⚛️ general relativity

Evolving wormhole cosmology: modified Friedmann dynamics and observational constraints

This paper proposes and validates an evolving wormhole cosmological model derived from a Morris-Thorne metric that yields a modified Friedmann equation, demonstrating its consistency with diverse observational datasets while offering a distinct geometric observable to differentiate wormhole spacetimes from standard dark energy models.

Original authors: Aritra Sanyal, Kazuharu Bamba, Prabir Rudra

Published 2026-09-10

📖 4 min read🧠 Deep dive

CC BY 4.0

Original authors: Aritra Sanyal, Kazuharu Bamba, Prabir Rudra

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

For decades, astronomers have watched the universe expand at an ever-faster pace. This acceleration was first spotted in the light of distant exploding stars and later confirmed by the faint afterglow of the Big Bang and the way galaxies cluster together. The standard explanation for this speeding-up is a mysterious force called dark energy, often imagined as a constant push from empty space itself. However, this idea leaves scientists with two nagging problems: why is the push so weak compared to what simple physics predicts, and why does it seem to be taking over the universe right now, just as matter is fading away? To solve these puzzles, researchers have proposed many alternatives, from invisible fields to changes in the laws of gravity. A new study suggests a different path, one that looks not at new fields, but at the shape of space itself.

The researchers, working from universities in India and Japan, explored the possibility that the universe is threaded with microscopic tunnels known as wormholes. In theoretical physics, a wormhole is a shortcut connecting two distant points in space, held open by a strange form of matter that pushes outward rather than pulling inward. While these tunnels are usually thought of as local curiosities, this team asked a bold question: what if a vast, invisible network of them exists throughout the cosmos? If such a network were spread out evenly, its collective presence could mimic the effects of dark energy, driving the universe's expansion without needing any new, invisible substances.

To test this idea, the team built a mathematical model of a wormhole that grows and changes as the universe expands. They started with a classic description of a wormhole and adapted it to fit inside a flat, expanding universe. A key part of their work was figuring out how to treat a single, tiny tunnel as if it were a fluid filling the entire cosmos. They developed a method to average the energy and pressure of these wormholes over a huge volume of space. This averaging process revealed that the wormholes behave like a cosmic fluid with a specific set of rules. The team found that the way the wormhole tunnels change size over time, combined with their specific shape, creates a single, predictable pattern that dictates how they influence the universe's expansion.

When the researchers compared their model against real-world data, the results were strikingly consistent. They tested their theory using three major types of astronomical measurements: the ages of ancient galaxies which reveal the current expansion rate, the sound waves frozen in the distribution of galaxies, and high-precision data from a massive new survey called DESI. The model, which includes a small correction term representing the wormholes, fit all these datasets perfectly. It predicted that the universe is currently expanding at a rate consistent with current measurements, a value that sits comfortably between the conflicting measurements that have puzzled scientists for years. The model also correctly identified the moment in cosmic history when the universe switched from slowing down to speeding up, which happened billions of years ago.

Perhaps the most exciting discovery is that this wormhole model makes a unique prediction that standard dark energy theories cannot. The study suggests that the size of the wormhole tunnels themselves changes as the universe evolves. In the early universe, these tunnels would have been smaller and denser, and they have been growing larger as space stretches. This changing size is a specific signature of the wormhole geometry. If future observations can detect this specific pattern of growth, it would provide a way to distinguish between a universe driven by a simple cosmological constant and one shaped by a network of these exotic tunnels. The findings do not prove that wormholes exist, but they demonstrate that if they do, their collective behavior offers a natural, geometric explanation for the accelerating universe that fits the data just as well as the leading theories.

Technical Summary: Evolving Wormhole Cosmology

Problem Statement
The paper addresses the theoretical and observational challenges facing the standard $\Lambda$ CDM cosmological model, specifically the cosmological constant problem (the fine-tuning of $\Lambda$ ), the coincidence problem, and the Hubble tension (the $\sim 5\sigma$ discrepancy between local and CMB-inferred values of $H_0$ ). While dynamical dark energy and modified gravity are common alternatives, the authors propose a geometric approach: treating the large-scale spacetime topology itself as a driver of cosmic acceleration. Specifically, they investigate whether a network of traversable wormholes, embedded in a Friedmann–Lemaitre–Robertson–Walker (FLRW) background, can collectively modify the Friedmann equations to mimic dark energy without introducing new scalar fields or ad hoc fluids.

Methodology
The authors construct a cosmological model based on the Morris–Thorne metric, generalized to include time dependence and cosmic expansion.

Metric Ansatz: They adopt a spatially flat FLRW background with a spherically symmetric, time-dependent wormhole throat. The line element is defined by a scale factor $a(t)$ and a separable shape function $b(r, t) = b(r)g(t)$ , where $b(r)$ describes the radial throat profile and $g(t)$ governs its evolution.
Shape Function: The primary analysis uses a power-law shape function $b(r) = r_0 (r_0/r)^n$ with $n > 0$ , alongside alternative parametrizations for robustness checks. The temporal factor is modeled as $g(t) = a^\gamma(t)$ , where $\gamma$ determines the throat's evolution relative to the Hubble flow.
Field Equations: The authors compute the Einstein tensor for this metric and derive the corrected energy-momentum tensor ( $T_{\mu\nu}$ ) associated with the wormhole geometry. Crucially, they identify an explicit $a^{-2}(t)$ dependence in the energy density components, arising from the spatial metric prefactor.
Volume Averaging: To connect the local, inhomogeneous wormhole geometry to a homogeneous cosmological fluid, they perform a volume-averaging procedure over a comoving Hubble volume. This yields a macroscopic energy density $\langle \rho_{WH} \rangle$ that scales with redshift as $(1+z)^\beta$ .
Modified Friedmann Equation: The averaged wormhole contribution enters the Friedmann equation as a correction term $\Delta_{WH}(z) = \alpha(1+z)^\beta$ , where $\alpha$ is a dimensionless density parameter and $\beta$ is a macroscopic exponent derived from the microscopic parameters $n$ and $\gamma$ .
Observational Constraints: The model is constrained using a Markov Chain Monte Carlo (MCMC) analysis against seven dataset combinations: Cosmic Chronometers (CC), standard Baryon Acoustic Oscillations (BAO), and Dark Energy Spectroscopic Instrument (DESI) Data Release 2 BAO data. The parameters constrained are $H_0$ , $\Omega_m$ , $\alpha$ , and $\beta$ .

Key Contributions

Derivation of the Macroscopic Exponent: The paper provides a closed-form derivation linking the microscopic geometric parameters to the macroscopic expansion behavior: $\beta = \frac{3\gamma(n+1)}{2n+2}$ . This establishes that the wormhole fluid behaves as a barotropic component with a constant equation of state $w_{WH} = -1 + \beta/3$ .
Consistency of Averaging and Conservation: The authors demonstrate that the exponent $\beta$ derived from the geometric volume-averaging procedure is identical to the exponent required by the covariant conservation law ( $\dot{\rho} + 3H(\rho+p)=0$ ), validating the separable shape function construction.
Traversability Verification: The model satisfies all traversability conditions (throat condition, flare-out condition, and asymptotic flatness) and explicitly confirms the violation of the Null Energy Condition (NEC) at the throat, consistent with the requirement for exotic matter in traversable wormholes.
Novel Observable: The model predicts a specific functional form for the physical throat radius evolution, $r_0(z) = r_{0,0}(1+z)^{-\gamma}$ , where $\gamma = \beta/3$ . This offers a geometry-specific observable to distinguish wormhole cosmology from phenomenological dark energy parametrizations (e.g., $w_0w_a$ CDM).

Results

Parameter Constraints: The joint fit of CC, BAO, and DESI data yields consistent parameters across all dataset combinations. The best-fit values are $H_0 \approx 68.53$ km s $^{-1}$ Mpc $^{-1}$ , $\Omega_m \approx 0.30$ , $\alpha \approx 0.018$ , and $\beta \approx 1.59$ .
Hubble Tension: The inferred $H_0$ is intermediate between local measurements (SH0ES) and CMB-inferred values (Planck), potentially offering a partial resolution to the Hubble tension.
Equation of State: The effective dark energy equation of state is found to be $w_{eff}(0) \approx -0.98$ , rising slightly to $-0.91$ at $z=2.5$ . The intrinsic wormhole equation of state is $w_{WH} \approx -0.47$ , placing it firmly in the dark energy regime but distinct from a pure cosmological constant ( $w=-1$ ).
Deceleration-Acceleration Transition: The model predicts a transition redshift $z_t \approx 0.66$ , consistent with independent determinations from supernova data.
Statistical Viability: The wormhole model fits the data as well as the standard flat $\Lambda$ CDM model (reduced $\chi^2 \approx 0.56$ vs. $0.53$ for CC data). The wormhole contribution acts as a small, sub-dominant correction ( $\alpha \sim 10^{-2}$ ) rather than a dominant new effect.

Significance and Claims
The paper claims to establish "evolving wormhole cosmology" not as a speculative afterthought, but as a well-precedented, peer-reviewed research direction grounded in the Morris–Thorne formalism. Its primary significance lies in:

Geometric Origin of Dark Energy: It demonstrates that the collective effect of a network of traversable wormholes can source a modification to the Friedmann equations that mimics dark energy, deriving the equation of state directly from spacetime geometry rather than postulating a new field.
Observational Discriminability: The model provides a unique, testable prediction—the evolution of the throat radius $r_0(z)$ —which serves as a discriminator between topological dark energy and standard fluid-based parametrizations.
Theoretical Consistency: The work bridges the gap between local wormhole physics (NEC violation, exotic matter) and global cosmology, showing how volume-averaging reconciles the local violation of energy conditions with a globally consistent, accelerating universe.

The authors conclude that while the wormhole contribution is currently a perturbative correction, the framework offers a robust, geometrically motivated alternative to the cosmological constant that is fully consistent with current high-precision cosmological data.

Technical Summary: Evolving Wormhole Cosmology

More like this