## ABSTRACT

The phenomenological Bose-gas picture rendered no quantitative account for the critical parameters of conventional low-temperature superconductors. Its failure stemmed from the very large diameter ξ of pairs in conventional superconductors which can be estimated using the uncertainty principle, ξ ≈ 1/δk. The uncertainty in the momentum 8k is estimated using the uncertainty in the kinetic energy δE ≃ v
_{F}
δk, which should be of the order of T
_{C}, the only characteristic energy of the superconducting state. Therefore, ξ ≈ v
_{F}/ T_{c}
turns out to be about 1 µm for simple superconducting metals where T_{c}
≃ 1 K and the Fermi velocity v
_{F} ≃ 10^{8} cm s^{−1}. This means that pairs in conventional superconductors strongly overlap and the Ogg–Shafroth model of real space pairs cannot be applied.