String Theory Explained Simply

The biggest dilemma of Einstein’s life represents the search for a unified theory. Scientists all over the world are currently engrossed in the quest for a unified theory. In this search, we unify all the laws of physics, particularly quantum mechanics and Einstein’s theory of general relativity. The goal is to bring them together within a single framework. Consequently, this framework could explain the workings of the universe.

Currently, we have multiple theories and suggestions for the unified theory. One of the long-explored and influential approaches is “the string theory.” However, other competing frameworks—such as loop quantum gravity and emergent spacetime—are also gaining attention.

For all those who would rather watch a video to better understand a topic, here is one by Kurzgesagt – In a Nutshell:

What Is String Theory?

In physics, string theory represents a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. For example, take a piece of wood. Inside it you would find millions of atoms bonded together. Inside every atom there is a nucleus. The atomic nucleus consists of nucleons—protons and neutrons. Protons and neutrons are made of quarks. According to string theory, quarks themselves may be manifestations of tiny vibrating strings. Different vibration patterns give rise to different particles and their properties.

How Does it Unify the Laws of Physics?

In physics we have four fundamental forces that underpin the universe: gravity, electromagnetism, strong nuclear force and weak nuclear force. Gravity is described by Einstein’s beautiful mathematics of curved space and time. But the other three forces are written in the language of quantum mechanics. These two frameworks work extremely well in their own domains, but they become difficult to reconcile under extreme conditions where both are important.

Presently the string theory says: Various vibrations of this stringy stuff correspond to each of the fundamental particles producing the properties of gravity, light and other elementary substances and laws. Consider these strings like the strings of guitar. Every unique vibration results in a unique musical note. Similarly, the vibrations of the strings cause the unique property of matter and the forces.

The Problem With String Theory

The mathematics of string theory is a little strange. In placing the pieces together, physicists needed to add more and more dimensions of space to make their theories work. In fact, this is many more than the three we experience in our everyday lives. Most versions of superstring theory require 10 spacetime dimensions. However, the broader framework known as M-theory requires 11 dimensions. The reason is that in three dimensions the strings won’t have enough room to wiggle and bring about the unique property.

One of the major challenges string theory faces today is the lack of empirical predictions that can be tested in experiments, which makes it hard to confirm or disprove. Despite decades of research, no direct experimental evidence for string theory has yet been found.

Theory of Dimensions

The very idea of extra dimensions dates back to 1919 (published in 1921) when German mathematician Theodor Kaluza suggested a very bold and in some ways very bizarre idea. Later, Oskar Klein extended this idea in 1926. He proposed that our universe might actually have more than the three dimensions that we are all aware of.

It’s a possibility that the dimensions might come in two varieties. There might be big easy to see dimensions but there might also be tiny curled up dimensions curled up so small even though they’re all around us that we don’t see them. In modern string theory, these tiny curled-up dimensions are often described using complex geometries known as Calabi-Yau manifolds.

For example consider bacteria on a paper. For the bacteria, the page would be three-dimensional as it would have height, width and length but for us it is only two-dimensional. So it could be true that the dimensions are curled up so small that our naked eyes or even our best microscopes cannot observe them. But in contrast, it might also be true that they are actually not large in the usual sense at all. Instead, they may be compactified or hidden in ways that prevent direct observation at accessible energy scales.

They might be described in some speculative models as extending into a higher-dimensional “bulk.” However, there is currently no experimental evidence supporting large, universe-spanning extra dimensions.

We might be living in a small part of the ten- or eleven-dimensional spacetime proposed in string theory and M-theory which is so huge that we comprehend it as only three-dimensional.

String Theory Books

• The Elegant Universe by Brian Greene
• The Little Book of String Theory by  Steven S. Gubser
• A First Course in String Theory by Barton Zwiebach
• The Trouble with Physics: The Rise of String Theory, the Fall of a Science and What Comes Next by Lee Smolin
• Hyperspace: A Scientific Odyssey by Michio Kaku

Conclusion

Some physicists feel that the theorists on the string theory bandwagon are heading down a dead-end path in the search for ultimate physics, and others feel it’s very promising. In fact, we absolutely don’t know. We don’t know if any of our ideas are truly inching a way towards the ultimate theory, or if a completely alternative approach is required. The debate over string theory’s future reflects the broader uncertainties in fundamental physics today.

We simply don’t know if a grand unified theory even exists. But this will not stop physicists from pursuing their search.

Also read:

1. Parallel Universe: We Might Be Living in an Alternate Reality!
2. How NASA Chose the First Astronauts to Walk on the Moon
3. What is Celestial Navigation?