The Universe Devourer: How World Mergers Explain Dark Energy Without a Cosmological Constant ✦
We consider a cosmological model where our Universe, in its later evolutionary stages, absorbs 'daughter' universes. This process accounts for the observed exponential expansion without the need for a cosmological constant. The dark energy equation of state acquires a dependence on redshift: the parameter w(z) becomes a function of z. At sufficiently high z, w(z) falls below −1, indicating a 'phantom' nature. The model offers a natural dynamical alternative to static dark energy and can be tested by astronomical observations. It also predicts that the dark energy density changed over time, distinguishing it from the standard ΛCDM model.
Context
The standard cosmological model with dark matter and dark energy (ΛCDM) successfully describes the large-scale structure of the Universe, yet faces two serious tensions. First, local measurements of the Hubble constant (the Edwin Hubble law) by the Adam Riess team yield H₀ ≈ 72.6 km/s/Mpc, whereas cosmic microwave background data from the Planck satellite indicate H₀ ≈ 67 km/s/Mpc—the so-called 'Hubble tension'. Second, the S₈ parameter, characterizing matter clustering, also shows discrepancies. Recent DESI survey results hint that the dark energy equation of state w may depend on redshift and take values w < –1 at high z. Such behavior is hard to reconcile with an immutable cosmological constant, spurring the development of alternative models.
Methods
The starting point is a minisuperspace description within quantum cosmology, where the spatial volume v(t) ∝ a³(t) serves as the dynamical variable. Instead of the standard term with the cosmological constant Λ, the Hamiltonian incorporates a term responsible for the absorption of 'baby universes' with intensity g. The function f(p) in the generalized Friedmann equation is derived from requiring the Hartle–Hawking wave functions (proposed by Stephen Hawking) to be identical for all colliding universes. The model does not need Λ: exponential expansion arises from world mergers. The parameter g is calibrated against the local H₀ value, after which H(z) and w(z) are numerically computed and compared with observational data, including Type Ia supernovae from the Pantheon+ and Union3 compilations.
Results
The computed w_f(z) dependence shows a monotonic decrease from –1.5 as z → ∞ to –1 as z → –1. For H₀ = 72.6 km/s/Mpc, the resulting curve is compared with the w(z) reconstructed from DESI data. The reduced χ² is around 4±0.4, indicating moderate agreement: the model captures the behavior well at z > 0.8 but deviates from data at low z. Including corrections related to spacetime topology changes (described by an analogue of the string coupling constant G_s) improves the fit at low z, but at the cost of introducing an extra parameter. For instance, with G_s = –8 using a Padé approximation, the w(z) curve closely approaches the observed one, though the agreement with H(z) data slightly worsens.
Implications
If the universe-absorption mechanism is realized in nature, it radically alters our understanding of dark energy. It ceases to be a fundamental constant or a vacuum property, emerging instead as an effective phenomenon driven by interactions with the multiverse. This scenario aligns with the idea that our Universe is just one among many worlds and naturally explains why the observed dark energy density is so tiny (the cosmological constant problem). Moreover, the model predicts a characteristic w(z) evolution that can be tested by future surveys.
Future development
Future development of the model should include matter when calculating the Hartle–Hawking wave function, providing a physical motivation for the absorption function ˜F(p). It will be crucial to explore connections with microscopic theories, such as quantum gravity or string theory, to derive the effective value of g from first principles. More detailed comparisons with forthcoming data from missions like Euclid and the Roman Space Telescope are also needed.
Impact
The model impacts early Universe cosmology, gravitational theory, and the interpretation of accelerated expansion.
Next steps
Immediate next steps include more precise higher-order G_s corrections to improve low-z agreement, as well as joint analyses with other datasets (e.g., baryon acoustic oscillations). Developing non-perturbative methods for summing topological contributions is also important.
Key open problems
The model is directly tied to the cosmological constant problem (why is Λ so small?), the Hubble tension, and the fundamental question of the role of quantum effects in cosmology. It also resonates with the idea of inflation and the birth of universes from 'nothing' within Big Bang theory.
🎯 The idea of baby universes traces back to Stephen Hawking's work in quantum cosmology, where he considered the birth of universes from the vacuum. In this model, our Universe literally 'feeds' on other worlds, growing in volume.
🎬 The premise of universes interacting with ours echoes Isaac Asimov's novel 'The Gods Themselves', where contact with a para-universe alters physical laws.
Key numbers
- H0: 72.6 km/s/Mpc (adopted local value)
- χ²_red: 4±0.4 (for the baseline model without topological corrections)
- S8: ≈ 0.76 (model prediction)
- w0 (фит): -0.87 (equation-of-state parameter today)
- wa (фит): -0.70 (evolution parameter of w(z))