Playing on the moon

One of the more easily stated mysteries of physics is the apparent identity of an object's gravitational mass (as measured by its weight) and its inertial mass (which represents its reluctance to change its state of motion). The most obvious way in which this identity manifests itself is the way in which (if other forces such as air resistance are taken into account) all objects fall at the same rate. For moon landing sceptics one of the hardest things to fake would have been the Apollo 15 feather and hammer drop. i.e. for this to happen doubling the inertial mass of an object must give it twice the weight. 

This might also remind you of Galileo's famous experiment at the Leaning Tower of Pisa, though whether or not he actually did this is debatable and the technical difficulties of judging whether or not two different sized cannonballs actually hit the ground at the same time (let alone were dropped at precisely the same time) mean that the outcome would never have been more than indicative. i.e. consistent with the hypothesis but not actual proof. More likely it was a way of illustrating the outcome of a thought experiment. 

Suppose you make the quite reasonable assumption that heavy objects fall faster than lighter ones. After all, this is consistent with our everyday experience. Then think of a heavy object that just happens to be made of two parts connected by a string. Then suppose that one part is heavier than the other. Using our assumption its clear that the heavy part will try to fall faster than the light part and therefore pull on the connecting string. Similarly the light part will try to slow down the heavy part. The end result of all this is that combined body will fall more slowly than the heavy part on its own. But the combined body is heavier than the heavy part alone so the hypothesis that heavier objects fall faster than lighter objects can't be true after all. Our assumption has led to a contradiction. In philosophy this type of argument goes under the glorious title of "reductio ad absurdam".

Now when my boys were little we used to watch the same videos again and again. The most popular were those involving steam engines, with a particularly fine one about the railway works in Swindon, and re-runs of a childrens' programme called Playdays and published alongside the programme was a simple magazine called, you guessed it, Playdays. To my surprise one of the editions carried an item on gravity. 

Now the magazine made the usual mistake of describing astronauts in orbit as weightless (i.e. not experiencing a force from gravity). Of course, since it's gravity that's holding the astronauts in orbit, otherwise they'd just head off in a straight line into space, they're not really weightless, it just seems that way because everything else around them is moving in the same way. I could pass this over without feeling the need to comment but the bit that got me going was the following. There's a picture of an astronaut on the moon accompanied by the following caption. "There isn't any gravity on the moon, that's why the astronauts wear heavy suits to hold them down". Two incorrect facts linked by a contradiction; well done.

In a slightly enraged state I wrote to the magazine pointing out the error and expressing surprise that no-one involved in the magazine's production, from sub-editors to type setters, had noticed the absurdity of the statement. Several weeks later I got what can only be described as a snotty letter in response which basically accused me of being rude and intolerant.

There's a fine line in science between getting complex things more or less right and simplifying them to the point where they no longer make sense. I think what most disturbed me about this, albeit minor, issue was the sheer unthinkingness of it. At its heart, science is about coming up with theories about the world that are then subject to the test of reality. It involves thinking about the world in a critical way and if your ideas don't match reality then they're quite simply wrong.

A friend and I produce course materials for Further Education colleges on environmental themes. We squabble as we do this. I want to aim at the more able students, on the grounds that most people miss a lot of what's being said anyway and they'll ignore the extra bits I want to put in, he argues for simplicity. Because he's the one that sells the courses I tend to give in and what we end up with is something that's as simple as possible but still just about true.

What really annoyed me about the Playdays nonsense was the lack of respect that it showed to the little people who were its expected audience, and it still does.

So, whilst there are some ways in which I am intolerant I think that they were the ones that were rude.

Postscript: The original title of this blog was "Cultural Inertia" and it was going to include ideas such as cognitive dissonance, memes, social identity theory and the second replicator. But when I started writing it I found myself talking about physical inertia and even a brief walk with the dog didn't help me to find a coherent way back on track. I did, however, remember the Playdays man on the moon.