On the Hubble expansion in a Big Bang quantum cosmology

Invited colloquium (Ariel University, Israel). We are living in a golden era of cosmology, marked by increasingly precise observational data and comprehensive surveys of the large-scale structure. While the standard cosmological model with Einsten's cosmological constant Λ (with cold dark matter, ΛCDM) remains a successful phenomenological framework, persistent tensions—such as those in Hubble constant measurements—indicate possible gaps in its theoretical foundation. To explore potential extensions, we consider the fundamental question: how general is general relativity? A structural analysis suggests that the Minkowski vacuum underlying general relativity is not equivalent to the cosmological vacuum, which undergoes conformal scaling. We propose that gravitation may couple to the trace J of the Schouten tensor, introducing sensitivity to background curvature in a Machian sense. Within this framework, we derive an analytic solution for cosmic expansion that shares the parameter space of ΛCDM but differs in vacuum structure: approximately 5/6 classical and 1/6 non-classical. This modified model—termed JCDM—remains in agreement with several key cosmological observations. These include the pattern of ancient light known as the Cosmic Microwave Background (CMB measured by the Planck satellite), current estimates of the Hubble expansion rate (based on distance measurements to nearby galaxies), and the large-scale distribution of galaxies, which preserves a subtle imprint of early-universe sound waves known as baryon acoustic oscillations (recently mapped by the DESI survey). Remarkably, JCDM predicts a slightly higher Hubble constant than the standard ΛCDM model—by a factor of $\sqrt{6/5}$—providing a potentially natural resolution to the ongoing discrepancy in Hubble constant measurements, through the model’s built-in sensitivity to background curvature. (Ref. van Putten, 2025, JHEAP, 45, 19)