-8

All waves transmit energy.

Water Waves

Let's say you're in the middle of a calm pond and you start moving your hand up and down. Transverse "waves" are generated, and they propagate perpendicular to the motion of your hand. But when we say that these waves are moving through the medium (the water), it seems like we are actually saying that something appears to move through the water. The water is actually just moving up and down. There is not a really existing physical thing that is moving through the water. And at the atomic/molecular level, it definitely does not make sense to talk about the water molecules following the wave describing the water waves themselves.

But what other kinds of waves also fit into this category?

Sound waves

Sound: The propagation velocity of a sound wave (a longitudinal wave) does not refer to the motion of the air molecules but rather to another abstract mathematical object. There is no physically existing thing actually moving through space at the speed of sound when sound "moves". We are simply referring to the motion of compressions and decompressions of air through space.

Electromagnetic Waves

When we talk about light as a wave, we are simply describing the oscillations of the electric and magnetic fields.

But we wouldn't say the maxima of the EM field are traveling through space at the speed of light, but I don't see any other way of imagining it...

Any help here would be appreciated!

DanBM
  • 37

2 Answers2

1

A mathematical wave is an abstract notion, a mathematical solution to a wave equation. In that sense, "waves" do not exist, because there are no systems that perfectly follow any differential equation.

But I would not say this is a physical definition of a wave. A wave, in general, is any kind of propagating disturbance, in particular one that carries information and energy. A water wave is a disturbance in the water level (an increase or decrease) that propagates. Since said disturbance obviously exists, the water wave also exists. This argument can be made for essentially any wave within a material medium.

For waves that are not propagated through a medium, like electromagnetic waves, the question is harder to answer, because there is no obvious disturbance (at least, obvious to our senses). We know however that electromagnetic phenomena exists, and we know that you can propagate information and electromagnetic energy. Said propagation of information and energy arguably is the wave, according to the definition above.

agaminon
  • 4,386
1

The problem here is confusing physics with reality.

Physics models reality. It aims to produce models which are accurate "enough" for a given purpose.

A water wave is a mathematical abstraction. This seems obvious to me.

And that's all a water wave is, unless you're surfing, swimming, sailing or using them to generate power. Then they're very real and you won't be wondering about whether they exist or not.

an amazing and accurate way to model reality

That's all physics requires of waves. The fact that they work at all is quite impressive, but "are they real" is a philosophical point which makes no practical difference to getting an end result or using a theory to make predictions of events. This is something like the various interpretations of quantum theory - it really makes no difference what interpretation you use if the theory produces the same result anyway.

Waves ("wavefunctions') in quantum mechanics are an entirely different reality, so I am less concerned about those...

If you're fine with waves in quantum theory, I don't understand why you're having problems with other less abstract and more tangible waves.

StephenG - Help Ukraine
  • 10,129