The Index of Refraction
Traffic was bad all the way out from the city to the airport, and he's
afraid he'll be late to meet her plane. After he parks, he's relieved when
he checks the information board and sees that her flight is running 20
minutes late. That lost 20 minutes makes him right on time.
It's unseasonably hot. The air in the terminal feels wet and thick. His head
swims. The crowd near the arrival gates seems to move in slow motion. Why
don't they turn on the air conditioning or a fan or something? He wonders.
Like a lot of airports, his hasn't handled new post-9/11 security well, and
they've simply packed everyone waiting for arriving passengers into a wide
cattle pen at the bottom of the escalators. He walks to the back of the
waiting area, hoping he can breathe back there.
He keeps his eyes on the
top of the escalator, wondering how long he'll have to wait. A small
brunette appears and he looks hopefully, but it isn't her. Traveling at
approximately 980,000,000 feet per second (noting that the speed of light is
slightly slowed by the atmosphere and suspended particulate matter in the
air), the light that carries the brunette's image takes around .0000000005
of a second to travel the distance from her face to his eye.
He looks around at the anxious crowd. A family with a couple of sullen children and
bright Happy Birthday Grandma balloons. An older couple who stare up at the
rolling escalator, but studiously ignore each other. A handsome long-haired
boy in a leather jacket leans against a cement pillar, fidgeting into just
the right pose for the pale goth girl slouching down the
He sees all of them, but is really seeing the past. Light
reflects from objects and people, moving through the air until it strike his
corneas. The light then passes through the vitreous humor inside his eyes to
focus an image on the retinas. From there, an electrical signal moves up his
optic nerves to the visual cortex of his brain.
All this activity
takes time. Transduction, converting light data into neural information,
occurs at the outer segment of the rods and cones in the back of the eye and
takes less than a millisecond. Signals propagate along the optic nerve at
around 10,000 centimeters per second. The few inches from his eyes to his
visual cortex takes another millisecond.
Before that, however, the light
slows and bends as it enters his eyes, due to refraction. The index of
refraction is the ratio of the phase velocity of light as it moves from one
medium (air) to another transparent medium (his cornea and eyeball fluid).
If light moves at 1n in a vacuum, it slows to 1.0003n in air. When it hits
the lenses in his eyes, the speed of light drops to 1.413n, but picks back
up to 1.336n in the vitreous humor. It takes approximately a millionth of a
second for light to hit the back of his eye.
He glances back up the
escalator, unaware that he's really looking at nothing more than ghost
images of the past. He checks his watch. Time crawls, he thinks. A watched
pot. He wishes he could have a cigarette. He remembers when you could still
smoke in airports. He'd been a kid. How long ago was that?
he sees dark hair cresting the top of the escalator. He stands up straight,
craning his head over the crowd. Waiting to make sure it's her, preparing to
catch her eye, if it is. The woman on the escalator is examining something
in her hand. Her hair, transit weary and messy, hangs down, covering her
face. The man frowns and repositions himself, trying to get a better
The woman is familiar, but not yet identified in his brain as his
wife. That he is looking at an illusion, echoes of his wife's image, doesn't
occur to him. These fractions of a second for information processing mean
nothing to him. It's still in the terminal and he feels as if he's
dreaming. Somewhere in the back of his brain an idea from some long
forgotten grade-school science class pops into his head: Moving on a
microscopic zip-zag course from the core where it was created, a light
photon takes 30,000,000 years to reach the surface of the sun.
the light that's reflecting off the woman and into his eyes was created, the
Earth was cooling and seasonal variations were just starting to become
common, prompting mass extinctions among animal species that thrived on a
year-round tropical steambath. Flowering plants were becoming the dominant
plant form on the planet. Mammals were thriving and the first ape-like
animals had just appeared. The crust of the Earth was writhing, buckling and
cracking in a million places as the Himalayan and Andean mountain ranges
rose from what had recently been the ocean floor. Australia was on its own,
having broken free of Antarctica. One of the largest predators in history,
the Carcharodon Megalodon shark, stretching 80 feet from nose to tail, ruled
After its journey to the surface, it still took the new light 8
minutes and 19 seconds to get from the sun to Earth.
thinking about any of that right that right now. The woman looks up. Her
face, that image, this moment, which has been in transit for roughly
30,000,000 years, 8 minutes and 19.01 seconds, hits him. He sees it's her
Editor's note: For extra credit, I suggest
Activity 5: Energy Flow in the Sun.
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Richard Kadrey is a member of a small group of innovative writers, including William Gibson, Bruce Sterling, John Shirley, Pat Cadigan, Tom Maddox, and others, who changed the face of science fiction in the 1980s. He also creates art. He lives in San Francisco.