This paper will discuss the video Gravitational Waves: A New Era of Astronomy Begins from the World Science Festival. This video tells about one of the most significant achievements in physics in the 21st century, the first direct detection of gravitational waves. The scientists, including those who made this discovery possible, discuss various aspects of the waves and the experiments conducted. It took a long way to go to detect gravitational waves, and this way is interesting to discuss.
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Gravitational waves can be called ripples in the fabric of space-time, traveling at the speed of light and carrying information about their massive accelerating sources, such as colliding black holes or neutron stars, or supernovae. These waves were predicted in 1916, almost a hundred years before their direct detection, by Albert Einstein in his general theory of relativity. The first attempts to detect the waves were conducted in the 1960s. However, at that time, it was not possible to catch gravitational waves.
Even the success of the modern experiment was rather unexpected. For the last several decades, it was obvious that gravitational waves exist. However, it was hard to imagine that people would have the capacity to detect them. As Brian Greene notes in his introduction, everyone was convinced of the success of the experiment with the Higgs boson (“Gravitational Waves” 00:01:52-00:2:06). Gravitational waves, in turn, were connected with much more uncertainty.
The scientists say they even did not believe at first in the successful detection. They caught “absolutely beautiful waveform,” and that made them suspicious (“Gravitational Waves” 00:16:38-00:16:40). To see the picture clear, it is necessary to imagine how these gravitational waves appear far away and long ago from two black holes colliding and having their way through space and time. After 1.3 billion years, they finally reach the Earth. Then, as Greene asks the scientists jokingly, “is it just so happens that just as it is rolling by Earth, you get this device just turned on and catches it?!” and the answer is “yes” (“Gravitational Waves” 00:19:45-00:20:17). In these circumstances, the success of the experiment seems like a miracle.
Another interesting point is that it is not possible to simulate the wave sources in the laboratory. The scientists point out that only the conditions of the Universe can provide the real opportunity for wave detection (“Gravitational Waves” 00:27:41-00:29:08). The sources of gravitational waves should be extremely massive: the black holes that have been observed have 30 times the mass of the Sun. In addition, the waves travel at the speed of light. These conditions, of course, are not achievable on Earth. In this regard, the experiment seems even more significant, as it interacts with the Universe itself.
Calculations for the experiment also required hard and long work. It was not an option to find all the solutions using just a pencil and paper. As Pretorius points out, things are very complicated with two black holes colliding, as there is no symmetry (“Gravitational Waves” 00:38:50-00:38:59). In this regard, computer methods were used to solve Einstein’s equations. However, even computers had certain difficulties when finding solutions. For instance, one of the problems was that “one physical space-time” can be represented through “the infinitely many ways,” and computers at first did not know which one of these infinitely many possibilities to solve (“Gravitational Waves” 00:40:04-00:40:50). The scientists had to cope with numerous technical issues to find ways to make things stable. Thus, the researchers were conducting work on different levels, and the experiment became possible due to the forces of many people.
As for the facilities, to detect gravitational waves, the Laser Interferometer Gravitational-Wave Observatory (LIGO) was created. It consists of two separate interferometers located far apart and operating simultaneously to detect gravitational waves. When planning the project, the researchers suggested using a two-stage approach that also contributed to the success of the study. As people were skeptical about the whole concept, the plan to create two LIGO systems made this project more likely to become real. Till 2010, “Initial LIGO” had been conducting science observations, the work that scientists already “knew how to do at that time” (“Gravitational Waves” 1:18:47-1:18:50). In this system, the calculations that were already made on a small scale, in detector prototypes, were moved to a large scale. Then the infrastructure was improved, and “Advanced LIGO” was used for things the researchers “thought they would do” (“Gravitational Waves” 1:18:47-1:18:50). In this version of LIGO, although possibilities were not high, the main experiment turned out to be successful, and gravitational waves were detected.
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From the point of view of engineering, LIGO also required hard work. One of the challenges was to isolate detectors from any forces apart from gravitational waves. In the video, the scientists demonstrate the prototype of an interferometer. The interferometer, in fact, consists of a laser producing beams of light, a beam splitter, a series of mirrors, and a photodetector. The two light beams generate an interference pattern that reacts to the disturbers that including gravitational waves. This demonstration has shown how sensitive the detector is, as it reacted to the voices and the applause. As Shoemaker also points out, real detectors could be influenced even by people passing nearby (“Gravitational Waves” 1:10:00-1:10:06). That is why the system was isolated from the outer influencers through the usage of multiple layers and materials with low mechanical losses.
Another challenge, naturally, was about the LIGO detectors’ sensitivity. When planning the project, people and, mostly engineers, as Weiss notes, were skeptical about the idea of doing “measurements at ten to the minus eighteen meters” (“Gravitational Waves” 1:13:50-1:14:00). Nevertheless, the engineers and scientists managed to achieve this level of sensitivity, and LIGO instruments are able to measure a motion 10,000 times smaller than the size of an atomic nucleus.
In the final part of the video, the scientists also discuss some ideas for future studies and achievements. Some of the most interesting thoughts are connected, for instance, with the string theory, the improvement of LIGO engineering, and numerical methods. In fact, if summarizing the main ideas of the discussion, it is evident that the detection of gravitational waves became one of the most significant achievements in the last decades. It required the significant work of many researchers, starting from Einstein’s theory at the beginning of the 20th century and resulting in the creation of LIGO, which is itself an important event. Nevertheless, there is still much space for future experiments and the development of science, including further investigation of gravitational waves.
“Gravitational Waves: A New Era of Astronomy Begins.” YouTube, 2016. Web.