astronomy Cosmology Creation/evolution Physics

Questions on the conventionality thesis and the one-way speed of light

The conventionality thesis and the asynchronous convention for the one-way speed of light (ASC) has been presented as a biblical creationist explanation for how light from the most distant sources in the cosmos reached Earth within the 6,000 years since the Creation, as determined from a straightforward reading of the Genesis account. There is no conflict with the true age of the universe because it simply is counted off by the years since creation.[1],[2],[3]

The conventionality thesis in Special Relativity relates to the synchronisation of clocks separated by a distance. It involves to the notion that the one-way speed of light, provided the two-way speed is c, can only be chosen by a convention, since it is impossible in principle to measure it. 

With respect to this subject, I address some issues raised from articles I have recently written on this subject.[4],[5],[6]

Innate bias

The first issue relates not so much to the science but to the mindset of the hearer when the topic is discussed. There seems to be in many of us an innate bias against accepting that the events (in light from stars, galaxies etc) we see in the cosmos are the same age as the earth and solar system. The idea is that all we see in the cosmos is occurring now, and not in some past epoch of time.  However due to our education among other factors we are biased into believing the starlight coming from the cosmos travels at a fixed speed of about 300,000 km/s and because of the distances involved it must have taken billions of years to reach Earth. We believe this even though it has never been measured.[7]

Last year I had the opportunity to share a PowerPoint talk titled “Can we see into the past?”[8] with a small group of friends who were all solidly biblical creationist in worldview. After I gave the PowerPoint presentation some questions were asked and one person, who does have some science training, said that he just could not get his head around it. I respect that but I believe it is a case where a little knowledge can be dangerous. In some cases a prior knowledge has led to a closely held belief, or an innate bias, which in turn can close off a person’s mind to new ideas without any logical reason. Such situations are well documented in science, particularly in fields that are undergoing revolutionary transitions. For example the case of phlogiston.[9]

Another man in that small group, who is physically blind and could not see my PowerPoint slides (so he did not have the advantage that the sighted people did), said that he had no problem understanding it. He said that he had had no science education and did not have any preconceived ideas (for example that the one-way speed of light must be finite, isotropic and equal to c, the measured two-way speed).

I made my PowerPoint talk available on my own website8 and various readers commented. You can read those comments there. What I want to highlight are some of the concise responses from different readers, which indicate clarity of understanding.

“Fascinating concept indeed—best explanation I’ve seen! Thanks”

“Read Jason Lisle’s book just before your new post on one way speed of light arrived. Appreciate your article on this matter and the analogy with geology and evolution.”

“Sincerely, I say ‘Thank You!’”

These are from 3 different readers. They are not comments from those who do not understand but those who do. In fact most of the comments and questions that were posted revolve around notions that involve an implicit assumption that the speed of light one-way must be the same in all directions and equal to c, the measured round-trip speed. There is that innate bias.

It is truly a psychological problem and I am not blaming anyone for holding onto old ideas as we are all subject to these biases. But bias of this type has actually impeded the progress of science at different times. Because some notion has been believed to be true the real truth has been ridiculed, overlooked or de-emphasized.

“All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.” — Arthur Schopenhauer, German philosopher (1788 – 1860)

If we take our lead from the biblical account, the natural language it uses suggests that the creation of the stars occurred in real time (Genesis 1:16-18). Thus what we see in the cosmos is happening now. A choice of the one-way speed of light from the ASC is consistent with this. Biblical creationists need to remain open to this possibility. Hopefully the following may help them to overcome any bias they may have against it.

Counterintuitive thinking

Some have said an anisotropic speed of light is an impossible situation, counterintuitive they say. But the problem is that what happens in the physical world is what it is. It does not depend on our personal preferences. There are several areas in physics which have this same problem, i.e. they have some counterintuitive aspect.

One famous area is the Young’s double-slit experiment, in particle physics. Electrons are shot at a screen with two holes, and an interference pattern is recorded on a screen behind the holes. If one does not ‘look’ at which hole any individual electron passes through, by means of a detector near a hole, then one gets an interference pattern that suggests each electron passed through both holes. But if one ‘looks’ at which hole they pass through one gets an interference pattern that suggests each electron went though only one hole. The suggested explanations are various in quantum mechanics but there is no definitive resolution. But this is very counterintuitive. Why should looking for the hole that the electron passed through change the pattern? And how can one electron pass through two holes at the same time?

The problem is not resolved by saying some electrons go through one hole and some through the other, resulting in a situation where interference of the wave functions[10] one with another occurs. The reason this is not the solution is that the experiment has been performed with emission of single electrons. After one electron has hit the screen another is emitted from the source and you still get the inference pattern as if the only electron passed through both holes simultaneously. To suggest that it was separate electrons interfering with each other you would have to say that each electron travels back in time to interfere with the previous one.

This problem is highlighted by the standard philosophy of quantum mechanics, which can be best illustrated by the analogy that my physics professor gave in my introductory class on quantum physics. He said: “If a tree falls down in the forest does it make a noise if there is no one there to hear it?” The correct answer is that you cannot ask the question.  Talk about counterintuitive.

Besides, Special Relativity (SR) is not intuitive either, quite the opposite. Depending on which synchrony convention (hence which value for the one-way speed of light) you choose you will determine a different age, not only of the universe, but also for any object in it. Based on ESC, the standard synchrony convention with one-way speed of light equal to c, i.e. isotropic, and the Earth’s motion around the sun, one would determine the age of a celestial object, like a galaxy, for example, to be greatly different when determined at two different times of the earth’s orbit, 6 months apart. This is because the earth would be moving towards the object for one measurement and away from it for the second, as the earth traverses the sun in its annual orbit. Opposite directions change the sign of the Doppler term used to calculate time dilation. This means the calculation of the age of the object will be quite significantly different. But under the ASC there is no difference in age as it does not depend on motion of the observer on Earth but only on the distance to the object.

So in this case it is not the ASC that is counterintuitive. The ESC, the standard synchrony convention, is counterintuitive.   

An arbitrary choice

Is the choice of one-way speed of light ‘ad hoc’ or arbitrary? Every observer may choose the one-way speed of light to be some value between ½c and infinity, but with the proviso that the round-trip speed average to the canonical speed, c. That is essential because that is the only measurement we can make. I know this sounds rather arbitrary but the choice is restricted within some definite range. And this applies to all possible synchrony convention choices. So the ESC is just as arbitrary as the ASC in that regards. You cannot say one is an arbitrary choice and the other is not.

But if you are looking for an absolute fundamental property of this created universe that you could say means that the one-way speed is such and such or even is equal to the canonical speed c, then that just cannot happen. It seems that this is due to the very nature of the physical creation. This is more than a convenient phenomenology, it has its substance in the very creation itself. It seems that this is another case where you cannot ask the question

Some have argued, and I have read this on atheist discussion sites, that creationists are just using the one-way speed of light argument as a sort of ‘loophole’ that solves their starlight travel time problem.  I would argue that this is not an applicable accusation, because it applies to any choice of the one-way speed, including the standard convention. We simply cannot know what it is. It is not really something we can know. So to say light from the stars actually took 10 billion years to reach Earth is not based on science but is an assumption. All a biblical creationist is doing is saying that he reads in the Bible that the universe is only about 6000 years old and that accords with the light arriving from the cosmos instantly or near-instantly under a non-standard synchrony convention. So what SR has shown us is that we can simply believe what the ancients have always thought when they read the Bible and applied it to the stars, though they had no knowledge of their distances. Now that we know these it changes nothing.

The reason I do not like the use of the term ‘ad hoc’ applied to the ASC is because it implies the choice is totally free. But it is not. As explained above, any choice of the one-way speed has rules connected with it. One of those is due to causality. And that requires that the one-way speed of light can only take a value between ½c and infinity, i.e. never less than ½c. However whenever we measure or calculate some value for a physical measurable, like energy or momentum of a photon, we will always use the two-way value, c. This is a universal constant and nothing in this changes that. All physics remains unchanged.  The only difference is to understand that the universe tells us nothing about the one-way speed of light and it is perfectly acceptable to choose its value within the specified range.

We cannot have absolute knowledge of a photon’s one-way speed.  Why does a photon always travel at the speed c regardless of the motion of the observer? This is what Einstein postulated (or stipulated) in one of two principles upon which he founded Special Relativity theory.

In classical physics it was believed that the speed of the observer would add to or subtract from the speed of light depending on the direction of the beam. That was the natural belief from addition of velocities for particles and projectiles etc. But Einstein posited that the speed of light, one-way in this case, was independent of the motion of the observer. It was not c + v or c – v in any thought experiment. Here v is the speed of the observer and c the speed of light.  This was counterintuitive at that time and it took 30 or 40 years for scientists to come to accept it.

But of course we cannot measure the one-way speed and it is only by first assuming that the speed is isotropic that any measurement of the speed of light could be related to this.  Regardless of his speed, an observer always measures the same speed for any photons, but it is always the two-way speed of light, the constant value that we call the canonical speed c.

Not only that, it is not possible to make any statement one way or another (pun intended) about any choice of the one-way speed, otherwise all we are doing is begging the question. I know this is frustrating but this is the nature of the creation we are to work with.

We cannot measure the one-way speed of the photons coming from the stars or even in the lab for that matter. We can only stipulate their speed by choice of a particular convention. Einstein used the same word ‘stipulate’ (in German of course) when describing this situation.

However John Winnie in 1970 was able to develop the equivalent equations of SR without specifying a choice.[11] By parametrising all choices of the one-way speed with the Reichenbach parameter ε Winnie was able to formulate the SR equations in the most general case. Those could be used in the most general way to show that all allowed choices of the Reichenbach parameter ε (0 < ε < 1) produced the exact same physical results—results that can be measured in an experiment. Einstein had chosen an isotropic speed where ε = ½, but all other choices where ε ≠ ½ produce the same physically measureable outcomes.

Process age in the cosmos

It is true that the ASC model2 predicts that there can be no structures in the cosmos that have a process age greater than about 6,000 years. To find a structure that can be shown to be older would be a disproof of the ASC model, but not of the conventionality thesis.

Figure 1: Supernova Remnant in Cassiopeia-A Credit: NASA Chandra X-Ray Observatory

The problem here is how to determine the age of a cosmic structure with any confidence. For example, a stage 3 supernova remnant. I have looked at this problem[12] and found that it requires uniformitarian assumptions, much like age determinations of fossils in the rocks.

Philip Gosse, just after Darwin’s publication of the Origin of the Species, proposed that God created the fossils in the rocks to give the ‘appearance of age’.[13] His idea was very damaging to creation science because it presented God as a deceiver, which is totally contrary to scripture. However ‘age’ has no appearance.  Age is inferred from appearance, after making certain assumptions about how processes might change over time, and about the unseen initial conditions. We need to question those underlying assumptions.

Astronomers today argues that the oldest supernova remnants have process ages greater than 6000 years. That means that they must have taken more than that time to develop. To counter that with a Gosse-type argument would mean that they must have been created with an appearance of age about 6000 years younger than what we now observe. That would mean the progenitor stars never existed. This idea is definitely rejected.

The resolution is to understand that the same problem exists in astronomy that exists in geology and palaeontology. We have no access to the past and cannot see past events happening. In the cosmos it is the same.

When we look at a supernova remnant we cannot see what occurred in its past history.  So to get around that astronomers look for other similar structures at different stages of development. They collect many of them and catalogue them into different types. From that they infer some evolution (meaning change in form over time) to try to get some idea of their past development. Using known laws of physics, and assumptions about initial conditions, they model the explosions of the progenitor stars to try to match the observed structures, but they have only one data point, the end result. At no time is the supernovae remnant observed going through the various alleged stages of its development.

Experiments change our thinking

What causes a change in our way of interpreting the evidence? It is usually new evidence by way of some measurements, or failure of some measurement as was the case of the Michelson-Morley effort to detect the aether. The latter was then consistent with Einstein’s constant speed of light postulate mentioned above. If an aether was detectable it would mean the motion of the observer (on the Earth) has an effect on the measured speed of light. That non-detection changed the way of thinking, via Einstein, as counterintuitive as it was and still is.

Young’s double slit experiment performed with large molecules

Had we not had the experimental evidence like in the Young’s double-slit experiment no one would have believed the predictive power that quantum mechanics can offer as counterintuitive as it may seem to be. The experiments are robust, and the quantum theory correctly predicts outcomes of those experiments but it is the interpretation of the experimental evidence that is still debated. How do you explain the collapse of the wave function of a pair of entangled states, which appears to be instantaneous action at a distance? This has been experimentally demonstrated, but there is no consensus on the underlying interpretation.

The same is the case here. We have definitive experimental evidence, i.e. the round-trip measurement of the speed of light, but no method of measuring the one-way speed of light. All such experiments have failed. However the interpretation involving the conventionality thesis is still argued over. Some claim it is conventional and some claim it is empirical. It can’t be both.


I do agree that ACS is seems to be counterintuitive. It even seems bizarre. But Special Relativity is bizarre, with observer-dependent time dilation of clocks and length contraction of rods. Even the light postulate itself is bizarre.

Perhaps we think this way because we are conditioned to believe in symmetry and homogeneity. We think this is how the universe ought to be. But we have no basis to believe that. We have no basis to assume the one-way speed of light is isotropic, and that it has some intrinsic value.

If there is one thing that empirical science has taught us, it is that unless an experiment has disproven our theory we can continue to apply it, and test it.  If we could measure the one-way speed of light, or calibrate clocks separated by a distance, we would have an experiment forcing a conclusion on us. But we don’t.

Philosophy is intrinsically tied to any measurement we make. It involves the starting axioms we postulate. We cannot make a measurement of time or length without first assuming axioms. In this case, one assumption (axiom) involves the one-way speed of light. If you assume it is isotropic – the standard Einstein convention – then you have what most people assume (incorrectly) to be some sort of absolute truth in the universe. It is often difficult for them to believe otherwise. It is a bias, and not based on any measurement. It is merely assumed to be true.

In over 110 years, since Einstein’s 1905 paper, there has not been successfully devised a thought experiment or an actual empirical measurement that could measure the one-way speed of light without assumption(s) on the synchrony of clocks separated by a distance. Many have been suggested, but others have followed showing the flaw in the design. Usually the flaw involves the implicit assumption (the petitio principia[14]) that the speed of light is isotropic. However if one such experiment was successfully demonstrated that would disprove the conventionality thesis. So far this has not happened.

References and notes

[1] Newton, R., Distant starlight and Genesis: conventions of time measurement, J. Creation 15(1):80-85, 2001;

[2] Lisle, J., Anisotropic Synchrony Convention—A Solution to the Distant Starlight Problem, Answers Research Journal 3:191–207, 2010;

[3] Lisle, J., The Physics of Einstein,, 2018.

[4] Hartnett, J.G., Einstein’s physics says there is no biblical creationist starlight travel‐time problem, Review of the book “The Physics of Einstein” by Jason Lisle, J. Creation (in press), 2019.

[5] Hartnett, J.G., New cosmologies converge on the ASC model—a review of two cosmology papers presented at the International Conference on Creationism in 2018, J. Creation 33(1):71–77, 2019.

[6] Hartnett, J.G., The conventionality thesis on the synchronisation of clocks separated by distance,, 31 May 2019.

[7] I am not referring to the often measured round-trip speed of light but the speed for the light coming one-way from the cosmos.

[8] Hartnett, J.G., Can we see into the past?, 1 January 2019.

[9] Psarris, S., Fire in the air, J. Creation 17(2): 83-86, 20013;

[10] A wave function in quantum physics is a mathematical description of the quantum state of an isolated quantum system. The wave function is a complex-valued probability amplitude, and the probabilities for the possible results of measurements made on the system can be derived from it.

[11] Winnie, J.A., Special Relativity Without One-Way Velocity Assumptions, J. Philosophy of Science, Vol. 37, Part I pp. 81-99  and Part II pp. 223-238, 1970.

[12] Hartnett, J.G., Supernova remnants and the age of the universe,, 26 January, 2015.

[13] Sarfati, J., God created with functional maturity, not ‘appearance of age’, 2015,

[14] A fallacy in which a conclusion is taken for granted in the premise; begging the question (different from the way the layman often uses the latter phrase.

By John Gideon Hartnett

Dr John G. Hartnett is an Australian physicist and cosmologist, and a Christian with a biblical creationist worldview. He received a B.Sc. (Hons) and Ph.D. (with distinction) in Physics from The University of Western Australia, W.A., Australia. He was an Australian Research Council (ARC) Discovery Outstanding Researcher Award (DORA) fellow at the University of Adelaide, with rank of Associate Professor. Now he is retired. He has published more than 200 papers in scientific journals, book chapters and conference proceedings.

13 replies on “Questions on the conventionality thesis and the one-way speed of light”

Proposal of synchronizing distant clocks and measuring one way speed of light:

Let’s have a solid square with small holes ABCD drilled close to each corner. Let A’B’C’D’ be laser points aligned exactly with ABCD when stationary.
Let’s move t the square ABCD away from lasers A’B’C’D’ and accelerate it to a constant speed . When no force is acting upon the square let it glide past lasers A’B’C’D’. When laser A’ hits the hole A, at the same time laser B’ will go through the hole B.
Since AB is perpendicular to the direction in which the square moves, there should be no length contraction of the distance AB regardless of the speed of the square. If there is a contraction of the distance AC (or BD), it should be relatively easy to measure it by measuring time of flight of a photon from A to B and comparing it with the time of flight from A to C.
Best regards,


Kris, It is not so clear to imagine your thought experiment. But assuming I do, where is the observer? Where does she measure with respect to, at A? How do you measure the time of flight from A to B? or A to C? Do you confirm that you have synchronised clocks at A, B, C and D? Are you saying the laser signals synchronise the points A and B? If so, if you are located at A how do you know B has received the laser signal at the same time A received it? The exercise cannot just ASSUME that the apparatus produces synchronised clocks but that it is measureable. If you assume that it does you have in fact assumed the standard Einstein convention.


The entire set up still behaves in a two way speed manner. This is the problem with one-way speed proposals, the moment they set up two distinct points A and B and a device which have supplementary lasers to catch the time of flight of the photon when passing through certain points, the set up automatically fails. People need to admit that the one way speed of light is not a measurable quantity, all proposals so far have failed and any ‘new’ proposals have a more sophisticated precedent tried in the past which also failed. Lastly, a proposed “result for a measured one-way speed” that equals the two way speed is already an admission of the proposer that he/she has assumed the ESC beforehand.

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Philip Gosse’s extra-Biblical explanation that God is a deceiver hurts the Creationists testimony…while standing on the truth will continue to confound the unbelievers. As technology advances, their explanations continue to become less and less plausible and they have begun to sound not as scientists but apologists for their own ‘religion’…with no real facts as a foundation.
We in the US are seeing this unfold with the abortion debate.
Is it a ‘tumor’…part of the woman’s body or actually a separate baby human?
Please pray for us.


Dr. Hartnett,
I have been fascinated by the distant starlight problem for many years and have been encouraged by the gravitational time dilation explanations proposed by Dr. Humphreys and by yourself in the past. I was shocked when I first heard of the ASC convention when Dr. Lisle published his paper on it. Like you said, my preconceived notions about the speed of light were definitely a stumbling block for me, but after reading about yours and others’ “conversion” to the theory, those walls were broken down.
You allude to data that could potentially indirectly falsify the theory, such as observing some stellar phenomenon we observe that had to have taken more than 6000 years to occur. I immediately thought about the crab nebula, which is a massive object 5.5 LY in size, about 6.5 LY from earth, yet known to have occurred as a result of a supernova observed 1000 years ago. The nebula itself was first observed in 1840. Obviously, this is not an object that would falsify the ASC. But dust from the supernova explosion spread to a diameter of 5.5 LY (radius 2.75 LY) in about 1000 years. That means the dust was ejected at an average velocity of 0.275% of c.
Are you doing or know of any research in this area, i.e. looking to see if there are phenomenon which could indirectly falsify the ASC idea?


What about measuring changes in the fine structure constant? This should show up in star light if stars are far away and millions of years old.


Fine structure constant (symbolised by the Greek letter alpha) measurements have been made for many years and those who claim the doublet and multiplet method is an accurate method to measure it in relativistic gas clouds at high redshift claim a variation away from the locally measured value of 1 part in 100,000. Various unprovable assumptions are made to determine this. They include the meaning of the host galaxy redshift. That it is a measure of both distance in the universe and age. Alternative interpretations say otherwise.

But even if we accept the variation as measured it does not imply that the gas clouds or host galaxies are actually billions of years old. It only implies that alpha in the cloud is not the same as local. Since alpha includes the canonical speed of light some have suggested that this implies a 1/100,000 change in the speed of light. Time and frequency metrologists have suggested instead a drift in the second. The speed of light is intrinsically connected to the second.

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Hello Dr. Hartnett; I know this is way off topic but what is your opinion on the supposed “mass” that was found beneath the moon’s surface. It was a very mysterious discovery by many accounts and I saw one article say it reminds us of the many unknowns about the birth of the solar system. I wonder how we as biblical creationist should view this new discovery? Thanks!


How do you interpret the following image, where the galaxy seems to have moved way more than 6000 light years? God moved it supernaturally fast during Creation Week or the trail does not imply it moved? (it says “Image is about 1.6 arcmin (about 100,000 light years”)


There is the problem. How do you determine the age of the structure? You can’t observe it’s formation and you can’t see into the past, so to say it is older than 6000 years you have to make some uniformitarian assumptions.


Hey Dr. John, this is sort of related to this post: I have read both the papers written by Tichomir Tenev et al and the one by Bryan Johnson, and I must say, Bryan does have some compelling arguments for his cosmology, but I’m still unsure about it. I much prefer a cosmology to the likes of Lisle’s ASC model and Tenev et al’s Creation Time Coordinate convention model. As they both take for granted that the two-way speed of light is constant. Johnson admits in the Discussion section that his model is in need of experimental test, even though he has cited literature documenting correlations and evidence of his thesis.
My comments on Tenev is more to do with some slight misunderstanding in part of how he perceived Lisle’s ASC model. One critique is Tenev thinks Lisle’s biblical reason for arguing ASC is because ancient people were “unsophisticated”. But I don’t think that’s what Lisle implies at all in his ARJ paper. Rather, Lisle argues that people in ancient time didn’t have the technological means to even use the ESC in their daily life. All timestamps were, by convention, anisotropic. This isn’t Lisle making anachronistic remarks or insulting ancient people’s intellect or technological capabilities, it’s a sociological acknowledgement, the ESC wasn’t put to practical use until the early 20th century. The rest of Tenev’s remarks does have some validity and fair points.


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