Musings on Crosstime Travel
In the last issue of POD I put in a short blurb about my thoughts on crosstime travel. Unfortunately, it was very much cut to the bone because I was looking to put in something that would fill the zine out to 50 pages, but not bulk it out beyond that. There is, however, considerably more meat to my thoughts on crosstime travel in general and plausible crosstime travel techniques in particular, so I am posting an in depth analysis here.
The first question that may occur to some of you is “why?” Well, it is certainly satisfying to write a “pure” alternate history that is simply a story set in an alternate timeline, but it is also very common to use “crosstime travel” so that different timelines can come into contact with each other. This has many potential uses, the most obvious and common of which is to make an alternate history story more accessible to the average SF reader by having our own timeline exist, but introducing an alternate timeline through having it come into contact with our own. This also allows the alternate timeline to be described without implausible info dumps, since the readers learn about the alternate world at the same time that the characters from our own world do. There are of course other ways to use crosstime travel, including for the phenomenon in itself – exploring its effects on society, rather than simply using it as a mechanism to access different timelines. The latter use is much less alternate history and more into the realm of traditional science fiction, but leaves plenty of room for the exploration of plausible alternate timelines.
Since crosstime travel is entirely hypothetical (albeit with some theoretical justification in quantum physics), and isn’t obviously related to many of the physical constraints of known science, there are a huge number of ways that a crosstime device could work without contradicting the known laws of physics. For story purposes, this means that one can create a crosstime travel device with virtually any capabilities desired. This does not, however, mean that all schemes are created equal. In fact some are much more scientifically plausible than others, because the ideas they are based on are an obvious progression from real scientific theories and hypotheses. More pragmatically, creating a crosstime travel device whose capabilities don’t match what you are trying to do with it in the story will harm the reader’s suspension of disbelief. One can also go to the opposite extreme – handwaving arbitrary restrictions for the method of travel that don’t follow logically from a simple set of initial assumptions, making it obvious to the reader that the method itself was a complete afterthought to the specifics of the story.
As one example, a lot of crosstime travel stories have handwaving that prevents someone from altering a timeline in certain ways, because if they did some hostile force in another timeline would detect the alterations. This is typically done to “handicap” someone from using a really obvious solution to their problems, artificially creating a situation where they have to do something much more complex and dramatic. An example that most POD members will probably be familiar with is the “no nukes” rule in the novel Drakon. The book presents the heroes with a problem that could be solved quite easily through an application of overwhelming firepower. Instead of changing the problem so that this would no longer work, the author decrees that powerful explosives cannot be used because enemy forces in another timeline would detect it. Obvious questions of plausibility and consistency are raised. If nukes are detectable because they’d alter the timeline too much from some “natural” state, why don’t massive changes to the planet’s entire technology base lead to detection? If nukes are detectable because of sheer energy release, how does the enemy differentiate it from timelines that are having natural nuclear wars, and why don’t the bad guys set off a few big ones as a beacon? These sorts of questions detract subtly from enjoyment of a story, when a plausible and consistent crosstime travel system could be adding to it.
First, what are the general concerns in creating a system which matches the kind of story one wants to tell? While things like the level of technology necessary for crosstime travel need to be considered, there are three big questions with great bearing on what the plausible results of crosstime travel would be.
First and most essential, is “navigation” possible? That is, will a crosstime traveler end up in a completely random timeline, or can they choose some or all of the characteristics of the destination timeline? If they leave a timeline completely behind, with no way to get to it via a still-open gateway or some such gimmick, can they find it again anyway? And will “tampering” with a timeline through outside interference, or engaging in crosstime travel itself, make one’s timeline detectable to forces outside it? These will greatly affect the actions of one’s crosstime travelers. If navigation is impossible, they end up wherever the author wants to send them, usually the best route. If it is possible, then you have to deal with the fact that they’re going to go to the sort of place they would aim to go to. In an infinite (or really huge) number of potential timelines, this opens up whole cans of worms as the characters try and go to whatever their idea of a utopian timeline is, or go somewhere that they can obtain the resources they need, or obtain allies from other timelines.
This sort of thing is potentially very unbalancing and must be dealt with cautiously. If a timeline can be found again even after totally losing contact with it, this gives a huge advantage to aggressors who can keep coming to a world again and again, even if they are kicked out the first time. If it can’t, then it becomes very important to protect one’s link between timelines. Last but not least, restrictions on “tampering” or crosstime activity will tend to make any realistic crosstime activity bring in the attention of powerful forces in short order. Great if you want to have a lot of wars, bad idea if you don’t, unless your crosstime travelers can be so unobtrusive that the changes they cause won’t be detectable until after they are long gone.
The second question is the power requirements of crosstime travel. How much energy (or other resources) does the travel itself require, and how does this requirement scale in relation to mass, volume, diameter of gateway, or other such factor? Low energy requirements, or requirements that don’t scale up very quickly as you send more stuff through, encourage large amounts of travel between timelines. In particular, crosstime trading and true crosstime wars become practical – and commonplace, if it’s also easy to find nice targets for conquest or good trading partners. High power requirements tend to make it very disadvantageous to ship weapons to another timeline or resources from it, meaning that crosstime travel is an endeavor of exploration and learning (knowledge has no weight). Crosstime conflict under restrictive energy requirements will tend to occur when societies are not looking for direct material gain. No matter how hard it is to conquer another society, it may be fairly easy for a small group to seize control of it from within. It is also easy to engage in pure destruction – a device that can ship a man can ship a nuclear bomb.
Third, what is the nature of the device itself, the actual mechanism for crosstime travel. If it requires a fixed gateway (either for all travel or for all high-volume travel), then one’s crosstime machine is going to be vulnerable to discovery on both ends, and particularly vulnerable to destruction. Using gateways to mount an invasion against an enemy who has no problems with nuking them, for example, presents problems. If it is a vehicle, then it may provide enormous freedom of movement, but again is vulnerable to destruction.
Perhaps the most versatile, and problematic, method of crosstime travel is the remote-operated teleporter. That is, a crosstime machine in one timeline that can send and retrieve things from other timelines, optionally to arbitrary locations in that timeline. The machine itself cannot be destroyed, and even if it relies on some sort of beacon or signal to maintain a link to the remote timeline, one could hide a beacon deep underground and have things actually appear elsewhere. If it can send people to unrestricted locations, then it’s not just a crosstime machine but a transporter in the tradition of Star Trek. You have to deal with the ability of the machine to materialize stuff virtually anywhere it wants, so long as it is from the other timeline. Additionally, you have to explain how the machine avoids materializing people inside solid objects, and optionally what happens if it does.
Now that I’ve referred to most of the major concerns, I will present the method of crosstime travel that has become my “personal favorite” since I came up with it many years ago in more detail. First, I start with a plausible scientific basis. The core assumption is that the “many worlds” hypothesis, or something similar to it, is true. For each possible decision or turning point in history, there exists a timeline where each alternative actually happened. This arises because each time a quantum particle may randomly exist in one position or another, a timeline comes into existence (or always did exist) where it exists in each possible position. There are no “magic additions”. Timelines don’t tend to merge back into one another if sufficient divergence does not occur to break some barrier, nor are there a finite number of timelines. All timelines have the same laws of physics.
Second, for travel between timelines to be possible, I add another hypothesis (courtesy of one of Stephen Hawking’s brainstorms). Timelines are actually linked to each other by “quantum foam” – holes in the “fabric” of space between timelines which are the size of quantum particles or smaller. Under natural conditions, the only result of their existence is that the occasional particle slips between timelines. As timelines “split” from each other, they remain connected by the quantum foam, with the connections decreasing in number and/or size over time.
Crosstime travel is thus a matter of picking one of these connections between timelines purely at random (there is no way to tell where they go), and pumping energy into it until it is large enough to send something through. The connection must be captured somehow to keep it in place, and the first thing that goes through to the other side should also be a device capable of capturing that end of the hole and propping it open from that end as well. Thus we end up with a wormhole to a random timeline, through which we can send objects.
Plausibly, the requirements for maintaining a wormhole of any size are quite large, and scale up quickly. Proportional to the square of its radius, or even the cube of its radius (surface area of a cross-section of the wormhole, or of an imaginary sphere within the wormhole, respectively). Wormholes will be kept quite small when in use, and only enlarged for a short period of time when something is actually to be sent through. If the wormhole is thus kept open for a short, minimum time to send something through, and is only made big enough for the object to fit, energy required becomes proportional to the volume of the object. Interestingly, since you are essentially pushing something through an imaginary door, you can’t “materialize” inside a solid object unless you exert enough force to push it out if the way.
To the technology I will make one addition which is plausible, and substantially increases the usefulness of the technology for certain kinds of stories. With sufficient knowledge, it is possible to “spawn” new wormholes from the original wormhole, which can either be propped open to serve as new gateways to the same timeline, or used to send something through in the instant before they deteriorate. Thus sufficiently advanced travelers have a sort of crosstime teleporter once an initial gateway exists, capable of “spawning” a wormhole which can send something to a place other than the original gateway, albeit for one shot since it will close and be lost in a very short period of time. Depending on how this aspect of it behaves, and indeed whether sending stuff through the gateway in general is instantaneous or not, the system may implicitly involve faster than light travel (an entirely new can of worms). If you have one origin point and send things to two separate destination points at the same time, and their cumulative time till arrival in the other timeline isn’t greater than the time it would take light to travel between the two destination points, you get FTL travel. To go into more detail requires some pretty deep relativity and causality.
Really advanced travelers can use the “spawning” feature as a crude sensor. They can spawn a large number of wormholes going to a vicinity in the destination timeline, and send a particle through each one. If the particle hits a particle in the destination timeline near the mouth of the wormhole it may be reflected back through the wormhole, with the chances of this happening obviously increasing if there are more particles near the mouth of the wormhole. Thus is created a limited but effective crosstime sensor, capable of discerning the density of areas in space on the other side. The only caveat is that to get a more accurate picture you need to send through more particles, making the activity easier to detect since a noticeable amount of energy is appearing from nowhere. It still isn’t really detectable outside of line of sight, since what is going through could be ordinary light or even atoms.
All this is very nice, you say, but what does it all mean in practical terms? Well, for your edification I will now attempt to describe what crosstime travel looks like under the parameters I have just set out. First off, it’s not around the corner. Manipulation of microscopic wormholes is required, something that is well beyond our current technological capabilities. At absolute minimum, a society using the simplest forms of this technology would have to be twenty years ahead of us technologically. More realistically, fifty years ahead, especially if they want to be doing things like spawning wormholes, or using the scanning system.
They also need a lot of power, something which is probably less of an issue at such a level of technology. As a guideline, sending a person to another timeline with these methods would require the level of technological development, resources, energy and money as putting them on the moon. Granted that putting men on the moon becomes easier as space travel technology develops, but crosstime travel technology would have to have that level of time and money as well in order for it to get cheaper in the same way. While the ability to teleport to unexpected locations on the other world might seem militarily attractive, the expense of shipping entire armies across timelines using this method is very high, outweighing any gain from attempting to strip the other timeline of resources.
Due to the scale of the endeavor involved, crosstime travel is a project engaged in by governments and large corporations – most probably governments, since it’s highly likely to be controlled technology, and at any rate most of its benefits are not in the “low-risk financial gain” category. It’s also fairly hard to keep secret, due to the resources involved and the fact that scientific theories which confirm its possibility would be very hard to keep under wraps. A likely profile, at least initially, for the development of crosstime technology is somewhat like NASA. An expensive, highly publicized agency whose primary purpose is the advancement of knowledge, with testing of new technologies and the advancement of “national goals” on the new frontier also being important.
The process itself is interesting but not complicated. First, open a random gate and send in a “beacon” to keep the wormhole open from the other end. Immediately scan the surrounding area for danger, and send in new beacons for redundancy. Next, send in probes to examine the place more closely. When safety is confirmed, send in explorers with additional power for the beacon.