By KP Mohanan and Tara Mohanan
Rafa: Mom? Samira: Yes? R: You said that all sensory perceptions are fallible. Including touch? S: Including touch. R: But there aren’t any illusions of touch. What we touch has to be real. S: You think so? Let’s try something. Which of these two paperweights on the table has greater weight? R: I don’t know. S: Why don’t you find out? R: Well, to find out how much each one weighs I’ll have to weigh them on a weighing machine. But when I lift them both, I can feel that the blue one is heavier. S: So your conclusion is based on the sensation of strain you feel on your muscles when you lift them, right? You are saying, I experience greater strain on the muscles when I lift the blue paperweight, so I conclude that it has greater weight. R: Yep. But you’re still talking weird, Mom. Normal people don’t say, “I conclude that it has greater weight.” We just say, “It’s heavier.” S: But academics do say such things. And we are engaged in academic inquiry, aren’t we? Since you say you want to be a scientist you better learn to talk weird if you want to learn to think like a scientist. Now, suppose you find a red suitcase and a blue suitcase on the floor. You lift the red one. It’s heavy, but you can lift it. But when you try to lift the blue one, however hard you try, it doesn’t come off the floor. You will conclude that the blue suitcase is heavier, right? R: Right… S: But you might be wrong. It is possible that the suitcase is empty, but someone has screwed it to the floor, which is why it doesn’t come off the floor. The sensation of strain on your muscles is the same as that for lifting a heavy suitcase. R: Wow! I hadn’t thought of that. S: That means what our sense of touch tells us can also be wrong. R: Is the muscular strain when lifting something part of the sense of touch? S: Strictly speaking, no. It is felt more by the muscles than by the skin. Let me give you an example of and illusion in the actual sense of touch. It comes from the ancient Greeks. They thought up this beautiful experiment in which you immerse one of your hands, say the left hand, in a bucket of very hot water for a minute or so, and your right hand in a bucket of very cold water. Now you take out both hands and immerse them in a bucket of water at room temperature. Your left hand will feel the water to be cold, but the right hand will feel the same water to be warm. It couldn’t be the case that both hands are telling you the truth, right? So at least one of them is mistaken, or may be both. R: What does all this have to do with the question I asked you about God? S: Remember we said you have to figure that out for yourself? Right now we’re talking about how to investigate any question. And we’re beginning with questions having to do with sensory perception. The point I was making was, we need to rely on our sense perception as reliable grounds for our knowledge of the world, but our senses are can make mistakes. They might tell us the truth, but they might also deceive us, so we have to examine critically whatever they are telling us. R: Oh, okay… Mom, I just thought of something. S: What? R: You asked me which paperweight has greater weight? S: Yes? R: Paperweights don’t have weight. S: What? R: They have mass, they don’t have weight. What we call weight is the effect of the earth’s gravity acting on something that has mass, and the greater the mass, the greater the pull. S: Okay, I see what you’re saying… R: You were talking about the strain on the muscles, right? The strain that we experience on our muscles is not a property of the paperweights, but the force that the earth exerts on the paperweights. Had we been on the moon, we would experience less strain on the muscles with the same paperweights, and in outer space, there wouldn’t be any strain. When we think of the paperweights themselves having weight, we’re mistaken. Another wrong inference of the senses. Yes? S: Absolutely! That’s a pretty good discovery for a fuzzyheaded teen! I am impressed. R: So you shouldn’t have asked me, “Which paperweight has greater weight?” Your question is misguided. S: Go away! Go do your homework!
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