Kara is reading “Citadel: Paths in Darkness” for the first time. She seems to be enjoying it (and particularly enjoying pointing out my typos and omissions … look for a second edition down the road). But over the weekend she came to the part of the story where I explain some of the physics behind the Lightrail.

I’m no physicist, even if I might pretend to be in some of my geekier fantasies. I do read a lot about the latest breakthroughs in science and technology, which is where a lot of this stuff comes from. The ideas I wrote about in “Paths in Darkness” were centered on some pretty basic principles of Newtonian and quantum physics. What I did with the scraps of information I know and used in the book, however, was really something of an intuitive leap. I thought I might walk through some of that, to try to explain how I think the Lightrail would work (or at least how it works in my universe, which may have drastically different laws of physics than the real one).

To start, the lightrail isn’t really a continuous beam of light. If you’re standing to the side, you aren’t really going to see anything. Unless, of course, you are standing to the side of one of the lightrail relays, in which case you would see a continuous glow of light with occasional flashes as a ship enters and exits the relay at near light speed.

The beam is “near coherent,” meaning it has enough density that the particles of light are able to push another object, in this case a spaceship, along at the same speed they are moving. Over a great distance the particles would lose their momentum, the power of forward movement, and whatever they are pushing would start to slow. To keep the party going, as it were, the lightrail network relies on a series of relays.

These relays are special. They are complete science fiction, because as far as I know there really is no way to take a signal in at one strength and push it back out at exactly the same strength. Not exactly. There’s something called “the law of diminishing returns,” and another thing called “the law of conservation of energy.” Together, these things mean there’s a constant loss in the exchange. The lightrail goes into the relay, and it may be boosted and retransmitted, but it would lose “something” in the exchange.

In my universe, however, some clever physicist came up with a way to mitigate that, or at least marginalize it to the point where it’s negligible. The lightrail relays, then, are the key to faster-than-light travel.

In “reality,” I think that the relay is really “generating” the lightrail, rather than transducing it. It’s as if the lightrail starts for the very first time in the core of the relay. Instead of passing through it, the lightrail (and the ship it’s pushing) become the start of a process in which everything is created brand new and starts a new journey altogether.

The key is “quantum tunneling.” So far, here on Earth and in our own time, physicists have managed to discover a way to entangle particles on the quantum level. The result, basically, is that whatever you do to Particle A will also happen to Particle B. That’s cool, and easy enough to understand (well … maybe not “understand,” but it’s easier to imagine).  But here’s the fun part … this effect happens regardless of how far apart these particles are.

That is mind blowing. Particle A can be in the U.S., while Particle B is in China, or even on Mars, and whatever we do to A will happen to B. Why, you may ask? Well, whoever figures out the answer to that question has a Nobel Prize and a place in history coming their way.

But there is this idea of quantum tunnel. And the way I’ve used it in the book is to say that somehow, on the quantum level, Particle A and Particle B are connected to each other through a tunnel that exists outside of space and time. Effectively, this means it exists outside of the known universe.

This is where the idea of “wormholes” comes in. A wormhole would essentially be a quantum tunnel that connects two points in space. Think about a sheet of paper. On either end of the paper is a dot. If you wanted to connect those dots, you could fold the paper until they overlap. But if you wanted an ant to move from one dot to the other, you would punch a hole through both, allowing the ant to tunnel through. Effectively, the ant has moved through a plane of space instantly, just by passing through the hole that connects the two dots.

Since we can’t bend space, we have to use some outside type of medium to make the “fold.” In this case, we’re stepping outside the laws of physics all together, outside the universe itself, so that we can travel between Point A and Point B instantly. We’re “folding space” to overlap two points of locality, then moving between them.

So here’s where the lightrail relays come in. These are our points in space. They’re the points on the pond’s surface where the stone hits as it skips. The light rail starts from one of these relays, pushing the ship ahead of it, and is picked up by another relay on the same “path,” then sent along to the next.

So remember that “slowing down” problem we discussed? That’s where things get tricky. Because in this scenario, there’s a sort of “imperfection” to the quantum tunnel. Actually, there’s a rule, and that rule is that you must be moving at the speed of light to stay in the tunnel. Over greater distances, the beam’s power starts to fade, and the ship starts to phase back into the universe. To get around this problem, the early colonists would drop more relays, which would pick up the beam, strengthen it, speed it back up, and send it back out.

This is how the network came to be built. It’s a little like sinking pylons into the bed of a lake in order to build a bridge across it. You bring the pylons with you as you travel, and drop them off at intervals. That way, you’re leaving behind a route that’s much easier for the next guy to travel.

So Earth Colony Fleet sends out a vessel on the light rail, to an area of space that isn’t already part of the network. The ship travels until it slows down enough to drop out of lightspeed (and back into the universe). It then drops a relay, which it can use to get back up to lightspeed (and back out of the universe) again. Then the cycle repeats. These forerunner ships are actually exploring the universe and cutting roads as they go.

This is dangerous, of course. If you come out of the lightrail too close to a planet or a star, you could be in trouble (as our heroes can attest). So there are safeguards. There are systems in place that keep that from happening. Essentially, feedback from the beam would tell a relay to adjust the power of the beam, therefore adjusting it’s “length.” If the beam is meeting resistance from a planet or some other celestial object, the relay will sense it and turn down the power. When the ship slows down in order to drop another relay, the next beam will more or less “tunnel through” the object, keeping the ship from being destroyed. Unless, of course, someone tampers with the system.

The relays aren’t unidirectional, by the way. They can transmit in any direction. The beam can even be “bent” to change course in mid flight. If you think about it, this makes sense. The ship is moving through non-space, but is generally moving from Point A to Point B. If the Captain decides they actually need to be at Point C, he can change direction by changing the way it affects the ship in motion. He’s still moving at the same speed, he just chooses a new place to end up. The only limitation is range. If the ship is already close to Point B, it will have to “double back” or otherwise extend its course to get to Point C.

In our story, the problems started when Captain Alonzo realized that they were not on the course they thought they were. He tried to alter course, but met with a saboteur’s handiwork.  If there’d been no sabotage, however, he could have changed the course of the ship and taken them to their original destination.

So here’s the basics:

  • ·      The lightrail is a quantum tunnel through which a near-coherent beam of light is pushing a spaceship
  • ·      The beam’s strength fades over time and the tunnel collapses, pushing the ship back into real space
  • ·      A relay picks up the weaker beam, strengthens it, and retransmits it back into “outside space”

Once the ship leaves the lightrail it can use its engines to push it to a local destination. So if the lightrail delivers it to the same solar system as a bunch of colony worlds, it can putter along to those worlds a fast but less-than-lightspeed pace.

And when the ship is ready to get back into the lightrail network, it uses it’s own built-in lightrail relay, otherwise known as a lightrail “conduit,” to generate a starter beam, which opens a quantum tunnel and pushes the ship into it, on its way to the next drop point or relay.

So why doesn’t the ship just keep generating lightrail jump points indefinitely, skipping the relays? Good question!

This fact hasn’t come up yet, but it probably will. Each ship carries enough charge in its lightrail conduit to get it back to the lightrail. This charge is depleted in the process, however. So each time it hits a relay in the network, it recharges itself back to full.

The lightrail relays that the ship is carrying also have a charge. Enough for one jump, essentially, until they recharge using various sources such as solar power and the stream of the lightrail itself, once the relay is part of the network. So it’s true, if you found yourself stranded, you could conceivably use the relays to jump back to civilization, barring any further complications.

So basically, each ship carries a set of “spares,” just in case. And in exploring the universe, once a ship gets down to its last relay, it turns around on the network and goes home to “reload.”

Now, doesn’t that clear everything up?

I know, it’s a mouthful. But you’ve made it this far, so I have to think that you’re interested. And yes, there are all kinds of holes in this idea. But I’ve put a lot of thought into it, and I continue to do so. And as the story evolves, some things change ever so slightly, so maybe this explanation will go right out the window. But until that happens, I hope this at least clears up some of the thought behind the lightrail network. It has for me!


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Kevin Tumlinson is the author of numerous novels, novellas, and non-fiction books, and the host of the Wordslinger Podcast. Try three of his best books for free when you download his starter library at kevintumlinson.com/starterlibrary.
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