103. M. Szydłowski, M. Heller, Z. Golda
Stochastic Time Scale for the Universe
Acta Phys. Pol. , vol. B17, pp. 19-24 (1986).
[abstract]

Abstract:
An intrinsic time scale is naturally defined within stochastic gradient dynamical systems. It should be interpreted as a ``relaxation time'' to a local potential minimum after the system bas been randomly perturbed. It is shown that for a flat Friedman-like cosmological model this time scale is of order of the age of the Universe.

104. M. Szydłowski, M. Heller, Z. Golda
Stochastic Properties of the Friedman Dynamical System
Acta Phys. Pol. , vol. B16, pp. 791-798 (1985).
[abstract]

Abstract:
Some mathematical aspects of the stochastic cosmology are discussed in its relationship to the corresponding ordinary Friedman world models. In particular, it is shown that if the strong and Lorentz energy conditions are known, or the potential function is given, or a stochastic measure is suitable defined then the structure of the phase plane of the Friedman dynamical system is determined.

105. Marek Szydłowski, Michael Heller, Zdzisław Golda
Structural Stability Properties of Friedman Cosmology
Gen. Rel. Grav., vol. 16, pp. 877-890 (1984).
[abstract] [journal]

Abstract:
A dynamical system with Robertson-Walker symmetries and the equation of the state $p = \gamma\epsilon$, $0 \leq\gamma\leq 1$, considered both as a conservative and nonconservative system, is studied with respect to its structural stability properties. Different cases are shown and analyzed on the phase space ($x = R^D$, $y = \dot{x}$).

106. Z. Golda, M. Heller and M. Szydłowski
Structurally Stable Approximations to Friedmann—Lemaître World Models
Astrophys. Space Sci., vol. 90, pp. 313-326 (1983).
[abstract] [journal]

Abstract:
Friedmann{--}Lema\^{\i}tre cosmology is briefly reviewed in terms of dynamical systems. It is demonstrated that in certain cases bulk viscosity dissipation structurally stabilizes Friedmann{--}Lema\^{\i}tre solutions. It turns out that, for $\Lambda = 0$, there are structurally stable solutions if $\zeta \sim \varepsilon^{1\slash2}$, where $\zeta$ is the bulk viscosity coefficient. For $\Lambda \neq 0$, structurally stable solutions are essentially those with $\zeta = \mbox{const}$. The role of structural stability in physics and cosmology is shortly discussed.