Emily A. Mullins
Phys 195, Introduction to Modern Astronomy
Web Project 2
Due: 22 November, 2013
Word Count: 663
Sources:
1. https://blackboard.wichita.edu/bbcswebdav/pid-705321-dt-content-rid-4478995_1/courses/PHYS-195-12193-201410/WP2%20-%20BadGravity.pdf
2. https://blackboard.wichita.edu/bbcswebdav/pid-705321-dt-content-rid-4478996_1/courses/PHYS-195-12193-201410/WP2%20-%20Nailing%20Down%20Gravity.pdf
3. http://news.yahoo.com/search-dark-matter-comes-empty-far-162116126.html
4. http://flamsteed.info/2012/05/dark-matter-a-two-handed-discussion/

Gravity is a rule of the universe that most people would never think to question. Astronomers in the past like Newton, who published his theory of gravity in 1687, believed that they had found the truth about gravity. However, discrepancies in the theories proposed by these men have been found. A great example that is often used to demonstrate these discrepancies is the Pioneer 10 and the Pioneer 11 spacecraft. The Pioneer 10 spacecraft was launched on March 2, 1972, and in December of 1973 Jupiter’s gravity threw it out of our solar system. It is currently traveling at a rate of approximately 2.5 AU per year. The Pioneer 11 spacecraft was launched on April 6, 1973, and Saturn’s gravity threw it out of our solar system in September 1979. 1 In 1998, a group of astronomers analyzed data from the Pioneer spacecraft. They looked over 11 years worth of data for the Pioneer 10, and four years of data for the Pioneer 11. Their research found that the Pioneer 10 was approximately 36,000 miles away from where calculations placed it using Newton and Einstein’s laws of motion. In accordance with this, they also found that the Pioneer 11 was 3,700 miles off of its predicted location. At first, it was thought that their was a spacecraft related force that caused the discrepancy, but none was found that gave an explanation. So what could possibly have caused two spacecraft’s speeds to change by the same amount in the same period of time? This question is what has caused scientists to question whether or not we really understand gravity.1 Tim Folger wrote an article in 2003 called “Nailing Down Gravity” in which he discusses the experiments being conducted to search for dark matter in the universe. The main experiment going on is called the Cold Dark Matter Search II. This experiment is hoping to detect the existence of WIMPs, or weakly interacting massive particles. These are clouds of cold dark matter particles. They’re trying to detect these by placing detectors of germanium and silicon crystal into and icebox. If a WIMP should hit one of the detectors, it would create the crystal lattice to vibrate very slightly, which would cause the absolute zero temperature in the icebox to spike. 2 Folger also discusses in his article the idea that has been postulated to “fix” gravity. There are