www.UsHumans.net: Chapter 3

Chapter 3

How and when the Universe began

What was the Big Bang and what measurements led scientists to think it had occurred? How and when did stars and planets form? How and when did atoms form, including those that are inside our bodies at this very moment? What is a supernova? You’ll find answers to questions like these in The Origin and Evolution of the Universe, Edited by Ben Zuckerman and Matthew A. Malkan, which was the source for some of the following sections.

    The size of the universe is almost unimaginably large. The distance from the Earth to the Sun is about one hundred million miles. Driving at one hundred miles per hour (160 km per hour), it would take about three thousand years to travel that distance. The closest stars are twenty-five million times farther than that. The radius of the universe is about fifty billion trillion miles. The increase in scale from your height to the width of the universe is much greater than the increase in scale from an atom to a person. You are a one hundred million times larger than an atom and one hundred billion times larger than a proton, but the universe is thirty million million times larger than you. You can zoom from above the Milky Way galaxy down to a planet, then a plant, then its cells, then its molecules, and then its nuclear particles by visiting the website http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/index.html

    When you look at the night sky, you see zillions of stars. For some centuries now, there have been thousands of astronomers who have spent their lifetimes measuring such things as the position, speed, temperature, and chemical composition of millions of these stars. (Each of these things is determined by measuring the light received from each star, as described below). Since we can see so many stars, we can appreciate the magnitude of the job the astronomers have been tackling. They have accumulated a base of millions of measured facts that enable them to understand much of the origin, development, and end of stars.

    The stars of the universe are currently seen to be spreading apart from each other. This also means that they had been closer together in the past. In fact, the only way for them to be moving apart today is for them to have been close enough together in the past to have been propelled apart. This observation and its related deduction led to the development of the Big Bang picture of the origin of the universe. The Big Bang is not a theory "out of nowhere" awaiting a confirming observation but is the name given to the observations plus deductions that have already occurred.

    To help understand this process, this chapter first contains a description of the extreme heating of a block. This is followed by a discussion of the methods used to measure the position, speed, temperature, and chemical composition of stars and galaxies. We next discuss the gravitational force of a spherical mass so that we can understand how stars and planets–including the Earth–form out of debris-filled regions of space containing unconnected pieces of material. The origin of atoms, including the atoms within our own bodies, is also described in this chapter. We'll see that when the universe first formed there weren't any atoms because it was too hot for them to exist. They began to occur only after the material of the universe had cooled a bit.

Extreme heating of a block of material is the reverse of the outwardly expanding and cooling universe

To begin with, we want to think about what happens when a block of material is heated: a lump of metal is most easily pictured. As described in the previous chapter, measurements show that the atoms of the metal jiggle increasingly rapidly as the block is heated. The heated block will first glow red and, with continued heating, will glow white and then blue (the temperature of a star is determined by analyzing its color in this way). The emitted light is increasingly energetic, from red to blue. The white color results when red, green, and blue are being emitted at the same time. You can measure the temperature at which this block melts into a liquid, and after further heating, the temperature at which it vaporizes into a gas of atoms. Continue heating an atom and its nucleus will separate into its constituent protons and neutrons. With further heating, these will separate into their constituent elementary particles and light. The temperatures and energies at which these events occur have already been measured.

    The reverse process also occurs. Take the same collection of energetic light and elementary particles and continue cooling until they gather into nuclei, then gaseous atoms, and then finally form into a solid block. The heating and cooling of this block are important to our discussion of the evolution of the universe. Instead of a small block of metal, we consider the matter contained within the entire universe at the moment that it comprised a single, compact blob. At first this blob was too hot for matter to exist in any form, even elementary particles could not exist; only light existed and it had energies much greater than even that of x-rays. As the blob expanded outward and cooled, its physical state went through the same sequence as did the cooling block just considered.

Measuring the distance, speed, and chemical composition of stars

Astronomers determine the chemical composition of distant stars and galaxies by looking carefully at the colors of light received from these objects. Each chemical has been found to emit its own unique set of colors of light. For example, neon emits a red color while mercury emits a purple color. The color-spectrums of many thousands of chemicals have already been measured and tabulated. The set of colors comprising the light received from a particular star is measured by passing the light through a prism to separate it such that each color becomes completely distinguished. The chemical composition of that star is then determined by comparing its light-spectrum with the previously measured color-spectrums of various chemicals.

    Astronomers measure the distance to a nearby star by comparing its position from two different viewpoints along the Earth's one-year orbit about the Sun. During one month of the year, say January, the angle between our Sun and that star is measured. Six months later, in July, the Earth has moved to the opposite side of the Sun and the angle is again measured. Distant stars will have a larger angle than do nearby stars but their apparent position will shift by a smaller amount. Trigonometry is used to calculate the star's distance knowing the measured angles and the size of the Earth's orbit about the Sun. However, this approach allows distances to be accurately measured only for the closer stars. David Nash has made an animation of the annually shifting positions of nearby stars against the background of more distant stars. To view it select Parallax Demo at www.astronexus.com/3duniv/anim.php.

    The approach used to measure the distance to more distant stars involves a comparison of their actual and apparent brightness. You may have noticed that a truly bright lightbulb, such as a car or a street light, appears to be dimmer when you look at it from a distance. It has been found that the apparent brightness of a lightbulb decreases as the square of its distance from you. There is a type of star for which its true brightness is known (they are called Cepheid stars) so that a measurement of its apparent brightness indicates how far the star is from the Earth. (You may have seen photographers using little machines that measure brightness.)

    Astronomers measure the speed of a star by measuring the Doppler shift in the light received from that star. We have all experienced the way in which the sound of a train or car-horn changes it passes you. The sound of the horn changes from high to low pitch as the train or car moves first toward you and then away from you. This is the Doppler shift and it happens to both sound waves and light waves. You can graphically see how wavelengths change with relative motion at www.astro.uiuc.edu/projects/data/Doppler/index.html.

    The color of light is determined by its frequency, that is, by how many waves per second arrive at your eyeball. When you look at red light, fewer waves per second are passing your eye than occurs when looking at green light; blue light contains more waves per second than does green light. Imagine you are standing still while looking at a green light. The light appears green because 5,500 million-million waves per second are moving past you. The distance between successive wave crests is 550 billionths of a meter. Now imagine the same green light is being emitted from a lightbulb placed on the train. Since it is moving toward you, more waves per second will arrive at your eyeball and this makes you think the light is more blueish. In the same way, as the train's light (and sound) moves away from you, fewer waves per second will reach your eyes and the light will appear more reddish. This "Doppler effect" is also used to measure the speed of the wind and rain to produce weather reports. Police radar uses the Doppler effect to measure automobile speeds. (Just yesterday, the speed of my car was measured this way.)

Gravitational formation of stars and planets

We want to understand how planets and stars form into spherically shaped objects due to the mutually attractive force of gravity among their material pieces. For example, I am standing at a particular spot on the surface of the Earth. There is a gravitational attraction between my mass and the mass of each piece of matter throughout the Earth, including the pieces that make up the Earth's core, the pieces that make up China and Africa, and the pieces right under my feet. The total force of gravity between me and the entire Earth comes from adding together each of these attractions. It turns out that calculus shows that you get the same total force when you replace the spread-out Earth with a single point-sized mass. This single mass is located at the center of the Earth and has the same mass as the entire Earth.


                                                                 . Greg .

                                                    .            ............              .

                                       .                      .                                  .

                          .                                   .                                               .

              .                                                .                                                            .

    ..............                                               \/                                                           ..............

    . John .              Greg is pulled downward                                      . Jeff .

    ..............                                                                                                                ..............

    To see how this can be true, imagine two persons–John and Jeff–pulling equally hard on ropes tied to Greg. Both John and Jeff are two steps in front of Greg but John is three steps to the left, while Jeff is three steps to the right. We can believe that Greg will move downward, in the direction shown, because portions of John and Jeff’s pull cancel each other. If we add two more equally-strong pullers, Kari and Bryan, right next to John and Jeff, the net or equivalent pull will still be in the same downward direction as before.

    Imagine now that John and Jeff are replaced with two equally sized portions of Earth which are below its surface. Greg is still being pulled equally hard by two symmetrically paired pulls, which are coming from pieces of the Earth. For example, the attraction between Greg and a piece of the Earth that is to his right but twenty miles down into the Earth can be combined to the attractive pull from a piece that is to his left and down twenty miles. If we think of these two pieces to his right and to his left, it is like a pair of ropes pulling him equally to the right and to the left but also downward. These right and left pulls cancel each other's effect. Greg is pulled equally by each so he will not move toward either; instead, he moves along the center line between those two pulls. The two sideway pulls add up to a single "gravity rope" pulling him straight toward the Earth's center.

    We can divide the entire material of the Earth into similarly paired blocks to see that they all add up to a single pull toward the Earth's center. In the same way there are pieces right under his feet that can be compared with far away pieces that are near the opposite surface. The nearby point pulls more strongly than does the far-away point. The far-away and nearby pulls add up to a single "puller" placed right at the center. This fact was first worked out by Isaac Newton in 1685. (Whenever one of us humans figures out a new fact, it is recorded and made available to everyone, used again and again, and never unlearned or forgotten.)

    We feel our own weight because that is how strongly all of the pieces of the Earth are pulling on the matter of our own body. If you stand on a scale and weigh yourself but then have somebody pull down on your feet, the scale will read as if your weight has suddenly increased. When you stand on the scale, the Earth is pulling on your feet with the force indicated by the meter. It is an attractive force between each piece of your body and each piece of the Earth. The more pieces you have the larger will be the force and the higher the scale reading.

    The point of this discussion is that each piece of the Earth thinks it is simply being attracted toward that single central point of the Earth's sphere. The gravitational force between you and the entire volume of the Earth is identical to the gravitational force between you and a point mass, whose mass equals that of the entire Earth, placed at the position of the center of the Earth. This gravitational force actually pulls each of us toward the center of the Earth; that’s why we don’t fall off . In the same way each piece of a star feels an attraction toward the star's center. And in interstellar space, a dispersed amount of gaseous debris can become gathered together through a mutual attraction toward its center and result in the formation of a spherical star. A planet also forms in this way. Another example is that all of the mass of the universe is gravitationally attracted toward its center, and this attraction slows the rate of expansion of the universe.

The Big Bang

Astronomers have measured the motion of many galaxies. The distances and speeds of these galaxies have been determined in the manner discussed above. We observe that, right now, all of the galaxies are moving away from each other such that the universe is seen to be expanding. The galaxies are moving away from each other in the same manner that raisins spread apart within a baking and expanding loaf of raisin bread. Another analogy is that the galaxies are moving away from each other in the same manner as do small pieces of paper glued to the surface of a balloon that is expanding as it is being blown up.

    It is natural to extrapolate backwards in time and conclude that in the past, the galaxies had been closer together. Even further back in time, all the galaxies had to be clumped together in one blob. Gravity doesn't push objects away from each other; it only pulls them together. The only way for the galaxies to have been propelled apart is by having been close enough together in the past for a non gravitational force to have been involved. Measurements and calculations show that about somewhere between twelve and fourteen billion years ago the universe began to expand from a single, very hot, compact blob. This was the "Big Bang." A video clip of the Big Bang can be seen at www.tufts.edu/as/wright_center/cosmic_evolution/docs/fr_1/fr_1_mov.html on the Tufts University website. An animation is available at www.schoolscience.co.uk/flash/bang.htm. See also, http://chandra.harvard.edu/resources/animations/bigbang.mov.

    This initial blob included all of the energy and matter of the universe, including the future contents of our bodies, and even space itself. Space itself is included because it has been found that the presence of mass bends the structure of space with the result that the mass then has to move along within the bent space. To visualize bent space, consider a horizontally stretched sheet of cloth with a heavy ball placed on its surface. That heavy ball bends the surface of the sheet in the same way that mass bends the space in which it travels. For a video clip, watch A New Picture of Gravity at www.pbs.org/wgbh/nova/elegant/program_d_t.html. When all of the mass of the entire universe was clumped into one small region just before the Big Bang occurred, space itself was also contained within that same region. Newly discovered Dark Matter may also be curving spacetime, as shown at http://chandra.harvard.edu/photo/2002/igm/Rivers.mov. This aspect of space is described by Einstein's General Relativity equations that he published in 1915. This interaction of space and mass has been measured in many ways–for example, by measuring the trajectory of light waves traveling past the massive Sun. This means that the galaxies aren't moving out into empty space that has been sitting there waiting for their arrival, but that the galaxies and space are both expanding outwards together. This means that not only is the matter of the universe expanding outward from the Big Bang but that space too is expanding outward. The matter of the universe is not expanding into previously-existing, empty space that has no edge. Our universe is comprised of both space and matter. The edge of our universe is expanding outward as space and matter move there.

    It is to be stressed that the observations came first, and that the Big Bang scenario was later developed to explain the observations. The observed expansion of the universe has lead to the description called the "Big Bang." It is not the case that the observed expansion of the universe came as later evidence to support the earlier "theory of the Big Bang."

    Each group of us humans have used our imagination to guess the nature of stars and the manner in which the universe began. It is fun to hear of the cosmological explanations of various cultural groups of us humans. Luckily, we have recently been able to make more concrete measurements of these processes. We have found that the actual workings of nature are more interesting and unbelievable than the explanations our imaginations have produced.

    The gravitational attraction of all of the matter of the universe is pulling all of the matter inward as described above. It is not known yet whether there is enough mass to pull the matter back into a centrally located clump. It may be that the contents of the universe repeatedly come together into a compressed compact region that then expands again in another Big Bang. This cycle could repeat over and over. Alternatively, it may be that an uncountable number of Big Bangs occur within the material of earlier Big Bangs like many bubbles expanding from the surface of many other bubbles forming a foam of bubbles. Absolutely unique events are rare in nature; if one occurs–including a Big Bang or the development of life–than there are likely to be many more. Much research is occurring right now, trying to figure out the basic nature of the Universe. You might like to join in the effort. Most every question pales in comparison with that of the origin and fundamental nature of the universe.

How and when atoms first formed

Give a physicist pictures of things like cows, dogs, toasters, lemons, boats, and shirts, and then ask her to classify these items. She will categorize them by such physical properties as electrical resistance, thermal conductivity, and nuclear structure. If you show a person to a physicist then she will want to know about its atomic structure. The following paragraphs contain a description of the formation of the atoms and molecules of our own bodies.

    Initially, the material of the Big Bang was too hot for atoms or even nuclei to exist. Our bodies consist mainly of atoms like hydrogen, carbon, oxygen, and iron and such. At the initial instant of the Big Bang, none of these atoms yet existed in the universe because its temperature was too high. Instead of containing particles, the early universe was flooded only with energetic light. The remnants of this light are still visible today as the background cosmic radiation that has cooled to a temperature of -270 Celsius (-460 Fahrenheit) degrees. This background radiation was first observed by Arno Penzias and Robert Wilson, for which they received the 1978 Nobel Prize in physics (Wilson’s Nobel prize acceptance lecture can be read at http://nobelprize.org/physics/laureates/1978/wilson-lecture.html. As the universe expanded and cooled, elementary particles were able to form.

    When physicists use particle accelerators to measure the properties of high energy, elementary particles, they are also measuring the properties of the early, energetic universe. These particle accelerators reproduce the energy that pieces of the universe had right after the very first instant–within a tiny faction of a second–of the Big Bang. They cannot quite reproduce the energy of the very instant of the Big Bang. This means that there are no measurements to give us a detailed understanding of that very first instant. Scientists propose mathematical descriptions of that first instant and then propagate their models of the newly formed universe forward in time a few seconds so that the model’s predictions can then be compared with the measured properties of the later universe.

    The material of the Big Bang continued to expand and cool, allowing the elementary particles to gather into neutrons and protons. When its temperature became low enough, the simplest atoms could form. Scientists have already measured the temperature at which each type of atom forms. The universe then consisted of the simplest chemical elements, including only hydrogen, helium, and tiny amounts of Lithium (which is used as a medication), and Beryllium. Stars consist mostly of hydrogen. Until there was hydrogen, there were no stars. We will see that the heavier elements are formed by stellar fusion and in supernova explosions.

Star formation and stellar fusion

Stars form as clumps of hydrogen gas gravitationally coalesce. Computer experiments involving the gravitational attraction of 10,000 mass points have shown that a slight clump in the hydrogen gas will coalesce into a star in 10,000 to 100,000 years. These clumps are often accompanied by a surrounding disk of material that will similarly coalesce into planet-sized clumps. For a two-minute animation of the gravitational accumulation visit http://wapi.isu.edu/Geo_Pgt/Mod02_SolarSys/images/nebula.GIF. Star formation is now occurring inside the gaseous clouds of the Eagle Nebula, see http://antwrp.gsfc.nasa.gov/apod/ap970119.html, and in the fuzzy spot you may have seen in the constellation of Orion. Visit the Tufts University website at www.tufts.edu/as/wright_center/cosmic_evolution/docs/fr_1/fr_1_mov.html for an animated video clip of the formation of our solar system. By the way, you can travel through the Orion Nebula by downloading C. Robert O'Dell’s mpeg movie from the website www.batse.msfc.nasa.gov/colloquia/abstracts_spring05/crodell.html.

    The weight of the central clump of a newly forming star will continue to increase as its gravitational pull brings in additional mass. The inward, gravitational pull of the star material causes the size of the clump to shrink. The centrally directed compression of an initially forming star (the same thing happens for smaller clumps that form planets) continually increases the central material's density, pressure, and temperature. The huge weight of the outer material of a star crushes its central material. Most of the star's mass consists of hydrogen atoms. When the star's weight becomes great enough that pairs of hydrogen nuclei are crushed together to form a helium nucleus, a great amount of previously-stored nuclear energy is emitted in the form of light and particles: this process is called "fusion." We see this energy as the sunlight that heats our planet. When a newly formed star first begins to shine, its outwardly moving light blows away the remainders of the dust cloud from which the star formed.

    The star's fusion process releases energy in the form of light and elementary particles. This results in an outward pressure that works to slow the inward collapse caused by the gravitational pressure. The fusion process continues to intensify until its outward pressure exactly balances the inward gravitational pressure. At the moment this occurs, the outward pressure is actually holding up the entire weight of the star and the radius of the just-formed star stops changing.

    A stellar-candidate clump will not be able to fuse hydrogen if it does not contain enough mass to supply the crushing weight needed to initiate fusion. A clump will never emit light if its mass is less than 8% of the mass of our Sun. Jupiter is an example of this; its weight is too small for fusion to occur. If a candidate clump's mass is one hundred times larger than that of our Sun, it will be too unstable to form a star.

    The energy released by this fusion process is humongous. Fusing the 30 grams (0.07 pounds) of deuterium found in one cubic meter of water releases the same amount of energy as that obtained by burning 240 tons of coal. The total energy contained in the ocean's deuterium amounts to 3 x 1031 Joules and would provide us with energy for the next ten trillion years if our civilization continued to use energy at its present rate of ten trillion Joules per second.

    Today's average U.S. home uses about one thousand watts of power, which is the same thing as one thousand Joules per second. (Until this century, a cooking fire supplied the only energy that each of us used in our home; our homes today use as much energy as thousands of homes had used a few centuries ago.) With the huge amount of energy that would be available from fusion, the average home would have access to one thousand to one million times our current energy usage. If each family throughout the world began using one million times as much energy as does the average family in the U.S. today, then the energy available from the ocean's deuterium would last for ten million years.

    For the last fifty years, scientists and engineers have been trying to build a fusion machine. (For an animation of a fusion machine, visit www.visionlearning.com/library/flash_viewer.php?oid=2747.) The difficulty has been that the machine needs to develop the temperatures and pressure found within stellar interiors. The center of our Sun has a temperature of fifteen million degrees. Within a couple decades–or ten–we might succeed in developing this fusion machine. It will be an important moment in our history when we do succeed. I can imagine that soon after fusion-powered electrical generating plants are successfully engineered we will have access to one megawatt of power in each of our homes; this is one thousand times the power we are currently using. This is enough power to change one chemical element into another by changing the number of protons in its nucleus. Such an energy would greatly improve the quality of life of us humans. It is hard to imagine the full impact of having so much energy available to each of us. For example, how will our daily life change, and how will our outlook on material possessions change, if each of us has a kitchen appliance that changes lead into gold. If you place a little carbon, hydrogen, and oxygen together with a few other chemicals into a container and then apply a few megawatts for a moment, you might be able to make a green chile–or at least a tomato.

    Our Sun gets its energy from this hydrogen-fusion process. Every process on the Earth gets its energy by absorbing sunlight (very few of the Earth’s life forms instead obtain energy from deep-ocean volcanoes). Sunlight from solar fusion heats the Earth and supplies the energy to drive the weather and all of the chemical processes that occur inside plant life. About 10% of the sunlight that falls on the Earth is absorbed by plants, mostly algae. As plants absorb sunlight, they convert its light-energy into stored, chemical energy. When we eat these plants, we convert their stored energy into our own heat and motion. We power much of our civilization with the coal and gasoline that comes from the energy stored within plants and animals that died and became buried long ago.

The products of aging stars and supernova explosions form the carbon, oxygen, iron and heavier atoms that are now part of our own bodies

A star will continue to convert its hydrogen into helium until much of the hydrogen is gone. An average star, like our Sun, converts about 700 million tons of hydrogen per second. At this rate the star's material lasts for about ten billion years. This is what is meant by the length of a star's lifetime. Stars with twenty times the mass of our Sun are seen to be able to crush the hydrogen together so strongly that the star exists for only ten million years; it lives a short and very bright life.

    As a star begins to run out of hydrogen, its hydrogen fusion process will slow. The outward pressure of the fusion products is then smaller, and the star's radius will again begin to decrease. The star will become more compressed, causing it to become hotter. When the temperature is high enough, the star's helium will begin fusing into heavier atoms. After its helium has all been fused, the star’s radius again shrinks, heating the star’s interior and causing yet heavier elements to fuse into even heavier elements. After such a series of differing elements being fused, old stars come to contain concentric, spherical layers of differing chemicals. (For a picture, see http://wapi.isu.edu/Geo_Pgt/Mod02_SolarSys/images/onionstar.GIF.) This atom-building process continues to result in increasingly heavier atoms until iron is created. The centers of these stars contain a lot of iron. Iron is the heaviest atom built by the fusion process occurring inside stars. Elements heavier than iron do not release energy when fused together; instead, they must absorb energy to be fused. Sufficient energy for this occurs only during supernova explosions.

    For smaller stars, like our Sun, the last stage of their lives results in an expansion. The usual lifetime of stars like our Sun is about ten billion years. Since our Sun is currently about five billion years old, it has another five billion years before its life ends in such an expansion. At that time, the radius of our Sun will increase outward beyond the Earth. We will then have to move somewhere else. Try to imagine how we might go about re-establishing the Earth’s life forms on another planet.

    For heavier stars the compression process wins, and the star becomes squeezed until its protons and electrons merge to form neutrons plus escaping light. The material of this star, much of which had recently been iron, is then nothing but neutrons. For this reason, it is called a neutron star. The star then has the density of a nucleus. A spoonful of this star would weigh millions of tons. As that final compression begins, the outer layers of these massive stars are ejected in a supernova explosion. It is only within these explosions that the elements heavier than iron are formed. These heavier elements include copper, lead, gold, and uranium, and such. You might visit the NASA websites www.nasa.gov/vision/universe/watchtheskies/grb_supernova.html and http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html to see animations of supernova explosions.

    The center of the Earth is nothing but a large piece of iron formed through stellar fusion. Except for hydrogen and helium, the heavier chemicals now found within the Earth–and within you, too–were created by stellar fusion or during stellar explosions. Supernova explosions eject these chemicals into space. The ejected material forms “dust clouds” in space, some of which later formed into the Sun, Earth, and us. Our Sun is a third generation star, meaning that some of its material has gone through two previous cycles of stellar formation and death.

    It is often said that we are made of the material of stars and supernova explosions. We can also claim to have been at the Big Bang because all of the universe was there, including the energy that later became the hydrogen atoms and other chemicals within our bodies. We were sort of there but spread out into many packets of energy. Some of our protons may have been temporarily held in a series of differing atoms within differing stars and dust clouds.

    While on the Earth, the atoms of our bodies have gone through similar cycles. The Earth’s carbon atoms have been on the planet since its formation, and they will remain there until the expanding, dying Sun engulfs and disintegrates the Earth. Each carbon atom now sitting inside your body has been within a series of living creatures, air parcels, and rocks during the last 4.5 billion years. It may have been eaten by one animal who in turn was eaten by another who exhaled it. After sitting on the ground for a million years it may have been taken up by a plant only to be eaten by another animal. It is within you only temporarily.

    When astronomers observed the spectra of the supernova cataloged as 1987a, they monitored the heavy element synthesis and observed the creation of the neutron star. This supernova converted a huge amount of mass, equal to about one-tenth of the mass of our Sun, directly to energy. This is described by Einstein's famous equation E=mc2, and is about the energy produced in one second by all of the observable universe. (A typical supernova explosion releases as much energy as five trillion trillion atomic bombs.) These are huge numbers. (Visit www.csun.edu/~gsl05670/619%20class%20projects/audio_files/einstein_speaks.mp3 to hear Einstein say his equation.)

    The ejected material flies outward into space, dispersing for some thousands of years. These expanding shells of gas can be seen in small hobby-sized telescopes. An example can be seen near the star Vega within in the constellation Lyra. This is the Ring Nebula, which is cataloged as Messier object 57. You can see a picture of it at the NASA website http://antwrp.gsfc.nasa.gov/apod/ap040704.html. About 10,000 years ago its star exploded, sending a spherical shell of material outward. It is about 25,000 trillion miles away and 12 trillion miles in diameter.

    Scientists have measured the percentage of each type of atom existing today. About 90% of the matter of the universe is found to consist of hydrogen. Scientists also start with the high-temperature, compressed material of the Big Bang, and then apply the equations for the energies and transition temperatures to calculate the percentage of each kind of atom that would develop from that cooling and expanding blob. They combine these figures with calculations of the amounts of each chemical that would be produced in stars and in supernova explosions. This allows them to start with the material of the Big Bang and then calculate the percentage of each type of atom that should be seen today. Since the results of this calculation matches the measured percentages, we know that we have a fairly complete picture of the way the universe is developing.

    The most important atoms of life are those that are also the most commonly occurring. It might be expected that life forms would develop from the most common types of atoms rather than from rare atoms. This argues that most of the universe's life forms, if others exists, are likely to consist of the most common chemicals. In addition, heavy elements are also needed for life. Astronomers observe that older, more metal-rich stars are found toward the centers of galaxies. Life might form on star-orbiting planets but only if those stars last long enough for this to occur. As mentioned above, medium-sized stars last about ten billion years while the brighter and larger stars last only ten million years. This means that the oldest life forms–and civilizations–may be found around the medium-sized stars that are located near the center of the galaxy. It would take a radio signal 50,000 years to reach them from here. For information about NASA’s search for planetary systems outside our own solar system, visit http://planetquest.jpl.nasa.gov/gallery/gallery_index.html.

    How long did it take for life to form on the Earth? The oldest geologic deposits of organically enriched carbon-12 sediments are known to have occurred within a few tens of millions of years after the formation of the Earth. The formation of life will occur more quickly on planets that have liquids because chemical mixing-rates are greatly increased within liquids. Heat from the radioactive decay of underground materials may result in liquid water occurring underneath the frozen surfaces of Jupiter’s moons Europa, Callisto, and Ganymede. Recently, the Huygens space probe landed on Saturn’s moon Titan and found liquid methane at a temperature of -290 degrees Fahrenheit (-190 Celsius). For more information about Huygens, visit the European Space Agency website at www.esa.int/SPECIALS/Cassini-Huygens. Will we find life on any of these moons or on other planets?

Our solar system

An exploding star sends its material outward. Debris from several stellar explosions can mix in one region of space and begin to coalesce gravitationally into a new star. This coalescence of debris is the way that our Sun and solar system formed. Computer simulations show that it takes from 100,000 to ten million years for gravity to form the large gaseous planets out of the disk of that proto-star. The rocky planets instead form through the accumulation of dust into larger and larger bodies.

    The spectrum of light we receive from our Sun tells us that 99% of its material consists of hydrogen and helium, but the planets of our solar system are composed of a larger proportion of heavier elements. The four gaseous planets–Jupiter, Saturn, Uranus, and Neptune–have been found to contain much less hydrogen and helium than does the Sun. The inner, terrestrial planets are rocky and are composed of little hydrogen and helium.

    Our solar system also consists of the asteroid belt, which is located between the Earth and Mars, and comets that move in large orbits around the Sun. The comets are remnants of the initial material that formed into our solar system. Scientists measure the chemical composition of comets to determine the chemical composition of the early solar system. This means that comets are like little “chemical time-packets” in that they are a record of the past. An iron meteorite is a remnant of the interior of a star.


The point of this chapter has been that the measurements of the positions and speeds of stars reveal that the universe –that is, its space and matter–is expanding outward. The material of the universe does not produce outwardly-directed expansive forces unless the material is contained within a tiny volume. The observed, ongoing expansion of the universe would not be occurring today if it hadn't been the case that the initial universe used to be contained within a volume that was small enough to allow the expansive forces to have been generated. This tells us that the universe has been expanding from an initial, central clump. This observation has been stated as the "Big Bang" scenario. Visit www.pbs.org/wgbh/nova/origins for a video series concerning the sequence of events from the Big Bang to biochemistry.

    There are one-hundred types of atoms; each forms a portion of all of the matter of the universe. These portions have been measured and found to agree with the portions expected from mathematical models of the expanding and cooling material of the Big Bang. This agreement shows that we understand the overall process of the creation and expansion of the universe. If the two did not agree then we would know that our model of the universe was still missing pieces of the actual process.

    Another point here is that our bodies consist of chemicals that did not exist at the moment of the Big Bang; instead, these chemicals were formed later within stars and supernova explosions. We have found that we are tiny, tiny constituents of the universe. Even the Earth and the Sun are found to be minuscule objects when compared with the entire universe. Our Sun is just one of the zillions of stars. The processes in which stars form, age, and die are well understood because millions of stars have been observed and studied.



1. How much has the Sun changed during your lifetime?

2. How much have the shapes of the constellation figures changed during your lifetime?

3. Is there life outside the Earth right now?

4. Will humans build cities on other planets?

5. Can you tell that the temperature of your camp fire is increasing as it first gets going? How does its color change? How is this color and temperature sequence related to a star's color and temperature?

6. Can you use trigonometry to determine your distance from a tree or a building of known height?

7. Find two trees separated by about one-hundred footsteps. Walk from the first tree toward the other and then go ten steps beyond the second tree. Now turn right by 90 degrees and as you walk ten more steps, make a note of the change in angle between your direction of motion and the positions of the two trees. The closer tree appears to move relative to the more-distant tree. This is called parallax and is the way astronomers measure the distance to nearby stars. Instead of moving ten steps, the Earth moves a distance equivalent to the diameter of its orbit as it circles halfway around the Sun.

8. Describe a machine that uses gravity.

9. When will we harness fusion power? If you had available for your own use as much energy as is currently used by all the people of the entire planet, what would you do with it? How would your life be different?

10. What does it mean that you have breathed the same oxygen atom that Julius Caesar had earlier breathed? During your lifetime, what percentage of the Earth's atmosphere will you have breathed? Are the oxygen atoms of our atmosphere disappearing? Are new ones appearing? Were any of the carbon atoms in your body today part of Caesar’s body in the past?

11. Did the copper atoms within everyone's body come from the same star or from many different stars?

12. The average atom in your body remains there for just a couple of years before being replaced by another. How can we still be the same person if each of our atoms are being replaced?

13. Will all of the stars eventually burn out? What happens then? You might like to read Heat death and the Phoenix: entropy, order, and the future of man, Norman H. Dolloff, 1975, Exposition Press, Hicksville, NY

14. Has there been a series of Big Bangs and Big Crushes within our universe? Some astronomers use the term Big Gnab for a Big Crush because it is the reverse process of a Big Bang.

Primary source for the chapter

The Origin and Evolution of the Universe, Edited by Ben Zuckerman and Matthew A. Malkan, 1996, Jones and Bartlett Publishers Sudbury, Mass.

Suggestions for further reading

     The Moment of Creation by James S. Trefil, 1983, Charles Scribner's Sons New York.

     The latest details concerning the Big Bang, and its first instant, are described in the following two books.

     The Whole Shebang, A State-of-the-Universe Report, Timothy Ferris, 1998, Touchstone Books, Simon & Schuster, New York.

     The Inflationary Universe by Alan H Guth, 1997, Addison-Wesley Publishing Company, New York.

     Universe in Focus by Stuart Clark, 1997, Barnes and Noble Books, New York.

     The Planetary System, David Morrison and Tobias Owen, 2003, Addison-Wesley Publishing Company, New York.

     Ancient Astronomers, Anthony F. Aveni, 1993, St Remi Press and Smithsonian Institution, edited by Jeremy Sabloff.



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