November 1, 2011 Issue

Physics To Go 118 - Special relativity

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Physics in Your World

Relativity Powers Your Car Battery image
image credit: Shaddack, Wikimedia Commons;  image source; larger image

Relativity Powers Your Car Battery

If you own a car with a lead-acid battery, you might be interested to know that 80% of the voltage comes from Einstein's theory of special relativity. Lead works so well in storage batteries because its atom has a large nucleus, and the innermost electrons rotate at a significant fraction of the speed of light, bringing relativity into play. To learn more, visit this American Physical Society site.

(This feature was updated on March 3, 2014.)

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Physics at Home

Time Traveler

Try these two activities showing how special relativity affects time during space travel:
-- NOVA's Time Traveler, in which the traveling twin ages less than the state-at-home twin
-- the Exploratorium's Voyage to Epsilon Eridani 3 on how the time of a journey is measured differently by the traveler than by someone who stays at home.


From Physics Research

Time Flies image
image credit: André Karwath, Creative Commons; image source; second image courtesy of NPL

Time Flies

Einstein's theory of special relativity says that a moving clock, when compared to a stationary clock, runs slow. And general relativity, his theory of gravity, says that the weaker the gravitational field, the faster a clock in that field runs. These predictions were tested in 1971 by flying atomic clocks around the world. Einstein's relativity theories correctly explained what happened.

To learn about a more accurate update to this experiment 25 years later, see Time Flies. Click on the image to see a photo of the atomic clocks in the updated experiment.

Worth a Look

Particles break light-speed limit

You may have heard the shocking news that an experiment at an Italian laboratory found the speed of a neutrino beam to be slightly greater than the speed of light. This directly violates special relativity, which predicts that no particle can move faster than the speed of light (please note that the "speed of light" referred to here is the speed of light in a vacuum). To learn more about this experimental result, see Particles break light-speed limit.

Update: It turns out that the neutrinos observed in this experiment were not going faster than light after all. As you can read in this short Science Magazine article, the error in the measurement was due to a loose cable connection.

(This feature was updated on September 21, 2013.)

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