Once the heart stops beating, blood flow to the brain and other organs ceases. This leads to the loss of consciousness, brain activity, and vital functions like breathing and circulation. Without oxygen, the body’s cells and tissues begin to break down. The brain stops functioning shortly after death. Without a supply of oxygenated blood, neurons die off, and consciousness, thoughts, and memories cease. This aligns with the medical definition of death as the irreversible end of brain activity. After death, the body undergoes decomposition. This process starts within hours as cells break down, and bacteria in the body start digesting tissues. Over time, the body decomposes into simpler organic matter, eventually returning to the environment as nutrients. Scientifically, the energy within a body—heat, chemical energy, etc.—follows the laws of thermodynamics. It is neither created nor destroyed but is converted and dispersed into the environment. This energy is released as heat, or it contributes to the ecosystem as the body decomposes.

Science doesn’t address the existence of an afterlife, as that falls more into the realm of philosophy or spirituality. From a purely biological standpoint, after death, a person’s physical body breaks down, and any remaining energy is absorbed by the environment.