  It is shown how the technique of restricted path integrals (RPI) or quantum
corridors (QC) may be applied for the analysis of relativistic measurements.
Then this technique is used to clarify the physical nature of thermal effects
as seen by an accelerated observer in Minkowski space-time (Unruh effect) and
by a far observer in the field of a black hole (Hawking effect). The physical
nature of the "thermal atmosphere" around the observer is analysed in three
cases: a) the Unruh effect, b) an eternal (Kruskal) black hole and c) a black
hole forming in the process of collapse. It is shown that thermal particles are
real only in the case (c). In the case (b) they cannot be distinguished from
real particles but they do not carry away mass of the black hole until some of
these particles are absorbed by the far observer. In the case (a) thermal
particles are virtual.
