  The article formulates the basic principles of microscopic physics of a
macroscopic ensemble of interacting helium-4 atoms. The concept of a vortex
field is introduced, which is caused by the motion of the particles of the
electron and nuclear subsystems of atoms of the macrosystem relative to each
other. It is assumed that helium-4 atoms "immersed" in the internal vortex
field acquire the properties of fermionic particles due to the atomic
pseudospins s=1/2 generated by the vortex. On this basis, a heuristic
evolutionary model of helium-4 as an ensemble of atom-like quasiparticles with
fermionic properties is constructed. As the temperature decreases, bonds are
formed between pseudofermionic quasiparticles by pairing their pseudospins. The
formation of a hierarchy of composite quasiparticles on this basis leads to the
transition of helium-4 atoms from the gas phase to the liquid state, then to
the state of incoherent Bose condensate, and finally to the state with a
long-range order of atom-like quasiparticles. The structural forms of composite
quasiparticles in different phases, the mechanisms of their formation, and the
temperatures of these phase transitions ($T_{cr}=5.22K$, $T_0=4.14K$ and
$T_\lambda=2.175K$, respectively) are determined. The ideas and calculations
presented in this paper form the basis for solving the problem of the
temperature dependence of the heat capacity of liquid helium-4 in both the
helium-I and helium-II phases. The obtained solution has a logarithmic
dependence of the heat capacity on the reduced temperature
(${|1-{T/T_\lambda}|}$) in the region of the $\lambda$-point of the phase
transition of helium-4 from a disordered to an ordered state. The numerical
calculations of the heat capacity in the vicinity of the temperature
$T_\lambda$ are in very good agreement with the experimental data.
