# Stephen Hawking was hoping that M-theory to explain the universe. What is this theory?

Legend has it that Albert Einstein spent his last hours on earth by drawing something formulate a theory of everything on a piece of paper in the last attempt. 60 years later, and another legendary scientist in the field of theoretical physics, Stephen Hawking, will leave this world with similar thoughts. We know that Hawking believed that the so-called M-theory - our best chance to create a complete theory of the universe. But what is it?

Since then, as in 1915, was formulated by Einstein's general theory of relativity, a theoretical physicist wanted to reconcile our understanding of the infinitely small world of atoms and particles with an infinitely large space scale. If the latter is perfectly described by the Einstein equations, the first with extraordinary precision is predicted so-called Standard Model of fundamental interactions.

Our current understanding is that the interaction between physical objects described by four fundamental forces. Two of them - gravity and electromagnetism - appear to us at the macroscopic level, we have to deal with them every day. The remaining two - the weak and strong interaction - are shown on a very small scale and only when we are dealing with subatomic processes.

The Standard Model of fundamental interactions provides a unified structure for three of these forces, but gravity does not want to fit into that picture. Despite the accurate description of the large-scale phenomena such as the behavior of the planet's orbit and dynamics of galaxies, the general theory of relativity ceases to operate at very short distances. According to the Standard Model, all the forces are mediated by certain particles. In the case of gravity performs work graviton. But when we try to calculate the interaction of these gravitons appear meaningless infinity in the equations. A complete theory of gravity must be working at all scales and take into account the quantum nature of fundamental particles. It would fit gravity into a unified structure to the other three fundamental interactions, thus creating the notorious theory of everything. Of course, since as Albert Einstein died in 1955, had done significant progress in this area. Our best candidate today bears the name of M-theory.

## The revolution of the strings

To understand the basic idea of M-theory, it is necessary to go back to the 1970s when scientists realized that, instead of describing the universe, based on point particles, they would be better described as an oscillating string (power tubes). A new way of understanding the fundamental constituents of nature led to the solution of many theoretical problems. First of all, a single oscillation of the strings can be interpreted as the graviton. And in contrast to the standard theory of gravity, string theory can describe its interactions mathematically and not get strange infinities. This means that gravity can be incorporated into a unified structure.

After that, the opening of this exciting, theoretical physicists have put a lot of effort to understand its consequences. But, as is often the case with scientific research, the history of string theory is full of ups and downs. At first, people were puzzled by the fact that it predicts the existence of a particle that moves faster than light, so-called "tachyon". This prediction came into contradiction with all experimental observations and cast a serious shadow over the string theory.

However, this issue was resolved in the early 1980s with the introduction of string theory in the so-called "supersymmetry". She predicts that every particle has its superpartner and, in an unusual coincidence, the same condition in fact eliminates the tachyon. This first success is widely known as the "first string revolution".

Another unusual feature is that string theory requires the existence of ten space-time dimensions. At the present time we know only four: the depth, width, height and time. Although it looks like a serious obstacle, it proposed several solutions, and now it all seems rather unusual feature, rather than a problem.

For example, we might exist in the four-dimensional world without any access to additional measurements. Or the extra measurements may be "compact" and umeschayas in such a small scale that we would not notice them. However, a variety of shrinking would result in different values of the physical constants and other laws of physics. A possible solution is that our universe is just one of many in an infinite "multiple universe" governed by different physical laws.

## M-theory

There was still one problem that haunted the string theorists of the time. Careful classification revealed the existence of five different consistent string theories, and it was not clear why nature has to choose one out of five.

And here comes into play M-theory. During the second string revolution in 1995, physicists have suggested that five consecutive string theories are actually different people unique theory which exists in eleven spacetime dimensions and is called M-theory. It includes every string theory of various physical contexts, while remaining working for everyone. This incredibly fascinating picture brought the majority of theoretical physicists to the idea that M-theory becomes a theory of everything - and it is also mathematically more consistent than the rest of the proposed theory. Whatever it was, until that M-theory could not make predictions that can be tested experimentally. Supersymmetry is currently being tested at the Large Hadron Collider. If scientists could find signs superpartners existence, it would have definitely strengthened the position of M-theory. But modern theoretical physics is still unable to provide testable predictions and experimental can not provide for this test experiments.

Most of the great physicists and cosmologists are obsessed with the desire to find it beautiful and simple description of the world that would explain everything. And although we are still far from it, without the brilliant and creative people like Hawking and it would be completely impossible.