# String theory

String theory
String theory is a scientific theory that uses complicated mathematics and physics to try to explain how the universe works.
String theory is an attempt to explain these four forces using one single theory (or unified field theory). This may also be a theory that can bring together other physics theories all at once.
If the string theory is true, it is one of the few theories that could explain why there is gravity. It explains gravity through quantum mechanics. With traditional physics theories, this was not possible.
Main idea.
Usually, scientists think of matter as being made of very, very small particles. These particles are so small (we are talking on a scale much smaller than an atom) we cannot observe them to see their shape. Currently, all mathematical formulas assume they are point-like and therefore have no size at all. The main idea behind string theory is that this assumption is wrong, and that these small particles are instead shaped as tiny strings.
The theory imagines that these strings are not precise particles (unlike things that are seen and counted). The strings are very small (10-35 m long), yet they seem to behave like regular particles. It explains how other particles and forces behave. Because they are so small their actual shape doesn't matter much when we are doing calculations of bigger objects.
Status.
It is used as a possible way of explaining how some things work; it is very hard for scientists to prove everything, or answer every question that they can imagine by using just one theory on its own. String Theory is slightly different from most other theories because it could help scientists get closer to explaining everything that they can think of, so many scientists are excited by the ideas that String Theory has to offer.
There are two mathematical models that predict the same physical observations of the whole universe. One is "as large as we think the universe is", about the 74 billion light years circumference predicted in Weeks' model. The other is much smaller than the Planck Length. Both mathematics are just as good to explain what we can see.
The Superstring theory is based on 10 or 11 dimensions. The Bosonic string theory has 26 dimensions. Gravity is the only real force in the theory. It says only four of the ten dimensions can be observed by us, and that the others hint at the other forces that are observed. It does not say that other physics theories are not true, or wrong.
String theory has led to advances in the mathematics of folding, knots and Calabi-Yau spaces.
Problems.
There are many different variations of string theory, and none of them is fully accurate. Often, many of them use only approximations. String theory proponents say this is because the theory is not finished yet.
Another problem is that the mathematical laws of string theory also gives lots of different possible solutions. Scientists that believe in string theory work around this problem by picking only the results that match our observations and saying that later we will find why the other ones are not good. Opponents argue that we can't ever know if a theory is true as a whole if we only take the bits that work. This also makes the theory of little use until the issue is solved, because mathematical laws are usually used to predict what will happen in a situation - but string theory cannot yet answer that question, because it needs to be tried first and then scientists can pick the answer that work.
Yet another problem is that it says our universe is made of at least 10 dimensions, while we only see four (width, height, depth, time). String theory proponents say some dimensions may not be visible to us, but others doubt there can be 6 or more hidden dimensions, or that we will never be able to access them even if they do exist.
String theory does not make predictions that can actually be tested by scientists today or in the near future. Some people say this makes the theory unscientific.