The second bridge is about bio-engineering and how we will soon be able to grow a new heart in situ, or be vaccinated against diseases that kill millions of people, such as cancer.

The third bridge is where we step into more familiar Kurzweil territory: it is about the benefits of technologies such as nanobots, strong artificial intelligence and full-immersion virtual reality...

When we cross the third bridge, [Kurzweil] says, nanobots will replace our digestive systems. We will dispense with our heart and replace it with nanobots that shuffle oxygen and carbon dioxide around our bodies.We hope that Kurzweil and Grossman are right, and that effective anti-senescence treatments will be available to all at modest prices in the not too distant future (hopefully soon enough for you and me).

Through the convergence of biotechnology, genomics, and nanotechnology, it seems very likely that the process of human aging will undergo a fundamental transformation sometime in the next few decades.

In the real world, however, development of benefits to slow, stop, prevent, or reverse aging depends not only on progress in medical labs, but more critically on our success in managing the earlier stages of nanotechnology.

Could public debate over the social, environmental, geopolitical, and economic impacts of advanced nanotechnology hinder or disrupt the availability of aging ameliorative nanomedicine? Or worse, could unwise policy -- or lack of policy -- result in conditions so disastrous that such research will no longer be performed?