Evidence for the Big Bang
The univercentric paradigm naturally raised the question, “How came the universe?” Not only does modern science show us the extent of the universe, but its understanding of the history of the universe is also highly detailed and exact. In 1929, Edwin Hubble proved that the universe was expanding. By observing distant galaxies and the light they emit, he showed that the further away a galaxy was from ours, the more rapidly it was moving away from it. As an analogy, consider a spherical balloon being blown up (Figure 1). The dots on the surface of the balloon are analogous to galaxies, and the inflating balloon is analogous to the stretching of space between the galaxies. An observer on any one of the dots would perceive the other dots to all be moving away from him at rates proportional to their distance away.
This expansion means that in the distant past the universe was much smaller than it is today. So, following Hubble’s discovery, scientists began to consider a model in which the universe started out extremely small, with all of the matter packed close together. Near the very beginning, the entire universe would have been extremely hot (at least 1032 degrees) and extremely small (10-33 cm, which is much smaller than an atom, in fact 1/100000000000000000000 times smaller than the tiny nucleus inside an atom). This model was called the Big Bang. Although some people use the term “Big Bang” as if it were a replacement for God, it is merely a scientific explanation of how the universe developed after the first instant (immediately after time t = 0).
The Big Bang was confirmed by several independent pieces of evidence. The first and best known is the verification of a specific Big Bang prediction, that the heat of the early universe should still be visible today as low energy radiation from all over the sky. This cosmic microwave background radiation was discovered unintentionally by two IBM employees in 1963.
Several independent lines of evidence point to billions of years of history since the Big Bang. Astronomers understand much of this history and have found no serious gaps, other than what happened to start the Big Bang. I understand this detailed history of the universe as the ongoing process by which God continually creates the universe.
Forces and Particles
Parallel to the development of modern cosmology in the twentieth century, physicists began a concerted drive to understand the forces of nature in a consistent, interrelated manner. Long before this, in 1687, Newton had worked out a basic understanding of the force of gravity. Two centuries later, in 1864, James Clerk Maxwell derived the fundamental equations of electromagnetism, thereby proving that electricity and magnetism were manifestations of a second force, one associated with light. From then until the 1930s, gravity and electromagnetism were believed to be the only forces. But with the discovery of the neutron in 1932, physicists learned of additional forces (what became known as the strong and weak nuclear forces). Although the first attempts to explain the strong nuclear force appeared in 1935, the first true models of the nuclear forces did not develop until the 1950s. Then in the 1960s, a way to combine electromagnetism with the weak nuclear force was discovered and referred to as electroweak theory. Simultaneously, understanding of the strong nuclear force was accomplished during 1963 to 1965. The related theory was named quantum chromodynamics (QCD). These theories showed that all the fundamental forces (with the exception of gravity) were related.
As the understanding of forces developed, physicists were also learning about the elementary particles that compose all matter. Around 1870, the periodic table of the elements was developed by Dmitri Mendeleev and others as a systematic way to organize the dozens of known atoms; today 117 types of atoms are known. In the early 1900s, physicists discovered that each atom is not solid like a billiard ball, but is made of more fundamental particles: protons and neutrons in a nucleus with electrons swirling around the nucleus.
Yet the protons and neutrons are still not the most fundamental: high- speed collisions in particle accelerators hinted at the existence of even more elementary particles. Experiments also began to reveal many particles besides protons, neutrons, and electrons. For a time, physicists were discovering new types of particles faster than they could explain them— there seemed to be a “zoo” of particles rather than orderly categories (see Figure 2).
Gradually a more orderly picture came together. Protons and neutrons were each discovered to be made of elementary particles called “quarks.” The two most common types of quarks are called up and down, and come in three varieties (called red, green, and blue). When you add in the electron and the electron neutrino, you get a family of eight elementary particles. All of the atoms in the periodic table can be explained with just those eight particles. That’s a lot simpler than 117!
Physicists also found that associated with each of these eight particles is an anti-particle. Anti-matter is commonly referred to in science fiction, as in Star Trek, making it sound very exotic. Yet the essential difference between anti-matter and regular matter is just the sign of the electric charge: if a particle is positively charged, its anti-matter partner carries a negative charge (or vice versa). The existence of anti-particles doubles the number of elementary particles in a family to sixteen.
As all of the elementary matter particles were discovered, physicists were also learning more about forces and discovered the existence of another category of particle: a “force-carrying” particle. This is difficult to picture, but you have already heard of one such particle, the photon. The photon is the force-carrying particle for electricity and magnetism. QCD is associated with eight force-carrying particles (called gluons, because like a glue, they cause quarks to stick together) and the electroweak force with four force-carrying particles (including the photon), making a set of twelve force-carrying particles (see Figure 3).
The left three columns show three families (“generations”) of matter particles (quarks and leptons, shaded purple and green). The right column shows force carrying particles (bosons, shaded pink). In addition to the particles shown, each quark comes in three so-called colors (red, green, blue), and each of those has an antiparticle with opposite color (anti-red, anti-green, or anti-blue) and opposite electric charge. Each lepton also has an anti-particle of opposite electric charge. Thus, there are 16 = 2*3 + 2*3 + 2 + 2 matter particles in each generation. The force carrying particles also come in more varieties than shown (a total of 12). This set of forces and matter particles became known as the Standard Model of Elementary Particle Physics. Next week we'll talk a bit more about the Standard Model and then turn to the relationships between the very small and the very large aspects of the cosmos.