By extension, it is not possible to compute the precise duration of a time interval that ends in the future and may encompass an unknown number of leap seconds (for example, the number of TAI seconds between "now" and 2099-12-31 23:59:59).
相应的，计算出一段以未来时刻为终点的时间间隔的时差也是不可能的，因为其中可能包含了数量不定的闰秒(比如，“现在”和“2099-12-31 23:59:59”之间有多少TAI秒)。