Blood in the Wall


A couple of years back, I put a torch behind my daughter’s hand, turned it on, and voila! Her hand appeared red in color. I told her it was because blood is red in color. Because that’s what I’d been told as a kid.

But that’s not the reason at all, as I learnt later. The correct reason is:
“Only one color of light passes completely through your hand- and that's why it looks red. All of the other colors are completely absorbed, either by the skin, bones, muscles, blood or other cells in your body. Most of the red light passes right through all of these cells…”
But wait, things are even more interesting:
“Most of the red light passes right through all of these cells except your blood cells- but not even all of your blood cells. Red light passes through the blood in your arteries, but is absorbed by the blood in your veins. That's why your veins appear black.”
(The difference between arteries and veins is the amount of oxygen in them, which affects how much of the red light they absorb. Cool, right?)

Obviously, this is way too complicated to explain to a kid, so I never corrected things to her. Not having corrected the “blood is red” reason led to a very amusing consequence recently.

While playing with a red rimmed torch, she placed it right against the wall, turned it on, and not surprisingly, the reflected light shining through the red rim looked… red. Upon which, she turned to me and announced:
“Look, this proves there is blood in the wall!”
As she said it, she had that wicked look of I-know-the-conclusion-is-wrong-but-show-me-the-flaw-in-my-reasoning.

It was a spectacular reminder of why reasoning from first principles is so important. As Shane Parrish explains:
“Reasoning by first principles removes the impurity of assumptions and conventions.”
Why we rarely do anything from first principles is because, as Elon Musk said, “That takes a lot more mental energy”. That all too common mental laziness is also what led Richard Feynman to lament:
“I don’t know what’s the matter with people: they don’t learn by understanding; they learn by some other way—by rote or something. Their knowledge is so fragile!”

Guilty as charged, Feynman.

Comments

  1. Ramiah KumarJuly 2, 2018 at 6:54 PM

    I fully agree with Feynman's opinion about people, "Their knowledge is so fragile". Of course, my 'people domain' is not limited to ordinary commoners who are ridden with 'mental laziness' because of which they develop skewed ideas having poor linkage to truth. I am inclined to believe that "on the whole, human knowledge itself is fragile". :-)

    I don't know what Feynman would say about children's way of reasoning. As far as we are concerned, the way children argue their points either wins our heart or make us light-hearted very often! I suppose we develop the ability to loosen ourselves when it comes to children, and simply appreciate their innocent and spirited ways.

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