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amazing theory of loop quantum gravity

Scientific American

January 2004 issue


Atoms of Space and Time

We perceive space and time to be continuous, but if the amazing theory of
loop quantum gravity is correct, they actually come in discrete pieces
By Lee Smolin

Little more than 100 years ago most people--and most scientists--thought of
matter as continuous. Although since ancient times some philosophers and
scientists had speculated that if matter were broken up into small enough
bits, it might turn out to be made up of very tiny atoms, few thought the
existence of atoms could ever be proved. Today we have imaged individual
atoms and have studied the particles that compose them. The granularity of
matter is old news.

In recent decades, physicists and mathematicians have asked if space is 
made of discrete pieces. Is it continuous, as we learn in school, or is it
more like a piece of cloth, woven out of individual fibers? If we could
probe to size scales that were small enough, would we see "atoms" of space,
irreducible pieces of volume that cannot be broken into anything smaller?
And what about time: Does nature change continuously, or does the world
evolve in series of very tiny steps, acting more like a digital computer?

...continued at Scientific American Digital (subcription required)
or in the print edition on newsstands now.