Extract the answer to the question from the following context. Question: If we are not talking about zero average values, but different kind of values, what are we talking about? Context: QED vacuum has interesting and complex properties. In QED vacuum, the electric and magnetic fields have zero average values, but their variances are not zero. As a result, QED vacuum contains vacuum fluctuations (virtual particles that hop into and out of existence), and a finite energy called vacuum energy. Vacuum fluctuations are an essential and ubiquitous part of quantum field theory. Some experimentally verified effects of vacuum fluctuations include spontaneous emission and the Lamb shift. Coulomb's law and the electric potential in vacuum near an electric charge are modified.
----
Answer: variances

Extract the answer to the question from the following context. Question: Which is not a last name, Robinson or Scout? Context: Tom Robinson is the chief example among several innocents destroyed carelessly or deliberately throughout the novel. However, scholar Christopher Metress connects the mockingbird to Boo Radley: "Instead of wanting to exploit Boo for her own fun (as she does in the beginning of the novel by putting on gothic plays about his history), Scout comes to see him as a 'mockingbird'that is, as someone with an inner goodness that must be cherished." The last pages of the book illustrate this as Scout relates the moral of a story Atticus has been reading to her, and in allusions to both Boo Radley and Tom Robinson states about a character who was misunderstood, "when they finally saw him, why he hadn't done any of those things ... Atticus, he was real nice," to which he responds, "Most people are, Scout, when you finally see them."
----
Answer: Scout

Extract the answer to the question from the following context. Question: How does the Julian calendar address the leap year? Context: The Gregorian calendar is a solar calendar. A regular Gregorian year consists of 365 days, but as in the Julian calendar, in a leap year, a leap day is added to February. In the Julian calendar a leap year occurs every 4 years, but the Gregorian calendar omits 3 leap days every 400 years. In the Julian calendar, this leap day was inserted by doubling 24 February, and the Gregorian reform did not change the date of the leap day. In the modern period, it has become customary to number the days from the beginning of the month, and February 29th is often considered as the leap day. Some churches, notably the Roman Catholic Church, delay February festivals after the 23rd by one day in leap years.
----
Answer:
every 4 years