Fantasy writers have long been captivated by
the possibility of preserving human life in a reversible state of suspended animation. In fictional tales the technique enables characters to "sleep" through centuries of interstellar travel or terrestrial cataclysms, then awaken unaffected by the passing of time. These stories are great fun, but their premise seems biologically far-fetched. In reality, we humans do not appear capable of altering our rate of progression through life. We cannot pause the bustling activity of our cells any more than we can stop breathing for more than a few minutes without sustaining severe damage to vital organs.