General Meeting 8 March 2000
Gravity Lensing, and who is Ray Bundle?
Speaker Dr. Christopher Fluke, Swinburne University.
The circadian sequence from day into night has fascinated humanity for centuries, for millennia, for aeons. The transition through dusk seems to stimulate our imagination. It makes us switch dependency between the senses. As the sun slowly sinks below the horizon the physical world appears to shrink, darkness envelops us and our horizons are determined by touch and sound. But looking upwards the normally opaque sky gradually turns translucent and there, miraculously stars appear and open up our vista to infinity. Like a curtain going up in a theatre, we suddenly become aware of the actors on the stage and, with our other physical senses shut off, watch the play evolve until the morning aurora draws the curtain shut again. It is mystery incorporated.
I have much the same feeling when I come to listen to an astronomy presentation. Initially I am aware of all the surroundings, the arrangement of chairs and tables, what people wear, the flat battery in the hand-held microphone etc. But then, as the speaker leads us through the introductory pleasantries into the essence of the talk, these ambient trimmings disappear as our senses concentrate on following his logical arguments. Even an initially annoying microphone-feedback can become part of the scene, a persistent celestial echo from the depth of space: Who is Ray Bundle?
Ray Bundle is an invention of Dr Christopher Fluke, a young 28 year physicist at Swinburne University. While endeavouring to model the parameters of the universe on a computer he hit on the idea of sending simulated bundles of light rays around a null geodesic line. By varying the properties of the medium (the amount of matter or mass in space) he and his team were able to duplicate conditions other astrophysical data from observational experiments seemed to suggest. They have created a workable computer model of the density of the Universe. Why?
One of the great puzzles in cosmology at the moment is the apparent conflict between visible matter and density of mass. Every aspect of Astronomy and Astrophysics is affected by this uncertainty: The ages of some globular clusters seem to exceed the age of the Universe; galaxies do not rotate as they are supposed to do; the universal expansion is in trouble; the Hubble constant in doubt. Consequently every cosmological statement has to have these conditionals attached to its conclusions. Astronomers desperately need to know the value of Omega.
Gravity lensing of light has been assumed to exist ever since Einstein’s prediction to the bending of starlight was confirmed by Eddington, way back in 1919. These days graphic pictures proof its reality, photographs with multiple images of celestial objects, rings (or partial rings) around massive, invisible gravity lenses. By using existing astronomical data on brightness and probability of standard distance candles, and running the “Ray Bundle” through numerous simulations of matter distributions, lensing magnifications above or below an arbitrary norm, μ = 1, could be established.
With numerous parameters to be tested (119 simulations) and endless repeats required to confirm the findings (50,000), it took months of supercomputer time to run the series. But the results of this “Ray Bundle” project are exciting: There is a measurable difference in what we see, depending on the mass and distribution of matter in the Universe. Astronomical analysis should now be done to establish which of the three models μ = 1; μ > 1; or μ < 1 agrees with actual observations.
Dr. Christopher Fluke’s “Ray Bundle” is lifting the curtain on a part of the cosmological stage that previously could not be seen. Alfred Klink