Temporal ordering in quantum mechanics

J. Oppenheim*, B. Reznik, W. G. Unruh

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We examine the measurability of the temporal ordering of two events, as well as event coincidences. In classical mechanics, a measurement of the order-of-arrival of two particles is shown to be equivalent to a measurement involving only one particle (in higher dimensions). In quantum mechanics, we find that diffraction effects introduce a minimum inaccuracy to which the temporal order-of-arrival can be determined unambiguously. The minimum inaccuracy of the measurement is given by δt = ℏ/Ē where Ē is the total kinetic energy of the two particles. Similar restrictions apply to the case of coincidence measurements. We show that these limitations are much weaker than limitations on measuring the time-of-arrival of a particle to a fixed location.

Original languageEnglish
Pages (from-to)7641-7652
Number of pages12
JournalJournal of Physics A: Mathematical and General
Issue number35
StatePublished - 6 Sep 2002


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