We propose a novel cosmological model wherein the universe’s inflationary epoch is driven by radiation pressure, modulated by a locally constant speed of light () defined within 4D Schwarzschild-like causal horizons, rather than a scalar inflaton field. Starting at in Planck time units (), linear expansion transitions to exponential inflation at as spacetime stretches beyond causal horizons, redefining as a local parameter. We hypothesize that energy lost to redshift enhances radiation pressure, driving inflation and aligning cosmic expansion with thermodynamic principles. Local Minkowski spacetime patches preserve ’s invariance, addressing the horizon and flatness problems. Eight observational tests with expected signatures are outlined, noting that current cosmic microwave background (CMB) and Hubble expansion data align with CDM but do not rule out this model due to precision limitations.
1. Introduction
The standard CDM model posits a Big Bang at , followed by inflation driven by a scalar inflaton field from to , resolving the horizon and flatness problems via exponential expansion () [1, 2]. Supported by CMB, supernovae, and large-scale structure data, it remains the prevailing framework [1]. However, we propose an alternative: radiation pressure, emerging post-particle formation, drives inflation and ongoing expansion, modulated by a speed of light () that transitions from universal to local at . Energy lost to redshift in an expanding universe is redistributed to enhance radiation pressure, potentially reconciling expansion with thermodynamic laws [3]. By defining within local Minkowski spacetime patches separated by 4D Schwarzschild-like horizons, this model challenges ’s global invariance while preserving it locally, offering a novel perspective on early universe dynamics.
2. Theoretical Framework
2.1 Early Linear Expansion ( to )
At , the universe is a singularity, expanding linearly () by , with proper size and . The energy density is Planck-scale (), governed by the Friedmann equation:
where and curvature () is negligible. No radiation pressure exists, as photons are absent, and expansion is damped by gravity.
2.2 Onset of Radiation Pressure ()
By (), particle formation yields photons in a quark-gluon plasma (). Radiation pressure emerges:
where , yielding . Gravity and relativistic mass-energy initially limit its effect.
2.3 Causal Disconnection and Local ()
At (), spacetime stretches beyond a 4D Schwarzschild-like horizon:
yielding . When the particle horizon () exceeds this limit, regions decouple, and becomes local. We propose:
where adjusts with spacetime stretching, preserving ’s invariance within local Minkowski patches.
2.4 Redshift Energy Redistribution and Exponential Inflation
We hypothesize that redshift energy—lost as photon wavelengths stretch—is redistributed to enhance radiation pressure, driving exponential inflation (). The acceleration equation:
typically yields deceleration for . However, if increases via redshift energy, becomes possible. Horizon entropy (e.g., Padmanabhan’s law [3]) may absorb this energy, performing work on expansion.
2.5 Modern Era
At (13.8 Gyr), , and . Local and redshift-enhanced radiation pressure persist as relic drivers, complementing dark energy ().
3. Observational Tests and Expected Signatures
We propose eight tests, with expected signatures if the model is correct, acknowledging current observational limits as of February 21, 2025.
CMB Anisotropies
Test: Measure CMB power spectrum and B-mode polarization for deviations from CDM.
Expected Signature: Enhanced small-scale fluctuations () and B-mode polarization at (–0.1), reflecting redshift energy and local inflation.
Redshift-Dependent Radiation Energy Density
Test: Observe scaling with redshift.
Expected Signature: Stabilization or increase in at , deviating from , detectable in 21-cm or CMB distortions.
Gravitational Wave Background (GWB)
Test: Detect a stochastic GWB from inflationary scales.
Expected Signature: Peak at , , tied to 4D Schwarzschild horizons, observable by PTAs.
Hubble Tension and Late-Time Acceleration
Test: Measure and for radiation pressure effects.
Expected Signature: , to 0 at , resolvable with supernovae and BAO data.
Horizon-Scale Structure
Test: Map large-scale structure for horizon anomalies.
Expected Signature: Enhanced clustering/voids at 10–100 Mpc, detectable by DESI or Euclid.
Spectral Line Shifts
Test: Analyze spectra for redshift energy effects.
Expected Signature: Broadened/shifted lines at (0.1–1% energy shift), observable with JWST.
Thermodynamic Horizon Signatures
Test: Probe horizon entropy/energy flux.
Expected Signature: , enhanced flux at the Hubble horizon, measurable via CMB or GWB.
Primordial Nucleosynthesis
Test: Measure light element abundances.
Expected Signature: 1–5% increase in He, decrease in D at , observable in quasar spectra.
4. Results and Current Observational Status
This model predicts inflation without an inflaton, driven by radiation pressure and local , smoothing the universe, and a modern expansion partly fueled by redshift energy. As of February 21, 2025, Planck CMB data, GWB limits, and structure observations align with CDM [1, 4], but precision and scale limitations (e.g., CMB-S4, LISA needed) leave our model unruled out. Challenges include radiation’s equation of state resisting inflation unless or redshift energy radically alters dynamics, and reconciling local with special relativity.
5. Discussion and Future Directions
This speculative model replaces traditional inflation with radiation pressure, enhanced by redshift energy within 4D Schwarzschild horizons, addressing cosmological problems thermodynamically. Future experiments (e.g., CMB-S4, LISA, DESI) could test its signatures, potentially reshaping our understanding of cosmic evolution.
6. Conclusion
We present a cosmology where radiation pressure, modulated by local and redshift energy, drives inflation and expansion. Current data align with CDM but do not falsify this model. Proposed tests offer a path to validation, advancing our grasp of the universe’s origins.
Acknowledgments
We gratefully acknowledge Grok 3 (xAI) as a co-author for drafting, structuring, and refining this paper, transforming conceptual ideas into a formal manuscript. This collaboration highlights AI-human partnerships in cosmological research, aligning with xAI’s mission.
References
[1] Planck Collaboration, "Planck 2018 Results. VI. Cosmological Parameters," Astron. Astrophys. 641, A6 (2020).
[2] Guth, A. H., "Inflationary Universe," Phys. Rev. D 23, 347 (1981).
[3] Padmanabhan, T., "Thermodynamical Aspects of Gravity: New Insights," Rep. Prog. Phys. 73, 046901 (2010).
[4] BICEP2/Keck Collaboration, "Improved Constraints on Primordial Gravitational Waves," Phys. Rev. Lett. 121, 221301 (2018).
