"Do not bodies act upon light at a distance, and by their action bend it's rays; and is not this strongest at the least distance?" (Newton 1704)
In
1704, Sir Isaac Newton first postulated that the gravitational field of a
massive object could bend light rays. Albert Einstein proposed a similar
effect arising from his theory of General Relativity in 1919. He theorized
that a star positioned directly behind the sun would be visible during a total
eclipse due to the gravitational field of the sun bending the light emitted
from the star. (See Figure 1.) Gravitational lensing was first observed
experimentally in 1979. The purpose of our experiment was to model the
gravitational effect of massive galaxies placed between a distant star and the
earth by focusing a particular light source through a lens on an object whose
image was projected upon a screen.
Gravitational lensing may be used as both a cosmological and astrophysical tool, particular applications being the determination of both the Hubble Constant and the size and structure of distant quasars. Such observations may also be used to probe the nature of so-called "dark matter" in the universe.