Some fascinating things about gravitational lensing:
It was the means by which the General
Theory of Relativity proposed by
Albert Einstein in 1915 was finally proved (by
Arthur Eddington and friends), in 1919. This first instance observed was very close to home, with the lensing being that which was caused by
Earth's own
Sun during a
lunar eclipse. The proposition that entire galaxies could serve as the lenses for even more distant light was proposed in 1937, but not proved until 1979.
Notably, some scientists have proposed that gravitational lensing could be used as a means of facilitating extremely long-distance signal-sending, a means of establishing interstellar or intergalactic
beacons, amplifying their output by pinpointing them towards the edges of the gravitational wells of massive stellar bodies. It could in theory even allow for intergalactic
communication in meaningful time by amplifying hypothetical faster-than-light signals in the same way as
telegraph signals are amplified by repeaters along their paths.
And one other thing about gravitational lensing -- it's a
barometer for the age of our
Universe. Here's the thing, you see -- some people claim our Universe is only a few thousand years old, and consequently that either the speed of light used to be much faster, or that light appearing to come from distant stars was simply created
in situ. But, like an arrow fired over the length of a field on a windy day, light is buffeted by the gravitational forces of the stars themselves. And other than the handful of stars closest to our own
Solar System,
all light from
all stars is bent by the gravity of stars passed by. And despite the many billions of bodies involved, it is possible for examining astronomers to calculate the impact of gravity wells on every portion of the paths and passage of the light waves traveling to us from distant stars. By looking to the expected point of origin, and the
bullseye which has been hit, measurements can confirm down to infinitesimal degrees that the light we see from even the farthest corners of our Universe has come to us not in a straight line or at a varying pace, but uniformly at the well-established
speed of light, subtly bent many times along this steady course.