Concocting a fourth spatial dimension that can support wormhole-like travel and not mess up life?

Question

Context: I'm a science fiction author. I need an excuse for FTL, and I'm pretty attached to the idea of a discrete fifth dimension, allowing (normal) fourth dimensional space to be bypassed in a similar manner to Interstellar's "pencil-passing-through-sheet-of-paper" wormhole metaphor for those who are familiar. Essentially, it'd be all kinds of awesome if I could concoct an at least vaguely scientific explanation for some beings having a fifth dimensional presence along with the "normal four".

However, a good (physics-minded) friend of me very reasonably informed me that an accessible fifth dimension would royally screw with the ability to form stars, life, and virtually everything as we know it. And... yeah, they have a point. If all particles can move not only on the x, y, and z axis, but also the w axis, reasonably they'd collide and interact much less frequently.

Can I construct a fourth spatial dimension that functions similarly to the other three and doesn't completely render life as we know it impossible?

The alternatives I've already somewhat considered are:

First, a discrete/detached plane similar to... um, Minecraft's Nether. (yeah go easy on me I couldn't think of a better example...) Ostensibly, this would effectively gatekeep particles from moving from one plane to the other willy-nilly, I just find it somewhat unfounded/uninteresting, plus it reeks of a thoughtless fantasy cop-out. Sub-question 1 is thus: is there any theory or way to make a literal warp plane less... simplistic?

• How would a warp plane work?
• How would entry/exit play out?
• Is there any scientific literature to back up its hypothetical function?

Second, Kaluza-Klein theory or its many permutations. Not going to lie, I understand very little of the actual theory from the papers I've read (numerous), I'm a biochemist for a reason. What I could however glean was that Kaluza-Klein operates on the subatomic level--- very friggin' tiny--- and, thus, wouldn't affect macro size anything much at all. Double edged sword. Kaluza-Klein looks promising because of just how diverse the theory and its successors have grown, but I don't know enough to even determine if it could be useful at all on the intergalactic and very much macro-scale application I'm gunning for. Does anyone know enough about the K-K theory to determine whether there's some subset that could permit a discrete 5th dimension that is travel-able by large objects and doesn't try to stab classical physics in its sleep?

I'd love to hear any two cents that you guys could throw into this pool. This one's been keeping me up for a bit.

Answer 1

I'm a science fiction author. I need an excuse for FTL

No, you don't. Come up with some arbitrary capabilities, constraints, and plot-relevant connections to other setting elements that suit your plot. Give the bundle of principles a name.

Then: either completely ignore the scientific principles involved (as opposed to the principles relevant to the plot and characterization)...

Or mention that the Ryker-Organa principle discovered in 2398 means that 21st century physics got a few things wrong, you just need to understand that the curvature of the Brannigan manifold over Reynolds space is transversely symmetric about the Connor meta-axis.

Which means nothing whatsoever, but it sure sounds like a justification.

Answer 2

Follow the Gravitons

One of the theories for why gravity is so weak is that it extends into other spatial dimensions. That is, that gravitons are slipping into those other dimensions, thus affecting 3D space less.

So, find a way to do the same. This will likely involve some truly strange and exotic methodology, since we haven’t even found, much less controlled gravitons, but perhaps in you future, this is possible. Ships with a graviton drive follow the gravitons into these extra dimensions.

Answer 3

If you want something that sounds sort of plausible, and links with current (or not-so-current) theories, try this:

It is thought that our universe is the three-spatial-dimensional surface of a four-dimensional hypersphere, and ordinarily all particles are constrained to the surface of the hypersphere... that's why the universe seems three-dimensional.

It is also said that the universe isn't smooth, but is wrinkled like a walnut.

If it is the case that the universe's hypersphere surface is wrinkled, then it would make sense that at the points where the wrinkles line up with one-another, you could 'drill' a hole from one part of the surface to the other, and end up with a 'wormhole', which you could use to shortcut the intervening space through the fourth dimension.

Answer 4

Plenty of authors have dipped their beaks into inhabited multidimensional worlds with good results.

Yes, the math of higher dimensional worlds make life or even matter as we know it impossible, but your work is a work of fiction, not a peer reviewed paper. As long as you don't break the suspension of disbelief, you will be fine talking about the 4D octopus and how it hunts the quasi-3D sole in the oceans of planet Buzzunzur, sole which the humans of Earth insist in calling buffalo.

Answer 5

Make it so that some physical constant changes across this 5th dimension such that particles really want to stay in a single plane across it, not moving up and down unless seriously convinced somehow. Then its basically just 4 dimensions with a 5th thats only exists 'sometimes'.

E.g. this 5th dimension could be 'triangular', such that the further you go from plane 0, the less distance there is between things. Thus, as particles bob up and down perpendicularly to this plane, they suddenly get very close to each other, and push each other apart, either away from 0th plane (which has even less space and thus is even more crowded, pushing things out), or towards 0th plane ('base reality'). Things wouldn't infinitely expand into that dimension because most particles exist in the widest one, thus gravitationally pulling everything together. An FTL drive in such a world would simply need to push/throw the vessel into this 5th dimension(maybe acting like a thruster or using a counterweight), while also counteracting the forces that squish and later stretch the craft. The light itself might be confined to a single plane because the effective refractive index changes so quickly across the 5th dimension that everything but the most energetic of gamma rays reflects from it like in a fibre optic cable.

Answer 6

4th and 5th dimensions cost something not naturally formed.

First off, you're an SF writer. This means you can already ignore some rules of nature from the get go. If it was something possible in the universe it would be Science Reality, and not fiction. Consider that the suspension of disbelief is very big. This is why SF or Fantasy works. People accept a person throwing a fireball, a fusion powered engine or Rambo not needing to reload. Generally if it fits with the story it'll work.

Travelling the 4th and 5th dimension

If you still want to get closer to realism, consider that travelling the 4th and 5th dimensions might not be a natural occurrence. That way everything can still form normally. Only intelligent intervention can make such travel possible. It still flies in the face of several current theories, but theories have been revised or thrown in the bin over time. Therevis no reason why an SF book can't state it doesn't violate the laws, as per definition of your book it is possible. You just need to apply the macguffin for the travel, which requires x or y that isn't naturally occurring.

Also keep in mind that these dimensions might not be able to be understood by us mere mortals. With trial and error or massively more intelligent computers or specially constructed brains we might be able to piece together how to traverse it without ever understanding what is happening while you are travelling there. Like the average person changing a channel on the TV without knowing the absolute gargantuan advancements in technology and accuracy required to make it happen. You press the button, and it has a desired effect. Everything that has happened in the milliseconds in between aren't registered nor understood.

People can come out of the 5th dimension without knowing time has passed, or didn't pass, or has been reversed, or if they even moved at all. They wouldn't know how they traveled or understanding what they saw, if they even could see anything.

Answer 7

The first thing to keep in mind is that spacetime curvature, as it is understood in general relativity, does not imply a higher-dimensional mathematical space into which our spacetime curves. It's just that the changing yardstick (and clock) as you move to different places is mathematically the same as what you would observe on a curved 4D "surface" (AKA manifold) sitting in some higher-dimensional space.

But that doesn't mean you can't say there really is such a higher-dimensional space.

All I think you have to do to save normal functioning in our universe is to assume some mechanism binding all the physics we know to our 3+1-dimensional manifold. A wormhole would only happen when the manifold intersected itself.

But then you could imagine that higher-dimensional space (four or five spatial dimensions plus time) has its own physics that had some very weak coupling to ours. Our universe could be some filamentary structure out in very "deep space" in their universe, and maybe beings there could discover it, and perhaps interact with it somehow. Maybe the coupling was only weak because there was nothing nearby in the higher-D universe.

One distraction is that string theory famously predicts our universe to be 11-dimensional, with all but four of them "rolled up" to be too small to observe. But we don't even know if string theory is right, so it would probably simplify things if you just assumed it isn't.

Three books worth looking at are:

• Flatland, by Edwin Abbott
• The Planiverse, by A. K. Dewdney
• The Shape of Space, by Jeffrey Weeks

Answer 8

On one side, I'd like to remind you that the world we live in isn't in 3 or 4 dimensions.

The dimensions you are talking about only exists as a mental model that was taught since school, but that doesn't make it real.

See this question for some mathematical background.

Basically, since Hilbert and Mandelbrot, we know that the dimension-ness value isn't an integer and more of the real number.

To paraphrase the topic, take a usual 2D Cartesian system where you're locating each point with 2 coordinates, X & Y (and an origin). Draw a spiral on this grid starting from the same origin.

The spiral is characterized by its step (that is, the distance between 2 entire rotations) and its origin. Those are fixed value, like the origin is in a Cartesian coordinate system.

Then any point on the spiral only require a single dimension to locate: the distance to travel along the spiral to that point.

Now, if you reduce the step of the spiral, you're increasing the distance a lot, but it's always finite.

At some point, the step is so small that your spiral will pass on every point you can physically reach (technically, it's at Plank's limit). It's not 0, so the distance is still not infinite.

Yet, with a single dimension (the distance on the spiral), you can reach any point in 2 dimensions Cartesian space. In fact, the spiral is a space filling curve but they are many space filling curve that travels along all dimensions (look up for Hilbert space filling curves for one).

In the end, using a single dimension with huge number to locate any point in space is possible, but it's inconvenient. It's much easier to abstract/fold huge number in more dimensions for our brains to grasp.

Put in another way, there's no reason that a particle/wave doesn't travel more dimensions that we planned, and we simply can't observe them.

For example, look at the Quantum tunneling experience: The wave function of a particle isn't zero after an obstacle.

Send a photon toward a opaque wall and since the wave function isn't zero after it, you might be able to capture it on a detector. How could that happens? If you consider pure physics (which is a wrong way of thinking here, BTW), the photon should have been absorbed or reflected by the wall, yet you detect it after it. The only possible explanation would have be for it to either have slalomed between all atoms of the wall without never interacting with any or it could simply have traveled along another dimension to reappear in the dimension of the experiment.

If you measure the timing for the detection, you'll see that it's geometrically impossible for the photon to have slalomed (it would have traveled a much longer distance and thus would be late on the detection), so the latter explanation is likely the right answer.

Yet, as you said, if such dimension was accessible, why wouldn't all particles "vanish" from our 3 dimension world in some higher dimensions?

Simply because there isn't any dimensions at all (only one). The particle doesn't care about your model's X or Y axis or direction. It follows (or is attracted) by the curve with the lowest energy (just like general relativity explains)

It's very likely our "mental model" dimensions are simply those with the lowest energy and a particle can escape our "mental model"'s 3 dimensions for a very short time because it acquired some much energy. Yet, it'll come back to our dimensions later on since it's were it can exists.

So when you're looking for a 4th or 5th dimension, you're asking the wrong question. There's no need to such a dimension.

And to answer your initial question:

How do you do FTL travel in current physics? You can't. Simply because matter as we know it is only safe/viable in our "mental model" 3 dimensions.

You can probably transmit information to/from higher "dimensions" FTL but you can only get back the result this transmission at light speed in our dimensions.

So you can, for example, expect that you'll never be able to observe the transmission (yet take for granted that the transmission worked). You can expect that some dude at whatever distance is able to receive it and rebuild the model you've sent in your transmission, but you'll never be able to get back the acknowledgement that he did (at least not in FTL mode).

That's adding a twist to your story, is true, is it a dream, are your crazy?

Answer 9

Holographic principle suggests an equivalency of a system with a lower dimensional boundary of that system. Thus, our (3+1)D universe is in reality just a (2+1)D surface. And it does not matter, since it contains equivalent information, until one day some tiny imperfections in the "hologram" are discovered that allow us to utilise small bits and pieces of the 4D "source". Which naturally appear to our holographic perception as an additional dimension.

Answer 10

I think you are going too deep. FTL travel is not possible in our universe and you want to make it possible for story reasons which is fine, but there is no point turning to real physics for an answer as there is none. You will have to assume something that isn't true at some point and hide it.

The easiest way of dealing with it is to ignore it and assume reality is different than it is. This sounds problematic, but only a tiny fraction of people really understand relativity and so it's quite easy to suspend disbelief for most people by assuming that relativity doesn't exist (although it does) and that the universe appears to work in the same way at high speed and large scale as it does just walking down the street (although it doesn't).

That said a lot of people (especially sci-fi readers) do understand that the speed of light is a barrier and needs to be got around somehow. Extra dimensions such as hyperspace provide good camouflage and that should be sufficient.

If you want to make hyperspace more realistic try to incorporate some restrictions on FTL travel such as entry to hyperspace needing a lot of energy and the closer you are to a gravitational field the greater the energy requirement etc.

With hyperspace be mindful of "edges", it might even be useful as a plot device, for example a small spherical "edge" into hyperspace might allow a small ship to pass through but a larger ship might find itself cut apart with a 3D slice through the ship going into hyperspace but the rest of the ship staying in our space. Such edges could be infinitely sharp.