>How would you measure a voltage without having any current flowing --
>i.e. without relocating some charge carriers?

You can't without relocating any charge carriers, so why not relocate some
and put them back immediately ? Like in a vibrating reed voltmeter/charge
meter. You have a moving electrode in an electrical field. The motion is
repetitive and the probe will sense an ac voltage with amplitude equal to
the difference in potential between the two extremes of the motion. It
need not touch anything. The energy comes from the mechanism that does the
moving, by moving the probe charge in the field. A small influence will be
sensed on the measured object but it will be ac. The electrophorus
operates on the same principle.

Peter

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.