Readers of a certain age may remember the excitement stirred up when various physicists proposed to add a third category of matter to:
- A. matter with zero rest mass (which always travels at the speed of light), and
- B. matter with rest mass (which always travels slower than light).
Now there’s C: matter whose rest mass is imaginary. For these hypothetical particles—tachyons—the speed of light may be a speed minimum, not a speed limit.
Tachyons may offer a way around that pesky light-speed barrier, and SF authors quickly noticed the narrative possibilities. If one could somehow transform matter into tachyons, then faster-than-light travel might be possible.
Granted, that’s a very big ‘if’ and, for reasons explained in this essay, tachyon drives are NOT a means of travel I’d ever use. But hey, the siren song of narrative convenience overrides all the wimpy what-ifs. Sure, getting every single elementary particle comprising the spaceship to transform simultaneously (whatever simultaneously means) could be tricky, but who wouldn’t risk being turned into goo if one could avoid spending decades or centuries travelling between stars? Fred Pohl’s Jem used tachyon conversion to get his near-future humans to a nearby star and the adventure awaiting them there.
Of course, even if tachyons didn’t permit faster-than-light travel, they might facilitate faster-than-light communication. Perhaps it would still take decades to get anywhere interesting, but at least one could talk to other entities on distant worlds. Sometimes, as in a Poul Anderson story whose title escapes me, this could facilitate doomed romances across distances too vast to cross. With a high enough bandwidth, one could even remote-control rented bodies, as postulated in Pohl and Williamson’s Farthest Star.
Farthest Star also explores the notion that one might record someone’s molecular pattern and beam it to a distant location, to be reconstituted there upon arrival. If one didn’t destroy the original while scanning it, one might even be able to create duplicate after duplicate to engage in high risk missions…
That’s all very well for the original. The copies might have a different perspective.
Any faster-than-light travel or communication also has the drawback (or feature, depending on your perspective) of allowing travel or communication with the past. Which leads to some interesting possibilities:
- This could change history: all efforts at reform, for instance, could be annulled by any fool with a time machine.
- Perhaps we would find that history is fixed, and we’re all puppets dancing to a pre-ordained script.
- Or perhaps time branches, in which case it sure is silly to have spent as much time as you did making important decisions while different versions of you were embracing all conceivable options.
The classic example of an intertemporal communication plot would be Gregory Benford’s Timescape, in which a scientist finds out what happens when one beams information into the past. I am not saying what happens, but it’s not happy. (Well, perhaps from a certain point of view…)
A 1970s paper whose title I have forgotten (and spent hours of poking through Google Scholar to find, and failed) drew my attention to another possible application, one that any M/m = edelta v/exhaust v-obsessed teen must have found as exciting as I did. IF we had a means to eject tachyons in a directional beam, we could use them to propel a rocket!1
Now, these tachyon-propelled rockets couldn’t break the speed of light—though they might get close to it. Regardless of the means of propulsion, the ships themselves are still subject to relativity, and nothing with a rest mass that is not imaginary can reach the speed of light. But what they could do is provide extremely high delta-vs without having to carry massive amounts of fuel.
And the very best thing? If the tachyons emit Cherenkov radiation, then tachyon rockets would emit that blue glow seen in so many cinematic magical mystery drives.
Tachyon rockets are therefore ideal from the perspective of SF writers2. They are, in fact, a replacement for our lost and lamented friend, the unrealistically effective Bussard ramjet.
Curiously, aside from one essay by John Cramer, and one novel, Joe Haldeman’s The Forever War 3, if SF authors did leap on the narrative potential of the tachyon rocket, they’ve been doing so in books I have not yet read. Pity.
Top photo courtesy Argonne National Laboratory.
1: In some frames of reference. In other frames, it would look as if the beam were pushing the ship. Agreeing on what happened and in what order it happened becomes problematic once one adds FTL to the mix—good news for people like me, who have trouble keeping tenses straight from one end of sentence to the other.
2: Well, there are a couple of minor catches. One is that there is no evidence that tachyons exist. Some might go so far as to say the evidence suggests they don’t. As if “there is no evidence this stuff exists” ever stopped SF authors from using wormholes, jump drives, or psychic teleportation. Also, some models suggest any universe that has tachyons in it is only metastable and might tunnel down to a lower state of energy at any moment, utterly erasing all evidence of the previous state of being. Small price to pay for really efficient rockets, I say.
3: “Wait, didn’t they travel faster than light in The Forever War?” I hear you ask. They did, but not thanks to the tachyon rockets. Ships circumvented vast distances by flinging themselves headlong into black holes (called collapsars in the novel). As one does. In The Forever War, this was not a baroque means of suicide; ships did re-emerge from distant collapsars. So, a slightly different version of wormholes. The tachyon rockets in the novel provided the means to get to the black holes, which were often inconveniently far from the destinations humans wanted to reach.
In the words of Wikipedia editor TexasAndroid, prolific book reviewer and perennial Darwin Award nominee James Davis Nicoll is of “questionable notability.” His work has appeared in Publishers Weekly and Romantic Times as well as on his own websites, James Nicoll Reviews and Young People Read Old SFF (where he is assisted by editor Karen Lofstrom and web person Adrienne L. Travis). He is surprisingly flammable.