## Basic metrology question

For the discussion of the sciences. Physics problems, chemistry equations, biology weirdness, it all goes here.

Moderators: gmalivuk, Moderators General, Prelates

### Basic metrology question

The metre is defined as the distance light travels in a certain length of time (in a vacuum). Does this assume an infinitely short wavelength (measured in metres!) or is there some sort of quantum uncertainty involved? I'd imagine our definition of the metre should actually have "...plus or minus half the Planck length" after it?

The Geoff

Posts: 137
Joined: Wed Jun 08, 2011 6:22 am UTC

### Re: Basic metrology question

No, it doesn't assume any wavelength; it doesn't need to. The basic units are all defined assuming a perfect world with no uncertainty; where physical constants need to be involved in this, those are defined to be exact as well. Thus, we get c being exactly 299792458 m/s, and μ0 being exactly 4π*10^-7 N/A2, etc.
starslayer

Posts: 231
Joined: Wed Dec 02, 2009 9:58 am UTC

### Re: Basic metrology question

It doesn't have to be defined for a magical world without uncertainty. It could simply be defined as the limit as uncertainty approaches zero.
In the future, there will be a global network of billions of adding machines.... One of the primary uses of this network will be to transport moving pictures of lesbian sex by pretending they are made out of numbers.
Spoiler:
gmss1 gmss2

gmalivuk
Archduke Vendredi of Skellington the Third, Esquire

Posts: 20290
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There

### Re: Basic metrology question

Our measurements are much less accurate than the Planck limit. As long as your definition has an error margin smaller than our capacity to measure it, you don't have to care about that error margin.
If there is no answer, there is no question. If there is no solution, there is no problem.

Waffles to space = 100% pure WIN.

idobox

Posts: 1592
Joined: Wed Apr 02, 2008 8:54 pm UTC
Location: Marseille, France