In the 2010 film Inception, Dom Cobb leads a team of corporate spies who infiltrate the dreams of wealthy executives to extract company secrets (about emerging products, trading strategies, business data, etc.) for their competitors and give them a strategic advantage. They use “shared dreaming” to be able to enter a dreamer’s world and interact with the “reality” of the dream. Of course, the dreamer’s world is often bizarre, unpredictable, and nonlinear in nature!
He is approached by Saito, portrayed by Ken Watanabe, with a unique proposition: instead of extracting information, he wants Cobb to perform inception on a competitor’s heir, Robert Fischer Jr., to plant an idea in his mind that would ultimately dismantle his father’s powerful empire.
The concept of subconscious security comes into play when Cobb and his team attempt to infiltrate Fischer’s mind on multiple dream layers. The deeper they go into the subconscious, the more they encounter security measures that protect Fischer’s mind from foreign invaders, like Cobb’s team.
The rules of the “real world” don’t always apply, and often gravity, time, other properties of physics and rationality are warped and distorted. In order to be able to navigate this world, Dom Cobb and his “crew” must be able to deal with lack of predictability. In addition, there can be multiple layers of dreams (“dreams within a dream”) where time progresses more slowly in the “deeper” dreams that they do in the “upper” levels of dreaming. So, an hour in one dream would seem like minutes in another, etc.
A totem, in the context of the movie, is a unique personal object that an individual uses to determine whether they are in a dream or reality. For Cobb, his totem is the spinning top. In reality, the top will eventually lose momentum and topple over due to gravity. When Cobb is in a dream, the top will continue spinning indefinitely without falling. By observing the behavior of the spinning top, Cobb can determine whether he is in his own reality or trapped in a dream.