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An Optical Demonstration of Gravitational Lensing
Samantha Scibelli and John Noé
Laser Teaching Center
Stony Brook University
Einstein’s theory of general relativity revolutionized modern physics in
the early 1900s by identifying gravity as a geometric property of space and
time, known as space-time; it follows that massive objects can distort
this space-time. Einstein's theory was confirmed by observations during a solar eclipse in 1919.
Today many other experimental
observations, such as gravitational waves, gravitational redshift,
gravitational time delay and gravitational lensing, have further confirmed
Einstein’s predictions. Gravitational lensing can be defined simply as the
focusing of light from distant stars or galaxies when the closer intervening object, or 'lens', is massive
enough. It
was not until 1979 that astronomers actually saw
evidence of these gravitational lenses [1]. If this lens is massive enough multiple images of the light
source can be produced, by what is known as strong lensing. Otherwise, sometimes
the image will only be distorted, in what is referred to as weak lensing.
The amount
of magnification and distortion will depend on the properties of the lens
as well as the relative distances of the observer, source, and galaxy.
While
gravitational lensing is best seen over the large scale of the
universe, we can also create optical experiments in the laboratory that
show the same effects.
In this project we are investigating a variety of ways to optically demonstrate and simulate gravitational
lensing.
It turns out
that the base of a wine glass
is the perfect shape to demonstrate this lensing effect [2]. (We
can use the inferred mass distribution from a galaxy size mass lens to
derive the corresponding refractive index distribution. A piece of glass
with
the appropriate shape can demonstrate the same lensing effect seen with
galaxies and galaxy clusters.) We have observed this lensing effect when the base of a wine glass was held
up to a concentrated light source, in our
case a small LED light. Under suitable circumstances, a very strong
gravitational lensing effect was seen
where a continuous image of the light source could be seen in a ring
shaped pattern (Einstein Ring) around the circular base of the wine glass. We hope to
describe these images by optical lens equations and model them in a computer
program [3].
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