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Optical interferometry is the use of the interaction between two or more waves of energy to collect information. They either come from the same source or are of similar frequency, and the interference generated within the measuring instrument offers important data about their behavior and the characteristics of the source. Experiments with this technique date to the early 1800s which played a key role in the development of theories about the nature of the universe. Scientists can apply optical interferometry to a number of measuring and calibrating tasks.
In a simple example of optical interferometry, an astronomer may choose to take measurements of the same point source, like a star, with two telescopes. Each telescope collects light from the star and feeds it to an interferometer, which combines the information. The astronomer can take note of the variations in the images and collect information about the location, size, and composition of the star. These observations may allow the astronomer to determine whether the star is approaching or receding, and to track its movement through the universe.
The word “optical” in the title can be misleading, as it can create the impression that optical interferometry involves working with visible light. In fact, energy in non-visible wavelengths can be collected as well, with the use of specialized optics devices. This can include radio waves, which are widely utilized in astronomy to collect data about extremely distant objects. Researchers can work with energy from a source of interest, or may generate energy with tools like lasers to take measurements and calibrate equipment.
Numerous pieces of equipment may be combined, such as a bank of radio telescopes, in optical interferometry work. As the wavelengths are combined and interference develops, observers may detect information in the fringes of the data that can provide insight into the nature of the sources being observed. This process can be useful for everything from taking extremely precise measurements of phenomena on earth to testing theories about the composition of distant stars.
Some early experiments with astronomical optical interferometry illustrated that previous theories about the composition of space were incorrect. For many centuries, people had believed that a substance known as “ether” was present in the atmosphere, and served as a conductor for sound and light. In the 1800s, observations taken with the assistance of optical interferometry poked some holes in the theory, and in the 1900s, science advanced by leaps and bounds to dismantle the theory altogether and replace it with other models to explain the universe.