It is widely believed that time travel is useless.
After all, everyone knows the Block Universe Theory and its limitations: changing the past is impossible, and as such all grandfather paradoxes are banned. Predestination paradoxes are permitted, but obviously only create the already-known current state of affairs, rather than alter it; while this admits of certain limited applications in commerce (such as negative-frequency trading, although as a practice this quickly drives the market volatility operator to zero per the Market Chronology Protection Theorem, eliminating its own profit potential) and in military affairs (knight’s-move bypass transits, including optional proleptic tactical data transfer, which in practice rapidly become zero-sum effective between technologically matched opponents), these are special cases, few and far between. And while looped objects “borrowing” mass-energy from the substrate for the duration of their existence are theoretically possible, the nature of the loop requires that such objects exist in a synthetic or simulated nullentropic state, since the quantum state information at the earliest point of the loop must correspond exactly to that extant at the latest point of the loop.
It would seem, therefore, that the Chronological Consistency Protection Theorem would ban all interesting applications of closed time-like curves.
This, of course, is not the case. While it prevents the construction of technologies based upon its violation, the existence of a universal “paradox censor” that forces the probability of all causally inconsistent events to zero is of great application in several families of technologies.
The best known of these is hypercomputation. Acausal logic processors operate – to paraphrase a series of complex operations – by receiving an answer to a problem from the future, verifying its correctness, and transmitting it back to themselves in the past if and only if the answer is correct. Since the only causally consistent scenario is that in which the correct answer is received, such a device always produces correct answers to any PSPACE-definable problem. (The extraction of information without apparent computation inherent in the operation of acausal logic processors poses interesting problems at the intersection between information physics and ontotechnology, currently the province of ongoing research.)
As well-known is the so-called “probability kiln”, a class of manufacturing devices which utilize such hypercomputation for phase-space pruning; that is, to isolate and remove from future worldlines all those possibilities in which low-yield operations fail, ensuring that the only causally correct possibility is their success, thereby operationalizing even otherwise extremely impractical industrial processes.
Then there is the third class of device, a defense research project designated UNMOVED MONAD.
UNMOVED MONAD makes use of an extremely simple form of synthetic closed time-like curve, in the form of a tangle channel constructed and manipulated such that it links two points separated along the time-like axis, rather than two points separated along the space-like axis. To this extent, it is merely a trans-temporal communications facility. However, unlike trans-temporal communications performed via conventional means or space-like tangle channel, UNMOVED MONAD derives another unique property from its time-like separation: indestructability.
It is important to note that UNMOVED MONAD is a singular device: the tanglebits within are entangled with themselves across time, rather than with a matched set elsewhere. Upon activation, an UNMOVED MONAD device receives a complex, full-width verification signal from itself in the future. As such, it cannot be destroyed until this signal has been sent: such destruction would cause the tanglebits to decohere, ensuring that the trans-temporal signal never could have been received; a causally inconsistent state. Thus, per the Chronological Consistency Protection Theorem, the probability of the UNMOVED MONAD device being destroyed in the interim is forced to zero.
Properly packaged and placed, UNMOVED MONAD can even function as the mythical “synthetic luck machine” – while it is entirely possible for a bearer of an UNMOVED MONAD or the local environment to be destroyed so long as the device itself remains intact, ensuring an event phase-space with plentiful higher-order probability events resulting in the survival of the device can avoid such low-likelihood outcomes; the CCPT worldline shifts tend to go through the highest probability alternative regions. The universe evidently prefers not to work any harder than it has to.
– Temporal Mechanics: The State of the Art, “Popular Physics”, Cailmaen 6722