People say yes, and give a wonderful example of vacuum tubes, CRTs. But can we really say that vacuum (..as in space) is a good conductor of electricity in a very basic sense?
Answer
The conductivity of the vacuum is not a very trivial issue. In fact, depending on how you look at it, it behaves in two different ways.
Firstly, there is no retarding force on any charged particle with constant velocity in vacuum. To this extent, no extra work is required in maintaining a constant current through any surface in vacuum.
In stark contrast however, is the presence of free charges in conductors. Normally, when an electric field $\mathbf{E}$ is applied across a conductor, we get a current density due to the 'internal' charge flow, given by: $$\mathbf{J} = \sigma\mathbf{E}$$ where $\sigma$ is the conductivity. Clearly, $\sigma = 0$ in a vacuum - electric fields do not spontaneously cause currents to flow. Thus, in this sense, the vacuum is not a conductor at all. Even everyday insulators have low but non-zero values of $\sigma$.
Thus, the resistance of the vacuum is in fact, infinite, as long as we define resistance in terms of the response of the charge carriers of a material. In this sense, we might say that it is an insulator - there are no charge carriers.
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