Planck units

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 physical constants take on the numerical value of 1 when expressed in terms of these units.We see that the question is not, 'Why is gravity so feeble?' but rather, 'Why is the proton's mass so small?' For in natural (Planck) units, the strength of gravity simply is what it is, a primary quantity, while the proton's mass is the tiny number ....ihre Bedeutung für alle Zeiten und für alle, auch außerirdische und außermenschliche Kulturen notwendig behalten und welche daher als »natürliche Maßeinheiten« bezeichnet werden können... ∇ ⋅ B = 0   {displaystyle abla cdot mathbf {B} =0 } ∇ × E = − ∂ B ∂ t {displaystyle abla imes mathbf {E} =-{frac {partial mathbf {B} }{partial t}}} ∇ × B = 1 c 2 ( 1 ϵ 0 J + ∂ E ∂ t ) {displaystyle abla imes mathbf {B} ={frac {1}{c^{2}}}left({frac {1}{epsilon _{0}}}mathbf {J} +{frac {partial mathbf {E} }{partial t}} ight)} ∇ ⋅ B = 0   {displaystyle abla cdot mathbf {B} =0 } ∇ × E = − ∂ B ∂ t {displaystyle abla imes mathbf {E} =-{frac {partial mathbf {B} }{partial t}}} ∇ × B = 4 π J + ∂ E ∂ t {displaystyle abla imes mathbf {B} =4pi mathbf {J} +{frac {partial mathbf {E} }{partial t}}} important lesson we learn from the way that pure numbers like α define the world is what it really means for worlds to be different. The pure number we call the fine structure constant and denote by α is a combination of the electron charge, e, the speed of light, c, and Planck's constant, h. At first we might be tempted to think that a world in which the speed of light was slower would be a different world. But this would be a mistake. If c, h, and e were all changed so that the values they have in metric (or any other) units were different when we looked them up in our tables of physical constants, but the value of α remained the same, this new world would be observationally indistinguishable from our world. The only thing that counts in the definition of worlds are the values of the dimensionless constants of Nature. If all masses were doubled in value you cannot tell because all the pure numbers defined by the ratios of any pair of masses are unchanged. 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 physical constants take on the numerical value of 1 when expressed in terms of these units. Originally proposed in 1899 by German physicist Max Planck, these units are also known as 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 (that would be arbitrarily chosen), but rather on only the properties of free space. Planck units have significance for theoretical physics since they simplify several recurring algebraic expressions of physical law by nondimensionalization. They are relevant in research on unified theories such as quantum gravity. The term 'Planck scale' refers to the magnitudes of space, time, energy and other units, below which (or beyond which) the predictions of the Standard Model, quantum field theory and general relativity are no longer reconcilable, and quantum effects of gravity are expected to dominate. This region may be characterized by energies around 1.22×1019 GeV (the Planck energy), time intervals around 5.39×10−44 s (the Planck time) and lengths around 1.62×10−35 m (the Planck length). At the Planck scale, current models are not expected to be a useful guide to the cosmos, and physicists have no scientific model to suggest how the physical universe behaves. The best known example is represented by the conditions in the first 10−43 seconds of our universe after the Big Bang, approximately 13.8 billion years ago.