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From this calculation (http://uk.answers.yahoo.com/question/index?qid=20080724101956AA4zed1), two protons seperated by the distance of one atom feel the electromagnetic force repelling them 1.239*10^36 stronger than the gravitational force attracting them.

This means that for gravity to be able to bring hydrogen atoms together to make stars, their overall charge must have to be PERFECTLY neutral. Is this level of symmetry surprising? Does it show protons and electrons were cut from the same cloth?


marked as duplicate by Qmechanic May 24 '16 at 13:07

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    $\begingroup$ You are assuming that the spill over electric fields of the Hydrogen atom would be repulsive, but the existence of H2 proves that they are attractive, so not to worry. $\endgroup$ – anna v Jan 22 '16 at 9:17
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    $\begingroup$ I'm not sure I understand your question. Fusion happens between nuclei, not atoms, they are therefore charged and not neutral. Moreover, temperature also has to play a role in this, as it has to be high enough for the kinetic energy to overcome the potential barrier due to coulomb repulsion between protons. $\endgroup$ – Dimitri Jan 22 '16 at 9:18
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    $\begingroup$ All of the universe is "cut from the same cloth", which is called the physical vacuum. The charge symmetry is one of the fundamental symmetries of the vacuum. Surprising? Only if you don't trust reality. Now, what would happen if the proton and the electron charge wouldn't be exactly the same? Then there would be more electrons in matter or more protons... it could still be neutral on average. $\endgroup$ – CuriousOne Jan 22 '16 at 9:22
  • $\begingroup$ @anna v, I wasassuming the hydrogen atom would be neutral, and therefore there would be be no attraction mediated by the electromagnetic force (therefore allowing gravity to do its work). However, you are saying there is an electromagnetic attraction even though their charge is neutral? $\endgroup$ – Amphibio Jan 22 '16 at 9:26
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    $\begingroup$ @Amphibio Yes, there are spill over fields, dipoles quadrupoles and higher moments. pa.msu.edu/~mmoore/Lect31_DipoleMoments.pdf . as I said, the existence of H2 means that there is an attractive mode. $\endgroup$ – anna v Jan 22 '16 at 10:28

The effects of gravity are really only observable to us on a macroscopic (large) scale. When a large enough number of (perfectly neutral) Hydrogen atoms come together they will gravitate towards each other. That sets things in motion for the Hydrogen to heat up. Once they reach a high enough temperature and density, they will ionize and the protons can approach each other close enough for the strong nuclear force to act. This force is approx. 2000 times stronger than the coulomb repulsion between the protons. Even with conditions found in our sun, the reaction rate for forming Deuterium is only about 5 * 10^(-18)/sec per proton. What keeps our sun radiating is the enormous number of reacting protons, on the order of 10^56, making the total reaction rate of the order of 10^38/sec. What’s astonishing to me is that the weakest force, gravity, can crush these particles together and create stars, neutron stars and even black holes.


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