by Laurance R. Doyle
SETI Institute and Principia College
Today’s announcement of the detection of gravitational waves by the LIGO (Laser Interferometer Gravitational-Wave Observatory) Team hallmarks the beginning of a new kind of astronomy (see Physical Review Letters 116, 161102-1). About the time the first plants appeared on Earth 1.3 billion years ago -- and long before any land animals -- two black holes (former suns) about 30-times the mass of our young Sun collided at almost the speed of light, producing enough energy to cause a measureable ripple in the very fabric of spacetime. That wave – if something that is millions of miles long and yet only sub-millimeter in height can be called a “wave” -- was headed for Earth, to arrive last September, and finally to lead to the announcement today of the detection of gravity waves. It has been one-hundred years now since Einstein predicted gravitational waves and he would have, no doubt, been amazed at the technology that enabled this detection. The LIGO observatory involves two laser beam paths that are combined so that any shift along one path will produce a change in the way the other path interacts with it, at the level of the wavelength of laser light. By measuring the change in distance between the two paths, one can tell if minute changes along any one path have occurred. Such a change is what the LIGO Team has detected. Today, the new observational field of gravitational-wave astronomy has come of age. With the electromagnetic spectrum – gamma rays through visible light and on to radio waves – one could have looked back only to about 380,000 years after the Big Bang, because the universe would not have become transparent until then (hot, ionized particles would have blocked the view). But, among other things, with gravitational waves one may peer back into the first few seconds of the universe. Thus today’s announcement is not just a celebration of Einstein’s amazing prescience, and the confirmation (if it was needed) of the reality of black holes, but it is the opening up to a whole new kind of astronomy, one that allows direct observations of the first few seconds of the universe. It’s an “I was there the day gravitational-wave astronomy came of age” day. It’s the day humankind first caught a gravity wave in the fabric of spacetime to surf into the future!