Aug 21 2017

Solar Eclipse and Coincidence

solar-eclipse-2017Today there will be a total solar eclipse making its way all across the continental US, from Oregon to South Carolina. Unfortunately I could not logistically travel to see it first hand. I’ll have to wait for 2024, when another total solar eclipse will hit America, making a trail from Texas through upstate New York. Here in CT we will get 75% coverage, which will be cool but nothing (from what I hear) like seeing totality.

Eclipses are one of the testaments to the power of science. We can predict them with incredible accuracy, because we have worked out in tiny detail how planetary orbits work. We can make careful observation and combine that with accurate theories about how the universe works and mathematics to make calculations, and predict these celestial events far into the future.

Some people, however, choose to see the eclipse as a testament to the existence of God. I first heard this argument when I was in college – a friend of mine who was also a fundamentalist Christian essentially ridiculed me for thinking that eclipses were just coincidence. The hand of God was clearly at work.

Eric Metaxas, who has a history of seeing God in the details of reality (as I have discussed before), has also unsurprisingly seized upon this argument. He writes:

What might be the odds of this just happening randomly? Almost all the planets in our solar system have no moons or many moons (Jupiter has 60) of incredibly varying sizes. So this sort of thing doesn’t happen anywhere else in our solar system. But our planet has just one moon that happens to be just the right size and just the right distance from Earth.

I found the precision necessary for all of this unbelievable. The more I thought about it, the more I knew that there was no way this could be a mere coincidence. It seemed almost planned. In fact, it seemed utterly planned, as all things of such precision must be.

Must it? It is an amazing coincidence that the apparent size of the moon and the sun as viewed from Earth overlap. The size of both vary over time. The apparent size of the sun varies by 3.3% and the moon by 10% because the orbits of the earth and moon are slightly elliptical. So they are not precisely the same size – their variability overlaps.

The apparent size of the moon has also been changing over historical time. The moon was once much closer to the Earth. It moves away from the Earth by 3.8 centimeters per year due to tidal forces which also have locked the moon’s rotation to the Earth, and will one day lock the Earth’s rotation to the moon. So we happen to be living in a window of about 100 million years where their apparent sizes overlap.

The fact that the sun and moon are in the same plane is not a coincidence at all. That is how solar systems develop. Most of the objects in the solar system are in roughly the same plane.

So it is actually not that much of a coincidence. Many planets have large moons like our own. If we think about 100 million years vs a 10 billion year lifespan of our solar system, that is 1/100 or 1%. That is small but not that small. Further, we are much more likely to be living in the middle of our sun’s lifespan, not at the very beginning or end, so the actual odds are greater than 1% of us falling within that window.

Metaxas is also committing the Texas Sharpshooter fallacy. There are many astronomical details of the universe, if we consider the size, position, orbits, and arrangements of all the bodies in our solar system. We could have had multiple moons that eclipse each other. We can also consider the apparent position of stars as viewed from Earth. We could also have had naked-eye viewable phenomena, like nebula, satellite galaxies, or globular clusters. Our sun may have been outside the plane of our galaxy, with a view of the spiral disk face-on.

Therefore, we cannot consider only the odds of having a moon and living in a window in which that moon eclipses our sun. We have to consider the odds of there being any astronomical coincidence – any at all. Metaxas is deciding after the fact that this one coincidence is evidence of God, but he could have said that about any cosmic coincidence (and he does). There is no reason a priori to conclude that eclipses specifically are evidence of divine tinkering.

So – what are the odds that, from the perspective of earth, there would be some (any) astronomical coincidence? It’s impossible to calculate such odds. But the fact that a 1% or so coincidence does exist hardly requires postulating divine interference, and certainly is not proof of God.

When you experience the eclipse today (if you are in its path) rejoice about the predictive power of our science. And be safe – everyone probably knows this now, but it is worth repeating. Don’t look at the sun at anytime during the eclipse. The exposed part of the sun can still damage your retina. If you are using lenses, make sure they are approved and actually work.

Happy eclipse day.

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