Part 22: The evidence for the Big Bang and cosmic inflation, as well as general cosmological concepts.
These short videos were created in August 2007 by Dr. Christopher D. Impey, Professor of Astronomy at the University of Arizona, for his students. They cover a broad range of terms, concepts, and princples in astronomy and astrobiology. Dr. Impey is a University Distinguished Professor and Deputy Head of the Astonomy Department. All videos are intended solely for educational purposes and are licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. The full list of collections follows below:
01. Fundamentals of Science and Astronomy
02. Ancient Astronomy and Celestial Phenomena
03. Concepts and History of Astronomy and Physics
04. Chemistry and Physics
05. Quantum Theory and Radiation
06. Optics and Quantum Theory
07. Geology and Physics
08. Solar Neighborhood and Space Exploration
09. Outer Planets and Planetary Atmospheres
10. The Solar System
11. Interplanetary Bodies
12. Formation and Nature of Planetary Systems
13. Particle Physics and the Sun
14. Stars 1
15. Stars 2
16. Stars 3
17. Galactic Mass Distribtuion and Galaxy Structure
19. Galaxies 2
20. Galaxy Interaction and Motion
21. Deep Space and High-Energy Phenomena
22. The Big Bang, Inflation, and General Cosmology
23. The Big Bang, Inflation, and General Cosmology 2
24. Chemistry and Context for Life
25. Early Earth and Life Processes
26. Life on Earth
27. Life in the Universe
28. Interstellar Travel, SETI, and the Rarity of Life
29. Prospects of Nonhuman Intelligences
Transcript: Cosmology is the study of the universe, its history, and everything in it. It comes from the Greek root of the word cosmos for order and harmony which reflected the Greek belief that the universe was a harmonious entity where everything worked in concert to produce a beautiful whole. The scientific method is challenged by the study of the entire universe. We only have one object to study. We cannot travel any distance in it, and we are trapped in time and space. In a sense it’s amazing that creatures as small and frail as humans can comprehend the cosmos at all, and the study of cosmology is one of the greatest human achievements.
Transcript: The creation of the universe is described in the oldest writings that come down to us from cultures like the Babylonian, the Egyptian, the Greek, the Chinese, and the Indian. In Indian legend the universe is a giant egg which is brought forth from the void by the creator Prajapati. In Tahitian legend Ta'aroa creates the universe out of the immensity of pure space and forms the rocky substance of the Earth. In the Norse legend there’s nothing at all with frost to the north and fire to the south until the heat melts the frost, and from the liquid drops the giant Ymir grows who creates the world. These are examples of mythological cosmology, the description of the universe that ties cosmology to human cultures and to the stories that people have always told about the night sky.
Transcript: The first scientific thinking about the universe dates back to the Greek philosophers of the fifth and sixth centuries B.C. They applied logic, they formed hypothesis, and they tried to test the hypothesis although this was a time two thousand years before the invention of the telescope, and there was a limit to what they could do with the naked eye. However, they made enormous strides. Aristarchus, for example, used logic and geometry to deduce a Sun-centered universe two thousand years before Copernicus, and in fact the biggest Greek universes that were calculated were many, many millions of miles across. They even came up with the idea of infinite space applying the mathematics of Euclid and realized the implications of an infinite universe. As Plato’s colleague Archytas put it, imagine you are at the edge of the universe, and you hurl a swift spear. Do you imagine that this spear hits something, finds a barrier, and bounces back, or should it travel forever? And if it should travel forever, what lies beyond the edge? The Greeks were thinking about the size of the universe, the implications of an infinite universe, and what an edge might mean two thousand years before scientists would address the problem with observations.
Transcript: Newton’s theory of gravity set the stage for physical cosmology, a study of the universe based on the idea of laws of physics that applied everywhere throughout space, and it gave rise to the idea of a clockwork universe, although we now know the universe is so complex that it is far from deterministic. Newton imagined the universe as infinite and filled with stars in random motion. This is essentially a static universe. Newton’s rational was as follows. If the universe had an edge, then the stars near the edge would feel a greater force inside than outside where there are no stars, and so the stars would move inwards. Thus a universe with an edge would be forced to be in motion and collapse. The only way around this is to have an infinite universe filled with stars. Of course, an infinite universe has infinite gravity. This was a problem Newton couldn’t address within his theory, so Newtonian cosmology had problems that were known even to Newton at the time.
Solution to Olber's Paradox
Transcript: The solution to Olber’s paradox is subtle and involves three different concepts. The first is the redshift of light that occurs due to the expansion of the universe. This means that the light from distant objects is redshifted or reduced in energy, so as we move further out from the Earth or the Milky Way the light from successively larger and larger distances is reduced relative to the inverse square law of light. So the light does not pile up infinitely. Second, there is a distance beyond which we cannot see in the universe which corresponds to the distance that light can travel in the age of the universe. Third, the universe is so big that light has not had time to utterly fill the space between galaxies. The sum of all these factors leads to the fact that Olber’s paradox is not true, and the night sky is indeed dark.
Einstein and Cosmology
Transcript: The modern idea of cosmology is based on Einstein’s theory of General Relativity. Einstein realized in a thought experiment that acceleration due to gravity could not be distinguished from acceleration due to any other force. He also knew that mass and energy were equivalent according to E = mc2. The two ideas combine to lead to the fact that mass can bend light. In Newton’s idea of an infinite universe space and time flow smoothly, and never bend, and are linear at all distances from the Earth. In Einstein’s theory they are replaced by the idea of space-time: space that is supple according to gravity and the distribution of matter and time that is also supple in the situation of strong gravity. The equations of General Relativity apply to the intense gravity of a black hole, but they also apply to the universe as a whole.