  We study the role of gravitational waves (GW) in the heat death of the
universe. %in the heat death. Due to the GW emission, in a very long period,
dynamical systems in the universe suffer from persistent mechanical energy
dissipation, evolving to a state of universal rest and death. With N-body
simulations, we adopt a simple yet representative scheme to calculate the
energy loss due to the GW emission. For current dark matter systems with mass
$\sim10^{12}-10^{15} M_\odot$, we estimate their GW emission timescale as
$\sim10^{19}-10^{25}$ years. This timescale is significantly larger than any
baryon processes in the universe, but still $\sim10^{80}$ times shorter than
that of the Hawking radiation. We stress that our analysis could be invalid due
to many unknowns such as the dynamical chaos, the quadrupole momentum of halos,
the angular momentum loss, the dynamic friction, the central black hole
accretion, the dark matter decays or annihilations, the property of dark energy
and the future evolution of the universe.
