This short contribution examines the difficulties that have not yet been fully overcome in the many developments made from the simplest (and original) tube model for entangled polymers. It is concluded that many more length scales have to be considered sequentially when deriving a continuum theological model from molecular considerations than have been considered in the past. In Particular, most unresolved issues of the tube theory are related to the length scales of tube diameter, and molecular dynamics Simulations is the perfect route to resolve them. The power of molecular Simulations is illustrated by two examples: stress contributions from bonded and non-bonded interaction, and the inter-chain Coupling, Which is Usually neglected in the tube theory. (C) 2008 Elsevier B.V. All rights reserved.