Kurzweil predicts machines with human-level intelligence will be available from affordable computing devices within a couple of decades, revolutionizing most aspects of life.

He says nanotechnology will augment our bodies and cure cancer even as humans connect to computers via direct neural interfaces or live full-time in virtual reality.

Reviewers appreciated Kurzweil's track record with predictions, his ability to extrapolate technology trends, and his clear explanations.

Searle deploys a variant of his well-known Chinese room argument, this time tailored to computers playing chess, a topic Kurzweil covers.

[2] Critics say predictions from his previous book The Age of Intelligent Machines "have largely come true"[3] and "anticipated with uncanny accuracy most of the key computer developments"[4] of the 1990s.

Today Ray Kurzweil works at Google where he is attempting to "create a truly useful AI [artificial intelligence] that will make all of us smarter".

[5] Kurzweil opens by explaining that the frequency of universe-wide events has been slowing down since the Big Bang while evolution has been reaching important milestones at an ever-increasing pace.

[10] Kurzweil defines the spiritual experience as "a feeling of transcending one's everyday physical and mortal bounds to sense a deeper reality".

The emergent techniques, neural nets and genetic algorithms, require significant training effort above and beyond creating the initial machinery.

Kurzweil says this trend will continue and that the technology will advance from macroscopic implants, to cellular sized insertions, and finally to nanotechnology.

Kurzweil admits that nanotechnology carries a big risk; a self-replicating substance, without the constraints of a living organism, might grow out of control and consume everything.

However he points out that today there are already technologies which pose grave risks, for example nuclear power or weapons, and we have managed to keep them relatively safe, so he feels we can probably do the same with nanotechnology.

[22] Kurzweil explains that in 1999 computers are essential to most facets of life, yet he predicts no major disruption related to the then-pending Y2K problem.

As examples Kurzweil cites computer-generated or assisted music, and tools for the automatic or semi-automatic production of literature or poetry.

For example, when discussing the year 2009 he makes many separate predictions related to computer hardware, education, people with disabilities, communication, business and economics, politics and society, the arts, warfare, health and medicine, and philosophy.

Kurzweil predicts life expectancy will rise to "over one hundred" by 2019, to 120 by 2029, and will be indefinitely long by 2099 as humans and computers will have merged.

[25] The book features a series of sometimes humorous dialogs between an initially unnamed character, later revealed to be a young woman named Molly, and the author.

For most of the book she serves as proxy for the reader, asking the author for clarification, challenging him, or otherwise eliciting additional commentary about the current chapter.

There is disagreement about whether the universe will end in a big crunch or a long slow expansion, Kurzweil says the answer is still up in the air because intelligence will ultimately make the decision.

[29] Kurzweil uses Deep Blue, the IBM computer that beat the world chess champion in 1997,[30] as an example of fledgling machine intelligence.

Searle argues that while Kasparov was "quite literally, playing chess" the computer in contrast was doing "nothing remotely like it;" instead, it was merely manipulating "a bunch of meaningless symbols".

[31] Colin McGinn, an author and philosophy professor at the University of Miami, wrote in The New York Times that machines might eventually exhibit external behavior at a human-level, but it would be impossible to know if they have an "inner subjective experience" as people do.

McGinn is skeptical of the Turing test, claiming it smacks of the long-abandoned doctrine of behaviorism, and agreeing with the validity of Searle's "quite devastating" Chinese room argument.

[32] McGinn says The Age of Spiritual Machines is "detailed, thoughtful, clearly explained and attractively written" as well as having "an engaging discussion of the future of virtual sex" and that the book is for "anyone who wonders where human technology is going next".

[32] However, Diane Proudfoot, philosophy professor at the University of Canterbury, wrote in Science that Kurzweil's historical details are inaccurate and his philosophical understanding is flawed and that these transgressions inspired "little confidence in his imaginings about the future".

[4] Jim Bencivenga, staff writer for The Christian Science Monitor, says Kurzweil "possesses a highly refined and precise ability to think exponentially about technology over time".

[35] On October 29, 2021, Our Lady Peace released a sequel album, Spiritual Machines 2, as an NFT that was made available on January 28, 2022, in traditional formats.