Tent Poles and the Knife's Edge

The trouble with time travel was that it ends up being it's own tent pole. Sure you could go back into the past and change things, but they remained only as long as you were there to observe them. Even staying long enough to reach the time when you left was no solution either. It ended up that things simply shifted back to the old timeline – you were returned to where you left. That didn't mean that it was completely without consequences though. A small echo was left on the restored timeline – a bit of deja-vu, a simple message with no source, but rarely anything tangible.

Most of the time, these never really added up to much. Too few things in life were ever hinged on a single moment – and those that were, weren't likely to be influenced by a dying glimmer of another possibility.

There were a handful of people though that were on the knife's edge. People that could accept a paradox of things both happening and not – and act on it. Every so often such individuals would get a glimpse of a life not lived.

Octonions

Octonions were the key. To the uninitiated, it was describing particles in terms of pure, if high level, mathematics. Once all the particles were calculated out, their interactions became possible to predict without exhaustive and expensive experiments. In a combination no-one thought to try before, a certain combination of fields at specific magnitudes caused a translation in time. As with any scientific endeavor, progress was slow. First mainly quantum levels effects, then nano-scale, and finally up to macroscopic.

At first, it wasn't quite obvious what was happening, some objects were coming back 'younger' while others seemed to return 'older'. Careful examination found that some of the experiments reversing the age of the target – macroscopic processes such as rust were undone, while others seemed to send the object back in time – albeit to a non-obvious place. Wherever this place was, it was inaccessible until the experiment had finished, at which point it became detectable again on the equipment, and a field reversal was possible.

Or so one thought, until an accident caused a field reversal to be generated before the de-timing field was activated. What materialized was their standard experimental block, but now engraved – “If you've found this, you're a big step forward.”