When it comes to alternative realities, Virtual Reality is as good as it gets. But although Virtual Reality is likely to be widely used in the near future, its limitations are already clear. The problem is that it is exactly that - virtual. Running around the living room with a headset on is never going to be the same as climbing Mt Everest, though it could be almost as dangerous. No pressure suit will ever be able to match the richness of touch our bodies can sense. And as for taste or smell . . . forget it!
In fact, implants which can feed sensory information directly into nerves are already being used. Cochlear implants convert sound into electrical signals which activate aural nerve fibres in the inner ear. This can restore hearing to some deaf people but it is far from perfect - it may take months for people who had these implants to learn to make sense of what they hear and even then it remains very crude. Speech sounds synthetic and music doesn't sound anything like music. This is because these implants only stimulate nerve fibres in a few places, whereas a normal ear has thousands of receptors.
Existing devices may be crude but they can make a big difference to people who would otherwise be completely deaf. Perhaps similar implants will be able to restore a measure of sight to blind people in the future. But will such devices ever give blind or deaf people sight or hearing which is comparable to that of everyone else? The problems are formidable.
Take the eye for example. The retina contains about 127 million receptor cells. There is some initial processing of information within the retina, so the optic nerve that carries visual information to the brain only contains about a million nerve cells. This means that an implant which provided normal vision would have to be connected to at least a million individual cells and capable of stimulating each one appropriately. This isn't even remotely possible yet.
You wouldn't be restricted to playing back your own experiences, although translating between the sexes could be tricky. Sportsmen and women could sell the rights to their experiences and allow them to be broadcast live during major events, enabling the audience to feel everything they feel. Instead of watching Linford Christie, you could be there on the track yourself, flying towards the finishing line. Not only would HyperReality have infinite possibilities for entertainment, it could be a very good educational tool. It could also be the first invention ever to seriously threaten the world's oldest profession!
The answer must be to stop people moving. This could be done by connecting to all the motor nerves leading from the brain to the muscles, and blocking the signals which tell the muscles to move. In other words, by causing complete temporary paralysis. But if people can't move then how do you measure their response? The only way to do it would be to determine what messages were being sent out to the muscles before blocking them, and then to use this information to work out how somebody would have moved, which is not as simple as it sounds.
For example, suppose someone is standing (in HyperReality) looking at the view and then turns around to see what is behind them. In reality the person is lying on their back not moving a muscle. So the thousands of nerve impulses being sent to hundreds of muscles would have to be redirected to some kind of computer system. This system would have to use this information to calculate exactly how their body would have moved if it had moved, and what sensations they would have experienced if they had moved in this way (that is, what they would see as they turned their heads, what they would feel their bodies doing, et cetera). All these calculations would have to be done in real-time and as anyone who has sat twiddling their thumbs whilst their computers struggle to cope with graphics files knows, this would require a lot more computing power than today's machines possess.
There's no reason why people interacting in hyper worlds should have to experience exactly the same environment. For example, from Tom's point of view, John might be sitting on the sofa in Tom's living room chatting away, whereas as far as John is concerned, they are both sitting outside in his garden. At a rock concert held in HyperReality, everyone could get a front-row seat - and even turn the volume down.
I do find this vision horrifying. But would it really be any worse than people spending their lives slumped in front of TVs or computers? At least HyperReality would engage all our senses and could allow us to give free rein to our creative impulses. It might actually encourage more human interaction, because people would always be in control and free from any physical danger. There is no need to worry about it though. HyperReality isn't likely become reality anytime soon.
Cause muscles to degenerate
Our brains and bodies have an amazing degree of plasticity. Muscles that aren't used at all waste away in a few days, joints seize up and bones become thinner. Connections between nerve cells are constantly formed and broken in our brain. For example, using your left instead of your right hand will cause cells in the corresponding area of the brain to develop more connections and even to expand into adjacent areas. What we do shapes our bodies and minds.
How their body would have moved
No two bodies are alike - the system would have to be capable of learning which nerve impulses lead to what movement in each individual.
Popular tourist sites
There are already plans to develop virtual tourism, to allow people to explore historic or cultural sites via the Net - even if the original buildings were destroyed hundreds of years ago. Check out Virtual Heritage for more info.
Some museums and galleries have already made pictures and information about their collections available on the Internet - the best of these is Le Webmuseum.
Relive it
While you might be able to experience every sensation, the actual enjoyment, the emotion you felt at the time would be missing, unless it is evoked by the sensations.
However it has been known for a some time that stimulating parts of the brain with an electrode can cause people to relive long forgotten events as they happened, warts and all.
For a fascinating account of this, read Part 3 of Oliver Sacks' The Man Who Mistook His Wife for a Hat
Some deaf people
Those who have damaged hair (receptor) cells, the cells which normally detect sound and activate the nerve fibres of the aural nerve. If the aural nerve is damaged, then cochlear implants are useless. But implants which can be inserted at the next point along the chain, where the aural nerve enters the brain, are being developed.
Stop people moving
To make people think they were moving, you'd have to send messages to the brain telling it that the body was moving, which means supplying it with the information normally detected by our sixth sense, proprioception. Proprioception tells you where your arms and legs are, whether or not you're upside down, and so on.
Translating between the sexes
Sensations from the nether regions would probably be discreetly censored in most cases. But there is a correspondence between the male and female sex organs (clitoris and penis, labia and testes), so it should be possible translate male sensation into female sensation or vica versa.
But would a man be able to experience what it is like to have a woman's body or vica versa?
I suspect not, because of the difference between sensation and perception. Perception is about making sense of sensations and involves the brain. We build up a mental picture of our bodies from experience, and this wouldn't be changed by a few unusual sensations. That is, a woman might experience the same sensations as a man but would perceive it to be happening to her female body.
However if people were prepared to remain in HyperReality and work at it for months or years, perhaps they could change the sex of their "mental bodies".