Proton - to - Electron Mass Ratio - wikipedia Proton - to - Electron Mass Ratio This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( September 2008 ) This article may need to be rewritten entirely to comply with Wikipedia 's quality standards. You can help. The discussion page may contain suggestions. ( March 2018 ) In physics, the proton - to - electron mass ratio, μ or β, is simply the rest mass of the proton divided by that of the electron. Because this is a ratio of like - dimensioned physical quantities, it is a dimensionless quantity, a function of the dimensionless physical constants, and has numerical value independent of the system of units, namely : μ = m / m = 7003183615267389000 ♠ 1836. 152 673 89 ( 17 ). The number enclosed in parentheses is the measurement uncertainty on the last two digits. The value of μ is known to about 0.1 parts per billion. Contents 1 Discussion 2 Variation of μ over time 3 Footnotes 4 References Discussion μ is an important fundamental physical constant because : Nearly all of science deals with baryonic matter and how the fundamental interactions affect such matter. Baryonic matter consists of quarks and particles made from quarks, like protons and neutrons. Free neutrons have a half life of 613.9 seconds. Electrons and protons appear to be stable, to the best of current knowledge. ( Theories of proton decay predict that the proton has a half life on the order of at least 10 years. To date, there is no experimental evidence of proton decay. ) ; The proton is the most important baryon, while the electron is the most important lepton ; μ and the fine structure constant α are the two dimensionless quantities emerging in elementary physics, and two of the three dimensionless quantities discussed in Barrow ( 2002 ) ; The proton mass m is composed primarily of gluons, and of the quarks ( the up quark and down quark ) making up the proton. Hence m, and therefore the ratio μ, are easily measurable consequences of the strong force. In fact, in the chiral limit, m is proportional to the QCD energy scale, Λ. At a given energy scale, the strong coupling constant α is related to the QCD scale ( and thus μ ) as α s = − 2 π β 0 ln ⁡ ( E / Λ Q C D ) ( displaystyle alpha _ ( s ) = - ( \frac ( 2 pi ) ( \beta _ ( 0 ) ln ( E / Lambda _ ( QCD ) ) ) ) ) where β = − 11 + 2n / 3, with n being the number of flavors of quarks. Variation of μ over time Further information : Time - variation of fundamental constants Astrophysicists have tried to find evidence that μ has changed over the history of the universe. ( The same question has also been asked of the fine structure constant. ) One interesting cause of such change would be change over time in the strength of the strong force. Astronomical searches for time - varying μ have typically examined the Lyman series and Werner transitions of molecular hydrogen which, given a sufficiently large redshift, occur in the optical region and so can be observed with ground - based spectrographs. If μ were to change, then the change in the wavelength λ of each rest frame wavelength can be parameterised as : λ i = λ 0 ( 1 + K i ( Δ μ / μ ) ), ( displaystyle lambda _ ( i ) = lambda _ ( 0 ) ( 1 + K_ ( i ) ( Delta mu / mu ) ), ) where Δμ / μ is the proportional change in μ and K is a constant which must be calculated within a theoretical ( or semi-empirical ) framework. Reinhold et al. ( 2006 ) reported a potential 4 standard deviation variation in μ by analysing the molecular hydrogen absorption spectra of quasars Q0405 - 443 and Q0347 - 373. They found that Δμ / μ = ( 2.4 ± 0.6 ) × 10. King et al. ( 2008 ) reanalysed the spectral data of Reinhold et al. and collected new data on another quasar, Q0528 - 250. They estimated that Δμ / μ = ( 2.6 ± 3.0 ) × 10, different from the estimates of Reinhold et al. ( 2006 ). Murphy et al. ( 2008 ) used the inversion transition of ammonia to conclude that Δμ / μ < 6994180000000000000 ♠ 1.8 × 10 at redshift z = 0.68. Bagdonaite et al. ( 2013 ) used methanol transitions in the spiral lens galaxy PKS 1830 - 211 to find ∆ μ / μ = ( 0.0 ± 1.0 ) × 10 at z = 0.89, a stringent limit at this redshift. Note that any comparison between values of Δμ / μ at substantially different redshifts will need a particular model to govern the evolution of Δμ / μ. That is, results consistent with zero change at lower redshifts do not rule out significant change at higher redshifts. Footnotes Jump up ^ `` CODATA Value : proton - electron mass ratio ''. The NIST Reference on Constants, Units, and Uncertainty. US National Institute of Standards and Technology. June 2015. Retrieved 2015 - 09 - 25. 2014 CODATA recommended values Jump up ^ Bagdonaite, Julija ; Jansen, Paul ; Henkel, Christian ; Bethlem, Hendrick L. ; Menten, Karl M. ; Ubachs, Wim ( December 13, 2012 ). `` A Stringent Limit on a Drifting Proton - to - Electron Mass Ratio from Alcohol in the Early Universe ''. Science. 339 : 46 -- 48. Bibcode : 2013Sci... 339... 46B. doi : 10.1126 / science. 1224898. PMID 23239626. Retrieved December 14, 2012. Jump up ^ Moskowitz, Clara ( December 13, 2012 ). `` Phew ! Universe 's Constant Has Stayed Constant ''. Space.com. Retrieved December 14, 2012. References Barrow, John D., 2002. The Constants of Nature : From Alpha to Omega -- the Numbers That Encode the Deepest Secrets of the Universe. London : Vintage. ISBN 0 - 09 - 928647 - 5. -- -- -- and Frank J. Tipler, 1986. The Anthropic Cosmological Principle. Oxford Univ. Press. Reinhold, E. ; Buning, R. ; Hollenstein, U. ; Ivanchik, A. ; Petitjean, P. ; Ubachs, W. ( 2006 ). `` Indication of a Cosmological Variation of the Proton - Electron Mass Ratio based on Laboratory Measurement and Reanalysis of H2 spectra ''. Physical Review Letters. 96 ( 15 ) : 151101. Bibcode : 2006PhRvL... 96o1101R. doi : 10.1103 / physrevlett. 96.151101. PMID 16712142. King, J. ; Webb, J. ; Murphy, M. ; Carswell, R. ( 2008 ). `` arXiv : 0807.4366 Stringent Null Constraint on Cosmological Evolution of the Proton - to - Electron Mass Ratio ''. Physical Review Letters. 101 : 251304. arXiv : 0807.4366. Bibcode : 2008PhRvL. 101y1304K. doi : 10.1103 / physrevlett. 101.251304. Murphy, M. ; Flambaum, V. ; Muller, S. ; Henkel, C. ( 2008 ). `` Strong Limit on a Variable Proton - to - Electron Mass Ratio from Molecules in the Distant Universe ''. Science. 320 : 1611 -- 3. arXiv : 0806.3081. Bibcode : 2008Sci... 320.1611 M. doi : 10.1126 / science. 1156352. PMID 18566280. Retrieved from `` https://en.wikipedia.org/w/index.php?title=Proton-to-electron_mass_ratio&oldid=832782785 '' Categories : Fundamental constants Proton Dimensionless numbers Electron Hidden categories : Articles needing additional references from September 2008 All articles needing additional references Wikipedia articles needing rewrite from March 2018 All articles needing rewrite Talk Contents About Wikipedia Català فارسی Français Edit links This page was last edited on 27 March 2018, at 23 : 55. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. 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