[alancalverd]

Why should a wave itself act as a source
of secondary waves? Why do we not include the secondary wave traveling in the backward direction from a given wavefront?

(a) because it doesn't - this is just a geometric construction
(b) because there is no evidence for a backward wave

Never confuse a useful model or geometric construction with reality or underlying physics!

[alancalverd]

Quote from: Bored chemist on Today at 08:26:29
Quote from: hamdani yusuf on Today at 06:26:05
How can you say that it's the same as interference?
Because the thing that causes the light to bend is interference.
Is it the same as refraction and reflection?

I think BC has slightly oversimplified his response. Huygens says that forward propagation is the result of an infinity of infintesimal hemispherical wavelets interfering - the only nonzero resultant is "forwards". If you truncate the infinity, say on the left, there is no source to the left to provide any destructive interference so to the left of the primary beam you can see the resultant of all the interfering wavelets from the right.   

[Bored chemist]

newer versions of diffraction gratings don't involve diffraction

Yes they do.

If you don't want to believe in the definition of diffraction, that's your problem.

[Bored chemist]

As regards his method, Aristotle is recognized as the inventor of scientific method because of his refined analysis of logical implications contained in demonstrative discourse,

That's not got much to do with the current definition of science, has it?
This guy
https://www.huffpost.com/entry/6-things-aristotle-got-wr_b_5920840
was not a founder of a principle that says "start with an observation", was he?

Ibn al-Haytham  may have a better claim but it seems that society wasn't ready for science back then. He seems to have been the only one who understood how science works.
That slightly validates my point. You can't, in general, do science on your own.
It typically requires independent confirmation.

Some theories which survived for thousands years turned out to be false.

Were any of them scientific theories, or are you just wasting time on irrelevances?

[alancalverd]

Nobody has falsified the hypothesis that human sacrifice guarantees good weather. And look what happens when you stop - global warming!

[hamdani yusuf (OP)]

As regards his method, Aristotle is recognized as the inventor of scientific method because of his refined analysis of logical implications contained in demonstrative discourse

Discourse is not experiment, nor does Aristotelian discourse seek counterexamples to the prevailing hypothesis.

If you follow the debate between Aristotle and Plato, it was Aristotle who emphasized the importance of observation.
On the other hand, Plato thought that the truth can be obtained through contemplation alone.

[hamdani yusuf (OP)]

Nobody has falsified the hypothesis that human sacrifice guarantees good weather. And look what happens when you stop - global warming!

Stopping human sacrifice without causing significant change in the weather should be enough.

[hamdani yusuf (OP)]

(a) because it doesn't - this is just a geometric construction

A geometric construction must be based on a clear rule, whether or not it reflects the physical reality.
What's the rule for Huygen's geometric construction?

[hamdani yusuf (OP)]

(b) because there is no evidence for a backward wave

Is it predicted by Huygen's geometric construction?

[hamdani yusuf (OP)]

Were any of them scientific theories, or are you just wasting time on irrelevances?

Even newer scientific theories can still be false. Atomic theories from Dalton, Thomson, Rutherford, Bohr, to Schrodinger are scientific, based on observations made by the tools available for them.

[hamdani yusuf (OP)]

How can you say that it's the same as interference?

Because the thing that causes the light to bend is interference.

Is it the same as refraction and reflection?

I think it's different.

[hamdani yusuf (OP)]

Huygens says that forward propagation is the result of an infinity of infintesimal hemispherical wavelets interfering - the only nonzero resultant is "forwards".

What cancels the backwards wave?

[hamdani yusuf (OP)]

If you truncate the infinity, say on the left, there is no source to the left to provide any destructive interference so to the left of the primary beam you can see the resultant of all the interfering wavelets from the right.   

I truncated a microwave beam using an aluminum plate, and found no diffracted wave.
I got diffracted microwave when the aluminum was shaped as a grid to allow some transmission. Just in case you are wondering what I mean,

How does it explain non-diffractive edges?

You still have to tell us what these are.

I better show you.

video #4 Non-diffractive Obstacle

I have uploaded new video showing diffraction in microwave frequency.

Basically, the experiment result leads us to conclude that diffraction comes from the material blocking the microwave path. When the obstruction is opaque enough, we find no diffraction. It's similar to my experiment using laser showing non-diffractive obstruction.

This result is not widely known yet.
 

[Bored chemist]

A metal plate in a microwave field is potentially an emitter rather than "truncating" the beam.

[alancalverd]

What microwave wavelength were you using?

I remarked previously that there is an increase in received signal at about 1:23, when the aluminum plate is to the right of the centerline, and I don't remember offering an explanation. Something to worry about!

[hamdani yusuf (OP)]

What microwave wavelength were you using?

I remarked previously that there is an increase in received signal at about 1:23, when the aluminum plate is to the right of the centerline, and I don't remember offering an explanation. Something to worry about!

10.5 GHz. I mentioned this in some of earlier videos.
The signal is due to reflection. It's definitely not diffraction, because it occurs not in the shadow region of the plate.

[hamdani yusuf (OP)]

A metal plate in a microwave field is potentially an emitter rather than "truncating" the beam.

What makes the difference?

[hamdani yusuf (OP)]

I got diffracted microwave when the aluminum was shaped as a grid to allow some transmission.

Just in case you are wondering what I was talking about.

I've made a new video investigating diffraction of microwave using metamaterials. Previously, it was shown that an aluminum plate, which virtually reflects all of microwave power, didn't show any observable diffraction effect. This time, we tested if diffraction effect can be observed in a partially transparent obstacle which is constructed as metamaterial. The metamaterial obstacle is made from an array of aluminum stripes. There will be some follow up videos to eliminate some uncertainties around diffraction phenomenon.

Here it is. I hope you enjoy it.

Edge effect on diffraction of microwave.

[alancalverd]

The signal is due to reflection.

The plate is perpendicular to the beam axis, which means that any reflected energy will be sent back upstream, surely? And the pulse is very narrow compared with the cone of the primary beam

Full marks for an experiment that was sufficiently precise  to display an anomaly!

[alancalverd]

Stopping human sacrifice without causing significant change in the weather should be enough.

Human sacrifice pretty well died out in 1800, around the date that climate "scientists" consider to be the beginning of anthropogenic global warming. The facts speak for themselves.