"It's not a miracle," said Dr Philipp Schiffer, "but it's kind of super-fascinating." A group of scientists in Russia had been examining a piece of soil from the Siberian permafrostAny ground that remains completely frozen for at least two years. Permafrost covers large regions of the Earth. . In it were two little roundworms which, when it thawed, came back to life. The scientists then set about finding out how old the soil was through carbon datingA method of finding out how old an object is by examining the carbon inside it. . The result: 46,000 years.

The worms had been able to shut down their bodies through a process called anabiosis, which brings the metabolismThe chemical processes within the body which produce energy. It derives from a Greek word meaning "change". to a halt so that the creature concerned goes into a deep sleep. Though some creatures, such as frogs, were already known to be capable of this, the limit was thought to be 40 years.

For those hoping to live for ever through cryonicsThe practice of freezing the bodies of people who have just died in the hope that future medical treatments will be able to save them. , the discovery was hugely encouraging. If worms could be preserved for so long and then revived, surely humans could too.

Cryonics, however, is far from simple. And Valeriya Udalova, the head of a Russian company which claims to be caring for 94 frozen bodies, sounds a note of caution: "I don't think that human metabolism can be radically restructured so that we also go into anabiosis like animals. It's probably easier to create new, artificial bodies."

The cryonics process has to begin within 15 minutes of the heart stopping. First the body is packed in ice and injected with chemicals to stop the blood from clotting. It is then cooled to just above OC and the blood is replaced with a solution to preserve the organs.

Another solution is injected to stop ice crystals forming. Then the body is cooled to -130C. Finally, it is stored in a tank of liquid nitrogen at -196C.

The idea is to keep it there until science has advanced sufficiently to repair cells and tissues damaged during the freezing process and cure the body of whatever the person died from.

But there is an intense debate about whether cryonics should be seen as a respectable science. Writing in MIT Technology Review, Professor Michael Hendrick describes its promises as "snake oilA term used to describe a product which claims to help your health, but for which there is no evidence. It roughly means "a scam". ".

Every brain is so complex and so different, he explains, that restoring the connections within one - or reproducing them via a computer - would be incredibly difficult. The technology to do so does not yet exist "even in principle".

Even if it did, the result would be "a new person who is like you but whose conscious experience you don't have access to".

Another leading scientist, Professor Martin Rees, calls the claims of cryonics ridiculous:¹ "In my view it is most unlikely that this is feasible - and even if it is, it should be discouraged."

But some of those within the industry claim that they are being unfairly stigmatisedTreat something in an unfairly disapproving way. . "For scientists who would like to discuss it open-mindedly, it tends to significantly hurt their career," says Dr Ramon Risco:² "in fact can potentially even get them kicked out of their scientific societies."

Unless people are afraid of the truth, he adds, "Why would you put barriers up?"

Yes: Science has made advances in recent decades that earlier generations could not have dreamed of. Now that the cryonics process is established there is every chance that problems will be ironed out.

No: There is no evidence whatsoever that cryonics could work. Organs like the heart have never been successfully frozen and thawed. It is even less likely a whole body could be without serious damage.

Or... Even if people could be brought back to life, it would be a terrible experience. They would find themselves in a completely unfamiliar world without friends or family to support them.