Is our world in free fall? A kinematic reinterpretation of cosmic expansion
Abstract
Based on entropy considerations, Boltzmann proposed that our universe might be a fluctuation within an eternal background. Combined with gravitation, this idea leads to an alternative cosmological scenario, the Boltzmann Universe (BU), where expansion and its apparent acceleration arise from gravitational free fall on hyperbolic trajectories. This collective inertial dispersion, in which cosmological redshift results from relativistic Doppler shifts along a geodesic congruence, reproduces key observational signatures such as the Hubble law, large-scale homogeneity, and effective spatial flatness. Although its theoretical foundations diverge from the standard FLRW paradigm (Standard Universe, SU), the BU maps onto several kinematic features of the SU through geometric representations, while leading to distinct distance-redshift relations. By reformulating cosmic dynamics in special-relativistic terms, the BU provides a kinematic model of large-scale expansion without a cosmological constant or exotic fields, in which the role attributed in the SU to dark energy, driving expansion against gravity, is instead fulfilled by standard gravity itself.
Related
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BibTeX
@misc{michel2026world,
title = {{Is our world in free fall? A kinematic reinterpretation of cosmic expansion}},
author = {Denis Michel},
howpublished = {HAL},
year = {2026},
month = jul,
url = {https://hal.science/hal-05002991v7},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Is our world in free fall? A kinematic reinterpretation of cosmic expansion
AU - Denis Michel
PY - 2026
DA - 2026/07/31
PB - HAL
UR - https://hal.science/hal-05002991v7
AB - Based on entropy considerations, Boltzmann proposed that our universe might be a fluctuation within an eternal background. Combined with gravitation, this idea leads to an alternative cosmological scenario, the Boltzmann Universe (BU), where expansion and its apparent acceleration arise from gravitational free fall on hyperbolic trajectories. This collective inertial dispersion, in which cosmological redshift results from relativistic Doppler shifts along a geodesic congruence, reproduces key observational signatures such as the Hubble law, large-scale homogeneity, and effective spatial flatness. Although its theoretical foundations diverge from the standard FLRW paradigm (Standard Universe, SU), the BU maps onto several kinematic features of the SU through geometric representations, while leading to distinct distance-redshift relations. By reformulating cosmic dynamics in special-relativistic terms, the BU provides a kinematic model of large-scale expansion without a cosmological constant or exotic fields, in which the role attributed in the SU to dark energy, driving expansion against gravity, is instead fulfilled by standard gravity itself.
ER -