(This is a reference post meant to simply and briefly explain a new concept. I will need to refer to it in other posts.)


'Info cone' is short for 'Information Cone'.

A future info cone is the path that a flash of information propagating at maximum speed, emanating from a single event (localized to a single point in space and a single moment in time) and traveling in all directions, would take through spacetime.

A past info cone behaves like the Future Info Cone in reverse: a n-sphere which contracts in radius at maximum information propagating speed until it converges to a point at an exact position and time.

In universes where the maximum speed at which information can propagate is the speed of light (or the speed of any boson really), then the info cones are of the same shape than light cones.

Note that, in practice, obstacles could block or slow down (ex.: through diffraction) the speed at which information can propagate, but the info cone is defined as the theoretical limit — in our universe that would mean in vacuum. I suggest using 'real info cone' to discuss the actual, idiosyncratic region that could receive a flashed message (similarly 'real light cone' when using light). Note that the 'real cone' isn't in fact a perfect cone.

Use cases

The concept of info cone can be useful to discuss concepts that are agnostic to the maximum information-propagating-speed or whether a universe has light, and so can apply to other universes as well. It's also particularly useful in discussing the implications that faster-than-light travelling in our universe would have, or how likely we are to be in such a universe.

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