In the principle study of the Pioneer Anomaly, John Anderson and Slava Turyshev suggested a speculative explanation for the apparent deceleration of the spacecraft: as an acceleration of the clock rate used for telemetry back on earth. To be clear, this explanation has been discounted- although it was explored further in this paper. The Pioneer Anomaly is generally considered solved, being due to asymmetric thermal radiation from the probes. My question is, if such a universal change in clock time did exist, i.e. that every subsequent second ticked by faster or slower than the one before it, how could we detect it? Can anyone imagine an Earth-based experiment? As I understand it, the effect that Anderson was proposing would be universal, effecting all clocks equally. Such an effect would be independent of special or general relativistic time dilations, occurring without any specific circumstances of motion or gravitation (although these effects would need to be subtracted from any experiment).The magnitude of the effect if it were to explain the Pioneer Anomaly, 2.9E-18 sec^-1, would exceed the uncertainty of an ordinary cesium atomic clock in a week. I suspect the most sensible comparison would be to compare the proper time of 2 observers at 2 different cosmic times. I'm not asking if this effect is real, I'm asking if we could make a practical experiment to detect something like it, or if it could even be logically possible for such an effect to exist. I proposed this thought experiment over at scienceforums.net, and we got as far as assuming light delay could put us in contact with a past rate of time (even of the very same clock, if a signal is bounced off something like the Pioneer probes), and so an interferometer with arms of very different lengths might register such an effect, but would require absurd precision for something on the order of magnitude of the Pioneer Anomaly.