You should be warned, however, before you jump into the nearest wormhole. There are dangers lurking in the multiverse that could mean the doom of yourself and your home timeline. The following are a few dangers to keep an eye out for if we ever perfect crosstime travel.
Native Americans were isolated from the rest of the world prior to 1492 and thus they did not gain the immunity to various diseases the rest of humanity gained. The arrival of Columbus and other Europeans changed everything and introduced diseases to a population that was not prepared for them. While the exact die-off is unknown, even conservative estimates put it into the millions.
Consider S. M. Stirling's Conquistador, where some of the characters stumble upon a portal in California to a timeline where the New World remains undiscovered by the Old. When they attempted to settle this timeline they ended up once again unleashing diseases on a people who were unprepared to deal with them. Consider the number of timelines we could infect with diseases that are only minor nuisances to ourselves, yet could collapse entire civilizations that are defenseless against the scourge.
The problem is the same could happen to us. An infinite multiverse has an infinite number of points of divergence where any number of unique diseases could exist that we are unprepared for. A crosstime traveler could inadvertently stumble upon a timeline where some common disease that does not threaten humanity at all OTL mutated into the cause of the zombie apocalypse. Now maybe I am exaggerating the dangers by using the zombie apocalypse trope. If you want a more plausible example, see Papatlaca at the Alternate History Wiki.
Preventing a viral outbreak could be next to impossible depending on the method of travel. If crosstime travel depends on a stationary location, than quarantine could prevent an apocalyptic outbreak. If the device necessary for crosstime travel, however, can be carried in an individual's pocket (like Sliders) than preventing unlicensed exploration of timelines would be almost impossible to prevent.
Randall Park at his blog FuturePundit touched on two possible scenarios involving crosstime travel:
If one could find worlds more technologically advanced one could use that tech (e.g. robots, AI, nanotech factories, rejuvenation tech using microfluidic devices) to an unpopulated world and create a luxurious community in a clean environment with no terrorism or pollution or resource depletion. On the other hand, if multiverse travel is possible how soon till multiverse invasions by hostile species?The idea of being invaded by aliens is not new to our culture. In fact, the famous scientist Stephen Hawking has even warned humanity that our first contact with an intelligent species may not turn out well for us. Yet while everyone is watching the stars in fear, perhaps Park is right that we should be worried about an attack coming from a different angle.
As I said before we exist in an infinite multiverse with an infinite number of PODs. It is possible that somewhere in the multiverse there is an Earth that experienced a vastly different evolutionary history. One example are the dinosaurs surviving and having one of their number evolving into an intelligent race. With millions of years more to advance their culture, we cannot always hope that they will remain a pre-industrial society like the evolved raptors in Anderson's Destroyermen series.
Yet we do not always need an alien species before the threat of multiverse invasions becomes a reality. We should worry about other advanced humans, like Stirling's Draka or the fascist space empires found in Ad Astra Per Aspera. Throughout human history, when an advanced culture came in contact with less advanced culture, the more advanced culture eventually subjugated the other. Our own history proves this again and again.
So if we stumble upon some advanced civilization on another timeline, we may be inviting them to attack us. Maybe they are desperate for resources, having used up their last deposits years ago. They could also be in competition with another crosstime capable Earth to grab as much of the multiverse as possible, much like the Scramble for Africa from OTL. They could have some ideological drive to spread their beliefs wherever there is some "unenlightened" population. The reasons are endless.
Regardless of the reasons, could we stop them? What are our counter-measures to nano-swarms that would disassemble our weapons into piles of dust, biological agents that would turn us all into meek slaves or space stations that could rain down nuclear fire at any signs of defiance?
For this reason alone, keeping the secret of crosstime travel of other timelines may be paramount for the survival of our own civilization.
Stay with me on this one. I know it sounds crazy, but this is an issue we should watch out for.
Larry Niven published a short story called "All the Myriad Ways". It is set in a timeline where the Cuban Missile Crisis escalated to a nuclear war. At the present time in this universe, crosstime travel has been invented and the corporation that invented it now profits from their discovery by the technology they discover from other Earths. The main character is a detective who is investigating an epidemic of suicides and murders. At the end (SPOILER ALERT) the main character realizes that the known existence of an infinite mulitverse means that all possible choices that might be made are actually made in other timelines, thus making free will meaningless. By committing suicide or committing murder, the person is abandoning the sense of choice.
Now whether Niven's depressing scenario is realistic is matter of opinion. Nevertheless, science fiction has a pretty good track record when it has come to predicting the future. There is also plenty of proof that people do not always have a healthy reaction to the harsh reality we inhabit. Author Steven W. White also had some comments on the story during an interview I had with him:
...If there are countless versions of you, in which you are rich, royalty, president, poor, imprisoned, quadriplegic, and dead... what's the point? They are just as real as you are. So why bother sweating over a tough decision? Why bother doing the right thing?
In other words, once you get really get your head around the multiverse, you become a nihilist (Niven is not a fan of alternate history, if that's not already clear).
In my opinion, Niven's idea scares me enough that research should be conducted on the psychological impact of crosstime travel if it is ever invented....How many versions of yourself could you meet before you got weirded out by it? What would that do to a person?
Often when we speculate on other timelines, we also discuss how human choices are the main cause and effect for the existence of the multiverse. In reality, the vast majority of all the timelines that make up the infinite multiverse have nothing to do with humanity. Consider the vast number of animals that exist today or have existed. Could there choices be factored into account? Is that not why we have the "butterfly effect"?
We are not talking about timelines with centuries of alternate history, but with billions of years worth of differences. Among these timelines could exist a collection of species and plants that are unrecognizable to anything that does or did exist on Earth. Now what would happen if they were unleashed on our Earth? What could an invasive alien species do to our environment? Already the ones that exist today cost billions of dollars a year, but the existence of some unknown species from some alternate Earth could possible mean massive ecological damage for our own Earth.
Read up on Green Antarctica to see what happens when alien species are unleashed on an unexpecting environment. What havoc could hive monkeys wreck on our own timeline? Or dinosaurs? Or man eating squids?
I write this article not to discourage future exploration of the multiverse. Instead I only suggest that the future chrononauts take the necessary precautions to protect our Earth from the dangers that may exist in the multiverse. Stay tuned when next week I discuss how exploiting the multiverse can make you a very rich individual.