Reality Check: Could cryopreservation work?
The Claim: A person's body can be preserved after death and revived in the future when scientific developments allow it.
Reality Check Verdict: It is very difficult in the sphere of science to say something can never happen. At the moment, there is no evidence to suggest reviving someone after a long period of being preserved at low temperatures will work. Our current medical capability certainly wouldn't allow for it. We can't know whether future technology will develop to this point.
The idea that you can preserve your body after death, in the hope that you may be revived at some point in the future has come to the fore following a historic court case.
A 14-year-old girl with terminal cancer won the right to have her body cryopreserved. She wrote a letter to the court, saying: "I think being cryopreserved gives me a chance to be cured and woken up - even in hundreds of years' time."
Cryonics involves cooling a recently deceased person to temperatures of around -120C to preserve their body until science develops to the point that we may be able to repair or replace tissues and revive them.
The deceased person's blood is drained and replaced with preservatives and medical-grade antifreeze, which prevents ice crystals from forming in the body and damaging the tissues.
If this is done immediately after the heart stops beating and while the tissues are still intact, the idea is that doctors and scientists of the future will have the best chance of success.
But can your body really be shut down, put into storage, and then brought back to life?
There is no hard evidence at the moment to say you can, but it is difficult for experts to say you definitely cannot - in theory, anything may happen with the development of technology.
Supporters of the process say the current concerns - that a body preserved for many years or decades and pumped with chemicals will be irreparably damaged - can be put aside because advances in nanotechnology will mean cells can be repaired by tiny machines.
We don't know what scientific advances the future may bring and so we can't categorically write that off.
Typing in the term "cryonics" into a major medical journal search engine throws up 16 papers - a very modest body of research. Around half of these discuss the ethical questions around the idea of cryonics, not its actual feasibility.
There are no proper trials indicating anyone could expect human tissue subjected to this process to be functional.
There has been some success with small organisms and animal organs, however.
Cryopreservation is already used in hospitals up and down the country to preserve simpler tissues, such as sperm, eggs, blood cells and embryos, which are all preserved using this technology.
But there is a high failure rate - many embryos that are preserved in this way, for example for use in fertility treatment, do not survive. When you are talking about a whole human body, the complexity is far greater, and the chance of all of the vital tissues surviving is lower.
The human body has a huge number of different and interdependent systems that rely on each other for us to live. It could turn out that some tissue makes it but other vital tissues, say more delicate organs like the kidneys, do not.
And the brain, the organ that people are most keen to preserve, is probably one of the most fragile and complex structures of them all.
Cooling technology is also used in other areas of medicine, but with significant limitations.
The preservation of human tissues, including organs for donation, involves cooling them down very quickly. Organs can then be preserved, warmed up after a period of hours and resume their normal function.
However, doctors are keen to stress this happens over a matter of hours. Any longer and it is very likely that tissue damage would occur. We do not have any evidence to suggest that tissue could be preserved through cooling over long periods of time. At the moment, we cannot freeze organs or preserve them long-term and so it is a big leap to think of preserving entire bodies.
Similarly, there are some forms of surgery, particularly on veins and arteries, that require a person's heart to be stopped temporarily. To prevent brain damage or other damage to the tissues, the patient is cooled to around 18C and packed with ice.
According to one anaesthetist, a surgeon then has between an hour and an hour-and-a-half before the patient starts to experience serious drops in the recovery of brain function.
In bodies that have been preserved in the long term, there is likely to be a significant amount of cell damage.
Ralph Merkle, a key supporter of the practice who sits on the board of directors of a cryonics facility in America, said in a paper in 1992: "The process of freezing inflicts a level of damage which cannot be reversed by current medical technology." He hypothesised that this damage may be reversible by future technology.
People working in this area do not make any guarantees. They are clear that they are gambling on a hope - although, they feel, a reasonable one - that science will make reviving preserved bodies possible.
It is an optimism shared by three Oxford University academics who decided to take a punt at cryopreservation in 2013, reasoning that it is worth it if it works, even if the chances are small.
But Prof Clive Coen, professor of neuroscience at King's College London, said: "Despite the claims made by cryonics companies, they've failed to demonstrate that the extraordinary mass of tissue that constitutes the human brain can be protected by the antifreeze that they try to pump through the body after death.
"Cryonics is based on wishful thinking rather than evidence."