The Age of Spiritual Machines is no mere list of predictions but a framework for envisioning the 21st century in which one advance or invention leads inexorably to another. After establishing that technology is growing exponentially, Kurzweil forecasts that computers will exceed the memory capacity and computing speed of the human brain by 2020, with the other attributes of human intelligence not far behind. By that time paraplegics will be able to walk by using a combination of nerve stimulation and robotic devices.