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The air in the science lab was, as usual, a careful compromise of atmospheric pressure.
Rocky was perched on their workbench on their half of the lab, their carapace tilted at an angle that Grace had learned meant the Eridian was concentrating hard on whatever it was that caught their attention. Next to them were two other Eridians, one a shiny jade color and the other blackstone.
Currently, all three Eridians were staring—or rather, the closest approximation of staring—at Grace.
"I understand," Rocky sang eagerly, the high melody betraying their excitement. "You see far wall. You see screen. You see me. All at same time."
"Yeah, buddy," Grace leaned back in his chair, adjusting his glasses. "I can see all of it. My eyes capture photons. Light. It bounces off everything in the room and goes into my eyes—actually, remind me to thank the biodome illumination team in person. They did a great job lighting up the place."
The second Eridian, whom Grace had affectionately nicknamed 'Darwin,' clicked furiously.
"Photon sensing is short-range for navigation? How far Grace see?"
Grace's brows furrowed as he contemplated.
"In here? To the wall—about six meters. But outside, or looking out into space? I can see things that are kilometers away. If it's a star, I can see it from light-years away."
All three Eridians clicked in surprise, the third Eridian—Grace nicknamed them 'Mendel'—wobbling on their stool in surprise.
"Light-years?!" Rocky chirped, melody rising. "You lie! Explain!"
"I'm not lying, Rock," Grace chuckled, holding up his hands. "Stars emit massive amounts of photons, and because space is a vacuum, those photons travel forever until they hit something. My eyes catch them. I can't see details, but I can see the point of light.
"Sense that works across vacuum," Darwin hummed a low tune. "Grace has superpower."
"Question!" Mendel chimed in, tapping their claw against the xenonite barrier. "Why see through barrier, but not through laboratory wall? Both solid. Both stop atmosphere. Explain?"
"It comes down to atomic structure and energy levels." Grace smiled, tapping the barrier as well. "This barrier is made of thin xenonite—thin enough that the atoms don't absorb all the visible light. The photons just pass straight through the gaps in the electron fields without interacting. The lab walls, however, are made of—well, xenonite too, but a more solid version. The electrons absorb the photons' energy immediately, stopping them. To my eyes, the walls are 'opaque' while the barrier is 'transparent.'"
Rocky leaned forward, carapace bumping against the divider. "So see through some, not all."
"Exactly," Grace gave an Eridian thumbs up.
"Grace mention color before," Mendel chittered eagerly. "What color are?"
"Oh, colors?" Grace gave a considering hum, grabbing a nearby blue quilt and an orange handkerchief. "Light isn't just one thing—it's a spectrum of different wavelengths. When full light hits this quilt, the material absorbs all the wavelengths except the blue ones, which bounce off and hit my eye. My brain has a special receptor for different wavelengths, and it interprets that specific wavelength as the color blue. This handkerchief, meanwhile, absorbs everything except orange. Humans also associate different colors with different things, like materials, health, temperature, emotions…"
"You look at object and brain makes translates?" Rocky tapped the ground twice in question. "Eridians use sound texture. Color is texture for sight."
"Exactly!" Grace gave a small clap. "That's a great way to put it."
Darwin, however, was quiet, curiously leaning a few inches forward.
"Question. Grace has object on face in front of photon-organs. Wires hold it behind human ears. What is purpose? Armor for photon-organs?"
Grace blinked before realizing they were talking about his glasses. He chuckled, reaching up to pluck them off his nose.
"Oh, these? These are my glasses. They're corrective lenses."
"Corrective?" Rocky clicked unhappily. "Something wrong with photon-organs? Is armor? Why take off?"
"No, no, it's not armor," Grace held the glasses up to the divider. "My eyes aren't perfect. The lenses inside my actual eyes are supposed to bend—or refract—the incoming light so it lands perfectly on the back of my eye, the retina, which is what sends the signal to my brain, but my eyes are slightly off. The light focuses a little bit in front of my retina, making everything far away look blurry and fuzzy."
He put his glasses back on, the world snapping back into focus. "These glasses are curved just right to bend the light before it hits my eyes, fixing the focus."
"Modify incoming photons to fix genetic flaw?" Mendel clarified. "All humans require?"
"Not all, but a lot," Grace thought back to the dozens of shops dedicated to glasses back on Earth. "Some humans are born with eyes that don't focus right. Some people have perfect eyesight when they're young, but as they get older, the muscles and lenses in the eye get stiff, so they need glasses later in life. Others get them because of illness or injury."
"Primary sense so fragile," Rocky complained. "Degrades with time, can be injured… humans leaky and fragile."
Grace laughed, tossing his head back.
"Yeah, I know, bud. I know."