# Classical uncertainty principle

• A
• Jeffrey Freed
In summary, the classical uncertainty principle applies to micro-level objects and it is a consequence of the Fourier transform and definition of frequency. It does not apply to macro-sized objects, such as a violin string, because everything averages out. When trying to measure the pitch of a violin string with high accuracy, a longer measurement time is needed and vice versa.

#### Jeffrey Freed

What assumptions underlie the classical uncertainty principle? The principle doesn't seem to apply when I want to know the precise pitch of a tone from a bowed violin string, since I can measure the duration (as precisely as I want) of the beats produced when I interfere it with a sine wave of known frequency. The violin string is fairly simple oscillator, not a completely unknown signal, and its frequency should be constant and stable. So, does the uncertainty principle apply only when you don't know the nature of the tone you're trying to determine the pitch of?

Jeffrey Freed said:
What assumptions underlie the classical uncertainty principle? The principle doesn't seem to apply when I want to know the precise pitch of a tone from a bowed violin string, since I can measure the duration (as precisely as I want) of the beats produced when I interfere it with a sine wave of known frequency. The violin string is fairly simple oscillator, not a completely unknown signal, and its frequency should be constant and stable. So, does the uncertainty principle apply only when you don't know the nature of the tone you're trying to determine the pitch of?
The uncertainty principle has nothing to do with violin strings, as far as I know, partly because they are macro-sized objects and everything averages out. The HUP is about micro-level things (electrons, etc) taken individually.

phinds said:
The uncertainty principle has nothing to do with violin strings, as far as I know, partly because they are macro-sized objects and everything averages out. The HUP is about micro-level things (electrons, etc) taken individually.

The OP is referring to the classical (AKA mathematical) UP which basically is a consequence of how the Fourier transform (and our definition of frequency) work.
In this context all it means is that if you want to measure the pitch of the string with a good accuracy you need to measure for a long time and vice versa.

f95toli said:
The OP is referring to the classical (AKA mathematical) UP which basically is a consequence of how the Fourier transform (and our definition of frequency) work.
Ah. Thanks for giving me that understanding.