Physical Cosmology, Lead: Eberhard Möbius

2/4/2003

Summary by Laura Baker:

Introduction to Physical Cosmology

Readings:
“Curtains at the Edge of the Universe” by Robert and Sarah Williams Scherrer
& “Origins of Everything”              from Astronomy Feb. 1998
“The Whole Shebang” by Timothy Ferris

Dr. Möbius initiated our discussion with several thoughts on the space shuttle Colombia’s disaster. It was not only important in this class to acknowledge what had happened, but it was important that we take time to think about the reasons, risks, and limits that are bound to space travel. Also, the question was raised, “How much do you do with man versus robot?”

Dr. Möbius led the discussion on the origins of the universe with an exercise on perspective of the Earth relative to the universe. He demonstrated where certain “landmarks” are relative to the distance of the Earth and Sun. For example, Saturn, Alpha Centauri, Milky Way, and other galaxies were drawn out in a simple model to demonstrate how far away they are from Earth. The myth about Earth being in the center of the universe has been proved wrong. E. Hubble is understood to be the scientist to prove this and therefore caused a paradigm shift to occur. Vicky asked the question, “If solar systems are so many light years away from each other, then what is in between them?” The answer given includes stars, vacuums, and minor galaxies.

The measurement of a light year was discussed next. A light year is the distance light travels in one year and this turns distance into time. Light from the sun is 8 minutes old, from Saturn it is 80 minutes old, from Andromeda it is 2 million years old and from Alpha Centauri it is four years old. Before Hubble reported that galaxies are moving away from the Earth, scientists believed the universe was not changing. The Big Bang Theory becomes central to our discussion here. Something must have happened in order to cause the universe to be expanding. Several supporting clues to the Big Bang Theory were discussed.

First, the principle of the Redshift of Galaxies was explained. Dr. Möbius explained that astronomical units based on the parallax method are used as a base calculation of distance. For instance, if I stick my arm out with my thumb up, I know the distance from my eye to my thumb. Then look at a point with just my right eye, and then look at it with my left eye, there is a jump in distance. With this method, distances in space can be calculated. This is one method of measuring distances in space as things are so far away. One example of this measurement could be taking the diameter of earth’s orbit and measuring the shift and location of nearby stars from one season to the next. The Redshift in Galaxies is measured in the following way: The spectrum of light from the sun goes from long wavelength radiation, which colored red, to short wavelength radiation, colored blue, and then radiation not seen by our eyes. There are lines in the spectrum, which belong to different elements, so we can determine the wavelength of these elements. Scientists can always detect Hydrogen, as it is so abundant in the universe. The red wavelengths of hydrogen that are detected move to the right because they are shifting farther away from the earth, hence the Redshift of Galaxies. The shift in wavelength is proportional to the speed in which the object is moving away from you.

A short film was shown and a graph was presented to help explain the expansion of the universe. In regards to the video, the scale of the universe was discussed and the reason for the “bubble” structure. Thom asked, “What is the map of the universe showing and its time relation?” The progression of thought leads to a four-dimensional space-time map which scientists are not sure of. Ed asked what distance measurements are used in this process and Dr. Möbius spoke about parallax idea again.

The discussion led to an explanation of the workings of a supernova. One way of determining distances from the Earth is by determining the luminosity of an object and then deducing its distance from that measurement. The most luminous objects in the universe are supernovas as they can outshine galaxies! The Standard Candle Method is used when a type IA star collapses when it is approximately 1.4 times the mass of the Sun. I asked if any patterns of timing and prediction of stars collapsing have been detected. This is not something that is found, but Robin said that if you know how old a star is, you can predict the collapse. Ed asked what distinguishes a nova from a supernova and an in depth answer was given on the process of a star moving from the giant stage, to a white dwarf, to producing a nova and finally a supernova.

After the discussion on the structure of the universe, we focused on “What does the expansion of the universe mean?” The Cosmological Principle states that the universe is homogeneous and everywhere you see the same picture. You can conclude that at a certain time everything was closer and that there must be a beginning.

Kevin started out an interesting discussion on what space really is. He asked, “How is it possible to differentiate motion through space and motion of space?” The answer was, “You can’t.” We talked about the expansion of space, the existence and non-existence of space, what makes up space, and how does it relate to humans. Gravity comes into play as the overwhelming force of the universe. Bill asked, “Is there more space as the universe expands or is matter being put somewhere that was previously empty?” The answer given was that at the beginning there was no space and space exists because matter is there. Tom was clarifying questions on space by comparing the idea of “space expanding” and “space already there while something is expanding into it.”

Sean offered some logic for thinking about space, while Jason mentioned the space-time continuity. Bill asked that if there was space that existed before matter, then how do speed of light and relative limits apply. Robin commented about the difference between an object moving through space and moving because space expands. The discussion on space could have gone on, but it was time to talk about how the universe started to expand in the first place.

Dr. Möbius explained that in the beginning there was light! Since the universe is expanding now, it had to be very compressed and small at the beginning. It would have been very hot because of compressed air and when the universe blew up, it started to expand and cool, which is still going on today. Somewhere there should be radiation that is 3 degrees K and Dr. Möbius demonstrated what happens when air is compressed. It created a spark of light and heat.

Robyn asked what the difference is between heat cooling and wavelength slowing. Thom explained the Cosmological Redshift as the answer. Connor asked about creating new space and if space is getting larger. James presented an example on the expansion of space as if it were a balloon being blown up. Other analogies were given. Erin asked about experiments of things traveling faster than the speed of light.

The next piece of evidence for the Big Bang Theory is the “cooking recipe” of the universe. Hydrogen, Helium and their respective isotopes are in abundance and this is what combines for nuclear fusion.

There are several problems that are not addressed by the Big Bang Theory.

• First, there is the flatness question. Scientists do not know if the universe will expand forever or if it will collapse. Ed spoke about gravity and time and the relationship to the Big Bang. Josh spoke about the “pulse” theory and evidence that the universe will expand forever. Dan said he was confused about the curtain of the universe. The curtain is the boundary in the universe where humans cannot see past (yet). If we could see past this curtain, we could possibly be able to observe more of the beginnings of the universe. To make things even more complex, Dr. Möbius told us about how space is not necessarily straight and that light does not come to us in a straight line. It takes the shortest path to get where it is going and wraps around gravity.
• The next problem with the Big Bang Theory is the “horizon problem.” That is the universe is the same in opposite directions but no communications happens.
• Finally there is the “matter problem.” If 2 lbs. of light = 1 lb of matter + 1 lb of anti-matter, then why is some matter left? There is no contradiction to the model but the model has no explanation! Cosmic inflation is an answer and this was briefly discussed.

To end the discussion, Dr. Möbius asked why this world harbors life. We know that the constant of forces have to be exactly right! Next time we will discuss the Strong Anthropic Principle (AP) and the Weak AP. The Strong AP states the universe is designed to support intelligent life and the Weak AP states that we happen to live in a random universe that happens to support life.