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Fossils: Microwave Radiation and Light Elements

P. J. E. Peebles

in Cosmology's Century: An Inside History of Our Modern Understanding of the Universe

This chapter focuses on the informative fossils left from a time when the universe was very different from now, dense and hot enough to produce the light elements and the sea of thermal radiation ... More

This chapter focuses on the informative fossils left from a time when the universe was very different from now, dense and hot enough to produce the light elements and the sea of thermal radiation that nearly uniformly fills space. It begins by reviewing the behavior of a sea of microwave radiation in an expanding universe. The chapter then considers how George Gamow and his colleagues, Ralph Alpher and Robert Herman, hit on the main elements of the hot big bang cosmology, including the sea of microwave radiation and the large helium abundance, but failed to capture the interest of the community. It assesses how it came to be seen that the abundance of helium is much larger than expected from production in stars but is readily understood as the result of thermonuclear reactions in the hot big bang cosmology. This attracted little attention prior to the recognition of a second fossil: the sea of microwave radiation. The chapter concludes with the steps to a persuasive measurement of the primeval abundance of deuterium and the implied baryon mass density.Less

The expanding universe and thermal relics

Ta-Pei Cheng

in Relativity, Gravitation and Cosmology: A Basic Introduction

The dynamics of a changing universe are determined by Friedmann equations, which have simple quasi-Newtonian interpretations. The universe began hot and dense (the big bang), and thereafter expanded ... More

The dynamics of a changing universe are determined by Friedmann equations, which have simple quasi-Newtonian interpretations. The universe began hot and dense (the big bang), and thereafter expanded and cooled. The early universe had undergone a series of thermal equilibriums (e.g., neutrino decoupling). The observed abundance of the light nuclear elements (helium, deuterium, etc.) match well with their being the product of the big bang nucleosynthesis. When the universe was 360,000 years old, photons decoupled, and they remain today as the primordial light having a blackbody spectrum with temperature T=2.725K. The cosmic microwave background (CMB) is not perfectly uniform. The higher multipoles contain much information about the geometry, matter/energy content of the universe, as well as the initial density perturbation out of which grew the cosmic structure we see today.Less

Pseudo-Creation of the Big Bang

Adolf Grünbaum

in Collected Works, Volume I: Scientific Rationality, the Human Condition, and 20th Century Cosmologies

Chapter finally considers the scientific credentials of the Big Bang model as compared to competing cosmological theories.

Resolving Puzzles, Problems, and Paradoxes from General Relativity

Michael Silberstein, W.M. Stuckey, and Timothy McDevitt

in Beyond the Dynamical Universe: Unifying Block Universe Physics and Time as Experienced

The main thread of chapter 3 introduces general relativity (GR), Big Bang cosmology, and closed timelike curves, showing how the ant’s-eye view leads to the puzzle of the creation of the universe, ... More

The main thread of chapter 3 introduces general relativity (GR), Big Bang cosmology, and closed timelike curves, showing how the ant’s-eye view leads to the puzzle of the creation of the universe, the horizon problem, the flatness problem, the low entropy problem, and the paradoxes of closed time-like curves. All these puzzles, problems, and paradoxes of the dynamical universe are resolved using the God’s-eye view of the adynamical block universe. Accordingly, Einstein’s equations of GR are not understood dynamically, but rather adynamically, that is, as a global self-consistency constraint between the spacetime metric and stress–energy tensor throughout the spacetime manifold. This is “spatiotemporal ontological contextuality” as applied to GR. The philosophical nuances such as the status of the block universe argument in GR and debates about the Past Hypothesis have been placed in Philosophy of Physics for Chapter 3. The associated formalism and computations are in Foundational Physics for Chapter 3.Less

How Cosmic Structure Grew

P. J. E. Peebles

in Cosmology's Century: An Inside History of Our Modern Understanding of the Universe

This chapter explores how the very evident departures from Albert Einstein's homogeneity—stars in galaxies in groups and clusters of galaxies—might have formed in an expanding universe. In the ... More

This chapter explores how the very evident departures from Albert Einstein's homogeneity—stars in galaxies in groups and clusters of galaxies—might have formed in an expanding universe. In the established cosmology, cosmic structure formed by the gravitational instability of the relativistic expanding universe. The early confusion about the physical meaning of this instability is an important part of the history. The chapter reviews these considerations, along with assessments of early scenarios of how cosmic structure might have formed. A theory of how the galaxies formed in the big bang cosmology has to provide a physically consistent picture of how cosmic structure evolved from the very different conditions in the early stages of expansion. That consideration is absent in the 1948 steady-state cosmology, so thinking about structure formation had to be different.Less

Expansion Everlasting

Steven E. Vigdor

in Signatures of the Artist: The Vital Imperfections That Make Our Universe Habitable

Chapter 5 presents experiments illuminating the cosmological evolution of the universe and its energy budget, accounting for its longevity. The observations establishing the Hubble’s Law linear ... More

Chapter 5 presents experiments illuminating the cosmological evolution of the universe and its energy budget, accounting for its longevity. The observations establishing the Hubble’s Law linear relationship between intergalactic distances and recession speeds, and their interpretation in terms of the expansion of cosmic space, are reviewed. The evidence for big bang cosmology from nucleosynthesis and the cosmic microwave background (CMB) is presented. The measurements that establish the ongoing acceleration of the cosmic expansion are reviewed: distant supernova recession speeds, tiny CMB anisotropies, baryon acoustic oscillations, and gravitational lensing. Excellent model fits to these data, assuming general relativity, cold dark matter, and a cosmological constant, lead to precise determinations of both the age of the universe and the energy budget of the universe. The cosmic history of the expansion rate and the energy budget are inferred, along with the remarkable flatness of cosmic space within the observable portion of the universe.Less

The Garland

Cheryl Colopy

in Dirty, Sacred Rivers: Confronting South Asia’s Water Crisis

Bundelkhand is a thirsty land. When I arrived there early in 2008, my skin—already parched from the dry winter air of Kathmandu and Delhi—immediately felt itchy. The cool air hit my sinuses with a ... More

Bundelkhand is a thirsty land. When I arrived there early in 2008, my skin—already parched from the dry winter air of Kathmandu and Delhi—immediately felt itchy. The cool air hit my sinuses with a prickly thud. They ached, and my eyes smarted as moisture left them. The land was an expanse of beige sand and rocks; beautiful, I thought, save for a dryness so intense it made me feel a little anxious. Most of the trees were not very tall, except for the water-thrifty “flame of the forest,” with its dark green dust-covered leaves, several inches wide. In the spring the leaves drop off and the tree’s bright orange blossoms, shaped rather like bird beaks, pop out to give the tree its other English name, “parrot tree.” Bundelkhand is sometimes called the heart of India. It sits in the center of the broad upper half of the subcontinent and its many ruins from the nation’s Mughal and Hindu past evoke the shifting suzerainty of pre-British India. Most of the ancient kingdom of Bundelkhand is now in Madhya Pradesh, also known as “MP,” or “middle province.” It’s a large landlocked state south of Delhi; Bhopal, the site of the devastating 1984 explosion at the Union Carbide pesticide plant, is its capital. The remainder of Bundelkhand is in Uttar Pradesh, “UP,” or “northern province.” Many would like to see Bundelkhand secede from both and become a separate state. With a population of fifteen million, it would be a sub-stantial state on its own. And some people believe this poor and undeveloped region will have a better chance of progress if it is independent of both MP and UP and their politics. I stayed in Jhansi, a large district in the UP portion of Bundelkhand, at the campus of a nonprofit endeavor called Development Alternatives. The group works to help people in Bundelkhand manage water and develop small industries as an alternative to agriculture. There was a simple guesthouse on the campus with hot showers, which revived me and rehydrated my dry eyes and nose in the evening. Less

Susu

Cheryl Colopy

in Dirty, Sacred Rivers: Confronting South Asia’s Water Crisis

“You’ll never get a dolphin with a digital camera,” Sushant Dey said, as we floated with the current on the Ganga. “They’re only on the surface for a second. By the time the shutter clicks, it’s ... More

“You’ll never get a dolphin with a digital camera,” Sushant Dey said, as we floated with the current on the Ganga. “They’re only on the surface for a second. By the time the shutter clicks, it’s already gone.” Early one morning in April 2007 I walked down to the bottom of a wide concrete stairway just outside Bhagalpur in the Indian state of Bihar to board an old fishing boat. Where the stairs met the river, the prow of the twenty-foot-long boat rested on the riverbank. A narrow plank, its ends positioned on the bank and the edge of the prow, allowed me to board. Sushant Dey and his brother Subhasis were taking me out to look for dolphins before the heat built up, when the dolphins might still be looking for food. Dolphins jump out of the water when they’re hunting, which they typically do early in the morning and again in the evening. The boatman tried repeatedly to start the wooden boat’s old diesel engine. Finally it coughed and caught; we chugged upriver a short way. He turned off the engine and we floated. After a few minutes, I heard a swish of water. A slick muscular body slipped back into the river before I could get a good look. A few minutes passed: another swish. I was looking in the wrong place and missed him. In spite of Sushant’s warning that my effort would be in vain, I tried again and again to catch a dolphin, pointing my camera to a likely spot on the opaque graygreen water where the animal might surface after I had missed a breach. Then I missed again. The Ganga flowed smoothly. It was about a half mile wide now, in the dry season. In the monsoon it grows to three miles wide and can be twenty-five feet higher in some places. The boatman took us to places where the dolphins were known to rest in the deep waters. I got half a dozen good glimpses as a dolphin surfaced briefly to breathe: an arc of dark gray, a shiny comma. Less

A Theological Critique of the Fine-Tuning Argument

Hans Halvorson

in Knowledge, Belief, and God: New Insights in Religious Epistemology

The fine-tuning argument attempts to use data from contemporary physics as evidence for God’s existence. In particular, contemporary physics suggests that—in absence of any divine intervention—there ... More

The fine-tuning argument attempts to use data from contemporary physics as evidence for God’s existence. In particular, contemporary physics suggests that—in absence of any divine intervention—there was little chance that a universe like ours would come into existence. The chapter points out a theological problem with the fine-tuning argument: since God can choose the laws of nature, God can set the chances that a universe like ours would come into existence. It argues, however, that if God could be expected to create a nice universe, then God could also be expected to set favourable chances for a nice universe. Therefore, the fine-tuning argument defeats itself.Less