Where did everything come from? People have asked this question for as long as there have been people, and every culture has answered it in its own way. Science tries to answer it with observations that anyone can check: light from distant galaxies, a faint glow that fills the sky, the ages of meteorites, and pictures of young stars still building their planets. Indigenous peoples in what is now Canada have also watched the sky carefully for thousands of years, passing down detailed knowledge of how the stars move with the seasons. In this lesson you will look at the scientific evidence for how the universe and solar system began and changed, and at how different ways of knowing the sky can work together.
The Big Bang theory
The Big Bang theory says that about 13.8 billion years ago the universe was extremely hot and dense, and that it has been expanding and cooling ever since. As it cooled, the first atoms formed, then gravity gathered gas into stars and galaxies. The name is misleading: it was not an explosion of matter flying out into empty space from one spot. Space itself has been stretching everywhere at once, carrying galaxies apart like raisins in a rising loaf of bread. In science, a theory is not a guess. It is a well-tested explanation that is supported by many independent lines of evidence and makes predictions that have been confirmed.
Evidence that the universe is expanding
When starlight passes through a prism or a spectroscope, it spreads into a rainbow called a spectrum. Each element absorbs certain exact colours, leaving dark absorption lines like a barcode or fingerprint. If a galaxy is moving away from us, its light waves are stretched to longer wavelengths, so the whole barcode shifts toward the red end of the spectrum. This is called redshift. In the 1920s, Georges Lemaître worked out from theory that the universe should be expanding. Edwin Hubble combined his own measurements of galaxy distances with redshifts measured by Vesto Slipher and showed that almost all galaxies are redshifted, and that the farther away a galaxy is, the bigger its redshift and the faster it is moving away. This pattern, called Hubble's law (or the Hubble–Lemaître law), is exactly what an expanding universe produces.
- Redshift of galaxies: distant galaxies are moving away from us, faster the farther they are, so the universe is expanding. Run the expansion backward and everything was once packed together.
- Cosmic microwave background (CMB): in 1965 Arno Penzias and Robert Wilson found a faint microwave signal coming almost equally from every direction. It is leftover heat from about 380 000 years after the Big Bang, when the universe first became transparent, now stretched into microwaves and cooled to about −270 °C. Big Bang scientists had predicted this glow before it was found.
- The mix of light elements: the theory predicts that the early universe made mostly hydrogen and about one quarter helium (by mass), which matches what we measure in the oldest stars and gas clouds.
How the solar system formed: the nebular hypothesis
About 4.6 billion years ago, our solar system began as a huge, slowly rotating cloud of gas and dust called the solar nebula (possibly squeezed by the shock wave of a nearby supernova). Gravity made the cloud collapse. As it shrank it spun faster, the way a figure skater spins faster when pulling in their arms, and it flattened into a disc. Most of the material fell to the centre and became the protosun; when its core got hot enough, fusion began and the Sun was born. In the disc, dust grains stuck together into larger and larger clumps called planetesimals, which collided and merged to form planets. Close to the Sun it was too hot for ices to survive, so only rock and metal could clump together, making small rocky planets. Beyond the frost line, ices were solid too, so planet cores grew large enough to pull in huge amounts of gas, making the giant planets.
- All the planets orbit the Sun in the same direction and nearly in the same plane, and the Sun spins in that same direction, just as you would expect from one spinning disc.
- Rocky planets are close to the Sun and giant planets are far out, matching the frost-line idea.
- The oldest meteorites are about 4.57 billion years old, giving the age of the solar system.
- Telescopes such as the ALMA radio telescope array have photographed discs of gas and dust around young stars, some with gaps where planets appear to be forming.
- Astronomers have confirmed more than 6000 planets orbiting other stars (exoplanets), showing that planet formation is common.
Diverse ways of knowing the sky
First Nations, Métis and Inuit peoples have observed the sky for thousands of years. Their knowledge, carried through languages, stories, ceremonies and practice, links the positions of stars to the seasons and guides hunting, harvesting, fishing, travel and gathering. This knowledge was built from careful, repeated observation over many generations, a strength it shares with science. Mi'kmaw Elder Albert Marshall describes Two-Eyed Seeing (Etuaptmumk): learning to see with the strengths of Indigenous knowledges through one eye and the strengths of Western science through the other, and using both eyes together. The examples below are shared as they appear in published, community-involved sources; each Nation has its own knowledge, and versions differ between communities.
- Mi'kmaw: Muin and the Seven Bird Hunters. The four stars of the Big Dipper's bowl are Muin, the bear. Seven hunters follow her: the three stars of the Dipper's handle and four stars of the constellation Boötes, named as birds (Robin, Chickadee, Moose Bird or Gray Jay, Pigeon, Blue Jay, Owl and Saw-whet Owl). Chickadee carries the pot for cooking, which is the faint star Alcor beside Mizar in the handle. The story follows the bear through the year: the hunt goes on through summer, some birds drop below the horizon as autumn comes, Robin's arrow strikes the bear in the fall and her blood colours the autumn leaves, and in winter her skeleton lies on its back while her life-spirit sleeps in a den, ready to begin again. The changing position of these stars in the evening sky through the seasons is real, and the story records it.
- Anishinaabe (Ojibwe): Ojiig, the Fisher. In Ojibwe sky knowledge, the Big Dipper is part of Ojiig, a fisher (a weasel-like animal): the bowl is his hindquarters and the handle is his long tail. Ojiig is remembered for bringing summer to the Earth from the Sky World. The Ojibwe Sky Star Map Constellation Guide (by Annette S. Lee, William Wilson, Jeffrey Tibbetts and Carl Gawboy) links Ojiig's position to the seasons: when Ojiig climbs high in the northeastern evening sky in late winter, it is maple-sugaring time.