# Question on Planck units

1. Feb 12, 2013

### Sunfire

Hello,

Planck units are defined here
http://en.wikipedia.org/wiki/Planck_units

Length, mass and time are defined via G, c and $\hbar$ and do not involve kB;
But temperature contains all G, c and $\hbar$ and kB;

Perhaps this is okay; just seems "uneven" that kB appears with a zero power in the definitions of length, mass and time but with nonzero power in the definition of temperature.

It seems a bit "ad hoc"... Would anyone have a comment on these definition choices?

2. Feb 12, 2013

### Staff: Mentor

Mass, space and time are connected both via gravity and via quantum theory. This is not true for temperature. It is just (directly) related to energy.

It is not a choice. If you set all those constants to 1, you have no choice how to get planck units (apart from constant prefactors).

3. Feb 12, 2013

### Sunfire

It says that c, G and $\hbar$ form a "vector basis" (1,0,0) (0,1,0) and (0,0,1) where adding vectors corresponds to multiplication of units.