ZPEnergy.com - 'RELATIVITY' SPEAKING

"If you want to assume something, fine. But just don't say Einstein assumed it also."

Ralph Baierlein, a professor in the Department of Physics and Astronomy at Northern Arizona University, believes that it is past time to address some common misconceptions about special relativity, and clear the air about an assumption that has been credited to famous physicist and theorist Albert Einstein.

Full story at http://www.physorg.com/news11829.html

In a piece published in the March issue of the American Journal of Physics, Baierlein addresses two of these misconceptions in a way that he hopes will help change the way young physicists are taught the theory of special relativity. “I’ve been teaching relativity theory for 40 years,” he says, “and it seemed like a good time to set things straight.”

Basically, the theory of special relativity addresses perceptions experienced in different frames of reference. For example, two observers in one frame of reference might agree that events at two separate locations took place at the same time. Even if the events took place in locations far apart, it is still possible to agree on the simultaneity of the events when observers are in the same frame of reference. However, someone in a different frame of reference would typically observe a different time interval. Perhaps the third observer, in a reference frame moving even at a snail’s pace difference, would say that the two events took place ten minutes apart, rather than at the same time. The observations made are relative to the particular frame of reference that one is in.

“People in two different frames of reference will typically not agree on whether the events happened at the same time,” Baierlein explains to PhysOrg.com. “The time interval between the events is changed, no matter how slowly one frame is moving in relation to the other. And by making the spatial separation large in the first frame, I can make the temporal separation in the second frame as big as I wish.”

The first misconception Baierlein addresses is the idea that as the difference in the relative speed of reference frames decreases, it is possible to cancel out the idea of perceptual relativity. Many are taught that if the difference in the speed of the reference frames is small enough, then whether or not two events happen at the same time no longer becomes a matter of perceptual difference. But, as his American Journal of Physics article indicates, it doesn’t matter how small the ratio of velocity to the speed of light. As long as the ratio is not zero, simultaneity is relative, and our third observer will typically never view the two events as taking place at exactly the same time.

Baierlein’s second point concerns the speed of light. The problem with the current idea of “the constancy of the speed of light” stems from a misunderstanding of the way the phrase was used in Einstein’s day and the way it is used now. “Very often the assumption is made that a given burst of light will have the same speed in all frames of reference.” While this is true with regard to how the phrase is viewed today, in Einstein’s day the phrase meant something different. Baierlein’s piece points out that when Einstein was working on the theory of special relativity, the phrase “the constancy of the speed of light” meant that the velocity at which a light source is moving has no bearing on the speed of the light that emanates from the source. The speed of light is constant, regardless of how fast or slow its source happens to be moving...

Full story at http://www.physorg.com/news11829.html