The Laser Interferometer Gravitational-Wave Observatory (LIGO) has successful detected gravitational waves twice over the course of two years. Scientist have been working on LIGO since 1994 but finally have the evidence to move forward with the investigation of gravitational waves with the data acquired from this initial data. Two 4km interferometry facilities are used to detect said waves to ensure experimental fidelity, one in Hanford, Washington and another in Livingston, Louisiana, pictured below. 

Source: LIGO website

Source: LIGO website

Our understanding of gravitational waves has been stagnate ever since Albert Einstein predicted them in the theory of relativity in the early 20th century. An experiment to verify the gravitational waves have eluded physicists and astrophysicist for years. But the cosmos gave researchers a spectacular opportunity with a stellar collision of two black holes 1.4 billion light-years away.

Interferometry as an experimental setup for gravitational wave detection is new, so scientists only have the capability to detect events that cause the largest gravitational waves. The colliding black holes first detected had masses 36 and 29 times that of our sun and scientists could only detect the last 0.2 seconds of their demise. In those last 0.2 seconds, the black holes cycled 10 times around each other before ultimately converging into one causing a warp in space-time that rippled throughout the cosmos eventually encompassing earth.

A laser interferometer layout for LIGO (Photo source LIGO/Caltech)

A laser interferometer layout for LIGO (Photo source LIGO/Caltech)

Laser Interferometer Gravitational-Wave Observatory (LIGO) uses interferometry as its fundamental science for detection. American Society of Physics Teachers defines Interferometry as, “Interferometry makes use of the principles of superposition to combine waves in to use as a diagnostic tool of the original state of the wave. When two waves with the same frequency combine, the resulting Intensity pattern is determined by the phase difference between the two waves – waves that are in phase will undergo constructive interference while waves that are out of phase will undergo destructive interference.” Once the laser experiences a phase change, the scientist will know a wave passed through its sensor. The biggest problem with use of an interferometer is noise from other wave sources.  The LIGO experiment must take out interference. Interference includes: seismic, audio, and other sources of electromagnetic waves. The sensors isolation is key for successful detecting of gravity waves.

Knowing the science of interferometry, you can scale the sensitivity of an interferometer and use it as a detector for gravitational waves. When the current LIGO sensors are upgraded by a factor of 10 (anticipated by 2019) scientists will be able to detect the number of cosmic events by a factor of ten.

There is a substantially more information on LIGO on their website linked below.https://www.ligo.caltech.edu/video/ligo20160914v1

Ask your students about on the characterisics of measurement:

  • What is the importance of scale
  • How do you verify what you're measuring is true
  • Precise vs accurate

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