  The recently discovered system J0651 is the tightest known detached white
dwarf (WD) binary. Since it has not yet initiated Roche-lobe overflow, it
provides a relatively clean environment for testing our understanding of tidal
interactions. I investigate the tidal heating of each WD, parameterized in
terms of its tidal Q parameter. Assuming that the heating can be radiated
efficiently, the current luminosities are consistent with Q_1=7*10^{10} and
Q_2=2*10^7, for the He and C/O WDs, respectively. Conversely, if the observed
luminosities are merely from the cooling of the WDs, these estimated values of
Q represent upper limits. A large Q_1 for the He WD means its spin velocity
will be slower than that expected if it was tidally locked, which, since the
binary is eclipsing, may be measurable via the Rossiter-McLaughlin effect.
After one year, gravitational wave emission shifts the time of eclipses by 5.5
s, but tidal interactions cause the orbit to shrink more rapidly, changing the
time by up to an additional 0.3 s after a year. Future eclipse timing
measurements may therefore infer the degree of tidal locking.
