In the present study, we propose a new perspective on thermal dissipation as an effective interaction described by TFD
theory. Once thermal disturbances are reduced, there appear effective interactions between the original and tilde spaces.
Using the effective interactions, we show the correspondence between a dissipative model and a finite size system as shown
in Fig. 2. By the way, as is well known [25], there appear thermal squeezed states on the dissipative TFD theory. However,
the present study does not consider the phase properties because it is not essential for the present discussions. In fact, it is
more important that the tilde space needs to be isomorphic to the original space, and then the same random noises appear in
both of the original and tilde spaces, as shown in Eqs. (9) and (26). It enables us to obtain the effective interaction between
the original and tilde spaces with reducing the thermal noises. In the case of single free spin, the role of tilde space is to
replace only mathematically the trace TrQρ(t) by the quantum average ⟨Ψ(t)|Q|Ψ(t)⟩. Nevertheless, in a physical system
with fluctuating forces, the tilde space is also integrated into the whole physical system Hˆ with such effective interactions
between the original and tilde spaces as it plays a role of thermal disturbance. The present perspective may also be important
to apply the TFD theory to thermal effects including entanglements and numerical studies. The alternative system described
in the double Hilbert space includes finite parameters while the heat bath includes infinite parameters. Then the present
perspective gives us a way to study the heat bath using finite size systems. It is useful for practical applications to study
thermal effects, because in the present way with the effective interaction ih¯Λˆ (t), only the same amount of computational
effort is simply required as in finite-size systems.