How do we KNOW light is a wave?

We might not have unified electrodynamics until 1865, but we've known light was a wave since the original double-slit experiment in 1801. Let's talk about diffraction and wave interference.
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VIDEO ANNOTATIONS/CARDS

Where Does Light Come From?
https://youtu.be/3TufSRaHB6g

What the HECK is Energy?
https://youtu.be/snj1wBtn6I8

The Color White Does NOT Exist:
https://youtu.be/-E6dxybpUvo
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RELATED YOUTUBE VIDEOS

Veritasium on Double-Slit:
https://youtu.be/Iuv6hY6zsd0
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LINKS TO COMMENTS

Photon Questions:
https://www.youtube.com/watch?v=3TufSRaHB6g&lc=UgxKhdP1c2l84L0qJPJ4AaABAg
https://www.youtube.com/watch?v=3TufSRaHB6g&lc=UgyQoADcf7PnNgzHo9t4AaABAg
https://www.youtube.com/watch?v=3TufSRaHB6g&lc=UgyhhUktuKtrdJmQLI94AaABAg
https://www.youtube.com/watch?v=3TufSRaHB6g&lc=UgyaqEhjv7T68RbuJn14AaABAg
https://www.youtube.com/watch?v=3TufSRaHB6g&lc=Ugy8p_KqsLuQM7nm-rd4AaABAg

Featured Comment:
https://www.youtube.com/watch?v=-E6dxybpUvo&lc=UgyUAPD5tU3zDq80E6J4AaABAg
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IMAGE CREDITS

Christiaan Huygens:
https://commons.wikimedia.org/....wiki/File:Christiaan
https://commons.wikimedia.org/....wiki/File:Web_Huygen

Isaac Newton:
https://commons.wikimedia.org/....wiki/File:GodfreyKne
https://commons.wikimedia.org/....wiki/File:Opticks.jp

Thomas Young:
https://commons.wikimedia.org/....wiki/File:Thomas_You