Particularly, what does it mean when you say "I love you to the moon and back"?

I'm sure most of us have heard or even used the phrase "to the moon and back." I love you to the moon and back! I used the phrase, "to the moon and never back," in the acknowledgment section of my undergraduate thesis just to be different, because I'm weird like that. But what does it mean, really?

A measurement

"To the moon and back" is considered a measurement of distance. Going to the moon and going back to the Earth takes a whole lot of distance (more than 400 thousands of miles); and when I say a lot, I mean a lot.

So basically saying "I love you to the moon and back" is equivalent to saying "I love you. A lot."

The farthest a human has ever gone to is the moon. An interesting theory to this is that when you tell a person "to the moon and back," you're basically telling them that you're willing to be with them even to the farthest place a human has ever gone to.

A lifetime

Of all things about this phrase that I've read so far, this one had to be the most interesting:

A human may live up to 70 years. Sometimes more. In one year, the human heart generates enough energy to drive a truck 7,300 miles (20 miles per day). If we consider the lifetime of a human to be 70 years, then our heart generates energy enough to drive a truck 511,000 miles.

Consider this:

20 miles × (365 days/1 year) × 70 years = 511,000 miles

The distance of the Earth from the moon is 384,400 km, which is approximately 238,855 miles. To the moon and back to earth,

238,855 miles × 2 = 477,710 miles

Therefore, when you say you love a person to the moon and back, you love this person with all the blood your heart has pumped... your entire life. And some more.

Of course, some reasons (arguments, really) why these calculations are believable or unbelievable exist. (Try to read it, it's an interesting read. However, if you hate geeky maths and arguments, then...)