cable: "expansion means light may travel longer distance, that's all."

Ah, I think I understand. But the electromagnetic waves we call light have a wavelength, a finite, linear length. Some electromagnetic radiation has wavelengths of several hundred meters.

So, visualize this: take a large, flat rubber band and cut it so you have one long length of rubber. Take a permanent marker and make a 1-centimeter-long mark on the rubber band. Now, stretch the rubber to 2 times it's original length. Just as you wrote, the mark is now farther from the end of the rubber band--but the mark itself is also longer! It is, I predict, exactly 2 centimeters in length instead of 1.

Thus, in an analogous way, the wavelength of light is stretched as the space through which it travels stretches.

A couple of notes on this: First, the rubber band trick is an analogy; space is NOT made of rubber! When you stretch the rubber band it pulls back, and the tension on the band rises. That doesn't happen in the expansion of space. Second, one might ask, if a meteorite were traveling through empty space between the galaxies, would it stretch just like the light? But nay, nay! The meteor is held together by electromagnetic forces and, on the subatomic level, by the strong force. These forces completely overpower the 'stretching' effect of expanding space. But these forces do not hold the wavelength of electromagnetic waves--light, photons--against the expansion. The four forces known to physics do not oppose the stretching of light, and so only the light--and not things made of matter--stretches with the expansion of space.

And you were absolutely right in saying that the light, and the hypothetical meteorite, must travel farther to reach a distant galaxy as a result of the expansion of space.

<font size=-1>[ This Message was edited by: DStahl on 2003-02-18 19:51 ]</font>