Science Memes

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submitted 1 day ago by [email protected] to c/[email protected]

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[–] [email protected] 27 points 1 day ago* (last edited 1 day ago) (1 children)

Not dietal calories.

The calorie numbers we assign to food, measure how much energy our body extracts from them when eaten.

In this context, plutonium is closer to 0

If we instead want to measure the actual total physical energy content of materia, we would turn to E=mc^2, telling us that a gram of anything has about 20 million kcal, no matter if its plutonium or diet coke. which is a slightly less useful value on food labels :D

[–] [email protected] 20 points 1 day ago* (last edited 1 day ago) (1 children)

Technically it measures how much you can heat up a known volume of water if you burn the food. We have no way of measuring how much of that energy released by combustion actually gets absorbed and translated to ATP in the body, but it’s the best estimation we have of the relative energy content of foods.

There’s some carbohydrates, proteins, and fats that our bodies don’t seem to convert to energy (or only partially convert) but still technically contain “calories” because they’re combustible. Sugar alcohols, fiber, etc.

Plutonium doesn’t combust, but it would heat up water in a calorimeter. Really the test method’s applicability kind of falls apart when you start testing undigestible materials.

[–] [email protected] 4 points 13 hours ago (2 children)

Plutonium actually does combust^1^. Even worse, it's pyrophoric^2^. I couldn't easily find kcal/g though.

^1^ Whoopie
^2^ Not a great source

[–] [email protected] 6 points 13 hours ago* (last edited 13 hours ago)

I did a little digging. The heat of decay (so plutonium 238 just sitting around, not burning) is about .48 kcal/hr per gram. So if we were able to convert that energy to ATP like we do carbohydrates, eating about 300g of plutonium would be like eating a twinkie (150kcal) every hour. In about 88 years the energy output of that plutonium would have reduced to about a half-twinkie per hour.

Assuming you need 2000 kcal per day to maintain weight, that’s only 83 kcal per hour needed. So, if you could survive eating it and actually utilize the energy generated, you’d be set for life on food after eating less than 300g. We’d have to come up with a dosing schedule or you’d have to work out pretty hard as a young person to keep from getting fat.

The heat of combustion for plutonium based on a very cursory search (take it with a grain of salt) is about 1 kcal/g. So assuming your body could oxidize it, you’d get a one-time burst of about 2 twinkies worth of energy immediately upon eating that 300g.

[–] [email protected] 1 points 13 hours ago

Oh no!