History of the Big Bang theory

The history of the Big Bang theory tells us how scientists learned about the start of our universe. The theory began with careful watching and good ideas about space and time. A priest named Father Georges Lemaître first shared the idea in a clear way in 1927.

One big clue came from Hubble's law. It showed that the universe is growing. This helped prove that the universe had a start, just like the Big Bang theory says. Today, scientists still work on the Big Bang model to find out more about how everything began.

Philosophy and medieval temporal finitism

In medieval philosophy, people talked about whether the universe had a start or was always there (see Temporal finitism). Aristotle thought the universe was eternal, but this didn’t agree with Jewish and Islamic philosophers who believed the universe was made.

Robert Grosseteste, an English thinker, wrote in 1225 about how the universe might have begun with a big explosion. He talked about how matter formed stars and planets around Earth. This was an early try to explain space using nature’s rules.

Later, Johannes Kepler used the dark night sky to guess the universe wasn’t endless. Isaac Newton also wrote about how things move in the universe.

Early 20th century scientific developments

In the early 1900s, scientists saw that most spiral galaxies were moving away from Earth. They used special tools to study light and found that galaxies moved faster the farther away they were.

Around this time, a famous scientist named Albert Einstein developed new ideas about space and time. These ideas showed that the universe could not stay still—it was either growing or shrinking. Another scientist, Alexander Friedmann, used Einstein's ideas to show that the universe was expanding.

In 1927, a scientist named Georges Lemaitre suggested that the universe began with a huge explosion from a very small point. In 1929, Edwin Hubble observed that galaxies were moving away from each other, and their speed increased with distance. This helped support Lemaitre's idea. Later, Lemaitre called this beginning the "primeval atom," which we now call the Big Bang.

1950 to 1990s

From 1950 to 1965, scientists had different ideas about how the universe began. The Big Bang theory helped explain why we see certain amounts of hydrogen and helium in space. Observations showed that objects like quasars and radio galaxies were more common a long time ago. In 1964, scientists discovered something called the cosmic microwave background radiation, which gave strong support to the Big Bang idea.

Even with the Big Bang theory, some questions remained during the 1970s and 1980s. Scientists kept searching for more details about the cosmic microwave background and some observations did not match what they expected.

1990 onwards

The 1990s and early 2000s helped us learn more about the Big Bang. We had better telescopes and satellites like COBE, the Hubble Space Telescope, and WMAP.

In 1990, COBE showed that the cosmic microwave background radiation looks just as we expect from a very hot, dense early universe. In 1998, we learned that the universe’s expansion is speeding up.

From 2001 to 2010, NASA’s WMAP spacecraft made detailed pictures of the universe. These pictures helped us learn that the universe is about 13.7 billion years old. Later, from 2013 to 2015, the Planck spacecraft made even more detailed pictures.

Today, scientists study how galaxies form and what happened right after the Big Bang. They also study mysterious parts of the universe like dark energy and dark matter.