How Is Energy Density High Enough

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I’m hoping someone can explain something that’s puzzling me.

In Big Bang Never Happened there is a chart that is titled “The Evolution Of The Universe”. In that chart it shows in the center of a star the maximum power density, in terms of ERG/SECxCM^2 is 1,000. Yet the energy density of a mammal is 30,000, or 30 times greater.

Elsewhere as I recall the energy output of the sun was on the order of 100 watts per cubic meter in the core of the sun.

What I can’t figure out is here in the core of the sun we’ve got all this fuel (hydrogen), it’s at very high temperature (millions of degrees) and it is very highly compressed. Why is the energy density so low then?

And how can we hope to get a greater energy density here on earth?

About the best guess I can come up with is in the core of the sun nucleii are constantly fusing and releasing energy, yet at the same time they’re splitting apart and consuming energy, and that the equilibrium condition is with a very small net outflow of energy combined with a very slow increase in the density of the fused nucleii.

But that doesn’t make sense. When hydrogen burns out and there is only helium, and the core contracts, and now helium starts to fuse at higher temperature, why wouldn’t it all rip apart back into hydrogen?

Anyway I’m hoping someone can explain this to me. Thanks.

-Dave

[Lerner]

The difference is fuel and temperature. The sun uses pure hydrogen–that’s a great fuel if you want something to burn nice and slow for 10 billion years. But on Earth, we need energy a lot quciker, so we use fuels that burn much quicker. Second, the temperature in the center of the sun is 10 million degrees.Tokamak are at 400 million degrees and focus fusion is at billions of degrees.

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Lerner wrote: The difference is fuel and temperature. The sun uses pure hydrogen–that’s a great fuel if you want something to burn nice and slow for 10 billion years. But on Earth, we need energy a lot quciker, so we use fuels that burn much quicker. Second, the temperature in the center of the sun is 10 million degrees.Tokamak are at 400 million degrees and focus fusion is at billions of degrees.

Thanks — that makes a lot of sense. I guess my intuition as to how hot it is inside the sun was the problem. It’s relatively cool in there, so the rate of fusion is actually much lower. Your answer explains why H-Bombs work also, they are probably highly concentrated deuterium or tritium which fuse much faster.

-Dave

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