Diffraction is the deviation of waves from straight-line propagation due to an obstacle or through an aperture, without any change in their energy.
I am trying to read up on and understand diffraction. The example of a water wave under Occurrences was quite easy to understand, especially when contrasted with light waves (image below). However, aren’t the water waves losing - and thus changing - their energy as they hit the narrow entrance by losing momentum? As I said, I do understand that the waves diffract from straight lines into curved lines, but the concept of not changing energy is hard to grasp.
What would diffracted light waves look like if they did change their energy at diffraction?
When a physical wave loses forward momentum, it typically gains amplitude. This conserves the energy of the wave at a lower speed.
Light waves don’t really lose speed, so loss of energy would be seen as a lower frequency.
This is nonsense. To change the frequency, you need highly nonlinear medium (like Raman mechanism in Ethidium bromide) or herald the wave pack, which is not something you probably had in mind.
Hello red shift?
Oh right I forgot to mention another effect that could be observed at high velocities (thousands of km/a for visible light), escaping a gravitational well, or when you expand the space itself. Sorry.
Nonsense? To the contrary, this is the answer to OPs question “What would diffracted light waves look like if they did change their energy at diffraction?” The light waves would change frequency if they lost or gained energy as the amount of energy carried by a photon is directly proportional to it’s electromagnetic frequency and is inversely proportional to it’s wavelength. So, Photon plus or minus energy equals frequency and wavelength change. Sensible, no?
Nope. Photon energy and the energy of waves are different energies: connected, but not interchangeable.