October 10, 2012
Solving The Pioneer Anomaly Could Make Interstellar Travel Easier One Day
April Flowers for redOrbit.com - Your Universe Online
Last month in Houston, Texas, Former President Bill Clinton addressed the 100 Year Starship Symposium to express his support for interstellar travel. The Symposium is an international event advocating for human expansion into other star systems.
Interstellar travel for humans will depend upon extremely precise measurements of every factor of the mission, and the knowledge of these factors may be improved by the solution to a puzzle that has stumped astrophysicists for decades recently found by a University of Missouri researcher.
“The Pioneer spacecraft, two probes launched into space in the early 70s, seemed to violate the Newtonian law of gravity by decelerating anomalously as they traveled, but there was nothing in physics to explain why this happened,” said Sergei Kopeikin, professor of physics and astronomy in MU´s College of Arts and Science. “My study suggests that this so-called Pioneer anomaly was not anything strange. The confusion can be explained by the effect of the expansion of the universe on the movement of photons that make up light and radio waves.”
To measure the Pioneer probes' movement, beams of radio waves were sent to and bounced off the spacecraft. The distance and speed of the spacecraft was calculated by the time it took for the photons to complete the round trip. The new study, published in Physical Review D, suggests that the photons move faster than the Newtonian theory could account for, thus causing the appearance of deceleration. Kopeikin says the craft were actually traveling at the correct speed predicted by the theory. Because the universe is constantly expanding, the Earth-based observations are altered, causing the Pioneer probes to appear to be slowing down.
“Previous research has focused on mechanical explanations for the Pioneer anomaly, such as the recoil of heat from the craft´s electrical generators pushing the craft backwards,” Kopeikin said. “However that only explains 15 to 20 percent of the observed deceleration, whereas it is the equation for photons that explains the remaining 80-85 percent.”
Kopeikin notes that physicists must be careful when dealing with propagation of light in the presence of the expansion of space because forces that are irrelevant in other equations affect it. The expansion of the universe affects photons, but it doesn't influence the motion of planets and electrons in atoms.
"Having accurate measurements of the physical parameters of the universe help us form a basis to make plans for interstellar exploration,” Kopeikin said. “Discerning the effect of the expansion of the universe on light is important to the fundamental understanding of space and time. The present study is part of a larger on-going research project that may influence the future of physics.”