[hamdani yusuf (OP)]

If you are trying to explain the lack of a "backwards" half of the wavelet, you can invoke the conservation or energy and momentum. There is a "clear reason".

What stops you doing the same with light?

Because they are different. The media of mechanical waves have inertial mass, while the vacuum of space doesn't.

[hamdani yusuf (OP)]

There's a substantial difference between the antenna array model and Huygen's model. In antenna model, the wavelets are always originated from an antenna, which must consist of charged particles. On the other hand, Huygen's principle says that the wavelets can originate from vacuum of space.

Every derivation of single slit diffraction using Huygen's principle assumes that the obstacles are completely opaque. But my experiments show that diffraction requires partial opacity/transparency.

[hamdani yusuf (OP)]

What I understand is diffraction is bending of a single wave of light around an obstacle,
whereas interference is the superimposition of two waves to form one wave.
difference_between_diffraction_and_interference.jpg (167.77 kB . 590x312 - viewed 762 times)
You can find some detailed differences here: https://dewwool.com/difference-between-diffraction-and-interference/

I found some inconsistencies in the article, where what it says in one part contradicts what it says in another part. I'll point out one by one in following posts.

Here's what I found in the opening paragraph.

Interference can be defined as the combination of two or more waves.

And this is from the table.

It occurs due to the superposition of two waves coming from two different coherent sources.

[hamdani yusuf (OP)]

They are of two types:
•Fresnel’s diffraction: If the source of light and the screen are kept at a finite distance from the diffracting obstacle then Fresnel’s diffraction occurs.
•Fraunhofer diffraction: Fraunhofer diffraction can be observed if the source of light and the screen are both at an infinite distance from the diffracting obstacle.    

There are two combination of distances left uncovered. Finite source but infinite screen, and infinite source but finite screen.

[hamdani yusuf (OP)]

They are (interference) also of two types:
•Constructive interference: Constructive interference is defined as the superposition of two waves to get a greater amplitude like we use speakers to get the greater amplitude of sounds.
•Destructive interference: When two waves in opposite polarity or direction superimpose on each other in a way that they cancel each other, destructive

Both must occur in the same pattern to call it an interference pattern.

[hamdani yusuf (OP)]

Fringes are of varying width in diffraction.   The fringe widths are constant in interference.

Many sources mentioning this difference offer single slit experiment as an example of diffraction, and double slit experiment as an example of interference. This is one of the most common misconceptions.

The formula commonly found in the explanation of single slit experiment indicates constant fringe width. The only fringe with different width is the center bright, which is twice as wide as the others.
In double slit experiment where the width of the slits are not much different than the distance between them, it's possible for the minima of the one slit "envelope" overlap with maxima of double slit interference pattern, producing dark fringes much wider than the other. The envelope can also reduce the width of some bright fringe.

[Bored chemist]

The media of mechanical waves have inertial mass, while the vacuum of space doesn't.

Light carries energy and momentum.
The conservation laws mean that it can't suddenly go backwards for no reason.

[hamdani yusuf (OP)]

I answered another question in Quora, Why are there dark fringes in a single slit experiment?
https://www.quora.com/Why-are-there-dark-fringes-in-a-single-slit-experiment

Because in a single slit apperture, there are two edges. They can act as light sources which then interfere constructively and destructively to create dark and bright fringes on a screen. Double slit apperture has 4 edges, hence there are more light sources which can interfere with each other.


Top picture is the pattern produced by the same double slit aperture as the bottom picture, but one slit is covered.

Many sources call the top picture as single slit diffraction pattern, while the bottom picture is called double slit interference pattern. In both cases, the intensity of the fringes vary. It's contrary to the statements in the link.

diffraction :
Bright fringes are of the same intensity.   

interference :
The intensity of successive fringes is not the same. The intensity decreases with fringes.

[hamdani yusuf (OP)]

Here's the next difference.

Obstacles are  necessary for diffraction    

An obstacle is not necessary for direction (interference) 

There's a typo, but apart from that,  the statement is correct.

[hamdani yusuf (OP)]

diffraction :
The contrast between maxima and minima is poor   

interference :
The contrast between maxima and minima is certainly good

It depends on the light source and the material of the obstacle.

[hamdani yusuf (OP)]

Wave propagation direction:   
It changes after diffraction   
It does not change after superposition

I don't know where it came from. Why superposition slips into the table, instead of interference.
But in case of double slit and single slit experiment, they both change the direction of light propagation.

[hamdani yusuf (OP)]

The media of mechanical waves have inertial mass, while the vacuum of space doesn't.

Light carries energy and momentum.
The conservation laws mean that it can't suddenly go backwards for no reason.

Can it go sideways for no reason?

[Bored chemist]

The media of mechanical waves have inertial mass, while the vacuum of space doesn't.

Light carries energy and momentum.
The conservation laws mean that it can't suddenly go backwards for no reason.

Can it go sideways for no reason?

On average, it doesn't.

[alancalverd]

Because in a single slit apperture, there are two edges. They can act as light sources

This is clearly nonsense. I have a comb, with hundreds of edges. It does not emit light, due to some ridiculous conservation law, but it can act as a diffraction grating.

[Bored chemist]

It does not emit light,

How can you see it?

[alancalverd]

Not at all, in a dark room. Unlike anything else I would call a light source.

Indeed, as it is a black comb, I tend to infer its existence from a periodic absence of white light.

[hamdani yusuf (OP)]

Because in a single slit apperture, there are two edges. They can act as light sources

This is clearly nonsense. I have a comb, with hundreds of edges. It does not emit light, due to some ridiculous conservation law, but it can act as a diffraction grating.

Why do you accept that a point in the vacuum of space can act as source of the wavelets?

[alancalverd]

Only a fool would do so. Huygens is geometry, not physics.

[Bored chemist]

Because in a single slit apperture, there are two edges. They can act as light sources

This is clearly nonsense. I have a comb, with hundreds of edges. It does not emit light, due to some ridiculous conservation law, but it can act as a diffraction grating.

Why do you accept that a point in the vacuum of space can act as source of the wavelets?

I might accept that the EM field at a point in space is a source of wavelets.

[hamdani yusuf (OP)]

Only a fool would do so. Huygens is geometry, not physics.

There are other cases where the geometry doesn't reflect physical objects, such us epicycles to describe planetary motion. They can produce precise predictions, but require ad hoc assumptions when the objects or situations are changed.
IMO, they will be replaced by some better models.