The longest story

A history course that began with the Big Bang

In 1989, at Macquarie University in Sydney, a historian of Russia began teaching a course that started 13.8 billion years ago. David Christian had spent years teaching Cold War Russian history, and he was troubled by what he called a subliminal message in it: that humanity falls into competing tribes. He wanted, as he put it, a history of humanity. Australia had no model for world history to borrow, so he built a course from the Big Bang forward, and invited colleagues in astronomy, biology, geology, and anthropology to teach its first weeks. At first, he later recalled, “none of us had a clue” how to join the pieces. The name he gave it, “big history,” appeared in print in a 1991 article; he later called the name over-blown, strident, and pretentious, but it stuck. His book Maps of Time (University of California Press, 2004) is the standard account, and his Origin Story (2018) is the short one.

Others had had the idea of a history that begins with the earth in space. H. G. Wells opened The Outline of History (1920) with “The Earth in Space and Time,” arguing that there could be no common peace and prosperity without common historical ideas. Carl Sagan’s “Cosmic Calendar,” in his book The Dragons of Eden (1977) and then in the television series Cosmos (first shown in the United States on 28 September 1980), squeezed the age of the universe into a single year. Fred Spier, Cynthia Stokes Brown, and the astrophysicist Eric Chaisson, whom we meet below, built on the same instinct. What Christian added was a university course, a name, and a structure of eight thresholds.

Around 2008 Bill Gates watched Christian’s lecture series from The Teaching Company, called Great Courses, and offered to help turn it into a high-school course. After pilot classes in 2011–12 the free online Big History Project opened to students in 2013. It was renamed the OER Project in 2019.

What does it mean to start a history there? Ordinary history begins with writing, and everything before it is “prehistory,” a word that quietly says the story has not yet begun. Big history drops the wall. In this course’s reading, the question it asks, how did we come to be as we are, can only be answered by going back past the first cities, past the first farms, past the first people, to the first atoms. This is a different scale from Braudel’s, in Lesson 2: his longest clock ran across millennia, and this one runs across billions of years.

A universe with a history

Until the twentieth century, nobody could write a history of the universe, because most scientists thought it had none. When Albert Einstein applied his equations to the cosmos in 1917 he added a term, the cosmological constant, to keep the universe still. The Russian mathematician Alexander Friedmann published expanding solutions in 1922, and the Belgian priest and physicist Georges Lemaître found one in 1927, but they were little read.

The change came from a photographic plate. On the night of 5–6 October 1923, at Mount Wilson in California, Edwin Hubble exposed a 45-minute plate of the Andromeda “nebula” with the 100-inch Hooker telescope. He had marked a star on it with an N for nova; then he crossed it out and wrote “VAR!” because the star varied in brightness. By early 1924 he had worked out that it was a Cepheid, a star whose pulse reveals its true brightness, with a period of about 31 days. That gave a distance, which he put at about 900,000 light-years (we now put it at about 2.5 million), far outside our own Milky Way. Andromeda was a galaxy of its own, and the Milky Way was one among many. The result was presented to the American Astronomical Society on 1 January 1925. In 1929 Hubble published the relation between the distances of galaxies and the speeds at which they recede. Lemaître had derived a similar relation in 1927, in French, and in 2018 the International Astronomical Union recommended, in a vote of its members, the name Hubble–Lemaître law. A universe that expands has a past: run it backward and it began, about 13.8 billion years ago (the best figure, from the Planck satellite in 2018, is 13.797 plus or minus 0.023 billion; 13.7 is the older figure from the early 2000s). Course 7, We are stardust, tells that story in full.

One correction to a popular telling: the physicist Alan Guth, who proposed cosmic inflation, had his “spectacular realization” on the night of 6 December 1979, published it in 1981, and wrote his popular book, The Inflationary Universe, in 1997. The “pocket universes” that the lecture series mentions are regions in an extension of the theory called eternal inflation. That part is speculation, and big history does not depend on it.

The calendar below puts the whole story on one year. It uses the numbers of this series: the universe 13.8 billion years old, the earth about 4.54 billion, life at least 3.5 billion years old, our species at least 300,000.

One line of the lecture series’ account of the cosmos needs correcting. It says that of 118 elements, 92 were made in stars and supernovae. The more careful statement is this. Only hydrogen, helium, and a trace of lithium came out of the Big Bang. Every other element found in nature was made later, mostly inside stars, in supernova explosions, and in the collisions of neutron stars, with lithium, beryllium, and boron largely made by cosmic rays. Of the 118 elements confirmed so far, 94 (up to plutonium, the last two only in traces) occur in nature; the rest have been made in laboratories. A neutron-star collision seen on 17 August 2017 showed signs of gold and platinum being made. “Nearly everything in your body except hydrogen was made in stars” is a fair short form, and Course 7 gives the long one.

Just right

Christian’s method has a recipe. Each threshold needs ingredients, “Goldilocks conditions,” and then something new appears. The phrase comes from the nursery tale. In the earliest printed version of the story (Robert Southey, 1837), an old woman breaks into the home of three bears, and tries their porridge; the little bear’s is “neither too hot nor too cold, but just right.” A girl replaced the old woman around 1850, and the girl was called Goldilocks by 1904. The astronomers’ “Goldilocks zone” of Course 7 uses the same idea for planets. Christian’s own wording, in a 2011 talk, is that conditions must be “not too hot, not too cold, just right for the creation of complexity.”

That is a way of telling a story, and, as the closing section stresses, it is hard to test. After the fact, any outcome can be called “just right.” Still, the pattern is easy to see. Stars needed gas clouds that were dense enough to collapse and cool enough to hold together. Life needed liquid water, a source of energy, and a workable range of temperature. Complexity needs what physicists call a gradient, a difference in energy that can be used, and it can neither be too steep nor too shallow.

The series this course draws on adds its own way of putting what complexity is. Everything complex, it says, is made of building blocks, and it is the connections between the blocks, and the order in which they are connected, that make something new. A molecule is atoms connected in a pattern; DNA is four kinds of blocks connected in a sequence; a computer file is the same on another scale. In this course’s reading, that is a useful short form, and it is the series’ formulation, not Christian’s. His is: ingredients, Goldilocks conditions, and new “emergent” properties. Emergence is the subject of Course 14, Chaos and emergence, and the question of how order grows where energy flows through a system is the subject of Course 15, Openness and evolution. Course 5, Energy, entropy, and order, explains why order can grow in an open system without breaking the second law.

Energy and complexity

The third of the series’ tools is energy flow. Anything complex, it says, needs energy running through it; with none it dies. Eric Chaisson, an astrophysicist at Harvard and Tufts, turned this into a number. His “energy rate density” is the amount of free energy that flows through a system each second, for each gram of the system, measured in ergs per second per gram (divide by 10,000 to get watts per kilogram). By his estimates, published in 2011, the Milky Way runs on about 0.5; the Sun on about 2; the earth’s physical systems on about 75; plants on average on about 900; an adult human body on about 20,000; a typical mammal on about 40,000; a primate brain on about 150,000; and human society, averaged over the mass of people, on about 500,000.

Look at the surprise in those numbers. A gram of you takes in about ten thousand times as much energy every second as a gram of the Sun. The Sun is vastly more powerful in total, but it spreads its power through a vast mass. The pattern, Chaisson argues, is that the more complex a thing is, the more energy flows through each gram of it, within a workable range. Complex things are starved below that range and destroyed above it.

The series draws a further conclusion that Chaisson does not. It says that the higher this density, the less stable the system and the shorter-lived. Chaisson’s paper says no such general law. It does note that very massive stars, which burn at a high rate, live only tens of millions of years against the Sun’s ten billion, so the live-fast pattern is real for stars, but that is not the same claim for brains, or for societies. Chaisson’s idea has not been widely adopted. Reviewers of his book Cosmic Evolution (2001) found it stimulating and at times inflated, and Chaisson himself says his values are estimates with ranges, and that energy is not the only possible measure.

Learning together

All this sets the stage for the human threshold. Our species, Homo sapiens, is at least about 300,000 years old: skulls from Jebel Irhoud in Morocco, dated in 2017, are about 315,000 years old, give or take 34,000, and show a mixture of modern faces and older-looking braincases. The skull called Omo I, from Ethiopia, is at least about 233,000 years old. The lecture’s “200,000 to 250,000” is the older figure. Its claim that symbolic language began about 135,000 years ago is not settled either. That date is a 2025 argument from genetics that the capacity for language must be at least that old, and others disagree: estimates run from perhaps 100,000 years to well over a million. What is firmer is the early use of symbols. In Blombos Cave in South Africa, two pieces of ochre engraved with cross-hatching are about 77,000 years old, a workshop that stored ochre paint in abalone shells is about 100,000 years old, and a cross-hatch drawn in ochre crayon is about 73,000 years old.

For Christian, the key to our species is “collective learning”: the capacity to share what one has learned so precisely and in such volume that knowledge accumulates from generation to generation. Other animals have culture. Chimpanzees in different communities have different customs, such as tool use, and a 1999 survey of seven long-term field studies counted 39 behaviors that were customary in some communities and absent in others. Sperm whales in the Pacific belong to clans that are told apart by their learned patterns of clicks. But no other species is known to build knowledge up over many generations the way people do. Psychologist Michael Tomasello calls the effect a ratchet: each generation starts where the last left off, and the knowledge does not slip back. Because it is shared in symbols, it can pass between strangers and across distance, as the series puts it, like information passing through a network. It is a good analogy, and no more.

Christian divides human history into three eras. In the first, the era of foraging, people lived by gathering and hunting for hundreds of thousands of years, until about 11,000 years ago (this course rounds Christian’s dates). In the second, the agrarian era, people farmed, and cities, states, and empires arose. It lasted until the third, the modern era, which begins around 1750 with fossil fuels and industry. (The lecture’s “8,000 years ago” for farming is too late. Farming began independently in several places beginning at least 11,000 years ago: wheat, barley, and sheep in southwest Asia; millet in northern China and rice in the south, about 9,000 to 10,000 years ago; maize in Mexico.) Population tells the story of the eras. In 1750 the world had roughly three-quarters of a billion people. It passed one billion about 1800, and the United Nations projected that it would pass eight billion on 15 November 2022. The energy each person uses has grown too, which is Chaisson’s last bar in the activity above.

The series ends with a thesis. People, it says, live under three forces at once: gravity, which governs all matter; genes, which govern all life; and culture, which governs us. It is a vivid way to put it, and it is the lecture series’ own formulation, not Christian’s. It resembles ideas elsewhere: Chaisson’s three phases of physical, biological, and cultural evolution; Richard Dawkins’s suggestion in 1976 that cultural units copy themselves like genes; the dual-inheritance theory of Robert Boyd and Peter Richerson (1985). The aim the lecturer draws from it is moral, as it is for Christian: a “shared humanity” and a world of citizens of a single planet, in place of the history of tribes. It is a hope more than a finding.