After the Kaluza–Klein scenario found a home in string theory, physicists became accustomed to the concept of extra space dimensions. Their presence was essential for the mathematical consistency of the theory. Adding extra dimensions of space now seemed natural and even necessary, but physicists shied away from adding also extra dimensions of time. Why? Extra time dimensions had actually been quite discouraging to a lot of theorists because extra times bring additional problems that nobody knew how to resolve for many decades.