[emailking]

What causes the internal temperature of the Sun if not gravity?

I still need some more convincing on this subject. The Sun's mass is always pushing the H atoms together, sustaining the reaction. I don't know if that's possible to do here on Earth. Granted there's energy in matter, that's e=mc[sup]2[/sup], but how do you continually feed matter into the reaction at the temperature and pressure needed to keep the fusion reaction going?

Hmm... maybe that's what ITER is going to find out?

Again, it's nuclear fusion that maintains the temperature, not gravity.

The H atoms are not being "pushed" together by gravity. Nuclear fusion happens because the temperature gives enough atoms enough speed and enough energy for certain three atom collisions to be likely enough to sustain a macroscopic fusion reaction. The fusion reaction produces vast quantities of energy in the form of electromagnetic radiation. This radiation interacts continuously with the particles present (it takes on average about a million years for a photon to escape the sun) maintaining the overall temperature.

Gravity did get things started in some sense. Stars start out as gigantic clouds of hydrogen which contract due to gravity. Eventually, the density gets so great that a fusion reaction does start, which provides the outward pressure to keep the cloud from collapsing any further. This is then a star. Gravity doesn't play a role after this, other than to keep the star from blowing apart due to the fusion reaction. It will have its day again when the star runs out of fuel to burn.

[joewp]

Isn't gravity playing the role of the "containment vessel" then? It's keeping the atoms close enough together to keep the temperature and pressure high enough to maintain the fusion reaction.

Just wondering, since it seems like this is one problem homo sapiens isn't going to solve, and it's probably a good thing we won't be able to, IMHO.

[emailking]

Isn't gravity playing the role of the "containment vessel" then? It's keeping the atoms close enough together to keep the temperature and pressure high enough to maintain the fusion reaction.

Just wondering, since it seems like this is one problem homo sapiens isn't going to solve, and it's probably a good thing we won't be able to, IMHO.

"So if gravity is what causes nuclear fusion, it looks like the gravity you put in should be equal to the radiation you get out of nuclear fusion. "

Your initial quote here and subsequent comment about gravity "pushing" the H atoms together indicated an apparent misunderstanding of what is happening. Gravity is not the energy generator, the driving force, or even the cause but merely the "containment vessel" as you say. I thought it was appropriate to clarify. Certainly the the whole picture makes it seem very difficult to conceive how we as humans can get around the problems involved.