Friday, November 1, 2013

Moon and sleep




Introduction

In the past few weeks, I heard from 2 friends (who don't know each other) the suggestion that their sleep or their child's sleep might be affected by the moon. In 1 case at least, it was a serious suggestion. In the other case, I'm not sure. Could there be any truth behind this story or not at all?


The gravity hypothesis

Of course, if you read Wikipedia's article, you'll get an exhaustive neutral summary of this subject. But this is my blog, with my side of the story and no claim to be exhaustive or neutral. That's what blogs are for.

There are 2 known ways in which the Moon can influence things happening on Earth:

  • light
  • gravity


We know that the Moon's gravity is responsible for ocean tides and we can be tempted to imagine that a comparable effect could apply to humans who are composed of whatever percentage of water. In fact, let's do the math! This is how the gravitation force works.

For this demonstration, we'll consider that M1 is the Moon, with a mass of 7.35x10²² kg (*)
And M2 is an average male human with a mass of 80 kg (*)
R = 378,000,000 m (*) (**)

(*) values rounded to a 0.5% precision
(**) Distance Earth-Moon (384,399 km) minus Earth's median radius (6,371 km)



F1 = F2 = G x M1 x M2 / (R x R)

F1 = F2 = 6.67e-11 x 7.35e+22 x 80 / (3.78e+8 x 3.78e+8)

F1 = F2 = 2.7e-3 Newton


In other words, the pull from the Moon on a person is equivalent to 0.3 grams (2.7e-3 N divided by the gravity constant of the Earth: 9.81). And this, of course, is much less than the weight of a pajama or bed sheets. If we also assume that we exhale and sweat a total of 25 mL of water per hour, the pull from the Moon is equal to the weight of water we lose through breath and perspiration every 43 seconds. What's more, the pull from the Moon changes very slowly as it takes roughly 12 hours for our satellite to travel across the sky. Final nail in the coffin on the gravity hypothesis: the effect of gravity is the same regardless of the phase of the Moon.


The other hypotheses

On the hypothesis of light having an effect, people report being disturbed by the Moon even when their curtains or blinds are closed. So... there's no reason to defend this hypothesis.

On the hypothesis of magnetism, it must be reminded that magnetism's effect is only strong at very short ranges. A few centimeters at most, unless you have a massive source of magnetism like the core of the Earth which is active due to the high temperatures and pressures. The Moon's magnetic field is 100 times weaker than Earth's magnetic field and its effects over the distance that separates it from our planet, its strength would be weakened by many orders of magnitude. So, the magnetism hypothesis is busted.

Energy? This is subject in and of itself, that sells books to the "New Age" aficionados. In many of the irrational beliefs and practices, the word "energy" is used for the supposed source of effects. In skeptical terms, it is called "magical thinking". The thing is: energy is not a supernatural unfalsifiable claim on which reason has nothing to say. Energy is something very concrete. It has to be stored somewhere, in some form, before it is released and produces very concrete effects. But the rational notion of energy is not what people allude to, when they invoke Energy as a cause for what they believe in.


The more rational approach

We have biases. When something happens to us, our brain naturally fills in the gaps of what we don't know to try and establish the cause of what happened. That's what creates superstitions. And we need recognizable points of reference. If we generally sleep well but have sleep problems on the night of a gibbous Moon or a crescent Moon: it's not an easy thing to remember. But if our sleep problem happens on a full Moon, that phase is very recognizable and easily remembered.


Conclusion

It's safe to estimate that the Moon doesn't affect our sleep... unless we keep the curtains open of course, in which case the light could reduce our sleep quality. But if we hold the superstition that a full Moon will be a problem, we might actually be disturbed by the anxiety of our superstition, thus turning it into a self-fulfilling prophecy.

Sleep tight! Don't let the bed bugs bite!

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