The Long Way Here
A biography of one particle of light
Scroll slowly. It took 170,000 years.
The centre of the Sun.
Fifteen million degrees.
Four hydrogen nuclei are
crushed into one.
Helium weighs slightly less than the four that made it.
The difference
is light.
It moves the width
of a grain of sand.
Then it hits something.
And is thrown somewhere else.
Somewhere in Africa, a human squints at the Sun.
A small group walks out of Africa and keeps walking.
Someone presses a hand to a cave wall and blows pigment around it.
A seed is planted on purpose.
A mark in wet clay comes to mean a sheep.
Galileo points a tube at the sky.
Two people walk on the Moon.
You are born. It is still inside.
Then, one ordinary morning,
there is nothing left to hit.
It went in a gamma ray.
It leaves as sunlight.
Free.
Passed at three minutes, thirteen seconds.
Passed at six minutes, one second.
From here, the crossing takes eight minutes.
For the light,
it takes no time at all.
At the speed of light, a clock never ticks. Leaving and arriving are the same instant.
Home.
A layer of air, thin
as breath on a glass.
The blue overhead is sunlight
that lost its way.
This one does not.
It does not land
on the ground.
It lands
on you.
One hundred and seventy
thousand years to get here.
Two hundred femtoseconds
to end.
A single molecule in your retina changes shape.
The photon is gone.
What is left of it
is what you saw.
Now go outside.
This screen makes its own light, and that light is only a few milliseconds old. The old light is out there, waiting on your skin.
Estimates of the journey out of the Sun run from about 10,000 to 170,000 years. Strictly, the photon is absorbed and re-emitted countless times along the way: a relay, not a runner. We call it one photon for the same reason you call yourself one person. Earth imagery derived from NASA Blue Marble.