# Hesienberg Uncertanity Principle

1. Aug 16, 2014

### Quarlep

I watched a video about particle physics and there I saw something strange(for me) (link is here) and there in 13:44 I saw [x,y] I didnt understand because I think uncertanity principle exist only between position and momentum but he make uncertanity between two coordinates .Can somebody explain to me how [x,y] works.

Thanks

Last edited by a moderator: Sep 25, 2014
2. Aug 16, 2014

### tom.stoer

He explicitly writes

$$[x,y] = 0$$
$$[p_x,p_y] = 0$$

So the uncertainty relation for x and y will read

$$\Delta x \; \Delta y = 0$$

Then he discusses the commutator for angular momentum.

$$[L_x,L_y] \neq 0$$

and from that one can derive an uncertainty relation for angular momentum.

3. Aug 16, 2014

### Quarlep

so theres no problem

4. Aug 16, 2014

### tom.stoer

no, there isn't

5. Aug 16, 2014

### Quarlep

thanks

6. Aug 18, 2014

### PhysicistMike

The expression [x, y] is called the commutator of x and y
http://en.wikipedia.org/wiki/Commutator

As you may know it's defined as [x, y] = xy - yx where x and y are any two operators. There's an uncertainty relation for any two observables A and B since [A,B] are what appear in the right hand side and the standard deviations of A and B appear on the left side of the inequality (uncertainty in Q = standard deviation in Q).

Last edited by a moderator: Sep 25, 2014
7. Aug 18, 2014

### MrRobotoToo

An uncertainly relation holds between any two non-commuting observables.