2 of 36

Relative

Write now Article Tools

Page 2 of 6

tubes need to be pointed, not at the star itself, but, rather, its "image." Indeed, the raises the thorny specter of scientific induction, but even if you can only catch the football in your own end zone, you're still going to have to make a run for it.

For embedded in this observation is a really useful and satisfactory theory of EVERYTHING. That is, if the speed of light is truly independent of the motion of the emitter, then it must transmit through space the same way that sound transmits through the air.

This means there must be some super-thin ultra-refined medium permeating all of space. Its eddies and whirlpools are responsible for magnetism and electricity, its pressure against the surface of the Earth would be a pretty good explanation for gravity, and organized ripples through it must surely be the mechanism for the transport of light. Good theory! No one check, though! We're sure it's right! Honest!

But in the 1880s, two scientists, Albert Abraham Michelson and Edward W. Morley, went looking for it.

Michelson, the son of German immigrants, was an Annapolis graduate recognized as a brilliant instrument builder, his specialty being optics. While an instructor at the U.S. Naval Academy between 1875-79, Michelson used a spindle of rotating mirrors to measure the terrestrial speed of light.

Now that I've hooked you with the gee-wiz element of the narrative, let's backtrack to pick up a crucial, however nerdly, bit of information.

In the 1830-40s, engineers were encountering signal loss in telegraph cables. The longer the line, the worse the problem got. When they started studying submarine cable telegraphy, the problems seemed insurmountable. They needed to nail down the electrical characteristics of the system, ALL of them. They already knew that the electrical field set up in a wire at an appreciable fraction of light. And, by this time, they knew the speed of light through space with great accuracy. The question is, what is its speed on Earth?

It fell to a Parisian, Louis Fizeau, to carry out a clever way of measuring it in 1849. His apparatus was basic, simple, and easy to describe, and remains the basic paradigm of very fast signal detection and measurement equipment. So it is best to review the experiment here:

Fizeau used a toothed wheel with 720 notches capable of rapid uniform (but variable) rotation, attached to a tachometer. Behind the wheel was a light source aimed at a mirror 8.6 km away on a hill in Monmarte. When the wheel spun, a pulse of light

• << previous page
• 1
• 2
• 3
• 4
• 5
• 6
• next page >>

Add your voice

Know something about Is time real or relative??
We want to hear your view. Write now!