The theory of superstrings, in popular language, represents the universe as a collection of vibrating energy threads - strings. They are the foundation of nature. The hypothesis also describes other elements - branes. All substances in our world consist of vibrations of strings and branes. A natural consequence of the theory is the description of gravity. That is why scientists believe that it contains the key to combining gravity with other interactions.
Concept is developing
The theory of a single field, the theory of superstrings, is purely mathematical. Like all physical concepts, it is based on equations that can be interpreted in a certain way.
Today, no one knows exactly what the final version of this theory will be. Scientists have a rather vague idea of its common elements, but no one has yet come up with a final equation that would encompass all theories of superstrings, and experimentally still has not been able to confirm it (although to refute it too). Physicists have created simplified versions of the equation, but so far it does not fully describe our universe.
Super String Theory for Beginners
The hypothesis is based on five key ideas.
- Superstring theory predicts that all objects in our world are made up of vibrating threads and membranes of energy.
- She is trying to combine the general theory of relativity (gravity) with quantum physics.
- Superstring theory will unite all the fundamental forces of the universe.
- This hypothesis predicts a new connection, supersymmetry, between two fundamentally different types of particles, bosons and fermions.
- The concept describes a series of additional, usually unobservable dimensions of the universe.
Strings and branes
When the theory arose in the 1970s, the threads of energy in it were considered 1-dimensional objects - strings. The word "one-dimensional" means that the string has only 1 dimension, length, in contrast to, for example, a square that has length and height.
The theory divides these superstrings into two types - closed and open. An open string has ends that do not touch each other, while a closed string is a loop without open ends. As a result, it was found that these strings, called strings of the first type, are subject to 5 main types of interactions.
The interactions are based on the ability of the string to connect and separate its ends. Since the ends of open strings can combine to form closed ones, it is impossible to construct a theory of superstrings that does not include looped strings.
This turned out to be important, since closed strings have properties, as physicists believe, that could describe gravity. In other words, scientists realized that the theory of superstrings instead of explaining particles of matter can describe their behavior and gravity.
After many years, it was discovered that, in addition to strings, theories needed other elements. They can be considered as sheets, or branes. Strings can be attached to their one or both sides.
Quantum gravity
Modern physics has two basic scientific laws: general theory of relativity (GR) and quantum. They represent completely different fields of science. Quantum physics studies the smallest natural particles, and GTR, as a rule, describes nature on the scale of planets, galaxies and the universe as a whole. The hypotheses that try to unite them are called theories of quantum gravity. The most promising of them today is the string.
Closed threads correspond to the behavior of gravity. In particular, they possess the properties of a graviton, a particle that transfers gravity between objects.
Joining forces
String theory tries to combine four forces - electromagnetic, strong and weak nuclear interactions, and gravity - into one. In our world, they manifest themselves as four different phenomena, but string theorists believe that in the early Universe, when there were incredibly high energy levels, all these forces are described by strings interacting with each other.
Supersymmetry
All particles in the universe can be divided into two types: bosons and fermions. String theory predicts that there is a connection between them called supersymmetry. In supersymmetry, a fermion must exist for each boson, and a boson for each fermion. Unfortunately, experimentally the existence of such particles is not confirmed.
Supersymmetry is a mathematical relationship between elements of physical equations. It was discovered in another field of physics, and its application led to the renaming of the theory of supersymmetric strings (or the theory of superstrings, a popular language) in the mid-1970s.
One of the advantages of supersymmetry is that it greatly simplifies the equations, eliminating some variables. Without supersymmetry, equations lead to physical contradictions, such as infinite values and imaginary energy levels.
Since scientists did not observe particles predicted by supersymmetry, it is still a hypothesis. Many physicists believe that the reason for this is the need for a significant amount of energy, which is associated with the mass of Einstein’s famous equation E = mc 2 . These particles could exist in the early universe, but since it cooled down and energy spread after the Big Bang, these particles moved to low-energy levels.
In other words, the strings that vibrated as high-energy particles lost energy, which turned them into elements with lower vibration.
Scientists hope that astronomical observations or experiments with particle accelerators will confirm the theory by revealing some of the higher-energy supersymmetric elements.
Additional measurements
Another mathematical consequence of string theory is that it makes sense in a world with more than three dimensions. There are currently two explanations for this:
- Additional dimensions (six of them) were curtailed, or, in the terminology of string theory, compactified to incredibly small sizes, which can never be perceived.
- We are stuck in a 3-dimensional brane, and other dimensions extend beyond it and are inaccessible to us.
An important area of research among theorists is the mathematical modeling of how these additional coordinates can be related to ours. Recent results predict that scientists will soon be able to detect these additional dimensions (if they exist) in upcoming experiments, as they may be larger than previously expected.
Understanding of purpose
The goal scientists are striving for when exploring superstrings is the “theory of everything”, that is, a single physical hypothesis that at a fundamental level describes all physical reality. If successful, she could clarify many questions about the structure of our universe.
Explanation of matter and mass
One of the main tasks of modern research is to find a solution for real particles.
String theory began as a concept describing particles such as hadrons by various higher vibrational states of a string. In most modern formulations, the matter observed in our universe is the result of vibrations of strings and branes with the least energy. Vibrations to a greater extent generate high-energy particles, which currently do not exist in our world.
The mass of these elementary particles is a manifestation of how strings and branes are wrapped in compactified extra dimensions. For example, in the simplified case, when they are folded in the shape of a donut, called a torus by mathematicians and physicists, a string can wrap this shape in two ways:
- short loop through the middle of the torus;
- long loop around the entire outer circumference of the torus.
A short loop will be a light particle, and a large one will be a heavy one. When wrapping strings around toroidal compactified measurements, new elements with different masses are formed.
Superstring theory briefly and clearly, simply and elegantly explains the transition of length to mass. The collapsed measurements here are much more complicated than the torus, but in principle they work as well.
It is even possible, although it is difficult to imagine that the string wraps the torus in two directions at the same time, resulting in another particle with a different mass. Branes can also wrap extra dimensions, creating even more features.
Definition of space and time
In many versions, the theory of measurement superstrings collapses, making them unobservable at the current level of technological development.
It is not clear at present whether string theory can explain the fundamental nature of space and time more than Einstein did. In it, measurements are the background for the interaction of strings and have no independent real meaning.
Explanations were proposed that were not fully developed regarding the representation of space-time as a derivative of the total sum of all string interactions.
This approach does not meet the ideas of some physicists, which led to a criticism of the hypothesis. The competitive theory of loop quantum gravity uses quantization of space and time as a starting point. Some believe that in the end it will turn out to be just a different approach to the same basic hypothesis.
Gravity quantization
The main achievement of this hypothesis, if it is confirmed, will be the quantum theory of gravity. The current description of gravity in general relativity is not consistent with quantum physics. The latter, imposing restrictions on the behavior of small particles, when trying to explore the Universe on an extremely small scale, leads to contradictions.
Unification of forces
At present, physicists know four fundamental forces: gravity, electromagnetic, weak and strong nuclear interactions. It follows from string theory that they were all once manifestations of one.
According to this hypothesis, since the early universe cooled down after the big bang, this single interaction began to disintegrate into different ones acting today.
High-energy experiments will one day allow us to discover the unification of these forces, although such experiments are far beyond the current development of technology.
Five options
After the superstring revolution of 1984, development was carried out with feverish speed. As a result, instead of one concept, five were obtained, named type I, IIA, IIB, HO, HE, each of which almost completely described our world, but not to the end.
Physicists, sorting out versions of string theory in the hope of finding a universal true formula, have created 5 different self-sufficient variants. Some of their properties reflected the physical reality of the world, others did not correspond to reality.
M-theory
At a conference in 1995, physicist Edward Witten proposed a bold solution to the problem of five hypotheses. Based on the recently discovered duality, they all became special cases of a single comprehensive concept called Witten's M-theory of superstrings. One of its key concepts is branes (short for membrane), fundamental objects with more than 1 dimension. Although the author has not proposed a full version, which is still missing, the M-theory of superstrings briefly consists of the following features:
- 11-dimensionality (10 spatial plus 1 temporal dimension);
- duality that leads to five theories explaining the same physical reality;
- branes are strings with more than 1 dimension.
The consequences
As a result, 10,500 solutions arose instead of one. For some physicists, this caused a crisis, while others adopted the anthropic principle that explains the properties of the universe by our presence in it. It remains to be expected when theorists find another way of orientation in superstring theory.
Some interpretations suggest that our world is not the only one. The most radical versions allow the existence of an infinite number of universes, some of which contain exact copies of ours.
Einstein's theory predicts the existence of a collapsed space called the Wormhole or Einstein-Rosen Bridge. In this case, two remote sites are connected by a short passage. Superstring theory allows not only this, but also the connection of distant points of parallel worlds. Even a transition between universes with different laws of physics is possible. However, it is likely that the quantum theory of gravity will make their existence impossible.
Many physicists believe that the holographic principle, when all the information contained in the volume of space corresponds to the information recorded on its surface, will allow a deeper understanding of the concept of energy filaments.
Some believe that the theory of superstrings allows the multiplicity of measurements of time, the consequence of which may be a journey through them.
In addition, under the hypothesis, there is an alternative to the Big Bang model, according to which our universe appeared as a result of a collision of two branes and goes through repeated cycles of creation and destruction.
The final fate of the universe has always occupied physicists, and the final version of string theory will help determine the density of matter and the cosmological constant. Knowing these values, cosmologists will be able to establish whether the universe will shrink until it explodes, so that everything starts again.
No one knows what a scientific theory can lead to until it is developed and tested. Einstein, having written the equation E = mc 2 , did not assume that it would lead to the appearance of nuclear weapons. The creators of quantum physics did not know that it would become the basis for creating a laser and a transistor. And although it is not yet known what such a purely theoretical concept will lead to, history indicates that something outstanding will surely turn out.
More information about this hypothesis can be found in the book by Andrew Zimmerman's Theory of Superstrings for Dummies.