Various snippets taken from Wikipedia:

Cryonics is the low-temperature preservation of humans and other animals that can no longer be sustained by contemporary medicine until resuscitation may be possible in the future. The rationale for cryonics is that the process may be reversible in the future if performed soon enough, and that cryopreserved people are not dead by the modern information-theoretic definition of death.

Information-theoretic death is the destruction of the human brain, and information within it, to such an extent that recovery of the original mind and person that occupied the brain is theoretically impossible by any physical means. The concept of information-theoretic death arose in the 1990s in response to the problem that as medical technology advances, conditions previously considered to be death, such as cardiac arrest, become reversible and are no longer considered to be death. In particular, the prospect of brain repair using molecular nanotechnology raises the possibility that medicine might someday be able to resuscitate patients even hours after the heart stops. The term "information-theoretic" is used in the sense of information theory.

Information-theoretic death is intended to mean death that is absolutely irreversible by any technology, as distinct from clinical death and legal death, which denote limitations to contextually-available medical care rather than the true theoretical limits of human survival. The paper Molecular Repair of the Brain [1] by Ralph Merkle defined information-theoretic death as follows:

A person is dead according to the information-theoretic criterion if their memories, personality, hopes, dreams, etc. have been destroyed in the information-theoretic sense. That is, if the structures in the brain that encode memory and personality have been so disrupted that it is no longer possible in principle to restore them to an appropriate functional state then the person is dead. If the structures that encode memory and personality are sufficiently intact that inference of the memory and personality are feasible in principle, and therefore restoration to an appropriate functional state is likewise feasible in principle, then the person is not dead.

The exact timing of information-theoretic death is currently unknown. It has been speculated to occur gradually after several hours of clinical death at room temperature as the brain undergoes autolysis. It can also occur if there is no blood flow to the brain during life support, leading to the decomposition stage of brain death, or during the progression of degenerative brain diseases that cause extensive loss of brain structure.

Information-theoretic death also arises in the context of cryonics, which can be viewed as the use of cryopreservation to attempt to prevent information theoretic death. The use of information-theoretic criteria has formed the basis of ethical arguments that state that cryonics is an attempt to save lives rather than being an interment method for the dead. In contrast, if cryonics cannot be applied before information-theoretic death occurs, or if the cryopreservation procedure itself causes information-theoretic death, then cryonics is not feasible.

It has been claimed that if technologies for general molecular analysis and repair are ever developed, then theoretically any damaged body could be “revived.� Survival would then depend on whether preserved brain information was sufficient to permit restoration of all or part of the personal identity of the original person, with amnesia being the final dividing line between life and death.

So, with this in mind, is there really such a thing as death?

Who knows? I am considering cryonics as a last resort if life-extension technologies do not pan out fast enough to extend my own life.

The only problem is if you loose too much of your brain cells before you're revived.

So in this sense "death" is the loss of identity.

Another age old consideration would be if your brain is restored to normal mostly from scratch - will that still be you or just a copy of you?

Yes I have been pondering on this myself. What are we really? If our brains were uploaded to computers - is that us or are the brain cells us? I think the main problem lies in the identity of the self.

I thought cryonics was fairly sci-fi at the moment, mainly because the quick-freeze and thawing actually damages tissue to the point of death anyway. Have they managed to sort out the problems with this cell fracturing?

Currently the damage of cryonics is not reversible.

Isn't the damage done on freezing not thawing? If so they will have to repair the body with nano-bots as it thaws, so succesful cryonic suspension is a long way off if it ever comes.

Well, they have frozen rabbit kidneys and then transplanted them into a rabbit and it lived.

They don't freeze the water either, they just get it really cold so it forms a glass.

However, thawing it out allows crystals to form and that is what destroys the cells.

Water molecules get in between the cells and crystallize, that is what causes the damage. They do have a cryonic fluid which they use to stop this, but currently the damage to the neurons is still to great and has not been reversed.

We need a kind of container in which time actually stops. Not easy.

Hmm good point, I suppose that is what is really trying to be accomplished. To stop or at the very least, severely slow down time.

I suppose that if something were at absolute zero, this would produce the desired effects. By stopping all atoms from moving, there should be no movement or reactions and thus, no time.

The only thing I wonder about is getting around the damage caused by the water molecules.