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This question (What is the capacitance between the Earth and Moon?) on EESE makes me wonder: How can a vacuum have a breakdown voltage?

If electrons can find the shortest path through a vacuum, how is that possible? With nothing to carry the charge, I can't understand how the charge can traverse a vacuum.

The value for dielectric strength of a vacuum comes from Wikipedia

Community
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David Wilkins
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The electrons (torn from one surface (electrode) through, say, electron field emission, just move in vacuum in electric field to the other surface (electrode).

akhmeteli
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    To what extent is this a property of the vacuum, rather than a property of the work function of the electrode surfaces? – rob May 23 '14 at 19:47
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    I'd say the surfaces play the leading role, the vacuum's role being rather passive (the electrons do move in vacuum, and the electric field exists in vacuum). – akhmeteli May 23 '14 at 20:42
  • The above is true for an electric field of reasonable strength and for a relatively long vacuum gap, when vacuum polarization is not important. – akhmeteli May 23 '14 at 20:47
  • I thought electromagnetic fields might have something to do with it, thanks. – David Wilkins May 23 '14 at 23:58