Now, that’s cool, but what would it be like? We don’t normally think about it, but the four fundamental force — gravity, electromagnetism, and the two nuclear forces — only have the properties and strengths that they do because they exist in the number of dimensions our Universe has. If we reduced or increased the number of dimensions, we’d change the way that, for example, field lines of force spread out.

This would be catastrophic if electromagnetism or the nuclear forces were affected immediately.

Imagine you’re looking at an atom, or inside the atom at our atomic nucleus. Nuclei and the atoms formed from them are the building blocks of all the matter that makes our world up, and they’re on extremely small scales: Ångströms for atoms (10^-10 meters), femtometers (10^-15 meters) for nuclei. If you allowed those forces to “bleed” into another spatial dimension, which they could do once that dimension reached a large enough size, the force laws governing them would change.

In general, those forces have more “space” to spread out into, meaning they get weaker with distance faster if there are more dimensions. For nuclei, the change might not be so bad: the sizes of nuclei would be slightly bigger, and some nuclei might change in their stability, either becoming radioactive or by having radioactive ones becoming stable. That part’s not so bad. But electromagnetism would be very problematic.

Image credit: Wikipedia page on Atomic Orbitals, via https://en.wikipedia.org/wiki/Atomic_orbital.

Imagine what would happen if all-of-a-sudden, the forces binding electrons to nuclei became weaker. If there was a change in how strong that interaction was. You don’t think about it, but at a molecular level, the only thing holding you together is the relatively weak bonds between electrons and nuclei. If you change that force, you change the configurations of everything. Enzymes would denature; proteins would change shape; ligand-gated neurons wouldn’t fit together anymore; DNA wouldn’t encode the molecules it was designed to encode.

In other words, if the electromagnetic force changed because that force made its way into a large, fourth spatial dimension that reached the scale of Ångströms or so, human beings would immediately have their bodies shut down and die.

Image credit: ligand-gated Q-cells from Biolin Scientific, via http://www.biolinscientific.com/sophion/products/?card=SP11. These would not work anymore.

But not all hope is lost! There are plenty of models out there — mostly inspired by string theory — where those forces, the electromagnetic and nuclear ones, are confined to three dimensions. Only gravity, then, would be able to navigate through the fourth dimension. What this would mean for us, as the fourth dimension grew in size (and hence, in its effects), is that gravity would begin “bleeding” into that extra dimension. And hence, objects would experience less attraction than we’re used to.

This would begin to result in a number of “weird” behaviors.

Image credit: flickr user Kevin Gill, based on a 3-D model of asteroid Itokawa by Doug Ellison / NASA-JPL. Via https://www.flickr.com/photos/kevinmgill/15148296739.

Asteroids, at first — the ones loosely held together that spun rapidly — would come apart, as their gravity would be insufficient to hold those rocks and grains onto their surfaces. Comets, when they came close to the Sun, would evaporate more quickly and develop more spectacular tails. And if the fourth dimension grew large enough, the gravitational forces on Earth would drop tremendously, causing our planet to grow larger, particularly along the equator.

Image credit: Sciencevibe, via http://sciencevibe.com/2015/03/24/did-you-also-know-that-the-sun-is-an-almost-perfect-sphere/.

People living near the poles would feel like they were in a reduced gravity environment, but people living on the equator would be in danger of being flung into space. On a macro level, Newton’s famous gravitational law — the inverse square law — would suddenly become an inverse cube law, falling off much faster with distance.

If the dimension grew as large as the Earth-Sun distance, in fact, everything in our Solar System would become unbound. If this lasted for more than a few days out of the year — even if gravity went back to normal for the other 50 weeks or so — our Solar System would dissociate completely in only a century.

Image credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI).

We would have periods on Earth where we’d not only perceive an “extra” way to move through space, where there was a fourth “direction” in addition to up-and-down, left-and-right, and forward-and-back, but where the properties of gravitation would change tremendously and not for the better. While high-jump and long-jump competitions would never be the same, the consequences for the stable Universe we hold so dear would be apocalyptic.

So be careful what you wish for, Kelly, as a fourth spatial dimension would bring a set of amazing experiences, but would also siphon off a significant part of the Earth, including our atmosphere and the equatorial regions, every time the fourth dimension became large enough. One positive, though?

Image credit: ©2010–2015 daniellf of deviantART, via http://daniellf.deviantart.com/art/Frozen-Planet-Earth-173423844.

We wouldn’t have to worry about global warming much longer, as the increased distance from the Sun would cool our world much, much faster than the increased atmospheric CO2 would warm it! There’s a silver lining to every cloud, and so even though we’d only have a few years to enjoy it, the experiences of having a new dimension might well be worth trading in the rest of our lives to know what that is.