Medical Time Travel
not yet reversible. But cryonicists would argue that this does
not imply death either because death only happens when bio-
chemistry becomes irreversibly damaged, and irreversibility
To clarify these issues, cryonicists have proposed the infor-
mation-theoretic criterion for death.  According to this
criterion, you are not dead when life stops (we already know
that from clinical medicine), you are not dead when bio-
chemistry is damaged, you are only dead when biochemistry
is so badly damaged that no technology, not even molecular
nanotechnology , could restore normal biochemistry with
your memories intact. By this criterion, someone who suf-
fered cardiac arrest days ago in the wilderness is really dead.
Someone who suffered only a few minutes of cardiac arrest
and cryoprotectant toxicity during morphological vitrifica-
tion may not be.
Whether or not one accepts this information-theoretic cri-
terion, the modern cryonics practice of using life support
equipment to resuscitate the brain after legal death raises
important issues. Among them is the scientific issue that cry-
onics cannot be dismissed simply by calling its subjects dead.
Two minutes of cardiac arrest followed by restoration of blood
circulation does not a skeleton make. There should be a rule
that no one is allowed to say dead when discussing cryonics.
It is usually a slur that communicates nothing scientific.
Whether cryonics can work depends on biological details of
cerebral ischemic injury (brain injury during stopped blood
flow), cryopreservation injury, and anticipated future technol-
ogy. There is much published literature on cerebral ischemia,
and a small, but growing body of writing on relevant future
technologies. [29 33] There is, however, very little informa-
tion on the quality of preservation achieved with cryonics.
[34;35] It would seem logical to look to cryobiologists for this