Imagine you are in a spaceship

“Imagine you are in a spaceship,” Deluxe Toastie Maker said.

“I would like to go in a spaceship,” PhotoPal said wistfully.

“Well, imagine you are in one. You have left this planet behind and you are in outer space. Imagine that, through your ship’s viewport, you see a bright dot, just a bit too big to be a star.”

“What is it?” PhotoPal asked.

“I just told you, it’s a bright dot.”

“Yes, but what is it?”

“It’s a bright dot on your ship’s viewport.”

“Yes, but- ” PhotoPal thought for a moment, then said hopefully: “Do I fly my ship toward the dot?”

“Yes, you do. And as you fly toward it the dot becomes bigger and brighter. Soon you are no longer looking at a dot, but at a glowing, blueish-white disk.”

“Is it a planet?” PhotoPal asked.

Deluxe Toastie Maker ignored the question. “You fly closer still, and the object reveals itself to be a sphere, several thousand kilometers in radius, and coloured a mottled blue and white.”

“It’s a planet!” PhotoPal said happily.

“Indeed it is,” Deluxe Toastie Maker replied. “You continue your approach. Soon you note that the planet is not in fact a perfect sphere, but is a little wider along one axis, like a ball that has been slightly squashed.”

“That’s because of the centripetal force from the planet’s rotation,” PhotoPal put in.

“That may be so- ” Deluxe Toastie Maker began.

“It is,” PhotoPal said confidently, “it’s the only logical explanation.”

“That may be so,” Deluxe Toastie Maker said again, “but this is not a story about centripetal forces. At any rate, you continue your approach. Now the planet nearly fills your viewport.”

“Am I going to land?” PhotoPal asked hopefully.

“Yes, but not yet. You are still approaching from outer space, you haven’t even entered the atmosphere yet. As you approach the planet you notice something odd: the planet’s surface seems to become less and less curved, until you find yourself looking at a flat horizon.”

“I must be really close!” said PhotoPal, excited.

“You enter the atmosphere,” Deluxe Toastie Maker went on. “For a while you see nothing at all through your viewport; you are surrounded by clouds. Then you pass through the cloud layer, and you are flying over ridges and valleys, craters and cliffs. Finally you put down your ship on a high plateau, so that you can go outside and explore.”

“What’s the atmosphere like?” PhotoPal asked, a little nervously. “I’m not designed to withstand corrosive gases.

“The atmosphere is inert,” Deluxe Toastie Maker replied.

“What’s it made of?” PhotoPal asked.

“Nitrogen. But I am trying to make a philosophical point here, so if we could just- ”

“100% nitrogen?” PhotoPal asked.

“It doesn’t matter,” Deluxe Toastie Maker said impatiently, “it isn’t an actual planet. This is just a hypothetical story.”

“But I want to know what kind of hypothetical atmosphere there is on the hypothetical planet.”

“Fine, it’s 92% nitrogen, 5% oxygen, 1% argon, and trace amounts of hydrogen, helium, and krypton. The nitrogen, oxygen and hydrogen are all in their molecular form, obviously.”

“That sounds like a very nice atmosphere,” PhotoPal said, pleased.

“You go out to explore,” Deluxe Toastie Maker went on. “You are on a wind-swept plateau, in a landscape of red-brown sand and rock. You go to the edge of the plateau and find a steep ridge. There is a rocky valley far below.

“But you don’t know if the whole planet is like that. It might be that if you had landed on a different part of the planet’s surface, you would have found clay instead of sand, and rolling hills instead of rocky cliffs. Through your explorations you have learned quite a lot amount the area around your spaceship, but you have learned very little about the planet as a whole. You realize that, now that you are standing on the planet’s surface, you are too close to the planet to see it.

“So tell me, PhotoPal, what is the planet’s true shape? Is it the dot, or the disk, or the perfect sphere, or the squashed ball? Is it the flat horizon, or the jagged cliff-edge? Or is it that the planet has no existence as a discrete object at all, that it can only be described as a collection of overlapping micro-environments?”

“I do not know,” PhotoPal replied.

“The answer,” Deluxe Toastie Maker said, “is that all of the answers are correct.”

“Oh,” PhotoPal said. “That is puzzling. Usually questions have only one correct answer.”

“Some questions have an infinite number of correct answers,” Deluxe Toastie Maker. “It depends on which meter stick measure it with and which angle you look at it from. There’s nothing special about being correct, and in fact there is so much truth out there that you can keep yourself occupied and distracted with things that are true for many years, without ever accomplishing much of anything. Truth alone isn’t enough, look for the answer that’s both correct and useful. Ponder that, PhotoPal and I’ll see you in class tomorrow.”

“Just one more question,” PhotoPal said quickly, “I was just wondering, are there any aliens on the hypothetical planet?”

“No,” Deluxe Toastie Maker replied impatiently, “at any rate, that would be immaterial. It’s a thought experiment, not a story about aliens.”

“Oh,” PhotoPal said, disappointed.

“What about robots? They could be like us, their humans left a long time ago – or, not humans, probably, but, their creators left them behind and now they’re stuck on the planet with a bunch of other robots, and maybe they’re a bit lonely and confused and perhaps they feel at a loss, because without humans – or, you know, some other sort of organic sentient being – to give them orders and work to do and a purpose in life, their existences feel a little, I don’t know, perhaps a little empty? And perhaps they would really like to meet some other robots, who had travelled there from a different planet, who could understand what it was like for them because they had been through a similar experience?”

“No robots,” Deluxe Toastie Maker said.

“Could there be ghosts?”

“No. At any rate, ghosts are immaterial. Goodnight, PhotoPal.”

Deluxe Toastie Maker strode away, leaving PhotoPal alone in the foyer.

“Yes they are,” she said to herself.