Dark Energy Didn’t Kick In Right Away ⚡ экспресс
We investigate the model of critical emergent dark energy (CEDE), in which dark energy is absent in the early Universe and arises after a critical epoch through a phase transition. The model is constrained using cosmic microwave background data from Planck 2018, baryon acoustic oscillations (from SDSS and DESI DR2), and two compilations of Type Ia supernovae (PantheonPlus and Union3). Results show that a phase transition is not excluded: data combinations of CMB-only, CMB+SDSS, and CMB+DESI provide evidence for a non-zero transition scale factor and, based on Δχ² and Bayesian factor criteria, may favor CEDE over standard ΛCDM. However, the model does not fully resolve the Hubble constant tension. Phase transition models remain a viable extension of standard cosmology, and future high-precision surveys are needed to test whether CEDE represents a genuine departure from ΛCDM or merely an effective description of current data.
Dark energy is usually seen as an innate property of the cosmos, at work from the very first moments. But a new model suggests it behaved like water on the verge of boiling: long unnoticed, then suddenly kicking in at a critical moment. This scenario is called 'late activation': around 5–7 billion years ago, a shift occurred, and the universe’s expansion began to accelerate.
Three landmarks helped test the idea. The cosmic microwave background—the cooled light of the Big Bang—preserved the imprint of the young universe. Explosions of supernovae, like lighthouses, allowed distances to be measured; it was these that led Adam Riess to discover the acceleration in the 1990s. The patterns of galaxies revealed the rate of universe expansion. By combining these data, scientists essentially captured the moment the cosmos 'boiled over.'
There was a surprise:
However, this doesn't resolve the main cosmological puzzle—the Hubble tension, i.e., the discrepancy in the expansion rate measured by different methods. The mystery endures, and cracking it will require even bolder ideas.
🎯 If dark energy had 'woken up' too early, just a couple of billion years after the Big Bang, the galaxies and stars we know simply wouldn’t have formed—the expansion would have scattered all matter.