As I am sure everyone is aware, there are still folks who don’t believe SRT and GRT. While 99.9% of them are nut-jobs, there is at least one that I respect – Tom Phipps specifically. I am not familiar with any of his writing before the advent of the GPS satellites. In any case, he now accepts “time dilation”, but not “length contraction”. The last I knew (~2006?) he claimed that it has never been proven empirically. I think he is wrong, and the most compelling evidence of length contraction for me is the explanation of magnetism / Ampere’s law given by Purcell. I assume that at least some of you are familiar with that? Briefly, the apparent length contraction of a passing line of charges enhances their influence on neighboring lines of charges. Thus “parallel currents attract”, i.e., Ampere’s law and magnetism, is so simply and elegantly understood as length contraction, or at least the apparent contraction of a line of charges. Finally getting to my question: The only objection to Purcell’s interpretation that I can think of is the excess negative charge on a current carrying wire (in the lab frame) that should appear during the starting transient. Since all practical circuits are grounded, I don’t suppose that such would be apparent. But can anyone think of a way to test that – does an excess negative charge appear on a current carrying wire during the starting transient? Or has someone already tested that? Thanks.