This is Ray Kurzweil's third book concerning the future of reductionist artificial intelligence design and it's possible effects on us in the decades yet to come. In THE AGE OF SPIRITUAL MACHINES, Kurzweil's previous book, which I enjoyed also, and this volume, he uses technological trends, including Moore's law and other tools, to show that a desktop computer will have achieved human level computational ability around the year 2020. Also, Kurzweil envisions that we will be able, sometime in the next few decades, to scan human brains and download that 'software' into these advanced computers to give them human level reasoning abilities, with the speed of computer neural nets, leaving humans behind, so to speak. Accordingly, it may also be possible to scan individual brains and load that information into an advanced computer (attached to a body of some kind), giving that person a sort of immortality. This is the gist of Kurzweil's argument, I hope I got it essentially correct.
What Kuzweil means by computers someday becoming 'spiritual' is that they may become conscious, and 'strong A.I.' is the view that "any computational process sufficiently capable of altering or organizing itself can produce consciousness." The first part of this book is an introduction to all of the above views by Kurzweil, followed by criticisms by four authors, followed in turn by Kurzweil as he refutes these criticisms.
Personally, I found most of the views expounded by the critics here to be either non-sensical, or 'beside the point'. One critic says that the life support functions of the brain cannot be separated from it's information processing function. Of course it can be, even the effects of hormones can be programmed into a downloaded brain, as well as other chemicals used by brains. Another critic states that possibly evolution is in error, and yet another criticism is that our machines will not be able to contact a divine entity and would thus be inferior.... give me a break, well...perhaps this is all true and maybe pigs will one day fly over the moon unassisted. I could go on and on, but this is the job of Ray Kurzweil and he defends himself admirably in the final chapters of this volume. Kurzweil does mention in this book that brain scanning machines are improving their resolution with each new generation, and eventually will reach a point where they should be able to image individual neurons and synapses in large areas, and allow the brain 'software' to be transferred to a suitable non-biological computing medium, my only criticism of Kurzweil here is that I think he should discuss this technology more, and where it is headed, his next book would be a great place for this.
One final point, it seems to me that when a new idea appears to be difficult and complicated to achieve, the pessimist says: "This is difficult and complicated, and may not work", whereas the optimist says: "This is difficult and complicated, but may work". Only time will tell for sure.