Sept. 18, 2008 -- About seven billion years ago, the universe went into a sort of pubescent growth spurt that as far we know hasn't slowed down. Scientists call the growth stimulus dark energy, for lack of a better term or an understanding of the mechanics. Now they've invented a tool called a laser comb that can measure expansion rates over time periods as short as 10 to 20 years. Ronald Walsworth, with the Harvard-Smithsonian Center for Astrophysics, offers this as an example: Say you want to figure out if something big, like your house, has moved a millimeter. If you counted on a measuring stick that chalked off miles, you'd never know. But if you had a ruler nicely hashed out by the millimeter, it'd be a cinch. Laser combs refine the technique of spectroscopy, a process that picks apart a photon's journey from its source to our telescopes by identifying what chemicals it has passed through. The fingerprints emerge by splitting the light into component wavelengths and comparing absorption lines in its spectrum with the wavelengths of laboratory sources. The laser combs take a target's light signature one step further. If you've ever sat at a railroad stop and heard the train whistle, you know how it changes pitch as it comes closer or as it recedes down the tracks. The same shift takes place not only in sound waves, but in all wavelengths, including visible and ultraviolet light. As the universe expands, distant galaxies, which are used to chart the universe's motion, move further away from Earth, with a corresponding shift in their spectra. Current tools to measure the shift would be like using the mile-marker to tag your house's re-location. |
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