Introduction
The Big Bang Theory is the idea that the universe started as a small singularity and either had a Big Bang or expanded from that state
Everything is packed together then it exploded outwards along with all the matter. When it started to condense it made galaxies then the galaxies condensed, making planets and stars
How theories of the universe have changed over time
Theories of the universes origins have changed and developed over time as technology has advanced. We can now tell which theories created in the past are right or wrong using the technology we have.
Throughout history different civilisations have individually developed their own theories of the universe and its origin.
Ancient Greek Philosophers
In ancient civilisations it was widely believed that the earth was flat until the 5th century B.C. The belief in a spherical earth only came about when Empedocles and Anaxagoras observed a lunar eclipse and saw the clearly rounded shadow of the Earth on the Moon.
Late in 5th century B.C, Greek philosophers Leucippus and Democritus suggested that the universe was made of very small, indestructible building blocks, which they called atoms, this is called the Atomism universe. They thought that all of reality was made of different arrangements of these atoms.
The theory of the Aristotelian universe is very different from the theories that are commonly believed in today showing how far we’ve come. The Aristotelian universe was created by the Greek philosopher Aristotle in the 4th century B.C.. He thought that the Earth was fixed in the centre of a geocentric universe, surrounded by planets and stars. He believed the universe to be finite in size and that it exists unchanged throughout history.
Galileo’s Theories
Copernicus first suggested that the sun was the centre of the solar system, not the earth. With the earth and other planets in orbit around the sun. 500 years ago, when he lived, his idea was not very popular and almost nobody believed his theory.
Galileo, the Italian physicist, astronomer and philosopher used telescope observations to support Copernicus’ theories 100 years after Copernicus had lived. Because the Catholic Church was very powerful at the time they did not support the idea that earth was not the centre of the universe. So in 1616 Galileo was tried for heresy which is the crime of being opposed to the church’s teachings.
He was cleared of heresy but told to no longer publicly state his belief of a non geocentric universe. Later after releasing a book stating his theory of the earth and planets revolving around the sun (1632) he was found guilty of heresy and sentenced to life imprisonments (1633) under house arrest. Galileo then died on January 8, 1642. He contributed heavily to today’s theories of the universe and its origins.
What is the Big Bang theory
The Big Bang theory is the leading explanation and the most commonly believed theory about how the universe began. Our view on the Big Bang theory comes from mathematical formulas as models.
It says the universe started as a small singularity then inflated over 13.8 billion years to what we know today. At first it was thought the universe was 13.7 billion years old but after the European Space Agency Planck satellite mapped the background in 2013, it was found that the universe is actually 13.82 billion years old.
Although most people believe in the Big Bang theory some astronomers believe, instead, in eternal inflation or an oscillating universe. An oscillating universe is the theory that the universe follows infinite self-sustaining cycles.
The modern Big Bang theory was developed in the 1940s by cosmologist and nuclear physicist George Gamow. People only started believing that the universe was evolving after the 1920s, when evidence and Albert Einstein’s theory of relativity started proving so. Before that it was only thought that the universe had existed forever in the same form or that is was created by a higher being.
In 1933 Lemaître described the expansion of the universe in a way everyone would understand, he suggested the universe started as a cosmic egg, expanding outward from a central point.
Redshift
The redshift is small changes in the colour and frequency of light which astronomers use to measure the distance of things in space, their speed and to track the expansion of the universe.
A simple way to explain the redshift is like when an ambulance or police car with sirens passes by and the pitch of the sound seems lower after the vehicle has passed. But instead of sound the redshift is with the frequency of colour. For example, if something was moving very fast through space, as it approaches you it would appear blue but as it passes it becomes red.
It happens because when an object moves away from you in space it’s light waves are stretched into longer wavelengths.
By measuring how far the pattern of lines in the spectrum of starlight moves from its original spots, astronomers can calculate the speed of the object in comparison to the earth. The opposite is when an object moves towards us, it’s light waves are compressed into shorter wavelengths, this is called the blueshift.
This is important in humans understanding of the universe because in the 1910s astronomers at Lowell Observatory discovered that nearly every galaxy was redshifted, meaning most galaxies in the universe were moving away from us. This lead to when Edwin Hubble uncovered that the further a galaxy the faster is receding, meaning the universe was expanding in 1929. This was the first key piece of evidence for the Big Bang theory.
Inflation
Inflation is the theory that during its first few moments the universe underwent rapid expansion and continues to expand gradually throughout its history. This theory was developed in the 1980s to explain the holes and problems in the Big Bang theory.
While the Big Bang theory is the most believed theory of the universe it has some major problems where some things just don’t add up. All of which the inflation theory, an extension of the Big Bang theory fixes.
Evidence that supports the Big Bang theory
The Big Bang theory is not the most commonly believed theory of the universe at this time for no reason. The famous theory has many pieces of evidence for it, but on the contrary it does have problems, some of which can be explained through extensions of the theory.
The red shift, as previously discussed, is a key piece of evidence in favour of the Big Bang theory. Along with the red shift, Cosmic Microwave Background radiation is huge evidence for the Big Bang theory. Astronomers use the cosmic microwave background to see the echo of the expansion.
The Big Bang theory states that the universe was once very hot, meaning someone remnant of this heat should be able to be found. According to NASA in the second the universe began the surrounding temperature was about 5.5 billion degrees Celsius. It also says that energy created just after the Big Bang is still travelling in space, the energy was later found as microwaves (electromagnetic waves) coming from every direction in space.
By 1965 no remnants of the heat from the Big Bang has been found. Until Arno Penzias and Robert Wilson discovered a 2.725 degree Kelvin (-273.15 degrees Celsius) Cosmic Microwave Background radiation, which is thought to be the remnant of the heat that was needed as evidence for the Big Bang theory. Penzias and Wilson were given a Nobel Prize for Physics for their discovery