Remarks on astrophysical origin of the knee in cosmic ray spectrum
  All astrophysical explanations of the knee in cosmic ray spectrum accept the hypothesis of its existence {\it a priori} without any doubt. But, there exist experimental evidences against this hypothesis. Experimental data on the knee in various secondary cosmic ray components obtained by KASCADE array as well as by many other arrays reveal the existence of the knee ($\Delta\gamma\approx0.4\div0.5$) in electromagnetic component (e and $\gamma$ including Cherenkov light) and the absence of it or a very small knee ($\Delta\gamma\approx0.1\div0.2$) in muonic and hadronic components. But, one could expect the inverse relationship in case of the astrophysical knee origin. A brief review of experimental data concerning this problem is given. 
Yuri V. Stenkin