122
R. Barrett and P. P. Delsanto
published the results of his deliberations in a paper that has become a classic
in the literature of physics.
While Special Relativity is very important, both for its scientific relevance
and for its applications, General Relativity owes its significance mostly to
its philosophical value. In fact there were very few practical applications of
General Relativity in the first fifty years of its existence, at which time, as
we shall see, solutions of Einstein’s equations were found for black holes,
and other celestial objects. Prior to this period, the vanguard of physics
lay with Quantum Mechanics, the other great 20th Century revolution.
Purely as an intellectual monument to human ingenuity, General Relativity
can be compared to other momentous achievements of humankind, such as
the ninth symphony of Beethoven, Leonardo’s Giaconda and the Egyptian
Pyramids.
7.3 The Principle of Equivalence
Let us begin our intellectual journey into General Relativity, as Einstein
did, with another thought experiment. Consider a passenger travelling in an
elevator, as shown in Fig. 7.1.
If the speed of ascension in the first example in Fig. 7.1 is constant, then
the passenger is in an inertial frame of reference, and the theory of Special
Relativity applies, as we saw in the last Chapter. However, suppose that
Fig. 7.1 Passenger in rising elevator (1) and free falling elevator (2)
R. Barrett and P. P. Delsanto
published the results of his deliberations in a paper that has become a classic
in the literature of physics.
While Special Relativity is very important, both for its scientific relevance
and for its applications, General Relativity owes its significance mostly to
its philosophical value. In fact there were very few practical applications of
General Relativity in the first fifty years of its existence, at which time, as
we shall see, solutions of Einstein’s equations were found for black holes,
and other celestial objects. Prior to this period, the vanguard of physics
lay with Quantum Mechanics, the other great 20th Century revolution.
Purely as an intellectual monument to human ingenuity, General Relativity
can be compared to other momentous achievements of humankind, such as
the ninth symphony of Beethoven, Leonardo’s Giaconda and the Egyptian
Pyramids.
7.3 The Principle of Equivalence
Let us begin our intellectual journey into General Relativity, as Einstein
did, with another thought experiment. Consider a passenger travelling in an
elevator, as shown in Fig. 7.1.
If the speed of ascension in the first example in Fig. 7.1 is constant, then
the passenger is in an inertial frame of reference, and the theory of Special
Relativity applies, as we saw in the last Chapter. However, suppose that
Fig. 7.1 Passenger in rising elevator (1) and free falling elevator (2)