At some point I got curious about a question that sounds almost silly at first: how do we actually know when someone has died? It caught my attention because the exact moment a person is legally considered dead is, surprisingly, a defined part of how “life” itself gets treated in medicine and law.
In practice, someone’s death is essentially equivalent to brain death — more specifically, brainstem death. But how is that actually determined? It varies country to country. Some places require the judgment of a single practicing physician; others require confirmation from multiple specialists, sometimes as many as four.
The cleanest, most direct test: shine a light into the person’s eyes. If there’s no pupil constriction reflex, there’s roughly a 99% likelihood the person has died — though certain kinds of brain damage can also suppress this reflex without death having occurred, so it’s not airtight on its own.
A second method: check for electrical activity via EEG. No signal generally indicates death — but certain powerful anesthetics can also flatten EEG readings in a living person. Because of that, the standard approach is to take two EEG readings 24 hours apart; if both show no activity, that’s considered strong, reliable confirmation of death.
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