When someone mentions "other dimensions" out loud, we start thinking about all sorts of parallel universes - alternative realities that exist parallel to ours, but in which everything works or happens differently. However, the reality of dimensions and the role they play in our ordering of the universe is seriously different from this popular explanation.
In simple terms, dimensions are different facets of what we perceive as reality. We are most familiar with the three dimensions that surround us every day - those that determine the length, width and depth of all objects in our universes (the X, Y and Z axes, respectively).
Apart from these three visible dimensions, scientists speculate the existence of others. The theoretical underpinnings of superstring theory say that the universe exists in ten different dimensions. These various aspects define the Universe, the fundamental forces of nature and all the elementary particles in it.
The first dimension, as we noted, gives the length (aka the X-axis). A good description of a one-dimensional object is a straight line that only exists in terms of length and has no other discernible qualities. Add to this a second dimension, the Y-axis, or height, and you get an object that has become two-dimensional (for example, a square). The third dimension includes depth (Z-axis) and gives all objects volume. A perfect example is a cube that exists in three dimensions and has length, width, depth, and therefore volume. In addition to these three, there are seven other dimensions that do not immediately catch our eye, but can still be perceived as having a direct effect on the universe and reality as we know it.
Scientists believe that the fourth dimension is time, which determines the properties of all known substances at any given point. Along with three other dimensions, knowledge of the position of objects in time is essential for determining the position in the universe. Other dimensions go much deeper, and their explanation is sometimes difficult to understand even for physicists.
According to superstring theory, the fifth and sixth dimensions arise in the same place as the concept of possible worlds. If we could see in the fifth dimension, we would notice that that world is slightly different from ours, and get mechanisms for measuring the similarity and difference between our world and the other possible.
In the sixth dimension, we would see the plane of possible worlds on which we could compare and place all possible Universes, which began with the same initial conditions as ours (that is, from the Big Bang). In theory, if you could master the fifth and sixth dimensions, you could travel back in time or choose a different future.
In the seventh dimension, you have access to possible worlds that started with different initial conditions. If in the fifth and sixth the initial conditions were the same and only the subsequent actions were different, here everything will be different from the very beginning of time. The eighth dimension again gives us the plane of all possible histories of the Universe, each of which starts with different initial conditions and branches out endlessly (they are called infinities, obviously).
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In the ninth dimension, we can match all possible histories of the universe, starting with all possible laws of physics and initial conditions. In the tenth and final dimension, we come to a point where we can embrace everything possible and imaginable. Beyond these limits, we mere mortals cannot imagine anything, this is a natural limitation of what we can comprehend in terms of dimensions.
The existence of these extra six dimensions, which we cannot perceive, is necessary for string theory to be a candidate for a fundamental explanation of interactions in nature. The fact that we can only perceive four dimensions of space can be explained by one of two mechanisms: either the extra dimensions are compact and located on the smallest scales, or our world lives in a three-dimensional submanifold corresponding to the brane, which will limit all known particles, except for gravity (brane theory).
If the extra dimensions are compact, then the extra six dimensions should be in the form of a Calabi-Yau manifold (pictured above). Invisible to our senses, they could determine the formation of the universe from the very beginning. Therefore, scientists believe that by looking back in time and detecting the light of the early universe with telescopes (which was emitted billions of years ago), they could see how the existence of these extra dimensions could have affected the evolution of the cosmos.
Like other Grand Unified Theory candidates - the "theory of everything" - the assumption that the universe is made up of ten dimensions (or more, depending on the string theory model you use as a basis), this is an attempt to reconcile the Standard Model of particle physics with the existence of gravity. In short, this is an attempt to explain how all known forces in our universe interact and how other possible universes might work.
ILYA KHEL