Throughout history, scientists have been finding theories that explain our world and beyond. However, when two of the most prominent theories of all time are irreconcilable, it became the science community’s number one priority to unite the two. The two theories were Quantum Mechanics and General Relativity.
Picture of Quantum Mechanics

Quantum mechanics is the body of scientific principles which attempts to explain the behavior of matter and its interactions with energy on the scale of atoms and atomic particles. Basically it tries to explain the world of the infinitesimally small.

The basic idea behind General Relativity is that it bends space and time.

On the other hand, Einstein’s General Relativity deals with the immensely big, theorizing that the observed gravitational attraction between masses results from their bending of space and time. because of the vast difference in the size of the scales the two theories are working in, it has continued to be hard to fuse the two into on fluent theory.

String theory is the most well-known attempt to reconcile the two ideas of quantum mechanics and general relativity. Many have theorized that it could become the final theory of everything. String Theory suggests that the tiniest subatomic bits that make up atoms are actually vibrating strings of energy.
Picture of what the "strings" of String Theory may look like.

One problem with string theory is that is requires 11 dimensions to be free of mathematical anomalies, which is not only hard for most people to come to terms with, but also makes the theory especially difficult to test, which is why the theory has so many critics.

Lee Smolin

One of the most well known critics is Lee Smolin, an American theoretical physicist, a researcher at the Perimeter Institute for Theoretical Physics, and an adjunct professor of physics at the University of Waterloo. Smolin is best known for devising several different approaches to quantum gravity, in particular loop quantum gravity. Smolin’s theory of loop gravity predicts that space is like atoms: there is a discrete set of numbers that the volume-measuring experiment can return. It predicts that volume comes in separate pieces, that space and time actually come in distinct parts, rather than it being continuous.

Peter Woit

Peter Woit is a Departmental Computer Administrator and Senior Lecturer in Discipline at Columbia University, and is known for his criticisms of String theory in his book Not Even Wrong, and his blog of the same name. He is critical of string theory on the grounds that it lacks testable predictions and is promoted with public money despite its failures so far. One of Woit’s biggest problems with String Theory its idea of the universe having ten dimensions, rather than the four the world can see: three space and one time dimension. Because it has been calculated that string theory most logically makes sense in 10 dimensions, yet it has been discovered that discovered that there are basically an infinite number of ways of choosing the size and shape of the six-dimensional space, scientists can’t use string theory to predict anything you can observe, which is why Woit argues that under the normal standards of scientific conduct, String Theory is a failure.

Although String Theory has its flaws and critics, it still remains the leading theory to linking quantum mechanics and general relativity. Scientists around the world are currently working to find a way to prove, experimentally, that String Theory is in fact fact. The largest problem with String Theory, similar to that of problem it sets out to solve, is its ambiguity. String Theory, as it is currently understood, has several possible solutions, and because they are all unable to be tested, they leave the answer to the universe unknown. In order to figure out the universe lived in today, scientists will have to continue the hunt for a testable and workable solution.