What's more murky is the idea of dream-sharing -- that several people can engage in the same subconscious experience. While groups of dream sharers exist, evidence of dream sharing is more anecdotal than evidential.
"You'll find it in mystical works going back thousands of years," said Dr. Matthew Edlund, author of "The Power of Rest." "You'll find in some cultures that priests are thought to be able to enter into people's dreams, like a Shaman can enter into a sick person's dream and help them with their illness."
That said, it's not unheard-of to dream the same dream as someone else.
"The psychologist Carl Jung felt, and writes about this, that people's psyches are not contained and that we dream each other's dreams," said Gary Toub, director of training at the C.G. Jung Institute of Colorado. "So a husband and wife could have each other's dreams. There's some kind of fluidity in the unconscious."
The bottom line: an army of subconscious spies and thieves like Cobb and his cronies won't come together anytime soon. But what fans of "Inception" can take away from the movie is that dreams are crucial to creativity. It's little surprise that Nolan, who directed the thrilling tangle of "Memento" and the epic Batman film "The Dark Knight," says he came up with this summer's most think-outside-the-box movie while he was dreaming.
"In dreams normally, you're remaking the brain," Edlund said. "You're taking old memories and putting them together with what happened in the last 24 hours. And as we rebuild our brains at night, we create new ideas, we create creativity."
Deirdre Leigh Barrett, professor of psychology at Harvard Medical School, offered the following tips -- known as "incubation" instructions -- for people who want to use their dreams to solve problems and increase their creativity:
Psychologists have developed incubation rituals to encourage problem-solving dreams. These usually target interpersonal and emotional problems, but they are also relevant to objective creative tasks. Incubation instructions usually include:
1) Write down the problem as a brief phrase of a sentence and place this by the bed.
2) Review the problem for a few minutes just before going to bed.
3) Once in bed, visualize the problem as concrete image if it lends itself to this.
4) Tell yourself you want to dream about the problem just as you is drifting off to sleep.
5) Keep a pen and paper -- perhaps also a flashlight or pen with a lit tip -- on the night table.
6) Upon awakening, lie quietly before getting out of bed. Note whether there is any trace of a recalled dream and invite more of the dream to return if possible. Write it down.
Sometimes the incubation also involves:
7) At bedtime, visualize yourself dreaming about the problem, awakening, and writing on the bedside note pad.
8) Arrange objects connected to the problem on the night table or on the wall across from bed if they lend themselves to a poster.