The Weight of the World

Here is a theoretical question with which to short circuit your children’s brains (or your own).
If half of the Earth’s population (Say 3 billion people) each lost 10 pounds, would our planet weigh 60 billion pounds less? In other words, is the weight of the world constant, or can it be changed?

“A fundamental principle of classical physics is the law of conservation of mass, which states that matter cannot be created or destroyed. This law holds true in chemical reactions but is modified in cases where atoms disintegrate and matter is converted to energy or energy is converted to matter.”
Microsoft® Encarta® Encyclopedia 2003. © 1993-2002 Microsoft Corporation. All rights reserved.

When we build skyscrapers or pave half of our cities with asphalt, all of the materials that we use come from the earth at some point. We are essentially creating no new matter. The entire water supply on the planet is constantly being recycled, but not added to or subtracted from.
Similarly, when we plant grain for the purpose of producing more grain or a baby grows from an embryo to a 40 year old adult, new matter is not being created, although at first glance, you’d think so. Living things reproduce tissue or reproduce themselves by converting one form of matter, water and nutrients already in existence, into another form of matter, new cells. So, in all these things, we are affecting the globe, but not its weight.

One exception to the law of the conservation of mass stated above (or should I say modification?), is when energy is converted to matter. Then your talking about the theory of relativity, E=mc2, and reactions taking place on the particulate level and very quickly you get way beyond me. However, I think I understand it enough to say that it probably isn’t going to affect the weight of the world.

When we exercise, however, we convert matter (our fat) into energy (or modification #2). Energy weighs nothing. At least I assume it weighs nothing. If enough weight was “lost” would you be able to measure the change if you had a scale big enough?

By the “weigh”, the Earth weighs 6 x 1024 kilograms. Roughly.

Now for the answer, and, Yes, I had to look it up. The weight of the earth and its gravitational pull, my weight and my gravity and that of everyone else all interact and affect each other. Weight really is more about gravity and mass, than, well…weight. If everyone on the planet got in spaceships and left, the affect would be almost unnoticeable. The total mass and gravity of humans, all six-point-something-billion of us, is insignificant compared to the Earth. And the Earth is rather insignificant in the grand scheme of this galaxy. And the Milky Way Galaxy is insignificant in the grand scheme of the Universe. Feel small yet?
God chose to love you and me and sent his only Son for us in spite of our insignificance. What’s more, he created us in His image. How’s that for a quick pick-me-up?

*originally written 3/18/06