Learning from the Past in Science and Technology: From Measuring Light to Observing Waves of Matter

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Scientific Common Sense

Learning from the Past in Science and Technology: From Measuring Light to Observing Waves of Matter

In 1887, Michelson and Morley conducted an experiment that, in later generations, would be known as the greatest failed experiment in history. Failure is something that should be remembered much longer than success, but, in reality, this is not often the case. However, Michelson’s failure later led him on the path to achieving the honor of being the first American to be awarded the Nobel Prize. In order to prove the existence of aether, which was a very hot topic of debate at the time, Michelson designed and implemented the most precise measurement method. Now known as the Michelson interferometer, it is a simple device that uses interference to measure light by dividing it into two paths and then connecting them again. When the light is divided into two, if there is a relatively subtle change on either side, a change in the brightness of the combined interference pattern can be observed.

At the time of Michelson’s experiment, there were more physicists who believed that light waves moved through different media, just as sound waves and seismic waves do. This unknown medium of light that filled the universe, although invisible, was referred to as “aether.” Michelson and Morley believed that the relative speed of light moving through the aether would be measured differently according to the Earth's rotation and orbit. As such, they made every effort to ensure that the interferometer would not be affected by ambient temperature changes or vibrations. In the basement of an insulated building, they placed the interferometer in a bath filled with mercury to prevent any vibrations. However, the measurement results were different from what they had hoped. The speed of light did not significantly change as a result of the earth's rotation and orbit. Since then, scientists have attempted to make the interferometer more precise, but, unsurprisingly, they all failed to measure any changes in the speed of light caused by the surrounding aether.

In the basement of an insulated building, they placed the interferometer in a bath filled with mercury to prevent any vibrations. However, the measurement results were different from what they had hoped. The speed of light did not significantly change as a result of the earth's rotation and orbit. Since then, scientists have attempted to make the interferometer more precise, but, unsurprisingly, they all failed to measure any changes in the speed of light caused by the surrounding aether. It was Einstein, a denier of the concept of aether, who played the decisive role in transforming Michelson's failure into a success. Maxwell, a remarkable physicist in the 19th century, argued for the existence of aether with very complex explanations. However, in his theory of electromagnetic waves, the speed of light was, paradoxically, always a constant.

It was Einstein, a denier of the concept of aether, who played the decisive role in transforming Michelson's failure into a success. Maxwell, a remarkable physicist in the 19th century, argued for the existence of aether with very complex explanations. However, in his theory of electromagnetic waves, the speed of light was, paradoxically, always a constant. Based on this fact and the failure of the aether measurement experiment, Einstein argued that the speed of light is always constant in an empty space (vacuum). Moreover, he believed that the relative speed of light did not change even when moving at a constant speed. Let us use our imagination just as Einstein did. The speed of sunlight measured by two spacecrafts moving at high speeds in opposite directions, either leaving or entering the solar system, is the same. On the other hand, it is not so difficult to assume that time, which everyone had believed to be always constant, appears to pass relatively differently. And so, the special theory of relativity was born. Everyone now accepts the fact that light moves faster than anything else in the world and that is speed is constant regardless of who observes it.

Later on, Einstein predicted the existence of gravitational waves with the theory of general relativity. When an empty space meets gravity, it behaves like a material that bends or becomes twisted. Gravity waves that are propagated as space grows or shrinks are difficult for humans to accept, due to a sense of perception that is reliant on experience. Regardless, since they are waves created by a space of nothing without mass, the speed of a matter wave is the same as that of light. In September 2015, humans succeeded in actually measuring the gravitational waves created by the collision of black holes one hundred years after the event occurred. This historical measurement was immediately awarded the 2017 Nobel Prize in Physics. Ironically, the core technology of the “Laser Interferometer Gravitational-Wave Observatory”, or “LIGO,” which made decisive contributions to this success, was the Michelson interferometer. Although cutting edge laser technology and precision machinery and electronics were all utilized, the core of the technology was improving the precision of the Michelson interferometer, which uses interference to divide the light into two and then recombining it, by greatly increasing its size. While the interferometer originally consists of two perpendicular tunnels about 4 km long, a Pabry-Perot type resonator was added. Through this resonator, light travels back and forth hundreds of times to make the light path hundreds of times longer. As such, the effective size of the interferometer could be hundreds of thousands of times larger than that of the device used in 1887.

Both of these optical technologies were made in the 19th century. The field of science can be seen as the process of gradually adding small stones to a stone tower that was made over a long period of time. Although something might be considered a failure at first, it is the hard work and countless measurements done to strengthen precision of those findings that ultimately lead to today’s success.