Fanghur Posted October 31, 2009 Posted October 31, 2009 I was watching a documentary show on the History channel talking about the Sun and it said that nuclear fusion is the only thing known to man that could power the sun. Now I'm not saying that I don't think this is true; but I'm just wondering if we actually have definitive proof that it it fusion that powers it or is that just the only explanation that makes sense? P.S. I do think that nuclear fusion is the explanation; I'm just wondering if it's been proven.
ydoaPs Posted October 31, 2009 Posted October 31, 2009 (edited) I was watching a documentary show on the History channel talking about the Sun and it said that nuclear fusion is the only thing known to man that could power the sun. Now I'm not saying that I don't think this is true; but I'm just wondering if we actually have definitive proof that it it fusion that powers it or is that just the only explanation that makes sense? P.S. I do think that nuclear fusion is the explanation; I'm just wondering if it's been proven. It's just a theory in the same sense that gravity is just a theory or evolution is just a theory. Absolute proof is only in the realm of logic and mathematics. In science, theory has a specific meaning. It isn't a wild guess. What science does is collect data to provide more supporting evidence for the theory. That's really not quite true, actually; science tries to collect data to prove the current theory wrong! Through this process we limit the uncertainty. Yes, there is overwhelming evidence to support fusion in stars. Yes it is the only current explanation that co-insides with the evidence we have. Edited October 31, 2009 by ydoaPs
ajb Posted October 31, 2009 Posted October 31, 2009 It was Sir Arthur Eddington in 1920 who first suggested that the Sun was "burning" hydrogen to produce Helium + energy. The first proof I believe came from solar neutrinos. The Sun produces lot of neutrinos whose origin is the nuclear burning. However, there were far fewer detected that expected. This was the famous solar neutrino problem. This lead to a modification of the standard model of particle physics to include neutrino oscillation. In short, the detection of neutrinos from the Sun prove fusion is at work and the details led to new physics. See "How the Sun Shines" on the Nobel prize website.
ydoaPs Posted October 31, 2009 Posted October 31, 2009 See "How the Sun Shines" on the Nobel prize website. Why does the sun shine? 3JdWlSF195Y Why does the sun REALLY shine? sLkGSV9WDMA 1
gre Posted October 31, 2009 Posted October 31, 2009 (edited) A little off topic, but can pressure alone cause nuclear reactions? How much pressure is required to fuse Hydrogen atoms? edit: Two deuterium atoms rather. Edited October 31, 2009 by gre
Fuzzwood Posted October 31, 2009 Posted October 31, 2009 Pressure is needed for proximity. Heat is needed for the actual kinetic energy needed for collisions leading to fusion.
ydoaPs Posted October 31, 2009 Posted October 31, 2009 A little off topic, but can pressure alone cause nuclear reactions? How much pressure is required to fuse Hydrogen atoms? A lot. You have to be able to fight the electrostatic repulsion long enough to get past the coulomb barrier. As you can see, when you get closer, the electrostatic repulsion dramatically increases(see coulomb's law) until you reach the barrier and the nuclear force kicks in rapidly making the two particles a bound system. I don't only know how to tear atoms apart, but I know how to mash them together too!
gre Posted October 31, 2009 Posted October 31, 2009 How could you calculate a specific pressure between two D atoms? Is there a cetain distance that will cause two deuterium nucleui fuse and make He, if pushed together? I have a feeling this can occur without an external heat source.
ydoaPs Posted October 31, 2009 Posted October 31, 2009 Is there a cetain distance that will cause two deuterium nucleui fuse and make He, if pushed together? I have a feeling this can occur without an external heat source. Yes. The graph above is potential vs distance. The peak is what is called the coulomb barrier. You just have to get them closer than that.
Mr Skeptic Posted October 31, 2009 Posted October 31, 2009 Wow, that is sharp. I would have expected it to be a little smoother, with the strong force partially canceling the electrostatic repulsion over some interval. I don't think that graph tells us the pressure needed to get fusion at cold temperatures, but I guess it would give the energy required to compress it? Anyhow, getting fusion via compression seems like a recipe for a supernova (the fusion would increase temperature and therefore pressure and cause a shockwave of fusion?).
ydoaPs Posted October 31, 2009 Posted October 31, 2009 Anyhow, getting fusion via compression seems like a recipe for a supernova Or a star in general.
Mr Skeptic Posted October 31, 2009 Posted October 31, 2009 Or a star in general. Nope, a star also has heat. Yes, I know the heat is due to compression. But the point is that it will be in equilibrium, with the heat from fusion preventing further compression. But say if you have a star forming very slowly so that it has time to cool before adding more mass, then when fusion starts it would not be in equilibrium. Or so I would think.
ydoaPs Posted October 31, 2009 Posted October 31, 2009 Nope, a star also has heat. Heat that comes from........compression! Yes, I know the heat is due to compression.But the point is that it will be in equilibrium, with the heat from fusion preventing further compression. But say if you have a star forming very slowly so that it has time to cool before adding more mass, then when fusion starts it would not be in equilibrium. Or so I would think.If the fusion from the star didn't start with pressure due to gravity, how did it start?
John Cuthber Posted November 1, 2009 Posted November 1, 2009 I don't know because I wasn't there at the time but I think it might have been started with a combination of heat and pressure. A meteor falling to earth gets hot as it travels through the air. The energy to heat it comes from its kinetic energy and that, in turn, comes from gravitational potential energy. Imagine a big lump of rock in space. Things would be atracted to it by gravity- they would crash into it and warm it up slightly. Imagine that process carrying on until you had a star's worth of material. I think it would be pretty hot before any nuclear reaction started.
Severian Posted November 2, 2009 Posted November 2, 2009 I think once a theory has evidence which has reached a 5 standard deviation significance, we should regard it as fact.
bascule Posted November 2, 2009 Posted November 2, 2009 I was watching a documentary show on the History channel talking about the Sun and it said that nuclear fusion is the only thing known to man that could power the sun. Now I'm not saying that I don't think this is true; but I'm just wondering if we actually have definitive proof that it it fusion that powers it or is that just the only explanation that makes sense? P.S. I do think that nuclear fusion is the explanation; I'm just wondering if it's been proven. If you were watching History's The Universe they gave extensive information about how fusion reactions in the sun actually work.
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