Saturday, June 16, 2018

Even Darker

In 1929 Edwin Hubble made a discovery that revolutionized our understanding of the universe. He measured the relative velocity between our Milky Way galaxy and 46 other galaxies and observed that the galaxies were all moving away from each other. In addition, the farther apart the galaxies were from each other, the faster they were receding from each other. The most straightforward interpretation of this observation is that the universe is expanding. Subsequent observations have revealed that the galaxies are not simply moving away from each other, but that the fabric of space itself between the galaxies is actually expanding.

With the knowledge that the universe is expanding, scientists have wondered about the future of the universe. Will it expand forever? Will it eventually stop expanding and collapse in on itself? The answer to these questions depends partially on the amount of matter in the universe because every object in the universe is attracted to every other object by the force of gravity. Gravity should cause the expansion of the universe to gradually slow down and, if there is enough matter, to eventually stop and collapse. To illustrate this consider two plastic balls connected by a rubber band. If you were to hold one ball in your hand and throw the other ball outward, eventually the speed of the second ball would decrease as the rubber band stretched because the rubber band acts as an attractive force between the two balls. In the same way, the attractive force of gravity should be causing the expansion of the universe to slow down. Because the strength of gravity depends on how much matter is in the universe, if there is enough matter, the very strong attractive force should eventually cause the expansion to stop and the universe to collapse back in on itself. The attractive force of gravity should be slowing down the expansion of the universe. But that is not what is happening.

Friday, June 8, 2018

The Dark Side

In the 1920's a number of experiments observed that certain nuclei would decay by emitting a "beta" particle in a process called beta decay. Although the beta particle itself was shown to simply be an electron, the process of beta decay exhibited some strange and unexplained properties. In particular, the decay products did not conserve energy, momentum, or angular momentum. Up until that time, all known physical processes had conserved these three quantities. That is, the amount of energy, momentum, and angular momentum at the end of any process was exactly the same as the amount at the beginning of the process. However, beta decay seemed to violate these well known conservation laws. A number of explanations were proposed including the possibility that these conservation laws were not absolute. However, one explanation seemed much more simple and elegant. The physicist Wolfgang Pauli proposed that another particle was also emitted during beta decay along with the electron, but this other particle was nearly impossible to detect. For all practical purposes it was invisible to any experimental detectors of the time. Now it may seem crazy to postulate an unknown, nearly undetectable particle simply to preserve well-established laws of physics, but consider the genius of this idea. By simply proposing the addition of one unknown entity all of the problems with beta decay could be solved. Enrico Fermi named the unknown particle a "neutrino," or "little neutron" in Italian. It took about 25 years to experimentally confirm the existence of this particle, but eventually the neutrino was discovered in 1956. The simple but elegant introduction of a nearly undetectable neutral matter particle was the solution to multiple problems.

Today we have a similar situation to that of the 1920's. When we observe the cosmos we find that there are a number of problems that seem to violate well established laws of physics. Einstein's theory of general relativity, which describes how gravity works, is a remarkably successful theory with tremendous predictive power, but when we try to use that theory to explain certain observed effects, the theory doesn't quite work. For instance, when we watch how fast the stars in galaxies rotate about the galactic center we find that the outer part of the galaxy doesn't obey Einstein's theory if we assume that we can actually see all of the matter in the galaxy. (See the graph at the end of this blog post.) We also find that the large scale distribution of galaxies throughout the universe has some problems if we assume that we can observe all of the matter that is there. (See the opening figure of this blog post.) In addition, we know that gravity can actually bend the path of light, but the amount of bending we observe is much greater than what we would expect using the theory of general relativity and the amount of visible matter.

Monday, May 28, 2018

A Look at the Top Quark

All the known matter in the universe is composed of two classes of particles: quarks and leptons. There are six types, or flavors, of quarks and six types of leptons. The figure to the left shows these fundamental particles. Three of the leptons, the electron (e), the muon (μ), and the tau lepton (τ) have an electrical charge that is a factor of 1 that of a proton, and three of the leptons, called the electron neutrino (νe), the muon neutrino (νμ), and the tau neutrino (ντ) have zero electrical charge. Quarks are named (in order of increasing mass) up (u), down (d), strange (s), charm (c), bottom (b), and top (t). The up, charm, and top quark have a charge that is +2/3 that of a proton, and the down, strange, and bottom quarks have a charge that is 1/3 that of a proton.

Therefore, in an atom composed of a nucleus surrounded by electrons, the electrons are fundamental particles, which means they are not composed of anything smaller as far as we know. But the nucleus is composed of neutrons and protons, which are themselves composed of quarks. At a very basic level a proton is made up two up quarks and a down quark with electric charge +2/3 + 2/3  1/3 = 1 while a neutron is made up of one up quark and two down quarks with an electric charge of +2/3  1/3  1/3 = 0. The two quarks and two leptons in the first column in the figure are called the first generation of particles, the second column is the second generation of particles, and the third column is the third generation of particles. Most of all the matter we know of is made of the first generation of particles since atoms are made of neutrons and protons and electrons with the neutrons and protons made of up and down quarks.

Saturday, May 5, 2018

A City Center Conversation: The Coherence Between Science and Scripture


Today's Arkansas Democrat-Gazette newspaper has an article discussing my upcoming conversation in Little Rock, Arkansas at City Center Conversations. If you are near Little Rock and can attend this event on Tuesday, May 8, 2018 at 6:30 at the Statehouse Convention Center, I invite you to come. City Center Conversations is an open interview and dialogue between Dr. Steven Smith, the pastor of Immanuel Baptist Church in Little Rock and an invited guest. Steven's vision is to host speakers who are living out their faith in the public square to have open conversations about some big questions regarding God, life, and faith. In the past, Dr. Smith has invited Eric Metaxas and Lee Strobel to the first two previous events in this series, and I will be the third invited guest.

The article in the Democrat-Gazette was written by Francisca Jones who is the religion editor for that newspaper. My interview with her, as well as a recent comment left on my blog, highlighted once again for me how entrenched is the view among many nonbelievers and believers that science and the Bible are at odds. Many of the questions that Ms. Jones asked were about the apparent conflict between science and the biblical text and why I am among the few scientists who see no conflict between them. The comment left on by blog accused me of "bending" the biblical text to accommodate a 14 billion year old universe. (If I had a dollar for every time that accusation has been made I would not have to work anymore).

Sunday, April 15, 2018

Are Miracles Unscientific? Part 2


In "Are Miracles Unscientific? Part 1" several features of miracles were discussed. I defined a miracle as an exceptional action of God within the natural world, distinct from the usual processes of nature, for some specific purpose of God, which can have detectable consequences. I established that if there is a transcendent God who created the universe he could certainly intervene in unusual ways at times. Finally, I listed some different definitions of science including a broad definition based on the etymology of the word science, which means "knowledge" that would certainly admit miracles as a possibility. The last two paragraphs of that blog entry set the stage for this follow up entry on miracles. Because miracles are not repeatable events they cannot be established through a strictly controlled scientific experiment but can be reliably confirmed using a scientific and historical investigative method, in the same way other past events are established beyond a reasonable doubt.

Sunday, April 1, 2018

Are Miracles Unscientific? Part 1

The question of whether or not miracles are scientific is a multifaceted question having to do with the definition of miracles, the definition of science, and the characteristics of God. The Merriam-Webster Dictionary defines a miracle as an "extraordinary event manifesting divine intervention in human affairs" such as "the healing miracles described in the Gospels." The second definition listed is "an extremely outstanding or unusual event, thing, or accomplishment" such as "the bridge is a miracle of engineering." Of course any controversy over miracles involves only the first definition, not the second. We can assume that the 1980 “Miracle on Ice” was not a miracle, though it was certainly an exciting and unexpected sporting outcome. I would define a miracle as an exceptional action of God within the natural world, distinct from the usual processes of nature, for some specific purpose of God, which can have detectable consequences.