"High-frequency trading" carried out by computers often depends on differing prices of a financial instrument in two geographically-separated markets.
Exactly how far the signals have to go can make a difference in such trades.
Alexander Wissner-Gross told the American Physical Society meeting that financial institutions are looking at ways to exploit the light-speed trick.
Dr Wissner-Gross, of Harvard University, said that the latencies — essentially, the time delay for a signal to wing its way from one global financial centre to another — advantaged some locations for some trades and different locations for others.
There is a vast market for ever-faster fibre-optic cables to try to physically "get there faster" but Dr Wissner-Gross said that the purely technological approach to gaining an advantage was reaching a limit.
Trades now travel at nearly 90% of the ultimate speed limit set by physics, the speed of light in the cables.