The Universe
From an Earth at the centre to an accelerating cosmos of dark energy — how we found our place in space.
Each star is a thinker or work; solid lines draw the constellation of a school, dashed threads the passage of ideas between eras.
Select any point on the timeline to read about it.
All entries by era
The Universe 350 BCE – 2030 CE
From an Earth at the centre to an accelerating cosmos of dark energy — how we found our place in space.
- 150 CE
Ptolemy, Almagest. Ptolemy perfects the geocentric system, using epicycles and deferents to predict planetary motion with remarkable accuracy. Placing a motionless Earth at the centre, his model matches the sky well enough to reign as astronomy's standard for fourteen centuries.
- 1543 CE
Nicolaus Copernicus, De revolutionibus. Copernicus places the Sun, not the Earth, at the centre and sets the planets — Earth among them — in orbit around it. Though still wedded to circular orbits, the shift dethrones humanity from the cosmic centre and launches the astronomical revolution.
- 1609 CE
Johannes Kepler, Astronomia nova. Working from Tycho Brahe's precise data, Kepler discovers that planets move in ellipses, sweeping equal areas in equal times. By discarding the perfect circle held sacred since antiquity, he turns Copernican astronomy into an accurate, predictive science.
- 1610 CE
Galileo Galilei, Sidereus Nuncius. Turning his telescope skyward, Galileo finds moons circling Jupiter, phases of Venus and countless stars in the Milky Way. The observations shatter the crystalline heavens of tradition and provide the first direct evidence for the Copernican system.
- 1687 CE
Isaac Newton, Principia. Newton shows that a single law of universal gravitation governs both a falling apple and the orbiting Moon. The cosmos becomes a lawful mechanism, its motions calculable from first principles, and physics and astronomy are joined into one science.
- 1915 CE
Albert Einstein, general relativity. Einstein recasts gravity not as a force but as the curvature of spacetime by mass and energy. His field equations describe the universe as a whole for the first time and predict phenomena — bending starlight, black holes, an expanding cosmos — that Newton could not.
- 1929 CE
Edwin Hubble, redshift–distance law. Measuring galaxies, Hubble finds that the farther they are, the faster they recede — the universe is expanding. The discovery, building on Lemaître's theory, transforms the cosmos from a static stage into something with a history and, by implication, a beginning.
- 1931 CE
Georges Lemaître, 'primeval atom'. Lemaître proposes that if the universe is expanding, it must have begun from a single dense 'primeval atom' — the germ of the Big Bang. A priest and physicist, he gives cosmic evolution a starting point and turns the origin of everything into a testable question.
- 1965 CE
Penzias & Wilson, cosmic microwave background. Penzias and Wilson stumble on a faint microwave hiss coming from every direction — the cooled radiation left over from the hot early universe. This cosmic microwave background is the decisive evidence for the Big Bang, settling a long debate with the steady-state model.
- 1980 CE
Alan Guth, cosmic inflation. Guth proposes that in its first fraction of a second the universe underwent an exponential burst of expansion. Inflation elegantly explains why the cosmos looks so uniform and flat, and why tiny quantum ripples grew into the seeds of galaxies.
- 1998 CE
Supernova surveys, dark energy. Two teams measuring distant supernovae find the expansion of the universe is speeding up, not slowing down, driven by a mysterious 'dark energy'. It appears to make up most of the cosmos, revealing how little of the universe we actually understand.
- 2016 CE
LIGO, gravitational waves. LIGO detects ripples in spacetime from two merging black holes, confirming Einstein's century-old prediction and opening a new sense with which to observe the cosmos. Gravitational-wave astronomy lets us witness events that emit no light at all.
The milestones
c. 150 CE
Ptolemy, Almagest
The Earth-centred cosmos
Ptolemy perfects the geocentric system, using epicycles and deferents to predict planetary motion with remarkable accuracy. Placing a motionless Earth at the centre, his model matches the sky well enough to reign as astronomy's standard for fourteen centuries.
1543
Nicolaus Copernicus, De revolutionibus
The Sun at the centre
Copernicus places the Sun, not the Earth, at the centre and sets the planets — Earth among them — in orbit around it. Though still wedded to circular orbits, the shift dethrones humanity from the cosmic centre and launches the astronomical revolution.
1609
Johannes Kepler, Astronomia nova
Orbits are ellipses
Working from Tycho Brahe's precise data, Kepler discovers that planets move in ellipses, sweeping equal areas in equal times. By discarding the perfect circle held sacred since antiquity, he turns Copernican astronomy into an accurate, predictive science.
1610
Galileo Galilei, Sidereus Nuncius
The telescope opens the sky
Turning his telescope skyward, Galileo finds moons circling Jupiter, phases of Venus and countless stars in the Milky Way. The observations shatter the crystalline heavens of tradition and provide the first direct evidence for the Copernican system.
1687
Isaac Newton, Principia
One law for heaven and earth
Newton shows that a single law of universal gravitation governs both a falling apple and the orbiting Moon. The cosmos becomes a lawful mechanism, its motions calculable from first principles, and physics and astronomy are joined into one science.
1915
Albert Einstein, general relativity
Gravity as curved spacetime
Einstein recasts gravity not as a force but as the curvature of spacetime by mass and energy. His field equations describe the universe as a whole for the first time and predict phenomena — bending starlight, black holes, an expanding cosmos — that Newton could not.
1929
Edwin Hubble, redshift–distance law
The expanding universe
Measuring galaxies, Hubble finds that the farther they are, the faster they recede — the universe is expanding. The discovery, building on Lemaître's theory, transforms the cosmos from a static stage into something with a history and, by implication, a beginning.
1931
Georges Lemaître, 'primeval atom'
A universe with a beginning
Lemaître proposes that if the universe is expanding, it must have begun from a single dense 'primeval atom' — the germ of the Big Bang. A priest and physicist, he gives cosmic evolution a starting point and turns the origin of everything into a testable question.
1965
Penzias & Wilson, cosmic microwave background
The Big Bang's afterglow
Penzias and Wilson stumble on a faint microwave hiss coming from every direction — the cooled radiation left over from the hot early universe. This cosmic microwave background is the decisive evidence for the Big Bang, settling a long debate with the steady-state model.
1980
Alan Guth, cosmic inflation
A split-second of vast expansion
Guth proposes that in its first fraction of a second the universe underwent an exponential burst of expansion. Inflation elegantly explains why the cosmos looks so uniform and flat, and why tiny quantum ripples grew into the seeds of galaxies.
1998
Supernova surveys, dark energy
An accelerating cosmos
Two teams measuring distant supernovae find the expansion of the universe is speeding up, not slowing down, driven by a mysterious 'dark energy'. It appears to make up most of the cosmos, revealing how little of the universe we actually understand.
2016 →
LIGO, gravitational waves
Listening to the universe
LIGO detects ripples in spacetime from two merging black holes, confirming Einstein's century-old prediction and opening a new sense with which to observe the cosmos. Gravitational-wave astronomy lets us witness events that emit no light at all.