1. Introduction

Max Planck

In particle physics and physical cosmology, Planck Units are a set of units of measurement defined exclusively in terms of five universal physical constants, in such a manner that these five constants take on the numerical value of 1 when expressed in terms of these units. Originally it was proposed in 1899 by a German physicist Max Planck, these units are also known as the 'Natural Units' because the origin of their definition comes only from properties of nature and not from any human construct. Planck units are only one system of several systems of natural units, but Planck units are not based on properties of any prototype object or particle, but rather on only the properties of free space.

The term “Planck scale” refers to the magnitudes of space, time, energy and other units, below which the predictions of the Standard Model, quantum field theory and general relativity are no longer considerable, and the quantum effects of gravity are expected to dominate. This region may be characterized by energies of around the Plank energy, the time interval of around the Plank time and length of around the Planck length. The best known example for this is represented by the conditions in the first 10^-43 seconds of our universe after the Big Bang, approximately 13.8 billion years ago.

The five universal constants that Planck units, by definition, normalize to 1 are :-

>>> the speed of light in a vacuum (c)

>>> the gravitational constant (G)

>>> the reduced Planck's constant (h)

>>> the Coulomb's constant (k_e)

>>> the Boltzmann's constant (k_B)

Each of these constants can be associated with a fundamental physical theory or concept such as 'c' with special relativity, 'G' with general relativity, 'h' with quantum mechanics, 'k_e' with electromagnetism and 'k_B' with thermodynamics or statistical mechanics.