Georges Lemaître, a Belgian Catholic priest who proposed the Big Bang theory in 1931, became president of the Pontifical Academy of Sciences in 1960.

A Belgian Catholic priest was the first to come up with the idea for the Big Bang

In 1931, Georges Lemaître presented his radical idea that the universe came from a “primeval atom,” challenging the long-held belief that the universe had always existed. Einstein initially dismissed Lemaître’s work as having “abominable” physical insight, only to accept it later.

The Big Bang theory describes how the universe began and continues to expand

Rooted in Lemaître’s 1927 idea of a growing universe and confirmed by Hubble’s redshift data, the theory is backed by evidence like cosmic microwave background radiation—remnants of the universe’s fiery birth detected in the 1960s. The radiation was first misidentified as interference from pigeon droppings inside a telescope antenna.

Edwin Hubble showed that the universe is full of galaxies and is expanding

In the 1920s, Hubble showed that the Andromeda "nebula" was another galaxy. He later discovered that galaxies move away from us at speeds proportional to their distance—a breakthrough now known as the Hubble-Lemaître law, foundational to Big Bang cosmology.

The Big Bang theory explains the expanding universe and its fiery early origins

The term “Big Bang” was initially coined by a skeptic of the theory, but the name stuck despite the theory not depicting a "bang." The event took place everywhere in the universe at once, and the theory explains the abundance of hydrogen and helium in the universe.

Alternative models to the Big Bang lack as much scientific evidence

The cosmic microwave background radiation and the observed expansion of the universe suggest that the cosmos began from a tiny, dense state, whose resulting properties we see throughout space. While physics allows for cyclical expansions and crunches, ongoing inflationary aeons, and localized inflation to create bubble universes, evidence for these alternatives has not yet been found.

The Big Bang theory explains the universe’s expansion, not its origin

While we have strong evidence that the universe expanded from an extremely hot, dense state, we can only trace events back to a tiny fraction of a second after that point. Earlier stages, like inflation and potential force unification, remain unproven and unobservable with current tools.

Why the Big Bang theory is the most well-supported explanation for the origin of the universe

Multiple independent lines of evidence—galactic redshift, element ratios, cosmic microwave background radiation, and large-scale cosmic structure—all point to a single origin about 13.8 billion years ago. Before Edwin Hubble, many astronomers believed the entire universe was contained within our galaxy.

After the Big Bang, the universe's current composition was built in stages

The Big Bang theory describes the universe beginning 13.7 billion years ago as an ultradense point, followed by stages, like the radiation- and matter-dominated eras. Each era was responsible for a unique element, such as the cosmic microwave background and atomic nuclei.

The universe might have emerged from a quantum fluctuation—not absolute nothing

Traditional physics breaks down at the moment of the Big Bang, but quantum theory suggests that “empty” space is never truly empty. In 1973, physicist Edward Tryon proposed that our universe began from a quantum energy blip in the quantum vacuum.

Galileo Galilei—considered the father of modern science—was once president of the Academy of Lynxes and used the name Galileo Galilei Linceo on the title pages of his works in its honor.

The Big Bang became physically plausible thanks to Stephen Hawking’s thesis

Stephen Hawking's PhD thesis mathematically showed that singularities—points of no volume and infinite density—are an expected feature of nature. It laid the theoretical groundwork for a model of the universe where everything originates from a single point.

Understanding how and when time began requires a theory of quantum gravity

Rewinding the universe to the big bang compresses all matter, energy, space, and time into a single point, necessitating a model that combines general relativity with quantum mechanics. Although physicists understand time to have begun when the universe did, a clear understanding of the mechanisms involved remains unclear.

From the Big Bang to present—a timeline

A timeline for everything, from the Big Bang to the beginnings of life on Earth. This article lays out, in spans of billions of years, what was happening in the universe as it became the universe. Starting from the Planck era, the earliest known meaningful time, to the probable "Big Crunch" 30 billion years from now, see how the universe has existed and persisted.

The cosmic dark ages: before stars existed

The theories behind the Big Bang suggest the process of the universe beginning to the creation of stable, neutral atoms took just half a million years. But the transition from such atoms to star formation took surprisingly much longer, upwards of 100 million years. Why? This deep dive explores the science behind the unique physical composition of the so-called cosmic dark ages.

One study suggests that dark matter may have originated from a dark Big Bang

A student-faculty team at Colgate University modeled the event as occurring months after the conventional Big Bang and determined the potential gravitational wave signal that would have been left behind. Future gravitational wave detectors are expected to be sensitive enough to observe this signal, if it exists.

The quantum model of the atom resulted from over two millennia of scientific thinking

In 440 BCE, Democritus proposed that everything was made up of tiny particles surrounded by empty space, which varied in size and shape based on the substance's properties. It was not until the 20th century that experimental evidence validated elements of Democritus' model.

The cosmic microwave background radiation is the oldest light in the universe

Just after the Big Bang, the high-density universe prevented light from traveling very far before being absorbed and emitted repeatedly by free-floating particles. As the universe expanded, electrons and protons combined to form hydrogen, thereby freeing up space for light to travel unimpeded, creating the background light we observe today.

The universe expands by stretching space itself, not into anything beyond it

Thanks to Einstein’s relativity and Hubble’s observations, scientists understand that space stretches, like rising bread dough between raisins, with no "outside" to expand into. Some theories suggest our universe might be just one "bubble" in a vast multiverse, possibly floating on a higher-dimensional surface called a brane.

Pigeons were thought to be the cause of what would be evidence of the Big Bang

In 1964, Arno Penzias and Robert Wilson accidentally detected the CMB while trying to eliminate persistent static from their radio antenna. The pair initially blamed the signal on pigeon droppings inside their antenna—cleaning it didn’t help, but it did win them a Nobel Prize.

Modern physics suggests that many universes with different physical laws could exist

Physicists suggest that quantum fluctuations in the early universe could have given rise to these universes. Ancient Greek philosophers like Chrysippus proposed a version of the multiverse over 2,000 years ago—millennia before its adoption into various theoretical frameworks today.

Fritz Zwicky predicted the existence of dark matter and neutron stars

The former resulted from analyzing the motion of galaxies in the Coma Cluster, a subset of the approximately 30,000 galaxies he cataloged during his life. When hypothesizing an origin for observed high-energy particles called cosmic rays, Zwicky and colleague Walter Baade thought they could come from exploding stars, or supernovae—a term he coined—which would leave behind a collapsed star made entirely of neutrons.

There are statistically significant discrepancies in measured universal expansion

Using data from the cosmic microwave background, which allows astronomers to model the universe's conditions since its earliest moments, yields a rate of expansion—the Hubble constant—lower than values obtained from multiple techniques measured locally at more recent timescales. Reconciling the discrepancy, known as the Hubble tension, will require a third independent measurement method between the two scales

Scientists are experimenting with ways to probe the multiverse theory

Researchers are simulating vacuum bubbles—the theorized starting points of universes—using quantum computers, digital models, and exotic lab setups to study how they form, expand, and possibly collide. One experiment aims to "blow" artificial universe-like bubbles inside ultra-cold quantum gases, potentially capturing real-time glimpses of cosmic birth processes in a lab.

Discoveries in electromagnetism became the catalyst for overturning Isaac Newton

To maintain the consistency of experimental results involving electricity, magnetism, and light, time and space had to cease being absolute and could change in value to keep the speed of light constant. This cosmic speed limit forced Einstein to revise the existing model of gravity.

As of 2025, the best cosmological model of the universe includes dark energy

The Lambda cold dark matter model uses the Greek letter to denote the presence of a cosmological constant version of dark energy, alongside slow-moving dark matter and ordinary visible matter. It can account for the observed distribution of galaxies, the structure of the cosmic microwave background, the acceleration of the universe, and the abundance of hydrogen.

The 2011 Nobel Prize in physics was awarded for the discovery of dark energy

Through the use of standard candles—objects whose brightness is well-known—astronomers can determine distances by recognizing that the same phenomena will dim in predictable ways with increasing distance. By observing the same type of bright stellar explosion at various locations, Saul Perlmutter, Brian Schmidt, and Adam Riess identified that the universe's expansion was increasing.

Einstein created a mathematical term for anti-gravity to keep the universe static

General relativity predicted that the gravity of all the matter in the universe would cause it to collapse, contradicting the belief at the time that the universe was constant and unchanging. Albert Einstein added the cosmological constant to his equations, which acted like anti-gravity, to "fix" his math.

Webb discovers galaxy that formed 280 million years after the Big Bang

The James Webb Space Telescope has discovered a galaxy that formed just 280 million years after the Big Bang. It is another in a series of increasingly ancient galaxies that, according to current formation models, should not have been able to form so quickly after the birth of the universe.

The universe may have been reborn from a state of emptiness

Some physicists propose the universe might be the latest in an eternal cycle of universes, each emerging from the empty remains of the one before. This model is inspired partly by Norse and Egyptian myth, suggesting the universe is a cosmic ouroboros—a self-consuming serpent representing an eternal return.

As of 2026, the Pontifical Academy of Sciences, which advises the pope on scientific matters, has included 90 Nobel laureates among its members.

Cecilia Payne-Gaposchkin discovered stars are mostly made of hydrogen and helium

At 25, her doctoral thesis challenged the then-common belief that stars were composed similarly to Earth. Several years later, Henry Norris Russell, who had initially dismissed her findings, independently made the same discovery and received credit for it.

A 1919 eclipse validated general relativity and made Albert Einstein a celebrity

According to the theory, starlight should deflect around massive objects due to the warping of spacetime light travels through on its way to Earth. Comparing the locations of stars behind the Sun during the eclipse with their positions at night showed deflections that popularized Einstein's model.

Albert Einstein's equations predicted black holes decades before their discovery

For nearly 50 years, scientists dismissed black holes as implausible oddities, despite solutions to the equations indicating their existence. But the 1970s discovery of intense X-rays from Cygnus X-1 and its massive hidden companion flipped the consensus.

The theory of axiogenesis may explain the matter-antimatter asymmetry in our universe

Axiogenesis suggests that a theoretical particle field that evolved after the Big Bang may have spun like a marble around a wobbly “Mexican hat” energy landscape, producing excess matter over antimatter. This theoretical particle—the axion—may also make up dark matter, solving an additional mystery in astronomy.

Galileo's Jupiter discovery shattered Earth-centered universe beliefs

Using a telescope inspired by Dutch designs, Galileo spotted four moons orbiting Jupiter in 1610, providing undeniable evidence against geocentrism and fueled support for the heliocentric model. Galileo’s original telescope design stretched 20 meters long—a feat of optical engineering for its time.

The Lucasian Chair is among the most prestigious academic positions in science

Once held by icons like Newton, Dirac, and Hawking, the position was founded in 1663. "Star Trek" imagined the Lucasian Chair’s future holder as the android Data, cementing its mythos across scientific and science fiction realms.

Genetic analysis indicates that every organism on Earth evolved from a single cell

LUCA—the last universal common ancestor—lived about 4.2 billion years ago and likely obtained energy through the conversion of carbon dioxide and hydrogen gas consumed from atmospheric gases at the ocean's surface or hydrothermal vents—openings on the seafloor where fluid warmed and enriched with minerals by Earth's interior is expelled.

Humans have speculated about alien life since ancient times

Around 50 B.C.E., Roman poet and philosopher Lucretius shared the idea that alien life was possible, which was put forth by Greek philosopher Epicurus. The writing is believed to be the first straightforward assertion in Western literature that aliens must exist.

Space telescope development was driven by a desire to bypass Earth's atmosphere

The most important figure in the effort to create what would become the Hubble Space Telescope was Lyman Spitzer, who first proposed a telescope in orbit in 1946. The nearly 50-year endeavor led to space-based observatories, which are not limited by Earth's atmosphere absorbing or distorting most wavelengths of light.

A look at the giants of quantum mechanics

German physicist Max Planck publishes his groundbreaking study of the effect of radiation on a “blackbody” substance, and the quantum theory of modern physics

New ways of seeing the cosmos have redrawn the map of human identity

From Galileo’s crude spyglass to the James Webb Space Telescope, each technological leap has expanded our observational reach and redefined philosophical and moral conceptions of our place in the universe. Identifying signs of life through the study of exoplanet atmospheres would represent the next great revolution.

Before discovering cells, life was believed to emerge suddenly from inorganic matter

Popularized by Aristotle in the 4th century BCE, spontaneous generation was used to explain phenomena like mice appearing in seemingly sealed grain storage. The invention of the compound microscope in the late 16th century led to the identification of cells as the basic unit of life, but it was not until 1855 that their origin from preexisting cells was established.

Light has been modeled as a wave and a stream of particles throughout history

Isaac Newton first identified white light as composed of a spectrum of colors, which he believed consisted of particles of different hues. Various light phenomena, including refraction, led Christiaan Huygens to develop an alternative wave model. Quantum mechanics validated both models through the concept of wave-particle duality.

Particle accelerators allow physicists to create controlled nuclear experiments

Before the 1930s, scientists relied on naturally radioactive substances to learn about atomic nuclei. The first atom was split in 1932 when John Cockcroft and Ernest Walton fired a beam of accelerated protons at a lithium atom, producing alpha radiation.

How upheavals in accepted scientific theories helped popularize the term 'paradigm'

When Thomas Kuhn published "The Structure of Scientific Revolutions" in 1962, he described the history of science as comprising periods of "normal science" where these accepted frameworks—paradigms—gradually accumulate anomalies until they cannot describe nature. Revolutionary science, such as the development of a new theory, results in a paradigm shift, another term Kuhn helped popularize. (Some readers may experience a paywall.)

Meet Hipparchus, the Greek astronomer who created the world's first star map

Astronomer Hipparchus created accurate maps of the night sky way ahead of his time, with coordinates sometimes within a single degree of modern values. Hipparchus founded a new theory of star motion, modeling the sky as a celestial sphere with coordinates similar to latitude and longitude—concepts only recently created in Hipparchus' time.

Italian physicist Enrico Fermi (1901–1954) on the Standard Model

"If I could remember the name of all these particles, I'd be a botanist."

The theory of plate tectonics was not initially accepted until evidence became undeniable

Alfred Wegener proposed continental drift—the movement of large landmasses—in 1912 to explain why similar rock layers, plant and animal fossils, and glacial deposits were found on continents that were then unconnected. In the early 1960s, this was combined with evidence of seafloor spreading, mantle convection in Earth's interior, and earthquake and volcanic data outlining plate boundaries to produce the accepted theory.

Explaining the Higgs boson, also known as the 'God Particle'

The Higgs boson is a long sought after fundamental particle that—within the framework of high-energy physics—gives other particles their mass. Having captured public attention when it was discovered in 2012 at the Large Hadron Collider, and its...

Explore an interactive map of the unified theories of everything

This interactive concisely describes many highly complex theories ranging from quantum gravity and black holes to dark matter and energy. Supplementary resources, key questions, and possible solutions accompany each description. As of 2026, no developed theory provides an accepted explanation of all observed phenomena in the universe at all scales.