Max More runs Alcor, an American company which, in exchange for $200,000, will store your corpse in liquid nitrogen until the science exists to revive you. Tim Cannon is a computer programmer who implanted a device the size of a pack of cards into his arm, without the aid of anaesthetics. Zoltan Istvan recently ran for US president and publicised his campaign by driving across the country in a huge vehicle modified to look like a coffin.

These are among the unusual individuals Mark O’Connell interviews in his travelogue-style exploration of transhumanism, the movement that campaigns for the direct incorporation of technology into our bodies and minds, and strives to remove ageing as a cause of death. “What are my chances, would you say, of living to a thousand?” the author asks Aubrey de Grey, an established figure in this strange world: “I would say perhaps a little better than fifty-fifty,” is the serious reply. “It’s very much dependent on the level of funding.”

O’Connell is a highly sceptical observer, sometimes horrified and often amused, but offers reminders that this is not a simple tale of eccentrics and the freaky fringe. Some very rich and influential people dabble in aspects of transhumanism, and his series of reports, taken together, provide a commentary on the (at times) sinister and (always) hubristic faith in technology radiating outwards from Silicon Valley. The PayPal cofounder, Facebook investor and Trump backer Peter Thiel, for instance, is well known for pumping millions into “the cause of vastly extending human life spans, in particular his own”. O’Connell quotes Thiel’s belief that computational power will be brought increasingly to bear on the domain of biology, permitting us to “reverse all human ailments in the same way that we can fix the bugs of a computer program … Death will eventually be reduced from a mystery to a solvable problem.”

Google’s head of engineering, Ray Kurzweil, inventor extraordinaire and popper of 150 pills a day (vitamins mostly), has predicted that if he can live to 120, he will live forever – presuming a rapid increase of knowledge about how to restore an ageing body’s molecular and cellular structure. He is also the prophet of the “Technological Singularity”, the moment when AI will usher in, to use O’Connell’s words, a “new human dispensation, a merger of people and machines”. (It is supposed to happen in a dozen years or so.) For Kurzweil, the “Singularity will allow us to transcend” the “limitations of our biological bodies and brains. We will gain power over our fates. Our mortality will be in our own hands.” Google has invested hundreds of millions into anti-ageing research, including its biotech outfit Calico (California Life Company) – which is too secretive to let journalists, including O’Connell, anywhere near.

Conversational and approachable, To Be a Machine is an attempt to understand the transhumanist movement on its own terms

Plenty of other tech billionaires – among them Elon Musk, Steve Wozniak, Dmitry Itskov – are mentioned in To Be a Machine, as the author investigates the mindset of west coast “radical optimism”, as part of which every difficulty, even getting old and dying, has a technical solution. Your body has failed? Not a problem: we’ll upload your mind! Tricky questions surrounding who gets selected or the nature of consciousness are pushed to one side. O’Connell writes of a “narcissistic fantasy of heroism and control – a grandiose delusion, on the part of computer programmers and tech entrepreneurs and other cloistered egomaniacal geeks, that the fate of the species lay in their hands”.

Aside from the billionaire techno-utopians, serious funding for human augmentation comes from the US government, in the form of Darpa: the Defense Advanced Research Projects Agency, set up in the golden age of the space race. O’Connell attends a cheerful Darpa showcase, in which robots fall about in slapstick fashion failing to overcome obstacles. But, as he realises, behind the agency’s seemingly pure pursuit of technological advance has always lurked “an interest in the methodology of efficient violence”.

To Be a Machine is an attempt, nonetheless, to understand the transhumanist movement on its own terms; it’s a conversational, approachable book, resembling a set of magazine articles skilfully bonded together. Even the more ridiculous of O’Connell’s subjects – such as Roen Horn, founder of the Eternal Life Fan Club, who does his best to avoid calories and is a virgin saving himself for sexbots (a “real girl could cheat on you, sleep around. You could get an STD”) – largely escape his condescension. Istvan, De Grey and the others have all been written up before, but O’Connell, in embarking on a longer quest, is able to draw out similarities in the lives of many of his believers, including libertarian politics and an unsurprising early interest in science fiction novels.

A detail from The Fountain of Youth, 1546, by Lucas Cranach the Elder.

The shared vocabulary is also striking, especially the frequent software metaphors, and the dismissive description of human bodies as mere “meat”, with the brain as “wetware”. “People really suck at decisions,” Cannon argues. “The hardware we do have is really great for, you know, cracking open skulls on the African savannah, but not much use for the world we live in now.” Prominent within O’Connell’s thinking is the idea that transhumanism, in its rejection of the body and embrace of a kind of spirit, has much in common with religions. It is no coincidence that Horn’s parents, with whom he still lives, turn out to be “devout Calvinists who believed in eternal life in paradise for the elect”.

It’s O’Connell’s lack of stridency, as well as his often splendid writing, that makes him such a companionable guide. He brings out the bathos of visiting Alcor, on an industrial estate in Arizona, with its so-called “patient care bay” full of severed heads kept upside down in Perspex containers, and stainless steel corpse-filled cylinders, like gigantic vacuum flasks. When More, showing him around, mentions that the first human to be cryopreserved is housed at the facility, a man born in 1893, and claims that this makes him “the world’s oldest living person”, O’Connell gently suggests that it is “a bit of a stretch to call him living”. The warehouse seems to the author a “mausoleum … of modern delusions”, a dark twist on a very American idea of the endless possibilities of individual betterment.

It turns out that “turn-on, tune-in, drop-out” acid guru Timothy Leary was a long-standing advocate of life extension and a supporter of Alcor, to the point of hosting its annual turkey roast. But, as O’Connell notes, “when the time came to make the necessary arrangements, he went for the more show-stopping option of having his cremated ashes shot into space from a cannon”. It’s still a sore point within the cryonics community – Leary’s decision has been criticised as a capitulation to “deathist” ideology.

O’Connell expresses little desire to go gonzo and insert implants under his skin like the Pittsburgh-based biohacker and recovered alcoholic Cannon. It’s alarming enough for the author to be a fixture in the passenger seat of Istvan’s touring RV, which is prone to overheating and which has failing brakes, not to mention a driver who, despite his determination to outwit death, is surprisingly reckless behind the wheel. As they hurtle down mountain roads in New Mexico, O’Connell faces the unedifying irony of meeting his end strapped inside the “Immortality Bus”.

To Be a Machine implicitly recognises that there is a vast, less extreme territory of bodily enhancement to be navigated – involving smart drugs, wearable technologies and other small steps towards bioengineered “post-humans”. But O’Connell chooses to zero in on the transhumanists’ desperation to escape what one biohacker refers to as “miserable biological lives”. With the help of anecdotes about his very young son, he signals his contrasting belief that our animal, fallible, bodily nature is the essence of being human. And isn’t it the very fact that we are here for so brief a time, he writes, that makes “life so intensely beautiful and terrifying and strange?” The privileged white male gods of Silicon Valley are obsessed with their own mortality, but is “dying of old age not … the ultimate First World Problem?”

One of Thiel’s current health interests is reportedly the process of putting young blood into older mice, which has had “a massive rejuvenating effect”, though there is no evidence that the venture capitalist has ever received “parabiosis” treatments himself. In 1492 the gravely ill Pope Innocent VIII is said to have drunk the blood of three healthy 10-year-old boys whose youth and vigour, it was believed, he could absorb. According to the story, the boys all died, and so did the pope: not even his God could save him.

• To Be a Machine is published by Granta. To order a copy for £11.40 (RRP £12.99) go to bookshop.theguardian.com or call 0330 333 6846.