No other subject in astronomy may be more exciting or more controversial than cosmology. Virtually every culture throughout history has struggled with its own cosmology, attempting to explain the universe and the presence of life within it. Before the first decade of the 17th century, humanity’s view of the universe was limited to what could be seen with the eyes. But when the telescope was invented, everything changed.
For the first time in human history people were able to glimpse a cosmos of grand dimensions swarming with “bazillions” of objects. Though some people immediately thought of this new “instrument” as the work of the devil, others realized its significance and began using it to explore the heavens. Today, astronomers continue the search for our own cosmology, with ever bigger and better telescopes, spacecraft, and computers, hoping to capture the essence of the Big Bang and beyond. No doubt the cosmology of today will be altered by some future cosmology, that’s the way science works. But for now we are no different than all our curious ancestors before us as we search the sky for answers to the ultimate questions.
The term cosmology is a portmanteau of the Greek words “cosmologia” which means order or orderly arrangement and “logos” which means reason or plan. This field of study focuses on analyzing the whole universe and has been the subject of three domains of thought: philosophy, religion, and science. This article, however, will only discuss the scientific modes of thought surrounding cosmology.
About scientific cosmology
In the scientific community, cosmology is also known as physical cosmology. People in this field of study concern themselves with how the universe began, its nature, and its evolution over time. The earliest cosmologists simply studied the physical mechanics of the solar system, e.g. how the planets and stars moved and interacted with each other. Several theories were developed by philosophers such as Aristotle, Aristarchus of Samos, and Ptolemy.
Perhaps the most well known theories of the mechanics of the “heavens” came from Ptolemy and Copernicus. Ptolemy proposed that the Earth was the center of the universe and everything else in the heavens revolved around it. The Ptolemaic system featured planets that spun around the solar system in perfect circles and used epicycles to explain how the celestial bodies moved in relation to the Earth and each other.
Less well-known Indian, Greek, and Muslim scholars had contended that the sun, not the Earth, was then center of universe. However, it wasn’t until the 16th century when the astronomer Copernicus supported that idea with his paper detailing his heliocentric ideas. Many in the scientific community consider this to be the most important event to occur in the history of astronomy.
Sir Isaac Newton
Perhaps most known for the “apple incident” that inspired his theory of gravity, Sir Isaac Newton published his monograph Principia Mathematica that, among other things, provided a mechanical foundation for Kepler’s laws of planetary motion. His gravitational theory resolved the inconsistencies that grew out of the interactions between the planets. Though he called it “universal gravitation”, Newton only applied his theory to the local solar system. It wasn’t until Albert Einstein came along that the theory was applied to the universe as a whole through the mathematical formulas he developed.
For a time it was believed that the Milky Way was the universe. However, Heber D. Curtis theorized that the spiral nebulae being observed were independent star systems. Edwin Hubble confirmed that there was more space beyond our galaxy when he observed novae in the Andromeda galaxy in 1923 to 1924.
At that time, though, it was still believed that the universe was static, but even that belief was challenged a scant few years later. First, models of the universe using a cosmological constant developed by Einstein suggested that the universe was expanding. Hubble provided support for this idea in 1929 when he noticed that light in distant galaxies had shifted away from the Milky Way.
In 1917, Albert Einstein published a paper called “Cosmological Considerations of the General Theory of Relativity” in which he finalized his theory of gravity. Many who study cosmology consider this to be the start of modern scientific cosmology because it inspired those analyzing the universe at that time, such as Karl Schwarzschild, Willem de Sitter, and Arthur Eddington, to study the significance of Einstein’s theory of relativity.
Although Einstein’s theory supported a changing and expanding universe, he believed what Harlow Shapely – an astronomer from Mount Wilson – had to say about the cosmos; that it was a static place consisting only of the Milky Way Galaxy. To align his theory with his beliefs, Einstein added the “cosmological constant” to his equation that ensured the model would remain unchanged. Thankfully, he later changed his mind. Calling the constant a big mistake, he disavowed it.
What is now known as the Big Bang theory started in 1931 with speculation by a Belgian priest named Georges Lemaitre that a creation event in the universe’s past is probably the reason why it is expanding. He theorized that the cosmos came from an egg that was designed to continue expanding until modern times. While there were lots of people producing rival theories to the Big Bang hypothesis, cosmic microwave background radiation discovered by Robert Woodrow Wilson and Arno Penzias in 1964 eliminated many of them.
Once considered a speculative science, cosmology is now regarded as a predictive science due to the accurate observations of the background radiation by WMAP and COBE satellites. These observations conform to the predictions made by Alan Guth, an American physicist who came up with the idea of Cosmic Inflation in 1981. This version of the Big Bang theory explains how the universe expanded and resolves many other problematic areas.
However, there are still many areas where the creation of the universe cannot be adequately explained scientifically. To solve this puzzle, many scientists are concentrating on quantum cosmology that tries to connect quantum physics and general relativity. It is a work in progress.