ELI5: Why are cable boxes so big, yet more technologically advanced devices such as smart phones can fit in the palm of our hands?

Theoretically, yes. Practically, no.

The heart pumps because it contracts in well defined patterns. When that pattern is disrupted and the muscle cells lose their synchronization, we call that fibrillation. It kills, because in this state the heart is no longer actively pumping blood.

The heart's cells contract in response to electrical signals that propagate through the tissue in an orderly manner. Specifically, each cell contracts in response to a change in the voltage level across its cellular membrane (known as membrane potential). This process is more generally known as an action potential and you see it in all sorts of electrically active cells (e.g., neurons). Cells create voltage levels they use in normal functioning by pumping around ions. E.g., a cell can decrease its voltage by pumping positive ions out of itself and into the extracellular fluid that surrounds it.

Now, what kills you is when those membrane potentials in the heart are disrupted in a non-uniform way. This leads to irregular firing, which in turn leads to a state of fibrillation in which the heart. The muscle cells are contracting, but they're no longer contracting in a synchronized and organized way. The heart remains active, but it is no longer effectively operating as a pump.

So how does electric current do this? Well, when a current is flowing through your body, it does so by creating bulk movement in all the ions in your internal fluids. That bulk movement disrupts the careful balance of ionic concentrations that all your cells have created. This causes some cells to fire uncommanded, while others to not fire at all. In the heart, this leads to disorganized activity and produces the state of fibrillation.

Theoretically, if you could generate a sufficiently large electric field without also producing a current, it could directly disrupt the bioelectrical mechanisms of your body. But there's no known way to do that.

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