DIY double-slit light experiment (video)

Looking Glass Universe, Kathy Sarpi, 11/11/22; CC Liu, Sheldon S. (eds.), Wisdom Quarterly

I did the double slit light experiment at home

(Looking Glass Universe) Supported by Screen Australia and YouTube through the Skip Ahead initiative.

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Safety and where to get the supplies

Oh, Buddha, help me understand these maths.
It's too hard for the God of Hosts, who's at war.

I would love for you to try this experiment at home, but please be careful with the lasers. If you're going to buy a green laser then it's crucial that you buy a proper one. Green lasers emit light with a lot of invisible IR light, and in cheap lasers this often isn't filtered out well.

Blue/violet lasers can also be dangerous for another reason. Our eyes are terrible at seeing these wavelengths, so the laser will look much less strong than it actually is, which means you might be playing with a dangerously strong laser without realizing it.

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Red lasers are generally the safer bet. I saw the effect I was looking for even when I used cheap ~1mW red lasers, so it will work for you. If you'd like to invest in a nice laser though, this article has some trustworthy green laser brands: planetguide.net/astronomy...

Another way to buy lasers that are eye safe is to get them from school science lab suppliers.

• (NOTE: In some countries it's illegal to sell lasers over 1mW. Check laws where you live. In the USA the limit is 5mW).

The smoke machine I got used glycerol. I’m very suspicious about breathing in such smoke though, especially since the room can't be too well-ventilated or the experiment won't work. Fine particulate matter is a serious health risk in general. So even though glycerol is nontoxic, I think it may still be hazardous to inhale.

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I recommend wearing an airtight N-95 mask or similar protection while doing this experiment. I found it a bit tricky to source the double slit cheaply in Australia. Your best bet might be a science lab supplier. In the USA you can get it on amazon.com though.

VIDEO CREDITS: The beautiful animations in this video are made by Kathy Sarpi: kathysarpi.com. Thanks to Screen Australia and Google Australia for funding this project, and to the wonderful people at Screen Australia who helped me throughout the process. Also thanks also to all my beta testers (aka friends)!