Before we begin contemplating how sliding actually works based on show continuity, you need to take a look at the basics presented in Nigel Mitchell's Sliding Technical Manual.
Since the creation of Nigel's Technical Manual in 1996, many new things have arisen on the show concerning interdimensional travel. This section will atempt to explore and give explanation for why things work the way they do. To begin with, one small correction to the Sliders technical manual needs to be added. At the 1997 DragonCon, Tracy Tormé explained to fans that the timer actually is a sliding machine and not just a remote. To go along with that, script outtakes from the Pilot episode provided by Expert explain that the timer has a self contained regenerative power chip which allows the small device to achieve it's goal of breaking the dimensional barrier. And lastly, the 29.7 year rule for sliding and why they have to obey the time limit countdown is explained in the "Summer of Love" missing scene which is now officially a part of continuity thanks to season four and Bill Dial.
Sliding in Layman's Terms
Below is my interpretation of the fundamentals of sliding after viewing the series and reading through all the research listed above.
On each world, the Sliders have to wait for a window...they have to wait for the dimensional movement to bring a dimension close enough that a bridge can be created on the modest power that is left after a damaging timer advancement (the original timer was damaged and they had no choice...I believe the Egyptian timer was modified to the countdown as just a precaution). It is this dimensional movement which explains the "Summer of Love" incident and why the Sliders often land in a different physical location from where they left.
The sliding tunnel is like a tether between dimensions. The Sliders open it from whatever point they are on in their dimension at the time, and it reaches out to the other dimension at whatever point that dimension is in the movement (which is often a different physical location). When this happens, there is a magnetic anchor (see below) created in the new dimension by the exit vortex. The entrance and exit stay the same as the anchors...while the tunnel in between flexes with the movement of the dimensions (thus causing its twisty appearance). The power problem of the timer after the damaging advancement, however, limits how far the tunnel can extend (thus the entire reason why they have to wait for a dimension to come to them).
Also as we know, the entrance and exit only stay open for a limited amount of time (usually 60 seconds). What causes this time limit is once again the dimensional movement...as the dimensions move too far apart, the tunnel stretches and inevitably both ends contract to collapse and seemingly close. Depending on how fast the dimensions are moving, the time that a vortex stays open can differ (if the dimensions are moving faster, then the open time is shorter...if they move slower, then the open time is longer. But on average, the Sliders know it stays for about 60 seconds).
What happened in "Summer of Love" is that two Sliders slid and the vortex closed. Within just a few seconds, the vortex was reopened and the other two Sliders still wound up in the same dimension...just in a different geographical location. The reason for this is that the timer was very weak (Quinn even stated it was almost fried)...it used the power it could to create a bridge, but the result was that the tunnel was so weak that it ultimately destabilized before all could travel (they were just lucky it didn't collapse on somebody in transit). This collapse cut off the first anchor or exit point. When the vortex was reopened, the timer created a tunnel to a new exit point (since it had no tracking ability and was just firing in "a straight line"). The reason they ended up in a different location is because between the time of the closure and reopening, the dimension had moved (as they continually do) and the vortex didn't stay tethered in one spot as it usually does when it doesn't close...thus the new exit was in a different place...but still the same dimension since the dimension had not moved out of range.
A similar incident happened in "Lipschitz Live!" Due to the interference caused by the massive TV usage, the vortex could not anchor properly. It was much like having a dimension coated in teflon...the vortex exit just slid across the dimension as it moved. This is why the Sliders were scattered in different locations...they just exited wherever the endpoint had slid to at the time they reached it.
As mentioned in "Lipschitz Live!", the vortex stays stationary due to a magnetic anchor. While not explored on the show beyond what I've already stated, I believe this anchor to be part of the geographic spectrum stabilizer system that determines the sliding radius.
The anchor would need something to latch on to, and if it works on magnetics...then that gives one likely candidate that would be on all earths. The Earth is enveloped in something called magnetic ley lines. These are a network of magnetic currents that would provide a nice latching on point. Also, the lines stay generally the same for a given area (unless altered or diffused)...which means it could be like Earth's road map in a way...as long as it isn't tampered with. "Lipschitz Live!" would be an example where a man-made phenomenon had caused the ley lines to be weakened...thus making it where the vortex could not get a solid "grip".
Since the beginning of the series, the timer has had a set radius of geographic location in which the exit point appears. This radius is governed by a part known as the geographic spectrum stabilizer. The stabilizer determines the location based on a gyro system. Quinn's original timer used a refined laser gyro system which gave a radius of 2 miles within the San Francisco area - a small margin of error. Later on, Logan St. Clair's timer featured a "whispering gallery" gyro which worked more off principles of sonics. This sonic gyro was much less refined, and so it had a larger radius or margin of error from the San Francisco epicenter (400 miles to be exact - covering practically all of California and parts of Nevada and Oregon). As you know, Logan's stabilizer ended up in our Sliders' timer in the episode "Double Cross"...and was later transferred to the Egyptian timer (see the lost scenes for "Slide Like an Egyptian").
A common misconception is that the vortex simply exits at the geographic point where it was opened on the last world. This is not true after a timer advancement. If it were true, then why would there be radius for margin of error? To give episodic evidence, one can look in season one for comments about the original stabilizer Quinn designed. At the beginning of "The Weaker Sex", Quinn comments on how he can't control the landings. This occurred after the timer was advanced and was noticable directly after the advancement. Note in "The Pilot" how the Sliders ended up in Golden Gate Park after sliding out from in front of Quinn's house. Further examples can be seen at the beginning of "Prince of Wails". Of course, with such a small margin of error...the vortex still did end up in the same place much of the time...but it was not a guarantee. Once Logan's stabilizer was put in use, the Sliders began to seldom land in the same place. This is readily apparent after the switch at the end of "Double Cross"...when the Sliders slid out of San Francisco and landed in Los Angeles. It was covered again at the beginning of season four's "World Killer" when the Sliders comment on how they have a 400 mile radius and didn't move four feet. This obviously implies that they usually don't end up in the same place.
Another common misconception is that the radius follows the timer. This is not so. Take a moment to draw a diagram. Draw a dot for your center...and a circle around. If the radius followed the timer, then the next spot landed at would be the new center. So put a dot at the bottom of your existing circle...and draw a new one around it. You now have half the space outside your original radius. Draw another dot on the far right side of your new circle. Then draw a new circle. Now 75% of your radius is outside the original. The point is that if the radius followed the timer...then they wouldn't stay in California at all. They would eventually wander across the country...our example above has already placed them close to Colorado. If you need a more precise example...look at the start of the series. With a two mile radius...if the radius followed the timer, the Sliders would have soon been out of San Francisco. Yet...they stayed there for close to 3 years.
Now that we have established there is a set radius...this leaves one last question. What happens if you try to activate the timer outside of it? The only episode to explore this issue was season five's "Heavy Metal". Unfortunately, no answer was given. Diana theorized many possibilities...for one, they may just reset with a new radius (as I stated above, that isn't possible). On the other hand, they may just land back in their set California radius. And lastly, the timer may not work at all. Basically, the Sliders agreed that they just didn't want to find out what would happen. There was a very subtle clue given in a past episode, however: Season Two's "As Time Goes By". In this episode, the Sliders are deported at 5 am and are not freed until 10:15 am (the time in between being spent in travel). There is no real way the Sliders could have still been in the radius with that amount of travel time...yet they opened the vortex and traveled to the next world just fine. This suggests that the radius is a landing zone only, and does not govern the timer's function in any other way.
For more information, be sure to check out the Sliding Radius section of this site.
I believe this to be like space travel coordinates. Even though heavenly bodies are in constant motion...still in real life and even in almost all science fiction, a planet or solar system has a set coordinate that is used to locate it. Though usually not stated, that coordinate is actually the answer to a simple equation that is used to always determine its position in the universe given the time of year. I believe the coordinate system for dimensions is derivative of that...just like on Star Trek, Star Wars, or any other space navigation adventure.
The first and main step to controlling sliding which was introduced to us in the third season two parter "Exodus." This modification to the timer's circuitry allows for interdimensional coordinates to be input directly into the timer, thus doing away with the dependence of following another Slider if you wish to avoid sliding at random. Coordinate input works on the same basic principle as tracking, however.
For the most part, coordinates are obtained either through tracking or actually visiting a world at random first to store the coordinate. Therefore, when a coordinate (or equation for the coordinate) is re-input into the timer, the return trip takes you back to relatively the same spot you left from when you last visited the world (since that geographic location was part of the equation for the coordinate). This was proven in the third season episode "Exodus" when Quinn and Maggie always slid back to Jensen's lab (the place they left from) upon inputting coordinates. Again it was proven in "Dinoslide" when Rickman (and subsequently the tracking Sliders) ended up at relatively the same spot they last left that world from. Once more this was seen in the fourth season episode "Prophets and Loss" where our Sliders returned just feet from where they left Oracle world after re-inputting the coordinates.
In the case of return travel...I believe it depends on the power you have and where the other dimension happens to be (since we are dealing with rolling 3D movement, the dimension may be out of direct line of fire, but it could still be close by being just to the side, over, or even behind...that's speaking of this in relative terms, of course). But on Sliders, we've never seen them backtrack very far on purpose...the furthest was returning to the Exodus refugee earth after leaving it a little over a month before. And I believe even that was special circumstance...
Of course, this leaves the exception of using coordinates which you didn't obtain through visit or tracking. This in fact did not work until ciruitry was added to the timer in fourth season's "World Killer"...and even then the coordinates used were meant to take the Sliders to a specified location. The same holds true for "Slidecage."
As has been shown to us before in "The Pilot", the coordinate equation can be specifically modified to allow the Sliders to land wherever they want in the geographic spectrum (it is assumable that even though Quinn could not control where he wanted to go at the beginning, he had enough of the equations worked out to where it always landed him in the same place - such as his basement. This, however, only worked as long as the timer was at optimal capacity...which was soon lost after Quinn and co. began sliding). This ability to align the equations to take you to a specific place was shown with a unique twist with Colin (the quantum signature recognizer in "Oh Brother, Where Art Thou?") and with the trap mechanism in "Slidecage" (with some adjustment to the coordinate equations used for their earth, the people of Quinn's "real" homeworld actually found a way to be able to redirect people to another dimension entirely).
This concept was first introduced in the third season episode "Double Cross." The function is that this technological advancement allows one to track an object passing through a wormhole and thus be able to follow it. This is the first part of controlling sliding as it allows the Slider to pick their destination as long as it follows another Slider. There is another property of tracking that is never mentioned, however, but is proven in show continuity.
When one Slider tracks another, the tracking Slider will always land near the landing location of the Slider they tracked. This was proven time and again at the end of season three as our Sliders always landed within close proximity to where Rickman was or where Rickman had been before he vortexed out. This was also shown in the episode "Double Cross" which gives us yet another property of tracking. Apparently, you can go outside your timer's geographic radius if you are tracking another Slider and they land outside of it. This is shown by the fact that our Sliders landed in Los Angeles at the end of "Double Cross," yet Logan landed right behind them when her geographic spectrum stabilizer should have kept her in San Francisco (Logan had switched stabilizers with our Sliders and thus should have only had a two mile radius around San Francisco to slide in).
How is this possible you ask? Well, the very essence of tracking is hunting down exactly where someone went...even the exact point of exit on an earth...and as explained in "Double Cross", this tracking is done by following photon trails. For a photon trail to be left for someone to "see"...that must mean something remains of the Slider's tunnel out there (even though it gets continually smaller with time as it's stretched out)...and personally, I believe the tunnels never completely close even though they become microscopic...maybe even down to the quantum level. The tracking Slider ties into these remnants of a tunnel, and thus doesn't have to use as much power...they just enhance what was already there and left from the previous slide.
The theory of dimensional pollution arises from this tracking theory of continually stretching tunnels. With all this in mind...I believe that every tunnel the Sliders make is creating a permanent hole between dimensions (even though the exotic matter breaks down...once you rip a hole in reality, would it just completely go away? I've never seen a rip of any kind that did). Its size differs and it gets smaller with time...but it's there. And if enough of those holes are made on a given earth, I believe the barriers between dimensions could be broken down and thus two worlds would be destroyed...possibly starting a chain reaction of dimensional destruction reminiscent of the "Crisis on Infinite Earths" from 1985 DC Comics.
In season four, we were introduced to the concept of signatures. There are two types (commonly thought to be the same but actually separate): sliding signatures and quantum signatures.
First of all, let us look at the concept of quantum signatures. This concept which was explored in "The Alternateville Horror" states that each universe and all the contents of it have a universally unique signature (in other words, everything from that dimension has one signature...kind of the mark of the dimension permanently on everything that originated there. This was taken directly from a quote from Quinn - "Each universe has its own quantum signature"). One might say that these signatures are "roadmaps" back to your dimension of origin...and many speculate that this is how the Sorcerer was able to recalibrate the timer to send our Sliders briefly home at the end of the second season episode "Into the Mystic." The quantum signature was also used in locating Colin. As stated in "Oh Brother, Where Art Thou?", Colin's quantum signature was programmed into the coordinates found in Quinn's microdot. It took the integration of the "World Killer" tech Quinn used to get everyone back to the abandoned earth to make the Egyptian timer finally accept the code...thus leading our Sliders directly to Colin's stand-out quantum signature on Amish world.
A sliding signature is somewhat different. This is actually the "residue" signature left from sliding into another universe or the imprint of that dimension's quantum signature placed upon you when you arrive (hence the name change). The longer you stay in the dimension, the more pronounced that imprint will become (due to ingesting food, etc.) but it will never overshadow your original quantum signature. Also, the sliding signatures will fade with time as you slide more...and usually the last world you visited will be the most pronounced next to your original quantum signature.
The first look at sliding signatures came in the episode "World Killer" in which our Quinn used a bio-med scanner to determine the signature of the abandoned earth by scanning people from there. Once that was discovered, Quinn set the slide wave to only take people who had that signature in their systems (that's the only way the slidewave could have taken back our Sliders along with the missing population...our Sliders would have had the empty earth's signature as well from having just visited it...while people who originated on the overpopulated earth would only have their original quantum signature and thus they didn't slide). The concept of sliding signatures is also responsible for the mechanics of the feedback loop now in place at the "Slidecage." The computers just interpret the signature from the last world you visited and "rebound" you back there. If Quinn had set it for the quantum signatures...then he would have sent the Kromaggs back to the homeworld (their home dimension) which is what he was trying to avoid.
Another new concept for season four was the Slidewave. Having only made two appearances ("World Killer" and "Slidecage"), the slidewave phenomenon is fairly unexplored...but a few things are apparent from observation.
Apparently, the slidewave is generated whenever a massive amount of power is pumped through a sliding device...the vortex just reaches a point where the portal no longer gets any larger, but instead just becomes a wave of sliding force. Also, it would appear that this wave only affects animate matter with humanoid DNA (since animals and objects were left behind in "World Killer"). Furthermore, it is also apparent that the wave takes anything that a person is either holding or in possession of as well (such as clothing, guns, etc.). This rule also applies to pregnancies (since the baby would be in the mother).
One thing that fans have often wondered about is why different vortices have different colors. People who worked with Sliders say there was no relevant reason behind the color changes other than to just change things up...but I offer a different theory to think about. Could vortex color actually somehow denote the strength of the vortex through logical progression of color (with blue being "cold" and shades of red being "hot")?
Original timer's vortex and Egyptian timer's vortex after damage; the weakest vortex so far (slides four people safely)
Original timer's vortex on sparactic occasions and Egyptian timer's vortex after prolonged use following timer advancement; next level (strength unknown)
Egyptian timer's vortex when first used and for short time after; next level (strength unknown)
Logan's vortex; moderately strong (able to slide a "convoy")
Kromagg vortex; strong (able to slide at least one Manta ship)
Jensen's vortex; stronger (able to slide 150 people or over and all their equipment)
Slidewave; strongest so far (able to slide a planet's population)