Eli5 what is a “wave”?

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So when people say light exists as a particle and a wave, I understand what it means in terms of different behavior, but what “is” a wave? A photon is a light particle, is a light wave “made” of anything? Is a light wave just a way that a photon expresses itself? Is it just “energy”? But then, what is energy? Is a microwave “made” of anything, or is it just a way of describing how heat/light behaves under certain conditions?

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Anonymous 0 Comments

Ocean wave is described by a wave equation. A wave equation said that a point on the surface of water receive an acceleration opposite and proportional to the relative height of that point compared to those around it. More abstractly, the relative height value at a point will change by accelerating toward the relative height values at points near it. Of course, people don’t just declare that ocean wave follow wave equation just like that, we derive it from basic physic principles: Newton’s mechanics.

But now that we have a wave equation, we can apply it to many settings, as long as the physical principles give you the same equation. The wave equation describe how a “field” change. A field is something that assign a number to each point on a surface or in space at each point in time, and the wave equation describes how these values change over time.

So now we have light. The wave behavior of light is described by the theory of electromagnetic field. The physics of that field is described by Maxwell’s equation, which is completely different from ocean wave’s Newtonian physics. But yet – as it turns out – we still derive the wave equation from it. Because we get the same equation as the equation for ocean wave, we also call it a wave. Of course, there are some differences, but the mathematics similarities are enough to call it by that name. The field in electromagnetism describes the strength of electric and magnetic force, while the field in ocean wave describes the height of the water surface. Electromagnetism is also 3 dimensions in space, while ocean wave is 2 dimensions.

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