Measuring possible variations of the fine structure constant relative to the primordial universe, and possible variations of G, the gravitational constant, in high regimes and relative to the primordial universe.
To tackle these, the community is considering scaling up infrastructure, improving sensitivity through technology or the L2/Lunar environment, and cross-correlation — essentially multi-messenger astronomy, where cosmological laws intersect with particle physics.
Does the Fine Structure Constant Change with Cosmic Time? First Constraint from Galaxies at z 5 with JWST
What is this about?
The fine structure constant (α) is one of the fundamental constants of nature: it controls the strength of the electromagnetic interaction. If α had varied throughout the history of the universe, physics as we know it would be different. That is why measuring α in remote epochs of the cosmos is one of the most direct tests we have to know whether the fundamental laws are truly constant.
What did I do?
I used 212 galaxies at z 5 (when the universe was less than 1.2 billion years old) observed with the NIRSpec instrument on the James Webb Space Telescope, within the JADES DR3 survey. I combined the Hβ (4862.68 Å) and [OIII] (5008.24 Å) emission lines in a rest-frame stacked spectrum, and compared their positions with laboratory values to search for a possible relative variation Δα/α.
What did I find?
- Δα/α = +3.02 ± 5.73 ppm (statistical, via bootstrap with 100 iterations)
- Consistent with zero variation at 0.53σ
- 2σ upper limit: |Δα/α| < 1.15 × 10⁻⁵
The dominant systematic is the per-object dispersion (272 ppm), which I corrected with a multiline redshift (Hβ, Hα, [OIII], [NII]).
Why does it matter?
This is, to my knowledge, the first upper limit on Δα/α at z 5 using emission lines. The advantage of using emission instead of absorption (as is done with quasars) is that it eliminates the non-uniqueness of models that affects absorption studies, a potential bias of up to ~2.5 ppm.
What's next?
The current sensitivity floor is at ~10⁻⁵, dominated by Hβ. To reach 10⁻⁶ it would be necessary to model Hβ more carefully (broad wings, Balmer absorption) and refine redshifts with machine learning techniques. I also plan to extend the analysis to the CEERS, UNCOVER, PRIMER and Roman surveys, and to validate the method with JWST quasars at z 5.
Closing line for the post:
"At z 5, the fine structure constant remains consistent with a constant. But the precision is not yet enough to rule out variations of the order of 10⁻⁶. The next leap will come from the combination of JWST, Euclid and Roman."
Advanced strategies for measuring α in the primordial universe
Starting from the theoretical and methodological foundations of the VCV48 model — a new crystallographic alternative of the vacuum — together with the other six proposals detailed below, advanced procedures can be put forward to drastically improve the precision and sensitivity in the measurement of the fine structure constant (α) in the primordial universe and at high redshift.
The six main proposals (together with VCV48)
1. VCV48: crystallographic alternative of the vacuum
The VCV48 model proposes a crystallographic description of the quantum vacuum, where the vacuum lattice presents a coherent phase structure that can be modulated as a function of the baryonic density and the local gravitational field. This is the theoretical basis on which the following methodological proposals rest.
2. Stacking and strict S/N selection with JWST
Given the limitations of individual high-depth samples (low initial statistical significance), it is proposed to use raw spectroscopic data from JWST to implement massive galaxy stacking or apply rigorous filtering that selects only spectra with high S/N. This allows the experimental error bar to be reduced below the predicted drift threshold.
3. High-resolution spectrographs (ELT/ANDES)
Achieve an instrumental precision of ~ppm to isolate the signature of the vacuum lattice in regions of low cosmic density (voids). This is complemented by the application of the real-time drift test (Sandage effect) over a 20-year time horizon with cm/s stability.
4. High-statistics mapping (Roman)
Extend the void structural mapping analysis toward lower-z regimes by taking advantage of the large-area surveys of the Roman Space Telescope, focusing specifically on the evaluation of harmonic 10 to correlate local fluctuations with the orientation of the lattice.
5. Elastic response in protoclusters (Euclid + JWST)
Measure with high spectroscopic precision the spectral index in massive protoclusters at z ~ 2–4, seeking a direct correlation with halo mass, requiring a demanding instrumental stability threshold to overcome the variance in emission-line sensitivity.
6. Cross-correlation between the CMB and Large-Scale Structure (LSS)
Implement galaxy stacking on CMB temperature maps to isolate the modulation of the integrated Sachs-Wolfe effect (ISW), which depends directly on the elastic response function and the halo mass.
7. Optimization in local massive clusters
Prioritize the selection of galaxies in local massive clusters with moderate to high velocity dispersions (σ ~ 500–1000 km/s), because in this regime the phase coherence of the lattice reaches its maximum values and global systematic errors are duly bounded below 15%.
Why extreme cosmological scales?
To isolate and reveal a variation or sensitivity of α — beyond its static local value, already known with very high precision in terrestrial laboratories — it is imperative to resort to extreme cosmological scales, for three reasons:
- Accumulation of historical drift: the temporal or spatial variations predicted by vacuum rheological models are extremely subtle (ppm or fractional). Large distances and high z are needed for this drift to accumulate enough to be distinguishable from instrumental errors.
- Gravity and density regimes: the elastic response of the vacuum depends directly on the baryonic charge and the local gravitational field. High-density regions or non-linear gravity regimes act as amplifiers or modulators of the lattice tensions, making the sensitivity to α and its coupling with G or Ω_k measurable.
- Unique window: local laboratories fix with surgical precision the current starting point (z = 0), but the only window with the real potential to reveal whether α is dynamic is the study of the primordial universe, the cosmic background, and the kinematics of massive structures on large scales.
Vallejos, O. A. (2026). Constraint on the Fine Structure Constant at z 5 from Stacked JWST/NIRSpec Spectra. Zenodo. https://doi.org/10.5281/zenodo.23373471





















































