# Why there is electromagnetic resistivity in vacuum?

I cant understand that. If there isn't a material that makes it hard to pass, why there is a resistivity in vacuum?

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There is no resistivity in the vacuum (resistance would imply dissipation and nothing dissipates in the vacuum). There is only impedance. The impedance gives you the ratio of electric to magnetic field in an electromagnetic wave. This ration is dependent on the unit system chosen. In SI units it has the dimension of a resistance. You can choose other unit systems where it is just 1.

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