%0 Journal Article %T A Physical Explanation for Tilde System in Thermo Field Dynamics %A Dong Mi %A He-Shan Song %A Ying An %J Physics %D 2001 %I arXiv %R 10.1142/S0217732301003607 %X For a two-body quantum system, any pure state can be represented by a biorthogonal expression by means of Schmidt decomposition. Using this in the composite system which include a thermodynamic system and its surroundings, it is found that the tilde system in thermo field dynamics is just the surroundings of the real system. %U http://arxiv.org/abs/quant-ph/0102127v2