Lose weight in a slow and incredibly difficult way

Lose weight in a slow and incredibly difficult way

This seems simple enough. Your weight comes from the Earth’s gravity pulling you down. Earth’s gravity comes from its mass. Less mass should mean less gravity. Remove the mass from the Earth and you will lose weight.

You decide to try.

Removing a lot of mass from the Earth will require a lot of energy, so start by seizing the entire planet’s oil reserves.

You process the oil into fuel and use it to launch several hundred billion tons of rock into orbit. This removes an average of 0.2 mm of rock from the Earth’s surface. Jump on the scale.

Okay, it didn’t work. But that makes sense; a few hundred billion tons is a small fraction of the Earth’s mass.

Burning Earth’s other fossil fuels helps a bit—especially coal, which is quite a lot—and allows you to remove nearly a millimeter from the Earth’s surface.* Return to the ladder.

Damn it.

You need more energy.

You cover the entire planet with highly efficient solar panels and spend a year absorbing all the sunlight that hits Earth and using it to power your rock launchers. Humanity lives in the shadows beneath your panels. People are probably pretty mad at you right now.

A year of sunlight will give you enough energy to remove nearly 100 trillion tons of rock – a few centimeters from the planet’s surface. Unfortunately, this is not enough.

Clearly, this incremental approach is not working.

You need more power. Instead of capturing only a small fraction of the sun’s energy that hits Earth, you decide to capture all of its energy by building an energy-harvesting enclosure around it—a Dyson sphere. Once you’ve harnessed the entire output of the sun, you have enough energy to start moving away from the Earth’s surface much faster.

Earth’s rocks get hotter the deeper you go. After you remove a few hundred meters from the crust, people start to notice that the earth is warming. By the time you move a kilometer away from the rock, the surface is up to 40 degrees Celsius. It might feel good when you get out of bed on a cold morning, but it will make your life quite uncomfortable. Also, since you removed the tops of the various hotspots, all the volcanoes in the world would erupt.

You check the scale.

Damn it.

You use your Dyson sphere to remove more rock. You have now removed a layer of 5 kilometers, which takes about 20 minutes. (For good measure, spend a few more minutes removing the oceans.) Earth is no longer remotely habitable. Thanks to the magma exposed beneath the Yellowstone supervolcano, northwestern Wyoming is a lava lake. In most places, the earth is hot enough to boil water and light fire.

Try the scale again.

That’s fine, just remove more rock, maybe with some sort of solar powered vegetable peeler.

Cut through 20 kilometers of crust, which exposes the Earth’s mantle over much of the former sea floor.

Well, no one ever said lose weight easily. You remove another 20 kilometers, removing layers of molten mantle and pockets of deep crust.

Continue. After four hours of work with the planet peeler, you’ve removed 60 kilometers of mostly molten rock. When you step on the scale, you finally see a change.

You have a pound heavier.

How could this be?

If the Earth had a uniform density, removing the layers would make you lighter. But our planet gets denser the deeper you go, and density cancels out mass loss. The planet gets a little lighter as you move away from the surface, but you also get closer to that dense core. The net effect is that removing the outer layer of the Earth causes its surface gravity to be stronger.

Gravity continues to increase as you go deeper. It only levels off after you’ve shaved off about 3,000 kilometers, halving Earth’s diameter and ejecting two-thirds of its mass. (This takes the solar-powered planet peeler about a week.) Your weight peaks at about 207 pounds, after which it begins to decrease as you begin to remove the denser outer core.

Once you’ve removed 3,450 kilometers of rock, your weight returns to what it was when you started. After 3,750 miles of rock, you finally reach your goal of losing 20 pounds. At this point, you have removed 85% of the Earth’s mass. But you lost weight!

This plan has some flaws. It destroys the Earth, yes, but it’s also pointlessly ineffective. There is a much easier way to reduce the Earth’s gravitational pull on you without changing your mass or leaving the surface.

A spherical shell of matter exerts no gravitational force on objects within it, meaning that if you go underground, the layers of rock above you no longer contribute to your weight. From a gravitational point of view, it seems to disappear. You didn’t actually have to remove the mass from the Earth, you just had to go under it. You could have avoided all this work with a relatively simple tunnel.

Did you even avoid movement? A kind of. Your project ended up requiring you to do a lot of work. Removing the Earth’s surface required 5 x 1028 calories of energy, that is, more calories than would be burned if the entire human population started doing vigorous exercise 24 hours a day from now until the sun has burned out and its remains have cooled to room temperature.

If your goal was to avoid work, you couldn’t have failed worse.

Randall Munroe is the author of the #1 book New York Times The best sellers And if? and The explainer of things, the science Q&A blog What If, and the popular webcomic xkcd. A former NASA roboticist, he left the agency in 2006 to draw web comics full-time. He lives in Massachusetts.

Extracted from And if? 2 by Randall Munroe. Copyright © 2022 by Randall Munroe. Excerpted with permission from Riverhead, an imprint and division of Penguin Random House LLC, New York. All rights reserved. No part of this excerpt may be reproduced or reprinted without the written permission of the publisher.

* People might complain, but besides, that millimeter probably includes all the dirt and grime on the floor. Maybe you can spin it as a free cleanup.

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