A Primer Puzzle

There’s a film that I’m a huge fan of, called Primer. Since I first discovered it I’ve insisted on showing it at least twice at Troma Night (the second time just for the benefit of everybody who didn’t “get it” – i.e. everybody – the first time). If you haven’t already seen it, this post might be a little spoilery, so instead of reading it, you should warm up your time machine, go and watch the film, turn off the time machine, get into the time machine, come out again right now, and then read its Wikipedia page until you understand it. Then come back.

Time Travel in Primer. Click to embiggen.

Still with me? Right.

Why Primer is awesome, and why you should care

In Primer, the protagonists accidentally stumble across the secret of time travel and use it to cheat the stock market. The film isn’t actually about time travel or science-fiction: it’s actually about the breakdown in the relationship between the protagonists, but it’s got some pretty awesome science-fiction in it, too, and that’s what I’d like to talk about. The mechanism of time travel in Primer, for example, is quite fascinating: the traveler turns on the machine using a timer switch (turning it on in person risks the possibility of meeting a future version of themselves coming out of the machine). They then wait for a set amount of time, then they turn off the machine, get into it, wait for the same amount of time again, and emerge from the time machine at the moment that it was turned on.

This is a lot weaker than many of the time travel devices featured in popular science fiction literature, films, and television. It’s not possible to travel forwards in time (except in the usual way with which we’re familiar). Travelling backwards in time takes as long as it took the machine to travel forwards through the same period, making long journeys impossible. The machine has to be strategically turned on at the point at which you want to travel back to, reducing spontaneity, and it can’t be used again in the meantime without resetting it. Oh, and the machine is dangerous and causes long-term damage to humans travelling in it, but that’s rather ancillary.

There’s a certain believability to the time travel mechanic in Primer that gives it a real charm. As far as it is explored in the film, it permits a deterministic universe (so long as one is willing to be reasonably unconventional with one’s interpretation of the linearity of time, as shown in the diagram above), provides severe limits to early time travel (which are great for post-film debate), and doesn’t resort to anything so tacky as, for example, Marty McFly gradually “fading out” after he inadvertently prevented his parents from getting together in Back to the Future.

Marty begins to disappear. I love this film, too, but not even slightly for the same reasons.

Experiments in the Primer universe

I’ve recently been thinking about some of the experiments that I would be performing it I had been the inventor of the Primer time machine.

First and foremost, I’d build a second, smaller time machine of the same design. We know this to be possible because the first machine built by the protagonists is smaller than the ones they later construct. I want to be able to put one time machine inside another. Yes, yes, I know that this is what the protagonists do in the movie, but mine has a difference: mine is capable of being operated (power supply only needs to be a few car batteries, as we discover in the film) within the larger time machine. That’s right, I’m building a time machine inside my time machine.

  • Experiment One attempts to explore the relativism of time. Start the larger time machine and warm it up. Stop the larger time machine. Start the smaller time machine. Get into the larger time machine, carrying the smaller time machine, and travel back. Once back, turn off the larger time machine. Experiment with sending things forwards in time using the second time machine (which has traveled backwards in time but while running, from our frame of reference). If objects inserted into it come out in the future, before it is picked up, this implies that there might be a fixed frame of reference to chronology. It also indicates that it is possible to build a machine for the purpose of traveling forwards in time, too, although only – for now – at the usual rate.
  • Experiment Two attempts to accelerate the rate at which a traveler can move forwards or backwards through time. Based on the explanation given in the movie, the contents of the time machine oscillate backwards and forwards through the period of time between their being turned on and being turned off, for a number of repetitions, before settling. If we are able to synchronise the oscillations of two time machines, one inside the other (by turning them on and off simultaneously, using timers attached to each and their own distinct, internal, power supplies), might we be able to set up a scenario that, in X minutes, switches off, and we can get inside the inner machine and travel back to the switch-on time in X/2 minutes? If so, what happens if we send such a two-machine construction back in time as in Experiment One – do we then have a “time accelerator”?
  • Experiment Three takes advantage of the fact that for an object within the field, an extended period of time has passed (during the oscillations), while from the reference point of an external observer, a far shorter period of time has passed. Experiment with the use of an oscillating time period field to accelerate slow processes. Obvious ones to start with are the production of biologically-produced chemicals, as is done in the film (imagine being able to brew a 10-year-old whiskey in a day!), but there are more options. Processing time on complex computer tasks could be dramatically reduced, for example. Build a large enough time machine and put a particle accelerator in it, and you can bring masses up to relativistic speeds in milliseconds.
  • Experiment Four is on the implications on spacetime of sending mass back in time. As we know, flinging mass in a direction of space produces an equal and opposite acceleration in the opposite direction, as demonstrated by… well, everything, but let’s say “a rocket” and be done with it. Does flinging mass backwards through time produce an acceleration forwards through time? This could be tested by sending back a mass and a highly-accurate timepiece, removing the mass in the past, and letting the timepiece travel back to the future. The timepiece is checked when the experiment starts, when the mass is removed, and when the experiment ends. If the time taken for the second half of the experiment, from the perspective of the timepiece, is longer than the time taken for the first half, then this implies that Newtonian motion, or something equivalent, can be approximated to apply over time as well as space. If so, then one could perhaps build an inertia-generating drive for a vehicle by repeatedly taking a mass out of one end of a time machine, transporting it to the other, and sending it back in time to when you first picked it up.

The scientific possibilities for such a (theoretical) device are limitless.

But yeah, I’d probably just cheat the stock market, too. At least to begin with.