Evidence of the Big Bang Theory

Rochelle Enrera, Amy Meyers
  • Author
    Rochelle Enrera

    Rochelle has a bachelor's degree in Physics for Teachers from Philippine Normal University-Manila and has completed 30+ units in MS Geology at University of the Philippines-Diliman. She is a licensed teacher and has taught Grade 10 Physics for three years. She has been a science content writer and copywriter for over three years now.

  • Instructor
    Amy Meyers

    Amy holds a Master of Science. She has taught science at the high school and college levels.

Discover how scientists arrived at the Big Bang Theory and what proofs support it. Learn other pieces of evidence like the universe expansion and many other claims. Updated: 11/29/2021

Table of Contents


Evidence of the Big Bang Theory

The Big Bang is the most widely-supported theory today regarding the origin of the universe. It states that about 13.8 billion years ago, the universe expanded from an extremely small, hot, and dense point called a singularity. The term "big bang" was coined by an English astronomer named Fred Hoyle in 1949, who ironically opposed the said theory. The term is rather a misnomer because the theory does not describe the origin of the universe as a large explosion, but rather as an expansion of space.

A timeline of the expansion of space.

Diagram of the timeline of the Big Bang expansion

Even though it is the most widely accepted theory today, it is essential to note that it was not the sole theory proposed by scientists to explain the origin of the universe. Some of these theories include the Steady State Theory, which states that the universe is unchanging and remains in its original state. It proposed that as space expands, new galaxies are formed. Another theory is the Oscillating Universe Theory, which is a modification of the Big Bang theory. It suggests the reversal of the universe's expansion, resulting in a Big Crunch, that will lead to the start of another birth of the universe through expansion. This theory describes that the life of one universe may be finite, but the series of expansion and contraction through the Big Bang and Big Crunch may be infinite. Among these theories, the Big Bang theory is the one that explains the origin of known matter, supported by the laws of physics, and strengthened by several pieces of evidence observed until today.

The pieces of evidence of the Big Bang theory include the following:

  • redshifted galaxies and universe expansion
  • presence of the cosmic background radiation
  • percentage of light and heavy elements present in the universe

How does each piece of evidence for the Big Bang support the origin of the universe? Learn more about all of these in the next sections.

Universe Expansion and Red Shift

How do scientists and astronomers prove the Big Bang expansion?

In 1912, an American astronomer Vesto Slipher began to measure the radial velocities of spiral nebulae and discovered that these nebulae are receding from us at large velocities. He observed that these nebulae showed redshift, which means that their wavelengths shifted to longer or redder wavelengths, an indication that they are moving away relative to us. His observations became one of the bases of the idea that the universe is expanding.

In 1922, a Russian cosmologist named Alexander Friedmann derived equations named Friedmann equations that showed that the universe is in a state of expansion. He derived it from Einstein's equations for general relativity. At that time, Einstein supported the idea that the universe is static and he used the cosmological constant to support it. He then later removed it after Hubble's study showed proof of receding galaxies.

In 1929, Edwin Hubble, an American astronomer, extended the work of Slipher using a 100-inch Hooker Telescope located in Mount Wilson. He tried to calculate the velocities of the galaxies by measuring the shift in their specific spectral lines. He discovered that most of the galaxies exhibited redshift, indicating that galaxies are moving away from us. He also noticed that those that appear smaller in his observations have larger redshifts. He then plotted the velocity of these galaxies with their distances, inferring that those that appear smaller are located further from us. Despite a large scatter on his data, his graph showed an interesting relationship — a linear relationship between the distance of the galaxies and their velocities. This means that the further the galaxies, the faster they are moving away from us, a relationship now known as Hubble's law.

In 1927, a Belgian physicist and Catholic priest Georges Lemaitre derived the same equations as Friedmann. He then proposed that the receding galaxies suggest that the universe is expanding. In addition, he inferred that if the universe is really expanding, then it should have been smaller in the past, and may even be concentrated in a single small and dense point he called the "primeval atom". He proposed that this "primeval atom" is where the fabric of space and time originated. His proposal led to a series of debates about the origin of the universe. As mentioned previously, other theories were presented at that time but Hubble's observations strongly supported the idea of an expanding universe. The discovery of cosmic background radiation, which will be discussed in the next section, further strengthened the Big Bang theory.

Cosmic Background Radiation

The Big Bang theory describes that the universe is initially very hot and dense, and it cools as it expands. The remnant radiation from the Big Bang is called the cosmic microwave radiation (CMB). Today, this radiation is only 2.725 Kelvin or -270.4{eq}^{\circ} {/eq} Celsius, which is significantly lower than the initial temperature of the universe at around 10{eq}^{32} {/eq} K. The CMB is invisible to the naked eye and is found in the microwave spectrum of radiation. Despite its relatively low temperature, it is present in any direction, and the entire sky would glow uniformly if it would be visible to human eyes. It is another Big Bang theory proof because there is no other alternative source of this uniform radiation that fills the whole universe.

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Frequently Asked Questions

What is evidence for the Big Bang theory?

There are several pieces of evidence that support the Big Bang Theory. These are the following:

  1. Most of the galaxies appear red shifted, an indication that they are moving away from us and that the universe is expanding.
  2. The remnant radiation from the Big Bang is observed today as the cosmic microwave background radiation (CMB), a low-level radiation with a temperature of 2.725 K,
  3. The percentage of light elements such as hydrogen and helium agree with the idea that the universe started in a hot and dense phase.

Who found evidence for the Big Bang?

The pieces of evidence that support the Big Bang Theory evolve from the works of several scientists and astronomers. However, one of the strongest proofs of the theory is the observation of Edwin Hubble that the farther the galaxies are, the faster they recede. It supports the idea that the universe is really expanding. The cosmic microwave background radiation was discovered accidentally by Arnold Penzias and Robert Wilson. However, it was Georges Lemaitre who first proposed the idea the the universe originated from the Big Bang.

When did the Big Bang theory start?

In 1927, Georges Lemaitre derived equations that showed the universe's expansion. He then proposed that the receding galaxies suggest that the universe is really expanding. He also added that the universe should have been smaller in the past, concentrated in a single small and dense point he called "primeval atom." His theory was strengthened by Hubble's observations and the discovery of the cosmic microwave background radiation (CMB) by Penzias and Wilson.

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