Inception is a complex sci-fi thriller that lies somewhere between a James Bond film and The Matrix. We've assembled a spoiler-free guide to the science of the movie, and all you need to know about dreams and the unconscious mind.
In Inception, Dom Cobb (Leonardo DiCaprio) is a dream snatcher. He's an industrial spy, who steals secrets when his victims are at their most defenceless: when they are asleep, and dreaming. But he has an even rarer ability, that of inception. He can plant an idea in someone's sleeping mind, and watch it grow and take root in reality. "The most resilient parasite is an idea," he says.
Is it possible to directly access someone's dreaming mind?
In the movie, the dream-snatchers use a drug called somnacin and a dream machine to upload a scenario into someone's sleeping mind. One or more of them then go to sleep themselves, hooked up to the machine, and enter the target's dream.
This fictional dream machine is called a Portable Automated Somnacin IntraVenous (PASIV) Device.
A device does already exist that can effectively read someone's mind. A functional MRI scanner takes snapshots of brain activity, and then the software recreates images of what the subject was looking at.
The researchers say it has the potential one day be able to record someone's dream - without the mess and danger (or the fun) of actually sharing that dream.
Using drugs like somnacin to access a sleeping mind is not possible, but there are drugs that can drastically modulate our sleep. These include modafinal, which can promote continuous wakefulness, and new classes of sleeping pills that can deliver "super sleep".
How can I control my dreams?
The easiest way to experience a lucid dream is to train yourself to ask, "Am I dreaming?" while you are asleep. Keen video gamers, probably because they focus on a single task for hours per day, are particularly good at lucid dreaming.
The dream team of Inception is highly trained at this, which may be why they are able to perform complex tasks - such as reading - which most normal lucid dreamers find difficult. Some of the characters in the movie have also militarised their dreamscapes, to protect themselves against the invasive dream snatchers.
Do dreams have to obey the laws of physics?
This is a fondly debated topic, and Inception has it both ways. Sometimes impossible things happen - in one dream Paris gets folded like a huge sheet of paper - and optical illusions become "real". The endless staircases created by M. C. Escher, for example, exist in Inception dreams thanks to a manipulation something like that occurring in 3D virtual environments.
However, the dreams follow some "real life" rules. As writer and producer Jeff Warren wrote about his own dream investigations:
Without sensory input, consciousness appears to behave in predictable ways. Informal laws can be deduced, for example, the "law of self-fulfilling expectations" (what you expect to happen will happen), the "law of narrative momentum" (linger too long in one place and the dream world begins to fray.
In Inception, the dream world "frays" when external influences from the real world intrude.
What is the function of dreams?
Freud thought that dreams expressed our repressed desires. And so they do, sometimes, but much modern research suggests that dreams help in information processing and memory storage.
Dreams occur in both rapid-eye movement (REM) sleep, and non-REM sleep. REM dreams are more story-like, with emotion and aggression, and non-REM dreams often involve friendly social interactions. People with depression often experience more REM sleep than non-depressed people.
How does subjective time pass in a dream?
In Inception, dream time runs much slower than real time, and there is a scaling effect, such that if you dream within a dream, time passes even more slowly. So 5 minutes of real time equals 1 hour of dream time, a 5-minute dream inside a dream equals one week of real time, and so on.
This is perhaps the cleverest part of the movie, but though intuitively pleasing, there is little evidence for it. In fact there is some evidence that in lucid dreams, at least, the perception of time in similar to that when the dreamer is awake.
A more pressing question for researchers is what happens when our brain's time perception goes faulty. In fact, the illusion of time may be created by the brain itself, which is at least as much of a head-scratcher as the plot of Inception.