When Klaus Sames' life comes to an end, there is one thing he is sure about. "I don't want to become a corpse," he says, now age 85.
He is looking to cryonics to prevent that. Scientists will replace his blood with a form of medical anti-freeze and cool his body to -196 degrees Celsius, using liquid nitrogen, in a procedure called cryopreservation.
Later, at some point possibly in the distant future, Sames is hoping he can be thawed, to re-enter the world at a time when fatal diseases are curable and ageing can be reversed.
Many doubt this will ever happen, however.
But Sames is a pioneer of cryonics in Germany, a gerontologist who carried out extensive research after his retirement.
He was once driven by the desire to abolish ageing - though he didn't manage that, he says. So he is now focusing on cryonics, in what he sees as a logical continuation of his work - though critics of the process say this is not the right way to think about life.
Cryopreservation has long been used for sperm, eggs and embryos but Stefan Schlatt, Professor of Reproductive Medicine at the University of Münster, says it is unrealistic to think that it would also work for organs or entire bodies as they are too complex.
"We are getting better and better at freezing, but there will be no magic solution," he says.
He also does not see this as desirable. "It's the wrong attitude towards life."
In his view, every living creature has an internal clock that begins to tick with sexual maturity. "It is extremely important for evolution that living beings die and make way for the next generation."
But people have been dreaming of eternal life ever since time began and it features in countless science fiction novels and films, with many based on the idea of people sleeping for decades or centuries then being awakened from a cryogenic sleep.
When cryopreservation first emerged in the 1960s, it was itself a kind of science fiction, says Sames. "Now we have come a long way." Nevertheless: "It still doesn't work," he admits.
So what drives him?
"Cryonics basically promises the fountain of youth," says Eckhard Nagel, a physician at the University of Bayreuth, in the southern German state of Bavaria.
"It's a way of compensating for the fear of dying and an expression of the inability to come to terms with one's own mortality."
But the idea is absurd, says Nagel. "Even if it were possible to treat the cause of a person's death in the future and it were actually possible to restore function to a body flooded with antifreeze, you would mostly just be awakening a lived body at the end of its natural existence to a life without prospects."
But Sames sees no alternative. "Death or cryonics," he says.
The prospect of a new life in the distant future is worth a great deal to him and he is paying $28,000 to the Cryonics Institute in the United States to have his body stored there, hanging upside down in a cooling tank.
The institute says it is already storing 250 people this way, and almost 2,000 more have contracts like Sames.
The other major US provider, Alcor, has similar figures, but charges $200,000. Both were founded in the 1970s and describe themselves as non-profit organizations.
The appeal is not confined to older people.
Many young people are also concerned with the questions of what comes next and whether life really has to end at some point.
Two years ago, the physician Emil Kendziorra founded the start-up Tomorrow Bio in Berlin, which offers cryopreservation in Europe.
Some 400 to 500 people have signed up for the service, including himself, he says. Most are between 30 and 50 years old.
The company has converted several ambulances into mobile treatment rooms. Ideally, he says, a team would be on site shortly before a person dies, says Kendziorra.
Once they are declared clinically dead, the cryopreservation process can start. People's bodies are stored in a facility in Switzerland.
The whole process costs €200,000, with the majority of €120,000 going to a foundation that invests the money to finance the storage of the bodies for an indefinite period, Kendziorra says.
Nagel dismisses this, comparing it to the sale of indulgences in the Middle Ages when the church exploited people's lack of information and deep fear of eternal torment in hell to persuade them to pay for merciful treatment in the afterlife.
"Cryonics is doing the same thing today. That has obviously lost none of its relevance, nor has its reprehensibility," he says.
Schlatt, a specialist in reproductive medicine, also says this raises ethical questions. "It's an incredibly disgusting way of making money, based on the hope of something that will never happen."
Kendziorra disagrees. "I could make more money elsewhere." He says the company's goal is to make cryopreservation cheaper - and it will become cheaper if more people choose this option, he says.
But he acknowledges that the whole process is fraught with uncertainty. "To a certain extent, you're betting on future technologies."
And he cannot deny that there are many unanswered questions and problems with the process and he is open about this with clients.
"I don't want anyone to decide on cryopreservation without being aware of the issues."
Sames and Kenzdiorra are hopeful about the progress being made in nanotechnology, though a great deal of research is still needed, says Sames.
One major obstacle is warming the body after cryopreservation without causing damage though promising methods are being developed, he says.
There is also a further, larger problem, namely ways to reverse the ageing process and associated pathological changes. It will certainly take another 200 years before medicine is ready, says Sames.