My Private Photon

When I walked back from the gym tonight I could already see the stars starting to come out (it’s really getting dark early!) and in particular, I noticed the constellation of Pegasus (that one that looks like a kite) hanging right overhead, as I suppose it always does in the Northern hemisphere at this time of year.

Anyway, I was looking at the brightest star in the constellation, which I later looked up and discovered is called Alpha Andromedae, and it occurred to me that I should feel somewhat special to have gotten to see it in that moment. Granted, anyone who wants to see it can see it any night they want, during the right season. But from another perspective, think about what’s happening when I look at a star: photons from it are striking my retina and being absorbed by the atoms in my eye and converted into an image that my brain can process, right? Well that means something special just happened.

In particular, Alpha Andromedae is about 100 light-years away. So that means when I’m seeing a photon from it, my eye is the very first thing that that photon has interacted with in 100 years. That plucky little guy set out from the star where he was created and flew as fast as he could, at 300,000,000 meters per second, and crossed one-tenth of the width of the milky way galaxy, without stopping for anyone until he met me. He could have run into another star some place; after all there are some ten million of them in between us that he might have collided with. He might have struck any of the random comets and asteroids orbiting these planets. And in outer space there are always several hydrogen atoms per cubic meter, which isn’t many, but remember he crossed 9.5 quintillion meters to get to me. You’d think he might have bumped into one and said hi.*

Well, he didn’t. Instead, he traveled alone across the blackness of space for 100 years, starting his journey back when William Taft was president and nobody alive would think of the sinking ship or (let alone the stinking movie) when you said the word “Titanic.” For all that time he headed straight towards the star we call the sun, at just the perfect angle so that he would not hit Jupiter or mars on the way in. He wasn’t aimed at the planet earth; he was aimed at the place where the Earth, spinning rapidly around the sun, was going to be at 7:00 EST on October 10th, so that he arrived just in time. He made it through the atmosphere without being absorbed by any of the gas molecules he encountered on the way in, avoided scattering off the water droplets in a cloud, and slipping past an airplane, all the while watching the planet turn beneath him so that a little strip of an island west of New York twisted into view right below. And he pointed himself straight down toward Suffolk County, right towards Stony Brook University, and dodged past the tree leaves as my apartment complex rotated into view, and landed right in the middle of my eye, just as the rotation of the earth whisked me away from the place I had been. If he’d been there a moment later, I would have missed him. If I had happened to be blinking, he would have traveled alone for a century just for the privilege of whacking into my eyelid. But no, his timing was perfect. My private little photon travelled all that way just to see me, and he made it. So I got to see the star tonight, and his journey of across 600 quadrillion miles came to an end in my eye. And that made him one of only the tiniest fraction of all photons in the universe who will ever get the privilege of interacting with a human being, and thus be absorbed by a being which is aware of  the interaction that just taken place.

So next time you’re looking up at a star, say thank you to all the little photons who have braved the dangers of vast interstellar space to bring you the pretty picture you see that evening. Some of them have been traveling for almost a thousand years. On a clear night away from the city, you could be meeting photons who haven’t interacted with anything since before Jesus was born. It’s a big day for them, to finally meet the person they were destined to be seen by. So make sure you properly appreciate their spunky little trip across the universe just to see you.

*Okay buzz-kills with physics backgrounds: This visible photon wasn’t going to be absorbed by the neutral interstellar hydrogen. But it could still have scattered.


About Colin West
Colin West is a graduate student in quantum information theory, working at the Yang Institute for Theoretical Physics at Stony Brook University. Originally from Colorado (where he attended college), his interests outside of physics include politics, paper-folding, puzzles, playing-cards, and apparently, plosives.

3 Responses to My Private Photon

  1. Scott Gallagher says:

    Howdy Colin, i really enjoyed that piece. You will have a regular reader in me from now on…

    Hope you’re doing well.

  2. S says:

    Is this a long setup for an “eyegenstate” pun?

  3. Moominmamma says:

    The Little Photon That Could

    You could turn this into one of those chart-your-own adventure books, with a new ending for every possible obstacle the little fellow could encounter. This might actually make an interesting children’s/young persons book, or a useful tool for science teachers at an elementary/middle school.

    I’m glad you were able to appreciate the moment and share it with us in all its complexity.

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