Does the Mayan calendar predict that the world will end in 2012?

There are a number of theories that claim that the world
will end in December of next year.  They have sprung up, generally speaking, because of
the calendar system used by the Maya.

The Maya's calendar
system was based on three different calendars.  There was a sacred calendar of 260
days.  There was a solar calendar that had 365 days.  Finally, there was a "Long
Count."  This was based on the idea of 52 year cycles because the other two calendars
combine to make a cycle that repeats every 52 years.  Included in this idea of the long
count was the idea that they were living in a period that had begun in roughly 3100 BC
and would go for about 5125 years.  That period runs out next
year.

Some people say that this meant that the Maya thought
the world would end when that period ran out.  Others (see National Geographic link
below) argue that this is not that much different than the changing from the 1990s to
the 2000s -- it's just the start of a new cycle.

People now
worry that the world will end next year because of this, but it seems kind of strange
because by this calendar, the world only began in 3100 BC.  So I don't really see why
people believe that the world will end by this Long Count when it clearly didn't begin
when the Long Count said it did.