General Meeting Report October
Speaker: Dr Andrew Melatos B Senior Lecturer in the School of Physics at the University of Melbourne. Andrew=s topic for the evening was Gravity Waves: Echoes of Cosmic Cataclysms.
In a short introduction to proceedings Rod Brown, Director Historical and Demonstrators Section, reminded listeners that this October meeting was again dedicated, as Philipp Simon Memorial Lecture, to the memory of Philipp Simon, (1890-1991). Mr Simon came from Zuffenhausen near Stuttgart in Germany (home of Bosch and the Porsche sports-car); he joined the ASV in 1947 and was awarded honorary Life Membership in 1961. He was a prolific correspondent, a bibliophile and gifted public speaker with interests in astronomical phenomena, ancient and modern instruments, sundials and public education, and is remembered for his outstanding contributions to the ASV. Dr Melatos, in acknowledging the introduction, said it was a privilege to speak on this occasion.
The ASV is very fortunate to have specialist speakers like Dr Andrew Melatos keeping us informed on developments in astronomy and astrophysics. Andrew gained his BSc in 1991 and his PhD in 1995 from the University of Sydney. He was a Research Fellow (Astrophysics) at the California Institute of Technology from 1995 to 1997 and a Miller Fellow (Astronomy) at the University of California at Berkeley from 1997 to 2000. On his previous appearance at the ASV three years ago (October 2002) he spoke about Pulsars and Supernova Remnants, and the current topic Gravity Waves extends the cosmological implications of that subject.
There are three stages to this cosmic expose: Ripples in Space and Time (Gravity Waves?), Cataclysmic Interaction of heavenly bodies (Neutron Stars and Black Holes), and modern Gravity Wave Antennas (Interference Detectors). The Einsteinian concept is simple: Accelerating masses in space-time produce ripples in the fabric of space that propagate at the speed of light through space-time and cause a suspended pendulum to oscillate as the ripples wash past. Yes, the concept is simple. Then why can=t we find them? The first generation detectors (pendulums) were massive cylinders of temperature controlled aluminium suspended in a vacuum chamber. They measured everything from Earth tremors to traffic on the highway to ocean waves crashing on shore, but no gravity waves; no coalescing Neutron Stars, no merging galaxies.
In the meantime discovery and careful monitoring of twin Pulsars, such as the Hulse-Taylor Binary (1974), seemed to confirm the existence of gravity waves that were taking away energy from the pair at 3mm per 8hr orbit. Calculation of a typical wave amplitude resulting from this here on Earth gives the unimaginably small figure of 10 to the minus 26. Even at a detector separation of 4km it would need a measuring sensitivity of a one thousandth the diameter of a proton. A series of LIGO Installations around the globe (4km x 4km Laser Interferometer Gravitational Wave Observatories) are currently about one magnitude away from the sensitivity needed for a chance to detect any Gravity waves at all. But an Advanced LIGO proposed will have a factor of 10 greater sensitivity. The new instruments take advantage of research that has taken place since the initial instruments were designed in the mid-1990=s, and call for changes in the lasers (180 W highly-stabilized systems), optics (40 kg sapphire crystals), seismic isolation systems (using inertial sensing and feedback), and the way in which the microscopic motion of the test masses is detected. Since the volume of space that the instrument can see grows as the cube of the distance, this means that the event rates will be more than 1,000 times greater. Advanced LIGO will equal the 1-yr integrated observation time of initial LIGO in roughly 3 hours.
Question time was all-to-short, with unresolved (unanswerable?) questions reaching into the philosophical domain of cosmology. Can gravity, the only known physical force that is infinitely additive, shape itself in a self-sustained wave in space-time; a wave that carries away energy in stress amplitude variations at a finite propagation speed? Can the spread of gravity be subject to an AOlbers type paradox@, where galaxies beyond the edge of the visible universe no longer (or not yet) interact gravitationally with us? Is there a Gravity Horizon?
The closing vote of thanks was given by Lockie Creswell, Section Director Radio Astronomy, with the customary gold-wrapped present for the wine connoisseur. Whether LIGO or LISA (a space based version of LIGO) or the SKA=s Pulsar Interferometer eventually will detect moving ripples in space-time is not guaranteed. But whatever the outcome of these projects, the investment of financial, physical and intellectual resources in them has already increased our awareness, and will continue to increase greatly our understanding, of the dynamic forces at work in our universe, an understanding that in time will help determine our destiny.