# Planck Length

1. Mar 11, 2005

### Ed Quanta

Ok so I understand how we derive Planck Length using the natural constants G,h, and c. However, how do we know this indeed represents the smallest possible length an object in the universe? Or does Planck length just represent the smallest possible length under which gravity is still influential?

2. Mar 11, 2005

### Andrew Mason

The Planck length is thought to be a fundamental unit of length below which length or distance has no meaning. It is said to be the smallest distance that can exist and still have meaning. How do we know that? We don't. It is just a theory and has never been tested. (Mind you, no one has found anything smaller, yet).

Planck invented the concept of natural units of mass, length and time. The idea was that you could avoid having to use these constants if you expressed mass, length and time in terms Planck units (for example, you would forget about G and express gravitational force in terms of Planck mass and length, as $$n\frac{m_p^2}{l_p^2}$$).

That these units could also have physical meaning seems to me to be somewhat of a stretch.

AM