# Wavelength as a yardstick

1. Jun 25, 2010

### TrickyDicky

Could electromagnetic wavelength be used as a legitimate distance pattern? I mean is it OK to exchange geometrical length with physical wavelength? For example, given a bundle of light rays following geodesics in empty space, can the length between a given pair of geodesics be equivalent to a wavelength?
I recall vaguely that the General Conference on Weights and Measures in 1983 adopted as a primary length standard, or reference length, the wavelength of the iodine stabilized HeNe laser,He−Ne = 632.99139822 nm.Thus, in physical metrology seems to be a common practice to use an appropriate wavelength of electromagnetic radiation as the reference length. But I don't know if it is physically straightforward to interchange geometrical lengths with wavelengths as in switching in a given Physics formula the wavelength with an equivalent geometrical length.

Thanks

2. Jun 25, 2010

### rcgldr

There are devices that count wavelength cycles to determine distance (moved) for very precise measurements.

3. Jun 27, 2010

### TrickyDicky

I understand wavelengths are interchangeable with lengths in every physical situation.
Anyone thinks otherwise?

4. Jun 27, 2010

### HallsofIvy

Lengths are lengths. If doesn't matter what the length measures.

5. Jun 27, 2010

### Andy Resnick

It's not clear what you are asking; electromagnetic radiation is used as a *time* standard, not a length standard (frequency vs. wavelength). However, because 'c_0' is a constant, it's possible to think of the meter being standardized in terms of a wavelength as well- as long as you mean wavelength in vacuum, or otherwise correct for the index of refraction.

That said, 'length' is 'length'... I don't understand what you mean by 'geometric' length vs. 'physical' length. Certainly, it's possible to scale physical parameters in an equation to obtain nondimensional groups (scaling the navier-stokes equation to obtain the Reynolds number, for example).

6. Jul 2, 2010

### AJ Bentley

I Googled 'geometrical length' to try and find out what the OP is talking about.

I came up with this thread as the only reference. :rofl:

7. Jul 2, 2010

### my_wan

The speed of light is 'by definition' 299,792,458 metres per second. So yes, a wavelength is as good a distance measure as nature offers.