveyor of the electromagnetic force and the light that photographers are so grateful for :-) There is a theoretical force carrier particle for gravity called the graviton. It has yet to be observed in a lab or particle accelerator, but one theory says that the graviton, unlike the rest of the particles we know, isn't bound to the same spacial dimensions and literally floats off into other dimensions. This can explain it's weakness when compared to the other fundamental forces that particles are subject to.

Other theories like string theory say that there are up to 9 or 11 spacial dimensions, but unlike the 3 that we "inhabit," these extra dimensions are all twisted and curled up. Particles are actually strings of energy that vibrate through these dimensions and their vibrational patterns determine what they are (photon, quark, neutrino, etc.)

If this fascinates you but you are scared that it gets too complex too fast I strongly recommend reading Brain Greene's book Elegant Universe. It explains Einstein's theories and work and string theory in very clear, non-physicist language with many metaphors and examples. I it is a great book that will definitely open your mind to more of the universe than you probably realized was there.

Elegant Universe was also made into a NOVA program that is viewable on-line: www.pbs.org/wgbh/nova/elegant/program.html