How "living" dark energy reconciles cosmologists ✦
Scientists have long debated how fast the Universe is expanding. New data suggest: if dark energy isn't constant but can change, like a fluid that thickens or thins, the contradictions vanish. Two specific models — dilaton and tachyon — almost perfectly align early and late measurements. So, was the expansion mystery not about the measurements, but about our ideas of dark energy?
The expansion rate of the universe is measured in two ways: by ancient light — the cosmic microwave background and by nearby supernovae. The results differ — 67 vs. 73 km/s per 3 million light-years. This Hubble tension, named after Edwin Hubble, long stumped cosmologists. The standard model assumes dark energy is a cosmological constant, like an engine with fixed thrust. But then the discrepancy is inexplicable. New research treats dark energy as a changing field (k-essence): it alternately boosts and slows acceleration, like a driver playing with the throttle. Calculations for a tachyonic version of such a field reduce the tension almost to zero.
If the model is correct, the universe accelerates in spurts, and gravity on cosmic scales doesn't behave as Newton predicted. As Georges Lemaître suspected, the cosmological constant might be variable.
🎯 The name 'k-essence' comes from 'kinetic quintessence' (essence of motion). It was devised for inflation, and later unexpectedly proved useful for dark energy.
🎬 Tachyonic field sounds like an alien from 'Star Trek': there, tachyons are faster-than-light particles. But in cosmology, it's just a mathematical model that doesn't violate relativity.