LIGO: A shocking scientific discovery

Posted by Pranav Kakhandiki| Nov 12, 2018, 12:00:00 PM   

 

      A gravity wave is defined as a disturbance in the fabric of space time. First postulated by Einstein, gravity waves were nothing but a theory – until 2015. Thanks to the LIGO detector, a group of scientists at CalTech were able to confirm their physical existence in our universe.

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A visualization of gravity waves

     Gravity is known to warp space time. To better comprehend this effect, imagine a 2-dimensional cloth, which represents the fabric of space-time. When a mass is placed onto the cloth, the cloth sags, thus demonstrating how the mass stretches space into the 3rd dimension. This sag in the cloth causes other objects to roll toward the center of mass, demonstrating how gravity bends space time. Similarly, masses in the 3rd dimension change the structure of space time. Gravity waves, likewise, are produced when accelerating masses disturb space-time. The masses cause ripples in the fabric, and often happen when two high-density masses, such as black holes or neutron stars, form a twin-system.

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The LIGO detector

     Although the existence of gravity waves were predicted to exist in 1916, and proved mathematically in 1974, they were not physically detected until 2015. The LIGO detector, which stands for Laser Interferometer Gravitational-Wave Observatory, consists of two 4 kilometer buildings at a 90 degree angle with respect to each other. These buildings, often referred to as the “arms”, are narrow, perfectly straight, the exact same length, and transmit light waves. A light wave is produced, split using a mirror, then is sent down both arms. The two waves are then reflected back by mirrors at the ends of each arm and converge at the same point where they were split. Normally, the waves “cancel” each other out, as the troughs of one wave align with the peaks of the other.

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How two waves cancel each other out

     When gravity waves travel through the LIGO detector, one arm slightly lengthens. As the wave continues to pass through, the arms alternate between being longer and shorter. When one arm is longer than the other, the wave peaks and troughs do not cancel out, so the detector senses a signal. As the arms continually shift through being longer and shorter, the strength of the light signal detected varies. This variation detected is a gravity wave!

     From general relativity, to black holes, to Hawking radiation, the discovery of gravity waves was one of the biggest recent breakthroughs in physics. What will the next one be?

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