Time Travel Thought Experiment

TimeTravel has been in works of ScienceFiction such as GeneRoddenberry's StarTrek and HGWells' TheTimeMachine for a very long time. But TheoreticalPhysicists? such as AlbertEinstein, NielsBohr, StephenHawking and many others have theorized and debated the possibilities of real TimeTravel for almost as long.

In a TimeTravelThoughtExperiment, participants could make the assumption that TimeTravel will eventually be possible and that scientists will be looking for historical elements of support for their experiments. Put another way, if I am personally going to be successful in sending information backward in time, to myself, next year, then what do I need to do this year to be ready to receive that information? If receiving the information is technologically easier than sending it, perhaps I can conquer the easier issue first, by making for future selves a TimeTravelSandbox? which can be a place and time which will be safe for conducting time travel experiments.

So what might be needed in order for me to receive this information? Well probably quite a lot of things:

An agreed upon medium of information exchange. This medium would be selected based upon a best guess of what methods would be most easily accomplished by future scientists. Rather than simply listen for any communication from the future, we might have to actually specify it. And yet we would not be able to specify the results. Fortunately QuantumPhysics gives us several methods why which we might request to know the result of an experiment that can only be known after its observation.
We might hope to utilize communication with the lowest possible energy requirements - Assuming that we are the creators of the technology that succeeds one day in TimeTravel, we may as well make it easy on ourselves when we finally attempt to communicate with our own past. That means the method should require as little energy as possible, and communicate information as that is highly credible.
A set of rules may need to be designed as an experimental environment. This would be some set of controls to minimize the risk of any actual experiments. For example, if future scientists sent back information that TimeTravel was impossible, and that we must immediately abandon the idea, and if we were to believe them, then immediately a potential paradox is created. We would need to avoid paradoxes or situations that had the potential to create them.
There would have to be a fairly reliable way for future researchers to be made aware of the methods of the experiment.
A list of assumptions would have to be developed. For example, that TimeTravelParadoxes? are solvable or avoidable.
A list of issues would have to be maintained until the critical issues with a particular methodology were resolved.
Goals and scope for such an experiment would have to be defined.

The intent of such a ThoughtExperiment? is to hasten the development of technology that does not yet exist, by speculating about some of the historical needs of such experimentation and filling those needs now. Scientists participating in a TimeTravelThoughtExperiment by attempting to address these issues could be considered to be colleagues of their future counterparts who will be the actual TimeTravelers in the future.

Methods of a TimeTravelThoughtExperiment might overlap or be similar to the SearchForExtraterrestrialIntelligence? Project (SETI) and might even use data collected by SETI. Most certainly the exact methods will be a matter of collaboration using something like WikiWiki.

Ideas for sending information backward in time:
1. A signal fired at a wormhole
  1. Challenges
    1. Finding one
    2. Finding one where the time difference between the two blackholes is useful
    3. Receiving information out of the other side of the WormHole. If time-separated WormHoles are an extremely common occurrence of nature, and future TimeTravelers find one connected to our current SpaceTime, it would only be a matter of being prepared to receive information from it. Finding this WormHole could be a result of finding the information signal emanating from it. This however would provide information to future TimeTravelers about the existence of this WormHole and thus might create TimeTravelParadoxes? before any truly useful information is even sent.
  2. Given HawkingsEvaporation?, it might be possible that WormHoles could be infinitely small and exist anywhere. However, this might be subject to a period of time longer than the age of the KnownUniverse?, unless information could be preserved through multiple self-repeating BigBangs. Or unless very old shrinking BlackHoles could pass through WormHoles and thus move backward in time into the younger universe.
2. Perhaps one assumption is that no real TimeTravel (even of only information) is possible without inherently creating TimeTravelParadoxes?, and perhaps this is the ONLY reason that backward time TimeTravel is not possible.
3. An assumption could be made that backward TimeTravel does not create any greater number of paradoxes than forward TimeTravel, and thus would be equally possible. ManyWorlds? could be required specifically to resolve all possible paradoxes.

Assume ManyWorlds? is true, i.e., going back in time to kill Hitler does not change your original timeline T1 (or timepoint - where one is travelling from) but creates a new one where perhaps WWII does not occur, T2. Then since one could travel from T1->T0, if she could return from T0->T1, might it not be possible to go from T0->T2 instead (and stay there), effectively seeming to the traveller/observer that her timeline was changed?

The physics of WarpDrive technology applies to TimeTravel - it may be feasible to warp SpaceTime as a bubble around a vehicle using ExoticMatter, without creating or having to find WormHoles. See http://hcs.harvard.edu/~hsr/pdfsspring2002/lisanti48-51.pdf

If you have a WormHole that connects one part of space to another distant part (e.g. through a higher-dimensional "fold"), it's possible to turn it into a time machine. Just put one "end" of the WormHole on a ship that goes near the speed of light for a few years. Due to TimeDilation?, time will slow down for the moving end with respect to the stationary end. Thus you have constructed a time machine. Going through the end that was stationary will transport you to the past. This design has the limitation that you can't travel back to before the machine was built. -- Alan Balkany

If we assume that the universe EVER allowed the natural OR artificial occurrence of a WormHole, then according to Hawking's radiation these would eventually evaporate to an incredibly small mass. They should then be able to become small enough to pass backward in time through another WormHole.

We may not presently be able to send information backward in time, but we certainly can send information FORWARD in time, to a time when we ourselves are more capable of fulfilling a request for a WormHole-based experiment. Perhaps, as this page suggests, we can make some useful requests of our own future scientists.

For another intriguing point, let's suppose in a 6 years, in 2010, we begin to construct a time traveling WormHole (A) by by accelerating one of its BlackHoles at near the speed of light for 5 years. By 2015 we would then have WormHole A in which one end was (supposedly) in the year 2010 or so, and the other end in the year 2015. Let's suppose that we then construct WormHole B which connects the years 2015 and 2020.

What happens if we send the early end of WormHole B backward in time through WormHole A. It's early connecting point would then be in 2010, 5 years before it's creation! -- Faron Moore

You're ignoring NivensLawOfTimeTravel.

Actually NivensLawOfTimeTravel simply supposes that a universe in which backward TimeTravel is possible, looks exactly the same as one in which such a feat is not possible. In other words, "if X then likely never X". The creation of any law which states that "if X then not X" is simply a restructuring of the EpimonidesParadox?. Unfortunately, any such supposition cannot be used to produce logical statements in a confined universe. The ManyWorlds? view proposed above seems to be the only way to deal with this sort of problem.

What about our ability to modify the meaning of events which have occurred in the past? For example, the HistoricalSignificance? of an event cannot be fully determined without relating future events to that original event from the past. Take the problem of a secret. The significance of the secret depends both upon its actual content as well as whether it is eventually revealed or lost. There is no way to know for sure which type of significance will exist. Only the eventual full realization and application of the information can resolve its significance. (Can the value of information ever be fully resolved?) The interest in the idea of backward TimeTravel, stems from the mysteriously indominable hope that "mistakes" (though undefined) could somehow be corrected at a future time (by someone "out there") when there exists improved technological capacity, wisdom, historical insight and perhaps emotional fortitude to deal with the situation.

CategoryPhysics