I am new the the Astromony Cast forum, so let me first add to the chorus that the podcast is absolutely terrific. I look forward to each week's "episode" for the commute.

I have a question about the metaphor that everyone uses concerning the expanding universe -- that we are on the surface of the balloon.

So suppose I am on the surface and I take out my ruler and measure an object one foot away. To test this, I nail (OK tape, its a balloon after all) the ruler at point A and at point B. One foot. The balloon expands. Next time I look -- its still one foot. The balloon expanded, but so did the ruler. Relative to my world, on the surface of the balloon, the measurement did not change.

I think in the last episode Dr. Gay said that gravity and chemistry keep mass together while the universe expands around things. This is difficult to understand. It seems to be saying that "mass" exists independent of "space." That one can add "space" without making the mass any bigger.

Can someone explain this to a dense non-science type such as myself.