Strings, Branes, Dimensions and SUSY
What Does All of This Mean, A Reality Check for Our Universe
Strings, Branes, Dimensions and SUSY
INTRODUCTION
String theory is the most commonly known modern physics theory to the average person. What makes string theory so fascinating to people is its strange assessment of what, and how, all of the matter in universe is created. Specifically, the strings in string theory are only a single dimension. These single dimension strings make up the elementary particles that in turn make up everything in the universe. The second most attention grabbing commonly known part of string theory is that it exists in 11 dimensions. And, that most of these 11 dimensions are folded up and live in a space smaller than the space between the atoms that make up all of the matter in the universe.
The less commonly known, but just as important parts of string theory, are branes and SUSY; where SUSY stands for Super-Symmetry. SUSY is most commonly pronounced as something along the lines of Sue-See
All of the elementary particles that make up everything in the universe, and are made up of one-dimensional strings, are contained in what is commonly referred to as the standard model. Currently there are at least 17 elementary particles covered in the standard model. Some consider the Higgs Boson to also be a part of the standard model. One of the basic standard model particles is the gluon. However, there are 8 different gluons. So there are some cases that consider all of the gluons to be individual elementary particles.
Putting everything together, and depending on the point of view, the standard model could consist of 17, 18, 24 or 25 different elementary particles. For the purposes of this paper, the number of standard model particles is not important. Because, the information that will be covered in this paper applies to all of the elementary particles independently of how many there may be. SUSY is a major part of string theory because it is directly related to the standard model of particles. In essence SUSY invents a number of additional elementary particles that more than doubles the current number of elementary particles. SUSY is also considered to be an integral part of the the current string theory model. If SUSY fails, than the current version of string theory could also fail.
The last item of string theory to be covered in this paper are branes. The short answer of what branes are, branes are a two dimensional sheets that also exist in the extra dimensions of space that the strings exist in. The one dimensional strings have various interaction with the two-dimensional branes.
This paper will a provide simple evaluation of the four items of concern, Strings, Branes, Dimensions and SUSY, for their consistency with the universe we live in. The reader can use the information to form their own opinions about these items individually, or all together to decide if string theory is consistent with the reality of our universe.
DISCUSSION
String theory was first proposed in 1968 as a one-dimensional mathematical model. This is the first point that needs to be made, as a mathematical model string theory can never be experimentally proven. Its reality and existence is completely described in the mathematics of string theory. This mathematical description for string theory is then put forth as a reality of our universe. Since there are no experiments or physical tests for string theory the validity of string theory is current simply accepted because the math says it is valid.
In general, string theory is the theory that all elementary particles, the ones of the standard model, are actually one dimensional strings. These one-dimensional strings vibrate at different frequencies where the frequency of vibration accounts for the different elementary particles. The attention grabbing, fascinating part of string theory, is that these vibrating strings that produce the particles that make up everything in the known universe exist in a 10, 11 or 26 dimensional reality. That is, the mathematics of string theory is only valid in one of these 3 listed realities.
Digging a little deeper into how many dimensions can exist where string theory can live, the math associated with string theory puts the number at ten to the 500th power of dimensions. That is a the number 1 followed by 500 zeros. That is a lot of possible dimension to consider for string theory. The current conclusion is that the strings in string theory exist in a 10 dimensional reality. In other words, one case, out of a number of possibilities so big it is unimaginable, has been chosen. And, it is the simplest of all of the possible cases.
The current universe where everything, including us, exists has 3 dimensions of space and one dimension of time for four total dimensions. So where are the other 6 dimensions of space of string theory? They are folded up or rolled up into a space so small that it could fit in the distance between the atoms of a molecule. This distance has an official designation, it is called the Planck Length. This Planck Length is known as the smallest distance known to science. That is, nothing can go smaller than this distance. So the extra 6 dimensions of string theory, along with all of the strings needed for the mass of our universe exist in the smallest space known in the universe.
So, now we have one-dimensional strings, existing in the 6 infinitely large dimensions space that exist in the smallest space known. Given these characteristics the first and simplest question to ask, what are the strings made of? What is it that exists in the 6 dimensions of space folded up into the smallest distance known that can build the strings necessary to build the universe we live in? As far as I can tell there is no answer to this question. Part of the reason for no answer maybe based on the next question.
Just what is a “one-dimension” string, or any “one-dimensional” object for that matter? When looking at an object, and a string has to be an object, that is one dimension, it is best visualized as a line. This is consistent with what a string would look like. In one dimension you can only move in one direction. That is, forward or backward. To visualize one-dimension, consider a line drawn on a piece of paper. This is in essence one-dimension. Remember where this line is on the piece of paper. Now completely erase this line on the paper so you can’t see it. You now have what a one-dimensional string would be and what it would look like in reality.
The line you drew on a piece of paper was actually in three-dimension. The line on the piece of paper had a width to it. It was a very small width, but a width nonetheless. This width is in fact a second dimension. In order to be one-dimension, there can be zero width. Also, the pen or pencil left a mark on top of the paper. This is a height. Again, a very small height, but some amount of height. This height is a third dimension. Again, all height has to be removed in order to have one-dimension. The nothingness left of the line that you drew on the paper is one dimension
Once you loss height and width in the reality of our three-dimensional universe you are literally left with nothing. The question now, can something that is only a single dimension actually exist in our reality? Some related additional questions, what is it that makes up or causes nothing to exist? Maybe nobody knows what strings are made of because in reality they are nothing. And, how does a one-dimensional nothing suddenly pickup two more dimensions in order to become the reality that is the mass that makes up everything in the universe? Additionally, how does this one-dimensional nothing move out of the 6 infinite dimensions rolled up into the smallest space known in the universe into the three dimension of the real universe? Does the string transform from one-dimension to a three-dimensional particle before it leaves the 6 dimensions, or after it comes into the three dimensional universe?
There are many more questions about strings, but the discussion should move to branes. In general they are similar to strings except that they are two dimensional objects that exist in the 6 extra dimensions that are folded up into the smallest space known. Strings interact with branes in different ways. Like strings, there is no answer for what branes are made of.
So, what does two dimensions look like? This time take a piece of paper and place it on a hard surface. When you look at the top of that sheet of paper you see two dimensions. That is, you can move or draw a line on the surface of the paper that goes up and down on the paper and and a completely separate line that goes left and right across the paper. And these two lines can be perpendicular to each other. That is, if they crossed each other than the intersection where they cross has four 90 degree angles. But, just like the one-dimensional line before, the sheet of paper has height. Again, a very, very small height but some height nonetheless. So if you remove the height of the paper, once again you are left with just another nothing.
Here is another way you can think of two dimensions. If we take a bunch of our one dimensional lines and put them right next to each other, we can build a sheet. In other words, we can take a bunch of the one-dimensional strings, lay them out next to each other and build a two-dimensional brane. But, if the strings are nothing in our three-dimensional universe, then the branes must also be nothing. Specifically, you have a situation where you used one set of nothing to build another a bigger set of nothing. How can this be done in our universe? There is an additional problem, branes are not strings, they do different things. But, it was just shown how strings can make a brane. All of this coming from nothing, and all of it occurring in the smallest space known in the universe.
The above discussion of one-dimensional strings and two-dimensional branes provides insight about lower dimensional objects and their existence with respect to our three-dimensional universe. That is, there is the question as to how one and two dimensional “things” can exist at all. Furthermore, if they do exist, strings and branes exist in 6 dimensions that have to be infinitely large but are rolled up into the smallest space known to exist in this universe. Additionally, this total of a 10 dimensional universe that the current string theory model indicates we exist in is one of currently discovered 3 possible multidimensional universes where string theory can live. It is possible that there are far more than three possible multidimensional universes where string theory can thrive.
Recall that the current string theory mathematics shows that the number of possible universes that can exist is a one followed by 500 zeros. It is virtually impossible to check the mathematics of these possible dimensional universes for their compatibility with string theory. In other words, it is possible that a universe of over 250 dimensions is consistent with the current string theory model. Having a universe of over 250 dimensions would mean that over 246 infinite dimensions exists in the smallest space known in the universe. One of the first questions that comes to mind now is how does a one dimensional string move from the more than 246 rolled up dimensions, into our large three dimensional universe?
The last part of string theory to discuss in this paper is SUSY, or SuperSymmetry. SUSY was first proposed in 1977, 9 years after string theory. SUSY, or some version of it, is an integral part of the current string theory model. SUSY is generally based upon the concept of symmetry which is a basic property in physics. In general, symmetry says if one thing exists, then so should a related symmetrical item. The most common example, we can move forward in space. So we should also be able to move rearward in space. Which we can do. If there is a left, than there is also a right, if there is an up, than there is also a down. So, SUSY takes the concept of symmetry and applies it to the particles of the standard model thus more than doubling the current standard model.
On the left, the particles of the Standard Model. (The graviton is theoretical as it is currently undiscovered.) On the right are the corresponding particles of Supersymmetry. (CLAIRE DAVID/CERN/)
So what are the concerns about SUSY, the first is that the idea of symmetry to the standard model particles has already been handled. The real symmetry for the standard model that is already known about comes in the form of the “anti” particles that exist for all of the standard model particles. An example, consider the most commonly known particle in the standard model, the electron. Its anti-article is the positron, which exists in our universe. This means that it can be argued that the symmetry associated with Supersymmetry is a manufactured symmetry rather than a necessary symmetry associated with the standard model.
There is another significant issue associated with Supersymmetry that must be considered when evaluating its consistency and reality. That is, none of the Supersymmetry particles, also known as Sparticles, as shown above, have been discovered.
When Supersymmetry was first proposed sparticles were exactly the same size, mass and energy of their corresponding standard model particles. For example, the selectron was exactly the same size, mass and energy as the electron. The difference was that the selectron had a different function than the electron. Since all of the sparticles had the same physical characteristics as the standard model particles, all of the sparticles should have been discovered within our universe. However, they have yet to be discovered.
To account for the lack of discovery of sparticles in experiments, the original supersymmetry theory was modified by making all of the sparticles slightly larger than their standard model counterparts. However, these larger sparticles also were not found in experiments. So more modifications to the sparticles have been proposed to account for the fact that none of them have been found. Despite all of the modifications made, to date none of the sparticles has been discovered or seen in particle collisions and experiments.
Given the amount of modifications that have been made to the sparticles to account for their lack of discovery there is another significant problem that needs to be considered. The current characteristics of the sparticles are no longer close to the physical characteristics of the standard model particles. That is, in essence symmetry between particles and sparticles no longer exists.
One more consideration regarding SUSY, there are multiple questions, unknowns, and things that are not understood associated with the standard model. For example, particles come with a quantum characteristic called spin. Spin has two types, lefthanded and righthanded, and almost all of the particles of the standard model come in both righthanded and lefthanded spin versions. The exception, neutrinos, which are the most common particle in the universe. As you sit here and read this paper billions upon billions of neutrinos are passing through your body. It turns out that all of these neutrinos only come in the lefthanded spin version. There are no righthanded spin neutrinos. So, what kind of spin do the sneutrinos in the sparticle table have, lefthanded like the neutrino, or righthanded due to the symmetry that is the basis of SUSY?
If we don’t know all of the answers to the questions associated with the standard model and its elementary particles, how is it possible to double the size of the current particles without also doubling the problems and the unknowns? There are no answers for this.
String theory has 4 basic and necessary components, strings, branes, dimensions and SUSY. However, when these 4 items are examined it appears that they raise more questions then they provide answers toward understanding string theory in our universe.
THINKING OUTSIDE OF THE BOX
String theory is all about having 6 infinite dimensions existing within the smallest part of the universe as we know it. If it is possible for one-and two dimensional nothingness strings and branes to exist in 6 infinite dimensions rolled up into the smallest space known, then it should also be possible for our three dimensions to exist with more dimensions that exist above our three dimensional universe.
CONCLUSION
What was covered in this paper are just of the basic, fundamental issues and associated questions regarding string theory. There are so many additional parts and conclusions associated with string theory that are not understood and raise even more questions that currently have no answers. When all things are considered there is a basic question, with so much that is unknown, not understood and questions that have no answers, how can so much time and investment continue to be made in the mathematical model called string theory?
As I said at the beginning of this piece, string theory is a mathematical model that is trying to be used to describe the universe we live in. Given the information covered in this paper and the follow up questions, the final question that has to be asked, how does the math of string theory become the reality of our universe?
Is it possible that it doesn’t?
Steven Guderian, 5.9.23
