When does a measurement or event occur?

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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Within quantum mechanics, a complete set of commutting observables can be found which describe the attributes of a system at a given time. However, the correct way to describe attributes of a system in time is still an open question. We discuss the difficulties in extending the standard approach of quantum mechanics to describe attributes of a system in time. We find that measuring when an event occurred and measuring that it occurred, are complimentary in Bohr's sense. To exemplify the differences between measurements at a given time and in time, we will compare Rovelli's recent proposal (quant-ph/9802020), to determine "at what time does a measurement occurred" with another model of a continuous measurement in time. Rovelli's scheme answers the question "has the measurement already occurred at a certain time?" but does not answer to the more difficult question: "when did the measurement occur?". We also discuss the use of the probability current to measure the time at which a particle arrives to a certain location.

Original languageEnglish
Pages (from-to)107-118
Number of pages12
JournalFoundations of Physics Letters
Issue number2
StatePublished - Apr 2000


  • Arrival
  • Event
  • Measurement
  • Time


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