Art: Painters and photographers can use light and shadow to convey emotions. I can't think of an example in nature where duality doesn't play a part. Can you? Share in comments.
Astronomy: Like strobe lights that quickly flash on and off, pulsars' flashing dim and bright cycles rival atomic clocks in accuracy
Architecture: The grains of sand fuzz the boundary between lit and unlit, right side and left side.
Reproductive biology: Man and woman. *Did you know we all start out as female-formed embryos? When the y-chromosome is activated at about 7 weeks, the embryo starts developing maleness. If the process is incomplete (about 1 in 2,000 babies), the child is born intersex, having "ambiguous genitalia." Parents must wait for their child to know whether they are a girl or boy. Sometimes the child is nonbinary. (A cause for transgender identity has not been found.)
Organic chemistry: molecules can be the same in every way, except they can also be mirror images of each other. This is called chirality, or "handedness."
Philosophy: The Chinese yin–yang symbolizes opposite forces that belong together and balance each other: quiet, cool, and resting (yin), vs. bright, warm, and active (yang). I chose this gif because I think it better represents these forces.
Physics: Light is either/or: on or off. It is also both/and: particle and wave. Visibly, it is a spectrum.
Analog vs Digital. Bricks vs Clay. Legos vs. Play-Doh. Uncountable vs Countable.
Fiction: Angel Aziraphale and Demon Crowley from Good Omens. Through a yin yang lens: Angel Aziraphale:"I like to think none of this would have worked out if you weren't, at heart, just a little bit of a good person." Demon Crowley: "And if you weren't, deep down, just enough of a bastard to be worth knowing." Source:LucasWerewolf
