LESSON 1 – UNIVERSE AND THE SOLAR SYSTEM OBJECTIVES At the end of the lesson, you should be able to: 1. State the different hypotheses explaining the origin of the universe; 2. Discuss the story of the Big Bang; 3. Discuss the evidences supporting the Big Bang; 4. Compare and contrast the Big Bang and the Steady State theories; 5. Discuss the String Theory. SUBJECT MATTER Introduction to Science This course will probably be your first encounter of science under the Senior High School Program. Thus, now would be the right time for you to know what Science really is and appreciate how it works. Science came from the Latin word scientia which means “knowledge”. Science is a systematic body of knowledge that discovers the world through observation and collection of facts and establishes relationships among these facts by means of logic and reason. Figure 1.1. Science is basically done through this method. Any judgment In simpler terms, science that cannot be tested through this method is outside the realm of science. is done by observing the world through our senses and formulating theories that explain these observations. The theories are verified through repeated experimentation or testing and then accepted as long as all observed facts and experimental results satisfy the conditions of the theory. A single observation that does not fit into the theory is enough to reject or revise the theory. Hence, Science is not a mere collection of facts but is an active process of trying to look for explanations on how things work. The entire process is broken down into smaller steps and is called the scientific method (Figure 1.1). Since Science relies on repeated experimentations, it is limited only to being testable. Science cannot prove anything that is not testable. For example, there is no test to tell whether a philosophical belief is right or wrong; nor whether a work of art is beautiful or not. Nevertheless, Science still contributes in our daily lives in the sense that it has expanded our view of the world. In the first steps of our journey in Science, we will try to take a look at the scientific theories explaining how our Universe came into being. Creation Myths and Stories In ancient times, most people tried to explain natural events as a result of the action of gods and spirits. This includes the question on how the world, the Universe rather, came into being. A popular theory of the origin of the universe is the Figure 1.2. In the Bible, God created everything—from light to Biblical account of creation written life—in six days. in the book of Genesis where it says that God created everything in six days (Figure 1.2). In the Tagalog mythology of Malakas at Maganda, God (or Diyos in Filipino) created the entire world by raising His hand then pointing them down. Shortly, the first man and woman appeared from inside a bamboo shoot. These are just many examples of creation myths and stories passed down from generation to generation as a way of perpetuating the culture of a particular society. The ancient Greeks were among the first people to use systematic observation and reason to explain natural events. In fact, they were among the first ones to construct models of the entire universe. In Earth and Life Science, we will focus on the theories on how the universe began; models of the universe are discussed under Physical Science. Theories on the Origin of the Universe Under this course we will discuss four scientific theories on the origin of the universe, namely: (1) Big Bang Theory; (2) Steady State Theory; and (3) String Theory. Big Bang Theory We will dedicate most of our discussion of the origin of the universe in this section because the Big Bang theory is the most accepted theory on how the universe came into being. So far, the details of this theory are consistent with the known laws of physics. Do you recall a moment when Figure 1.3. Doppler effect as illustrated by a moving ambulance. The an ambulance was coming frequency decreases as it moves away and increases as it moves towards towards you, then away from the observer. you? You might have noticed that when it moved away from you, the pitch of its siren became lower. This phenomenon is called the Doppler effect (Figure 1.3). Waves, when coming from a moving source, decrease in frequency as it moves away and increase as it moves toward the observer. In the language of sound, a lower frequency means a lower pitch and a higher frequency means a higher pitch. A similar phenomenon is also present in light, a wave. In 1924, Edwin Hubble discovered that stars are not uniformly distributed in space, as seen by the naked eye in the night sky. Instead, stars form clusters called galaxies. The distance of any galaxy from the Earth can be estimated by measuring the amount of light the galaxy emits. Through this, Hubble found out that nearly all galaxies tend to move away from the Earth. His evidence is based from the fact that the Figure 1.4. Redshift—an illustration of measured light from galaxies tends to move towards how light also decreases in frequency as it the red end (lower frequency) of the visible light moves away from the source. spectrum, a phenomenon called redshift. If you look at Figure 1.4, the illustration of redshift is similar to that of the Doppler effect in the ambulance siren, implying a source that is moving away. With this observation, it was speculated that if the galaxies are moving away from us, there must have been some point in time when they must have been closer together in the past; they may have even come from a single point in the beginning. In 1927, George Lemaitre used this notion of an expanding universe to conceive the Big Bang theory. The Big Bang theory basically states that about 13.7 billion years ago, everything (every matter, energy, space and time there is) in the universe started from an infinitely small, infinitely dense, and infinitely hot entity called a singularity. Where this singularity came from and why it expanded in the first place is still unknown. Big Bang theory today also narrates how the fundamental particles and forces molded the universe as we know it today. It is summarized as follows: 1. Inflation – the universe exponentially expanded from a singularity to about 1035 meters in width. 2. Formation of the universe – as the universe expands, the four fundamental forces separated and the universe was made of elementary particles such as quarks, electrons, photons, and neutrinos. 3. Formation of proton and neutron - protons and neutrons were formed from quarks. 4. Nucleosynthesis – protons and neutrons combined to form the very first nuclei. One proton and one neutron became hydrogen; two protons and two neutrons became helium. 5. Radiation era – up to this time, the universe is dominated by radiation. Through time, this radiation is now in the form of cosmic microwave background (to be discussed later). 6. Matter domination – at this point, electrons joined hydrogen and helium to form the very first atoms. 7. Birth of stars and galaxies – hydrogen and helium, which are gases, were produced in large quantities and formed large masses of gas clouds. Under gravity, they began to increase mass and ignite to produce stars. Multiple stars also began to cluster together through gravity to form galaxies. Hubble’s discovery was not the only evidence presented to prove the Big Bang. Two more proofs, the (1) cosmic microwave background (CMB) and (2) the presence of hydrogen, helium, and lithium in stars, laid the foundations to solidify this comprehensive theory. In 1960, scientists Arno Figure 1.5. A map of the sky showing the values of the temperature of Penzias and Robert Wilson the cosmic microwave background. The temperature only ranges by tried to construct a radio ±200 microkelvins. antenna with zero background noise. However, no matter what point in the sky they point, there is still background noise. This background noise was speculated to be a remnant energy from the explosion of the Big Bang. Further data (Figure 1.5) shows that the radiation carries a temperature range of only ±200 microkelvins. This homogeneity suggests that these very distant radiations should have had interaction in the past. Thus, they might have been so close together back then, suggesting again the existence of a singularity that once contained all of them together. Modern technology enabled man to detect what elements are present in stars however far they are from us. The nucleosynthesis narrative of the Big Bang suggests that stars should be made of the simplest atoms hydrogen and helium. True enough, it was found out that stars indeed contained mostly hydrogen and helium, with little traces of lithium and beryllium. In its first version, the Big Bang has encountered problems: flatness, monopole, and horizon problems. These three problems were resolved by an elegant idea called the inflation theory, proposed by Alan Guth, Andrei Linde, Paul Steinhart, and Andy Albrecht. Through inserting an exponential inflation in the story of the Big Bang, the problems were resolved and the theory is back on track. The problems and the solutions are summarized in the table below. Problem Expectation (Big Bang says…) Reality (Observation says…) Solution (Big Bang + Inflation says…) Flatness The universe is curved The universe is nearly flat according to sophisticated measurements An exponential inflation allows a very large curved universe but we can only observe the flat geometry. In the same way that the Earth is curved but, in our scale, we perceive it as flat Monopoles There should be heavy stable magnetic monopoles in the early universe because of the very high temperature There are no magnetic monopoles detected so far Horizon The universe is about 13.7 billion years old. Everything 13.7 billion years ago must have been in contact with one another According to the math, the observable universe is 93 billion light years across. How can two points 93 billion light years apart have been in contact? An exponential inflation would have dramatically decreased the temperature of the expanding universe, no longer allowing monopoles to form An exponential inflation faster than the speed of light will allow these points to have been in contact 13.7 billion years ago Steady State Theory A theory opposing the Big Bang was proposed by Hermann Bondi, Thomas Gold, and Fred Hoyle in 1948. This theory states that though the universe is expanding, matter and energy density remains the same (Figure 1.6). The discovery of the CMB debunked this theory because we saw in Figure 1.5 that the universe is not constant in composition. String Theory Scientists did not stop at the Big Figure 1.6. A comparison of the matter density of Big Bang and Bang. They wanted to know what Steady State universe. Evidences suggest that the amount of came before it. However, knowing matter and energy in the universe is constant. Matter is diluted as space expands. what came before the Big Bang would require scientists to be able to come up with a theory that unifies the four fundamental forces of nature: strong nuclear, weak nuclear, electromagnetic, and gravitational force. The first three forces were discovered to be produced by elementary particles. Gravity, however, according to Einstein, is produced by curvature of spacetime, not by particles. In string theory, elementary particles are said to have been made from the mode of vibration of a string whose dimensions are smaller than a particle. This theory speculates the existence of gravitons—particles carrying gravity. The problem with this theory is that its mathematics can only work in a 10-dimensional space, something that has not yet been observed.
