Comment by Balgair
Aside: Veritasium had a great video similar to this on the paths that light takes. I'll link to the part where they do the best physics demo I have ever seen:
Aside: Veritasium had a great video similar to this on the paths that light takes. I'll link to the part where they do the best physics demo I have ever seen:
I'm sorry what?
What do you mean by diffraction here? Are you talking about the bokeh?
The laser isn't interacting with any other elements than the air before it makes the gradient sheet light up. And the permisivity of the air is about the same as vacuum here.
Like, the grating is going to show a diffraction pattern similar to any pinhole aperture source [0] because of the 'half cancellations' they kinda explain, but not all that in depth.
But since there are no elements in the path yet, the only conclusion we can make is that of Feynman's - that the light is in fact taking all possible paths and then cancelling out to make the laser light we normally experience.
What am I missing? To me this demo is like mind boggling as it shows that the wave model is the correct one even with a laser.
[0] https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2F...
Something like (a) above, though I'm not confident that this is really showing that exactly.
sadly the demo is not so impressive as they make it out to be: The extra-path light is 'caused' by exit diffraction of the light source.
Now, the same underlying theory also explains why there will always be diffraction from any finite boundary resulting in a reality which is indistinguishable from one where light actually takes all possible paths. But to argue that it actually does is arguably more meta-physics than physics. The demonstration is further compromised by the fact that the laser's diffraction performance is also presumably far from the physical limit.
So a cynic seeing that demo would say "Isn't that just due to some of the light from the laser being off-axis" -- and it absolutely is. The physics means that some of the light will always be off-axis, but the demonstration does nothing to establish that.