Fun with Cosmology: A Brief History Quiz

Quiz Answer Key and Fun Facts

1. Ancient cosmology was dominated by a geocentric model of the universe, that is, that the sun and other planets orbited a stationary earth. One of the most influential works of astronomy promoting geocentrism was "The Almagest," a treatise detailing the apparent motions of the stars and planets, written by which second century Greek polymath?

Answer: Ptolemy

As well as astronomy, Claudius Ptolemy wrote influential works on geography and astrology that were considered authoritative for up to 1200 years later. "The Almagest" not only provides a detailed explanation of the geocentric model, but included a catalogue of more than 1000 stars, as well as "Handy Tables" that could be used to calculate past or future positions of astronomical bodies.

The apparent retrograde (backward) motion of the planets in relation to the earth that was occasionally observed was explained by geometrical "epicycles," which means "a circle moving on another circle," which allowed for complicated but surprisingly accurate computations. Nowadays, we know that retrograde motion occurs because the earth is also moving in relation to the other planets as it orbits the sun, which occasionally causes them to appear to reverse course.

2. Copernicus revolutionised cosmology in the fourteenth century by publishing the heliocentric theory, which proposed the then radical notion that the earth orbits the sun. Unfortunately, like astronomers before him, Copernicus made the crucial error of assuming that the planets have perfectly circular orbits. Which astronomer later showed that the planets have elliptical orbits and formulated the laws of planetary motion?

Answer: Johannes Kepler

In ancient and medieval cosmology, it had been assumed, for philosophical reasons, that the planets' orbits must be circular. This was because it was believed that the circle was a perfect shape, and that because the planets' motions had been laid down by God, they must therefore follow a perfectly circular pattern.

However, this mistaken assumption meant that as long as the Copernican model adhered to this, it could not produce more accurate calculations than the existing geocentric model. Kepler discovered that the planets' orbits are ellipses. Unlike a circle, an ellipse has two central foci; for orbiting planets, the sun is at one focus, which Kepler incorporated into the first law of planetary motion.

This meant that planetary motions could be predicted with greater accuracy than was previously possible.

3. Galileo, who has been acclaimed as the "father of modern science", was famously forced to recant the heliocentric theory by the Church on pain of death in 1616. When did the Roman Catholic Church formally admit its error in forcing Galileo to recant his astronomical theories?

Answer: 1992

Although publicly forced to disavow his work, there is a legend that after his trial Galileo muttered, "all the same, it moves." The Church began lifting its bans on Galileo's works and on works promoting heliocentrism in the eighteenth century. However, it was not until October 31, 1992 that Pope John Paul II publicly and formally cleared Galileo of any wrongdoing, based on the findings of a committee that he had set up in 1979 to investigate the matter. Well, no-one could accuse them of being too hasty.

4. Most people take it for granted that the night sky is dark, but this simple fact posed a serious problem for cosmology that took centuries to resolve. The problem is that if the universe is infinite, eternal, and static, as was widely believed, then the light from distant stars should completely fill the sky with light, yet it clearly does not. How is this conundrum commonly known?

Answer: Olbers' paradox

The idea behind Olbers' paradox is that, if there were an infinite number of stars, then wherever we look in the sky, we should see the light of some star, so the sky should be brilliant with starlight. Although this idea has been around for centuries, it is today named after an amateur German astronomer named Heinrich Wilhelm Olbers who discussed it in 1823.

Modern cosmology has resolved the supposed paradox by showing that, although the universe could well be infinite, it has not existed eternally, having originated in the Big Bang, and that the stars themselves have finite life spans, as they are still being created and destroyed.

Hence, there has only been a finite time for starlight to reach the earth, and some stars are too distant for their light to have yet reached us.

5. Although it has long been known that light has wave-like properties, physicists used to be puzzled about how light waves could propagate through apparently empty space, which seemed impossible. It was therefore proposed that space was filled with what medium through which light waves moved?

Answer: Luminiferous aether

The idea of aether (also ether) goes back at least as far as Aristotle, who proposed that it was an element lighter than air that surrounded celestial bodies. Isaac Newton proposed that light moves through an "Aethereal Medium" that is responsible for the phenomenon of diffraction (light bending when it passes through water or glass, for example).

The concept of luminiferous aether was widely believed up until the Michelson-Morley experiment of 1887, which provided evidence that the luminiferous aether probably did not exist. Einstein's theory of special relativity eventually ruled out the existence of such a phenomenon and the concept was finally abandoned.

6. Isaac Newton's law of universal gravitation was of key importance in the development of modern cosmology, and depends on what mathematical principle?

Answer: Inverse-square law

Newton's law of universal gravitation states that every particle in the universe is attracted to every other particle. The application of the inverse-square law to this theory is that the attractive force between two masses is directly proportional to the product of their masses and inversely proportional to the square of their distance from each other, so that gravity becomes increasingly weaker as distance increases. Scientists before Newton had theorised about how gravity operates, but Newton's application of the inverse-square law allowed more precise mathematical calculations to be made.

7. A key discovery of quantum physics was the principle of indeterminacy, that the position and velocity of a subatomic particle cannot both be measured exactly, at the same time, even in theory. Einstein, who objected to this, once said, "God does not play dice with the universe." Niels Bohr, a pioneer of quantum theory, was said to have replied to this with what statement?

Answer: "Stop telling God what to do"

Several interpretations of quantum theory propose that events at the subatomic level can occur in a completely random and uncaused manner. Einstein hated this idea, as he believed that the universe was structured by strictly deterministic laws. Niels Bohr was a Danish physicist who made pioneering contributions to the understanding of atomic structure and the development of quantum theory.

Despite Einstein's objections, quantum theory has passed every scientific test that might have shown that it was wrong.

8. Einstein's theory of general relativity revolutionized our understanding of the relationship between space and time. However, he made an important oversight in assuming that the universe was static (neither expanding nor contracting). To allow for a static universe, he added what variable to his equations that would act as a counterbalancing force to gravity?

Answer: Cosmological constant

When Einstein formulated this theory, it was widely accepted that the universe was static. However, Einstein's equations predicted that without a counterbalancing force, gravity would cause the universe to contract. Therefore, he added a cosmological constant to represent the energy density of space, or vacuum energy.

When it was later discovered that the universe is actually expanding, Einstein described his failure to anticipate this as the greatest blunder of his career. For decades, it was assumed that the cosmological constant had a mathematical value of zero. Ironically, in the late 1990s, it turned out that some version of Einstein's idea is true, as it does appear that there is an antigravity force at work in the universe related to vacuum energy, as the expansion of the universe has been observed to be accelerating over time.

This antigravity force is now commonly referred to as dark energy and the cosmological constant has been assigned a positive value.

9. In 1929, astronomer Edwin Hubble's observations of distant galaxies confirmed that the universe is expanding. This led to a cosmological model in which the universe originated in a highly dense, high-temperature state. Who first described this as the "Big Bang Theory" as a sort of joke?

Answer: Fred Hoyle

Hoyle came up with this name ironically, as he thought that the theory implied that the universe was created a finite time ago, which he thought was pseudoscientific. He instead supported the steady state theory in which the universe has existed for an infinite amount of time. To accommodate the fact that the universe is expanding, he proposed that new matter is constantly being created that fills in the space between galaxies as they move apart.

This theory is now widely rejected by cosmologists.

Although the term "big bang" was intended by Hoyle as a mockery of the concept, it has caught on in both popular and scientific usage.

10. In 1964, radio astronomers Arno Penzias and Robert Wilson accidentally discovered what universal phenomenon that provided crucial evidence for the Big Bang Theory?

Answer: Cosmic microwave background radiation

One of the predictions of the Big Bang Theory is that because the universe has expanded from an initially hot, dense state, it should be filled with a remnant of radiation left over from this state. Arno Penzias and Robert Wilson discovered that a radio receiver they were building was picking up excess noise, the source of which they could not pinpoint.

They found that this noise was coming from every direction of space and realised that they had discovered the cosmic microwave background predicted by the Big Bang Theory. For this discovery, they were awarded the 1978 Nobel Prize in Physics.

The cosmic microwave background has been measured as only 2.725� above absolute zero, a faint ghost of the extreme temperatures prevalent at the beginning of the universe.

Source: Author agentofchaos

This quiz was reviewed by FunTrivia editor rossian before going online.
Any errors found in FunTrivia content are routinely corrected through our feedback system.

Since ancient times, people have tried to understand the universe. This quiz looks at some highlights in the development of cosmology over the centuries.

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