The first nuclear clock will test if fundamental constants change

Variation of Fundamental Constants

• Several comments focus on how much spatial or temporal variation in constants (fine-structure constant, G, proton–electron mass ratio) is compatible with existing observations. Current limits quoted are extremely small per year.
• Spectral lines from distant galaxies (e.g., hydrogen Lyman series) are emphasized as sensitive probes: redshifted spectra still have the same relative line spacings once redshift is corrected, strongly constraining variation.
• Oklo’s natural nuclear reactor is cited as evidence that the fine-structure constant has remained effectively unchanged over ~2 billion years.

Observational and Experimental Probes

• Spectroscopy of distant galaxies and quasars: compare line positions and spacings to local lab values; look for anisotropies or “stacked” features like the Lyman-alpha forest.
• Natural reactors and fossil processes (Oklo) provide long-baseline checks on nuclear physics parameters.
• Ultra-precise atomic and optical lattice clocks already detect gravitational time dilation over centimeter height differences; a thorium-229 nuclear clock would further tighten constraints and search for tiny drifts.
• Environmental noise (height changes, lunar/planetary tides, Earth’s orbit, mass redistribution) must be modeled out for such clocks.

Units, Dimensionless Ratios, and “What’s Really Fundamental”

• Strong debate over which quantities are truly fundamental. Many constants can be removed by choosing natural units; what remain are dimensionless coupling strengths and a small number of dimensionful scales.
• Some argue only interaction strengths (gravity, EM, strong, weak) are fundamental; particle masses and mixing parameters are then derived properties or ratios. Others point out that in the Standard Model a couple dozen parameters (including mass ratios and mixing angles) are empirically fundamental.
• It’s stressed that variation of dimensionless constants (e.g., fine-structure constant) is physically meaningful, whereas variation of a dimensionful constant alone can be partly a matter of convention.

Cosmology, Dark Matter/Energy, and the Big Bang

• Dark matter and dark energy are discussed as “placeholders” for discrepancies vs. as real but unknown substances. MOND and other modified-gravity ideas are mentioned but considered less successful overall than standard ΛCDM.
• Some speculate varying constants might mimic dark components or alter inferred expansion rates, but this is presented as highly constrained and speculative.
• There are side discussions about whether time existed “before” the Big Bang, cyclic/Big Crunch models, and whether changes in constants could trigger a bang; consensus is that such ideas are interesting but very hard to test.

Relativity, Time, and Clocks

• Gravitational time dilation is central: clocks at different heights tick at measurably different rates; modern optical clocks can see ~1 cm differences.
• The equivalence principle is noted to be only locally exact; for sufficiently large “elevators” tidal and redshift effects across the height become detectable.
• There is extended debate about photons, proper time, affine parameters, and the popular simplification that photons “experience no time.” Some call this a pedagogical oversimplification rather than literally correct.

Energy Conservation and Thermodynamics

• One commenter claims varying constants would break energy conservation and the second law. Replies counter that:
  • Energy conservation is subtle or ill-defined in general relativity; global conservation doesn’t strictly hold in expanding spacetime.
  • The second law is statistical and about entropy, not strictly tied to exact energy conservation; a varying total energy doesn’t automatically violate it.

Philosophical and Conceptual Debates

• Some propose unfalsifiable ideas (e.g., constants or outcomes differ when unobserved); others criticize this as definitional or god-of-the-gaps reasoning.
• There is discussion about whether existence and observability should be treated as equivalent, and the general impossibility of “proving a negative.”
• A meta-point: if everything changed, including our rulers and clocks, some kinds of variation might be intrinsically undetectable; only relative and dimensionless changes are operationally meaningful.

Why a Nuclear Clock Matters

• A thorium-229 nuclear clock would be sensitive to different combinations of constants than electronic/optical transitions, offering a new “ruler” to compare against existing clocks.
• If any drift is seen, cross-checks with other clocks and astrophysical data could reveal whether fundamental couplings are changing, which would force a major revision of current physics.
• If no drift is found at unprecedented precision, it further tightens bounds on any variation, reinforcing the assumption of constant laws across cosmological time and space.