The Big Bang Theory: How the Universe Began

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1 The Big Bang Theory: How the Universe Began The Big Bang Theory is the most widely accepted theory of how the universe began. It states that the universe started when all matter was contained in a small, extremely dense area, which then expanded rapidly in an event, like a big bang. Astronomers think that this event occurred 13.7 billion years ago, according to their most recent measurements and observations. If we go back in time to 13.7 billion years ago, what happened? What happened after the Big Bang? How did the universe get to its present state? First, scientists theorize that all matter in the universe was condensed into a highly dense, hot, point, called a singularity. This extremely dense, hot, and pressure-filled singularity was expanding and cooling in cycles. Suddenly, a change of state occurred, and the universe was expanding exponentially the Big Bang happened! All matter began to expand, with particles moving quickly and randomly away from each other in a phenomenon called cosmic inflation. All of this happened within less than 1 second. Still within that first second of history, subatomic particles were formed (for example leptons and quarks), which was followed by reactions that created atomic particles (for example, protons, neutrons and electrons). Later, neutrons and protons combined to form the universe s helium and deuterium. The remaining majority of protons remained uncombined as hydrogen nuclei. After about 379,000 years, electrons and nuclei combined into atoms. This process resulted in radiation being given off, which scientists call cosmic microwave background radiation. Over time, more combinations of electrons and nuclei occurred, which gives our universe its elements. Still the vast majority of atoms formed are hydrogen. Finally, over many thousands and millions of years, the slightly denser regions of matter in the universe attract more matter by the force of gravity. These dense regions become even more dense, forming gas clouds, stars, galaxies and other astronomical features we observe today. Surrounding individual stars, such as our sun, matter accretes, or gathers together, as it revolves around the star. These accretions of matter form our planets. Our own planet Earth appears on the scene about 4.54 billion years ago. A team of scientists, working at different times over the last century, has come up with the observations and data that support the Big Bang Theory. Indeed this theory is the best explanation that accounts for the phenomena we have observed and measured. The evidence for the Big Bang is often called The Four Pillars of the Big Bang. The first piece of evidence came from observations of redshift of galaxies made by Edwin Hubble in Redshift is the term for the accelerating movement of light away from a certain position. It is experienced by us as the Doppler Effect of sound, which changes in frequency when, for example, a large train moves by us in a parked car. As the train approaches, we hear the sound increase in volume (it has shorter wavelengths relative to the observer), with the volume receding from us as the train moves away down the 2012 abcteach.com

2 track (it has longer wavelengths relative to the observer as it moves away). Similarly, galaxies in the universe have been observed to give off light that is shifted toward the red end of the spectrum, where wavelengths are longer. Like the train streaming sound in flatter waves behind it, galaxies are moving away from Earth, streaming flatter waves of light behind them, relative to where we are positioned as observers on Earth. This is called redshift. It led Hubble to propose that galaxies are moving away from Earth at steady, measurable rates. This validates the Big Bang, which originally set all matter in motion. With no force to stop them, the galaxies are still on the move, and in a state of expansion. The second piece of evidence comes from detailed measurements of cosmic microwave background radiation, which corresponds to predicted values for the epoch in our universe s history when subatomic and atomic particles were formed. These measurements, started in 1964, with more made in the 1980 s and 2003, confirm the background radiation we predict from these particles being made after the Big Bang. Thirdly, scientists measure the same proportions of hydrogen, helium and deuterium present in space that they would expect from Big Bang Theory. Using mathematical models, it is possible to calculate the ratios of the light elements, such as deuterium, helium-3, helium-4, and lithium-7, to ordinary hydrogen. The measured abundance of these light elements matches fairly consistently with what Big Bang theory predicts mathematically. Finally, astronomers see the large scale distribution and apparent evolution of galaxies predicted by the Big Bang. Detailed observations of the shape and distribution of galaxies, through telescopes and satellites, shows us that galaxies change over time. Distant, older galaxies are observed as being different from closer, younger galaxies. For example, older galaxies may contain certain populations of stars, globular clusters, and other features. Scientists affirm, through their measurements and observations, that the Big Bang is the best theory currently available to explain the beginning and evolution of our universe. Previous to the past 100 years of thinking and research, many astronomers and philosophers believed that the universe was created and existed in a static condition. Similar to ancient views, which held that the Earth was flat, we now have an added dimension to understanding that we live in an expanding, changing universe.

3 Definitions: Write a definition for each of the terms below. You may use this article and other sources to obtain your answer. 1. Big Bang Theory 2. singularity 3. cosmic inflation 4. subatomic particles 5. atomic particles 6. cosmic microwave background radiation 7. galaxy evolution 8. redshift 9. light elements 10. globular cluster:

4 Answer the following questions in complete sentences. 1. What are the four pillars of the Big Bang? 2. Why do we observe light from stars as having a redshift? 3. How does redshift provide more support for the Big Bang theory? 4. Why does our universe have cosmic microwave background radiation? 5. How do observational differences about galaxies close to us versus those farther from us support the Big Bang further?

5 Teacher s Key to definitions 1. Big Bang Model: Current theory of how the universe began which states that all matter was once in a hot, dense, pressure-filled region, which expanded rapidly in an event like a big bang. 2. singularity: A theorized state of matter where it is combined into an extremely hot, dense region of space. Mathematical models of general relativity and quantum mechanics cannot be used to predict the behavior of particles in a singularity, such as before the Big Bang, or in a black hole. 3. cosmic inflation: Extremely rapid, exponential expansion of the universe immediately following the Big Bang. This inflationary epoch, where particles were moving rapidly away from each other, comprised the first microseconds of the universe. It is followed by an epoch of much slower expansion. 4. subatomic particles: Smaller particles composing nucleons and atoms, such as quarks, leptons, or gluons. 5. atomic particles: Larger particles which make up elements, such as protons, neutrons, and electrons. 6. cosmic microwave background radiation: A thermal radiation, detectable using instruments on Earth and by satellite, which fills our universe. This radiation is theorized to originate from the combination of particles to produce atoms, which gave off some radiation detectable in microwave wavelengths. 7. galaxy evolution: A term used to refer to the change of galaxies over time. This evolution results in observable differences, showing us that the universe is changing. 8. redshift: A phenomenon that happens when light seen from an object that is moving away is increased in wavelength toward the red end of the spectrum. This phenomenon is similar to the Doppler Effect for sound. 9. light elements: Elements formed at the beginning of the universe s evolution, like hydrogen, deuterium, and helium. These elements have small nuclei with few particles, so they are lighter in atomic weight. 10. globular cluster: a spherical group of stars that orbits a galaxy s core similarly to a satellite.

6 Teacher s Key to Questions (1) The four pillars of the Big Bang are observance of redshift in light from space, cosmic microwave background radiation, measurements of abundance of light(er) elements, and observation of galaxy evolution. (2) Light from stars is observed to have a redshift because the stars and thus the light they emit, are moving away from us. Similar to the Doppler Effect for sound, particles moving in waves away from an observer will have longer wavelengths. For light, the longer wavelengths show up on the red part of the spectrum, hence the term redshift. (3) Redshift provides more support for the Big Bang Theory because it affirms that stars and galaxies are moving away from Earth. This supports a theory of an expanding universe, set in motion by an original event, the big bang. (4) Cosmic microwave background radiation derives from the epoch in our universe s history when protons and electrons were coming together to form atoms. This process resulted in some thermal radiation being given off, which shows up for our measurement tools in the microwave part of the spectrum. (5) Observational differences about galaxies supports the Big Bang because we have observed differences in older galaxies farther away from Earth than for younger ones closer to Earth. Astronomers infer the age of galaxies from the presence of certain types of stars and other features.