# Thread: What (really) is a wave?

1. What (really) is a wave?

We commonly refer to waves in water, sound waves, electromagentic waves. We think about waves as undulations. But does a wave consist of any "stuff" (matter)?

We can conceive of a wave in water being caused by matter displacing the water at a point in the water and the rest of the water having to adjust its shape with respect to the displacement. The wave itself seems to be an expression of the displacement and isn't thought to consist of any "stuff" in itself.

Electromagentic waves travel through space and can be observed to behave both as waves and particles. Intuitively it seems wrong that a wave that does not consist of any matter can nevertheless have an effect on matter. Human intuition may of course be flawed!

If a wave in water is caused by matter displacing some of the water at a point in the water (changing its shape) then perhaps an electromagnetic wave in space is caused by charged particles displacing some of the space at a point in space (changing its shape)? Of course this would require space itself to consist of some substance.

2.

3. In the words of the Electric Boogey

"Its Electric"

4. Originally Posted by jonathancollins225
What (really) is a wave?

We commonly refer to waves in water, sound waves, electromagentic waves. We think about waves as undulations. But does a wave consist of any "stuff" (matter)?

We can conceive of a wave in water being caused by matter displacing the water at a point in the water and the rest of the water having to adjust its shape with respect to the displacement. The wave itself seems to be an expression of the displacement and isn't thought to consist of any "stuff" in itself.

Electromagentic waves travel through space and can be observed to behave both as waves and particles. Intuitively it seems wrong that a wave that does not consist of any matter can nevertheless have an effect on matter. Human intuition may of course be flawed!

If a wave in water is caused by matter displacing some of the water at a point in the water (changing its shape) then perhaps an electromagnetic wave in space is caused by charged particles displacing some of the space at a point in space (changing its shape)? Of course this would require space itself to consist of some substance.
There are couple of versions of "waves". There are standing waves, such as the configuration of the string of a violin after it is plucked. It vibrates, but has fixed points, called nodes, that do not undergo displacement. Then there are traveling waves, which appear as a periodic function being displaced in space. There are alos plane waves, common in electromagnetic theory, that are simple a plane wave front moving through space -- much like a piece of plywood being moved along.

The notion of electromagnetic waves propagating through a medium was quite common in the nineteenth centur. The medium was called the "aether". The idea of the "aether" was discarded as a result of the development of special relativity, since it is not consistent with the premise that the speed of light is constant in all inertial reference frames.

There is a minor resurgence in the notion of a medium for the propagation of photons. It involves the quantum theory of the photon, quantum electrodynamics, and the nature of the vacuum state in that theory. It is quite a bit more complicated and subtle than a simple medium for propagation of waves, as with sound in air or in the case of water waves.

You might enjoy the book QED by Richard Feynman. It is the text of some lectures that he gave for a general audience on the subject of quantum electrodynamics. Not only is Feynman terrific at explaining physics, he was one of the inventors, the primary inventor in terms of modern methods, of quantum electrodynamics. It is a good read.

5. Waves is energy and matter transport phenomenon. A mechanical wave transports energy and not matter. Becouse subatomic particles have dual nature, they can transport and energy and matter.

6. The first chapter of my optics textbook says something like:
Electromagnetic radiation has a dual nature in that it behaves like a wave or a particle in certain situations, but it is precicely neither.

Meaning that the simple fact that light behaves as one thing, and then can act like something else (according to us) just shows us that we really don't know what it is.
So, I wouldn't spend too much time trying to make sense of a "light wave" when clearly there is more to the story than that, and in fact we may even be very far away from the truth.

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