[Clarification of an XY Problem]
I am currently developing a world with a hard magic system based entirely on manipulating the natural order of reality in accordance with physical possibility. As long as the ultimate end-state of a magical act results in a universe that continues to follow physical law, and the intermediate states are well-defined enough to be abstractly formalized, the only barrier to magic is how much energy is expended in the process.
Naturally, simple alchemical processes like the spontaneous synthesis and transmutation of matter is possible in this system, so material currency, especially metal coins, wouldn't be impossible to create from scrap material to a sufficiently powerful mage. The shape and design of such coins could also be flawlessly reproduced for someone who has dedicated enough effort into analyzing, memorizing, and codifying the design as an arcane formula.
My question isn't exactly how to deter, prevent, or detect counterfeiting of currency, but rather a sold-state physical/material question:
What physical material would be the hardest to synthetically reproduce at an atomic level through physics-based magic
The factors at play:
- It is physically impossible to create an object through arcana if its composition is not sufficiently well-understood to be codified into a magic formula
- The amount of 'energy' consumed to perform a magic act is linked to the difference of inherent energy levels of a closed system before and after the magical effect is produced: he amount of 'energy' consumed to perform a magic act is linked to the difference of inherent energy levels of a closed system before and after the magical effect is produced: warming a glass of room-temperature water is less costly than boiling it
- If a process is possible without any arcane intervention, the arcane energy consumed by short-cutting the process via arcana is generally lower than trying to produce a non-mundane effect: combining carbon and iron into steel with magic is easier than turning lead into gold, even when the composition of steel and gold are both equally well understood
Given these parameters, what material would be the most difficult to create a facsimile of via arcana, either based on energy requirements or on complexity-based analysis-proofing?