Earth and the Solar System The Formation of the Solar System Write a number beside each picture to rank each from the oldest (1) to the youngest (4).
The universe includes everything that exists: all matter, energy, space, and time. But how did the universe come into existence? People in every culture throughout history have attempted to answer this question. Scientists are no exception. How do you think scientists attempt to study and answer questions about the universe s beginnings? What kinds of theories do you think scientists have proposed? What kinds of evidence might support these theories? Has the universe always existed or did it have a beginning? The Big Bang Theory It may be difficult to imagine the origins of the universe. After all, if the universe came into existence, it must have not existed once. Where did the universe and its components come from? Though scientists do not know the answer to the latter question, they have found solid evidence that the universe had a beginning. The big bang theory is the most widely accepted theory to explain the origin of the universe. According to this theory, the universe began as a single, tiny point smaller than an atom called a singularity. This singularity was infinitely hot and infinitely dense it contained all the matter and energy currently in the universe. The big bang occurred in the moment when all of this matter and energy suddenly expanded out from this singularity. The universe has been expanding ever since. The laws of physics, including gravity, came into effect during the big bang. In the first seconds after the big bang, gravity caused matter to come together to form the particles from which all components in the universe are made: protons, neutrons, and electrons. gravity: the force that attracts one object with mass to another As the universe cooled after the big bang, atoms of more complex elements formed. A nitrogen atom contains seven protons (+), seven electrons ( ), and seven neutrons (black). During these seconds, the universe was too hot for these particles to form atoms. Also, the clouds of subatomic particles protons, neutrons, and electrons were so dense that no light could shine through them. A few seconds after the big bang, the universe had cooled enough for protons and neutrons to start forming simple nuclei. nucleus: the center of an atom 1
After about 300,000 years, electrons joined with nuclei to form atoms of the simplest elements. Hydrogen, which contains only one proton per atom, was the first element to form. Helium, which contains two protons per atom, formed next. To this day, hydrogen and helium remain the most common elements in the universe. As atoms continued to form, the dense cloud of subatomic particles began to clear. For the first time, light could shine through the universe. In the 1920s, a scientist named Edwin Hubble discovered evidence that the universe was expanding by analyzing light from distant stars. Scientists worked to try to explain these observations. The big bang theory was not always the accepted theory of how the universe formed. Another theory proposed by Fred Hoyle, Thomas Gold, and Hermann Bondi was the steady state theory. The steady state theory hypothesized that although the universe was expanding, it was not changing because new matter was constantly being made, keeping the density of matter in the universe the same. Scientists worked to test both theories, and their discoveries have continued to support the big bang theory and disprove the steady state theory. Scientists cannot directly observe the beginning of the universe. How, then, do you think scientists can study the big bang? How can scientists know when the big bang happened? Take a moment to answer these questions for yourself, then read on to learn! The Expanding Universe and Redshift The fact that the universe is expanding was one of the most important early pieces of evidence for the big bang theory. To understand how scientists know the universe is expanding, you need to know a bit about light waves. When stars give off light, it travels in waves through space. Some waves are longer; we see longer waves as red light. Some waves are shorter; we see shorter waves as blue light. As the object moves away from the man and toward the woman, it gives off light waves (numbered 1-4 in this diagram). Each observer experiences these light waves differently. 2
The stars and galaxies that Edwin Hubble observed demonstrated redshift. In other words, they were moving away from Earth. If galaxies are moving away from Earth (and each other), the universe cannot exist in an unchanged state. Hubble ultimately concluded the universe must be expanding. He also discovered that galaxies farther from Earth demonstrate greater redshift. In other words, the farther a galaxy is from Earth, the faster it is moving away from Earth. Hubble concluded that not only is the universe expanding, it must be expanding more quickly all the time! Scientists can now measure the intensity of a galaxy s redshift and use this value to calculate the galaxy s speed of travel and distance from Earth. Scientists still have not developed a way to measure the current size of the whole universe. The Age of the Universe Visible light is a form of electromagnetic radiation: energy that travels at high speeds through space in wave-like patterns. In fact, this energy is the fastest thing in the universe. Electromagnetic radiation travels at a constant rate of about 300,000 kilometers per second. (We call this the speed of light.) Because the universe is so vast and light moves so quickly, light gives scientists a useful tool for measuring distances in space. As you will see, scientists can also use light to measure the universe s age. A light-year is the distance light travels in one year: about 9.5 trillion kilometers. If a star is four light-years from Earth, light from that star takes four years to reach Earth. If a star is four million light-years from Earth, light from that star takes four million years to reach Earth. This means scientists are looking into the past when they observe electromagnetic radiation in space. Scientists can estimate the age of the universe by observing the universe s oldest stars and the intensity of their redshift. Scientists can use these observations to calculate the rate of the expansion of the universe and work backward to determine when the expansion began. Using this method, scientists have estimated that the universe is about 13.7 billion years old. In other words, the big bang is estimated to have occurred 13.7 billion years ago. 3
Getting Technical: Remote Sensing Instruments Much of what we know about the nature and origin of the universe comes from studying visible light through light-sensing telescopes. However, all objects in the universe emit forms of electromagnetic radiation other than visible light. Scientists can use remote sensing instruments special telescopes and other tools to detect these invisible forms of electromagnetic radiation and study the objects that emit them. Remote sensing instruments are essential for studying far reaches of the universe. Many objects are too distant or dim to detect with visible light. They give off low energy forms of electromagnetic radiation such as radio waves, microwaves, and infrared radiation. Scientists can use large radio telescopes, similar in appearance to large satellite dishes, to detect radio waves from space. These radio telescopes are located on Earth s surface, but they allow us to study distant stars that would otherwise we could not observe. Scientists can use radio telescopes like this one to observe distant objects in the universe. Other remote sensing instruments are launched into space. This allows scientists to observe the objects in the universe without interference from man-made lights on Earth s surface or particles in Earth s atmosphere. One such instrument is the Wilkinson Microwave Anisotropy Probe (WMAP). WMAP is a satellite launched in 2001 to examine cosmic microwave background (CMB) radiation, which is electromagnetic radiation left over from the initial stages of the big bang. The massive expansion that started the big bang gave off tremendous amounts of energy. With the help of WMAP, scientists have been able to observe this leftover radiation throughout the universe. Having a clear picture of CMB radiation allows scientists to map out matter in the universe. CMB radiation also provides evidence for the big bang theory. Nearly all of the CMB radiation is the same temperature. This indicates that the radiation was released at the same time. Some small temperature variations do exist, however, indicating different amounts of matter in different parts of the universe. Areas where the CMB radiation indicates more matter was created in the early universe correspond to the stars, galaxies, and clusters of galaxies in the modern universe. The Wilkinson Microwave Anisotropy Probe (WMAP) is used to detect cosmic microwave background (CMB) radiation. 4
What Do You Know? The following image was created by WMAP. It is an image of the cosmic microwave background (CMB) radiation left over from the big bang. The different colors represent differences in temperature, which correspond to different densities of matter. (Red and yellow areas are hotter, and dark blue areas are cooler.) Take a few moments to study this image. Circle the areas in the image that you think indicate areas that contain more matter. Box the areas in the image that you think show areas containing less matter. Notice that most of the image is the same color, meaning most of the CMB radiation is the same temperature. Write a paragraph explaining in your own words how this observation provides evidence to support the big bang theory. 5
Visualizing the Big Bang To help your child visualize the big bang, try doing a simple demonstration together. Go outside and gather a handful of soil and clump it into a tight ball. Let your child feel the density of the soil when compressed. Then have your child throw the ball of soil down onto the sidewalk. You can put down a white piece of paper if a sidewalk is not available or will not provide enough visual contrast. Take a look at the soil together. Discuss how all of the soil expanded from a single point upon impact, and take a look at where the soil ended up after this expansion. Some of the soil will still be in a large clump in the middle, and some will have spread out at some distance. This can represent how matter expands at different speeds throughout the universe. The soil that is farther from the point of impact traveled more quickly than the soil that stayed in the middle. However, everything can still be traced back to that central point. This is similar to the way all matter in the universe expanded from a single point. The matter that is farther away is moving faster, but it can still be traced back to the original singularity. This is a simplified demonstration, but it may help your child visualize the expansion of the universe. Here are some questions to discuss with your child: How does the density of the soil change from its original state compared to its current state after the expansion? Why is some of the soil farther away than the rest of it? How does this demonstration relate to what you have learned about the big bang theory and the expansion of the universe? 6
Earth and the Solar System Timeline and Cross-Reference Activity During the reading of this STEMscopedia you will use previous knowledge gained from the reading in the DO Activity 2 Human Model of the Formation of the Solar System to make connections between how and when the Universe, the Solar System, and other planetary objects were formed. Complete the boxes in the time line activity below as you read the text. Fill in each box by giving the name of a part of the solar system in the order it was formed and then listing information about that topic. Focus on formation facts and time for the Universe, Sun, Solar System (inner planets and outer planets), and other planetary objects (moons, etc.). 1
Earth and the Solar System Compare and contrast the formation of the Universe and the Solar System in the space below. 2
Earth and the Solar System Reading Summary Sticky Note Chart Nouns Verbs Facts 1