called this Lineland. And he imagined a kingdom that existed in a universe with only two dimensions. He called this Flatland.”
Mr. Resnick raised his eyebrows. “So if there were a kingdom of people that existed in a universe with only one dimension, what would that kingdom be like?”
The siblings looked at each other perplexed. “I have no idea,” said Ryan for them both.
“Well, in Lineland, all the inhabitants would be line segments. And they could never change their order. Here, I’ll show you what I mean.”
He picked up a black marker and pulled off its cap with a loud pop. He went to the whiteboard and began writing squeakily.
Ben Resnick gave his kids a few seconds to digest his drawing and then, pointing to the line segment labeled, “The Queen,” he continued. “For example, if you were the Queen, you’d be stuck between the Court Jester and the King. Forever . Without any width dimension you couldn’t pass anyone—if you tried you would just slam into them. Like two trains trying to pass each other on the same track. Now if you could make use of the second dimension—move side to side—you could just move to a different track, so to speak, and easily get by. But a Linelander can’t. Their entire universe exists on a single line and they have no awareness of anything outside of this line.”
Mr. Resnick capped the marker and slid it onto the tray at the bottom of the whiteboard. He motioned to his desk. “I’m not a very good artist, so let’s move to my computer,” he said.
They walked a few yards to his glass-topped desk, on which sat a sleek laptop computer connected to a thirty-six inch monitor. In less than a minute of searching he found a cartoon drawing that would demonstrate his point and put it up on the screen.
Both kids smiled broadly and barely managed not to laugh when they saw it.
“Dad couldn’t draw that?” broadcast Ryan. “Really?”
“We’re lucky Dad has such a powerful computer,” replied Regan sarcastically.
“So this brings us to Flatland,” continued Mr. Resnick, unaware that his kids were teasing him telepathically. “Flatland exists in a 2D universe. So think of Flatland as a giant piece of flat notebook paper. And Flatlanders—who appear as circle-people in the figure—are totally, well … flat . Flatlanders have no idea there is such a thing as up or down. They can only look and move in sideways directions. So if a Flatland dad suggested to his kids there might be another direction to move in, other than back and forth and sideways, they would tell him he was crazy. Impossible, they would say.There is no such direction, they would say. To us 3D beings, the up direction is obvious. But to the poor 2D Flatlanders, no matter how much you told them about the up direction and described what it was like, they couldn’t even begin to imagine it.”
“Like we can’t even begin to imagine what direction the fourth dimension would be in,” said Regan.
“Exactly,” said Mr. Resnick happily. “And since their universe exists in only two dimensions, Flatlanders are completely unable to lift themselves off the page. Not even a billionth of an inch. Just like we’re unable to move even a billionth of an inch in the direction of the fourth dimension. Whatever direction that is. But unlike people living in the line universe, at least Flatlanders can move past each other.”
Regan raised her eyebrows. “That must be a relief,” she said playfully.
Regan dropped her empty yogurt container and spoon into a small wastebasket nearby. Ryan decided he was done eating also and did the same with his spoon, screwing the lid closed on the jar he had been holding and setting it down on one of the few empty spaces on his father’s desk.
Ben Resnick walked to the whiteboard once again and motioned for his kids to follow. “The key point is that the fewer dimensions you perceive and can operate in, the more limited you are.” He hastily drew another diagram
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