The Beginning of Physics: Thomas Young (Part-13)

The Beginning of Physics: Thomas Young (Part-13)

(Last Updated On: April 16, 2020)

Who’s this guy?

Thomas Young (1773-1829) was a man who “made a number of original and insightful innovations” in many fields of science, such as vision, lightsolid mechanics, energyphysiology, language,  musical harmony, and Egyptology.

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Thomas Young

Child Prodigy

Thomas Young was remarkable since his early childhood. He could already read by his 2nd birthday and with four years old he had read the bible twice.

While a teen, he could read Greek, Latin, Hebrew, Persian, Syriac, and Chaldean. He also started to teach himself calculus, studied the sciences, and learned medicine.

By age twenty he had also learned French, German, Spanish, Arabic and Italian. You might think of Young has a nerd by now, but that wouldn’t be true at all. He could sing, dance and ride horses (yes, this was cool at the time).

Also, much in 1814 Young deciphered the famous Rosetta Stone (an ancient Egyptian stone bearing inscriptions in several languages and scripts). This heavily helped further understanding of hieroglyphs.

Prom physician to physicist

Thomas began studying medicine in 1792, with the purpose of becoming a physician. He obtained the degree of doctor of medicine in 1796 from the University of Göttingen. In 1799 Young set up a medical practice in London.

While still a medical student, Young was heavily interested in optics. He discovered the way in which the lens of the eyes changes focus at different distances. By 1801, he was the first to have defined astigmatism.

In the same year, 1801, Young changed his focus to the study of light. At this time, the Newton view that light was a particle was still hold. Any opposing theory to this view was unthinkable. However, this didn’t stop Young from agreeing in disagreeing.

Young’s view of light

Since Newton’s times, light was viewed as a particle. It made sense, light rays go straight, it explained phenomena like refraction, among others.

There were however some problems with this theory. For example, there was the problem of color. Since there are different colors, and colors can’t transform into other colors (red can’t became blue), every color had to have its own particle. So for this theory to be right, there should exist an infinity number of different particles, each corresponding to some color.

Young didn’t agree to this view of light. So, in 1801 Young proposed a number of theoretical reasons for why light was a wave. Young demonstrated interference in the context of light as a wave with his Young experiment. You might be more familiar with this experiment other name, double-slit experiment.

This experiments consists in allowing light to pass through two slits very near each other onto a screen. See the image below for more clarification.

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The double-slit experiment. The dark bands is where a trough of a wave from one slit meets a crest of a wave from the other slit, and the two cancel out. The light band is where two crests, or two trough, of different slits meet and reinforce each other.

No person had ever done this experiment because the slits couldn’t be too big. This experiment can only take place when the slits are thin enough (the original experiment had slits of about 0.8mm). This experiment shows a phenomenon called diffraction, the deviation from rectilinear propagation when a small slit or hole is placed in the way of a light wave.

In Young’s mind, this experiment immediately proved that light was in fact a wave. However this idea would only be accepted years later in 1817, by Augustin-Jean Fresnel. Fresnel independently proposed his own wave theory of light at the Académie des Sciences. After a bit of resistance from others physicists, it was agreed: light was a wave.

Young on Energy

Young was the first person to use the term Energy, from the Greek word “ένεργεια” meaning efficacy or effective force. This was an abbreviation for the sum of the kinetic and gravitational potential energy of a body (although, the terms kinetic and potential energy didn’t yet exist at the time. They would only be coined by Gustave-Gaspard Coriolis in 1829 and William Rankine in 1853 respectively).

In the words of Thomas Young, in 1807 at a Royal Society lecture:

“The term energy may be applied, with great propriety, to the product of mass or weight of a body, into the square of the number expressing its velocity. Thus, if the weight of one ounce moves with a velocity of a foot in a second, we call its energy 1; if a second body of two ounces has a velocity of three feet in a second, its energy will be twice the square of three, or 18.”

– Thomas Young (1807), A Course of Lectures on Natural Philosophy and the Mechanical Arts Vol. 1
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Thomas Young’s book

Simplifying, Young described energy as E=mv^2.

Goodbye

Thomas Young would later die with 56 years old in London on 10 May 1829. His genius was admired by many others after his death. Sir John Herschel called him a “truly original genius”, Albert Einstein praised him on a foreword to an edition of Isaac Newton’s Opticks, among many others.

Inspirational phrases by Young

Whoever would arrive at excellence must be self-taught. There is, in reality, very little that a person who is serious and industriously disposed to improve may not obtain from books with more advantage than from a living instructor.”

— Thomas Young (1798), “Letter to brother”

“The longer a person has lived the less he gains by reading, and the more likely he is to forget what he has read and learnt of old; and the only remedy that I know of is to write upon every subject that he wishes to understand, even if he burns what he has written.”

— Thomas Young (1809), “Letter to Hudson Gurney”

Baltas Cruz

A 15-year-old Portuguese who at such a young age has the ambitions of becoming a theoretical physicist. Whilst maintaining his passion of becoming a physicist, he is also a chess player where he has won some local competitors alongside being a runner up in the local team also.

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