Summary: Is the velocity of light a fixed constant of nature, invariant over time? This page presents the available measurements of c and several statistical studies which suggest that c has decreased in the past 300 years. What other "constants" of physics might prove to be non-fixed? How would a non-constant c affect physical laws? Possible consequences for cosmology and the age of the universe. Responses and comments are solicited.

Of Special Interest

Your email comments and questions for Barry Setterfield are welcome, Barry Setterfield



by Alan Montgomery, Mathematician
218 McCurdy Drive, Kanata, Ontario K2L 2L6 Canada
Lambert Dolphin, Physicist
1103 Pomeroy Avenue, Santa Clara, CA 95051


The possibility that the velocity of light, c, is not a fixed constant is reconsidered by statistical analysis of the historical measurements collected from four sources. Our hypothesis testing of the selected data shows the measured value of the velocity of light has decreased over the past 250 years. Furthermore, the probability of some systematic or experimental problem was found to be low. Brief analysis of constants other than c suggests that those constants which involve atomic phenomena and units of time are also apparently changing. A third set of constants with no obvious dependence on c were analyzed and show no apparent variability with time. A variable velocity of light implies that atomic clocks and dynamical clocks do not run in step-that atomic time has been decreasing with respect to dynamical time.

Published in Galilean Electrodynamics, Vol. 4, no. 5, Sept/Oct 1993; PO Box 545, Storrs, CT 06268-0545. The c-data set is available in a tab-delineated text version, cdata.txt. A full list of 193 published c measurements with references, and the authors' selected best data set is also available: Data Tabulation: Velocity of Light These data are as complete as we could make them. If additional data points not listed in these tables is known, please contact one of the authors. Our Excel file with equations is also available.


Alan Montgomery presented a later paper entitled

"An Analysis of the Values of the Speed of Light to Determine Appropriate Data to Test the Setterfield Hypothesis"

---at the Pittsburgh Third International Conference on Creationism, Summer 1994. Copies of this paper may be obtained for $3.00 from Lambert Dolphin or from the author. For a tape ($5) or for the entire conference Proceedings ($39.95 plus shipping) write ICC, Creation Science Fellowship, Inc., PO Box 99303, Pittsburgh, PA 15233-4303.


The velocity of light data from four different sources are tabulated, edited, and analyzed to provide data sensitive enough to detect a decrease [in c] of the size claimed by Setterfield and Norman. Data is analyzed by weighted regression, time, distribution, accuracy and precision to test for a significant decrease and any influences which might help identify its cause(s).


by Barry Setterfield and Trevor Norman.
August 1987.

This was an invited research paper (a "white paper") prepared for Lambert Dolphin who was at that time a Senior Research Physicist at SRI International, Menlo Park, California. Not an official SRI report.

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You may write Barry Setterfield at Box 318, Blackwood, S.A. 5051, Australia.


The behavior of the atomic constants and the velocity of light, c, indicate that atomic phenomena, though constant when measured in atomic time, are subject to variation in dynamical time. Electromagnetic and gravitational processes govern atomic and dynamical time respectively. If conservation laws hold, many atomic constants are linked with c. Any change in c affects the atom. For example, electron orbital speeds are proportional to c, meaning that atomic time intervals are proportional to 1/c. Consequently, the time dependent constants are affected. Therefore Planck's constant, h, may be predicted to vary in proportion to 1/c as should the half-lives of the radioactive elements. Conversely, the gyromagnetic ratio, g, should be proportional to c. And variation in c, macroscopically, therefore reflects in the microcosm of the atom. A systematic, non-linear decay trend is revealed by 163 measurements of c in dynamical time by 16 methods over 300 years. Confirming trends also appear in 475 measurements of 11 other atomic quantities by 25 methods in dynamical time. Analysis of the most accurate atomic data reveals that the trend has a consistent magnitude in all quantities. Lunar orbital decay data indicate continuing c decay with slowing atomic clocks. A decay in c also manifests as a red-shift of light from distant galaxies. These variations have thus been recorded at three different levels of measurements: the microscopic world of the atom, the intermediate level of c measurements, and finally on an astronomical scale. Observationally, this implies that the two clocks measuring cosmic time are running at different rates. Relativity can be shown to be compatible with these results. In addition, gravitational phenomena are demonstrated invariant with changes in c and the atom. Observational evidence also demands consistent atomic behavior universally at any given time, t. This requires the permeability and metric properties of free space to be changing. In relativity, these attributes are governed by the action of the cosmological constant, Lambda, proportional to c squared, whose behavior can be shown to follow an exponentially damped form... This is verified by the c data curve fit. (Note: A dynamical second is defined as 1/31,556,925.9747 of the earth's orbital period and was standard until 1967. Atomic time is defined in terms of one revolution of an electron in the ground state orbit of the hydrogen atom. The atomic standard by the cesium clock is accurate to limits of ± 8 x 10-14.

A Quotation

"We know that the discovery of the fact that the speed of light, when measured both in the direction of the rotation of the earth and in the direction opposite to that rotation, is invariable, has confronted modern astronomers with the alternative either of accepting the immobility of the earth or else of rejecting the usual notions of time and space. Thus it was that Einstein was led into considering space and time as two relative dimensions, variable in function of the state of movement of the observer, the only constant dimension being the speed of light. The latter would everywhere and always be the same, whereas time and space vary in relation to one another: it is as if space could shrink in favor of time, and inversely...

"That the movement of light is a fundamental 'measure' of the corporeal world we willingly believe, but why should this measure itself be a number, and even a definite number? ...Now, what would happen if the constant character of the speed of light ever came to be doubted---and there is every likelihood that it will be sooner or later---so that the one fixed pivot of Einstein's theory would fall down? The whole modern conception of the universe would immediately dissolve like a mirage."--Titus Burckhardt, Mirror of the Intellect: Essays on Traditional Science and Sacred Art. (State University of New York Press; Albany, 1987), pp. 27-28.



William Q. Sumner (wsumner@cerf.net)
Box 588,
Kittitas, WA 98934


Vacuum permittivity, the measure of strength of electric fields in a vacuum, is a function of the spacetime geometry of Einstein's general relativity. This dependence on geometry was noted over 40 years ago by C. Moeller (1952) and has remarkable consequences. Variation in vacuum permittivity breaks the equivalence of physical measurements and mathematical coordinates postulated by Einstein. Physical lengths, as measured by a rigid rod, and physical times, as measured by an atomic clock, are not equivalent to the mathematical lengths and times of general relativity. This changes some concepts of space and time, invalidates stronger interpretations of the principle of equivalence, and requires that care be exercised in interpreting the speed of light. The laws of physics must be carefully used to understand the essential relationships between mathematical spacetime and physical measurements.

For Friedmann universes, vacuum permittivity is directly proportional to the Friedmann radius and is therefore a function of time. As the size of the universe evolves, the changing strength of the electrical force between charges shifts atomic energy levels, changing the wavelengths of emitted light. This shift in photon emission due to the evolution of electrical attraction in the atom is twice as large as evolutionary photon shift. Considered together, atomic and photon evolution reverse the interpretation of Hubble redshift to imply that the Friedmann universe is presently collapsing.

The Astrophysical Journal, 429: 429-491, 1994 July 10; Received 1993 March 31: accepted 1994 January 14.


"A Physical theory based solely on the first postulate of relativity"


Physics Department, University of Massachusetts, North Dartmouth MA 02747, and Physics Department, Harvard University, Cambridge, MA 02138, respectively.


Using the first postulate of relativity only, we develop a general theory, termed tajii relativity, which has four-dimensional symmetry and is consistent with experiments. Within this framework the speed of light is no longer a universal constant. Thus, quantum electrodynamics has only two fundamental constants, e(bar) and J, which are the analogues of e and h(bar). Some new results are implied.

Physics Letters A 196 (1994) 1-6.


Institute for Advanced Studies
1301 Capital Of Texas Highway S., Suite B 121
Austin, Texas 78746
(512) 328-5751

Note added July 1995: Barry Setterfield of Australia is currently working on a new cosmological model involving a near-static universe, zero-point energy, and a linearly decreasing velocity of light after creation until relatively recent times (followed by an exponential tail in the very recent epoch). Setterfield believes he has an explanation for a quantized red-shift of light from distant stars (U. of Arizona Astronomer Wm. Tifft's recent discoveries). Atomic Behavior, Light And The Red-Shift: Abstract and Summary. Hal Putoff's work is therefore believed by Setterfield to be especially relevant to developing models of the universe consistent with a decrease in the speed of light over time. For some possible theological implications see What Holds The Universe Together?



by V.S. Troitskii
Radiophysical Research Institute,
Gorky, USSR


A cosmological model is discussed which is based on interpretation of the red shift by decrease of the light speed with time everywhere in the Universe beginning with a certain moment of time in the past. The model is described by a metric in which the light speed depends on time and the radius of the curvature of three-dimensional space remains constant (c-metric). It is shown that this metric leads to the same observed facts and formulas of different characteristics that the metric of standard cosmology does but with essentially different physical interpretation. Such a property is the consequence of conformity of spaces being defined by both metrics. The agreement with the fundamental physics laws is achieved by introducing the evolution of a number of other fundamental constants synchronously with the variation of the light speed. The model considered connected the evolution of the Universe with evolution of physical constants and permits explaining some unclear phenomena--for example, a high isotropy of the relict background and superluminal speed in quasars.

Astrophysics and Space Science 139 (1987) 389-411.

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by Curtis E. Renshaw, President
William M. Kallfelz, M.S. Phys.
Tele-Consultants Inc.
10505 Jones Bridge Road, Alpharetta, GA 30202


Maxwell's equations do not in themselves predict a specific value for the constant (or variable) c which appears in them. This value is determined experimentally as the relative velocity at which a photon must strike an observer in order to be absorbed. By modifying the second postulate to state: "The observed velocity of light is c from all frames of reference," the radiation continuum model (RCM) of electromagnetic radiation is developed. On the basis of this model, a Galilean invariant form of Maxwell's equations is obtained. Equations for transverse and radial Doppler shift are derived. An analysis of the force on a moving charge above a neutral current carrying wire is provided from varying reference frames without resorting to SRT or Lorentz transformations. An application to particle accelerators explains the apparent mass increase with velocity.


Dimensional analysis of Maxwell's equations in a planar electromagnetic wave form implies wave propagation at a speed of c, defined as (e0 m0)-1/2. But such analysis does not specify anything at all about the specific values of e0 or m0. Thus Maxwell's equations in and of themselves say nothing about the specific velocity of propagation of an electromagnetic wave, nor of the detectable velocity or range of velocities in any particular observer's frame of reference. The generally accepted frame-invariance of c, and hence e0 and m0, constitutes an assumption. The Lorentz transformations allow the preservation of the form of Maxwell's equations in any inertial frame of reference (IFR) under this assumption, an assumption which Einstein raised to the status of a postulate.

But really it may be only the experimental means by which we measure the speed of light c, or e0 and m0, that produces the observed frame invariance...

Jan./Feb. 1996 GALILEAN ELECTRODYNAMICS, Vol. 1. #7.
PO Box 545, Storrs, CT 06268-0545.

Note added from a reviewer, 4/6/99: Curtis E. Renshaw, states that, in regards to the speed of light, "this value is determined experimentally as the relative velocity at which a photon must strike an observer in order to absorbed." This is absolutely false. While it is true the value is determined experimentally, the way this was done has absolutely nothing to do with what is stated in the article. First, e was a constant required to make the units square up in Coulomb's law. The magnetic permeability, m, was measured in the experimental derivation of the Biot-savart law for determining the magnetic field. These constants are found in Gauss law, which comes from Coulomb's law for the electric force on static, non-moving electrical charges. Mu shows up in Amperes law. When the curl is applied to Maxwell's equations this gives rise to the well known classical wave equation, and the constants e and m appear as the speed of the wave. When you multiply them out it turns out to be the speed of light.

Response from Curtis Renshaw: It is true that this product represents a speed, and the speed is the observed velocity of light, as it would have to be. This is actually my point. For example, if I measure m at one point in space in my reference frame, then you come by and measure m at the same point in space, yet traveling at some arbitrary velocity with respect to where I made my measurement, you will obtain exactly the same value. The same is true of e. Thus, in your reference frame, the speed of light observed by you will always be c, likewise in my reference frame. Again, this says nothing about the nature of the wave actually propagating through space, but rather only about our ability to observe or detect it. The characteristics of m and e, as measured locally by each of us, determine the velocity component of an expanding light wave to which we, in our respective reference frames, are susceptible. In subsequent presentations (Philadelphia, Russian Academy of Sciences 1998), I have used slides making exactly your point concerning m and e, and deriving the observed or detectable velocity component in that manner. (added January 10, 2002).


The Genuine Cosmic Rosetta, by Robert V. Gentry and David W. Gentry, (pdf)

A New Redshift Interpretation, by Robert V. Gentry (pdf)



Dr. Walt Brown is the Director of the Center for Scientific Creation. He is a retired full colonel (Air Force) and a West Point graduate with a Ph.D. in mechanical engineering from Massachusetts Institute of Technology. At M.I.T. he was a National Science Foundation Fellow. Dr. Brown has taught college courses in mathematics, physics, and computer science. While in the Army, he was a paratrooper and ranger. His most recent assignments during his twenty-one years of military service were Chief of Science and Technology Studies at the Air War College, tenured associate professor at the U.S. Air Force Academy, and Director of Benet Research, Development, and Engineering Laboratories in Albany, New York. Since retiring in 1980, Dr. Brown has been actively involved in speaking, writing, and research in creation-science.

Dr. Brown's book In the Beginning (6th Edition), now available on line, contains his own independent analysis of the speed of light information as well as a wealth of analytical information related to Biblical creation.

X. NEWS ITEM - November 15, 1998 - The London Sunday Times

From The London Sunday Times, (http://www.sunday-times.co.uk) - 25543

Speed of light 'slowing down'

by Steve Farrar, Science Correspondent

THE speed of light - the fastest thing in the universe - is getting slower. Physicists have devised a new theory to explain how the cosmos emerged from the big bang which overturns one of the central pillars of modern scientific belief - that the speed at which light travels has always been the same. The idea, proposed by two experts from Britain and America, could rewrite the textbooks and challenge Einstein's theory of relativity if space observations reveal evidence to support it.

Dr Joao Magueijo, a Royal Society research fellow at Imperial College, London, and Dr Andreas Albrecht, of the University of California at Davis, say the speed of light immediately after the universe was born may have been far faster than its present-day value of 186,000 miles a second. They say it has been slowing down ever since.

"If it's true, it would be a very big leap forward that will affect our perception of the universe and much of theoretical physics," said Magueijo. The effects predicted by the theory are to be published in the scientific journal, Physical Review D. One mystery that it seems to be able to explain is why the universe is so uniform - why opposite extremes of the cosmos that are too far apart to have ever been in contact with each other appear to obey the same rules of physics and are even at about the same temperature. It would only be possible for light to cross from one side to the other if it traveled much faster than today moments after the universe was created, between 10 billion and 15 billion years ago. Their hypothesis suggests it was so fast that it could have been traveling at 186,000 miles a second multiplied by a figure with 70 zeroes after it.

Calculations based on the theory also give the most elegant explanation for the speed at which the universe appears to be expanding, which is thought to be just fast enough to avoid an eventual collapse to a big crunch. Instead, the universe would simply grow for ever though at a decreasing rate, and its ultimate fate would be a slow, lingering death as all the stars burn out and every particle of matter within it separates. "It is remarkable when you can find one simple idea that has so many appealing consequences," said John Barrow, professor of astronomy and director of the Astronomy Centre at the University of Sussex, who has collaborated with Magueijo and Albrecht.

The new theory rivals the accepted theory, known as "inflation", to describe what happened immediately following the big bang.

  • "A Time Varying Speed of Light as a Solution to Cosmological Puzzles, " by Andreas Albrecht and Joao Magueijo, (PDF file, 288k)

  • Is Einstein About to be Dethroned?, by Nigel Hawkes

  • Speed Of Light May Not Be Constant, Physicist Suggests. Posted 10/6/99. A University of Toronto professor believes that one of the most sacrosanct rules of 20th-century science -- that the speed of light has always been the same - is wrong. Ever since Einstein proposed his special theory of relativity in 1905, physicists have accepted as fundamental principle that the speed of light -- 300 million meters per second -- is a constant and that nothing has, or can, travel faster. John Moffat of the physics department disagrees - light once traveled much faster than it does today, he believes.

    Recent theory and observations about the origins of the universe would appear to back up his belief. For instance, theories of the origin of the universe -- the "Big Bang"- suggest that very early in the universe's development, its edges were farther apart than light, moving at a constant speed, could possibly have traveled in that time. To explain this, scientists have focused on strange, unknown and as-yet-undiscovered forms of matter that produce gravity that repulses objects.

    Moffat's theory - that the speed of light at the beginning of time was much faster than it is now - provides an answer to some of these cosmology problems. "It is easier for me to question Einstein's theory than it is to assume there is some kind of strange, exotic matter around me in my kitchen." His theory could also help explain astronomers' discovery last year that the universe's expansion is accelerating. Moffat's paper, co-authored with former U of T researcher Michael Clayton, appeared in a recent edition of the journal Physics Letters.

    A University of Toronto Release. CONTACT: Bruce Rolston, U of T Public Affairs, (416) 978-6974, bruce.rolston@utoronto.ca

    M.A. Clayton, J.W. Moffat, Dynamical mechanism for varying light velocity as a solution to cosmological problems, Physics Letters B (460)3-4 (1999) pp. 263-270. ABSTRACT: A dynamical model for varying light velocity in cosmology is developed, based on the idea that there are two metrics in spacetime. One metric g(m nu) describes the standard gravitational vacuum, and the other (g) over cap(m nu) = g(m nu) + beta psi(m)psi(nu) describes the geometry through which matter fields propagate. Matter propagating causally with respect to (g) over cap(m nu) can provide acausal contributions to the matter stress-energy tensor in the field equations for g(m nu), which, as we explicitly demonstrate with perfect fluid and scalar field matter models, provides a mechanism for the solution of the horizon, flatness and magnetic monopole problems in an FRW universe. The field equations also provide a 'graceful exit' to the inflationary epoch since below an energy scale (related to the mass of psi(m)) we recover exactly the standard FRW field equations. (C) 1999 Published by Elsevier Science B.V. All rights reserved. Faster than Light, (Varsity Science and Technology)

  • IS THE FINE STRUCTURE CONSTANT CHANGING? Physics News Update, The American Institute of Physics Bulletin of Physics News, Number 410 (Story #1), January 13, 1999 by Phillip F. Schewe and Ben Stein. The inherent strength of the electromagnetic force is characterized by a parameter called the fine structure constant (denoted by the Greek letter alpha), defined as the charge of the electron squared divided by the product of Planck's constant and the speed of light. The size of alpha determines how well atoms hold together and what types of light atoms will emit when heated up. And just as the elastic band keeping a swimsuit snug will gradually relax with time, so it is reasonable to ask whether an atoms' elasticity (or alpha) might also vary with time, an idea broached by Paul Dirac in 1937. A group of scientists at the University of New South Wales in Australia (John Webb, jkw@edwin.phys.unsw.edu.au) test this proposition by sampling ancient light emitted by ancient atoms, and comparing them to modern light from modern atoms. In particular they looked at the relative spacing of doublets of absorption lines in the spectra of several types of atoms in distant gas clouds lying in front of still more distant quasars. The spacings, not easy to tease out from the faint spectra, are proportional to alpha squared. After taking into account Doppler effects owing to the expansion of the universe, the Australian scientists find that there is a consistent change in alpha with increasing redshift (z), especially above a z of one. Owing to the caution needed in claiming a "measurement" of alpha change, the researchers prefer to think of their result as constituting a new upper limit on the fractional alpha change for z>1 of about 2 parts in 10,000. (Webb et al., Physical Review Letters, 1 February 1999.) Search for Time Variation of the Fine Structure Constant

  • Is Nothing Sacred, by John D. Barrow, New Scientist, 7/24/99. | Physical Review paper (11/2/98)

  • Astrophysical Probes of the Constancy of the Velocity of Light, Ellis, Farakis, Mavromatos, Mitsuo, and Nanopoulos, (7/24/99).

  • Charge conservation and time-varying speed of light, Landau, Sisterna, and Vucetich, (8/13/02)

  • Slowing the Speed of Light (in ultra cold atomic gas)

  • Speed of Light Independent of Frequency, (AIP)

  • Cosmic Laws like the Speed of Light May be Changing, Study Shows (NY Times, (8/15/01)

    Related Web Links Concerning the Constants of Physics

    Speed of Light (Basic Information and Measurement Methods)

    The laws list (Laws of Physics)

    Physical Reference Data (NIST)

    The Speed of Light - A Limit on Principle? (Laro Schatzer, Swiss Physicist)

    Alexander Shlyakhter (Oklo reactor, fundamental constants, cosmology, fine-structure constant, neutron cross sections)

    Notes and Links on Leap Seconds (various sources)

    Notes on the Quantization of the Red-Shifted Light from Distant Galaxies

    The Fine Structure Constant, by James Gilson

    On the Speed of Gravity

    The Speed of Gravity - What the Experiments Say, by Tom Van Flandern

    There was once a young man from Wight
    Who could travel faster than the speed of light.
    He went out one day
    In a relative way
    And returned home the previous night.

    On the Constancy of the Velocity of Light

    Barry Setterfield's Library | Lambert Dolphin's Library Last update 8/13/03.


    spelling and punctuation checked 27June02 RPS