  It is shown that from the expectation values of obervables, which can be
measured for a single system using protective measurements, the linear
structure, inner product, and observables in the Hilbert space can be
reconstructed. A universal method of measuring the wave function of a single
particle using its gravitational field is given. Protective measurement is
generalized to the measurement of a degenerate state and to many particle
systems. The question of whether the wave function is real is examined, and an
argument of Einstein in favor of the ensemble interpretation of quantum theory
is refuted.
