Humanity gain the ability to slide between alternate realities. Contains TF and TG.
|The specifics of exactly how and why are still unclear, but mankind has been granted the ability to step between realities, The ability is known as 'Sliding', is innate and instinctive, and was conferred simultaneously upon two-thirds of the human race by a mysterious wave of cosmic radiation, an event that became known as Open Day. With a single thought, a person can now cross through into one of billions (possible infinite) alternate Earths.|
The other realities vary wildly - many of the Earths are desolate arid rocks, others are merely uninhabited, worlds where homo sapiens failed to evolved, while some are almost identical to our own, differing only in a few details. Some are utterly alien, hosting lifeforms, civilizations and sentient races never seen on Earth Prime.
A rare few, known as 'Joker' worlds, operate on physical principles that make a mockery of conventional Earth Prime physics. Examples include Chocolate World, Balloon Animal Planet, and Backwards Land, where time flows in reverse. There are even worlds that run on cartoon logic, where people can be squashed, dismembered and exploded without harm, and realms where magic is real and Gods walk upon the Earth. The existence of these worlds and their warped, whimsical logic have driven many of the scientists struggling to comprehend the sliding phenomenon into apoplexy.
Each human is granted one reality that is keyed to them and them alone. Only that one person can slide directly into "their" reality. though sliding leaves behind a portal through which others can follow. Interestingly, most alternate Earths seem to relate to the person matched with it, often fashioned after their personalities and desires in some fashion.
In addition, sliders may make a "blind slide" whereby they jump to any one of the infinite Earths of the multiverse completely at random. Blind slides are dangerous, both for their debilitating effects on sliders, and because they do not leave behind a portal. The person is stranded, and the only way to return home is to continue blind sliding in the hope of landing back on Earth Prime, though the chances of this are astronomically slim.
When people slide into their personal realities, they leave behind a silhouette, a person-shaped portal in the air shaped which connects the two worlds and remains open for as long as a person is inside their reality. It is through this portal that a slider must return in order to get back to Earth Prime, and others may travel freely through an open portal while it remains open. Care must be taken in exploring another person's world, however. Sliding into your own reality is not possible while in somebody elses, only from Earth Prime, and should the person whose reality you are in return to Earth Prime, the portal closes behind them, trapping you inside. Should they die, the portal will begin to destabilize, and will vanish completely after 24 hours.
If a traveler enters a dimension significantly different to their own, there is a strong chance that their physical forms will be altered to match the rules of the new reality. The person may attempt to fight off these changes, however the reality will start to reject the incongruous "fly-in-its-ointment" if they do so. A series of improbable, life threatening events will begin to occur in the vicinity of the dimensional traveler, escalating until the traveler either leaves or accepts the changes. If a slider is unconscious, they are unable to resist the changes.
These changes are almost always reverted upon returning to Earth Prime. When blind sliding, these changes are only ever compounded. For example, if a traveler enters a world where only women exists and becomes a woman, then blind-slides to one where zombies are the dominant lifeform, he will become a female zombie.
There are other risks, not just to sliders but to the wider world of Earth Prime. The other worlds are frequently dangerous, containing hostile creatures; strange, infectious diseases unknown to medical science; and sentient races that will cross back into Earth Prime through open portals if given the chance. Earth Prime is swiftly losing grip on normality as the oddities of the alternate dimensions migrate in. An international task force has been established to police this new phenomenon, deporting inter-world immigrants, sealing off dangerous worlds, even chasing criminal fugitives into their own warped realities in order to bring them to justice.
Rules of Sliding (tl;dr)
1. Each human may slide to their personal dimension, but only from Earth Prime. This leave behind a stable, two-way portal.
2. Portals vanish when a person returns home, and swiftly destabilise if a person dies.
3. Each person may "blind slide" from any dimension, jumping at random to one of the infinite Earths. The portal destabilizes almost instantly.
4. Duplicates of people may exist in other dimensions. When attempting to enter a world where a version of themselves already exists, a slider will replace the original.
5. A slider's physical form may be changed if it conflicts with the rules of the new dimension. A slider can fight the changes, but the dimension will not like it. A slider who is unconscious cannot fight the changes.
6. Sliding while in contact with something or someone carries the risk of fusing the two into a single individual.
7. All changes are reverted upon returning to Earth Prime, but compounded when "blind sliding". Any changes inflicted while in another reality (by surgery, magic or other means) do not revert.
Rules of writing
1. The multiverse is truly infinite. Don't see a reality you like? Make one!
2. Kill characters is fine. However, if the protagonist dies, the story continues, from the POV or one of the other characters.
(With thanks to Sliders, and Terry Pratchett and Steven Baxter's The Long Earth.)