Do Other Dimensions Really Exist？

One, ever-present theme in science fiction is the notion of other dimensions we cannot normally see. But in special circumstances, we can. Such as something horrible coming from another dimension to destroy us and many other interesting plots. But it's not quite accurate to the basic idea of dimensions. That sort of thing only comes into play in later ideas about dimensions, but it's not really how sci-fi predicts when you get into it. Rather, it's a trope, but not a very accurate one. The universe we know has three dimensions of space, that is length, height, and width. It's a 3D universe. But time also appears to be a kind of dimension as well. That while we are always moving forward through, but as far as we know, it's impossible to go backward if you're a human. A particle? Not so clear. But the question is, are the dimensions we see all that actually exist? Or are there more? Regardless of what those dimensions do, that you could actually use, the answer is actually a very tricky one. It's maybe. And there are hints at something, as far as other dimensions. But that may not matter if you want to go to another dimension and grow a beard there, or shave off the one you had to be a villain version of yourself. Perhaps the biggest hint of something else going on dimensionally is quantum entanglement. There, two entangled particles can be separated by any amount of space and still instantly react if one of the two particles changes state. This happens instantly, regardless of the dimensions we know. So it could be, at least according to one idea, that the particles are not separated at all in some other dimension we can't otherwise see, but they are still glued together in the dimensions we do see, yet they counter-intuitively seem to be widely separated. Others have put forth ideas that the particles doing that actually do operate through a known dimension, time, and that the change occurs by the particles referencing their past. In short, backwards time travel of information. But it's useless information, because the outcome of the change is random. People often suspect there is a way to send information using entangled particles, and you'd initially think so, but the problem is the moment you interact with the system to build your message, it decouples and the particles are no longer entangled. Interaction with the outside breaks the entanglement, and you've got nothing to work with. The universe appears to not let us communicate this way. Famously, however, there are the predictions of string theory, which in one major form known as m-theory, predicts ten dimensions of space and one dimension of time. But in variants of string theory, such as superstring theory, it can be just ten. But in other takes, the number of dimensions can actually be significantly higher, an indefinite number of dimensions in the view of some. But in recent years, string theory overall has not fared well. It's not easy to test under any take on it, and what little we could do does not seem to indicate that it's correct. Some other experiments suggest it may be partly correct, but that's for another video. One idea from string theory is that other dimensions can't be seen because they are essentially crumpled or curled up to the point they are no longer visible. Oddly, string theory gives some possible mechanisms for the big bang here. Why that happened, and why there is anything here at all. That the ten dimensions of space represent an empty universe that was before the big bang. All dimensions were visible then, and the event represented the dimensions overall splitting into two groups, one group curling up, the other group remaining visible in the new universe. Interesting idea, but no one knows if that was the case. It has to be said though, it does offer a possible explanation of why the big bang happened. It's that the original state of the universe was unstable. Unstable universes are scary stuff indeed. Is ours truly stable? We don't know. But when dealing with dimensions, it pays to cover how physics sees dimensions. It's not the same as how science fiction and pop culture often depicts it, such as interdimensional travelers. That actually doesn't make much sense, and goes against what we use to define dimensions. Quite simply, dimension just means direction. So it's a pair of directions opposite to each other, and at right angles to other dimensions. You can describe this as length, width, and height, but also x, y, and z. Or ultimately forward, backward, left and right, up and down. That's it. Time is included because it too has a direction, forward and backward, future and past. But time is a one way dimension so far as we know, and the others are not. So the popular view of things like interdimensional portals to other places or times is simply not what the original idea of dimensions comes from. What it does come from is when you start asking how many dimensions there are in the universe. Within the framework of string theory, all dimensions have a specific function. With the predictions there, we know enough to explore what they are like. We know of four of them, but again, there may be more. But if string theory is wrong, you may need no other dimensions at all, no matter what they look like. But in string theory, take for example when you invoke a fifth dimension. In a fifth dimension, if you could see it, you would see a world somewhat different from ours. And those differences could include things like alternate timelines and evil Spock. Or they may not. And there may be no way to access them, even though you could perceive them. And we'd just see a somewhat different world around us. A sixth dimension is thought to allow you to see all the possible variants of the world that begin with the same initial conditions, but later all evolve differently. That would be strange indeed. The seventh would extend that to worlds that did not start with the same initial conditions as well. It would allow us to see all possible universes at one time. The ninth and finally tenth allow you to see everything possible to see. There, the science fiction view has some legs, but if string theory is correct, what it says about those dimensions is that they are infinitesimally small and curled up, thus we can't access them at all. As weird as they may be, or have been, you can't get there now. But any of that boils down to string theory being right and it certainly may not be. That's a problem for hard sci-fi too. Remove the reason to suspect other dimensions exist, or any way to prove them, and you get undermined and those ideas become fantasy. This also affects pop-cultural ideas of inter-dimensional beings interacting with us as well. You need a mechanism for that. And there wouldn't be much to chew on without string theory right now. Other future theories may come, however. Science is a process of revision, and just when you think you might not have anything interesting left to discover, a totally new avenue opens up that is mind-blowing and something no one had ever thought of before. But there was one way, it turns out, to do a test here with string theory and dimensions. In 2017, two neutron stars collided in another galaxy. It's gravitational waves, and there, we do not know all the rules. Studying gravitational waves is new, and there are many unanswered questions, like an old map that says here be beasties and monsters, or not. String theory predicts that gravitational waves should weaken over intergalactic distances. Interestingly, this would cause the universe over time to accelerate its expansion. Which is indeed happening. We know the expansion of the universe is accelerating, driven by something, we call it dark energy. This weakening should occur because of gravity leaking, for lack of a better term, into the other curled up dimensions. The observations of the gravitational waves from the neutron star merger, however, showed no hint of such leakage on scales up to 80 million light years. The predicted effect of the other dimensions is simply not there. So if it is there, if it exists, it must be so subtle that you only see it at scales larger than 80 million light years. That would mean the higher dimensions are very small indeed, or alternatively, inconceivably vast. Or, they simply do not exist. Vastness creates problems for the reality we see, and that gets into what we don't know. But they might actually be incredibly small. There is a concept known as the Calabi-Yau manifold, and if valid, it may serve to confine the other dimensions to only be relevant on the subatomic scale. Very small effects indeed, but still there. But you and I here in the world of the large cannot use this much, if it's true. You won't find a portal here you can walk into, but you still might be able to detect the existence of those dimensions by their effects on time, which they have affected cumulatively over the life of the universe so far. CERN might be able to provide insights on this eventually. This is famous stuff, creating micro black holes and looking into gravitons that carry the force of gravity and dark matter. And all of those ideas, all hypothesized but not detected yet. Those might, as they are researched further and the experiments done, give us insights on whether there really are other dimensions. For right now, the entire concept relies on physical determination that we can move up or down, left or right, backwards or forwards, x, y, z axis and so on. And not so much that we could open a portal to or through another dimension and use it for messing with the universe and our existence as we know it. But there are cracks in these ideas. The aforementioned quantum entanglement seems to suggest that there are things about the dimensions we do know that remain unanswered. Or maybe that's not due to dimensions at all, rather something else we don't know. There may still be things about the universe, and there are good reasons to consider this, that we have no clue exist yet, and only further scientific inquiry and thought will lead us to ways and methods to figure out. That's the beauty of science, it's a process of learning and revision, it's not a story set in stone. And there may yet be entirely new avenues that fire a new generation of science fiction, not so beholden to the tropes like other dimensions. But I do wonder about the areas of astrophysics and cosmology that we don't know exist yet. We certainly know that our theories are incomplete, but we do not know the unknown country that links them all together, such as relativity and quantum mechanics, and how they do not always agree. A good example is if the graviton were detected, and we could experiment with it. What happens if it obeys the double slit experiment? Can you manipulate gravity somehow, and what do you do with that? We need to see a graviton first, to try to figure that out. And what does that allow you to do with manipulating time under relativity? Open questions. But I leave you with this. The ideas of other dimensions and how they are depicted in sci-fi, and the idea of influences on our universe on a basic physical level, are largely just fictitious plot lines and stories of one sort or another. But the root core of what alternate dimensions are comes from physics, and then things went further out there from there, but are actually a lot more complicated than we might have thought, and we don't know enough about the rules of that to make many predictions about it, whether through physics, dimensions, or speculation. Food for thought. Thanks for listening! I am futurist and science fiction author John Michael Godier currently sitting at my studio desk with a quantum mechanical possum staring at me. This is not a pet folks, he's not laying in a comfy bed on the floor here, he's levitating around and clearly knows more than any of us about the universe. He's lived here for years now and it's very disturbing, but he does make good food when Anna gives him recipes, especially cookies. And be sure to check out my books at your favorite online book retailer, and subscribe to my channel for regular, in-depth explorations into the interesting, weird, and unknown aspects of this amazing universe in which we live.