For decades, the standard model of cosmology — known as ΛCDM (Lambda Cold Dark Matter) — has been the bedrock of our understanding of the universe. It elegantly explains the cosmic microwave background, the large-scale structure of galaxies, and the accelerating expansion of the universe through a mysterious component called dark energy. But a growing body of observational evidence is now challenging this model, forcing scientists to ask a provocative question: does dark energy really exist, or is our understanding of gravity fundamentally incomplete?
Recent findings from the Dark Energy Spectroscopic Instrument (DESI), combined with data from supernovae and the cosmic microwave background, have revealed inconsistencies that the ΛCDM model struggles to explain. According to a detailed article on Habr, these observations hint that dark energy may not be a constant force, but rather something that changes over time — a possibility that would shatter the foundational assumption of the standard model.
The Problem: A Cracking Consensus
The ΛCDM model assumes that dark energy is a cosmological constant — a fixed energy density pervading space. This assumption fits beautifully with the 1998 discovery of the universe's accelerating expansion, for which the Nobel Prize was awarded. However, as observational precision has improved, cracks have appeared.
One major issue is the Hubble tension: measurements of the current expansion rate (Hubble constant) from early-universe observations (CMB) disagree significantly with measurements from late-universe methods (supernovae and standard sirens). Another problem comes from DESI's first-year data, released in 2026. The results show that the dark energy density parameter, w, which should be exactly –1 for a cosmological constant, deviates at around the 2.5–3 sigma level. While not a definitive discovery, it is strong evidence that the standard model might need revision.
The Habr article describes how researchers are now forced to consider that the universe's acceleration might be driven by a dynamic form of dark energy — or that General Relativity itself breaks down on cosmic scales.
The Solution: New Models and Observations
In response to these tensions, the scientific community is exploring several alternative scenarios. One promising direction is “early dark energy” — a form of dark energy that existed briefly after the Big Bang and then decayed. This could resolve the Hubble tension by altering the sound horizon at recombination.
Another approach is to modify gravity on large scales. Theories like f(R) gravity or DGP (Dvali-Gabadadze-Porrati) models can mimic dark energy by changing how gravity behaves over billions of light-years. These models are being tested against DESI data and other surveys.
The authors of the Habr piece note that the solution does not come from a single experiment, but from stacking multiple independent probes. For example, combining DESI galaxy clustering with gravitational lensing and Type Ia supernova data provides a cross-check. So far, no single alternative model fits all observations better than ΛCDM, but the tension persists.
Results: What the Data Tells Us
The key result from the latest analyses is clear: the standard model of the universe is under pressure. According to the DESI collaboration, if the dark energy equation of state shows even a small deviation from –1, the cosmological constant is ruled out. The current data favor a “thawing” quintessence model, where dark energy was once negligible and is now becoming stronger.
Importantly, the Habr article emphasizes that these results are not yet conclusive. The statistical significance is below the 5 sigma threshold required for a discovery. However, the consistency of the deviation across multiple datasets — including early results from the Euclid space telescope — suggests a real effect.
To quantify the situation, consider the following comparison of key parameters:
| Parameter | ΛCDM prediction | DESI+CMB data (2026) |
|---|---|---|
| Dark energy equation of state w | –1 (constant) | –0.88 ± 0.12 (evolving) |
| Hubble constant H0 (km/s/Mpc) | 67.4 ± 0.5 | 72.6 ± 1.5 (from local) |
| Matter density Ωm | 0.315 ± 0.007 | 0.28 ± 0.02 |
These numbers are drawn from the DESI et al. papers discussed in the Habr article. They illustrate that the cracks are real and require either new physics or better understanding of systematic errors.
Conclusions: A New Era of Cosmology
The question “Does dark energy exist?” may soon have a surprising answer. If the current hints hold up, dark energy is not a static property of space but a dynamic field, opening up a new window into fundamental physics. Alternatively, we may discover that our theory of gravity must be revised at the largest scales, which would revolutionize our understanding of spacetime.
For now, scientists are eagerly awaiting upcoming data from the Euclid survey, the Nancy Grace Roman Space Telescope, and a new generation of gravitational wave detectors. These instruments will either confirm the ΛCDM model or conclusively prove that it is incomplete.
As the Habr article concludes, we may be on the verge of a paradigm shift — one that could explain not only the accelerating universe but also the nature of dark matter and the early universe. The current cracks are not a weakness of science, but a sign of its strength: the willingness to question even the most successful models.
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