While several huge ah-ha moments occurred during completion of the Big Bang and the atom puzzles, the discovery of energy and its conservation was not as clean-cut.  The Big Bang was an event, the atom an object, and each was a product of nature.  Each leant itself to true discovery.  But energy was different.  It was a man-made concept based on many observations relating to motion and change.  It wasn’t sitting there waiting to be discovered.  It was an abstract concept waiting to be created. 

The Ancient Greeks provided the first recorded ideas about motion. The creation process ended with the independent and simultaneous efforts of many scientists in Western Europe in the mid-1800s. Without understanding this history, one can’t appreciate the achievement.  Galileo can’t be understood without Aristotle, Newton can’t be understood without Galileo, and Einstein can’t be understood without Newton.

Aristotle turned man’s mind towards the natural world

For lack of more ancient records, history of mechanics starts with Aristotle – René Dugas [1]

Aristotle may have been the last person to know everything there was to be known in his own lifetime – Daniel Tunkelang [2]

A student of Plato, Aristotle (384 – 322 BC) played the dominant role in leading the evolution of thought from the internal mind to the natural world, addressing in the process man’s need to understand causality. But while a recognized genius, Aristotle was not perfect.  Many of his ideas were right, but some significantly weren’t.

Specifically regarding the concept of motion, Aristotle considered two separate forms: 1) the motion of objects such as projectiles and falling bodies, and 2) the motion associated with the use of simple machines such as the lever.  The developments of each took different evolutionary paths, with (1) evolving from Aristotle to Galileo to Newton, when this issue was finally resolved through Newton’s Laws of Motion and his discovery of one of the four fundamental interactions, Universal Gravitation, and with (2) evolving to the early concepts of work and the impossibility of perpetual motion, the forerunner to energy and its conservation. These two paths met again by 1750 when an early form of the conservation of mechanical energy based on both kinetic and potential energies was realized.  It would take another 100 years to link this law to the concept of heat—motion of the invisible—as a form of energy and so finalize the concept of energy and the law of its conservation. But I’m getting ahead of myself.

Aristotle’s beliefs on motion

Aristotle believed the following [3]:

1. A body removed from all external influences will be at rest.
2. The speed of a falling body increases with weight.
3. All that moves contains something else doing the moving. 

These beliefs became the challenge that Aristotle presented to those who followed.  While (1) successfully led to the concept of the inertial state once the equivalence between rest and uniform straight-line motion was realized, (2) and (3) were just plain wrong.  Regarding (3), Aristotle proposed that a thrower transfers something, an impetus, to the layer of the object being thrown that remains with the object during the motion, providing continual action to the body until it disappears once the object lands.

Why do I raise these three notions?  Because they evolved into an extremely deep paradigm about motion that subsequent generations first embraced and then rejected.  For while (1) set man on the right path, (2) and (3) each contributed to the misleading and stifling paradigm that surrounded scientists for the subsequent hundreds of years.  To truly appreciate the genius of Galileo and his subsequent breakthroughs, one must first appreciate the world in which he lived, and this world was significantly influenced by Aristotle.

What did Galileo do that made the difference? Data!

It’s fascinating to know that while everyone from Aristotle to those immediately preceding Galileo thought about all sorts of things, many of the same things that Galileo was to think about, none of them took any measurements. Galileo measured while others thought. Think Leaning Tower of Pisa. We see this around us today. Much thinking, proposing, and speculating. But without measurements, it really doesn’t mean anything. As a former boss of mine once wisely said, “One data point is worth one thousand opinions.” Rarely has this been better put.

Thank you for reading my post on the scientific origins of the study of motion. I go into much greater detail on this topic Chapter 6 of my book Block by Block – The Historical and Theoretical Foundations of Thermodynamics.

References

[1] Dugas, René. 2012. A History of Mechanics. Courier Corporation, p. 19.

[2] Tunkelang, Daniel. 2009. Faceted Search. Morgan & Claypool Publishers, p. 3.

[3] Dijksterhuis, E. J. 1969. “The Origins of Classical Mechanics from Aristotle to Newton.” In Critical Problems in the History of Science (Edited by Marshall Clagett; 547 Pages), 163–84. University of Wisconsin Press, pp. 163-184.