18 February 2016 | by Guy Consolmagno
The discovery of gravitational waves
confirms Einstein’s insight that Creation is stranger and more wonderful than
the clockwork universe imagined by Enlightenment scientists
At the museum of the history of
science in Florence, honouring its famous local son Galileo, one can find a
marvellous display of the seventeenth-century glass technology that made Italy
the birthplace of the scientific revolution.
In another room you will find mechanical devices produced in Britain and Germany a century later that made more precise measurements of our universe possible. Now the observation of gravitational waves shows again how our knowledge of ourselves and our place in the universe is advanced by our ability to measure nature ever more precisely.
To detect the tiniest ripple in the space-time continuum, the Laser Interferometer Gravitational-wave Observatory (LIGO) experiments in Louisiana and Washington state had to compare the space between two four-kilometre paths, set at right angles to each other, with a precision of better than one thousandth the radius of a proton.
The “laser” in the LIGO made this possible. Each arm of the detector is kept at a vacuum and precisely isolated so that no vibrations will mask the tiny signal. Laser beams are sent down each tunnel, reflected back by superbly figured mirrors, and then compared. Much like how a piano tuner listens to the blend of a piano string’s note against a tuning fork, a slight difference in the lengths of the tunnels will cause the combined beam to show an “interference” pattern (the “I” in LIGO) that can be used to detect tiny differences in path lengths between the two beams.
Why should the beam lengths vary? In the late sixteenth century, Isaac Newton had described how gravity controls the orbit of a moon or the fall of an apple, but he famously refused to guess what gravity actually was; when challenged, he replied, “hypotheses non fingo” (“I feign no hypotheses”).
In 1915 Einstein took up that challenge, proposing in his General Relativity theory that gravity was the result of matter warping space and time (which he had united as “spacetime” in his earlier Special Theory of Relativity). Einstein’s idea imagines that spacetime could be represented in two dimensions as a flat sheet of rubber. Any mass (such as a star or a planet) warps spacetime the way a weight placed on the rubber bends it out of shape. A violent change in the position of that weight – caused, perhaps, by two such weights spiralling into each other or colliding – could set up ripples in the rubber sheet that might propagate like waves of gravitational warping (hence the “G” in LIGO).
In our three-dimensional universe, such ripples would manifest themselves as the fabric of spacetime itself slightly shrinking and growing in the direction that the waves travel. Of course, such ripples grow weaker and weaker as they fill more and more space, radiating away from their source.
Collisions between such massive objects – say, two black holes in space – do not happen every day; at least, not close enough to us that we could expect to see one within the lifetime of an observer – unless the observer has such a delicate detector that even events in incredibly distant volumes of space can be observed.
The first version of LIGO, set up in 1999, failed to see any confirmed gravitational wave events. But in late 2014 an improved version, 10 times more sensitive, came into operation. Last September, the event just announced was captured by the detector in Louisiana.
The next step was to see if the same event was recorded by the second detector in Washington. It was. Furthermore, the Washington detector registered it a few microseconds later, as would be expected for a wave travelling at the speed of light across the 3,000km between the two sites.
Theorists had been working for years to calculate just what sorts of events might give rise to gravitational waves, and what the signal of each sort of event might look like. Such calculations were essential in designing the detectors, so that the engineers would have an idea of the precision that they would have to achieve in order to get reasonable results.
Comparing the predictions with the observations allowed the observers to figure out what sort of event they were seeing. The slowly increasing amplitude of the observed signal, followed by its abrupt ending, matched the predictions for two massive black holes spiralling together and then colliding.
The time difference between the detectors told us the direction back to where the waves came from. The magnitude of the signal let them calculate how far away the event was (a bit over a billion light-years distant) and how massive the black holes were (roughly 30 times the mass of the Sun). They even concluded that roughly half the mass of the combined system had to be converted from mass into energy (thanks to Einstein’s famous “E=mc2”rule) at the instant of collision. The system briefly emitted as much energy as all the stars of the visible universe combined.
The experiment did more than merely confirm the existence of gravitational waves; it served as a way to observe the black holes that caused the wave. Hence the “observatory” in LIGO. The massive gravity of black holes prevents light from escaping their surfaces; only gravity waves can be transmitted directly from them to us.
While the physicists are understandably delighted with this new tool to observe the universe, there are also some interesting lessons for the rest of us. This project has orchestrated the talents of many people, over many years, to a cause that produced neither money nor power nor, for most of them, fame.
To uncover the most subtle understandings of reality, large organisations and big hierarchies are absolutely necessary. This was science that no lone visionary, no matter how bright, could have accomplished. It shows what promise and power humans can achieve when we join together for a common cause.
It also confirms, in the strongest way yet, the core of Einstein’s insight. The laws describing Creation are far more surprising, strange and delightful than the simple Deist clockwork conceived by Isaac Newton.
Br Guy Consolmagno SJ is the director of the Vatican Observatory.
In another room you will find mechanical devices produced in Britain and Germany a century later that made more precise measurements of our universe possible. Now the observation of gravitational waves shows again how our knowledge of ourselves and our place in the universe is advanced by our ability to measure nature ever more precisely.
To detect the tiniest ripple in the space-time continuum, the Laser Interferometer Gravitational-wave Observatory (LIGO) experiments in Louisiana and Washington state had to compare the space between two four-kilometre paths, set at right angles to each other, with a precision of better than one thousandth the radius of a proton.
The “laser” in the LIGO made this possible. Each arm of the detector is kept at a vacuum and precisely isolated so that no vibrations will mask the tiny signal. Laser beams are sent down each tunnel, reflected back by superbly figured mirrors, and then compared. Much like how a piano tuner listens to the blend of a piano string’s note against a tuning fork, a slight difference in the lengths of the tunnels will cause the combined beam to show an “interference” pattern (the “I” in LIGO) that can be used to detect tiny differences in path lengths between the two beams.
Why should the beam lengths vary? In the late sixteenth century, Isaac Newton had described how gravity controls the orbit of a moon or the fall of an apple, but he famously refused to guess what gravity actually was; when challenged, he replied, “hypotheses non fingo” (“I feign no hypotheses”).
In 1915 Einstein took up that challenge, proposing in his General Relativity theory that gravity was the result of matter warping space and time (which he had united as “spacetime” in his earlier Special Theory of Relativity). Einstein’s idea imagines that spacetime could be represented in two dimensions as a flat sheet of rubber. Any mass (such as a star or a planet) warps spacetime the way a weight placed on the rubber bends it out of shape. A violent change in the position of that weight – caused, perhaps, by two such weights spiralling into each other or colliding – could set up ripples in the rubber sheet that might propagate like waves of gravitational warping (hence the “G” in LIGO).
In our three-dimensional universe, such ripples would manifest themselves as the fabric of spacetime itself slightly shrinking and growing in the direction that the waves travel. Of course, such ripples grow weaker and weaker as they fill more and more space, radiating away from their source.
Collisions between such massive objects – say, two black holes in space – do not happen every day; at least, not close enough to us that we could expect to see one within the lifetime of an observer – unless the observer has such a delicate detector that even events in incredibly distant volumes of space can be observed.
The first version of LIGO, set up in 1999, failed to see any confirmed gravitational wave events. But in late 2014 an improved version, 10 times more sensitive, came into operation. Last September, the event just announced was captured by the detector in Louisiana.
The next step was to see if the same event was recorded by the second detector in Washington. It was. Furthermore, the Washington detector registered it a few microseconds later, as would be expected for a wave travelling at the speed of light across the 3,000km between the two sites.
Theorists had been working for years to calculate just what sorts of events might give rise to gravitational waves, and what the signal of each sort of event might look like. Such calculations were essential in designing the detectors, so that the engineers would have an idea of the precision that they would have to achieve in order to get reasonable results.
Comparing the predictions with the observations allowed the observers to figure out what sort of event they were seeing. The slowly increasing amplitude of the observed signal, followed by its abrupt ending, matched the predictions for two massive black holes spiralling together and then colliding.
The time difference between the detectors told us the direction back to where the waves came from. The magnitude of the signal let them calculate how far away the event was (a bit over a billion light-years distant) and how massive the black holes were (roughly 30 times the mass of the Sun). They even concluded that roughly half the mass of the combined system had to be converted from mass into energy (thanks to Einstein’s famous “E=mc2”rule) at the instant of collision. The system briefly emitted as much energy as all the stars of the visible universe combined.
The experiment did more than merely confirm the existence of gravitational waves; it served as a way to observe the black holes that caused the wave. Hence the “observatory” in LIGO. The massive gravity of black holes prevents light from escaping their surfaces; only gravity waves can be transmitted directly from them to us.
While the physicists are understandably delighted with this new tool to observe the universe, there are also some interesting lessons for the rest of us. This project has orchestrated the talents of many people, over many years, to a cause that produced neither money nor power nor, for most of them, fame.
To uncover the most subtle understandings of reality, large organisations and big hierarchies are absolutely necessary. This was science that no lone visionary, no matter how bright, could have accomplished. It shows what promise and power humans can achieve when we join together for a common cause.
It also confirms, in the strongest way yet, the core of Einstein’s insight. The laws describing Creation are far more surprising, strange and delightful than the simple Deist clockwork conceived by Isaac Newton.
Br Guy Consolmagno SJ is the director of the Vatican Observatory.
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