Origin of the Universe: Scientific Theories

Steady State Theory/Continuous Creation Theory/Infinite Universe Theory

Proposed by Thomas Gold, Fred Hoyle, Hermann Bondi; the universe is unchanging in time and is uniform in space; the density of matter remains unchanged due to the continuous creation of matter, adhering to the perfect cosmological principle which states that the observable universe is basically the same at any time and place; the continuous creation of matter from nothing was criticized by the scientific community (arguing that if matter is continuously created everywhere, then the average age of the stars in one section of the universe should be the same throughout the cosmos), and astronomers found this to be untrue; although disproved, it provided substantial contributions; one of the experimental evidences was the discovery of cosmic microwave background (considered as remnant radiation)

Big Bang Theory

Proposed by George Lemaître (the father of the theory, a Belgian priest) and Alexander Friedmann (whose equations govern the homogenous and isotropic expansion of space within the context of general relativity); the prevailing cosmological model of the early development of the universe; 13.7 billion years ago, there was a rapid expansion, the event hurling matter and energy (including time and space) in all directions in the universe; at the center, all matter and energy were contained in a compact point called singularity; Lemaître based his assumptions on Albert Einstein’s theory of general relativity and on the simplifying assumptions of homogeneity (equal at every point) and isotropy (equal in every direction)

Evidence supporting the big bang theory

1) Galaxies moving away: Edwin Hubble (invented the telescope) revealed that the light from galaxies showed that they move away at a recessional velocity proportional to their distance as summarized in Hubble’s law. This observation is manifested in the redshift of light spectra. In the spectrum of visible light, red light has the longest wavelength. When an object that gives off light (like a galaxy) is moving away, the motion lengthens the wavelengths, causing the light to be red-shifted. It supports the expansion of the universe and suggests that the universe was once compacted. 2) Presence of cosmic microwave background (CMB): In 1964, Arno Penzias and Robert Wilson accidentally discovered cosmic microwave radiation. This radiation was speculated to be the leftover energy from the formation of the universe, associated with the recombination era when atoms were just beginning to form. 3) Abundance of light elements: Elements such as helium, hydrogen, and trace amounts of lithium and beryllium found in the observable universe agree with the hypothesis of the big bang theory. Their abundance is checked from the spectra of the oldest stars and gas clouds. The ratio of these light elements matched with what was expected from the big bang nucleosynthesis.

Unresolved problems of the big bang theory

1) Flatness: The Wilkinson Microwave Anisotropy Probe (WMAP) revealed that the geometry of the universe is almost flat. However, according to the big bang theory, the universe should exhibit curvature as time grows. 2) Monopole: The big bang theory predicted the production of heavy, stable magnetic monopoles in the early universe. However, there were no magnetic monopoles that have been observed. 3) Horizon: Based on the Big Bang expansion, distant regions of space in opposite directions of the sky are so far apart that they could never have been in casual contact with each other. However, the evidence showing the uniformity of cosmic microwave background temperature suggests that these regions must have had contact in the past.

Cosmic Inflation Theory

Proposed by Alan Guth, Andre Linde, Paul Steinhart, and Andy Albrecht in 1980 offered solutions to the unresolved problems revolving the big bang theory; proposed a period of exponential expansion of the universe, estimated to have happened 10^-35 to 10^-33 s, prior to the more gradual Big Bang expansion. Guth believed that this inflation was driven by the repulsive force of gravity, a behavior that was previously predicted by Einstein’s theory of relativity. During the rapid expansion, the energy density of the universe was dominated by cosmological-constant type of vacuum energy. Later on, this decayed to produce the matter and radiation that filled up the universe.

Steady State Theory proposers

Proposed by Thomas Gold, Fred Hoyle, Hermann Bondi

Steady State Theory description

The universe is unchanging in time and is uniform in space; the density of matter remains unchanged due to the continuous creation of matter, adhering to the perfect cosmological principle which states that the observable universe is basically the same at any time and place.

Big Bang Theory proposers

Proposed by George Lemaître (the father of the theory, a Belgian priest) and Alexander Friedmann (whose equations govern the homogenous and isotropic expansion of space within the context of general relativity)

Big Bang Theory description

13.7 billion years ago, there was a rapid expansion, the event hurling matter and energy (including time and space) in all directions in the universe; at the center, all matter and energy were contained in a compact point called singularity

Evidence: Galaxies moving away

Edwin Hubble (invented the telescope) revealed that the light from galaxies showed that they move away at a recessional velocity proportional to their distance as summarized in Hubble’s law. This observation is manifested in the redshift of light spectra. In the spectrum of visible light, red light has the longest wavelength. When an object that gives off light (like a galaxy) is moving away, the motion lengthens the wavelengths, causing the light to be red-shifted. It supports the expansion of the universe and suggests that the universe was once compacted.

Evidence: Presence of cosmic microwave background

In 1964, Arno Penzias and Robert Wilson accidentally discovered cosmic microwave radiation. This radiation was speculated to be the leftover energy from the formation of the universe, associated with the recombination era when atoms were just beginning to form.

Evidence: Abundance of light elements

Elements such as helium, hydrogen, and trace amounts of lithium and beryllium found in the observable universe agree with the hypothesis of the big bang theory. Their abundance is checked from the spectra of the oldest stars and gas clouds. The ratio of these light elements matched with what was expected from the big bang nucleosynthesis.

Problem: Flatness

The Wilkinson Microwave Anisotropy Probe (WMAP) revealed that the geometry of the universe is almost flat. However, according to the big bang theory, the universe should exhibit curvature as time grows.

Problem: Monopole

The big bang theory predicted the production of heavy, stable magnetic monopoles in the early universe. However, there were no magnetic monopoles that have been observed.

Problem: Horizon

Based on the Big Bang expansion, distant regions of space in opposite directions of the sky are so far apart that they could never have been in casual contact with each other. However, the evidence showing the uniformity of cosmic microwave background temperature suggests that these regions must have had contact in the past.

Cosmic Inflation Theory proposers

Proposed by Alan Guth, Andre Linde, Paul Steinhart, and Andy Albrecht

Cosmic Inflation Theory description

Period of exponential expansion of the universe, estimated to have happened 10^-35 to 10^-33 s, prior to the more gradual Big Bang expansion. Guth believed that this inflation was driven by the repulsive force of gravity, a behavior that was previously predicted by Einstein’s theory of relativity. During the rapid expansion, the energy density of the universe was dominated by cosmological-constant type of vacuum energy. Later on, this decayed to produce the matter and radiation that filled up the universe.

Solution: Flatness

From the perspective of someone living on a ball, the surface is obviously curved. Yet, if its size is increased to the size of the Earth, it would appear flat even though it is still a sphere. In astronomical proportion, it would appear flat because inflation stretches any initial curvature of the universe to almost completely flat.

Solution: Monopole

The inflation theory allows the existence of the monopoles as long as they were produced prior to the inflationary epoch. During the rapid expansion, the density of the monopoles dropped exponentially to an undetectable level.

Solution: Horizon

The inflation theory assumes a burst of exponential expansion in the early universe and follows that the distant regions were much closer with each other prior to inflation. Expansion is so fast that temperature cannot follow.

Cosmic Inflation Theory: Dark energy and dark matter

The inclusion of the idea of a rapid inflation in the big bang model may have explained some observations, but also required the addition of the principles of dark energy and dark matter to complete the new model. The nature of dark energy and dark matter are unknown. Dark energy is the energy of the empty space and is causing the expansion of the universe to accelerate. Dark matter is considered a hypothetical kind of matter that cannot be seen with telescopes. It is believed to account for most of the matter in the universe. The universe is believed to be composed of dark energy, dark matter, radiation, and ordinary matter (atoms, ions, protons, electrons, stars, galaxies, and life).

Cosmic Inflation Theory: Gravitational waves

The much-needed conclusive evidence to support the inflation theory came in the form of the predicted gravitational waves. Gravitational waves are distortions in space-time. The gravitational waves generated at the birth of the universe should have interacted with the cosmic background radiation, creating characteristic patterns that could be interpreted.

Cosmic Inflation Theory: Existence of gravitational waves

On March 17, 2014, a team of astronomers led by John Kovac of the Harvard-Smithsonian Center for Astrophysics detected ripples called gravitational waves in the fabric of space-time. These gravitational waves were supposedly created in a violent inflationary event at the dawn of time. The ripples manifested themselves as faint spiral patterns in the cosmic microwave radiation. According to Kovac, the existence of gravitational waves is directly linked to the exponential expansion that is intrinsic to the inflation theory. The image of the cosmic microwave background as observed by the European Space Agency's Plank Space Observatory taken in 2013 showed tiny temperature fluctuations. The findings concluded that all matter had the same temperature and started at the same place as assumed by the inflation theory. in the non-inflationary model, there would have been wide temperature differences between the different parts of the universe.