The Planck Length

The Planck Length

There is a problem at the heart of all science.

We have two theories that describe the fundamental nature of the universe. General Relativity and Quantum Mechanics.

They do this by explaining the four fundamental forces, which are the laws of nature that determine how everything in the universe interacts with everything else.

These laws include gravity, which draws together objects with mass, and the electromagnetic force that gives us electricity.

On their own, General Revativity and Quantum Mechanics are spectacular theories.

General Relativity is Albert Einstein’s most lasting and well-known contribution to physics, and has stood up to decades of observational evidence.

Physicist Richard Feynman once said that Quantum Mechanics has been shown to be so precise, that it can make measurements equivalent to the width of North America accurately to within the width of one human hair.

But one of them is wrong.

When you put the equations of each one together, they produce impossible gibberish.

Fortunately for most practical tasks that scientists do, it doesn’t matter. General Relativity describes gravity in the world of huge objects, like the orbits of planets and stars. Quantum Mechanics describes the world inside the atom.

It’s largely in two special circumstances that scientists would want to combine the two theories, and the gibberish becomes an issue;

  1. When studying black holes
  2. When studying the Big Bang

While both of these cases are important to scientists, the bigger problem is that we don’t want two of our most important theories to be inconsistent. We have to work it out.

Enter the ‘planck length’. The planck length is an incredibly tiny distance at which the force of gravity starts to merge with the world of quantum mechanics. If there is an answer for to how to make the theories consistent with each other, it happens at the planck length.

The leading theory is called ‘String Theory‘. It proposes that the particles of Quantum Mechanics emerge from musical notes produced by tiny vibrating strings. The length of the string is equal to the planck length.


The only problem is that it is really, really small. One of the smallest things that we have ever measured is the radius of the electron, which is about 10-22 meters. The planck length is estimated to be ten trillion times smaller at 10-35 meters.

Things this tiny are way beyond our ability to experiment on right now, and as a consequence, solving the inconsistency between two of our greatest theories in physics is likely to remain a mystery for some time.

The world of the planck length is a distant new frontier for science, and what we find there could redefine everything that we thought we knew about the universe.

Additional notes