Basic Information
A Tipler Cylinder is a type of Time Machine first proposed by physicist Frank J. Tipler in 1974. The Tipler Cylinder exploits a geometric oddity of spacetime to create a very large closed timelike curve. Essentially, the Cylinder is no more complex than an extremely large and massive cylinder, spinning rapidly along its axis. Any spacecraft that accelerates into it will travel backwards in time. The limit of this Time Travel is back to the moment of the Tipler Cylinder's creation.
There's obviously issues of practicality involved, which may hamstring the usefulness of a Tipler Cylinder. You'd need a really big cylinder, for one thing. Astronomically huge. In fact, it's only been mathematically proven to work for a cylinder of infinite length, though Tipler's initial paper proposes that a smaller cylinder would suffice if it were rotating very fast. Just a guess, but I'd say that if you've got the power and resources to build an infinitely long megastructure, and spin it at or near the Speed of Light, you can probably find an easier way to time travel.
In his Chronology Protection Conjecture, Stephen Hawking illustrated some other mathematical issues with the Tipler Cylinder, as apparently it would require Exotic Matter and/or negative energy. Way over my head, I'm afraid. Luckily, most Time Travel campaigns are by definition almost certain to ignore the Chronology Protection Conjecture in favor of the Novikov Self-Consistency Principle, Branching Time, or Temporal Paradox and the Rule Of Cool.
Sources
Game and Story Use
- Continuum has a small section on the Tipler Cylinder, and even has the Big Bads of the setting attempt to turn The Sun into a huge Tipler Cylinder to destroy the future (our present and all of recorded history), using nothing but Geomancy, a Neolithic equivalent of a Supercomputer, and the Rule Of Cool.
- Sufficiently Advanced Aliens could build a huge Tipler Cylinder out of Phlebotinum to unlock the Fourth Dimension and expand their Space Empire.
- Then some tragic end happens to their culture, perhaps even the result of side effects or implications of the Cylinder. They become the long lost Precursor Race, and ages later human astronauts discover their monolith - I mean cylinder - floating in deep space. The PCs can travel to the alien's time, but once you've done so, you can't go home again.
- Discussion of what it might take to build something this big can be found on the Stellar Megastructure page.
- The computer controlling the rotation of the Tipler Cylinder becomes self aware. It is a Spaceship Girl, a Fourth Dimensional Lifeform, and an Eldritch Abomination (since AI Is A Crapshoot), all rolled up into one infinitely-long space-burrito. Kiss your galaxy goodbye.