this post was submitted on 03 Apr 2024
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Science Memes

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submitted 5 months ago by [email protected] to c/[email protected]
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[–] [email protected] 40 points 5 months ago (2 children)

http://www.jaygarmon.net/2010/09/according-to-einsteins-famous-equation.html?m=1

Apparently 21.5 billion calories per gram of matter

Not sure what this meme is getting at, then, since it seems to be significantly undercounting it

[–] [email protected] 36 points 5 months ago (3 children)

Meme is referring to nuclear reactors, not complete antimatter annihilation.

Nuclear reactors don't "burn" everything

most of the matter stays (this is what nuclear waste is). So you can only apply E=mc^2 to the difference in mass, not the mass of the fuel.

[–] [email protected] 15 points 5 months ago* (last edited 5 months ago) (1 children)

You know it's funny, technically a calorie is just a measure of how much energy it takes to heat up 1 gram of water 1° C I never really thought about it but it could totally be applied to other things and nuclear reactor plants that literally just heat up water to spin a turbine would be the perfect thing to measure in calories. So would regular electric plants for that matter. It might just be literally calories.

Oh shoot that would be some wild math to figure out how hungry they all are.

[–] [email protected] 6 points 5 months ago

Except that 1 gram of water is at 1 bar. Heating up 1 gram of water from 300°C to 301°C takes 1.38 calories.

[–] [email protected] 5 points 5 months ago (2 children)

Can they really get out THAT many calories from a gram of Uranium?! That's insane!

I wish I cared more and would verify it

[–] Voroxpete 9 points 5 months ago

Calories are just a measure of the energy released by a material.

Normally they're measured by burning the material, so it's not really accurate to say that you can get that many calories from uranium. On the other hand the whole concept is fucking stupid anyway, because it's measured by burning the material. Technically, a kilo of dry sawdust has 4800 calories (more than double the daily calorie requirement of the average person).

[–] [email protected] 3 points 5 months ago

I just googled around and I think the meme inflated the numbers. Fast neutron reactor gets 28GJ/g, which is "only" about 7 million food (kilo) calories.

[–] [email protected] 4 points 5 months ago* (last edited 5 months ago) (1 children)

The numbers don't add up. If you can get 21 billion US food calories from total annihilation (which I checked is right), you'd get nowhere near 18 billion food calories from a fusion reaction. Maybe it works if you assume "calories" for the fission reaction means metric calories, since US food calories are metric kilocalories.

I hate the way the word "calorie" ended up with two wildly different definitions.

[–] [email protected] 5 points 5 months ago (1 children)

Yeah, I looked up energy density assuming fast neutron reactor, and it's "only" 7 million US food calories.

[–] [email protected] 3 points 5 months ago

US calories are equal to the real metric unit of kilocalories. Maybe the meme above used real calories

[–] [email protected] 3 points 5 months ago (3 children)

I also think it’s an interesting choice to use uranium. Wouldn’t osmium be a better choice due to its increased density?

[–] [email protected] 8 points 5 months ago

I think more people know what uranium is. I, for one, had never heard of osmium until right now. Jokes are funnier if you don't have to explain them.

[–] [email protected] 6 points 5 months ago (1 children)

Picking a higher density of the material just means the one gram would occupy less volume, it doesn't affect how much energy that gram is equivalent to in terms of E=mc2. For that calculation, as the equation implies, only the mass matters; a gram of feathers is equivalent to the same amount of energy as a gram of lead for that equation. Now, this equation is in fact a simplified assumption; if you launch your feather at relativistic speed, then we're talking

[–] [email protected] 3 points 5 months ago* (last edited 5 months ago)

This is true. This is why I compared them using the fixed volume of one cubic centimeter rather than using something like specific gravity. The only thing that differs is the mass, which is of course, directly proportional to the energy.

[–] [email protected] 3 points 5 months ago (1 children)

How much more matter is in a gram of osmium than in a gram of uranium?

[–] [email protected] 2 points 5 months ago* (last edited 5 months ago)

Given that mass behaves the same regardless of what is providing that mass in a gravity field, I imagine it simply the ratio of the weights. I’m assuming NewtonIan physics here.

Osmium is 22.59 g/cm3.
Uranium is 19.1 g/cm3

I would therefore expect about 10% more energy if it was made of osmium, simply equating mass and energy here with the famous crazy-haired guy equation.