Most Americans, myself included, are not getting enough sleep. Maybe your job demands too much time, maybe your back hurts sometimes for no apparent reason like mine does. Maybe you're too worried at night to sleep. What is sleep? Why is it important? And can we somehow do it in less time?
All animals with a brain need to sleep. Kind of. Fish sleep by entering a semi-conscious daze, the kind a human being experiences when being shown a really boring slide show. If a danger emerges, the fish will swim away fully awake, but the fish can't really concentrate on details like the presence or absence of food, react to mates, or tell you what color this rock is. (Although the last one cannot be done by the fish when it is fully awake, because fish cannot talk. And are kind of stupid.)
So all animals need to sleep, despite this being a glaring obvious weakness in both predator and prey. Predators lose track of prey when they sleep, and prey are easily eaten if they are discovered. Nonetheless, a brain stops working correctly in a state of sleep deprivation. We humans are not an exception just because we invented civilization and changed the very face of the planet. No, not even to land that sweet, sweet, million dollar deal. You must sleep. Even dolphins, who would drown if they stopped swimming, have developed an elaborate system of being able to sleep one half of their brain at any given time just to make sure they can. Sleep is that important.
While awake, our brains have a particular pattern of electrical energy, the beta wave. If we get drowsy or meditate, we get a different pattern, the alpha wave. In an alpha-wave state, you are relaxed, but suggestible. Should you go to sleep, your brain wave will slowly shift to a third pattern, the theta, then to a slower pattern, the delta. Your brain shifts around its information, cutting its useless connections, strengthening the useful ones, and storing important memories in long term memory. This cycle lasts for a while, then it reverses. Your brainwaves speed up again until a beta-like pattern is achieved. But you are not awake at this point. You are paralyzed and dreaming. This happens seven or eight times per night, but you forget most of your dreams. They are not important. However, some studies say that your dreams can help you with the problems you face during the day. Russian cosmonauts take a nap if confronted by a frustrating problem, because it's easier to think of a solution while asleep. Video gamers note that if they game very heavily that day, the game will appear in their dreams.
In humans, sleep need actually decreases with age. Fetuses are basically nearly constantly asleep. An infant needs to sleep 16 hours per day, a child needs 9-10 hours, and most adults need 8. But we're not getting 8 hours of sleep, and in our groggy state suffering vehicle accidents, stupid behavior, crankiness, and incessant weight gain as the body figures that the lack of sleep indicates some kind of desperate emergency that it needs to preserve every calorie to survive. (Yes, your body is wrong about many things that go on in your daily life.)
So maybe sleep could be accelerated slightly. There's a theory of brainwave synchronization, in which listening to a tone matching your current brainwave would encourage your brain to follow the tone, which then slowly slides to the desired brainwave. You would put on a pair of headphones, lie down, and listen to the beta-wave tone. (Since you are awake and not meditating, your are almost assuredly in the beta wave.) As you relax, the tone starts to shift to theta, putting you to sleep. It slides down to delta, and your brain repairs itself. It slides a bit faster than you would change states naturally, encouraging your brain to work quickly. After a few REM cycles, it shifts to alpha and then beta to wake you back up.
I'm hoping this allows eight hours of sleep to be crammed into six, but find this dubious. There's no reason that the brain would necessarily follow a tone just because it heard it.