I have a question about zero reference. Let us assume the expansion of the universe is due to the expansion of space-time. The analogy I have heard is sort of an expanding foam to account for the faster expansion of the perimeter. Here is the question, if we assume our earth reference, within the middle of the expanding foam, is zero reference, does that imply the perimeter is heading toward negative reference? In other words, how can space-time continue to expand if it has already reach zero reference on earth. Does that mean we are not in zero reference?