Overview on Physical Cosmology
Lead: Eberhard Möbius

1/31/2011

Summary by Susan Dolan

Everything out of Nothing?

Reading:

M. Gleiser “Tear at the Edge of Creation” Parts of Sections 11 - 25.
P. Davies, The Goldilocks Enigma Ch 1, 2;
"Curtains of the Universe", Astronomy, March 95; Lecture Notes (www); (On Blackboard)

Tonight’s lecture was focused on an introduction to how physicists view cosmology. The lecture began with how complex the universe is to study. The discussion outlined the limitations and paradoxes that the field of physics encounters when attempting to seek specific answers to some key questions about the universe.

The lecture began with the basic understanding of how scientists attempt to describe, predict, control and explain the natural world around us. In normal scientific environments, science attempts to perform multiple experiments on multiple objects that share common characteristics. The universal question asked when discussing the universe is: Is the Universe infinite or finite? Does it remain static or does it behave in a dynamic fashion? Examples of dynamics would include changes as in galaxy size, molecular composition, and evolving life. Additionally, are there multiple universes? The current accepted explanation of the origin of the universe is the Big Bang model derived from the theory of quantum mechanics. Quantum mechanics states that matter and energy can appear spontaneously out of the vacuum of space due to a quantum fluctuation. If this is the case, that a “hiccup” in the energy field could assist in creating a universe, then cosmologists theorize, that other quantum fluctuations could have spawned other universes. This is problematic, because scientists do not have the ability to test this theory. In attempting to answer these questions regarding the universe, scientists are limited to the one universe they reside in. Physicists are limited to this universe due to the inability to see outside of this universe. Although they have been able to perform a battery of tests, it still is performed on the same object repeatedly.

In discussing cosmology, the study of the universe, the first discussed paradox of a physicists’ explanation of the universe was Olbers’ paradox (a German physician and amateur astronomer in the 19th century). In physical cosmology, Olbers’ paradox states that the darkness of the night sky conflicts with the belief in an infinite and eternal static universe. If there were an infinite universe, at any angle from the earth, the sight line out into the night sky would end in the view of a star. Therefore, if this were the case, the night sky would continuously be lit up. In fact, this is not the case.

To discuss the possibility of a finite or static universe, one has to discuss and outline the scale of the universe. This was the next topic outlined in class. The presenter “shrunk” the solar system to demonstrate the size of the solar system. He presented a 14 cm ball that represented the sun. This ball was smaller than the actual Sun by 1 to 10 billion times. The actual size of the sun is 1.4 million km in diameter. The earth, (the size of a pin) would then be 15 meters away. The size of Saturn’s rings is at the size of a quarter in this shrunken system, and it would be located approximately 150 meters from the 14 cm diameter Sun. The nearest star (Alpha Centauri) would be located across the country.

Other historical ideas about the universe were discussed in class, specifically, defeating the idea that Earth was the center of our universe. However, we are in the center of our observable Universe. This is trivial due to the fact that we cannot observe farther than the ripples of our expanding universe. Additionally, the speed of light correlates to what we can observe. It takes light from the Sun eight minutes to reach Earth. It takes light 4.3 years to reach us from Alpha Centauri. The light that reaches the Earth from Andromeda is over 2 million years old. Therefore, what we are seeing today happened in Andromeda over 2 million years ago. It enables us to peer back in time.

Edwin Hubble challenged early scientific consensus of a static universe. Hubble outlined his observations using the Redshift Effect. He discovered as he peered out into the universe, the farther away the galaxies that he observed, the stronger the red shift of their spectral lines. This exemplifies that the universe is expanding, which contradicts the idea of a static universe. (As the universe expands, from Earth’s vantage point, the universe appears to grow continuously on all sides. This explanation assists in the understanding of the Cosmological Principle: The properties of the universe are the same for all observers. That is, there is no place special in the universe. The universe looks the same from any vantage point in the universe and abides by the same scientific laws.

When internalizing the idea that the Universe is continually expanding, the next question to ponder was to imagine to what extent would the universe expand? Will it go on indefinitely? To demonstrate this, the presenter blew up a balloon and outlined the physical laws of the expansion of the universe. The result was the identification of the time that the universe began. The model outlined that the universe was compressed and then rapidly expanded.

There were a few scientists, mainly Fred Hoyle, Hermann Bondi and Wickramasinghe, who maintained that, if there was no special place in the universe, the universe should exhibit similar characteristics throughout time. If this is true, scientists postulated that the density of the universe should be the same. Scientists went back and forth on the idea of how the universe began. Eventually, the Big Bang model was developed. This model outlined that the universe was compressed and very hot during the beginning. To demonstrate the laws of thermal energy under compression, the presenter took a glass tube with a cotton ball and rapidly compressed the air surrounding the cotton ball. The cotton ball exploded into flames. Therefore, radiation must have been given off. In fact the radiation that existed from the beginning of the Big Bang, which was observed in 1965, assisted in validating the Big Bang Model.

Holes in the Big Bang models were discussed. Three unsolved questions were discussed regarding the Big Bang theory.

The first was the horizon problem. When looking at the background radiation of the universe, it is evident that opposite regions in the sky were separated too far to have ever been able to communicate with each other through signals traveling at the speed of light. And if this is true, how did they know to have the exact same properties?

The second was the flatness problem. If the mass density of the universe were uniform and its gravity just balancing the expansion speed, the universe would be said to exhibit flat characteristics.

The third unanswered question was known as the matter problem. Why didn’t all matter and anti-matter interact and cancel each other out. Why is it that matter and anti-matter did not convert to energy? Or better yet, why is more matter left than anti-matter?

Along came the inflation model. The inflation model stated that at the beginning of the Big Bang, the universe expanded and cooled rapidly. With this rapid expansion, the universe became flat. Inflation also addressed the horizon problem. Initially, all parts of the universe were in contact, it was only after the rapid expansion did they become too far apart to communicate. Also, the matter problem was addressed by the inflation theory. As the universe cooled rapidly, the universe lost its symmetry. The presenter used an analogy of water rapidly cooling to demonstrate this. As smooth water rapidly cools, its symmetry is lost, and chunky ice appears. This rapid cooling assisted energy turning into matter.

The presenter addressed that scientists so far have been working with only three percent of the universe. According to the most recent observations and inferences, the other ninety seven percent is composed of dark matter and energy.

To close the presentation, the presenter discussed the question of why did the universe begin this way? The scientific community came up with the Anthropic Principle. There were two scenarios that were discussed.

• The Strong Anthropic Principle – The universe was set up to provide for life.
• The Weak Anthropic Principle – we live in one of the few right ones out of many.

Can science really answer all of these questions since we are limited to our observations within our universe?

The following questions were asked after the presentation:

1) What was the observational information that led to the postulating that dark energy and dark matters that led to the acceleration?

There were two things.

If you look at galaxies and you measure their rotation, dark matter can be deduced from the fact that you see the stars furthest out moving much faster than you would calculating the mass of all the stars together. That mass is much less than it would take hold to these stars in the out curves in their orbits. They would fly away.

The dark energy is deduced from inflation. If you want to make space flat, the universe would have to expand exactly at the right rate. Too fast, it would be curved in a twisted fashion like a saddle; it expands too little, like a balloon. If it were so, the universe would collapse again. In between lies flat. This was predicted by inflation, but it has also been tested.

2) Is there any empirical evidence of a fourth dimension?

If you take Einstein’s theory of relativity you predict the motion of the closest planet to the Sun. Mercury has an elliptical orbit; its major axis goes slowly around the sun. If you take Einstein’s model, which puts in spatial curvature, you come up with the observed value. Although physical space is observed to have only three dimensions, there is a possibility that many more dimensions exist. In the case of string theory, mathematically, it is possible to have 10 dimensions. Human minds have difficulty visualizing more than three dimensions because we can only maneuver in three spatial dimensions. The way to think about additional dimensions is to visualize them strictly in a mathematical representation, rather than physical space.

3) Are the three problems solved by the inflation model?

The inflation model addressed the problems with the Big Bang model, so the Big Bang model did not need to be abandoned. It is a newer version.

4) Does life require another explanation or is it part of the Big Bang process?

This class was an explanation of Physics and the Big Bang. It has nothing to do with the Origin of Life. We can only reason about events after the Big Bang because time started with the Big Bang. Our science goes back to the Big Bang, but we are part of the universe. This issue will be discussed in a future class in more detail.

5) How does the Horizon problem relate to the Cosmological Principle?

The background radiation is very homogenous in the universe. When you examine the conditions in different parts of the universe, the conditions described by the radiation appear to be very similar even between places in the universe that are so far apart that there would be no communication between them. Therefore, the conditions may not have had enough time to equilibrate The observation of the smoothness and the homogeneity of the background radiation support the Cosmological Principle. In other words, if all places in the universe that we can examine through the background radiation exhibit the same conditions, then our place should exhibit the same conditions as well. The inflation model suggests that this may be true due to a rapid expansion of the universe during the Big Bang.

6) Would Hoyle be pleased by the Horizon problem?

Hoyle would take any problem of the Big Bang model, then point to it and say it doesn’t work. However, if you take a model and push it beyond the range where it is valid, you may need to include something else and develop it further.