Technicians prepare a patient for
Cryonics is the low-temperature preserva-
tion of humans and animals that can no
longer be sustained by contemporary medi-
cine until resuscitation may be possible in the
future. Currently, human cryopreservation is
not reversible, which means that it is not cur-
rently possible to bring people out of cryop-
reservation. The rationale for cryonics is that
people who are considered dead by the cur-
rent legal or medical definitions will not ne-
cessarily be dead by future standards—the
information-theoretic definition of death;
and that such people could be brought out of
cryopreservation in the future.
In the United States, cryonics can only be
legally performed on humans after they have
been pronounced legally dead.
The word cryonics
is derived from the
Greek word κρύος (kryos), meaning cold.
Note that "cryonics" is often mistaken for the
concept of suspended animation.
Cryonics is not a panacea for future im-
mortality. Cryonics advocates point out that
prognosis for cryonics patients is variable,
with braindead patients having little chance
of meaningful recovery even with foreseeable
cryonics technology, while patients who are
vitrified immediately after irreversible cardi-
ac arrest is ascertained would fare the best.
Most proponents of cryonics see it as a spec-
ulative medical technology, no different in
principle from the defibrillator or advanced
cardiac life support.
Premises of cryonics
The central premise of cryonics is that
memory, personality, and identity are stored
in cellular structures and chemistry, princip-
ally in the brain. While this view is widely ac-
cepted in medicine, and brain activity is
known to stop and later resume under cer-
tain conditions, it is not generally accepted
that current methods preserve the brain well
enough to permit revival in the future. Cryon-
ics advocates point to studies showing that
high concentrations of cryoprotectant circu-
lated through the brain before coo