Elevator Paradox - More Than One Elevator

More Than One Elevator

Interestingly, if there is more than one elevator in a building, the bias decreases — since there is a greater chance that the intending passenger will arrive at the elevator lobby during the time that at least one elevator is below them; with an infinite number of elevators, the probabilities would be equal.

In the example above, if there are 30 floors and 58 elevators, so at every minute there are 2 elevators on each floor, one going up and one going down (save at the top and bottom), the bias is eliminated – every minute, one elevator arrives going up and another going down. This also occurs with 30 elevators spaced 2 minutes apart – on odd floors they alternate up/down arrivals, while on even floors they arrive simultaneously every two minutes.

Watching cars pass on an oval racetrack, one perceives little bias if the time between cars is small compared to the time required for a car to return past the observer.