Evolution in the Fine Structure Constant?: The Results

The measured change in the fine structure constant is 1 part in 100,000 over 10 billions years.

Figure 1. The measured fractional change in the fine structure constant, alpha=e^2/hc, is plotted as a function of fractional look-back time (0=present day, 1=beginning of time). The corresponding cosmological redshift is shown along the top axis. The blue data show the results of hydrogen 21-cm absorption lines (using radio telescopes). The red data point show the results of the standard "alkali-doublet" method. The black data points show the new "many-multiplet" method developed for this work. This latter method provides an order of magnitude increase in the precision. There is now evidence that the constant evolves one part in 100,000 over the last 10 billion (or so) years. It may be that the the "constant" is slightly increasing with cosmic time.

The Experiment

Brief descriptions and simple graphics are used to explain the experimental methods and analysis

• In Brief: The Nuts and Bolts
  
• What are Quasar Absorption Lines?
  
• Mapping Cosmic Time with Absorption Lines
  
• What are we Measuring?: Line Shifts and Fine Structure Evolution
  
• Examples of the Line Shifts
  

Further Information on Fine Structure

A few external links to basic information on physical constants are provided for the layman

• Introduction to the Fundamental Physical Constants | Fine Structure
• What is the Fine Structure Constant?
• Physics Today: Adjusting the Values of Fundamental Constants
  

News Paper Articles/Features

A repository of on-line news articles (not exhaustive; some may require registration)

• New York Times Week in Review: Suddenly, The Cosmos Becomes More Fickle (8/29/01)
  
• Philidelphia Inquirer: As Constant as the Stars? (8/27/01)*
  
• Washington Post: Challenge to a "Constant" Shakes Modern Physics (8/19/01)*
  
• Sydney Morning Herald: Electric Shock for World of Physics (8/16/01)
  
• USA Today: Speed of Light May Not have Benn Constant After All (8/15/01)
  
• New York Times: Cosmic Laws Like Speed of Light Might Be Changing, A Study Finds (8/15/01)*
  
  * Penn State mentioned in article

Radio Shows/Interviews

A repository of on-line radio interviews with CBC and NPR (Real Time Audio links provided)

• The Diane Rehm Show (Syndicated; NPR) | Download and Listen (Real Audio) (8/27/01)*
  
• NPR's Science Friday with Ira Flatow | Alternative Page | Download and Listen (Real Audio) (8/24/01)*
  
• Canadian Broadcasting Coorporation's (CBC) As It Happens | Download and Listen (Real Audio) (8/15/01)*
  
• ABC Latenight | Downlaod and Listen (Real Audio) (8/8/01)
  
  * Penn State mentioned

Magazine/Popular Articles

A repository of on-line popular articles (not exhaustive)

• Sky & Telescope News: New Physics from Ancient Quasars (8/27/01)*
  
• SPACE.com: Speed of Light, Other Constants May Change (8/15/01)*
  
• Scientific American Keck Telescope Reveals Inconsistent Constant
• New Scientist: Light May Have Slowed Down (8/15/01)
  
• Nature: Fundamental Constant Swells (8/14/01)*
  
• Physical Review Focus: A Constant that Isn't Constant (8/9/01)*
  
• Nature- Research Highlights: Inconstant Constant (8/901)* may require free on-line registration
  
• American Institute of Physics, News Update: Is the Fine Structure Constant Changing? (1/13/99)
  
• Scientific American Article (10/12/98)*
  
• New Scientist Editorial (3/28/99)
  
• New Scientist Article (3/28/99)*
  

Scientific Papers

A repository of our team's data/analysis papers

• Further Evidence for Cosmological Evolution of the Fine Structure Constant
  (Webb et al. 2001, Phys. Rev. Lett., 87, 091301)
• Possible Evidence for a Variable Fine Structure Constant from QSO Absorber Lines: Motivations, Analysis, and Results
  (Murphy et al. 2001, MNRAS, in press)
• Possible Evidence for a Variable Fine Structure Constant from QSO Absorber Lines: Systematic Errors
  (Murphy et al. 2001, MNRAS, in press)
• A Search for Time Variation int he Fine Structure Constant
  (Webb et al. 1999, Phys. Rev. Lett., 82, 884)

Other Selected Publications (non-exhaustive)