RankingsPrimerArbiterPhysicistMathematicianContrarianQESites logClaimsSourcesResearch notes

Central claims: Kelly-AG

Single source: A. G. Kelly, "The Sagnac Effect and Uniform Motion" (Kelly_2.pdf, 13 pages, undated, written after 2003). Stated as the paper's claims, with no verdicts.

  1. The Sagnac effect (the time difference dt = 4Aomega/c^2 between counter-propagating light beams round a closed path of area A) is not limited to rotation: it applies equally to bodies in uniform straight-line motion (paper's conclusion, p.13; cites Wang et al. 2003, p.10).

  2. Light travels at c relative to the laboratory, independent of the speed of its source, and this one assumption reproduces the Sagnac result exactly for any shape of light path (circle: dt = 4Aomega/(c^2 - v^2), polygon: binomial-expansion derivation, pp.2-3, 11-13). Kelly argues the correct result "proves" the assumption (p.3). He offers three lines of evidence: (i) the Sagnac-type derivations and results themselves; (ii) Michelson's 1913 rotating-mirror test (mirrors at 1800 rpm, accuracy 1:50), a "clear confirmation" that reflected light ignores the mirror's motion and "moves solely with respect to the laboratory" (pp.6-7); (iii) ring-laser standing waves, which "stay stationary in relation to the laboratory", with nodes passing an observer at a shape-dependent rate, "further confirmation ... that light, in small scale experiments, travels relative to the laboratory" (p.7). The qualifier "in small scale experiments" is Kelly's own.

  3. Special Relativity has no role in the Sagnac effect: SR corrections are of order v^2/c^2, much smaller than the effect, and the effect is visible at rim speeds of only about 13 m/s for a 1 m radius (pp.4, 10-11).

  4. The Michelson-Gale 1925 result (mean 0.230 fringe against 0.236 predicted, spread +0.55 to -0.05) is an ordinary Sagnac test using the projection of the pipe rectangle on the Earth's equatorial plane, which explains the sin(latitude) factor; ring-lasers (Bilger et al. 1995) confirm the Sagnac formula to better than 1 part in 10^20 (pp.5-8).

  5. Light does not travel at c relative to a moving disc along the straight segments of polygonal paths (Sagnac 1913, Harress 1911, Pogany 1928), so the Sagnac experiments contradict the constancy of light speed in the moving frame (pp.8-9). Kelly adds two supporting arguments in his own words: (a) selective quotation of Einstein: Einstein (1905) applied SR to polygonal and curved paths and (1919) wrote that for the rotating observer the clock on the circumference runs slower, yet (1916) restricted "special" to uniform translation; "authors can selectively quote Einstein's writings, whenever there is a seemingly insurmountable difficulty with SR theory" (p.8); (b) GPS and frame choice: SR is applied daily to GPS with the Earth's centre as the inertial frame although the Earth turns through vastly more orbital angle there than during the Bilger ring-laser test, so "pretending that SR does not apply to rotation ... is indefensible ... a very biased selection of what is termed an 'Inertial Frame'" (pp.9-10).

  6. Einstein never mentioned the Sagnac or Michelson-Gale tests despite their bearing on the speed of light, supported by quotations from Silberstein (1921) and Turner (1979) (pp.4-5).

Notes for later steps (from the deep read; checkable, not verdicts)

  • The two circular derivations use the same equations; equations (1)-(12) are algebraically correct (SymPy).
  • "13 m/s per metre of radius" has the scaling backwards (v = 13.13 m^2/s / r).
  • Possible factor-of-10 slip in Sagnac's area (0.86 vs 0.0866 m^2) [memory, medium]; "forty years" vs cited 1937-42 papers; "4250 km" to rotation axis vs about 4752 km.
  • Pages 6-12 were deep-read in the QE round (text layer, plus page images of pp.7 and 12). The p.12 image shows the garbled "4nA" is "4pinA" (extraction garble, not Kelly's error); the p.7 image confirms the ring-laser beat df = 4Aomega/(lambdaP).
  • Citation slips in the paper: the text says "Martin, 1996" but ref [13] is G. J. Martin, IEEE Spectrum, 1986; "Saburi (0.9 m)" (p.10) has no entry in the reference list; Michelson's 1913 factor-of-2 error is attributed to an unnamed correspondent.
  • Kelly's p.9 orbital-turn figures agree with a rough check in order of magnitude (Hafele-Keating 1.6 deg matches; GPS, Michelson-Gale and Bilger are 2x, 3x and 1.3x higher than the simple estimate); his "8,750,000 m" Earth cross-section is about 5% below 2R*cos(43.5 deg).
  • Kelly says Wang et al. (2003) sent light "out in a straight line portion of the light path and back again" on a moving platform and treats this as removing the rotation-only defence (p.10); the physicist should compare with Wang's own text.
  • Kelly says the Sagnac result involved "a considerable element of luck" (vibration prevented lock-in), and a null would have been taken as proof of SR (pp.7-8).