Cosmos: A Spacetime Odyssey Episode 5: Hiding in the Light — What do the scientific method, Lao Tzu, and a German glassmaker have in common? An understanding of how light tells us everything.
This week’s episode of Cosmos: A Spacetime Odyssey talks about properties of light and the secrets those properties reveal. To get a basic understanding of how those discoveries were made, we get a brief history of the scientific method, revisit our old friends Isaac Newton and William Herschel, and learn the origins of spectrometry and astrophysics. Oh my goodness. Here are five pioneers in these amazing discoveries.
Mozi and Lao Tzu. Over 2,000 years ago, Mozi figured out how to project images using a hole in a wall and some light. This became what is now known as a camera obscura. The trial and error of this process provided a foundation for some of the work of Lao Tzu. His writings included the earliest recorded account of a method to determining truths. His suggestions included questioning the basis of a perceived truth, verifying that the information can be understood by common folk, and asking if new information is applicable. It’s a basic form of the scientific method. However, Chinese imperial history was not kind to those who questioned authority, what with the family of those who asked questions getting executed and all.
Ibn al-Hazen. Fast forward a thousand or so years to the golden age of science in the Islamic world. This was a time when everyone sought knowledge, going on pilgrimages to acquire books to better understand the world. During this era Arabic numerals (such as the number 0) and terminology—algebra, algorithm, alchemy—came into vogue. Also, experiments with camera obscura allowed Ibn al-Hazen to learn quite a bit about optics. For example, the aperture allowing light led to the discovery that light travels in straight lines. Although these discoveries could only be made via sunlight, it provided the foundation for creating lenses, which led to the development of telescopes. Ibn al-Hazen’s experiments led him to expand on the rudimentary scientific method. His suggestions: withhold judgment, question writings, listen only to argument and experimentation, and question your own ideas to avoid prejudice.
William Herschel. Newton coined the term spectrum after seeing what happens when light goes through a prism. Herschel conducted the first controlled experiments on the various colors of light. One experiment attempted to measure the amount of heat given off by each color. Herschel’s control variable was a thermometer kept out of where red light would hit it. Although he discovered red gives off more heat than blue, the control thermometer was significantly warmer than red. This was the discovery of infra-red light and the invisible spectrum. So there’s more to light than what meets the eye…
Joseph von Fraunhofer. Orphaned at the age of 11, Fraunhofer was taken in by a mirror maker who should not have kids. After a house collapse, Fraunhofer became a ward of Maximilian II of Bavaria and eventually ended up with an optician job. During his time as a master lensmaker, Fraunhofer discovered black lines within the spectrum. What did those lines mean? It turns out they are shadows caused by the travel of electrons. While an electron orbits a nucleus, it does not follow a consistent path. Every time it gets hit by a photon, the electron jumps to a higher level of orbit. When the electron jumps to a lower level of orbit, it gives off energy at the same level as color. The reason for these jumps is a question for quantum mechanics, but these shadows reveal more than weird behavior. Since atoms vary in the number of electrons they carry, looking at a given spectrum will be able to inform the viewer what elements exist in the light source. This was the birth of spectrometry, which allows us to figure out the composition of anything in the universe. This in turn originated the science of astrophysics.
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