A Brief History of Time: Chapter 1 Summary & Analysis

When a famous scientist (possibly Bertrand Russell) gave a public astronomy lecture, he described the orbits of the planets in the solar system and how the sun orbits the center of our galaxy. After he finished, an old lady at the back told him he was talking nonsense, as the world is flat and sits on the back of a tortoise. When he asked what the tortoise stands on, she replied it is tortoises all the way down.

Although the old lady’s image is ridiculous, do scientists really know better? New technologies are helping to offer answers to age-old questions about the universe and where humans came from. Maybe one day the answers will seem as obvious as the earth’s orbit, or as ridiculous as the image of the tortoises. Time (whatever it is) will tell.

Greek philosopher Aristotle gave two good arguments for the earth being a sphere instead of flat. First, a lunar eclipse must be the earth blocking the sun’s light, and the shadow is always round, not elongated as it would be if the earth was flat. Second, the Greeks saw that the North Star (which lies over the North Pole) is more central in the sky the further north you sail, and closer to the equator the further south you travel. From this, Aristotle could even make an educated guess about the distance around the earth. Another point the Greeks noticed is that when ships came over the horizon, one always sees the sails first, and later the hull.

Yet Aristotle believed the earth was fixed in place at the center of the universe, and all the other heavenly bodies moved around it in perfect circular orbits. Ptolemy took this idea further in the 2nd century AD, creating a cosmological model consisting of eight spheres—one for the moon, sun, stars, and the five known planets. Each moved on their own complicated paths in these spheres while the fixed stars remained in the same formation at the outer limit, rotating together across the sky. Anything beyond that limit was unknown.

Ptolemy’s model could fairly accurately predict the movement of each heavenly body. But for it to be correct, the moon would have to pass by the earth twice as close as normal every now and then, something that bugged Ptolemy, as it ought to have appeared twice as big as normal at those times. But the model was generally accepted anyway, including by the Christian church, as there was lots of space outside the model for heaven and hell.

Nicholas Copernicus, a Polish priest, proposed a simpler model in 1514, publishing anonymously at first to avoid being called a heretic. It took nearly a century for his idea, that the sun sat stationary at the center of the planets, to be taken seriously. German astronomer Johannes Kepler and Italian Galileo Galilei backed his theory, even though it was not perfect based on the observable movements in the cosmos.

The final blow came to the ancient model with the invention of the telescope. Galileo observed Jupiter and found it had several satellites, meaning not everything orbited the earth. Those moons could still primarily orbit the earth and have very complicated journeys that also cause them to appear to orbit Jupiter—but Copernicus’s idea was simpler. Kepler added the idea that orbits could be elongated, not perfectly circular, and finally the theory worked with the observable movement of the heavenly bodies.

Kepler didn’t like the idea of elliptical (elongated) orbits as much as perfect circles, but the theory seemed to work well in practice. Now the problem was that this didn’t seem to work with the idea that magnetic forces controlled all this movement. It wasn’t until Sir Isaac Newton’s Philosophiae Naturalis Principia Mathematica came out in 1687 that an explanation was offered.

Newton’s work offered the math to back up his ideas about how things move in space and time. His law of universal gravitation suggested everything is attracted to everything else, with the force being stronger when those things are closer together and bigger. That’s why things fall to the ground. Newton mentioned the idea coming to him as an apple fell to the ground, though the idea that the apple hit him on the head was probably added by others later. Regardless, his theory showed the moon moves in an elliptical orbit around the earth, while the planets have an elliptical orbit around the sun.

The idea of a natural boundary to the universe was thrown out along with Ptolemy’s celestial spheres, replaced with the Copernican model. Thus, the new assumption was that the fixed stars were not so fixed after all, but very far away and hard to measure. In fact, given his idea of gravity, these stars should all be moving around each other, and at some point should fall together. If there are finite stars in a finite universe, the stars would fall into each other, Newton wrote in a letter to a friend in 1691. But infinite stars spread uniformly across an infinite universe would not, as there would be no center, he reasoned.

This is one of many snares when talking about the infinite. In an infinite universe every point is the center because every point has infinite stars either side. These days, it is now thought the finite model must be correct. Adding more stars beyond the limit of that boundary (i.e. picturing a bigger universe with more stars) makes no difference—all the stars will still fall in on each other at the same pace. It is now known there cannot be a model of an infinite universe where all the bodies are always attracting each other.

Before the twentieth century, no one had suggested the universe was expanding or contracting, which reveals the way people were thinking back then. Everyone either thought the universe had always existed in its current state, or that it was created at a certain point in the same state it is now. This could have been because of people’s belief in eternal truths, or perhaps the comfort of the idea of an unchanging universe, eternal even after their own deaths.

Even though Newton’s theory showed that the universe was not static, people did not immediately consider that it might be expanding. Instead they toyed with the idea that at great distances gravity could be repulsive, rather than attractive. It allowed the stars to remain in equilibrium. But now such a model is considered unstable, as movements in either direction would create increasingly strong repulsive or attractive forces.

German philosopher Heinrich Olbers wrote in 1823 that in an infinite static universe, every line of sight would end on a star. Others had made similar arguments, even at the same time as Newton, but Olbers’s objection to Newton’s concept of an infinite, static universe was the first to be widely noted. Thus, the night sky ought to be as bright as daylight. The only way to explain the night sky was that each star was created at a finite time. If so, the light from those stars might not have reached us yet. But this, in turn, raised the question of when the stars came to be.

The idea of a beginning to the universe was not new. Religious thought had already put the beginning at a not too distant time in the past. One line of reasoning for the beginning was a “First Cause,” which caused everything else in a connected line of causality. St. Augustine put Creation—as per the book of Genesis in the Bible—at around 5,000 BC. That’s not that far off the end of the last Ice Age in around 10,000 BC, when civilization took off.

But Greek philosophers, including Aristotle, did not like the idea of a beginning because it sounded like divine intervention. They thought people and the world had existed and will exist forever. They had also considered the ideas of cultural and scientific progress toward greater understanding, but argued that large disasters had always put the human race back to square one.

Philosopher Immanuel Kant later considered the question of whether the universe had a beginning in time and if it is limited in space, in his Critique of Pure Reason, published in 1781. He called the questions antinomies, meaning contradictions, of pure reason, because both ideas—that the universe had a beginning, and was eternal—had compelling arguments.

Kant reasoned that if the universe did not have a beginning, the time before any event was infinite, which seems ridiculous. If the universe started at a particular time, the time before that was infinite, so why would it start at any specific time. Both arguments are really the same—they assume time moves back forever, whether or not the universe exists. But really, the concept of time itself did not exist before the beginning. This is an idea St. Augustine used, when asked what God did before the beginning. He stated time is a concept only within Creation, and did not exist before it.

The question of the beginning was largely related to metaphysics or theology back when everyone thought of the world as static and unchanging. The world looked much the same from both ends of the argument. That changed in 1929 when Edwin Hubble saw that all distant galaxies are moving rapidly away from each other. As such, at some point, possibly 10 billion to 20 billion years ago, all the matter in the universe must have been in one tiny place of zero size, meaning the density of the universe was infinite. This realization made the question of beginnings one about science.

Hubble’s discovery created the idea of the big bang, a time when the universe was tiny and infinitely dense before rapidly expanding. At that time, all laws of science would break down, meaning time had its beginning in the big bang, because any previous times would no longer have any bearing.

This new idea of the creation of time is completely different to any that preceded it. In an unchanging universe, some outside power determines the start, and there is no physical need for a beginning. But if the universe is expanding there could be physical reasons behind the need for a beginning. An expanding universe does not rule out the existence or involvement of God, but it does determine when time started.

To discuss all these questions, first one needs to know what a scientific theory is. A theory is a model of the universe, or one part of it, and rules that link aspects of that model to what we can observe. It exists only in our minds (whatever that means). Theories are good if they can explain observations with a few factors, and can accurately predict outcomes in future observations. For example, Empedocles’s idea that the four elements were earth, air, fire, and water is simple, but cannot make any predictions. By contrast, Newton’s theory of gravity, which is determined by mass and distance, is even simpler, but can accurately predict the movements of the stars.

Any physical theory cannot be proved entirely. Even if every test has backed up the theory so far, one cannot prove that the next test will not disprove it. Even one single piece of evidence contradicting the theory can disprove it. Philosopher of science Karl Popper said that confidence in any theory grows with each accurate prediction, but that theory must be cast aside or adapted if even one test outcome or observation contradicts it. (Although in reality, one can always question the competence of the observer.)

Usually, new theories are largely extensions of previous theories. For example, Mercury’s movement diverged slightly from predictions made by applying Newton’s law of gravity. Albert Einstein’s slightly different prediction, via his general theory of relativity, matched with what was seen, a critical confirmation of his new theory. Newton’s theory is still used in most cases, as the differences are so tiny and no difference is visible in day-to-day usage. Newton’s theory is also much simpler to use.

Science’s ultimate goal is to offer one theory for the entire universe—a theory of everything. But usually scientists deal with it in one of two ways. First, they apply the laws that explain how things move through time to make predictions. Second, there is the question of the initial state of the universe. Some think only the first question is strictly science; the second is metaphysical or do to with religion. They say God can do whatever he likes. While that could be true, he made the universe in a way that is governed by certain laws, meaning there are also laws determining the beginning.

It is tricky to offer one theory for the whole universe right now. Instead there are numerous partial theories. This could be the wrong approach. If everything in the universe fundamentally depends on everything else, only looking at certain parts cannot reveal the whole picture. But, that is how progress has been made so far. For example, gravity depends only on mass, not the content of an object, so we do not need a theory on the construction of the sun to predict its movement.

Scientists now describe the universe in terms of the general theory of relativity and quantum mechanics—both great achievements of the first half of the 20th century. The first relates to gravity and large to really large-scale structures of the universe. The second relates to miniscule matter a billionth of an inch wide. But, the two do not relate and cannot both be correct. What is needed is a quantum theory of gravity, but it might be some time until we have one. Many of the aspects and predictions of that theory are already known, though.

If the universe is not chaotic, but rather is governed by laws, all the partial theories must fit into one overarching theory of everything. But there is a fundamental contradiction in that search. We’ve assumed so far that we are rational beings that can know the world, which would mean we can progress to such knowledge. But if there really is such a theory, it would determine our own actions too, meaning the theory would determine its own discovery. Why would discovery be the ultimate conclusion, rather than a wrong conclusion, or no conclusion?

Charles Darwin’s theory of natural selection might offer an answer. He stated that genetic differences occur in any group of self-reproducing beings, and that certain differences will result in strengths that cause those beings to be more likely to survive. So far in history, intelligence and science have indicated a survival advantage. Today, our discoveries could well kill us all. Also, a unified theory might not affect our likelihood of survival. But, given the regular evolution of the universe, our logical reasoning as developed by natural selection means we should be able to make the right conclusions.

The theories we have so far work for the wide majority of cases. As such, searching for the ultimate theory becomes hard to justify. Then again,  people argued this about relativity and quantum mechanics, which eventually gave us nuclear power and microelectronics. Thus, the search for a theory of everything might not help us survive, or ever change our lives all that much, but it does tackle questions we have asked for millennia. People want to understand the world and its order, where we came from and why we’re here. This deep longing is the justification for this mission, a mission that asks for a complete description of the world we live in.