How Many Dimensions Does The Universe Have?

 When someone mentions "different dimensions," we tend to think of things like parallel universes - alternate realities that exist parallel to our own, but where things work or happened differently. However, the reality of dimensions and how they play a role in the ordering of our Universe is really quite different from this popular characterization.

Introduction

To break it down, dimensions are simply the different facets of what we perceive to be reality. We are immediately aware of the three dimensions that surround us on a daily basis – those that define the length, width, and depth of all objects in our universes (the x, y, and z axes, respectively).

Beyond these three visible dimensions, scientists believe that there may be many more. In fact, the theoretical framework of Superstring Theory believes that the universe exists in ten different dimensions. These different aspects are what govern the universe, the fundamental forces of nature, and all the elementary particles contained within.

The world as we know it has three dimensions of space—length, width and depth—and one dimension of time. But there’s the mind-bending possibility that many more dimensions exist out there. According to string theory, one of the leading physics model of the last half century, the universe operates with 10 dimensions. But that raises a big question: If there are 10 dimensions, then why don’t we experience all of them or haven’t detected them? Lisa Grossman at Science News reports that a new paper suggests an answer, showing that those dimensions are so tiny and so fleeting that we currently can’t detect them.

What is Dimension?

In physics and mathematics, the dimension of a mathematical space (or object) is informally defined as the minimum number of coordinates needed to specify any point within it. Thus a line has a dimension of one (1D) because only one coordinate is needed to specify a point on it -for example, the point at 5 on a number line. A surface such as a plane or the surface of a cylinder or sphere has a dimension of two (2D) because two coordinates are needed to specify a point on it -for example, both a latitude and longitude are required to locate a point on the surface of a sphere. The inside of a cube, a cylinder or a sphere is three-dimensional (3D) because three coordinates are needed to locate a point within these spaces.

Secret dimensions

In everyday life, we inhabit a space of three dimensions – a vast ‘cupboard’ with height, width and depth, well known for centuries. Less obviously, we can consider time as an additional, fourth dimension, as Einstein famously revealed. But just as we are becoming more used to the idea of four dimensions, some theorists have made predictions wilder than even Einstein had imagined.

String theory intriguingly suggests that six more dimensions exist, but are somehow hidden from our senses. They could be all around us, but curled up to be so tiny that we have never realized their existence.

String theory

 In particle physics, a theory that attempts to merge quantum mechanics with Albert Einstein's general theory of relativity. The name string theory comes from the modeling of subatomic particles as tiny one-dimensional “string-like” entities rather than the more conventional approach in which they are modeled as zero-dimensional point particles. The theory envisions that a string undergoing a particular mode of vibration corresponds to a particle with definite properties such as mass and charge. In the 1980s, physicists realized that string theory had the potential to incorporate all four of nature’s forces—gravity, electromagnetism, strong force and weak force—and all types of matter in a single quantum mechanical framework, suggesting that it might be the long-sought unified field theory. While string theory is still a vibrant area of research that is undergoing rapid development, it remains primarily a mathematical construct because it has yet to make contact with experimental observations.

String theory claims to make that dream a reality. In simple terms, it does this by re-imagining what reality is made of. Instead of treating subatomic particles as the fundamental building blacks of matter, string theory says that everything is made of unbelievably tiny strings, whose vibrations produce effects that we interpret as atoms, electrons and quarks.

In order for that to work, string theory has to make one more radical assumption. That instead of living in a universe with three dimensions of space and one of time, we live in one with either 9, 10 or 25 dimensions of space. These extra dimensions are then curled up so tightly that we don’t notice them – much like a silken thread appears one-dimensional until you get close enough to notice its width.

This process of curling up, or “compactification”, can be done in countless billions upon billions of different ways. Each compactification produces a different spacetime, meaning that string theory can realistically predict a multiverse populated by 10^500 different universes.

M-theory

But there was one remaining pressing issue that was bothering string theorists at the time. A thorough classification showed the existence of five different consistent string theories, and it was unclear why nature would pick one out of five.

This is when M-theory entered the game. During the second string revolution, in 1995, physicists proposed that the five consistent string theories are actually only different faces of a unique theory which lives in eleven spacetime dimensions and is known as M-theory. It includes each of the string theories in different physical contexts, but is still valid for all of them. This extremely fascinating picture has led most theoretical physicists to believe in M-theory as the theory of everything – it is also more mathematically consistent than other candidate theories.

Nevertheless, so far M-theory has struggled in producing predictions that can be tested by experiments. Supersymmetry is currently being tested at the Large Hadron Collider. If scientists do find evidence of super-partners, that would ultimately strengthen M-theory. But it still remains a challenge for current theoretical physicists to produce testable predictions and for experimental physicists to set up experiments to test them.

Most great physicists and cosmologists are driven by a passion to find that beautiful, simple description of the world that can explain everything. And although we are not quite there yet, we wouldn't have a chance without the sharp, creative minds of people like Hawking.

Superstring theory (sometimes just called string theory) has as its basic premise the belief that the four fundamental forces of nature (gravity, electromagnetism, and strong and weak nuclear forces), as well as all matter are simply different manifestations of a single essence. This essence, the material making up all energy and matter, is thought to consist of tiny (a hundred billion billion times smaller than the nucleus of an atom) vibrating strings that exist in a multi-dimensional (10 or 26 dimensions) hyperspace. The extra dimensions (beyond the ones we recognize: three spatial dimensions and time) are thought to be compactified, or curled up, into tiny pockets inside observable space. The particular vibrations of the strings within this multidimensional hyperspace are thought to correspond to particles that form the basis of everything - all matter and energy - in existence.

Bosonic String Theory

In 1974, Claude Lovelace discovered that bosonic string theory could only be physically consistent if it were formulated in 25 spatial dimensions, but so far as anyone knows, we only have three spatial dimensions! Dimensions are the pieces of information needed to determine a precise point in space. (Dimensions are generally thought of in terms of up/down, left/right, forward/backward.)

Relativity treats space and time as a continuum of coordinates, so this means that the universe has a total of 26 dimensions in string theory, as opposed to the four dimensions it possesses under Einstein’s special and general relativity theories.

Einstein’s relativity has three spatial dimensions and one time dimension because those are the conditions used to create the theory. He didn’t begin working on relativity and just happen to stumble upon three spatial dimensions, but rather intentionally built it into the theory from the beginning. If he’d wanted a 2-dimensional or 5-dimensional relativity, he could have built the theory to work in those dimensions.

With bosonic string theory, the equations actually demanded a certain number of dimensions to be mathematically consistent. The theory falls apart in any other number of dimensions!

Conclusion

The physical conception of these extra dimensions was (and still is) the hardest part of the theory to comprehend. Everyone can understand three spatial dimensions and a time dimension. Given a latitude, longitude, altitude, and time, two people can meet anywhere on the planet. You can measure height, width, and length, and you experience the passage of time, so you have a regular familiarity with what those dimensions represent.

What about the other 22 spatial dimensions? It was clear that these dimensions had to be hidden somehow. The Kaluza-Klein theory predicted that extra dimensions were rolled up, but rolling them up in precisely the right way to achieve results that made sense was difficult. This was achieved for string theory in the mid-1980s through the use of Calabi-Yau manifolds.