# Is there a plausible way to exchange matter between spatial dimensions?

Assuming humans live in dimension 3+1; 3 spatial dimensions, length width and height, and one dimension of time,

Is it possible to move matter from our dimension 3+1 to another, such as 4+1 (adding a spatial dimension) or 2+1 (removing a spatial dimension)?

• This would have the practical application of allowing access matter we previously couldn't get to; think of a flat, two dimensional being entering the third dimension and realizing the amount of resources it could take back home now that its one plane extended in another direction
• This could also apply to travel in another spatial dimension or storage of three-dimensional matter in a "pocket" space

This question is similar to mine, but the top answer only describes grafting a three-dimensional space, for example, onto the second dimension in order to have interactions.

I want to know if it's possible to convert matter between spatial dimensions without just isolating it in a bubble of its relative geometry, and if so, the methods with which this could be done.

• I do not think there is a science based answer to this. You should remove that tag. – kingledion Oct 21 '16 at 2:24
• I think the [science-based] tag is fine, but I wouldn't put [hard-science] on this. – user6511 Oct 21 '16 at 2:26
• @kingledion How would you say yes or no to this without using science? You must disprove or prove it somehow, is there another way to do that? – Zxyrra Oct 21 '16 at 2:44
• @Zxyrra This is philosophy, not science. At best it is fiction, at worst completely unscientific. There are no equations or generally accepted theories about 'convert(ing) matter between spatial dimensions' – kingledion Oct 21 '16 at 4:20
• @kingledion The nature of reality is philosophy but the conversion of matter and resulting changes are completely within the scientific realm. If there were generally accepted theories about this, I would not have to ask this question. Finally, this site is about WorldBuilding. We're all here for fiction. – Zxyrra Oct 21 '16 at 4:26

I really like your [spatial dimensions]+[time dimension] notation, so I'll use that.

Generally speaking, if additional spatial or time dimensions were possible, it is not possible for 3+1 matter to exist in either a 2+1 universe, or a 4+1 universe. There's a graphic that has been used on other Q&A sites, and will be useful here:

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This chart shows how orbits will look in the various n+m dimensional space. as you can see, orbits become unstable in 4+1 space: this applies not only to the orbits of masses in space, but to the "orbits" of electrons around the nuclei of their atoms.

Prof. Max Tegmark has a more technical discussion of it on his website, and there is an analysis by Dr. Stein on Quora (including maths that I do not have the expertise to parse), but the long and short of it is that any 3+1 matter that was introduced to the 4+1 universe would either have to have some form of shielding containing 3+1-space for it to exist in, or it would immediately turn to plasma, due to the instability of the electrons in their "orbits."

• That's a very interesting graphic. I like the notion of ultrahyperbolic being unpredictable. I can't help wondering if there are other higher dimensional configurations that are stable and predictable. That's probably too much to hope for. – a4android Oct 21 '16 at 4:04
• I don't know how useful that chart is. How can a tachyon-only universe exist? If a tachyon is a particle that is faster than light, then how do photons (which travel at the speed of light) provide a reference velocity in a tachyon-only universe? – kingledion Oct 21 '16 at 14:49
• The chart is based on mathematics as extrapolated based on knowledge from this universe. If a 1+3 universe existed, no, no life would develop to be able to consider the speed of the particles there--that's the point. – Justin Eiler Oct 21 '16 at 15:17

I think this is going to remain implausible. The premise supposes an extra dimension exists that we don't yet know about, and that all the $3+1$ dimensional matter we see day-to-day is really just $4+1$ affixed to a common plane on one of those spatial dimensions.

Which is fine up until you realise that matter not on our common plane has mass too, and we should feel the gravity of that matter.

But we don't. And it'd be hard to imagine a world where we would feel this extra gravity and still have relate-able experiences.

## But what if the universe was mostly empty in the extra dimension?

Well that would fit suitably, but it implies there's something special or different about that dimension. It's not a normal spatial dimension.

Let's forget about that for a moment though. Let's pretend we have a $4+1$ space, and for whatever reason, matter is all on one hyper-plane of that space.

Gravity feels exactly the same in this as it does in 'normal' space. In fact, mathematically, it's impossible to observe the difference.

By definition, there's no extra stuff in the extra dimension, so we can't mine it for valuables.

Transportation is basically wormholes, but gravity leaks through - in both directions! You could be tempted to hop off the conventional hyper-plane to travel in a straight line from $A$ to $B$, but there would be no ground to prevent gravity from sucking you down into the centre of the Earth.

Another question I have relates to light. If the fourth spatial dimension is behaviourally, the same as the other three, light should travel through it just fine. Anything that produces light in our dimensions should also produce light in that one too!

Quantum mechanics gets interesting here, as mass curves space, and light follows that curvature. Squint your eyes and look at this from a funny angle and you could justify this as an explanation for quantum tunnelling.

And here's where it goes to hell. Electrons have mass, and electrons are also very well known to exhibit quantum tunnelling. Following the idea of photons, electrons are temporarily venturing off our hyper-plane to tunnel around solid matter. Protons and neutrons do this too. Small atoms do it. Large atoms do it. Small molecules do it. There's an unspoken contest within the physics community to demonstrate larger and larger objects exhibit quantum mechanical effects.

There's literally no reason why mass shouldn't be everywhere in this extra dimension.

I think you want a dimension that doesn't follow the 'normal' physics rules.

You might prefer $3+2$ dimensions. But you might get weirder results from that.

• 3 + 2 dimensions! Weirder results, indeed! Time travel for starters. It also comes in several flavours. – a4android Oct 21 '16 at 3:05
• Could the unseen gravity be explained by dark matter or dark energy; i.e. forces we cannot explain in our dimension could be gravity from others? Or is that plausible instead? In addition my extra resources idea was based on how a flat plane inside a 3+1 world only accesses .. well, a plane of what there is to harvest. Could that not work from 3+1 to 4+1 in the same way? – Zxyrra Oct 21 '16 at 3:12
• This is mostly correct, but if there was a macroscopic extra spatial dimension, gravity would scale as 1/r^3, since it would "dilute" into the 4th dimension. Most extra dimension theories use compactified extra dimensions. – Snyder005 Oct 21 '16 at 3:13
• @Zxyrra, would be right if things were going the opposite direction. Dark Energy is expanding the universe, despite the pull of gravity. More junk in another dimension would pull things in! PS: Physicists call it 'dark' because they can't see it. They'll stop calling it dark once someone builds the right flashlight. – user6511 Oct 21 '16 at 3:19
• I disagree about gravity being $1/r^3$. It would still be $1/r^2$, but $r$ would be calculated differently (reposted because spelling mistakes). – user6511 Oct 21 '16 at 3:23