imageYou’ll hear any reputable Star Wars fan point it out eventually: Han Solo's famous boast that the Millennium Falcon “made the Kessel Run in less than 12 parsecs" may have sounded impressive, but from an astronomical perspective, it made no sense. A parsec is a unit of distance, not time, so why would Solo use it to explain how quickly his ship could travel?

There are two stories going on here. The first is that Solo's famous line of dialog was simply a mistake of terminology. The second – the one I choose believe – is far more interesting, because it means that when Obi-Wan sat down across from the wryly smiling Han Solo in that cramped cantina, he met a time-traveling smuggler born at least 40 years before the events of The Phantom Menace ever took place.

A Parsec by Any Other Name ————————–

First coined in 1913 by British astronomer Herbert Hall Turner, the term "parsec" is a portmanteau of "parallax" and "second," and is defined as the distance from the Sun to an object that has a one-arcsecond (1⁄3,600 of a degree) parallax. What this awesome-to-say description really means is that if you were to draw a straight line between an object and the Earth, and a straight line between the object and the Sun, if the angle between the lines is one-arcsecond, then the object is one parsec away – or 3.26 light-years.

According to Star Wars: The Essential Atlas, the Kessel Run was an 18-parsec (59 light-year) route used by smugglers to get around Imperial blockades. So why would Solo describe how quickly he traveled it using a word that described distance?

It turns out that the expanded universe of the Star Wars franchise – the additional books and content created within the Star Wars universe but outside of the films – contains an answer to that question. The Essential Atlas maps a Kessel Run whose path travels around “The Maw,” a cluster of black holes. To cut down on the distance traveled, pilots could dangerously skirt the edges of the black holes, while trying to avoid spaghettification. If Solo was a skilled enough – or crazy enough – pilot to deviate from the typical route and fly close enough to the black holes to cut nearly 20 light-years off his space odometer, then his ship was fast indeed — the power required to stay out of the gape of an event horizon is something worth bragging about.

Image: Star Wars: The Essential Atlas

So by being able to dance around singularities, the Millennium Falcon establishes itself as a fast ship – and Solo's famous brag makes sense. But this brings up a bigger, more inherent problem: The Kessel Run that Solo completed covered nearly 40 light-years of cosmos. If the blasters and speeders and starships of Star Wars more or less follow the laws of physics, taking that famous run even once would change the entire chronology of Han Solo’s life.

One Hour, Three Years ———————

In A New Hope, Solo establishes that the Millennium Falcon can go “0.5 past light speed,” dashing the hope for a completely scientifically accurate discussion. Light speed is the universal speed limit, and nothing can outrun it, not even Han’s beloved vessel. Try as you might, E=mc2 is our description of nature’s constant attempt to foil your “jump to hyperspace.”

So for the purposes of calculating the Kessel Run, let's say the Millennium Falcon is the fastest ship ever. Somehow able to withstand the forces involved (perhaps it has something to do with that sweet tractor-beam tech), we can calculate what happens when Han and his baby go 99.9999999 percent the speed of light, or 0.999999999c.

t': This is the amount of time passing for a stationary observer. Because of special relativity, time dilates or expands outward as the moving observer travels faster and faster. The faster Han goes, the less time he experiences — even if we see him traveling over light years. t: This is the amount of time passing for a moving observer. This is what Han Solo experiences in the Millennuum Falcon.

v: This is the velocity of the moving observer — Han Solo. c: This is the speed of light in a vacuum or around 186,000 miles per second.At these ludicrous speeds, time itself contracts. The faster you go, the slower you wade through time’s river. A clock running on a ship moving 99.9999999 percent the speed of light actually ticks more slowly for someone on that ship than a clock for an outside observer. Not only do clocks obey this contraction, but biology does too. Anyone on a hypervelocity ship will age more slowly than those not on the ship. It’s an astonishing conclusion, but it’s how the world actually works. For example, if we transport a super-accurate atomic clock across the globe by plane, we have to correct for the discrepancy between it and another clock on the ground. After six months in the International Space Station, orbiting astronauts have aged 0.007 seconds less than the rest of us.

Unfortunately for Han Solo – and the larger hope of long-distance, high-speed travel – time only contracts for the person who's moving. It marches on the same for everyone else. Using the equation for time dilation, we can see how much slower Han’s clock ticks while on the Millennium Falcon traveling at 99.9999999 percent the speed of light. Experiencing just one hour on the Falcon, Han returns to find everyone three years older.

Because the shortened Kessel Run spans 12 parsecs (39.6 light-years), a ship traveling nearly light-speed would take a little more than 39.6 years to get there. Factoring in time dilation, anyone watching the Kessel Run would see Solo speeding along for almost 40 years, but Solo himself would experience only a little more than half a day.

If you haven’t picked out the potential pitfall for the Star Wars timeline I’ll spell it out: In the time it takes Han to complete just one Kessel Run, the rest of the galaxy battles, negotiates, and force-chokes its way through almost 40 years – and pushes the date of Solo's birth 40 years further into the past.

The Long Con ————

In the Expanded Universe of Star Wars material, the timeline is numbered using the designation BBY, or “Before the Battle of Yavin,” which is the mustering of the rebellion and the destruction of the first Death Star. According to this timeline, the Millennium Falcon was constructed in 60BBY, so we know that there couldn’t have been a Solo Kessel Run in it before then. We also know that Han Solo won the Falcon from Lando Calrissian in a card game at 2BBY. Lastly, we're told that Han is around 29 years old at 0BBY.

A 40-year Kessel Run would mean that Han is chronologically much older than his physical appearance would indicate. In order to appear 29 years old during A New Hope, Han would have to be 29 years old 40 years before the events of the film. This pushes his birthday back from 29BBY to 69BBY, meaning that Han would have been born before Obi-Wan. Of course, Solo would literally not age a day from when he started the run, but the rest of the galaxy would age without him. Taking the Kessel Run would mean that Solo was entering his teens long before Anakin Skywalker was born, trained, and turned to the Dark Side.

In this alternate, physics-friendly timeline, Han Solo and Lando Calrissian are born almost 70 years before they ever lay eyes on Princess Leia’s hair buns. Once they are both around 30, they bet the Millennium Falcon in a card game, which Lando loses (if Han did make a Kessel Run with the Falcon, he would have to have won it long before 2BBY). Han then takes Lando and his prize out for a spin and sets a record by navigating a shorter route close to the black holes of The Maw on a journey to Kessel. When they return, they remain around 30 years old, but almost four decades have passed, and the Empire is amassing its forces.

Of course, there is the warp drive loophole. If you can traverse less distance by folding space itself, there is no time dilation problem. But because Han made that “0.5 past light-speed” remark – and because a warp drive device is never explicitly mentioned in Star Wars, as it is in say, Star Trek: The Next Generation – we still have all the chronological problems that come along with forward-only time travel.

And even if Han never personally jumped in the “fastest hunk of junk in the galaxy” and made the Kessel Run in less than 12 parsecs, the chances are still pretty good he made the run without it. The Kessel Run was one of the most trafficked smuggling routes in the galaxy according to additional Star Wars canon. And Han was a seasoned smuggler at the time of A New Hope, already indebted to some unsavory slugs and charmingly shooting his way through Chia Pet-looking aliens. If he didn’t do it with the Falcon, he did it with some other ship. And a slower ship would only move his birth further into the past.

Extending the adventure in pedantry, we can graph the rapidly increasing age of Han Solo as a function of how many Kessel Runs he has been on. If we put his age at 29 in A New Hope, then each Kessel Run would cause his birthday to move further back into history. With only two runs under his belt, Han would be older, chronologically, than Emperor Palpatine.

One wonders how a smuggling run with such consequences could even work. Who has the foresight to smuggle something the other party won’t see for 40 years? And imagine how it would work for the smuggler. Off he goes on a Kessel Run, and barely 16 hours later – from his perspective – he returns to find a world changed: the remnants of a galactic clone war, the fall of one Jedi order and the rise of another, and the floating remnants of two Death Stars.