Page 76 of Project Hail Mary

He holds up a finger. Using my own sign language against me. Now I have to wait! I guess that’s fair. I hold up my finger to acknowledge it.

He opens a circular door leading into his ship. It’s the right size for an Eridian—I would have a hard time squeezing through if that ever became a plan. He disappears inside, leaving the door open. I’d love to know what’s beyond the door, but I can’t see anything. It’s pitch-black in there.

Hmm. Interesting. It is completely dark in his ship. That door probably leads to an airlock. But even an airlock would have some lights in it, wouldn’t it?

Rocky didn’t have any problem getting around. But I know he can see—he responds to my gestures. This lends strength to my earlier theory about Eridian vision: I think they see a different part of the spectrum than humans do. Maybe they see entirely in infrared or entirely in ultraviolet. That airlock might be perfectly lit up as far as Rocky’s concerned and I can’t see a thing. Conversely, my lights are completely useless to him.

I wonder if we have any wavelengths in common. Maybe red (the color with the lowest wavelength that humans can see) is “???,” the highest wavelength they can see. Or something. Might be worth looking into. I should bring a rainbow of lights in and find out if he can—oh, he’s back.

Rocky bounces into the tunnel and spider-walks along the rails to the dividing wall. He’s incredibly graceful at it. Either he’s very seasoned at being in zero g or Eridians are just really good at climbing around. They have five hands with opposable fingers, and he’s an interstellar traveler, so it’s probably a little bit of both.

With one of his hands, he holds a device up for me to see. It’s…I don’t know what it is.

It’s a cylinder (man, these people like cylinders), a foot long and maybe 6 inches wide. I can see that his grip deforms the casing a little bit. It’s made of a soft material, like foam rubber. The cylinder has five horizontally aligned square windows. Inside each window is a shape. I think they might be letters. But they’re not just ink on paper. They’re on a flat surface, but the symbols themselves are raised an eighth of an inch or so.

“Huh,” I say.

The symbol on the right rotates away to be replaced by a new symbol. After a couple of seconds it happens again. Then again.

“It’s a clock!” I say. “I showed you a clock, so you showed me a clock!”

I point to my clock, still taped to the wall, and then to his. He does the jazz hands with two of the hands he’s not using at the moment. I do jazz hands back.

I watch the Eridian clock for a while. Rocky just holds it in place for me to see. The symbols—numbers, probably—cycle through on the rightmost window. They’re on a rotor. Like an old-school digital clock back home. After a while, the rotor one step to the left of it changes one position. Aha!

As far as I can tell, the right rotor changes once every two seconds. A little more than two seconds, I think. It cycles through six unique symbols before repeating: “l,” “I,” “V,” “λ,” “+,” and “V,” in that order. Whenever it reaches “l,” the next rotor to the left advances one step. Eventually, after about a minute of this, that second-from-the-right rotor works its way through all the symbols, and when it reaches “l,” the third rotor from the right advances.

Looks like they read information from left to right—same as English. Neat coincidence. Though not incredibly unlikely. I mean, there’s really only four options: left to right, right to left, top to bottom, or bottom to top. So there was a 1 in 4 chance we’d be the same.

So his clock is intuitive for me to read. And it works like an odometer. “l” is clearly their 0. From that, I know that “I” is 1, “V” is 2, “λ” is 3, “+” is 4, and “V” is 5. What about 6 through 9? They don’t exist. After “V” we go back to “l.” Eridians use base six.

Of all the things I teach my students, numerical bases are the hardest to make them truly understand. There’s nothing special about the number 10. We have ten unique digits because we have ten fingers. Simple as that. Rockies have three fingers per hand and I guess they only like to use two hands when counting (they probably keep the other three feet/hands on the ground to stay steady). So they have six fingers to work with.

“I like you, Rocky! You’re a genius!”

And he is! With this simple act, Rocky showed me:

How Eridian numbers work (base six)

How Eridian numbers are written (l, I, V,λ,+,V)

How Eridians read information (left to right)

How long an Eridian second is