In the 20th century, physicists sought to take all of the work in physics and create a single coherent structure, a grand unified theory, a theory of everything. Many different kinds of unified theories have been discovered.
Occam’s Razor: The Principle of Parsimony
William of Occam is the name most associated with the principle of metaphysical parsimony that is explicitly stated in Aristotle. This principle has been called Occam’s Razor: all else being equal, choose the explanation that requires the fewest hypotheses.
Reality, according to Aristotle and Occam, is elegant; it contains no more things than it needs. So, when deciding between two possible explanations for things that happen in the universe, the better one is that which adds the least number of things to help everything make sense.
William Whewell and the Idea of Consilience
This sentiment just refers to the metaphysical aspects of scientific theories. A similar principle holds true in terms of the explanatory power of scientific theories. William Whewell was a scientist. In fact, he was one of Darwin’s professors and his views greatly influenced the structure of Darwin’s arguments.
Whewell held that a significant mark of a true scientific theory is what is termed ‘consilience’: the ability to bring together results and to make predictions in fields of science other than that which the theory was created to explain.
Scientists find classes of phenomena they want to explain, and they come up with theories to do so. But when a theory designed to explain phenomenon A is also found, with minor modifications, to explain phenomenon B—which was not being considered by the scientist—it gives the scientist reason to think the theory may be true of the world in general. Good scientific theories, Whewell argues, simplify science. They bring together what seemed like different fields into a single explanatory scheme.
Learn more about defining reality.
René Descartes and the Unification of Mathematics
René Descartes in the 17th century pointed out that people prefer buildings that were constructed from plans developed by a single architect to those that were built piecemeal. Those built from a plan developed by a single mind have a coherence, an elegance, that people admire.
The intellectual edifice of human knowledge, Descartes contended, should be similar, and he sought to rebuild all human knowledge in a clear, systematic way. Indeed, his famous dictum, “I think, therefore I am”, is the justification for the first absolute truth—the existence of the self as a thinking thing—that he would use in this project.
Descartes would go on to apply this unifying project when he developed what is called analytic geometry. Before Descartes, it was thought that mathematics was comprised of two distinct areas: one that dealt with numbers and equations—arithmetic, algebra—and another that dealt with shapes and space—geometry.
But Descartes figured out that shapes could be translated into equations; that the behavior of lines and circles could be described numerically. This unified theory of mathematics allowed us to create equations of motion for complex trajectories of real objects in real space and opened the door for the modern mathematical approach to physics.
This is a transcript from the video series Redefining Reality: The Intellectual Implications of Modern Science. Watch it now, on The Great Courses Plus.
Newton and the Theory of Gravitation
Newton extended Descartes’ analytic geometry in the creation of his mathematical theory of fluxions, now called calculus, which was used by its co-creator, Newton’s rival, the German philosopher, physicist, and mathematician, Gottfried Wilhelm Leibniz. But Newton’s name is known much better than Leibniz’s, in part because Newton used his fame and power to try to destroy Leibniz, but also because of what Newton did with the calculus. He created a unified scientific theory that replaced Aristotle’s theories of the universe.
Aristotle believed that physics and astronomy dealt with different substances, and so were different sciences that required different sorts of accounts.
But Newton gave us the three laws of motion and a law of universal gravitation. The important word here is ‘universal’. Newton’s law of gravitation applies to everything.
The story goes that he was at home, sitting under an apple tree and looking up at the Moon. He was wondering what kept the Moon in its orbit when suddenly, an apple dropped from the tree in front of him.
Seeing the apple fall to the ground in front of the Moon, Newton came to realize that both phenomena were caused by the same force. He unified physics and astronomy into one single study of nature. His combined theory of mechanics and gravitation became celebrated, Whewell contended, because it was a grand example of consilience.
Newton’s theories explained phenomena from many different fields of study: astronomy, the falling of objects, the tides, and so much more. Newton was great because he unified science.
Learn more about how terrestrial and celestial gravity are the same.
Maxwell and Electromagnetism
Similarly, James Clerk Maxwell, in the middle of the 19th century, changed how the universe was seen by taking the apparently separate laws for electrical phenomena and magnetic phenomena and bringing them together into a single coherent theory.
This single theory showed that electricity and magnetism were just flip sides of a single coin, that what were thought to be two separate aspects of reality were different expressions of a unified picture of reality.
It got even better when it was shown that light could be understood in this way as well. Optics was thought to have nothing to do with either electricity or magnetism, but here was one coherent approach that showed them all to be interrelated in a way that simplified the underlying picture of reality. It made the universe a more elegant place by creating a single theory that unified understanding of the things that happen within it.
Common Questions about Early Unified Theories
Occam’s Razor is the idea that the number of causative agents of a phenomenon should not be unnecessarily increased. In other words, an explanation that requires the fewest assumptions should be chosen over others.
William Whewell said that a good scientific theory must have consilience: the ability to bring together results and to make predictions in fields of science other than that which the theory was created to explain.
René Descartes, in the process of developing what is called analytic geometry, discovered that geometrical figures such as lines and circles could be described using arithmetic and algebra. Thus, he unified these areas of mathematics which were thought to be different.
James Maxwell took the apparently separate laws for electrical phenomena and for magnetic phenomena and brought them together into a single coherent theory. Later, it was shown that light could also be understood in this way.