# Is there plank speed?

1. Apr 5, 2013

### brianhurren

If plank time is the time it takes a photon to travel a plank length and speed is d/t or meters/second. then is the speed of light c plank speed? is the constant speed of light evidence of plank time?

2. Apr 5, 2013

### CompuChip

Yep, I guess.

Note however, that the speed of light is a physical constant and in fact the meter is defined in terms of it. A unit like the Planck time and Plank length are also defined in terms of other fundamental constants, e.g. $t_\mathrm{P} = \ell_\mathrm{P} / c$ where $\ell_\mathrm{P} = \sqrt{\hbar G c^{-3}}$ is defined in terms of c and two other fundamental constants. So it's basically by construction, which I wouldn't call "evidence".

3. Apr 5, 2013

### Staff: Mentor

What does that mean? Do you need evidence of ounces, or teaspoons? What does it mean to have evidence of a unit?

4. Apr 5, 2013

### roldor

Meter is a definition, second is. (Teaspoons also). So it is better to set c as 1. And lp as 1.

Sincerely.