LIGO’s Discovery: Understanding the Gravity of the Situation

By: Alex Zapien

History was made on February 11, 2016 when the Laser Interferometer Gravitational-Wave Observatory (LIGO) Scientific and Virgo collaboration teams confirmed the existence of gravitational waves, ripples that propagate in the fabric of spacetime generated by gravitational interactions once predicted by Albert Einstein. The announcement sparked widespread excitement in the scientific community. Many described the discovery as one of the most important discoveries in physics in the past several decades: as LIGO Executive Director David Reitze remarked, “this was truly a scientific moonshot, and we did it, we landed on the moon” (1-2). LIGO’s revolutionary project has pushed society to greater understanding of the universe.

LIGO, which is funded by the National Science Foundation, is a pair of ground-based observatories in Livingston, Louisiana and Hanford, Washington. They were built and operated by the California and Massachusetts Institutes of Technology (3-4). The detector, shaped like an “L,” senses the space distortions that occur when a gravitational wave passes through the Earth (3). Amazingly precise atomic clocks measure how long it takes for laser light to bounce back and forth, reflecting off of mirrors, throughout the legs. Usually, light takes exactly the same amount of time to traverse each leg, which are exactly the same length; however, when a gravitational wave passes through, the detector and the ground beneath it expand and contract a miniscule amount in a particular direction. As a result, the two legs are no longer the same length, and the light travel time changes (3). The original waves were first detected in September 14, 2015 but were not confirmed until February 2016. The waves were caused by a 1.3-billion-year-old collision between two black holes, weighing between 29 and 36 solar masses (5.8 x 1031 kg and 7.2 x 1031 kg, respectively). Traveling at the speed of light, the waves did not reach Earth until this past year. The actual black hole collision incredibly happened in a very short period of time – fractions of a second – releasing tremendous amounts of energy while producing massive ripples in the fabric of spacetime (5).

The original LIGO proposers, Professors Kip Thorne, Rainer Weiss, and Ronald Drever, have provided evidence for and strengthened modern physical theories and have ushered in a new era where the field of gravitational astronomy

is a reality. Black holes and gravitational waves were first predicted by Albert Einstein in his General Theory of Relativity in 1915, more than 100 years ago (4). Several decades later, in 1974, physicists Joseph Taylor Jr. and Russel Hulse demonstrated the existence of the waves when they discovered a binary system composed of a pulsar, a rapidly rotating neutron star that emits radiation in pulses, in orbit around another neutron star. They found that the pulsar’s orbit was gradually shrinking over time because of energy being released in the form of gravitational waves. For the discovery of the pulsar and for showing that it was possible to make measurements of gravitational waves, Drs Taylor and Hulse were awarded the Nobel Prize in Physics in 1993 (4). With the success of the LIGO project, Professors Thorne, Weiss, and Drever are expected to win a Nobel Prize in the nearby future.

The future is bright for gravitational astronomy, and a third advanced LIGO detector is scheduled to be built in India within the next decade (2). Ultimately, the LIGO discovery is a triumph for humanity that will further enlighten future generations about the dark, large fractions of the endless universe.

Alex Zapien ‘19 is a freshman in Canaday Hall.

WORKS CITED

[1] Graham Peter. Newsweek: Tech and Science. http://www. newsweek.com/quora-question-how-important-discovery-gravitational-waves-427437 (accessed Feb. 21 2016). “Quora Question: How Important is the Discovery of Gravitational Waves?”

[2] Moskowitz, Clara. Scientific American. http://www.scientificamerican.com/article/gravitational-waves-discovered-from-colliding-black-holes1/ (accessed Feb. 21 2016). “Gravitational Waves Discovered From Colliding Black Holes.”

[3] NASA: Solar System and Beyond. http://www.nasa.gov/ feature/goddard/2016/nsf-s-ligo-has-detected-gravitational-waves (accessed Feb. 21 2016). “NSF’s LIGO has Detected Gravitational Waves.”

[4] LIGO: Caltech. https://www.ligo.caltech.edu/news/ ligo20160211 (accessed Feb. 21 2016). “Gravitational Waves Detected 100 years After Einstein’s Prediction.”

[5] O’Neil, Ian. Discovery: News: Space. http://news. discovery.com/space/weve-detected-gravitational-waves-so-what-160213.htm (accessed Feb. 21 2016). “We’ve Detected Gravitational Waves, So What?”

Categories: Spring 2016

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