History of String Theory: The Enlightened Universe
The history of string theory includes the history of cosmology and astrology. In the 1500s, the geosynchronous model was replaced with the heliocentric model, in which the sun was at the center of the solar system. (Heliocentric models had originally been proposed by Greeks such as Aristarchus, but Aristotle’s model gained greater popularity.)
The work of Nicholas Copernicus and Galileo Galilei was key to this revolution, which dislodged us from our special place at the center of the universe. The result has become known as the Copernican principle, which says that space looks the same no matter where you view it from.
Copernicus corrects what’s where in the universe
The Ptolemaic model was based on the idea that all the celestial objects — planets, moons, stars, and so on — were on concentric spheres, each of which was centered on Earth. Over the centuries (from about 150 BC to 1500 AD), though, observations made it clear that this wasn’t the case.
To preserve the Ptolemaic model, it was modified over the years. Celestial objects were mounted on spheres that were then mounted on other spheres. The very elegance that made the Ptolemaic model so appealing was gone, replaced with a mishmash of geometric nonsense that only partially conformed with scientific observations — which were growing more and more precise due to new technologies.
In his book, On the Revolutions of the Celestial Spheres, the Polish astronomer Nicholas Copernicus explained his heliocentric model, making it clear that the sun, not Earth, sat at center stage. He still used spheres, though, and made other assumptions that haven’t born the test of time, but it was a major improvement over the Ptolemaic model.
Copernicus published his heliocentric model upon his death in 1543, fearing retribution from the Church if he published it earlier. Some Indian writers made this heliocentric claim as far back as the seventh century AD, and some Islamic astronomers and mathematicians studied this idea as well, but it’s unclear to what degree Copernicus was aware of their work.
Copernicus was a theorist, not an observational astronomer. His key insight was the idea that Earth didn’t have a distinct position within the universe, a concept that was named the Copernican principle in the mid-20th century.
Beholding the movements of heavenly bodies
One of the greatest observational astronomers of this revolutionary age was Tycho Brahe, a Danish nobleman who lived from 1546 to 1601. Brahe made an astounding number of detailed astronomical observations. He used his family’s wealth to found an observatory that corrected nearly every astronomical record of the time, including those in Ptolemy’s Almagest.
Using Brahe’s measurements, his assistant Johannes Kepler was able to create rules governing the motion of the planets in our solar system. In his three laws of planetary motion, Kepler realized that the planetary orbits were elliptical rather than circular.
More importantly, Kepler discovered that the motion of the planets wasn’t uniform. A planet’s speed changes as it moves along its elliptical path. Kepler showed that the heavens were a dynamic system, a detail that later helped Newton show that the sun constantly influences the planets’ motion.
Galileo, by using the telescope, later realized that other planets had moons and determined that the heavens weren’t static. The Catholic Church charged him with heresy. To get away with only house arrest, Galileo was forced to recant his observations about the movements of heavenly bodies. Reportedly, his final words on his death bed were, “But they do move!”
Galileo’s work, together with Kepler’s, laid the foundation for Isaac Newton’s law of gravity. With gravity introduced, the final nail had been placed in the scientific consensus behind the geosynchronous view. Astronomers and physicists now knew that Earth circled the sun, as the heliocentric model described. (The Catholic Church officially endorsed the heliocentric view in the 19th century. In 1992, Pope John Paul II officially apologized for Galileo’s treatment.)