Let
M
M
be the
(
n
+
1
)
(n + 1)
-dimensional Minkowski space,
n
≥
3
n \ge 3
. The energy of a solution
ψ
\psi
to Dirac’s equation in
M
M
is a sum of
n
n
terms, the
j
j
th term depending on
ψ
\psi
and the space derivative
∂
ψ
/
∂
x
j
\partial \psi /\partial {x_j}
. We show that if the Cauchy datum for
ψ
\psi
is compactly supported, then each of these terms is eventually constant. Specifically, if
ψ
\psi
is initially supported in the closed ball of radius
b
b
about the origin in space
(
R
n
)
\left ( {{R^n}} \right )
, then for times
|
t
|
≥
b
\left | t \right | \ge b
, the
j
j
th term is equal to the energy of the
j
j
th Riesz transform
(
−
Δ
)
−
1
/
2
(
∂
/
∂
x
j
)
ψ
{( - \Delta )^{ - 1/2}}(\partial /\partial {x_j})\psi
, which also solves Dirac’s equation.