  We show that if the excitations which become gapless at a quantum critical
point also carry the electrical current, then a resistivity linear in
temperature, as is observed in the copper-oxide high-temperature
superconductors, obtains only if the dynamical exponent, $z$, satisfies the
unphysical constraint, $z<0$. At fault here is the universal scaling hypothesis
that, at a continuous phase transition, the only relevant length scale is the
correlation length. Consequently, either the electrical current in the normal
state of the cuprates is carried by degrees of freedom which do not undergo a
quantum phase transition, or quantum critical scenarios must forgo this basic
scaling hypothesis and demand that more than a single correlation length scale
is necessary to model transport in the cuprates.
