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 2 added 226 characters in body edited Jan 3 '15 at 22:20 Brionius 7,10411 gold badge2323 silver badges2727 bronze badges It's not very useful to think of the frequency as negative. The wave vector $$\vec{k}$$ should be interpreted as the indicating the direction of the wave, so if the wave is going in the opposite direction, then $$\vec{k}$$ should be made negative, not $$\omega$$. Here is an animation that may help you. It shows the two propagating waves, and the resulting standing wave. It's called a "standing" wave in the sense that the nodes (places where the wave function has a value of zero) of the wave do not move. It's a little odd to say you have standing waves that are propagating, but yes, you will have a two dimensional standing wave, with a different wavevector in each dimension. Here is a visualization of it frozen in time (I used $$|\vec{p}| = |\vec{q}| = 1$$ for simplicity). It's not very useful to think of the frequency as negative. The wave vector $$\vec{k}$$ should be interpreted as the indicating the direction of the wave, so if the wave is going in the opposite direction, then $$\vec{k}$$ should be made negative, not $$\omega$$. Here is an animation that may help you. It shows the two propagating waves, and the resulting standing wave. It's called a "standing" wave in the sense that the nodes (places where the wave function has a value of zero) of the wave do not move. It's a little odd to say you have standing waves that are propagating, but yes, you will have a two dimensional standing wave, with a different wavevector in each dimension. It's not very useful to think of the frequency as negative. The wave vector $$\vec{k}$$ should be interpreted as the indicating the direction of the wave, so if the wave is going in the opposite direction, then $$\vec{k}$$ should be made negative, not $$\omega$$. Here is an animation that may help you. It shows the two propagating waves, and the resulting standing wave. It's called a "standing" wave in the sense that the nodes (places where the wave function has a value of zero) of the wave do not move. It's a little odd to say you have standing waves that are propagating, but yes, you will have a two dimensional standing wave, with a different wavevector in each dimension. Here is a visualization of it frozen in time (I used $$|\vec{p}| = |\vec{q}| = 1$$ for simplicity). 1 answered Jan 3 '15 at 20:40 Brionius 7,10411 gold badge2323 silver badges2727 bronze badges It's not very useful to think of the frequency as negative. The wave vector $$\vec{k}$$ should be interpreted as the indicating the direction of the wave, so if the wave is going in the opposite direction, then $$\vec{k}$$ should be made negative, not $$\omega$$. Here is an animation that may help you. It shows the two propagating waves, and the resulting standing wave. It's called a "standing" wave in the sense that the nodes (places where the wave function has a value of zero) of the wave do not move. It's a little odd to say you have standing waves that are propagating, but yes, you will have a two dimensional standing wave, with a different wavevector in each dimension.