On February 11th, 2016, researchers working at the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced that, for the first time ever, gravitational waves had been directly observed. The discovery of these waves provides further confirmation of the scientific theory of general relativity, which was first promoted by German-born theoretical physicist Albert Einstein. Given today would have been Albert Einstein’s 137th birthday, we wanted to revisit this recent discovery and explore what it means for the future of scientific research.
The gravitational waves observed at LIGO were formed by two black holes converging at a distance of more than one billion light years away from Earth. The phenomenon took place 1.3 billion years ago and involved massive black holes, one which was 36 times the mass of our sun, the other one 29 times the sun’s mass. The holes likely orbited each other for billions of years before colliding together at the speed of light within a fraction of a second. The event converted approximately three times the sun’s mass into gravitational waves which were detected by LIGO at 5:51 AM on September 14th, 2015.
The existence of gravitational waves proves that there are ripples in spacetime as theorized by Einstein more than 100 years ago. To understand the enormity of this discovery, it’s important to remember that gravity is, as Einstein argued, a force created when massive stellar bodies warp the spacetime fabric which exists around them. Time is not constant throughout space and a clock on Earth will tick slightly faster than a clock positioned on a much larger body, such as Jupiter. A greater understanding of gravitational waves gives scientists another means by which to investigate the universe around us, along with infrared or optical means of viewing space. The LIGO detection event is also the first direct observation of a binary black hole system as well as the first observation of black holes merging.
Einstein first published his theory of general relativity in 1915, challenging notions on gravity that hadn’t changed since Newton’s law of universal gravitation. Instead of gravity as a force being emitted from a massive body, Einstein conceived of gravity as distortions created by those bodies in the spacetime continuum, a fabric which stretches across the universe. Einstein’s theory of general relativity accounts for certain astrological peculiarities, such as the gradual shift of Mercury’s orbit around the sun and gravitational lensing, a phenomenon by which light bends around the gravitational field created by a massive object. Although Einstein theorized that gravitational waves existed and could be created by violent interstellar acts, they were thought to be so weak as to be nearly undetectable; certainly they were given the conventional technologies available in 1915.
We’re taking some time during the current presidential election cycle here on IPWatchdog to explore the issue of immigration and its effects on American innovation and the overall economy. We recently discussed how many products traditionally seen as American, including hot dogs, blue jeans and processed cheese, actually come to us thanks to inventors who immigrated to the United States from abroad. We would be remiss if we did not point out Einstein’s contributions to the U.S. after he fled from a Nazi Germany which was becoming increasingly hostile in 1933. In 1939, Einstein wrote a letter to then U.S. President Franklin Delano Roosevelt warning him that the Germans were working on an atomic bomb, essentially kickstarting the Manhattan Project (although he did not contribute to the scientific research of that project).
The gravitational wave detection techniques employed by LIGO were first developed in the 1960s by scientists looking to test Einstein’s theories of general relativity. Einstein’s theories had been known since 1915 but had been primarily thought of as mathematical concepts until the discovery of lasers and other technologies which enabled highly precise methods of observing physical characteristics of the universe. The early development of LIGO picked up in 1975 after an invitation from then-Massachusetts Institute of Technology (MIT) physics professor Rainer Weiss to Kip Thorne, then a theoretical physicist working at the California Institute of Technology (Caltech), to speak in front of a NASA committee in Washington, D.C. The two shared a hotel room and reportedly wound up discussing the possibility of building a gravitational wave detector into the wee hours of the morning. The duo would work with Ronald Drever, an experimental physicist from the University of Glasgow, and although the partnership among academic institutions was at times troubled, the LIGO system would be completed in 2001 for its first run of tests.
The two detecting stations which make up the LIGO system are separated by 1,895 miles, one located on the Hanford Site in Washington, the other in Livingston, LA. Each facility uses two arms comprised of a series of vacuum tubes which stretch along 4 kilometers (about 2.5 miles) of ground. Measurements of the lengths of the vacuum tubes are taken by pulsing a laser which is split by an interferometer to transmit laser pulses down either arm. The beams hit a mirror at the end of the tube and recombine at the point where they were split. Any misalignment in the lasers indicates that a gravitational wave caused a distortion in the length of one antenna arm relative to the other. To ensure that the distortion is caused by gravitational waves and not other vibrations, two interferometer stations which are separated by large geographical distances must operate in tandem.
LIGO relies on a series of innovative technologies in order to accurately detect the weak force of a passing gravitational wave. Because the antenna system is finely tuned to pick up the smallest vibrations, LIGO incorporates a seismic isolation system which includes active and passive damping elements to keep the system’s primary mirrors, also known as test masses, from being affected by environmental vibrations. The laser travels through the world’s second-largest vacuum, smaller only than the vacuum built for the Large Hadron Collider at CERN, where the atmospheric pressure is one-trillionth that of air pressure at sea level, keeping heat and dust from interfering with the laser signal. The optics system used by LIGO involves a series of lasers, mirrors and a photodetector to measure light levels. Mirrors are made from pure fused silica, which absorbs a tiny fraction of the heat created by the laser, preventing deformations to the mirrors caused by heat. The terabytes of data generated each day by LIGO is analyzed by supercomputers located at both observatory sites, Caltech, MIT and elsewhere.
The breakthrough in the detection of gravitational waves was largely enabled by recent developments in the Advanced LIGO (AdLIGO) system. AdLIGO increases the sensitivity of prior LIGO systems by ten-fold and allowed researchers to explore more than a thousand times the volume of space that could be investigated prior to the upgrade. The AdLIGO system comprises a multitude of changes to the initial LIGO, including increasing the laser power, from 10 watts to about 200 watts, as well as the weight and diameter of the fused silica test optics, respectively helping to eliminate radiation pressure noise and thermal noise. According to MIT’s AdLIGO page, the system is the most sensitive interferometer that can be constructed with known technologies; it can detect changes in the antenna arm length which are smaller than one-ten-thousandth (1/10,000th) the diameter of a proton.
There are many exciting implications that come now that the existence of gravitational waves have been proven. It’s possible that gravitational waves consist of quantum particles known as gravitons similar to the way that light waves are made up of photons. It also enables further testing of Einstein’s theory of general relativity for greater scientific research into gravity, taking such science out of the theoretical realm and into the experimental. Amateur scientists who would like to be a part of the mission towards a greater understanding of gravity can lend processing resources from a personal computer by downloading a screensaver known as Einstein@Home. As the screensaver runs, the computer’s processor analyzes data produced by LIGO and other astronomical observatories to search for weak astronomical signals. Einstein@Home, a joint project of the National Science Foundation, the Max Planck Society and the American Physical Society, has already identified fifty new neutron stars.