Sunday, March 14, 2010

Getting it Right. More or less...

What follows is mostly nonsense but illustrates the traps we fall into when thinking is muddled. When I do a physics demonstration, my students assimilate that demonstration into what they already know about the world and how it works. They know that heavier things like bowling balls fall faster than lighter things like feathers, so when I drop a tennis ball and a basketball from the same height at the same time and they hit the ground together, well, the student body cries, they must weigh the same, right?  
First misconception.
Misconceptions are how we see the world. We each of us create a universe which we clothe with our misconceptions. We build our imperfect understanding of the world on cumulative experiences, most of which are subjective and misleading. What else could we do?
When we get more sophisticated, we call misconceptions “models”. The only difference is  - we know about them now.  For instance, I might have a misconception about alpha decay. A radioactive nucleus fires an alpha particle in one direction and, like the butt of a rifle; the nucleus recoils in the opposite direction. I’ve compared a microscopic event to an everyday occurrence, and it makes sense to a fourteen-year old.
Only it’s wrong. There’s no mechanism, spring, or store of potential energy inside a nucleus to allow it to fire off an alpha particle. Instead what happens is two protons and two neutrons suddenly, with no previous training or experience and, it seems, quite by accident find themselves stuck together and outside the nucleus by a process called quantum tunnelling. Which ones were 'chosen'? Er - dunno. Once there, the positive charge of the alpha and the much larger positive charge of the nucleus push against each other, sending the alpha flying in one direction and the nucleus recoiling in the other.
Oh, but that’s wrong, too. Alphas aren’t particles, at least not until I observe them, they're waves. The alpha is not in the nucleus, not really, but exists in all parts of the universe. It’s just that the most likely location is inside the nucleus – but just outside is relatively possible, too. And when the wave function collapses, the alpha might be in that relatively possible place that causes the pushing of positive against positive.
Good isn't it. We’re getting there, slowly.
I am used to a macroscopic world, where things like refrigerator magnets can repel one another. I know what that feels and looks like, and I imagine it for alpha particles, too. But that’s not right. Instead, virtual photons from the alpha and the nucleus interact, and that interaction produces the positive and negative momentum that sends the alpha and the nucleus flying.
Then there’s the fact that the alpha isn’t really made of two protons and two neutrons, but instead is made of  twelve quarks, each of which might actually just be a string, each of which . . .

As an afterthought, today is Pi day - 3/14 - geddit - the most transcendental, beautiful, irrational number, and also dear old uncle Albert's birthday. Sweet. Google's masterful design deserves a whirl because it'll be gone by tomorrow. Hope they don't mind...



  2. How very cool. Maybe I gave up on mathematics too soon? I. Don't. Think. So. I'll leave the 'masterful' logic to you, and live with 'miscalculations.' Life is more fun that way; things don't have to be quite so exact when numbers don't matter. And I assure you; my miscalculations are very special.

    Take fridge magnets for instance... :)

  3. And happy birthday to the oh-so-strange Mr. Einstein. Maybe that's why I'm so unenthusiastic about a head full of formulae. Name a sexy mathematician.

    I rest my case.

  4. Remarks about fridge magnets are very much south of the equator.
    Even for you.


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