The Ship of Theseus is an ancient philosophical problem to get you thinking about what identity means, and it goes like this. Theseus, the mythical king of Athens, took on the Minotaur while renovating his ship one piece at a time. After a while, he had completely repaired the ship with 

, clean sails, and fresh rigging. But was it the same ship or a different one entirely? And what if Theseus had one ship made out of all the new parts and built another ship with all the old parts? Which one would be the original ship?

The kings and queens of another fantastical world, though this time a contemporary one — 

 — are pondering a similar question, with the advent of medical technology that they hope will make them live for hundreds of years, and perhaps even forever.

"There are more than 140 biotech companies devoted to researching and reversing the effects of ageing..."

It might sound like the stuff of science fiction, but hundreds of millions of dollars are being poured into the rejuvenation and longevity businesses. In 2018 alone, investors sank $850m (£601m) into the industry, and this number continues to grow. According to one tally, there are more than 140 biotech companies devoted to researching and reversing the effects of ageing (one of them is even called Ship of Theseus, and looks into stem cell therapy).

Investors in this booming field include technology titans like Jeff Bezos and Peter Thiel, as well as Michael Greve, the German internet entrepreneur, and Steve Aoki, the American DJ and heir to the Benihana hibachi restaurant fortune. These big shots all hope that imminent scientific breakthroughs will be able to cure and prevent the diseases and disabilities of ageing, and keep them going for decades to come. Advocates of longevity research hope to perfect and tweak the processes that remove extracellular junk and make cancerous mutations harmless, preventing diseases that come with grey hair. They also say that, depending on your age, there is a decent chance that you — reading this article right now — will be one of the lucky humans who could live to blow out 500 birthday candles.

And so if Theseus were kicking around today, he might have been interested to mull over another question… if Bezos and Thiel replaced their organs with artificial ones, and had their veins transfused with younger blood, or connected their minds to a bespoke robot body, would they still be humans? Or would they be something else, perhaps, as the imagination suggests: unstoppable cyborgs with guns for hands and eyeballs that, instead of registering light, are sensitive to worker productivity?

Legendary stories about reversing the process of ageing — like the Fountain of Youth and the philosopher’s stone — are as old as time. Today, it’s worth noting the difference between genuine scientific endeavour and the misinformed habits of one-percenters.

Consider, for instance, the regimen of Jack Dorsey, the billionaire CEO of Twitter. He begins each day with a circuit of saunas and ice baths, gobbles what he says is “at lot” of vitamin C, and then works by the light of a near-infrared bulb, which — depending on who you believe — can either induce “full-body detoxification” or just damage your skin. During the week, the only food to pass Dorsey’s lips is a spartan dinner of protein and greens, with berries or chocolate for pudding, washed down with the occasional glass of red wine. From Friday until Sunday evening, he fasts, claiming it has improved his focus, sleep, and energy levels. Only in California could an expensive eating disorder pass for a wellness routine.

"It's worth noting the difference between genuine scientific endeavour and the misinformed habits of one-percenters..."

Then there’s Gwyneth Paltrow, purveyor of Goop’s “cleansing” yoni eggs — “$66 rocks to stick up your hoo-ha”, as one commenter observed, noting that these stones have no medical benefit, and are unlikely to be hygienic. There’s also Mark Wahlberg, of course, who wakes up at 2.30am, breakfasts at 3.15am, enters a cryo chamber at 9.30am, works in the afternoon, and goes to bed at 7.30pm. Grimes, the singer, once parodied these routines by claiming she spent her day sword fighting, engaging in screaming therapy and sensory deprivation, and benefiting from experimental surgery that removes blue light from her vision.

Rejuvenation experts have long battled against this nonsense. It’s why Dr Aubrey de Grey, the chief scientific officer for SENS Research Foundation, sports such a fantastic beard. When he started his rejuvenation work 15 years ago, speaking in front of sceptical audiences, he had to separate himself from all the perma-tanned hucksters shilling Goopian-like muff guff. “It was very advantageous to me that I look the way I do,” he tells 

, in between strokes of his Rasputin-grade facial hair. “It’s impossible to maintain the view that I could be in this for financial gain.”

After a decade and a half of convincing the scientific community about the possibilities of rejuvenation medicine, de Grey is now the big daddy in his field, and embodies the phrase misattributed to Gandhi: “First they ignore you, then they laugh at you, then they fight you, then you win.”

De Grey describes the human body like a car — it does itself damage over time, but, with savvy repairs, can keep functioning far beyond its warranty. He says that if we can reverse seven categories of physical damage done to the body by age — such as restoring tissue suppleness, replacing dud cells, and cleaning up their waste products — we could extend our lifespan by centuries. He has won financial backing from Peter Thiel as well as Vitalik Buterin, founder of the Ethereum cryptocurrency, and Michael Antonov, co-founder of the virtual reality company, Oculus. These Silicon Valley elites have become transfixed by the prospect of “longevity escape velocity”, a land where life expectancy extends longer than the passage of time.

De Grey describes the human body like a car — it does itself damage over time, but, with savvy repairs, can keep functioning far beyond its warranty...

While de Grey has made great progress in his efforts to convince the scientific world of regenerative medicine — his categories have become widely accepted — not everyone is so keen. This is what he calls the “pro-ageing trance”, an assumption that ageing is immutable and even desirable. Some of his rich backers have stopped writing cheques after their partners threatened divorce for wasting money.

“I’m afraid there are a couple of examples of very wealthy supporters who either have never given us any money, or abruptly stopped giving us money, and who have told me that it’s because their wife doesn’t want them to,” he says. Perhaps it was the prospect of being married off for eternity that put the partners off.

Critics of longevity medicine say it heralds a practical and ethical nightmare. Yuval Noah Harari, in his book 

, raises a few concerns. First: could a 500-year-old man or woman get so concerned about staying alive that they would be consumed by fear of death? Second: might the advent of eternal life create a gap between the rich who can afford it and the poor who can’t? Third: couldn’t dictators end up staying in power indefinitely, oppressing their citizens for centuries?

The pro-ageing trance gang tend to dismiss de Grey’s vision as the musings of a red-eyed teenager subsisting on a diet of weed and Asimov. But anyone who has endured the pain of losing a friend or relative knows grief provokes the intoxicating wish for a little more time with the one who died. Longer life is a worthy goal — if this medical technology exists and is within our grasp, it would be immoral to keep it from treating the debilitating, humiliating effects of ageing. One hundred thousand people die from old age every day and that should be reason enough to pursue de Grey’s research.

Beyond SENS, biotech companies are cooking up a load of exciting inventions to lengthen our lives. Take powered exoskeletons. Bioservo is a Swedish firm that makes wearable muscle strengthening systems, sort of like the pieces of a low-tech Iron Man suit that are nonetheless meant to increase grip strength, which deteriorates as we age. Older wearers could slip on a Bioservo Carbonhand glove that is connected to a power unit clipped onto a belt, and improve their grip.

On that note, a study in 2019 reported that a man paralysed after falling 40ft off a nightclub balcony was able to walk again using an experimental exoskeleton controlled by his brain. Remarkable footage showed the French man named only as Thibault, who is tetraplegic, taking his first steps in years thanks to recording devices implanted in his head. Those monitors read the part of his brain that controls motor function and relayed those signals to the exoskeleton and, amazingly, moved.

"When one plank decays, install a newer one and keep sailing..."

Biotech companies are also exploring whether vital organs might possibly be 3D-printed, or even grown in pigs that have been genetically altered to make their cells more human-like, so they can be safely transplanted. When one plank decays, install a newer one and keep sailing.

Some of the companies in this space, such as Google’s Calico (California Life Company) are more than a little secretive. The $1.5bn (£1.1bn) research centre is tight-lipped about what it’s doing, beyond investigating ways to “harness advanced technologies to increase our understanding of the biology that controls lifespan”. This secrecy has done no favours to the other forms of longevity research like parabiosis, or injecting oneself with the blood of a younger human. Peter Thiel earned a reputation as a vampire after saying he found parabiosis “really interesting” as a personal health treatment. The Dracula label has stuck — unfairly in part, as parabiosis has long appeared to be a promising field.

"It might be the act of sucking the blood of younger patients that lends itself to unfavourable vampirish comparisons..."

Alexander Bogdanov, an eccentric Soviet physician, experimented with blood transfusion in the 1920s. Eleven procedures were said to have improved his eyesight and energy, but the twelfth, taken from a donor stricken with malaria and tuberculosis, killed him.

It might be the act of sucking the blood of younger patients that lends itself to unfavourable vampirish comparisons. It also doesn’t help that one of the companies Thiel was reported to be interested in was Ambrosia, a beleaguered company that offers transfusions of plasma (the liquid component of blood, without the blood cells). Back in 2019, the US Food and Drug Administration warned customers about the lack of proven clinical benefits and potential safety risks of this type of treatment, leading Ambrosia to briefly close its doors. It has since reopened, and now sells a litre of plasma for $5,500.

Despite these associations, there is much excitement among the scientific community about what parabiosis might offer. Alkahest, a medicine research company, did a trial of Alzheimer’s patients and plasma, reporting an arrest in their expected mental decline. Elevian, another biotech firm, is researching the effects of GDF11 — a protein in plasma — on recovery in patients after strokes.

Such treatments, particularly those involving stem cells, attract support from the rich and the famous. Joe Rogan, the American podcaster and UFC commentator, has spoken highly of Dr Neil Riordan’s stem cell clinic in Panama, which offers injections beginning at $23,150 (£16,383) for adults. According to Rogan, his mother saw a drastic improvement on her damaged knee after receiving stem cell therapy — and she also looks younger. His fighter colleagues from UFC have also travelled to Panama for similar procedures.

The scientists of Silicon Valley are divided into two main schools. You’ve got “Healthspanners” who believe clever tweaks to the human body could add decades to life expectancy. Then you’ve got “Immortalists”, who have their own camps: Meat Puppets, like de Grey, and RoboCops, like Ray Kurzweil, the American author who predicts a merging of man and machine.

Elon Musk is a keen RoboCop, and hopes to one day achieve “symbiosis with artificial intelligence”. His Neuralink Corporation is experimenting with implantable brain-machine interfaces. Just last month Neuralink demonstrated how a monkey named Pager could play Pong using only the power of his mind. He was pretty good.

"In around 30 years, the technology will exist to make humans live forever...

Dr Ian Pearson, a Brit who has carved out what must be an enjoyable career as a futurologist, shares the grand RoboCop vision. He says that in around 30 years, the technology will exist to make humans live forever — or as he likes to joke, “death will no longer be a career problem”.

“Electronic immortality is possible by around 2050,” Pearson says, proclaiming there is a near future in which humans will be able to connect their brains to computers and achieve cloud-based immortality. “You could replace the body with an android — you can choose what that looks like, such as when you did when you were 25, or your favourite celebrity. You could link that to your mind, in the same way your mind was connected to your biological body before you died.”

He adds that because your mind, or similar aspect of consciousness, will be stored in the cloud, it might be possible for you to copy it as many times as you want and connect other versions of yourself into different android bodies. Imagine an army of Elon Musks: one running SpaceX, one developing underground trains, one assisting overseas rescue operations, one hosting 

Pearson’s excitement for this future world is charming, although a little harder to see coming any time soon. Besides Musk, there aren’t as many RoboCops as there are Meat Puppets, who boast an industry of large, well-funded firms operating at a fearsome clip. For instance, the 2045 Initiative, backed by the Russian billionaire RoboCop Dimitry Itskov, believes this type of artificial body tech will be ready within 24 years. And all this, despite having a website that’s so up to date, it still lists a conference event from 2013…

De Grey says he prefers the “boring, wet approach” to staying alive, adding that the cloud option is “a long way off”. Plus, “most of us rather enjoy being made out of meat,” he says.

Poor Theseus. Imagine what he’d make of it all: monkey brains hitched up to computers, humans walking aided by mechanically enhanced exoskeletons, organs harvested from pigs, and blood sucked out of the young to transfuse into our elders…After one look at the Silicon Valley rejuvenation industry, I bet he’d decide to get back in his ship and take his chances with the Minotaur.

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