The average person will spend 50,000 hours of his life dreaming -- more than two hours a night, every night. For an activity that consumes so much of our time, however, scientists still don't completely understand why we dream or what dreams mean.

In this five-part series, "In Your Dreams," the Post-Gaztte provides the latest information and newest theories on dreaming. We talked to dozens of sleep researchers and dream experts from around the nation, as well as everyday people who are fascinated by the subject and keep track of their dreams in elaborate journals. Our goal: To shed as much light as we could on the mysteries of the night.

Day One: The Science of Dreams

Illustrations by Stacy Innerst, Post-Gazette

After centuries of research, scientists still can't explain why we dream or what our dreams mean, but they're learning more all the time. We know more about dreams, but not much Humanity shares its common dreams The 12 Universal Dreams Dreams and the arts: PG critics assemble their dream theme team Dreams: a decade-long journal provides insight A dream journal "how-to"

In 1953, a graduate student's experiment with his son opened the door to research about sleep patterns and their link to dreaming. After 50 years, the veil begins to lift Experts trying to awaken Pittsburgh interest in dream study Society strives to find middle ground between science, symbolism Dream Journal: Tara Deringor

Nightmares are common among children, who mostly grow out of them. But not everyone. Nearly 14 million American adults each night suffer recurring nightmares. Nightmares can be very, very scary One solution: Imagine a better ending Night terrors are rare, but normal for children Helping children cope with nightmares Resources: Learning more about nightmares Dream Journal: Jean-Jacques Sene

Normally our muscles are virtually paralyzed when we dream. But some people walk, talk, fight and even eat while sleeping. When dreams become a real-life nightmare Bloomfield woman never dreamed her problem was sleep eating Readers share their dreams Dream Journal: Jocelyn Hillen Dream Journal: Peter Baynes

Can you control your dreams? Those who believe it's possible have promoted the concept of "lucid dreaming." Others, however, wonder whether we're meant to control our dreams. 'Lucid' dreamers say they can learn skills, cure ills Resources for learning how to dream lucidly Lucid Dreams: A sample Dream Journal: Robert Brust Readers share more dreams The Dream Team: The Post-Gazette staffers behind the series