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On the large scale, gravity is much stronger than electromagnetic force. But in what cases was the electromagnetic force stronger than gravity on the large scale i.e. objects of the size of the Earth, Moon, Sun, etc? Put in another way, what are the largest objects ever to experience an electromagnetic force stronger than the gravitational force?

BTW, this question was inspired by What is the smallest item for which gravity has been recorded or observed?

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  • $\begingroup$ On Earth? Mag-lev trains I suppose, but that is a boring answer because it is an engineering answer and something could be built bigger if desired. $\endgroup$ – dmckee --- ex-moderator kitten Nov 3 '15 at 3:34
  • $\begingroup$ @dmckee no, objects the size of earth! $\endgroup$ – TanMath Nov 3 '15 at 3:45
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It is not obvious that, say, two charged neutron stars cannot interact with Coulomb forces larger than gravitational forces. For example, authors of article http://www.if.ufrgs.br/hadrons/MMalheiro.pdf consider charged stars and note: "If these highly charged compact stars exist, they need to be isolated systems since outside the star, the Coulomb force will overwhelm the gravitational one."

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    $\begingroup$ How exactly would a highly charged neutron star even form? $\endgroup$ – Emilio Pisanty Nov 12 '15 at 0:54
  • $\begingroup$ @EmilioPisanty: The mechanism is discussed, say, in the first two paragraphs of the introduction of the article I quote. I am not quite sure this mechanism is correct, but it is not obvious that it is incorrect:-) $\endgroup$ – akhmeteli Nov 12 '15 at 3:24
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The problem with large charged objects is that they quickly neutralize themselves; for instance, the most massive charged objects that theoretically exist are charged black holes which obey something called the Reissner–Nordström metric. However, as the universe is neutral, and the electromagnetic force is very strong compared to the gravitational force, these black holes quickly neutralize themselves and we effectively never see them. Also taking into account that charged objects the size of planets as you ask must necessarily be extremely far away, it becomes difficult to measure the charges of such objects (especially when compared to measuring their masses).

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