In the latter part of the 17th century, the world's first physicist, Sir Issac Newton, expanding on the work of Galileo, posited that gravitational waves traveled faster than anything else in the universe. But in 1915, Einstein disputed this concept of Newtonian physics when he published the General Theory of Relativity and suggested that nothing can travel faster than the speed of light, even gravitational waves.
TL;DR (Too Long; Didn't Read)
The importance of gravitational waves:
- Opens a new window into the cosmos
- Proves Einstein's theory of general relativity
- Disproves Newton's theory that gravitational events occur everywhere at once
- Led to the discovery of the gravitational wave spectrum
- Could lead to potential new devices and technologies
An Epic Event
On September 14, 2015, when the first-ever measurable gravitational waves reached the Earth at the exact same time as the light waves did from the collision of two black holes near the edge of the universe 1.3 billion years ago, Einstein's general relativity theory proved correct. Measured by the Laser Interferometer Gravitational-Wave Observatory in the U.S., the Virgo detector in Europe and 70 or so space and ground-based telescopes and observatories, these ripples opened a window into the gravitational wave spectrum – a brand-new frequency band – through which scientists and astrophysicists now eagerly gaze across the fabric of space-time.
How Scientists Measure Gravitational Waves
In the U.S., LIGO observatories sit on the ground in Livingston, Louisiana and Hanford, Washington. The buildings resemble an L from above with two wings that span 2 1/2 miles in perpendicular directions, anchored at the 90-degree crux by the observatory buildings that house a laser, the beam-splitter, light detector and control room.
With mirrors set at the end of each wing, a laser beam – split in two – speeds down each arm to hit the mirrors at the end and bounces back almost instantaneously when it does not detect a gravitational wave. But when a gravitational wave passes through the observatory with no effect on the physical structure, it distorts the gravitational field and stretches the fabric of space-time along one arm of the observatory and squeezes it on the other, causing one of the split beams to return to the crux slower than the other one, generating a small signal only a light detector can measure.
Both observatories function at the same time, though the gravitational waves hit at slightly different times, and provide scientists with two data points in space to triangulate and track back to the event's location.
Gravitational Waves Ripple the Space-Time Continuum
Newton believed that when a large mass moves in space, the entire gravitational field also moves instantaneously and affects all gravitational bodies across the universe. But Einstein's General Theory of Relativity suggested that was false. He asserted that no information from any event in space could travel faster than the speed of light – energy and information – including the movement of large bodies in space. His theory instead suggested that changes in the gravitational field would move at the speed of light. Like tossing a rock into a pond, when two black holes merge, for example, their movement and combined mass sparks an event that ripples out across the space-time continuum, lengthening the fabric of space-time.
Gravity Waves and the Effects on Earth
At the time of publication, a total of four events in which two black holes merge as one at different locations in the universe provided scientists with multiple opportunities to measure light and gravitational waves at observatories around the world. When at least three observatories measure the waves, two significant events occur: first, scientists can more precisely locate the source of the event in the heavens, and second, scientists can observe the patterns of space distortion caused by the waves and compare them against known gravitational theories. While these waves distort the fabric of space-time and gravitational fields, they pass through physical matter and structures with little to no observable effect.
What the Future Holds
This epic event occurred just short of the 100th anniversary of Einstein's presentation of his general relativity theory to the Royal Prussian Academy of Sciences on November 25, 1915. When researchers measured both gravitational and light waves in 2015, it opened a new field of study that continues to energize astrophysicists, quantum physicists, astronomers and other scientists with its unknown potentials.
In the past, each time scientists uncovered a new frequency band in the electromagnetic spectrum, for example, they and others discovered and created new technologies that include such devices as X-ray machines, radio and television sets that broadcast from the radio wave spectrum along with walkie-talkies, ham radios, eventually cellphones and a slew of other devices. What the gravitational wave spectrum brings to science still awaits discovery.
- LIGO Scientific Collaboration: Introduction to LIGO & Gravitational Waves
- Stanford University: Special & General Relativity Questions and Answers
- Cal Tech: What Are Gravitational Waves?
- Space.com: Epic Gravitational Wave Detection: How Scientists Did It
- Oberlin College & Conservatory: Professors Break Down Importance of Gravitational Wave Detection
- Cal Tech: Why Detect Them?
- Princeton University: Was Einstein the First to Discover General Relativity?