Gravitational waves
Many optimizations were also required in order for this experiment to be complete. The smoothest mirrors ever created were required. [13] This was to ensure as much light as possible is reflected to increase the signal output of the lasers for a positive result. They reflect all but one in every 5 million photons which hit them. There are many strict measures to ensure that the mirrors are seismically isolated. The 40kg [14] mirrors are suspended by silica threads twice the thickness of a hair to isolate them from their environment. [13] This, in addition to the masses used (see fig. 9), all culminate in reducing the effect of seismic activity in the mirrors. The most distinguishing feature of LIGO is the arms. Each arm in the two LIGO sites is 4 km long. Two sites are used in order to not rely on one which may be perturbed by local seismic activity or a faulty reading. [11] The arms are made to be so long in order to maximize the effect of a gravitational wave passing through them. A change over a larger distance is easier to detect than one over a small distance. The effect of the long arms is put to good use due to the implementation of ‘Fabry Perot cavities’ (see fig. 10). In these cavities light is reflected to about 300 times. [15] This is done to increase the effective distance which the light travels from 4km to 1200km. This greatly increases the sensitivity of LIGO. All of these procedures are needed to create the most precise ruler ever, as it can measure the infinitesimally small effect of a gravitational wave which has an effect 1/10,000 th the diameter of a proton. [16]
Figure 9: Anatomy of one of LIGO’s Mirrors. Credit: LIGO
Figure 10: LIGO with the Fabry Perot cavity included. Credit: LIGO
This all leads to the 14 th September 2015. The newest version of LIGO was built called Advanced LIGO which contained many upgrades on the previous iteration. [4] While warming up this new iteration, gravitational waves were unexpectedly detected for the first time. The two LIGOs both detected a 0.2 gravitational wave signal within 0.7 milliseconds of each other. This was a surprise to the scientists involved but a happy one. The scientists were able to determine through comprehensive data analysis that the gravitational wave was emitted from two black holes, one of 36 solar masses (1 solar mass= the mass of the sun) and one which was 29 solar masses. [17] The resulting black hole was 62 solar masses, meaning that 3 solar masses were emitted via gravitational waves, due to energy being related to mass by Einstein’s equation E=mc 2 . The consequences of this are yet to be fully understood but could be really significant. Gravitational waves are not affected by matter to the same degree as electromagnetic radiation (light). They open a new way to view the cosmos. They are as distinct as vision is to hearing. [18] Due to this, we can look through space with a whole new perspective, as if mankind gained an ear whilst only being able to see for their entirety of their preceding history. It may allow us to do things such as seeing into a black
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