Overview of Contemporary Astronomy
The Second Evening


Quoting from Alan Lightman's, "A Modern Day Yankee In A 
Connecticut Court and other essays on Science".
Conversations with Papa Joe

The Second Evening
  Read:   Conversations_with_Papa_Joe_II.pdf
  Listen: Conversations_with_Papa_Joe_II.mp3

  Key Words and Phrases:
    Expansion of the Universe
    Big Bang - Tests of the big bang theory
    Earth younger than the universe
    Radioactivity - Radio dating
    Multiple independent measurements

HOW DO WE DETERMIN AGE (Bones, Earth, Solar System) Wikipedia -- Radiometric Dating https://en.wikipedia.org/wiki/Radiometric_dating https://en.wikipedia.org/wiki/Radiocarbon_dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay. The use of radiometric dating was first published in 1907 by Bertram Boltwood and is now the principal source of information about the absolute age of rocks and other geological features, including the age of fossilized life forms or the age of the Earth itself, and can also be used to date a wide range of natural and man-made materials. Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geologic time scale. Among the best-known techniques are radiocarbon dating, potassium-argon dating and uranium-lead dating. By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts. Wikipedia -- Chondrite https://en.wikipedia.org/wiki/Chondrite Chondrites were formed by the accretion of particles of dust and grit present in the primitive Solar System which gave rise to asteroids over 4.54 billion years ago. These asteroid parent bodies of chondrites are (or were) small to medium-sized asteroids that were never part of any body large enough to undergo melting and planetary differentiation. Dating using 206Pb/204Pb gives an estimated age of 4,566.6 +/- 1.0 Ma, matching ages for other chronometers. Another indication of their age is the fact that the abundance of non-volatile elements in chondrites is similar to that found in the atmosphere of the Sun and other stars in our galaxy. Although chondritic asteroids never became hot enough to melt based upon internal temperatures, many of them reached high enough temperatures that they experienced significant thermal metamorphism in their interiors. The source of the heat was most likely energy coming from the decay of short-lived radioisotopes (half-lives less than a few million years) that were present in the newly formed solar system, especially 26Al and 60Fe, although heating may have been caused by impacts onto the asteroids as well. Many chondritic asteroids also contained significant amounts of water, possibly due to the accretion of ice along with rocky material.

BIG BANG COSMOLOGY Tests of Big Bang Cosmology https://map.gsfc.nasa.gov/universe/bb_tests.html https://map.gsfc.nasa.gov/universe/bb_tests_exp.html The Big Bang Model is supported by a number of important observations, each of which are described in more detail on separate pages: The expansion of the universe Edwin Hubble's 1929 observation that galaxies were generally receding from us provided the first clue that the Big Bang theory might be right. The abundance of the light elements H, He, Li The Big Bang theory predicts that these light elements should have been fused from protons and neutrons in the first few minutes after the Big Bang. The cosmic microwave background (CMB) radiation The early universe should have been very hot. The cosmic microwave background radiation is the remnant heat leftover from the Big Bang. These three measurable signatures strongly support the notion that the universe evolved from a dense, nearly featureless hot gas, just as the Big Bang model predicts. _____________________ The Big Bang model was a natural outcome of Einstein's General Relativity as applied to a homogeneous universe. However, in 1917, the idea that the universe was expanding was thought to be absurd. So Einstein invented the cosmological constant as a term in his General Relativity theory that allowed for a static universe. In 1929, Edwin Hubble announced that his observations of galaxies outside our own Milky Way showed that they were systematically moving away from us with a speed that was proportional to their distance from us. The more distant the galaxy, the faster it was receding from us. The universe was expanding after all, just as General Relativity originally predicted! Hubble observed that the light from a given galaxy was shifted further toward the red end of the light spectrum the further that galaxy was from our galaxy. The specific form of Hubble's expansion law is important: the speed of recession is proportional to distance. Hubble expressed this idea in an equation - distance/time per megaparsec. A megaparsec is a really big distance (3.26 million light-years). The expanding raisin bread model illustrates why this proportion law is important. If every portion of the bread expands by the same amount in a given interval of time, then the raisins would recede from each other with exactly a Hubble type expansion law. In a given time interval, a nearby raisin would move relatively little, but a distant raisin would move relatively farther - and the same behavior would be seen from any raisin in the loaf. In other words, the Hubble law is just what one would expect for a homogeneous expanding universe, as predicted by the Big Bang theory. Moreover no galaxy, occupies a special place in this universe. Every observer appears to be at the center of the expansion. Wikipedia -- Spectral line https://en.wikipedia.org/wiki/Spectral_line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identify atoms and molecules. These "fingerprints" can be compared to the previously collected "fingerprints" of atoms and molecules, and are thus used to identify the atomic and molecular components of stars and planets, which would otherwise be impossible. Spectroscopy 101 - Types of Spectra and Spectroscopy https://webbtelescope.org/contents/articles/spectroscopy-101--types-of-spectra-and-spectroscopy The basic premise of spectroscopy is that different materials emit and interact with different wavelengths (colors) of light in different ways, depending on properties like temperature and composition. We can therefore use spectra-the detailed patterns of colors-to figure out things like exactly how hot something is and exactly what elements and compounds it is made of, without ever sampling it directly. Wikipedia -- Doppler Effect (Redshift) https://en.wikipedia.org/wiki/Doppler_effect https://en.wikipedia.org/wiki/Redshift In physics, redshift is a phenomenon where electromagnetic radiation (such as light) from an object undergoes an increase in wavelength. Whether or not the radiation is visible, "redshift" means an increase in wavelength, equivalent to a decrease in wave frequency and photon energy, in accordance with, respectively, the wave and quantum theories of light. There are three main causes of redshifts in astronomy and cosmology: 1. Objects move apart (or closer together) in space. This is an example of the Doppler effect. 2. Space itself is expanding, causing objects to become separated without changing their positions in space. This is known as cosmological redshift. All sufficiently distant light sources (generally more than a few million light-years away) show redshift corresponding to the rate of increase in their distance from Earth, known as Hubble's law. 3. Gravitational redshift is a relativistic effect observed due to strong gravitational fields, which distort spacetime and exert a force on light and other particles. Knowledge of redshifts and blueshifts has been used to develop several terrestrial technologies such as Doppler radar and radar guns. Redshifts are also seen in the spectroscopic observations of astronomical objects. Its value is represented by the letter z.

BOOK RECOMMENDATION: The Age of the Earth by G. Brent Dalrymple https://www.amazon.com/Age-Earth-G-Brent-Dalrymple/dp/0804723311 This is a definitive, masterly history and synthesis of all that has been said (by theologians and scientists) and is known (to science) about the question, How old is the Earth? It explains in a simple and straightforward way the evidence and logic that have led scientists to conclude that the Earth and the other parts of the Solar System are not several thousand years old, as some today would have it, but four and one-half billion years old. It is a fascinating story, but not so simple as single measurement. Our universe is a large, old, and complicated place. Earth and other bodies have endured a long and sometimes violent history, the events of which have frequently obscured the record that we seek to decipher. Although in detail the journey into Earth's past requires considerable scientific skill, knowledge, and imagination, the story is not so complicated that it cannot be explained to someone who wants to know and understand the basic evidence. This book, then, has been written for people with some modest background in science, but at a level that will allow the material to be useful and accessible to those without a deep knowledge of geology or physics or mathematics. The First Three Minutes: A Modern View of the Origin of the Universe by Steven Weinberg https://www.amazon.com/First-Three-Minutes-Modern-Universe/dp/0465024378 "The book is the first I have seen to put the details, both historical and conceptual, of the origin of the Universe within the grasp of the general reader... As such, it is a tremendous service to us all." ~Isaac Asimov "His book is science writing at its best." ~Martin Gardner, New York Review of Books "Weinberg builds such a convincing case...that one comes away from his book feeling not only that the idea of an original cosmic explosion is not crazy but that any other theory appears scientifically irrational." ~Jeremy Bernstein, New Yorker "A most remarkable achievement...presented with clarity...and great scientific accuracy." ~T.D. Lee, Nobel Laureate in Physics WEBSITE RECOMMENDATION: Astronomy Picture of the Day https://apod.nasa.gov/apod/astropix.html Astronomy Picture of the Day (APOD) is originated, written, coordinated, and edited since 1995 by Robert Nemiroff and Jerry Bonnell. The APOD archive contains the largest collection of annotated astronomical images on the internet. APOD in general and the APOD site served from NASA specifically places links solely on information content and does not endorse any commercial product nor guarantee claims or sales made on any linked pages. In real life, Bob and Jerry are two professional astronomers who spend most of their time researching the universe. Bob is a professor at Michigan Technological University in Houghton, Michigan, USA, while Jerry is a scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland USA. They are two married, mild and lazy guys who might appear relatively normal to an unsuspecting guest. Together, they have found new and unusual ways of annoying people such as staging astronomical debates. Most people are surprised to learn that they have developed the perfect random number generator. sam.wormley@gmail.com