"Oh, you can't get to Heaven
On a Tachyon
'Cause it goes too fast
To sit upon."
Tachyons are hypothetical subatomic particles that always move faster than light. You can't slow them down.
None the less, they've crept into science fiction enough that mentioning them provokes a vague popfinition-esque recognition - upon hearing the term "Tachyon", you can't help but think it's somehow scientific or science fictional. Star Trek: The Next Generation, for example, liked to us Tachyon as a buzzword but rarely showed any signs of understanding what they were talking about.
Varieties of Tachyon?
Technically, tachyons are not necessarily a single particle, but could actually be a class of particles, with many different types. One way of looking at particles is to divide them into three categories. Normal matter that you're used to has mass and moves slower than light. As a class, normal matter is sometimes called tardyons or ittyons. Luxons are massless particles that always move at the speed of light - specifically the photons of light. In theory, there could be tachyonic equivalents to matter; objects or even life that constantly moves faster than light. (Again, it's not terribly likely to work out that way in the real world, but all is fair in fiction and gaming.) Such tachyonic matter might be massless like light, have normal mass but incredible speed, or might even be exotic matter that exhibits antigravity properties.
Because they move faster than light, you also can't tell the difference between Tachyons being emitted and being absorbed, or between Tachyons going backwards in time or forwards in time. Which means that any Tachyon detector could also be creating the Tachyons it detected.
If something were made of tachyonic particles, it would have properties similar to what is described above. Assuming the tachyonic matter interacted with light, it would be visible, but in ways that boggle the mind. Since it would move faster than the light it was reflecting, it would reposition itself before the light reached you. If a tachyonic alien were traveling towards you, you'd actually see it in reverse. It would arrive (and assuming it somehow waited around for you to react), and then you'd see it's approach. However, you'd see the reflected light from the closer parts of its approach before the light would arrive from further back on its voyage. While it was standing next to you, you'd effectively see its approach in reverse. You'd actually see two (or more) of it, one standing next to you and another receding backwards away from you at a rapid pace, like a video feed on rewind.
Of course, being made of tachyons, the object or creature would have to constantly move. Tachyons always move faster than light, they just can't slow down. So it wouldn't be waiting next to you. The tachyonic being would zip right past you before you were even aware of it. Then light it reflected would start bouncing towards you, coming from both where it's going and where it's coming from. Visually, you'd see the object recede away in two opposite directions. Unless the tachyonic object had an obvious "front" and "back" orientation, you wouldn't be able to tell which way it was going and which way it came from. (Maybe with advanced scientific equipment you'd be able to figure it out by analyzing the red shift and blue shift of the light waves that reached you.) This effect is why (as mentioned in the first paragraph of this page) you can't tell the difference between tachyons you're detecting and those you're creating.
Here's the coolest (or creepiest) part of what you'd see: The first image of the tachyonic matter you'd see would be it at whatever the closest point it passes by you is. Then you'd see it recede in two directions, as mentioned above. This would happen so fast, that it would look as though the object suddenly materialized next to you without warning, split in two, and then run away faster than a rocket in two directions. That should have your brain doing somersaults.
Game and Story Use
- They travel faster than light, back and forth in time, and you can't tell if you're detecting them or creating them. Sounds like Mad Science to me!
- Tachyons are a possible phlebotinum for FTL especially FTL Communication or FTL Sensors.
- Here's a messed up it's the end of the world as we know it scenario for you: One day, suddenly, the earth is all-but destroyed, without warning. They sky lights up, then there's massive earthquakes, volcanism, giant storms, and huge clouds of debris. Most of mankind is snuffed out in seconds. Perhaps either the earth or the moon is knocked slightly off orbit and now wobbling. Maybe there's something akin to a nuclear winter, and post-apocalyptic decay sets in. Once the clouds of ash and dust have settled enough that you can again see the night sky, two glowing comet-like objects can be seen racing away from the earth and each other. It turns out the tachyonic equivalent of a rogue planet or asteroid passed close to the earth, and it's reverse gravitational field was the source of all the destruction.
- Tachyonic Life, that is aliens whose bodies are made of tachyons, would be about as alien as you can imagine. They'd make a truly mind-blowing background detail or plot device, but us slow-poke humans would find it almost impossible to interact with them at all.
- Cause and effect get kinda iffy where Tachyons are concerned. They're like a natural Temporal Paradox, and potentially on a galactic scale since they move so darned fast. So they'll be of interest to the Temporal Physics Professor and the Temporal Meddler, and could be vital to the construction of a time machine or stable time loop.