135 MEDICAL TIME TRAVEL A QUESTION OF SCIENCE Brian Wowk, Ph.D. Time travel is a solved problem. Einstein showed that if you travel in a spaceship for months at speeds close to the speed of light, you can return to earth centuries in the future. Unfor- tunately for would-be time travelers, such spacecraft will not be available until centuries in the future. Rather than Einstein, nature relies on Arrhenius to achieve time travel. The Arrhenius equation of chemistry describes how chemical reactions slow down as temperature is reduced. Since life is chemistry, life itself slows down at cooler tem- peratures.  Hibernating  animals  use  this  principle  to  time travel from summer to summer, skipping winters when food is scarce. Medicine already uses this kind of biological time travel. When  transplantable  organs  such  as  hearts  or  kidneys  are removed from donors, the organs begin dying as soon as their blood supply stops. Removed organs have only minutes to live. However with special preservation solutions and cool- ing  in  ice,  organs  can  be  moved  across  hours  of  time  and thousands of miles to waiting recipients. Cold slows chemical processes that would otherwise be quickly fatal.