  The isoscalar monopole excitation of 4He is studied within a few-body ab
initio approach. We consider the transition density to the low-lying and narrow
0+ resonance, as well as various sum rules and the strength energy distribution
itself at different momentum transfers q. Realistic nuclear forces of chiral
and phenomenological nature are employed. Various indications for a collective
breathing mode are found: i) the specific shape of the transition density, ii)
the high degree of exhaustion of the non-energy-weighted sum rule at low q and
iii) the complete dominance of the resonance peak in the excitation spectrum.
For the incompressibility K of the alpha-particle values between 20 and 30 MeV
are found.
