Software Musings

Making My Head Spin

Posted on: 06/01/2007

Every Friday I click on the James Randi Educational Foundation to get my weekly fix of the world’s inanities and foolishness. This week, however, his commentary ends with a link to this Youtube Video which shews a hapless competitor, “aided” by the studio audience trying to answer the question:

Which of the following orbits around the earth: the moon, the sun, mars venus?

When I went there I was the 186,273rd viewer which is almost significant if you still happen to think in imperial units. The answer to the question was eventually given as “the moon”. This is the sort of thing that makes me angry and I have just fired off an email to Randi:

At the conclusion of this week’s commentary you say, “As if we needed verification of the scientific illiteracy of this generation, I direct you to, where you’ll see a French-language edition of the “Millionaire” TV show which offers the contestant four choices in response to the question: “Which of these is in orbit around the Earth: the Moon, the Sun, Mars, or Venus?””

Having seen the clip I agree that the audience was probably answering out of ignorance rather than deeper knowledge but, with deeper knowledge, it’s clear that Copernicus’ (and before him the Arabs’, Greeks’ and Indians’) move from an earth-centric solar system based on planets following complex epicycles around the earth to a sun-based solar system with the planets, including earth, revolving in slightly misshapen ellipses is simply a computational convenience, not a reflexion of reality. If I want to send a rocket from earth to the moon, it is certainly simpler to assume that the moon revolves around a stationary earth (or more precisely, their common centre of gravity). If I were to send a rocket from the moon to the earth it may be very much simpler to assume that the earth orbits the moon.

The planets follow complex paths through space in relation to each other and the sun. The point we assume to be fixed (the earth, the moon, the sun, mars) and around which we do the calculations is purely a matter of computational convenience. Perhaps this is what was going through the head of the hapless competitor and studio audience. Perhaps not.

I really find it infuriating that people confuse a computational convenience for some truth about the world. Relative motion cannot be described by a single true description. It can be described by creating equations of motion around any point.


3 Responses to "Making My Head Spin"

Although it is true that you can set your origin at any location and then determine the motion of the objects around it, the attractive influence of objects is still proportional to their mass. As the sun contains the bulk of the mass of the solar system, it dictates the motions of the ‘fluff’ in it’s near neighbourhood (ie things tend to be stuck going round it).
I do hope that the email to Mr Randi does not set up some “battle fo the beards”.



PS Slightly frustrated by technology as I originally replied on my phone but it seems not to have worked.

So is the general rule that, when two bodies move relative to each other, the motion should always be described as though the more massive (or larger?) is at rest? That sounds pretty arbitrary.

Is the Moon out tonight? I don’t know if it’s cloudy or bright ‘cos my head’s in a whirl…


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January 2007
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The author of this blog used to be an employee of Nortel. Even when he worked for Nortel the views expressed in the blog did not represent the views of Nortel. Now that he has left, the chances are even smaller that his views match those of Nortel.
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