CoitTower_40 The advent of the Internet and its associated modern communication tools seems to make physical space less meaningful. When a collaborator or a loved one on the other side of the planet is just a Skype call away, what does distance really mean? When Amazon offers free two-day shipping and burritos are delivered in minutes by automated drones, who cares about physical space? The answer will quickly spring to the minds of anyone interested in high finance, or video games, or physics: lag.

Among the mind-blowing implications of relativity is the following: the speed of light imposes a fundamental limit on how quickly information can travel through space. Our “light cone” means that we can be influenced by events sufficiently far in the past, and can have our own influence on events in the future, but that we cannot influence events happening in the present when they are not happening near us. No matter how advanced our fiber optic networks become (limited, presently, by the necessity of repeaters and the like), information can never (for instance) make a round trip of the earth in less than 133 milliseconds.
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