Eternal Universe Theory - An Inflation-Free Cosmology with a Single Axion

Following critical re-examination, EUT v5.0 abandons the previous void-amplification mechanism and adopts a heavier axion mass m_a = 8×10⁻¹⁸ eV. At high temperatures the axion undergoes a natural kinetic-dominated stiff-matter phase (w = +1) lasting ∼65 e-folds, significantly ameliorating the horizon and flatness problems without inflation or fine-tuning. The resulting fuzzy dark matter has a present-day de Broglie wavelength ∼42 pc and forms solitonic cores of radius 150–300 pc in low-mass halos, consistent with observed dwarf galaxy properties. The model lies within current Lyman-α and black-hole superradiance constraints and makes no strong claims on cosmological tensions. Minor primordial black hole formation (M ∼ 10²⁵–10²⁷ kg, f_PBH ≲ 10⁻⁸) remains possible but cosmologically irrelevant. Future high-resolution observations (Euclid, LSST) will test the predicted ∼100 pc-scale structure.