  It is of broad interest to understand how the evolution of non-equilibrium
systems can be triggered and the role played by external perturbations. A
famous example is the origin of randomness in the laminar-turbulence
transition, which is raised in the pipe flow experiment by Reynolds as a
century old unresolved problem. Although there exist different hypotheses, it
is widely believed that the randomness is "intrinsic", which, however, remains
as an open question to be verified. Simulating the modeled Rayleigh-Benard
convection system by means of the so-called clean numerical simulation (CNS)
with negligible numerical noises that are smaller even than thermal
fluctuation, we verify that turbulence can be self-excited from the inherent
thermal fluctuation, without any external disturbances, i.e. out of nothing.
This reveals a relationship between microscopic physical uncertainty and
macroscopic randomness. It is found that in physics the system nonlinearity
functions as a channel for randomness information, and energy as well, to
transport microscopic uncertainty toward large scales. Such scenario can
generally be helpful to understand the various relevant phenomena. In
methodology, compared with direct numerical simulation (DNS), CNS opens a new
direction to investigate turbulent flows with largely improved accuracy and
reliability.
