Creation Science Issues

Lunar Recession

First Published 7 July 2014

This is a subject that is much loved among YECs, and has repeatedly come up in recent years. See for example:

http://creation.com/the-moons-recession-and-age

http://www.trueorigin.org/moonmb.asp

https://answersingenesis.org/astronomy/moon/lunar-recession/

https://answersingenesis.org/answers/books/taking-back-astronomy/the-age-of-the-universe-part-2/

Briefly, the argument is that since we know from laser measurements that the moon is currently receding from the earth at about 3.8 cm per year, it could not possibly be as old as current mainstream science accepts, nearly 4.5 Ga (billion years). In fact, a backwards extrapolation (see below) would place the moon at the Roche limit only about 1.4 billion years ago (The Roche limit is the distance at which the difference in the near-side and far-side gravitational pull from the earth would equal the moon’s own self-gravitation, so that if the moon were any closer, it would break up.)

This is yet another example of a phantom problem. YECs love to raise these, and try to give the impression that mainstream scientists (“evolutionists”) are floundering around in a desperate struggle to salvage their belief in long ages, and avoid the obvious conclusion that there’s no answer except the YEC one. But usually the problem, if it ever existed, has been solved many years ago, as a simple Google or Wikipedia search will show—but of course the YECs conveniently ignore this. These phantom problems also show that the YEC position is fundamentally antithetical to science. YECs stridently deny this, yet time and time again they write off scientific research into a question as a lost cause, since actually we know that God simply did it.

Now the question of the lunar recession is a classic example. YECs use a simple back extrapolation of the moon’s orbit which ignores most of the variables. Yet they say that if we actually try to work out the science of what’s going on, we could only be motivated by a determination to prop up our untenable evolutionary presuppositions. The articles I referenced above say as much. For example, in my last reference, Jason Lisle says (in reference to lunar recession), “Secular astronomers who assume the big bang is true must invoke other explanations to get around this. For example, they might assume that the rate at which the moon was receding was actually smaller in the past (for whatever reason), but this is an extra assumption needed to make their billions-of-years model work.” How is this pro-science? Study of a topic is simply written off as motivated by a long-age presupposition. Lisle, who has a PhD in astrophysics, should know better. His comment totally fails to acknowledge the complexity of the problem and with a wave of the hand, dismisses the efforts that have been put into studying it. In fact if we look at these efforts, we find that good progress has been made in recent years, and it’s significant that papers cited in the YEC articles tend to be 20 or 30 years old, or sometimes even older (excepting citations from YEC authors, of course). I maintain that this is anti-science.

So why is the moon receding? This is due to a transfer of angular momentum from the earth’s rotation to the moon’s orbital motion. In simple terms, this transfer occurs because of the tidal bulges that the moon induces in the earth, since the moon’s gravitational pull is greater on the near side than the far side of the earth (there is one bulge on the near side, and one on the far side.) These bulges are primarily the oceanic tides. These get pulled by the earth’s rotation in front of the moon’s position, and gravitationally pull the moon forward so it gains momentum, and this causes it to move outward. There is a corresponding drag on the earth’s rotation, so that this rotation is also slowing down. I recommend an article by Tim Thompson:

http://www.talkorigins.org/faqs/moonrec.html. This article gives a good introduction to the subject, with excellent diagrams.

Now if the tidal bulges could move around the earth without friction, they would stay aligned with the moon and no angular momentum transfer would take place. So if the earth were entirely covered by an ocean of constant depth, this is what would happen. It’s therefore clear that the amount of tidal drag on the earth, and angular momentum transfer to the moon, is critically dependent on the configuration of oceans and continents. This drag is also dependent on the distance. If everything else were constant, it would be inversely proportional to the sixth power of r, the average distance from the center of the earth to the center of the moon (Thompson’s article gives the details). YECs use this figure to calculate that the time of lunar recession from the Roche limit to its present position is 1.4 Ga. The error is obvious. Everything else was not constant. Why would it be? At the very least, the continents have not always been in their current positions. This is not a desperate attempt to salvage a 4.5 Ga old moon, it’s simply fact. There is now excellent evidence that the current rate of lunar recession is indeed anomalously high, and has only been around its current figure for about 1 Ga.

This paper shows that we need to take into account factors such as the natural tidal modes of the oceans, which have a rich spectrum of resonances. With these factors taken into account, there is no great anomaly in the moon’s orbit, and this was known in the 1990s (Bills and Ray’s paper dates from 1999). Obviously this area of study is highly complex, but my point is that the recession of the moon is not inconsistent with a 4.5 Ga age, and this fact has been known for a long time. YECs love “god of the gaps” arguments, but in many cases such as these, there simply isn’t a gap. The only “gap” is in the YEC acknowledgement of good scientific research!

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