Physical Cosmology, Part I, Lead: Eberhard Möbius

1/29/2001

Summary by Erik Wochholz:

Introduction to Physical Cosmology

In our search for knowledge, one might first ask why we search for knowledge to begin with. Why do we want to know about, for example, the galaxyÕs far away and the atoms that are in our finger? Are we better off with such knowledge? Many would answer yes to this question. For it seems obvious to many individuals that it is our occupation as humans to inquire into the realm of the unknown. The less mystery the better it seems. Hence, we inquire into the universe. We inquire into how the universe was formed and what its boundaries are? We wonder how big the universe is and whether it will ever end? More importantly, however, we inquire into how science can better our understanding of the universe.

Many individuals have the misconception that science is nothing more than analytic facts and experiments. However, science is much more than what you might find within a textbook. Science is a spiritual journey, a pursuit by which we unravel not only the existence of the universe but also human cosmology or how we see ourselves in the universe. Nonetheless, our understanding of the universe is certainly limited to what contemporary science can and canÕt do. On the one hand, science will never be able to explain everything there is in the universe. After all, it has taken humans eons of time simply to scratch the surface of the cosmological unknown. Hence, we must find ways in which to cope with mystery.

One such way in which we deal with the mystery in the universe is religion. For religion does its best to explain things that science cannot. Religion gives meaning to love and compassion. Religion gives meaning to death and life. Religion even attempts to explain why humans are here and what their purpose is.

Humans have developed many cosmological pictures using religion. For instance, many cultures articulate the mystery and behavior of the universe through mythology. Judeo-Christian mythology, for example, represents the beginning of the universe through a cosmic ŌlightÕ. New Guinea mythology, however, views the universe as Death the Creator, enunciating the power by which life and death seem to complement each other. For it is often that the death of one will give life to another. Likewise, the symbols of Yin and Yang in Northeast Indian mythology, represents the opposing but complementary forces within the universe.

How we see ourselves in the universe complements our cosmological picture. And it is how we see ourselves in the universe that is constantly changing. For at one time we believed that are earth was flat rather than round. Before Copernicus we had also believed that the earth was the center of the universe. Now we know this to be false, for we have been able to develop measuring techniques by which we draw clear pictures of the universe. We know, for example, where other galaxies and stars lie in the universe in relation to the earth. We can even calculate the distance between the earth and these galaxies. One particular measurement technique we have developed deals with the amount of light that is brought to us by neighboring galaxyÕs and stars. So depending on the amount of light that we see from a star (or a galaxy) in relation to the total amount of light that it put out, for instance, we can determine the distance of that star (or galaxy) in relation to the earth. According to the behavior of light, it reaches us by means of distance and constant speed. In a way light enables us to go back in time. For when we view any light, we view it in the past, since it takes a certain amount of time to reach us.

We have discovered many new things with the measuring techniques we have been able to develop. We have discovered Alpha Centauri, our closest star (besides our sun). We have discovered the Andromeda Galaxy, our closest neighboring galaxy. We have even measured very large galaxy clusters that surround our Milky Way galaxy.

In the attempt to measure the entire universe, or at least the known universe, that is the boundary by which we can measure and observe, we come up with no concrete number. But we do know that the known universe is somewhere in the vicinity of 10-15 billion light years. In other words, it would take around 10-15 billion years for light to travel the distance of the universe. But this is only what we know of the observable universe. The more we discover the bigger the universe gets. So is the universe infinite? Many would say no according to the redshift phenomena and the expansion of the universe. For astrophysics tells us that the shifting wavelength of a light source is the result of the movement of that light source. A shift to the red side of the spectrum means that the location of the source is moving away from us. So since we can supposedly observe that the light from far away stars are moving towards the red part of the spectrum, we are almost certain that the universe is expanding.

It is however a misinterpretation to think of an expanding universe as everything in the universe expanding away from the earth. This interpretation is just as inaccurate as the Ptolemaic picture of the earth being the center of the universe. To give a better a picture of the universe let us imagine a balloon with many single dots in various locations on it. While you continue to fill the balloon with air, the dots of the balloon move further and further away from each other. This is exactly what occurs in our universe. In expanding we move apart from one thing just as much as that thing moves away from us. However, our solar system is not expanding as our universe is. Our solar system is fixed by the power of gravity. Hence, our entire galaxy is shifting, while it is not fixed by the same forces as our solar system is.

April 1, 2001