Hold your right hand in front of a mirror. Or, just place your left hand in front of your right with palms facing. Now (in 3D) try to “swap in” (superpose) your left for your right hand. It’s not a replacement, eh.
So, chirality. “Chiral” – a word that’s hugely important in physics.
(Wiki)
The term was first used by Lord Kelvin in 1893 in the second Robert Boyle Lecture at the Oxford University Junior Scientific Club which was published in 1894:(quote) I call any geometrical figure, or group of points, ‘chiral’, and say that it has chirality if its image in a plane mirror, ideally realized, cannot be brought to coincide with itself.
This difference in symmetry becomes obvious if someone attempts to shake the right hand of a person using their left hand, or if a left-handed glove is placed on a right hand.
Lookup “chiral” in the dictionary. The word’s origin is “late 19th century from Greek kheir ‘hand’ + -al.”
It’s yet another word that you’re unlikely to ever hear in public conversations. Although in the gym I regularly talk with trainers about asymmetry in posture, left & right side muscle strength, flexibility, etc.
• Wired > “How the Universe and Its Mirrored Version Are Different” by Zack Savitsky (Jun 22, 2025) [reprinted with permission from Quanta Magazine] – From living matter to molecules to elementary particles, the world is made of “chiral” objects that differ from their reflected forms.
When objects appear different in the mirror, scientists call them chiral.
Lactose, the sugar found in milk, is chiral. While either version can be synthesized, the sugars produced and consumed by living organisms are always the right-handed ones. In fact, life as we know it uses only right-handed sugars—hence why the genetic staircase of DNA always twists to the right. The root of this “homochirality” remains one of the biggest mysteries clouding the origins of life.
Nowadays, physicists consider chirality a fundamental property of all elementary particles, just like charge or mass. The particles that don’t have mass are always traveling at the speed of light, and they also all carry an intrinsic angular momentum as though they’re spinning like a top. If the particles are flying in the direction of your thumb, their spin follows the direction your fingers curl—on either your right hand or your left.
Almost every elementary particle [one current exception is the neutrino] has a twin through the looking glass. A negatively charged left-handed electron is mirrored by the anti-positron, a negatively charged right-handed particle.