April Statistical Fool

The Chinese space station Tiangong-1 is about to  dive back to Earth – on April 1, probably.

Tiangong-1

It could be a day earlier, or a day later, but April 1 is the current best guess.  And “this is not an April Fool joke,” says at least one report.

“Should we worry?  No.”  That’s true, but not quite so true as the soothing statements claim.

We are assured that there is zero chance that a piece will hit us.  The chance may be called “essentially zero,” or “vanishingly small,” or the qualifiers may be dispensed with.

The vehicle weighs eight tonnes, its orbit has decayed down to about 240 kilometers above the surface, it will descend through thicker layers of the atmosphere, most or all of it will burn up.  Since China has not released details, we do not know quite how to evaluate that “most or all” and the sizes of pieces that might fail to burn up.

And “essentially zero”?  Earth’s surface is 70 percent water.  The satellite’s orbit is inclined 43 degrees to the equator, which means that it passes over latitudes between 43 north and 43 south.  That includes all of the Americas between the Great Lakes and southern Argentina, all of southern Europe, Asia from Korea south, all of Africa and Australia and the East Indies.  So there are a few tens of millions of square miles of land, and more of water, that a descending piece may choose to hit.

It’s true that the chance of its hitting you is vanishingly small.  As is the chance of its hitting your nephew, or a certain turtle or northern white rhinoceros.

But there is a logical error in this way of using statistical chances.  The chance of a meteorite hitting a certain exact spot in Arizona, now called Meteor Crater, rather than some other spot, was vanishingly small, but it did hit that spot.  The chance for a certain woman that in 1997 she would get hit on the shoulder by a small piece of space debris that was probably part of a Delta rocket was vanishingly small, but she did get hit.

Only classes of events have large chances of happening.  Individual events have such small chances of happening that they may seem impossible, but they are not.  You have a vanishingly small chance of being alive.

 

9 thoughts on “April Statistical Fool”

  1. Oh My! I just read your post. I am a long time fan, and so I claim the fun of teasing you:

    “The chance of a meteorite hitting a certain exact spot in Arizona” or anywhere else is zero!

    Reason is by definition, the object is a meteor until it impacts and then any solid debris that are the remains of the meteor
    after impact are termed meteorite.

    I do not mean this post to be haughty, and apologize if it sounds that way, but I could not resist the tease.

    1. Technically the thing is a meteoroid when it is traveling unseen through space, a meteor when its light is seen, a meteorite if it reaches the ground. I I think either the second or third term would be generally understood in this context and the first would not.

      1. so, to continue this line of thought, it would then be OK to say, conversely, here is a meteor I found in Antarctica.
        It would not be correct. it is a meteor before it hits, a meteorite after it hits.

        Those are the definitions used in astronomy. What is “commonly understood” doesnt matter.
        You pride yourself on accuracy.

    1. P.S. Got the above quote from vaccine opponents.

  2. After all this hype about it falling, I heard that it finally did, but still know not where or how and details. Can anyone direct me to a link that’ll give me such info?

  3. I’m sure I speak for many of your readers to observe that I hope the fact that you took the time to prepare this post is an indication that you have reached some level of resolution to your problem of having to move out of your Greenwich residence and into an as-yet-unknown new residence. So long as you stay in England, you will indeed have a zero percent chance of being hit by debris from the satellite. You will, however, still have a much greater than 50% chance of residing in a non-EU country by sometime next year unless you move to Ireland or the continent!

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