Clinically, we understand death to mean the state that takes hold after our hearts stop beating. Philosophically, though, our definition of death hinges on something else: the point past which we're no longer able to return. Those two were more or less the same until about 50 years ago, when we saw the advent of CPR. Modern resuscitation ... blew apart our understanding of what it means to be dead. Without many people returning from the dead to show us otherwise, it was natural to assume, from a scientific perspective, that our consciousness dies at the same time as our bodies. Over the last few years, though, scientists have seen repeated evidence that once you die, your brain cells take days, potentially longer, to reach the point past which they've degraded too far to ever be viable again. People who survive medical death frequently report experiences that share similar themes: bright lights; benevolent guiding figures; relief from physical pain and a deeply felt sensation of peace. Because those experiences are subjective, it's possible to chalk them up to hallucinations. Where that explanation fails, though, is among the patients who have died on an operating table or crash cart and reported watching ... as doctors tried to save them, accounts subsequently verified by the (very perplexed) doctors themselves. How these patients were able to describe objective events that took place while they were dead, we're not exactly sure. But it does seem to suggest that when our brains and bodies die, our consciousness may not.