Physics: Principles and Problems


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Speed of Light Slowing Down?
February 2003


What travels at 300,000 kilometers per second, is constant, and travels faster than anything else in the galaxy? Did you answer light? It seems like a reasonable answer, but recent findings suggest that the speed of light may not be constant—it may be slowing down.

John Webb, a professor at the University of New South Whales in Sydney, Australia has suggested that the speed of light has changed. He based his suggestion on data collected while studying a distant quasar. Quasars are distant, high-energy objects that are hypothesized to be associated with black holes. Quasars are so far away that the light they produced billions of years ago is just now reaching Earth.

Spectra of astronomical objects are produced by photons of certain wavelengths knocking electrons into higher energy levels. Then, photons at other distinct wavelengths are emitted and the electrons drop back to lower energy levels. According to our law of physics today, only certain wavelengths can alter the position of electrons in atoms, and the wavelengths are different for each type of atom. The quasar that Webb observed appeared to absorb a different wavelength than what was expected. This meant that either the charge on an electron has changed, thereby altering the energy level structure of the atom, or the speed of light has changed.

Physicist Paul Davies of Sydney's Macquarie University headed a team of scientists that tried to determine which one of the laws might be the culprit. The team studied black holes which have such a large gravitational pull that light cannot escape them. They also applied other physical laws such as the second law of thermodynamics, which essentially states that you cannot get something from nothing. This law would be violated if the charge on an electron had changed.

What implications would a change in the speed of light have on the study of physics and the world? According to Davies, many of the laws of the universe would be affected, such as the theory of relativity and E = mc2.

Some scientists believe that a change in the speed of light would only matter in the large scale structure of the universe and its origins. For example, one theory of the origin of the universe - the Big Bang - indicates that early on, the edges of the universe were spread out further than light could have traveled if the speed of light was constant. The findings of Webb, which indicate that the speed of light was once faster than it is now, seem to support this theory.



Activity
The question of whether or not the speed of light is constant has been debated for several years, with much of the information being presented in August of 2001. Research recent evidence for or against the speed of light being constant and present the information to your class. Include the possible affects that a change in this law would have in how science is taught.

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Physics: Principles and Problems