Fungible
#big-ideas #nft #note/boat🚤
The term "fungible" comes from law, where it describes things deemed interchangeable for practical purposes.
Dollar bills are fungible—borrow one, return any. Barrels of oil are fungible. Horses are not: you must return the specific horse you borrowed, not its twin.
But physicist David Deutsch draws a crucial distinction between legal fungibility and physical fungibility. Legal fungibility is about treating things as if they're identical. Physical fungibility means they actually are identical—in literally every way except that there are two of them.
The philosopher Gottfried Leibniz thought this was impossible, declaring in his "identity of indiscernibles" that no two things could be truly identical. He was wrong. We now know that photons can be physically fungible. Under certain conditions, even atoms can be. Not just treated as the same, but actually, genuinely, impossibly identical. It's a counter-intuitive property that challenges our everyday understanding of what it means for something to be unique.