Richard Feynman, in his book QED, says “the theory of quantum electrodynamics describes Nature as absurd from the point of view of common sense.” He recalls that in the early days, “one had to lose one’s common sense to understand what was going on at the atomic level.” Think of something absurd. Then lose your common sense.
“I can run faster than you can.”
“No you can’t.”
“Yes I can.”
“No you can’t.”
“Yes I can times a hundred.”
“No you can’t times a thousand.”
“Yes I can times a million.”
“No you can’t times infinity.”
“Yes I can times infinity and one.”
Familiar to us is the above exchange between children. In the heat of this contest of superposition, one child attempting to best the other, eventually they confuse (how cute!) infinity with a really big number. Everyone knows that nothing is bigger than infinity! Silly kids.
Except the infinity we know and love—the counting numbers—is only one of many infinities, each new infinity larger than the last one in an eternal version of the playground argument. In fact, there are an infinite number of infinities. The silly kids were right all along.
Here is where the common sense police come to put a stop to this nonsense. Gather the pitchforks; light the torches. We will not have infinity escaping on us. We like the old infinity, the tame one. The one that wasn’t so—infinite.
Common sense is exactly what it claims to be: common. But common never discovered anything. Common never cured the common cold. Common never challenged anything, except the new and the bold. Common always is but never does. Common sense tells me never to use “you” in writing. It also tells me to avoid clichés. Common sense abhors a sentence ending with a preposition. And last but not least, why are you always saying that “and” is a bad word to start a sentence with?
Most people today who encounter the uncertainty of quantum mechanics or the inconceivable enormity of the infinite infinities find them absurd. But we have no choice but to accept them because they contain the legal tender of the universe—truth. Quantum theory correctly predicts measurable events. Until another theory surfaces that predicts better or predicts more, we must assimilate the absurdity. The infinite infinities can be rigorously proven from previous mathematical conclusions. We cannot afford to reject them because they seem absurd.
Most people today also forget just how absurd new ideas always seem. For example, the teaching “the meek shall inherit the Earth” seemed absurd enough to first century Jews that their common sense necessitated the silencing of its teacher. Newton was absurd because he contradicted Aristotle; likewise, Einstein was absurd because he contradicted Newton. From our (clearly superior) modern perspective, the absurdity lies in the old ideas, in what was once common sense. Can you believe they used to think the Earth was the center of the universe? How naïve. Silly medieval people. Everyone knows that the sun is the center of the universe. Silly kids. Everyone knows that nothing is bigger than infinity.
[This was written for the University of Chicago, their last option in which you write your own question. It's a bit glib, but it got me in I guess.]