Some stock trades close faster than the human eye can blink

On today's stock exchanges, a huge share of trading volume — in some market segments, even the majority — is no longer carried out by humans clicking "buy" or "sell," but by high-frequency trading (HFT) algorithms making and executing decisions on a timescale measured in microseconds.

The twist: firms in this business pour enormous sums not into better market analysis, but into physical proximity to the exchange's servers — because the speed of light through a fiber-optic cable becomes a real bottleneck, and an edge measured in fractions of a millisecond can decide profits worth millions.

There's a known case of a company building a special, almost perfectly straight fiber-optic cable between two US cities for the sole purpose of shaving a few milliseconds off the transmission time of stock market data — construction cost ran into the hundreds of millions of dollars.

The stakes: this shows just how far modern financial markets have drifted from human timescales — decisions that used to be made in a broker's office now unfold in a world beyond human perception, governed by the physics of the speed of light.