I can't even begin to express how conceptually and experimentally wrong this 
demonstration is. The first thing is the perpetuation of the mistaken idea that 
photons are wiggling in a sinusiodal fashion. When you see that sine wave, it's 
a graph of the varying field as the wave propagates. It's not the wave itself. 
This is such a common miscommunication that physics students often have a hard 
time getting over it.

Just for the sake of context, this guy should have at least mentioned the 
practical application of this phenomenon, which is the polarizing 
saccharimeter. Wine makers, for example, use this device to measure the amount 
of dextrose (glucose) in grape juice so they can harvest the grapes at their 
peak. So next time you're enjoying that glass of wine, think, 

The experimental setup in this demonstration has, in my opinion, a fatal flaw. 
The light source seems to be too broad to test the phenomenon. Furthermore it 
appears to be tilted at an angle at the entrance to the tube. Both of these 
factors will have the light glancing off the interior of the tube. At least 
some of the light will be at Brewster's angle for the interface between the 
sugar solution and the tube. So the interior of the tube becomes its own 

Another thing that should have been mentioned is that the light, while 
circularly polarized in the sugar solution, emerges linearly polarized. Maybe 
that's obvious, but it should have been stated.
Having said all that, it's a hell of a beautiful demonstration. It should be 
repeated with a narrow beam of light just to see the results.

------- Original Message -------
On Sunday, September 10th, 2023 at 1:15 AM, H L V <hveeder...@gmail.com> wrote:

> The well known mathematics youtuber 3Blue1Brown recently published two 
> interesting videos on polarized light passing through a clear glass tube 
> filled with dissolved sugar in water. (He is working on a third video.) 
> Normally he explains mathematical concepts with nicely rendered visual 
> explanations so the inclusion of a physical demo is something new for his 
> channel. The mathematical explanation offered in part 2 seems to 
> qualitatively account for what is observed in part 1 but there is a lively 
> discussion in the comment section on part 2 where it is pointed out that his 
> explanation makes a prediction that he acknowledges is not actually observed. 
> I enjoy it when textbook science bumps up against reality! It will be 
> interesting to see if he can account for this theoretical weakness in his 
> third video.
> This demo tests your understanding of light | Barber pole, part 1
> https://www.youtube.com/watch?v=QCX62YJCmGk
> This demo tests your understanding of light | Barber pole, part 2
> https://www.youtube.com/watch?v=aXRTczANuIs&t=0s
> Harry

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