We have determined the phase coherence time, tau(phi), from magnetoresistan
ce measurements of long, narrow wires of Au, Ag, and Cu, over the temperatu
re range 40 mK-6 K. In the Cu and Au wires, tau(phi) saturates at low tempe
rature. In the Ag wire, tau(phi) continues to increase down to the lowest t
emperatures measured; moreover, its temperature dependence below about 1 K
is consistent with theoretical predictions of Altshuler, Aronov and Khmelni
tskii published in 1982. These results cast doubt on recent assertions that
saturation of tau(phi) at low temperature is a universal phenomenon in met
al wires. We compare these results with those of recent experiments on ener
gy relaxation in similar metallic wires. The results of the two experiments
are strongly correlated, suggesting that a single (unknown) mechanism is t
he cause of the enhanced phase and energy relaxation observed in some sampl
es.