Since no one has ever compared every snowflake that exists or every fingerprint, what gives anyone the right to make such a statement?
Nothing. In fact, out of the billions of snowflakes that fall every winter, there are surely some that are virtually identical. However, there is sufficient variety in the way each snowflake crystallizes that it is very unlikely that any individual will find two that are alike.
“No two snowflakes are alike” is something that is told to children to impress them. It’s not actually true. However, in practical terms it might as well be true, since it’s difficult to disprove.
This site explains in a little more detail. Some key points:
-
On a molecular basis, no two snowflakes are alike. The number of possible different arrangements of the water molecules in a snowflake makes it unlikely that two absolutely identical ones have been produced in the history of the Earth.
-
On a larger scale, many snowflakes are simple hexagonal crystals. Many of these crystals look essentially the same.
-
For more complex crystals, there is great enough variation that it would be extremely unlikely to actually find two that look the same. (However, such crystals may sometimes occur.)
About fingerprints, I’ve heard of cases where people have been wrongfully convicted of crimes because “their” fingerprints were found at the crime scene, but in fact it was someone else who had nearly identical fingerprints! In at least one or two cases, the mistake was only discovered because the real criminal confessed.
Same could be said about trees, leaves or Big Macs.
It can be said about virtually every object that consists of more than a few molecules. Snowflakes frequently are used as an example because they superficially all look the same (as they are coming down). If you look at them more closely, because of their complex structure the differences between them are obvious and impressive.
Grains of sand are also each unique. However, because their structure is simpler than that of snowflakes, they don’t make as arresting an example.
To the same line of thinking: are all the atoms of one element , for example, helium the same?
Nope, there are seven known isotopes of Helium which vary by the number of neutrons.
Apparently, no two pieces of Ikea furniture are identical, either. The word “unique” is so universally applicable that it has no meaning.