Class Warfare Blog

June 3, 2016

Argh, Please, Dr. Carroll Say It Ain’t So

I have been reading Sean Carroll’s latest book “The Big Picture” in which he heroically tries to bring the gap between how people see the world and how it actually is (well, he doesn’t include thoseThe Big Picture Cover who see unicorns, but most other “ontologies”). It is extremely well-written and when I finish it I suspect I will be recommending it to those of you who enjoy good scientific and philosophic writing. (The writing is very, very good.)

But then I hit a speed bump—there I was reading along, learning things and appreciating where he was going when he introduces the Thompson atom, the first atom model featuring subatomic particles. He includes a graphic depiction of an hydrogen atom, which typically is a single electron associated with a single proton (a nucleus). But the illustration! Imagine a ping pong ball with a BB sitting next to it and inch or so away. The particles are depicted with simple circles, black on white, nothing fancy and oh, so misleading! The Thompson atom model, expanded by many others (Bohr, etc.) has electrons traveling in orbits around their nuclei, like planets about a star. We have since found out that this simplistic model does not work and orbits do not show up in current models, but he was specifically addressing that earliest model, so that is all good. My problem is with the scale. If one were to put the two particles at their proper distance, one would be hard pressed to print dots small enough to depict the actual size of the two particles, in fact, you cannot print them as small as they are. (In fact we still don’t know how big an electron is, all we know is it is substantially smalled than a proton or neutron).

So, I ask, why the grotesque distortion of the scales involved?

I suspect it is because we were taught with such erroneous illustrations and “a picture is worth a 1000 words.”

To show you how hard it is to depict what an atom seems to “look like” I used to put my students through this exercise. I would have them take a completely blank piece of paper. It would be best to use black paper as it is dark in the atomic realm but black paper and white ink are hard to come by, so this is a “negative” we are drawing.

I then asked them to draw, in pencil or ink, the smallest possible dot they could in the exact center on the page. That dot is the nucleus to scale. Then they had to draw in a wispy, cloud-like spherical shape around that dot, with the “cloud” being denser closer in and fading out toward the edge of the paper (atoms have to outer edge, they just fade away). The catch is that the electron represented by that “cloud” is almost 2000 times less massive than the proton, so they could only use 1/2000 of the amount of pencil lead or ink they used to draw the nucleus.

When they finished, I had to explain that at that scale of the cloud they drew was much too small, it would have to be many times bigger to be actual scale.

We tend to think atoms are these hard little bits of matter but the only thing “hard” in the atom is the nucleus and it takes up only about a 100 million millionth of the atom’s volume and it is way down toward the middle of the atom where little can get to it. The rest is very, very nebulous (but also highly electrically charged).

None of the behaviors of atoms make any sense unless we are true to the scales involved. Peddling poor illustrations because “we’ve always done it that way” or “that’s what they will recognize” won’t do, especially in books intended to expand the understanding of science in the lay public.


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