The Big Bang Theory

Planet earth initially was a barren, rocky, and hot object with a thin atmosphere of hydrogen and helium. During the cooling of the surface, gases and water vapor released from the inner solid Earth. When cyanobacteria evolved at least 2.4 billion years ago, they set the stage for a remarkable transformation. They became the first photo-synthesizers on Earth, making food using water and the Sun's energy, and releasing oxygen. Cooperating cells eventually became the first animals, which DNA evidence suggests evolved around 800 million years ago. Sponges were among the earliest animals. While chemical compounds from sponges became preserved in rocks as old as 700 million years, molecular evidence points to sponges developing even earlier. The Cambrian Period (541-485 million years ago) witnessed a wild explosion of new life forms.

Along with new burrowing lifestyles came hard body parts like shells and spines. Hardbody parts allowed animals to engineer their environments more drastically. A shift also occurred towards more active animals, with defined heads and tails for directional movement to chase prey; this started the evolution of the present atmosphere and led to the evolution of life on Earth's surface.

Purpose

Students will examine the scientific evidence of the Big Bang Theory and discuss the three main pieces of scientific evidence that support this theory. Students will also survey the physical laws that control the solar system and the origin of life on Earth. 

Learning Outcomes

• Cite and describe evidence used to develop and verify the scientific Big Bang Theory and the origins of the Universe.
• Recognize components and facts of the solar system.
• To describe the current theory of the origin of life on Earth.

Instructions

• Read the materials and watch the videos. Write a reflective essay (a minimum of 250 words, 12-point font, double spaced) about what you found most interesting in the material presented for this assignment. Upload your reflective essay via Canvas. The essay assignment is worth 25 points.
• In the Discussion Form entitled The Big Bang Theory. Share a summary of your Big Bang Theory reflective essay. Respond to the summary of two other students' posts. The discussion part of the assignment is worth 25 points. 
• Complete the multiple-choice quiz: The Big Bang Theory Quiz. The quiz is worth 50 points.
• The essay, discussion and quiz are due March 14 and 15, 2021. This assignment is worth a total of 100 points.
• Come to class prepared to participate in the discussion.

Context

Life began on Earth at least 3.5 to 4 billion years ago, and it has been evolving ever since. All living things on Earth were simple, single-celled organisms. The single-celled organisms consumed the Sun's energy. As a waste product, this cyanobacterium eventually filled the oceans and atmosphere with oxygen. Next, an oxygenated atmosphere paved the way for more complex life forms to exist. The first multicellular organisms evolved, and after that, Earth's biodiversity significantly increased.  At about 100,000,000 years ago, dinosaurs roamed the Earth until their abrupt extinction. Approximately 10,000,000 years ago was the age of mammals; these mammals are our direct ancestors. 

Watch the video: The Big Bang Theory Overview

The development of human physical and cultural endowments covered roughly 5 million years, from a hominoid stage. It was 100,000 years ago when homo sapiens evolved and progressed from bipedal locomotion, the acquisition of language, the origins of agricultural practices, changes in a foraging economy to the transition to subsistence economies, and an increase in societal complexity (social hierarchy, religion, warfare, social control, etc.). 

Discoveries in astronomy and physics have shown beyond a reasonable doubt that our Universe did have a beginning. Before that moment, there was nothing; during and after that moment there was our Universe.  The Big Bang is a scientific theory describing the origin of all space, time, matter, and energy approximately 12 to 13.7 billion years ago from a singular point of extremely high density and temperature. The Big Bang Theory is an effort to explain what happened during and after that moment. The Big Bang Theory is also called an expanding universe hypothesis.

The "Big Bang Theory" does not describe how the Universe appears, but rather, how the Universe evolves as it ages. Scientists say that there was no explosion. Imagine a balloon expanding: an infinitesimally small balloon expanding to the size of our current Universe. Rather than a balloon popping and releasing its contents. The earliest indications of the Big Bang occurred due to deep-space observations conducted in the early 20th century. In 1912, American astronomer Vesto Slipher conducted a series of observations of spiral galaxies (believed to be nebulae) and measured their Doppler Redshift. In almost all cases, the spiral galaxies were observed to be moving away from our own.

In 1922, Russian cosmologist Alexander Friedmann developed what is known as the Friedmann equations, which were derived from Einstein's equations for general relativity. Contrary to Einstein's advocacy at the time with a Cosmological Constant, Friedmann's work showed that the Universe was likely in a state of expansion. In 1924, American astronomer Edwin Powell Hubble's measurement of the great distance to the nearest spiral nebula showed that these systems were other galaxies. At the same time, Hubble began developing a series of distance indicators at Mount Wilson Observatory. In 1927, Georges Lemaitre, a Belgian physicist, and Roman Catholic priest proposed an expanding model for the Universe to explain the observed redshifts of spiral nebulae and calculated the Hubble law. He based his theory on the work of Einstein and De Sitter and independently derived Friedmann’s equations (a solution of Einstein's equations of general relativity with flat spatial sections describing a cosmological model) that suggested that the Universe must be expanding. The distant galaxies were moving away faster, which was what was predicted by Lemaitre's solutions. By 1929, Hubble discovered a correlation between the galaxies' distance and the amount of redshift in that galaxy's light -- known as Hubble's law.

In 1931, Lemaitre went further with his predictions, extrapolating backward in time and discovering that the matter of the Universe would reach an infinite density and temperature at a finite time in the past. The predictions meant the Universe must have begun in an incredibly small, dense point of the matter, called a "primeval atom." The fact that Lemaitre was a Roman Catholic priest concerned some, as he was putting forth a theory that presented a definite moment of "creation" to the Universe. After all, the Judeo-Christian tradition had propagated a similar idea for millennia. Lemaitre insisted that there was neither a connection nor a conflict between his religion and his science. He kept them entirely separate, treating them as different, parallel interpretations of the world, both of which he believed with personal conviction. When Pope Pius XII referred to the new theory of the origin of the Universe as a scientific validation of the Catholic faith, Lemaitre was somewhat alarmed. Delicately, he tried to separate the two: "As far as I can see, such a theory remains entirely outside any metaphysical or religious question. It leaves the materialist free to deny any transcendental Being. For the believer, it removes any attempt at familiarity with God. It is consonant with Isaiah speaking of the hidden God, hidden even in the beginning of the Universe."

Edwin Powell Hubble, the Hubble Space Telescope, was named one of the leading astronomers of the twentieth century. His discovery in the 1920s that countless galaxies exist beyond our own Milky Way galaxy revolutionized our understanding of the Universe and our place within it. He is credited with the idea of the Big Bang theory. In 1929, after nearly a decade of observations, Edwin Hubble published his definitive report that the redshift in the light coming from distant galaxies is proportional to their distance, effectively confirming Lemaitre's prediction of an expanding universe. He surmises that the Universe went through a stage where its contents were highly compressed and very hot. The three observable demonstrations of this stage are (1) the present-day expansion of the Universe, (2) the existence of the cosmic microwave background radiation, and (3) the cosmic abundance.

These discoveries triggered a debate between physicists throughout the 1920s and 30s. Most of these scientists advocate that the Universe was in a steady state. In this model, new matter is continuously created as the Universe expands, thus preserving the uniformity and density of matter over time. Among these scientists, the idea of a Big Bang seemed more theological than scientific, and accusations of bias were made against Lemaitre based on his religious background. Other theories were advocated during this time, such as the Milne Model and the Oscillatory Universe model. Both of these theories were based on Einstein's theory of general relativity (the latter being endorsed by Einstein himself), and held that the Universe follows infinite, or indefinite, self-sustaining cycles.

After World War II, the debate came to a head between proponents of the Steady State Model (which had begun to be formalized by astronomer Fred Hoyle) and proponents of the Big Bang Theory – which was growing in popularity. Ironically, Hoyle coined the phrase "Big Bang" during a BBC Radio broadcast in March 1949, which was believed by some to be a pejorative dismissal (which Hoyle denied). Eventually, the observational evidence began to favor Big Bang over Steady State. The discovery and confirmation of the cosmic microwave background radiation in 1965 secured the Big Bang as the best theory of the origin and evolution of the Universe. From the late 60s to the 1990s, astronomers and cosmologists made an even better case for the Big Bang by resolving the theoretical problems it raised.

Watch the video: Big Bang Theory

These included papers submitted by Stephen Hawking and other physicists showed that singularities were a necessary initial condition of general relativity and a Big Bang model of cosmology. In 1981, physicist Alan Guth theorized a period of rapid cosmic expansion (aka. the "Inflation" Epoch) that resolved other theoretical problems. The 1990s also saw the rise of Dark Energy as an attempt to resolve outstanding issues in cosmology. In addition to providing an explanation as to the Universe's missing mass (along with Dark Matter, originally proposed in 1932 by Jan Oort), it also explained why the Universe is still accelerating well as offering a resolution to Einstein's Cosmological Constant.

Significant progress was made thanks to advances in telescopes, satellites, and computer simulations. These have allowed astronomers and cosmologists to see more of the Universe and gain a better understanding of its actual age. Today, cosmologists have reasonably precise and accurate measurements of many of the parameters of the Big Bang model, not to mention the age of the Universe itself. The consensus among scientists, astronomers, and cosmologists is that all of the current and past matters in the Universe came into existence at the same time, roughly 12 to 13.8 billion years ago. All matter was compacted into a tiny ball with infinite density, and intense heat called a Singularity. Also known as the Planck Epoch (or Planck Era), this was the earliest known period of the Universe.

The significant evidence which supports the Big Bang theory are:

• First of all, we are reasonably sure that the Universe had a beginning.
• Second, galaxies appear to be moving away from us at speeds proportional to their distance -- this is called "Hubble's Law," named after Edwin Hubble (1889-1953), who discovered this phenomenon in 1929. This observation supports the expansion of the Universe and suggests that the Universe was once compacted.
• Third, if the Universe was initially very hot as the Big Bang suggests, we should be able to find some remnant of this heat. In 1965, Radio astronomers Arno Penzias and Robert Wilson discovered a 2.725-degree Kelvin (-454.765-degree Fahrenheit, -270.425 degree Celsius) Cosmic Microwave Background radiation (CMB) which pervades the observable Universe. Penzias and Wilson shared in the 1978 Nobel Prize for Physics for their discovery.
• Finally, the abundance of the "light elements" Hydrogen and Helium found in the observable Universe are thought to support the Big Bang model of origins.

Watch the video: We Are Part of the Big Bang Links to an external site.

Sources

Georges Lemaitre: Life, Science, and Legacy by Rodney D. Holder (Editor), Simon Mitton (Editor).

The Day Without Yesterday: Lemaitre, Einstein, and the Birth of Modern Cosmology by John Farrell (Author).

Strauss, Bob. "Prehistoric Life During the Pleistocene Epoch." ThoughtCo, Feb. 6, 2019, thoughtco.com/the-pleistocene-epoch-1091371.